WO2021026802A1

WO2021026802A1 - Timing advance adjustment for downlink carrier aggregation

Info

Publication number: WO2021026802A1
Application number: PCT/CN2019/100541
Authority: WO
Inventors: Bo Chen; Chenxi HAO; Chao Wei; Hao Xu
Original assignee: Qualcomm Incorporated
Priority date: 2019-08-14
Filing date: 2019-08-14
Publication date: 2021-02-18

Abstract

Methods, systems, and devices for wireless communications are described to enable a UE, a primary cell (PCell), and a secondary cell (SCell) to identify and use an adjusted transmission timing offset for reference signals transmitted to the SCell on a component carrier. The UE may receive downlink transmissions from the cells, determine a difference in transmission timing offsets, and transmit a report to the PCell. The PCell may adjust a timing advance (TA) command for the reference signals based on the report. The PCell may transmit a TA command to the UE indicating for the UE to autonomously adjust the transmission timing offset associated with the carrier of the SCell based on a difference between transmission timing offsets. One of the cells may trigger the UE to perform a random access procedure with the SCell over the carrier to determine a TA command for the reference signals.

Description

TIMING ADVANCE ADJUSTMENT FOR DOWNLINK CARRIER AGGREGATION

FIELD OF TECHNOLOGY

The following relates generally to wireless communications and more specifically to timing advance adjustment for downlink carrier aggregation.

BACKGROUND

Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power) . Examples of such multiple-access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal frequency division multiple access (OFDMA) , or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) . A wireless multiple-access communications system may include a number of base stations or network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE) .

In some wireless communications systems, a UE may communicate with one or more cells that support one or more frequency carriers, in a carrier aggregation configuration. Some carrier aggregation configurations may not support the one or more cells in one or more locations (e.g., non-collocated cells) . Some carrier aggregation configurations may support non-collocated cells, but such configurations may cause interference.

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support timing advance adjustment for downlink carrier aggregation. Generally, the described techniques provide for a user equipment (UE) to communicate with one or more base stations, or one or more cells, in a carrier aggregation configuration and using an adjusted timing advance (TA) . The UE may be configured with a first carrier corresponding to a first base station (e.g., a primary cell (PCell) ) and a second carrier corresponding to a second base station (e.g., a secondary cell (SCell) ) . The UE may be configured such that communications with the PCell over the first carrier may include both downlink and uplink transmissions and such that communications with the SCell over the second carrier may include downlink transmissions and uplink reference signals transmissions (e.g., sounding reference signals (SRSs) ) associated with a reference signal carrier switching configuration.

The UE and the cells may identify and use an adjusted transmission timing offset for reference signals transmitted to the SCell on the second carrier. In a first example, the PCell may configure the UE to determine a difference between transmission timing offsets of downlink transmissions from each of the cells. The PCell may transmit a configuration for a differential downlink timing reference (DDTR) report to the UE, and the UE may receive downlink transmissions from the cells and determine a difference in subframe start time (e.g., difference in transmission timing offsets) . The UE may transmit the report to the PCell and the PCell may adjust a TA command for the reference signals based on the report. In a second example, the PCell may transmit a TA command to the UE including an indicator designating the UE to autonomously adjust the transmission timing offset associated with the second carrier of the SCell. As such, the UE may determine a difference between transmission timing offsets of downlink transmissions from each of the cells and may adjust the transmission timing offset accordingly. In a third example, one of the cells may trigger the UE to perform a random access procedure with the SCell over the second carrier. As part of the random access procedure, the SCell may determine a TA command for the UE and may transmit the TA command to the UE. The UE may transmit one or more reference signals to the second base station based on the adjusted TA.

A method of wireless communications at a UE is described. The method may include identifying a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration, identifying a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, determining a difference between the first transmission timing offset and the second transmission timing offset, and transmitting a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset.

An apparatus for wireless communications at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration, identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, determine a difference between the first transmission timing offset and the second transmission timing offset, and transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset.

Another apparatus for wireless communications at a UE is described. The apparatus may include means for identifying a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration, identifying a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, determining a difference between the first transmission timing offset and the second transmission timing offset, and transmitting a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset.

A non-transitory computer-readable medium storing code for wireless communications at a UE is described. The code may include instructions executable by a processor to identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration, identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, determine a difference between the first transmission timing offset and the second transmission timing offset, and transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a DDTR reporting report to the PCell that indicates the difference between the first transmission timing offset and the second transmission timing offset.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a configuration for the DDTR reporting report.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the DDTR reporting report may be configured as aperiodic, periodic, semi-persistent, or a combination thereof.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the configuration may be received via radio resource control (RRC) signaling.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the DDTR reporting report may be transmitted via a physical uplink shared channel (PUSCH) , a physical uplink control channel (PUCCH) , or both.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving an indication of an identification of the second carrier via RRC signaling or downlink control information (DCI) .

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a TA command indicating the adjusted transmission timing offset.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the TA command indicating the adjusted transmission timing offset may be based on the DDTR reporting report, the reference signal transmitted to the SCell, or both.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a TA command from the PCell that includes an indication for the UE to autonomously apply the adjusted transmission timing offset.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for adjusting, at the UE, the second transmission timing offset to the adjusted transmission timing offset based on receiving the TA command from the PCell, the difference between the first transmission timing offset and the second transmission timing offset, or both.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting the reference signal or a data signal to the PCell using the timing offset for the PCell, and switching to the SCell to transmit the reference signal to the SCell using the adjusted transmission timing offset.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the PCell and the SCell include different radio frequency bands.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, a radio frequency band of the PCell may be lower than a radio frequency band of the SCell.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the PCell and the SCell may be non-collocated cells.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the reference signal includes an SRS.

A method of wireless communications at a UE is described. The method may include configuring a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receiving a trigger to initiate a random access procedure on the second carrier, receiving, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset, and transmitting a reference signal on the second carrier using the adjusted transmission timing offset.

An apparatus for wireless communications at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to configure a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receive a trigger to initiate a random access procedure on the second carrier, receive, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset, and transmit a reference signal on the second carrier using the adjusted transmission timing offset.

Another apparatus for wireless communications at a UE is described. The apparatus may include means for configuring a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receiving a trigger to initiate a random access procedure on the second carrier, receiving, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset, and transmitting a reference signal on the second carrier using the adjusted transmission timing offset.

A non-transitory computer-readable medium storing code for wireless communications at a UE is described. The code may include instructions executable by a processor to configure a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receive a trigger to initiate a random access procedure on the second carrier, receive, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset, and transmit a reference signal on the second carrier using the adjusted transmission timing offset.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving an indication of a random access preamble for the UE to use for the random access procedure on the second carrier, and transmitting a random access preamble message on the second carrier according to the random access preamble.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the random access preamble may be indicated based on a physical downlink control channel (PDCCH) order or RRC signaling.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a subsequent TA command in a random access response message, a medium access control layer control element, or both, that indicates a further adjusted transmission timing offset.

A method of wireless communications is described. The method may include configuring a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receiving a DDTR reporting report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier, and transmitting a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR reporting report.

An apparatus for wireless communications is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receive a DDTR reporting report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier, and transmit a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR reporting report.

Another apparatus for wireless communications is described. The apparatus may include means for configuring a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receiving a DDTR reporting report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier, and transmitting a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR reporting report.

A non-transitory computer-readable medium storing code for wireless communications is described. The code may include instructions executable by a processor to configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receive a DDTR reporting report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier, and transmit a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR reporting report.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a configuration for the DDTR reporting report.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the configuration may be transmitted via RRC signaling.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the DDTR reporting report may be received via a PUSCH, a PUCCH, or both.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting an indication of an identification of the second carrier via RRC signaling or DCI.

A method of wireless communications is described. The method may include configuring a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration and transmitting a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.

An apparatus for wireless communications is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration and transmit a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.

Another apparatus for wireless communications is described. The apparatus may include means for configuring a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration and transmitting a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.

A non-transitory computer-readable medium storing code for wireless communications is described. The code may include instructions executable by a processor to configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration and transmit a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the TA command may be transmitted via a random access response message or a medium access control layer control element.

A method of wireless communications is described. The method may include configuring a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, transmitting a trigger to initiate a random access procedure on the second carrier, transmitting a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, and receiving the reference signal from the UE according to the adjusted transmission timing offset.

An apparatus for wireless communications is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, transmit a trigger to initiate a random access procedure on the second carrier, transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, and receive the reference signal from the UE according to the adjusted transmission timing offset.

Another apparatus for wireless communications is described. The apparatus may include means for configuring a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, transmitting a trigger to initiate a random access procedure on the second carrier, transmitting a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, and receiving the reference signal from the UE according to the adjusted transmission timing offset.

A non-transitory computer-readable medium storing code for wireless communications is described. The code may include instructions executable by a processor to configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, transmit a trigger to initiate a random access procedure on the second carrier, transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, and receive the reference signal from the UE according to the adjusted transmission timing offset.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting an indication of a random access preamble for the UE to use for the random access procedure on the second carrier, and receiving a random access preamble message on the second carrier according to the random access preamble.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the random access preamble may be indicated based on a PDCCH order or RRC signaling.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a subsequent TA command in a random access response message, a medium access control layer control element, or both, that indicates a further adjusted transmission timing offset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a wireless communications system that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a wireless communications system that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 3 illustrates an example of a transmission configuration that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 4 illustrates an example of a process flow that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 5 illustrates an example of a process flow that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 6 illustrates an example of a process flow that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIGs. 7 and 8 show block diagrams of devices that support timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 9 shows a block diagram of a communications manager that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 10 shows a diagram of a system including a device that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIGs. 11 and 12 show block diagrams of devices that support timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 13 shows a block diagram of a communications manager that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIG. 14 shows a diagram of a system including a device that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

FIGs. 15 through 25 show flowcharts illustrating methods that support timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

A user equipment (UE) may communicate with one or more base stations, or one or more cells, using a carrier aggregation configuration. In one example, the UE may be configured with a first carrier corresponding to a first base station (e.g., a primary cell (PCell) ) and a second carrier corresponding to a second base station (e.g., a secondary cell (SCell) ) , for downlink carrier aggregation. The UE may be configured such that communications with the first base station over the first carrier may include both downlink and uplink transmissions and such that communications with the second base station over the second carrier may include downlink transmissions and uplink reference signals transmissions (e.g., sounding reference signals (SRSs) ) associated with a reference signal carrier switching configuration. While the examples discussed herein may refer to base stations, the same examples may also apply to cells.

In the above-described carrier aggregation configuration, the UE may be limited to perform random access procedures with the first base station (e.g., the PCell) over the first carrier. Accordingly, transmission timing offsets (e.g., timing advances (TAs) ) for transmissions to both base stations may be based on the TA for the first base station (e.g., which may be based on the random access procedures with the PCell) . However, the TA for the first base station may be inapplicable to transmissions to the second base station, for example, due to different round trip times for different frequency bands or because the base stations may be non-collocated.

As such, reference signals (e.g., SRS transmissions) transmitted from the UE to the second base station may not coincide with other transmissions received by the second base station and may cause interference. For example, the UE may transmit a reference signal to the second base station, and the reference signal may arrive at the second base station after (e.g., offset from) a beginning of a subframe of the second base station. A second UE may transmit an uplink transmission to the second base station such that the uplink transmission from the second UE may arrive at the second base station at the beginning of the subframe. The misalignment between the reference signal and the uplink transmission from the second UE may cause interference with one or both transmissions at the second base station. The interference may reduce reliability and accuracy of communications between the second base station and the UE.

Accordingly, the UE and the base stations may identify and use an adjusted TA or transmission timing offset that may be specific to reference signals transmitted to the second base station over the second carrier. In a first example, the first base station may configure the UE to determine a difference between transmission timing offsets of downlink transmissions from each of the base stations. The first base station may transmit a configuration for a report to the UE, and the UE may receive downlink transmissions from the base stations and determine a difference in subframe start time (e.g., difference in transmission timing offsets) . The UE may transmit the report to the first base station and the first base station may adjust a TA command for the reference signal based on the report. In a second example, the first base station may transmit a TA command to the UE including an indicator designating the UE to autonomously adjust the TA associated with the second base station. As such, the UE may determine a difference between transmission timing offsets of downlink transmissions from each of the base stations and may adjust the TA accordingly. In a third example, one of the base stations may trigger the UE to perform a random access procedure with the second base station. As part of the random access procedure, the second base station may determine a TA command for the UE and may transmit the TA command to the UE.

The UE may transmit one or more reference signals to the second base station based on the adjusted TA. The second base station may receive the reference signals from the UE and may use the reference signals to perform carrier switching for one or more component carriers associated with the second base station (e.g., associated with the second carrier) . Performing the carrier switching may support higher communication quality and throughput for downlink communications from the second base station to the UE.

Aspects of the disclosure are initially described in the context of wireless communications systems. Aspects of the disclosure are further illustrated by and described with reference to a transmission configuration, process flows, apparatus diagrams, system diagrams, and flowcharts that relate to timing advance adjustment for downlink carrier aggregation.

FIG. 1 illustrates an example of a wireless communications system 100 that supports timing advance adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The wireless communications system 100 may include base stations 105, UEs 115, and a core network 130. In some examples, the wireless communications system 100 may be a Long Term Evolution (LTE) network, an LTE-Advanced (LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. In some cases, the wireless communications system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, communications with low-cost and low-complexity devices, or any combination thereof.

Base stations 105 may be dispersed throughout a geographic area to form the wireless communications system 100 and may be devices in different forms or having different capabilities. Base stations 105 and UEs 115 may wirelessly communicate via one or more communication links 125. Each base station 105 may provide a coverage area 110 over which UEs 115 and the base station 105 may establish communication links 125. The coverage area 110 may be an example of a geographic area over which a base station 105 and a UE 115 support the communication of signals according to one or more radio access technologies.

UEs 115 may be dispersed throughout a coverage area 110 of the wireless communications system 100, and each UE 115 may be stationary, or mobile, or both at different times. UEs 115 may be devices in different forms or having different capabilities. Some example UEs 115 are illustrated in FIG. 1. The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115, base stations 105, and/or network equipment (e.g., core network nodes, relay devices, integrated access and backhaul (IAB) nodes, or other network equipment) , as shown in FIG. 1.

Base stations 105 may communicate with the core network 130, or with one another, or both. For example, base stations 105 may interface with the core network 130 through backhaul links 120 (e.g., via an S1, N2, N3, or other interface) . Base stations 105 may communicate with one another over backhaul links 120 (e.g., via an X2, Xn, or other interface) either directly (e.g., directly between base stations 105) , or indirectly (e.g., via core network 130) , or both. In some examples, backhaul links 120 may be or include one or more wireless links.

One or more of base stations 105 described herein may include or may be referred to by a person of ordinary skill in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB) , a next-generation NodeB or giga-NodeB (either of which may be referred to as a gNB) , a Home NodeB, a Home eNodeB, or other suitable terminology.

A UE 115 may include or may be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client, among other examples. A UE 115 may also include or may be referred to as a personal electronic device such as a cellular phone, a personal digital assistant (PDA) , a tablet computer, a laptop computer, or a personal computer. In some examples, a UE 115 may include or be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, a machine type communications (MTC) device, or the like, which may be implemented in various objects such as appliances, vehicles, meters, or the like.

The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115 that may sometimes act as relays as well as base stations 105 and network equipment including macro eNBs or gNBs, small cell eNBs or gNBs, relay base stations, and the like, as shown in FIG. 1.

UEs 115 and base stations 105 may wirelessly communicate with one another via one or more communication links 125 over one or more carriers. The term “carrier” may refer to a set of radio frequency spectrum resources having a defined physical layer structure for supporting communication links 125. For example, a carrier used for a communication link 125 may include a portion of a radio frequency spectrum band (e.g., a bandwidth part (BWP) ) that is operated according to physical layer channels for a given radio access technology (e.g., LTE, LTE-A, LTE-A Pro, NR) . Each physical layer channel may carry acquisition signaling (e.g., synchronization signals, system information) , control signaling that coordinates operation for the carrier, user data, or other signaling. The wireless communications system 100 may support communication with a UE 115 using carrier aggregation or multi-carrier operation. A UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both frequency division duplexing (FDD) and time division duplexing (TDD) component carriers.

In some examples (e.g., in a carrier aggregation configuration) , a carrier may also have acquisition signaling or control signaling that coordinates operations for other carriers. A carrier may be associated with a frequency channel (e.g., an evolved universal mobile telecommunication system terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN) ) and may be positioned according to a channel raster for discovery by UEs 115. A carrier may be operated in a standalone mode where initial acquisition and connection may be conducted by UEs 115 via the carrier, or the carrier may be operated in a non-standalone mode where a connection is anchored using a different carrier (e.g., of the same or a different radio access technology) .

Communication links 125 shown in the wireless communications system 100 may include uplink transmissions from a UE 115 to a base station 105, or downlink transmissions from a base station 105 to a UE 115. Carriers may carry downlink or uplink communications (e.g., in an FDD mode) or may be configured to carry downlink and uplink communications (e.g., in a TDD mode) .

A carrier may be associated with a particular bandwidth of the radio frequency spectrum, and in some examples the carrier bandwidth may be referred to as a “system bandwidth” of the carrier or the wireless communications system 100. For example, the carrier bandwidth may be one of a number of predetermined bandwidths for carriers of a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 megahertz (MHz) ) . Devices of the wireless communications system 100 (e.g., base stations 105, UEs 115, or both) may have hardware configurations that support communications over a particular carrier bandwidth or may be configurable to support communications over one of a set of carrier bandwidths. In some examples, the wireless communications system 100 may include base stations 105 and/or UEs 115 that support simultaneous communications via carriers associated with multiple carrier bandwidths. In some examples, each served UE 115 may be configured for operating over portions (e.g., a sub-band, a BWP) or all of a carrier bandwidth.

Signal waveforms transmitted over a carrier may be made up of multiple subcarriers (e.g., using multi-carrier modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT-S-OFDM) ) . In a system employing MCM techniques, a resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme, the coding rate of the modulation scheme, or both) . Thus, the more resource elements that a UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. A wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers or beams) , and the use of multiple spatial layers may further increase the data rate or data integrity for communications with a UE 115.

One or more numerologies for a carrier may be supported, where a numerology may include a subcarrier spacing (Δf) and a cyclic prefix. A carrier may be divided into BWPs having the same or different numerologies. In some examples, a UE 115 may be configured with multiple BWPs. In some cases, a single BWP for a carrier is active at a given time, and communications for the UE 115 may be restricted to active BWPs.

Time intervals for base stations 105 or UEs 115 may be expressed in multiples of a basic time unit which may, for example, refer to a sampling period of T _s=1/ (Δf _max·N _f) seconds, where Δf _max may represent the maximum supported subcarrier spacing, and N _f may represent the maximum supported discrete Fourier transform (DFT) size. Time intervals of a communications resource may be organized according to radio frames each having a specified duration (e.g., 10 milliseconds (ms) ) . Each radio frame may be identified by a system frame number (SFN) (e.g., ranging from 0 to 1023) .

Each frame may include multiple consecutively numbered subframes or slots, and each subframe or slot may have the same duration. In some cases, a frame may be divided (e.g., in the time domain) into subframes, and each subframe may be further divided into a number of slots. Alternatively, each frame may include a variable number of slots, and the number of slots may depend on subcarrier spacing. Each slot may include a number of symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period) . In some wireless communications systems 100, a slot may further be divided into multiple mini-slots containing one or more symbols. Excluding the cyclic prefix, each symbol period may contain one or more (e.g., N _f) sampling periods. The duration of a symbol period may depend on the subcarrier spacing or frequency band of operation.

A subframe, a slot, a mini-slot, or a symbol may be the smallest scheduling unit (e.g., in the time domain) of the wireless communications system 100 and may be referred to as a transmission time interval (TTI) . In some cases, the TTI duration (e.g., the number of symbol periods in a TTI) may be variable. Additionally or alternatively, the smallest scheduling unit of the wireless communications system 100 may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs) ) .

Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. A control region (e.g., a control resource set (CORESET) ) for a physical control channel may be defined by a number of symbol periods and may extend across the system bandwidth or a subset of the system bandwidth of the carrier. One or more control regions (e.g., CORESETs) may be configured for a set of UEs 115. For example, UEs 115 may monitor or search control regions for control information according to one or more search space sets, and each search space set may include one or multiple control channel candidates in one or more aggregation levels arranged in a cascaded manner. An aggregation level for a control channel candidate may refer to a number of control channel resources (e.g., control channel elements (CCEs) ) associated with encoded information for a control information format having a given payload size. Search space sets may include common search space sets configured for sending control information to multiple UEs 115 and UE-specific search space sets for sending control information to a specific UE 115.

Each base station 105 may provide communication coverage via one or more cells, for example a macro cell, a small cell, a hot spot, or other types of cells, or various combinations thereof. The term “cell” may refer to a logical communication entity used for communication with a base station 105 (e.g., over a carrier) and may be associated with an identifier for distinguishing neighboring cells (e.g., a physical cell identifier (PCID) , a virtual cell identifier (VCID) , or others) . In some examples, a cell may also refer to a geographic coverage area 110 or a portion of a geographic coverage area 110 (e.g., a sector) over which the logical communication entity operates. Such cells may range from smaller areas (e.g., a structure, a subset of structure) to larger areas depending on various factors such as the capabilities of the base station 105. For example, a cell may be or include a building, a subset of a building, exterior spaces between or overlapping with geographic coverage areas 110, or the like.

A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs 115 with service subscriptions with the network provider supporting the macro cell. A small cell may be associated with a lower-powered base station 105, as compared with a macro cell, and a small cell may operate in the same or different (e.g., licensed, unlicensed) frequency bands as macro cells. Small cells may provide unrestricted access to UEs 115 with service subscriptions with the network provider or may provide restricted access to UEs 115 having an association with the small cell (e.g., UEs 115 in a closed subscriber group (CSG) , UEs 115 associated with users in a home or office, and the like) . A base station 105 may support one or multiple cells and may also support communications over the one or more cells using one or multiple component carriers.

In some examples, a carrier may support multiple cells, and different cells may be configured according to different protocol types (e.g., MTC, narrowband IoT (NB-IoT) , enhanced mobile broadband (eMBB) , or others) that may provide access for different types of devices.

In some examples, a base station 105 may be movable and therefore provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap, but the different geographic coverage areas 110 may be supported by the same base station 105. In other examples, overlapping geographic coverage areas 110 associated with different technologies may be supported by different base stations 105. The wireless communications system 100 may include, for example, a heterogeneous network in which different types of base stations 105 provide coverage for various geographic coverage areas 110 using the same or different radio access technologies.

The wireless communications system 100 may support synchronous or asynchronous operation. For synchronous operation, the base stations 105 may have similar frame timings, and transmissions from different base stations 105 may be approximately aligned in time. For asynchronous operation, the base stations 105 may have different frame timings, and transmissions from different base stations 105 may, in some examples, not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operations.

The wireless communications system 100 may be configured to support ultra-reliable communications or low-latency communications, or various combinations thereof. For example, the wireless communications system 100 may be configured to support ultra-reliable low-latency communications (URLLC) or mission critical communications. UEs 115 may be designed to support ultra-reliable, low-latency, or critical functions (e.g., mission critical functions) . Ultra-reliable communications may include private communication or group communication and may be supported by one or more mission critical services such as mission critical push-to-talk (MCPTT) , mission critical video (MCVideo) , or mission critical data (MCData) . Support for mission critical functions may include prioritization of services, and mission critical services may be used for public safety or general commercial applications. The terms ultra-reliable, low-latency, mission critical, and ultra-reliable low-latency may be used interchangeably herein.

In some cases, a UE 115 may also be able to communicate directly with other UEs 115 over a device-to-device (D2D) communication link 135 (e.g., using a peer-to-peer (P2P) or D2D protocol) . One or more UEs 115 utilizing D2D communications may be within the geographic coverage area 110 of a base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of a base station 105 or be otherwise unable to receive transmissions from a base station 105. In some cases, groups of UEs 115 communicating via D2D communications may utilize a one-to-many (1: M) system in which each UE 115 transmits to every other UE 115 in the group. In some examples, a base station 105 facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between UEs 115 without the involvement of a base station 105.

The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) or 5G core (5GC) , which may include at least one control plane entity that manages access and mobility (e.g., a mobility management entity (MME) , an access and mobility management function (AMF) ) and at least one user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW) , a Packet Data Network (PDN) gateway (P-GW) , a user plane function (UPF) ) . The control plane entity may manage non-access stratum (NAS) functions such as mobility, authentication, and bearer management for UEs 115 served by base stations 105 associated with the core network 130. User IP packets may be transferred through the user plane entity, which may provide IP address allocation as well as other functions. The user plane entity may be connected to the network operators IP services 150. The operators IP services 150 may include access to the Internet, Intranet (s) , an IP Multimedia Subsystem (IMS) , or a Packet-Switched Streaming Service.

Some of the network devices, such as a base station 105, may include subcomponents such as an access network entity 140, which may be an example of an access node controller (ANC) . Each access network entity 140 may communicate with UEs 115 through a number of other access network transmission entities 145, which may be referred to as radio heads, smart radio heads, or transmission/reception points (TRPs) . Each access network transmission entity 145 may include one or more antenna panels. In some configurations, various functions of each access network entity 140 or base station 105 may be distributed across various network devices (e.g., radio heads and ANCs) or consolidated into a single network device (e.g., a base station 105) .

The wireless communications system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz) . Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band, since the wavelengths range from approximately one decimeter to one meter in length. UHF waves may be blocked or redirected by buildings and environmental features, but the waves may penetrate structures sufficiently for a macro cell to provide service to UEs 115 located indoors. Transmission of UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 kilometers) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

The wireless communications system 100 may utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communications system 100 may employ License Assisted Access (LAA) , LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz industrial, scientific, and medical (ISM) band. When operating in unlicensed radio frequency spectrum bands, devices such as base stations 105 and UEs 115 may employ carrier sensing for collision detection and avoidance. In some cases, operations in unlicensed bands may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA) . Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, P2P transmissions, D2D transmissions, or the like.

A base station 105 or UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. The antennas of a base station 105 or UE 115 may be located within one or more antenna arrays or antenna panels, which may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some cases, antennas or antenna arrays associated with a base station 105 may be located in diverse geographic locations. A base station 105 may have an antenna array with a number of rows and columns of antenna ports that the base station 105 may use to support beamforming of communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations. Additionally or alternatively, an antenna panel may support radio frequency beamforming for a signal transmitted via an antenna port.

Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station 105 or a UE 115) to shape or steer an antenna beam (e.g., a transmit beam, a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining the signals communicated via antenna elements of an antenna array such that some signals propagating at particular orientations with respect to an antenna array experience constructive interference while others experience destructive interference. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying amplitude offsets, phase offsets, or both to signals carried via the antenna elements associated with the device. The adjustments associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., with respect to the antenna array of the transmitting device or receiving device, or with respect to some other orientation) .

The wireless communications system 100 may be a packet-based network that operates according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use error detection techniques, error correction techniques, or both to support retransmissions at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between a UE 115 and a base station 105 or core network 130 supporting radio bearers for user plane data. At the Physical layer, transport channels may be mapped to physical channels.

A UE 115 115 may communicate with one or more base station 105s 105, or one or more cells, using a carrier aggregation configuration. In one example, the UE 115 may be configured with a first carrier corresponding to a first base station 105 (e.g., PCell) and a second carrier corresponding to a second base station 105 (e.g., SCell) , for downlink carrier aggregation. The UE 115 may be configured such that communications with the first base station 105 over the first carrier may include both downlink and uplink transmissions and such that communications with the second base station 105 over the second carrier may include downlink transmissions and uplink reference signals transmissions (e.g., SRSs) associated with a reference signal carrier switching configuration. For example, the second carrier for the second base station 105 may be configured with resources for transmission of an SRS, but may not be configured for PUSCH and PUCCH transmissions. Such a configuration may be referred to as a PUSCH-less cell configuration. While the examples discussed herein may refer to base station 105s, the same examples may also apply to cells.

In the above-described carrier aggregation configuration, the UE 115 may be limited to perform random access procedures with the first base station 105 (e.g., the PCell) over the first carrier. Accordingly, transmission timing offsets (e.g., timing advances (TAs) ) for transmissions to both base stations 105 may be based on the TA for the first base station 105 (e.g., which may be based on the random access procedures) . However, the TA for the first base station 105 may be inapplicable to transmissions to the second base station 105, for example, due to different round trip times for different frequency bands or because the base stations 105 may be non-collocated.

As such, reference signals transmitted from the UE 115 to the second base station 105 may not coincide with other transmissions received by the second base station 105 and may cause interference. For example, the UE 115 may transmit a reference signal to the second base station 105, and the reference signal may arrive at the second base station 105 after (e.g., offset from) a beginning of a subframe of the second base station 105. A second UE 115 may transmit an uplink transmission to the second base station 105 such that the uplink transmission from the second UE 115 may arrive at the second base station 105 at the beginning of the subframe. The misalignment between the reference signal and the uplink transmission from the second UE 115 may cause interference with one or both transmissions at the second base station 105. The interference may reduce reliability and accuracy of communications between the second base station 105 and the UE 115.

Accordingly, the UE 115 and the base stations 105 may identify and use an adjusted TA or transmission timing offset that may be specific to reference signals transmitted to the second base station 105 over the second carrier. In a first example, the UE 115 may receive downlink transmissions from the base stations 105 and determine a difference in subframe start time (e.g., difference in transmission timing offsets) . The UE 115 may transmit the report to the first base station 105 and the first base station 105 may adjust a TA command for the reference signal based on the report. In a second example, the first base station 105 may transmit a TA command to the UE 115 including an indicator designating the UE 115 to autonomously adjust the TA associated with the second base station 105 (e.g., based on a difference between transmission timing offsets of downlink transmissions from each of the base stations 105) . In a third example, one of the base stations 105 may trigger the UE 115 to perform a random access procedure with the second base station 105 using the second carrier to determine a TA command for the UE 115.

The UE 115 may transmit one or more reference signals to the second base station 105 based on the adjusted TA. The second base station 105 may receive the reference signals from the UE 115 and may use the reference signals to perform carrier switching for one or more component carriers associated with the second base station 105 (e.g., associated with the second carrier) . Performing the carrier switching may support higher communication quality and throughput for downlink communications from the second base station 105 to the UE 115.

FIG. 2 illustrates an example of a wireless communications system 200 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. In some examples, wireless communications system 200 may implement aspects of wireless communications system 100. Wireless communications system 200 may include base stations 105-a and 105-b, as well as UE 115-a, which may be examples of base stations 105 and a UE 115 described with reference to FIG. 1. In some cases, UE 115-a may communicate with one or more base stations 105 (e.g., base stations 105-a and 105-b) , or one or more cells, using a carrier aggregation configuration. While the examples discussed herein may refer to base stations 105, the same examples may also apply to cells. In one example, UE 115-a may be configured with a first carrier corresponding to base station 105-a (e.g., a PCell) and a second carrier corresponding to base station 105-b (e.g., an SCell) for downlink carrier aggregation. In some cases, the first carrier may be located in a lower frequency band (e.g., a low-frequency FDD band) than the second carrier.

UE 115-a may be configured for carrier aggregation such that communications with base station 105-a over the first carrier may include both downlink and uplink FDD transmissions and such that communications with base station 105-b over the second carrier may include downlink TDD transmissions and uplink reference signals transmissions (e.g., SRS) associated with a reference signal carrier switching configuration. For example, UE 115-b may be located within an uplink coverage area 110-a of base station 105-a and outside of an uplink coverage area 110-b of base station 105-b (e.g., base station 105-b may be uplink coverage limited in TDD) . In some cases, the coverage areas 110 of base stations 105-a and 105-b may be based on one or more frequency bands associated with uplink transmissions to the respective base stations 105. For example, high-frequency TDD transmissions may provide a smaller uplink coverage area 110 than low-frequency FDD transmissions. In some cases, the coverage provided by base station 105-a (e.g., the PCell) may be referred to as uplink coverage enhancement.

UE 115-a may transmit uplink reference signals 230 to base station 105-b without transmitting other uplink transmissions. As such, base station 105-b (e.g., the SCell) may be referred to as a PUSCH-less cell. The reference signals 230 may support carrier switching on the high-frequency TDD band for achieving higher transmission performance on the TDD downlink transmissions. In some cases, UE 115-a may perform reference signal power-boosting or reference signal repetition when transmitting the reference signals 230. In the above-described carrier aggregation configuration, UE 115-a may be limited to perform random access procedures with base station 105-a (e.g., the PCell) over the first carrier. Accordingly, transmission timing offsets (e.g., TAs) for transmissions to both base station 105-a and base station 105-b may be based on the TA for base station 105-a (e.g., which may be based on the random access procedures) . However, the TA for base station 105-a may be inapplicable to transmissions to base station 105-b, for example, due to different round trip times for different frequency bands or because base stations 105-a and 105-b may be non-collocated.

When using the TA for base station 105-afor uplink transmissions (e.g., reference signals 230) from UE 115-a to base station 105-b, the uplink transmissions may not coincide with other transmissions received by base station 105-b (e.g., may not arrive at a beginning of a subframe of base station 105-b) and may cause interference. For example, UE 115-a may transmit one or more reference signals 230 to base station 105-b, and the one or more reference signals 230 may arrive at base station 105-b after (e.g., offset from) a beginning of a subframe at base station 105-b. A second UE 115 may, at least partially concurrently, transmit an uplink transmission to base station 105-b, such that the uplink transmission from the second UE 115 may arrive at base station 105-b at the beginning of the subframe. The misalignment between the one or more reference signals 230 and the uplink transmission from the second UE may cause interference with one or both transmissions at base station 105-b. The interference may reduce reliability and accuracy of communications between base station 105-b and UE 115-a.

Accordingly, UE 115-a and base station 105-a or 105-b may identify and use a TA or transmission timing offset that may be specific to uplink transmissions (e.g., reference signals 230) to base station 105-b. In a first example, base station 105-a may configure UE 115-a to determine a difference between downlink timing references (e.g., transmission timing offsets) of

downlink transmissions

205 and 210 from base stations 105-a and 105-b. For example, base station 105-a may transmit a configuration (e.g., as part of downlink transmission 205) for a differential downlink timing reference (DDTR) report 215 to UE 115-a. The configuration may indicate for UE 115-a to determine a difference (e.g., a time) between a start of a downlink subframe from base station 105-a and a start of a downlink subframe from base station 105-b.

UE 115-a may receive

downlink transmissions

205 and 210 from base stations 105-a and 105-b, may determine the difference in subframe start time, and may transmit the DDTR report 215 to base station 105-a indicating the difference between the transmission timing offsets of base station 105-a and 105-b. Base station 105-a may adjust a TA command 220 for the reference signals 230 based on the DDTR report 215 and may transmit the adjusted TA command 220 to UE 115-a (e.g., via a MAC control element (CE) ) or may indicate for base station 105-b to transmit the adjusted TA command 220 to UE 115-a. UE 115-a may transmit the reference signals 230 to base station 105-b based on the adjusted TA command 220, which may reduce interference and increase communication accuracy and reliability at base station 105-b.

In a second example, base station 105-a may similarly configure UE 115-a to determine a difference between downlink timing references (e.g., transmission timing offsets) of

downlink transmissions

205 and 210 from base stations 105-a and 105-b. For example, base station 105-a may transmit a TA command 220 to UE 115-a, where the TA command 220 may include an indicator designating UE 115-a to autonomously adjust the TA associated with base station 105-b (e.g., associated with uplink transmissions to base station 105-b) . Accordingly, UE 115-b may determine a difference (e.g., a time) between a start of a downlink subframe from base station 105-a and a start of a downlink subframe from base station 105-b. UE 115-a may adjust the TA associated with base station 105-b based on the difference and may transmit the reference signals 230 to base station 105-b based on the adjusted TA. The adjusted TA may reduce interference and increase communication accuracy and reliability at base station 105-b.

In a third example, base station 105-a or 105-b may trigger (e.g., via a physical downlink control channel (PDCCH) or RRC signaling) UE 115-a to perform a random access procedure 225 with the carrier for base station 105-b that is configured for transmission of reference signals 230. In some cases, the random access procedure 225 may be a contention-free random access procedure 225, and base station 105-aor 105-b may assign a preamble to UE 115-a (e.g., via the trigger to start the random access procedure) for the random access procedure 225. Accordingly, UE 115-a may initiate a random access procedure 225 with base station 105-b (e.g., by transmitting a random access request) . Base station 105-b may transmit a random access response to UE 115-a (e.g., as part of the random access procedure 225) including a TA command 220 corresponding to base station 105-b (e.g., corresponding to uplink transmissions to base station 105-b) . In some cases, base station 105-b may additionally transmit a MAC CE to UE 115-a, including a TA command 220 that may be used to further adjust a TA associated with uplink transmissions to base station 105-b. UE 115-b may receive one or both of the TA commands 220 and may use the TA from the one or both TA commands 220 to transmit the reference signals 230 to base station 105-b. The configured TA may reduce interference and increase communication accuracy and reliability at base station 105-b.

Base station 105-b may receive the reference signals 230 from UE 115-a and may use the reference signals 230 to perform carrier switching for one or more component carriers associated with base station 105-b (e.g., associated with the second carrier) . Performing the carrier switching may support higher communication quality and throughput for downlink communications from base station 105-b to UE 115-a.

FIG. 3 illustrates an example of a transmission configuration 300 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. In some examples, transmission configuration 300 may implement aspects of

wireless communications systems

100 or 200. For example, one or more UEs 115 and one or more base stations 105 may perform the transmissions illustrated in transmission configuration 300, where the UEs 115 and the base stations 105 may be examples of UEs 115 and base stations 105 described with reference to FIGs. 1 and 2. In some cases, a UE 115 may communicate with a first base station 105 and a second base station 105 (e.g., or with one or more cells) using a carrier aggregation configuration. While the examples discussed herein may refer to base stations 105, the same examples may also apply to cells. In one example, the UE 115 may be configured with a first carrier corresponding to the first base station 105 (e.g., a PCell) and a second carrier corresponding to the second base station 105 (e.g., an SCell) .

In some cases, communications between the UE 115 and the first base station (e.g., the PCell) 105 may include both downlink and uplink FDD transmissions, while communications between the UE 115 and the second base station 105 (e.g., the SCell) may include downlink TDD transmissions and uplink reference signals transmissions (e.g., SRS) . For example, as discussed above, the SCell may be a PUSCH-less cell where a carrier is configured with resources for SRS transmission but is not configured for PUSCH or PUCCH transmisisons. In one example, the first base station 105 may transmit a downlink transmission 305-a to the UE 115 at 335 (e.g., at a beginning 350 of a subframe of the second base station) , and the downlink transmission 305-a may take a time period 325 (e.g., an over-the-air time, T ₂₂) to arrive at the UE 115. The second base station 105 may transmit a downlink transmission 305-b to the UE 115 at 335, and the transmission may take a time period 320 (e.g., an over-the-air time, T ₁₂) to arrive at the UE 115.

In some cases, the UE 115 may be configured to transmit uplink reference signals 310 to the second base station 105 without transmitting other uplink transmissions (e.g., because of a reference signal carrier switching configuration) . In some cases, transmission timing offsets (e.g., TAs) for transmissions to the second base station 105 may be based on a TA for the first base station 105 (e.g., which may be based on one or more random access procedures with the first base station 105) . The TA for the first base station 105 may correspond to time period 325 (e.g., T ₂₂) and may be inapplicable to transmissions to the second base station 105 (e.g., which may instead correspond to time period 320 or T ₁₂) .

When using the TA for the first base station 105, some uplink transmissions (e.g., reference signals 310-a) from the UE 115 to the second base station 105 may be unsynchronized (e.g., may not arrive at the beginning 350 of the subframe) and may cause interference. For example, the UE 115 may transmit a reference signal 310-a to the second base station 105 at 340, using the TA for the first base station 105 (e.g., corresponding to time period 325) . The reference signal 310-a may arrive at the second base station 105 after time period 320 and at an offset 330 from the beginning 350 of the subframe (e.g., based on the over-the-air time T ₁₂, or time period 320) . A second UE 115 may, at least partially concurrently, transmit an uplink transmission 315 to the second base station 105, such that the uplink transmission 315 arrives at the second base station 105 at the beginning 350 of the subframe. The misalignment between reference signals 310-a and the uplink transmission 315 may cause interference with one or both transmissions 310-a or 315 at the second base station 105. The interference may reduce reliability and accuracy of communications between the second base station 105 and the UE 115.

Accordingly, as described with reference to FIG. 2, the UE 115 may be configured to identify a TA for the second base station 105 and to use the TA to transmit one or more reference signals 310 (e.g., reference signals 310-b) . As described with reference to FIG. 2, the UE 115 may be configured to transmit a DDTR report to the first base station 105, may autonomously configure the TA, or may perform a random access procedure with the second base station 105 to identify the TA. The UE 115 may transmit a reference signal 310-b at 345 and using the identified TA, such that the reference signal 310-b arrives at the second base station at the beginning 350 of the subframe.

If the UE 115 is configured to transmit a DDTR report or to autonomously configure the TA, the UE 115 may also be configured to measure or determine a difference (e.g., a time) between downlink timing references (e.g., transmission timing offsets) of downlink transmissions 305-a and 305-b. For example, the UE 115 may identify an offset between a time when downlink transmission 305-a arrives and downlink transmission 305-b arrives (e.g., identify a difference between

time periods

320 and 325, or between T ₁₂ and T ₂₂) . In some examples, the difference or offset may be equal to offset 330. The UE 115 may include the difference in a DDTR report to the first base station 105 and may receive an adjusted TA command for transmission of reference signals 310-b based on the DDTR report. Additionally or alternatively, the UE 115 may be configured to autonomously apply the difference to the TA for transmission of reference signals 310-b. If the UE 115 and the second base station 105 perform a random access procedure, the second base station may identify a TA corresponding to the time period 320 and may configure the UE 115 to use the TA for transmission of reference signals 310-b.

The second base station 105 may receive the reference signals 310-b from the UE 115 and may use the reference signals to perform carrier switching for one or more component carriers associated with the second base station 105 (e.g., associated with the second carrier) . Performing the carrier switching may support higher communication quality and throughput for downlink communications from the second base station 105 to the UE 115.

FIG. 4 illustrates an example of a process flow 400 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. In some examples, process flow 400 may be implemented by, or relate to, aspects of

wireless communications systems

100 or 200. Process flow 400 may also implement aspects of transmission configuration 300. Process flow 400 may be implemented by a UE 115-b and base stations 105-c and 105-d, which may be examples of a UE 115 and base stations 105 described with reference to FIGs. 1–3. UE 115-b may communicate with base station 105-b and base station 105-d (e.g., or with one or more cells) using a carrier aggregation configuration. While the examples discussed herein may refer to base stations 105, the same examples may also apply to cells. In one example, UE 115-b may be configured with a first carrier corresponding to base station 105-c (e.g., a PCell) and a second carrier corresponding to base station 105-d (e.g., an SCell) , where base station 105-c and base station 105-d may represent non-collocated cells. In some cases, base station 105-c may configure UE 115-b to transmit a DDTR report to base station 105-c, where base station 105-c may use the DDTR report to adjust a TA command associated with reference signal transmissions from UE 115-b to base station 105-d.

In the following description of the process flow 400, the operations between the UE 115-b and the base stations 105-c and 105-d may be transmitted in a different order than the order shown, or the operations performed by the base stations 105-c and 105-d or the UE 115-b may be performed in different orders or at different times. Specific operations may also be left out of the process flow 400, or other operations may be added to the process flow 400. Although the base stations 105-c and 105-d and the UE 115-b are shown performing the operations of process flow 400, some aspects of some operations may also be performed by another wireless device.

At 405, base station 105-c may configure UE 115-b with a first component carrier of a PCell (e.g., base station 105-c) and a second component carrier, or one or more second component carriers, of an SCell (e.g., base station 105-d) for downlink carrier aggregation. In some cases, base station 105-d may configure UE 115-b with the second carrier of the SCell. In some cases, uplink transmissions from UE 115-c to base station 105-d (e.g., over the second carrier) may be reserved for reference signal transmissions according to a reference signal carrier switching configuration. The carrier aggregation configuration may limit UE 115-b to perform random access procedures with base station 105-c (e.g., the PCell) . In some cases, transmission timing offsets (e.g., TAs) for transmissions to base station 105-d may be based on a TA for base station 105-c (e.g., which may be based on the random access procedures) . When using the TA for base station 105-c, reference signals (e.g., SRS) transmitted from UE 115-b to base station 105-d may arrive at incorrect times (e.g., may not arrive at a beginning of a subframe of base station 105-d) and may cause interference. As such, base station 105-c may configure UE 115-d to transmit a DDTR report which base station 105-c may to adjust a TA command associated with reference signal transmissions from UE 115-b to base station 105-d.

At 410, base station 105-c may transmit (e.g., via RRC or DCI) a configuration for the DDTR report to UE 115-b, where the DDTR report may be configured as aperiodic, periodic, semi-persistent or a combination thereof (e.g., based on an RRC configuration) . Base station 105-c may initiate the DDTR report if reference signal transmissions from UE 115-b to base station 105-d are unsynchronized (e.g., arriving at incorrect times as described above) . For example, base station 105-d may determine that one or more reference signal transmissions from UE 115-b arrive at base station 105-d at an offset from a beginning of a subframe or radio frame of base station 105-d. Accordingly, base station 105-d may indicate to base station 105-c (e.g., via a backhaul link or other network connection) that the one or more reference signal transmissions are unsynchronized, and base station 105-c may initiate the DDTR report.

Base station 105-c may configure UE 115-b to determine a difference between downlink timing references (e.g., transmission timing offsets) of downlink transmissions from base stations 105-b and 105-c. For example, the DDTR configuration may indicate for UE 115-b to determine a difference (e.g., a time) between a start of a downlink subframe from base station 105-c and a start of a downlink subframe from base station 105-d. In some cases, the DDTR configuration may indicate for UE 115-b to measure a difference in timing between downlink synchronization signals or reference signals associated with base stations 105-c and 105-d. Base station 105-c may additionally indicate (e.g., via RRC or DCI) a target downlink carrier identification or identifier (ID) corresponding to base station 105-d (e.g., the SCell) for UE 115-b to measure, with respect to the downlink carrier corresponding to base station 105-c, for the DDTR report.

At 415, base station 105-c may transmit, to UE 115-b, a first downlink transmission corresponding to the first component carrier (e.g., the downlink carrier associated with base station 105-c) . In some cases, the first downlink transmission may include one or more synchronization or reference signals.

At 420, base station 105-d may transmit, to UE 115-b, a second downlink transmission corresponding to the second component carrier (e.g., the downlink carrier associated with base station 105-d) . In some cases, the second downlink transmission may include one or more synchronization or reference signals.

At 425, UE 115-b may identify a first transmission timing offset (e.g., a timing reference, such as a beginning of a subframe or radio frame) for the first carrier of base station 105-c (e.g., of the downlink carrier aggregation configuration) . UE 115-b may also identify a second transmission timing offset (e.g., a timing reference, such as a beginning of a subframe or radio frame) for the second carrier of base station 105-d (e.g., of the downlink carrier aggregation configuration) . As described above, UE 115-b may identify the transmission timing offsets using a time of a start of one or more received subframes corresponding to one or more downlink transmissions, such as synchronization or reference signals.

At 430, UE 115-b may determine a difference between the first transmission timing offset and the second transmission timing offset. For example, UE 115-b may identify a time lag between a start of a received downlink subframe from base station 105-c and a start of a received downlink subframe from the target carrier belonging to base station 105-d (e.g., as specified by the carrier ID) .

At 435, UE 115-b may transmit the DDTR report to base station 105-d that indicates the difference between the first transmission timing offset and the second transmission timing offset. UE 115-b may transmit the DDTR report to base station 105-c via a PUSCH, a PUCCH, or both.

At 440, base station 105-c may transmit (e.g., via a MAC CE) , to UE 115-b, a TA command indicating an adjusted transmission timing offset (e.g., adjusted TA) for transmissions (e.g., reference signal transmissions) to base station 105-d. The adjusted transmission timing offset may be based on the difference between the first transmission timing offset and the second transmission timing offset (e.g., as indicated in the DDTR report) . For example, base station 105-c may adjust the TA command based on the DDTR report as well as a TA command for uplink transmissions to base station 105-c (e.g., may subtract the difference from the DDTR report from the TA command for base station 105-c) . In some cases, base station 105-d may transmit (e.g., via a MAC CE) , the adjusted TA command to UE 115-b.

In one example, the TA command for base station 105-c may be given by:

-2×T ₂₂, (1)

where T ₂₂ is an over-the-air time for a transmission from UE 115-b to reach base station 105-c, or vice-versa. The difference between the first transmission timing offset and the second transmission timing offset included in the DDTR report may be given by:

T ₁₂-T ₂₂, (2)

where T ₂₂ is the over-the-air time for a transmission from UE 115-b to reach base station 105-c, or vice-versa and T ₁₂ is an over-the-air time for a transmission from UE 115-b to reach base station 105-d, or vice-versa. Accordingly, base station 105-c may determine an adjusted TA command using:

-2× (T ₁₂-T ₂₂) -2×T ₁₂, (3)

where T ₂₂ is the over-the-air time for a transmission from UE 115-b to reach base station 105-c, or vice-versa and T ₁₂ is the over-the-air time for a transmission from UE 115-b to reach base station 105-d, or vice-versa.

At 445, UE 115-b may transmit a reference signal (e.g., an SRS) to base station 105-d using the adjusted transmission timing offset (e.g., based on the difference between the first transmission timing offset and the second transmission timing offset) . For example, UE 115-b may apply the TA from the adjusted TA command to reference signal transmissions to base station 105-d. In some cases, UE 115-b may transmit a reference signal (e.g., SRS) or a data signal to base station 105-c using the timing offset for base station 105-c and may switch to base station 105-d to transmit the reference signal to base station 105-d using the adjusted timing offset.

Base station 105-d may receive the reference signal from UE 115-b and may use the reference signal to performing carrier switching for one or more component carriers associated with base station 105-d. Performing the carrier switching may support higher communication quality and throughput for downlink communications from base station 105-d to UE 115-b.

FIG. 5 illustrates an example of a process flow 500 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. In some examples, process flow 500 may be implemented by, or relate to, aspects of

wireless communications systems

100 or 200. Process flow 500 may also implement aspects of transmission configuration 300. Process flow 500 may be implemented by a UE 115-c and base stations 105-e and 105-f, which may be examples of a UE 115 and base stations 105 described with reference to FIGs. 1–4. UE 115-c may communicate with base station 105-e and base station 105-f (e.g., or with one or more cells) using a carrier aggregation configuration. While the examples discussed herein may refer to base stations 105, the same examples may also apply to cells. In one example, UE 115-c may be configured with a first carrier corresponding to base station 105-e (e.g., a PCell) and a second carrier corresponding to base station 105-f (e.g., an SCell) . In some cases, base station 105-e may configure UE 115-c to autonomously apply an adjusted transmission timing offset to reference signal transmissions (e.g., SRS) from UE 115-c to base station 105-f.

In the following description of the process flow 500, the operations between the UE 115-e and the base stations 105-e and 105-f may be transmitted in a different order than the order shown, or the operations performed by the base stations 105-e and 105-f or the UE 115-e may be performed in different orders or at different times. Specific operations may also be left out of the process flow 500, or other operations may be added to the process flow 500. Although the base stations 105-e and 105-f and the UE 115-e are shown performing the operations of process flow 500, some aspects of some operations may also be performed by another wireless device.

At 505, base station 105-e may configure UE 115-c with a first component carrier of a PCell (e.g., base station 105-e) and a second component carrier, or one or more second component carriers, of an SCell (e.g., base station 105-f) for downlink carrier aggregation. In some cases, base station 105-f may configure UE 115-c with the second carrier of the SCell. In some cases, uplink transmissions from UE 115-c to base station 105-f (e.g., over the second carrier) may be reserved for reference signal transmissions according to a reference signal carrier switching configuration. The carrier aggregation configuration may limit UE 115-b to perform random access procedures with base station 105-e (e.g., the PCell) . In some cases, transmission timing offsets (e.g., TAs) for uplink transmissions to base station 105-f may be based on a TA for base station 105-e (e.g., which may be based on the random access procedures) . When using the TA for base station 105-e, reference signals (e.g., SRS) transmitted from UE 115-c to base station 105-f may arrive at incorrect times (e.g., may not arrive at a beginning of a subframe of base station 105-f) and may cause interference. As such, base station 105-e may configure UE 115-d to autonomously apply an adjusted transmission timing offset to reference signal transmissions from UE 115-c to base station 105-f.

At 510, base station 105-e may transmit (e.g., via a MAC CE or a random access response) a TA command to UE 115-c, where the TA command may include an indication for UE 115-c to autonomously apply an adjusted transmission timing offset (e.g., adjusted TA) to reference signal transmissions from UE 115-c to base station 105-f. For example, the TA command may include an indicator that indicates for UE 115-c to autonomously apply the adjusted transmission timing offset. The indicator may include an ID corresponding to a carrier to which UE 115-c is to apply the adjusted transmission timing offset (e.g., the second carrier of base station 105-f) . In some cases, UE 115-c may report its capabilities for autonomous adjustment of the transmission timing offset to base station 105-e or 105-f (e.g., via a capability report transmission) and the presence of the indicator may be based on the capabilities of UE 115-c.

The TA command may indicate for UE 115-c to determine a difference between downlink timing references (e.g., transmission timing offsets) of downlink transmissions from base stations 105-e and 105-f. For example, the DDTR configuration may indicate for UE 115-c to determine a difference (e.g., a time) between a start of a downlink subframe from base station 105-e and a start of a downlink subframe from base station 105-f. In some cases, the DDTR configuration may indicate for UE 115-c to measure a difference in timing between downlink synchronization signals or reference signals associated with base stations 105-e and 105-f. Base station 105-e may indicate (e.g., via RRC or DCI) a target downlink carrier ID corresponding to base station 105-f (e.g., the SCell) for UE 115-c to measure, with respect to the downlink carrier corresponding to base station 105-e, for the DDTR report.

At 515, base station 105-e may transmit, to UE 115-c, a first downlink transmission corresponding to the first component carrier (e.g., the downlink carrier associated with base station 105-e) . In some cases, the first downlink transmission may include one or more synchronization or reference signals.

At 520, base station 105-f may transmit, to UE 115-c, a second downlink transmission corresponding to the second component carrier (e.g., the downlink carrier associated with base station 105-f) . In some cases, the second downlink transmission may include one or more synchronization or reference signals.

At 525, UE 115-c may identify a first transmission timing offset (e.g., a timing reference, such as a beginning of a subframe or radio frame) for the first carrier of base station 105-e (e.g., of the downlink carrier aggregation configuration) . UE 115-c may also identify a second transmission timing offset (e.g., a timing reference, such as a beginning of a subframe or radio frame) for the second carrier of base station 105-f (e.g., of the downlink carrier aggregation configuration) . As described above, UE 115-c may identify the transmission timing offsets using a time of a start of one or more received subframes corresponding to one or more downlink transmissions, such as synchronization or reference signals.

At 530, UE 115-c may determine a difference between the first transmission timing offset and the second transmission timing offset. For example, UE 115-c may identify a time lag between a start of a received downlink subframe from base station 105-e and a start of a received downlink subframe from the target carrier belonging to base station 105-f (e.g., as specified by the carrier ID) .

At 535, if the indicator is present in the TA command, UE 115-c may transmit a reference signal (e.g., an SRS) to base station 105-f using the adjusted transmission timing offset (e.g., based on the difference between the first transmission timing offset and the second transmission timing offset) . The adjusted transmission timing offset may be based on the difference between the first transmission timing offset and the second transmission timing offset (e.g., as identified by UE 115-c) . For example, UE 115-c may adjust the transmission timing offset (e.g., TA) based on the the identified transmission timing offsets. In some cases, UE 115-c may transmit a reference signal (e.g., SRS) or a data signal to base station 105-e using the timing offset for base station 105-e and may switch to base station 105-f to transmit the reference signal to base station 105-f using the adjusted timing offset.

In one example, the TA for base station 105-e may be given by:

-2×T ₂₂, (4)

where T ₂₂ is an over-the-air time for a transmission from UE 115-c to reach base station 105-e, or vice-versa. The difference between the first transmission timing offset and the second transmission timing offset may be given by:

T ₁₂-T ₂₂, (5)

where T ₂₂ is the over-the-air time for a transmission from UE 115-c to reach base station 105-e, or vice-versa, and T ₁₂ is an over-the-air time for a transmission from UE 115-c to reach base station 105-f, or vice-versa. Accordingly, UE 115-c may determine an adjusted TA using:

-2× (T ₁₂-T ₂₂) -2×T ₂₂, (6)

where T ₂₂ is the over-the-air time for a transmission from UE 115-c to reach base station 105-e, or vice-versa and T ₁₂ is the over-the-air time for a transmission from UE 115-c to reach base station 105-f, or vice-versa.

Base station 105-f may receive the reference signal from UE 115-c and may use the reference signal to performing carrier switching for one or more component carriers associated with base station 105-f. Performing the carrier switching may support higher communication quality and throughput for downlink communications from base station 105-f to UE 115-c.

FIG. 6 illustrates an example of a process flow 600 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. In some examples, process flow 500 may be implemented by, or relate to, aspects of

wireless communications systems

100 or 200. Process flow 600 may also implement aspects of transmission configuration 300. Process flow 600 may be implemented by a UE 115-d and base stations 105-g and 105-h, which may be examples of a UE 115 and base stations 105 described with reference to FIGs. 1–4. UE 115-d may communicate with base station 105-g and base station 105-h (e.g., or with one or more cells) using a carrier aggregation configuration. While the examples discussed herein may refer to base stations 105, the same examples may also apply to cells. In one example, UE 115-d may be configured with a first carrier corresponding to base station 105-g (e.g., a PCell) and a second carrier corresponding to base station 105-h (e.g., an SCell) . In some cases, base station 105-g may configure UE 115-d to autonomously apply an adjusted transmission timing offset to reference signal transmissions (e.g., SRS) from UE 115-d to base station 105-h.

In the following description of the process flow 600, the operations between the UE 115-e and the base stations 105-g and 105-h may be transmitted in a different order than the order shown, or the operations performed by the base stations 105-g and 105-h or the UE 115-e may be performed in different orders or at different times. Specific operations may also be left out of the process flow 600, or other operations may be added to the process flow 600. Although the base stations 105-g and 105-h and the UE 115-e are shown performing the operations of process flow 600, some aspects of some operations may also be performed by another wireless device.

At 605, base station 105-h may configure UE 115-d with a first component carrier of a PCell (e.g., base station 105-g) and a second component carrier, or one or more second component carriers, of an SCell (e.g., base station 105-h) for downlink carrier aggregation. In some cases, base station 105-g may configure UE 115-d with the first component carrier of the PCell (e.g., base station 105-g) and the second component carrier, or one or more second component carriers, of the SCell (e.g., base station 105-h) for downlink carrier aggregation. In some cases, uplink transmissions from UE 115-d to base station 105-h (e.g., over the second carrier) may be reserved for reference signal transmissions according to a reference signal carrier switching configuration. The carrier aggregation configuration may limit UE 115-b to perform random access procedures with base station 105-g (e.g., the PCell) . In some cases, transmission timing offsets (e.g., TAs) for uplink transmissions to base station 105-h may be based on a TA for base station 105-g (e.g., which may be based on the random access procedures) . When using the TA for base station 105-g, reference signals (e.g., SRS) transmitted from UE 115-d to base station 105-h may arrive at incorrect times (e.g., may not arrive at a beginning of a subframe of base station 105-h) and may cause interference. As such, base station 105-g may configure UE 115-d to autonomously apply an adjusted transmission timing offset to reference signal transmissions from UE 115-d to base station 105-h.

At 610, base station 105-h or base station 105-g may transmit (e.g., via PDCCH) , to UE 115-d, a trigger to initiate a random access procedure on the second carrier (e.g., corresponding to base station 105-h) . In some cases, the random access procedure may be a contention-free random access procedure. In some cases, the trigger may include a base station-assigned preamble for the random access procedure to start the random access procedure (e.g., for a contention-free random access procedure) . In some cases, the preamble may be signaled via a PDCCH order or RRC signaling.

At 615, UE 115-d and base station 105-h may perform the random access procedure. For example, UE 115-d may transmit a random access request (e.g., message 1 (msg1) or message A (msgA) ) to base station 105-h. If assigned a preamble by base station 105-g or 105-h, UE 115-d may include the assigned preamble in the random access request. Similarly, base station 105-h may transmit a random access response (e.g., message 2 (msg2) or message (msgB) ) to UE 115-d (e.g., in response to the random access request) .

At 620, base station 105-h may transmit, to UE 115-d, a TA command indicating an adjusted transmission timing offset (e.g., adjusted TA) . In some cases, the TA command may be included in the random access response to UE 115-d, in a MAC CE transmitted to UE 115-d, or both. The TA command may identify that UE 115-d is to adjust the transmission timing offset for one or more reference signal transmissions (e.g., SRS) directed to base station 105-h (e.g., over the second carrier) . UE 115-d may receive the TA command in the random access response and adjust the transmission timing offset for the one or more reference signals. In some cases, UE 115-d may receive a subsequent TA command in a MAC CE and may further adjust the transmission timing offset for the one or more reference signals.

At 625, UE 115-d may transmit a reference signal (e.g., an SRS) to base station 105-h using the adjusted transmission timing offset (e.g., based on the random access procedure) . For example, UE 115-d may apply the TA from the TA command to reference signal transmissions to base station 105-h. In some cases, UE 115-d may transmit a reference signal (e.g., SRS) or a data signal to base station 105-g using the timing offset for base station 105-g and may switch to base station 105-h to transmit the reference signal to base station 105-h using the adjusted timing offset.

Base station 105-h may receive the reference signal from UE 115-d and may use the reference signal to performing carrier switching for one or more component carriers associated with base station 105-h. Performing the carrier switching may support higher communication quality and throughput for downlink communications from base station 105-h to UE 115-d.

FIG. 7 shows a block diagram 700 of a device 705 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The device 705 may be an example of aspects of a UE 115 as described herein. The device 705 may include a receiver 710, a communications manager 715, and a transmitter 720. The device 705 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 710 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to TA adjustment for downlink carrier aggregation, etc. ) . Information may be passed on to other components of the device 705. The receiver 710 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The receiver 710 may utilize a single antenna or a set of antennas.

The communications manager 715 may identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration, identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, determine a difference between the first transmission timing offset and the second transmission timing offset, and transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset.

The communications manager 715 may also configure a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receive a trigger to initiate a random access procedure on the second carrier, receive, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset, and transmit a reference signal on the second carrier using the adjusted transmission timing offset. The communications manager 715 may be an example of aspects of the communications manager 1010 described herein.

The communications manager 715, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 715, or its sub-components may be executed by a general-purpose processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

The communications manager 715, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 715, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 715, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

The transmitter 720 may transmit signals generated by other components of the device 705. In some examples, the transmitter 720 may be collocated with a receiver 710 in a transceiver module. For example, the transmitter 720 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 720 may utilize a single antenna or a set of antennas.

The actions performed by the communications manager 715 as described herein may be implemented to realize one or more potential advantages. For example, communications manager 715 may increase communication reliability and accuracy at a UE 115 by reducing interference for uplink reference signal transmissions, which may reduce transmission delays, improve transmission accuracy, and reduce retransmissions. Similarly, communications manager 715 may save power and increase battery life at a UE 115 by reducing interference for uplink reference signal transmissions and thus reducing retransmissions.

FIG. 8 shows a block diagram 800 of a device 805 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The device 805 may be an example of aspects of a device 705, or a UE 115 as described herein. The device 805 may include a receiver 810, a communications manager 815, and a transmitter 855. The device 805 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 810 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to TA adjustment for downlink carrier aggregation, etc. ) . Information may be passed on to other components of the device 805. The receiver 810 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The receiver 810 may utilize a single antenna or a set of antennas.

The communications manager 815 may be an example of aspects of the communications manager 715 as described herein. The communications manager 815 may include a carrier identification component 820, a secondary carrier identification component 825, a timing difference component 830, a reference signal transmission component 835, a carrier aggregation configuration component 840, a trigger reception component 845, and a TA command reception component 850. The communications manager 815 may be an example of aspects of the communications manager 1010 described herein.

The carrier identification component 820 may identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration. The secondary carrier identification component 825 may identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The timing difference component 830 may determine a difference between the first transmission timing offset and the second transmission timing offset. The reference signal transmission component 835 may transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset. The reference signal transmission component 835 may transmit a reference signal on the second carrier using the adjusted transmission timing offset.

The carrier aggregation configuration component 840 may configure a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The trigger reception component 845 may receive a trigger to initiate a random access procedure on the second carrier. The TA command reception component 850 may receive, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset.

The transmitter 855 may transmit signals generated by other components of the device 805. In some examples, the transmitter 855 may be collocated with a receiver 810 in a transceiver module. For example, the transmitter 855 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 855 may utilize a single antenna or a set of antennas.

A processor of a UE 115 (for example, controlling the receiver 810, the transmitter 855, or the transceiver 1020 as described with reference to FIG. 10) may increase communication reliability and accuracy by enabling the UE 115 to transmit uplink reference signals such that associated interference is reduce (e.g., via implementation of system components described with reference to FIG. 9) . Further, the processor of the UE 115 may identify one or more aspects of a carrier aggregation configuration and/or one or more transmission timing offsets to perform the processes described herein. The processor of the UE 115 may use the carrier aggregation configuration and/or one or more transmission timing offsets to identify a transmission timing offset (e.g., a TA) for uplink reference signal transmissions, which may increase communication accuracy and reliability. The processor of the UE 115 may further use the carrier aggregation configuration and/or one or more transmission timing offsets to save power and increase battery life at the UE 115 (e.g., by reducing retransmissions and by strategically decreasing interference for uplink reference signal transmissions) .

FIG. 9 shows a block diagram 900 of a communications manager 905 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The communications manager 905 may be an example of aspects of a communications manager 715, a communications manager 815, or a communications manager 1010 described herein. The communications manager 905 may include a carrier identification component 910, a secondary carrier identification component 915, a timing difference component 920, a reference signal transmission component 925, a DDTR report component 930, a TA command reception component 935, an autonomous adjustment component 940, a carrier aggregation configuration component 945, a trigger reception component 950, and a preamble identification component 955. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The carrier identification component 910 may identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration. In some cases, the PCell and the SCell include different radio frequency bands. In some cases, a radio frequency band of the PCell is lower than a radio frequency band of the SCell. In some cases, the PCell and the SCell are non-collocated cells.

The secondary carrier identification component 915 may identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The timing difference component 920 may determine a difference between the first transmission timing offset and the second transmission timing offset.

The reference signal transmission component 925 may transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset. In some examples, the reference signal transmission component 925 may transmit a reference signal on the second carrier using the adjusted transmission timing offset. In some examples, the reference signal transmission component 925 may transmit the reference signal or a data signal to the PCell using the first transmission timing offset for the PCell. In some examples, the reference signal transmission component 925 may switch to the SCell to transmit the reference signal to the SCell using the adjusted transmission timing offset. In some cases, the reference signal includes an SRS.

The DDTR report component 930 may transmit a DDTR report to the PCell that indicates the difference between the first transmission timing offset and the second transmission timing offset. In some examples, the DDTR report component 930 may receive a configuration for the DDTR report. In some examples, the DDTR report component 930 may receive an indication of an identification of the second carrier via radio resource control signaling or DCI. In some cases, the DDTR report is configured as aperiodic, periodic, semi-persistent, or a combination thereof. In some cases, the configuration is received via radio resource control signaling. In some cases, the DDTR report is transmitted via a PUSCH, a PUCCH, or both.

The TA command reception component 935 may receive, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset. In some examples, the TA command reception component 935 may receive a TA command indicating the adjusted transmission timing offset. In some examples, the TA command reception component 935 may receive a subsequent TA command in a random access response message, a MAC CE, or both, that indicates a further adjusted transmission timing offset. In some cases, the TA command indicating the adjusted transmission timing offset is based on the DDTR report, the reference signal transmitted to the SCell, or both.

The autonomous adjustment component 940 may receive a TA command from the PCell that includes an indication for the UE to autonomously apply the adjusted transmission timing offset. In some examples, the autonomous adjustment component 940 may adjust, at the UE, the second transmission timing offset to the adjusted transmission timing offset based on receiving the TA command from the PCell, the difference between the first transmission timing offset and the second transmission timing offset, or both.

The carrier aggregation configuration component 945 may configure a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. In some cases, the PCell and the SCell include different radio frequency bands. In some cases, a radio frequency band of the PCell is lower than a radio frequency band of the SCell. In some cases, the PCell and the SCell are non-collocated cells. In some cases, the reference signal includes an SRS.

The trigger reception component 950 may receive a trigger to initiate a random access procedure on the second carrier. The preamble identification component 955 may receive an indication of a random access preamble for the UE to use for the random access procedure on the second carrier. In some examples, the preamble identification component 955 may transmit a random access preamble message on the second carrier according to the random access preamble. In some cases, the random access preamble is indicated based on a PDCCH order or radio resource control signaling.

FIG. 10 shows a diagram of a system 1000 including a device 1005 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The device 1005 may be an example of or include the components of device 705, device 805, or a UE 115 as described herein. The device 1005 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1010, an I/O controller 1015, a transceiver 1020, an antenna 1025, memory 1030, and a processor 1040. These components may be in electronic communication via one or more buses (e.g., bus 1045) .

The communications manager 1010 may identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration, identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, determine a difference between the first transmission timing offset and the second transmission timing offset, and transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset.

The communications manager 1010 may also configure a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receive a trigger to initiate a random access procedure on the second carrier, receive, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset, and transmit a reference signal on the second carrier using the adjusted transmission timing offset.

The I/O controller 1015 may manage input and output signals for the device 1005. The I/O controller 1015 may also manage peripherals not integrated into the device 1005. In some cases, the I/O controller 1015 may represent a physical connection or port to an external peripheral. In some cases, the I/O controller 1015 may utilize an operating system such as

or another known operating system. In other cases, the I/O controller 1015 may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller 1015 may be implemented as part of a processor. In some cases, a user may interact with the device 1005 via the I/O controller 1015 or via hardware components controlled by the I/O controller 1015.

The transceiver 1020 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1020 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1020 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1025. However, in some cases the device may have more than one antenna 1025, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 1030 may include random access memory (RAM) and read only memory (ROM) . The memory 1030 may store computer-readable, computer-executable code 1035 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 1030 may contain, among other things, a basic I/O system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 1040 may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 1040 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 1040. The processor 1040 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1030) to cause the device 1005 to perform various functions (e.g., functions or tasks supporting TA adjustment for downlink carrier aggregation) .

The code 1035 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1035 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1035 may not be directly executable by the processor 1040 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 11 shows a block diagram 1100 of a device 1105 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The device 1105 may be an example of aspects of a base station 105 as described herein. The device 1105 may include a receiver 1110, a communications manager 1115, and a transmitter 1120. The device 1105 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 1110 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to TA adjustment for downlink carrier aggregation, etc. ) . Information may be passed on to other components of the device 1105. The receiver 1110 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The receiver 1110 may utilize a single antenna or a set of antennas.

The communications manager 1115 may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receive a DDTR report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier, and transmit a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR report.

The communications manager 1115 may also configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration and transmit a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.

The communications manager 1115 may also configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, transmit a trigger to initiate a random access procedure on the second carrier, transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, and receive the reference signal from the UE according to the adjusted transmission timing offset. The communications manager 1115 may be an example of aspects of the communications manager 1410 described herein.

The communications manager 1115, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 1115, or its sub-components may be executed by a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

The communications manager 1115, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 1115, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 1115, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

The transmitter 1120 may transmit signals generated by other components of the device 1105. In some examples, the transmitter 1120 may be collocated with a receiver 1110 in a transceiver module. For example, the transmitter 1120 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The transmitter 1120 may utilize a single antenna or a set of antennas.

FIG. 12 shows a block diagram 1200 of a device 1205 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The device 1205 may be an example of aspects of a device 1105, or a base station 105 as described herein. The device 1205 may include a receiver 1210, a communications manager 1215, and a transmitter 1250. The device 1205 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 1210 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to TA adjustment for downlink carrier aggregation, etc. ) . Information may be passed on to other components of the device 1205. The receiver 1210 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The receiver 1210 may utilize a single antenna or a set of antennas.

The communications manager 1215 may be an example of aspects of the communications manager 1115 as described herein. The communications manager 1215 may include a carrier aggregation component 1220, a DDTR report manager 1225, a TA command transmission component 1230, an autonomous adjustment manager 1235, a trigger transmission component 1240, and a reference signal reception component 1245. The communications manager 1215 may be an example of aspects of the communications manager 1410 described herein.

The carrier aggregation component 1220 may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The carrier aggregation component 1220 may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The carrier aggregation component 1220 may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration.

The DDTR report manager 1225 may receive a DDTR report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.

The TA command transmission component 1230 may transmit a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR report. The TA command transmission component 1230 may transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell.

The autonomous adjustment manager 1235 may transmit a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.

The trigger transmission component 1240 may transmit a trigger to initiate a random access procedure on the second carrier. The reference signal reception component 1245 may receive the reference signal from the UE according to the adjusted transmission timing offset.

The transmitter 1250 may transmit signals generated by other components of the device 1205. In some examples, the transmitter 1250 may be collocated with a receiver 1210 in a transceiver module. For example, the transmitter 1250 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The transmitter 1250 may utilize a single antenna or a set of antennas.

FIG. 13 shows a block diagram 1300 of a communications manager 1305 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The communications manager 1305 may be an example of aspects of a communications manager 1115, a communications manager 1215, or a communications manager 1410 described herein. The communications manager 1305 may include a carrier aggregation component 1310, a DDTR report manager 1315, a TA command transmission component 1320, an autonomous adjustment manager 1325, a trigger transmission component 1330, a reference signal reception component 1335, and a preamble transmission component 1340. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The carrier aggregation component 1310 may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration.

In some examples, the carrier aggregation component 1310 may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. In some examples, the carrier aggregation component 1310 may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. In some cases, the PCell and the SCell include different radio frequency bands. In some cases, a radio frequency band of the PCell is lower than a radio frequency band of the SCell. In some cases, the PCell and the SCell are non-collocated cells.

The DDTR report manager 1315 may receive a DDTR report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier. In some examples, the DDTR report manager 1315 may transmit a configuration for the DDTR report. In some examples, the DDTR report manager 1315 may transmit an indication of an identification of the second carrier via radio resource control signaling or DCI. In some cases, the DDTR report is configured as aperiodic, periodic, semi-persistent, or a combination thereof. In some cases, the configuration is transmitted via radio resource control signaling. In some cases, the DDTR report is received via a PUSCH, a PUCCH, or both.

The TA command transmission component 1320 may transmit a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR report. In some examples, the TA command transmission component 1320 may transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell. In some examples, the TA command transmission component 1320 may transmit a subsequent TA command in a random access response message, a MAC CE, or both, that indicates a further adjusted transmission timing offset. In some cases, the reference signal includes an SRS.

The autonomous adjustment manager 1325 may transmit a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier. In some cases, the TA command is transmitted via a random access response message or a MAC CE. In some cases, the reference signal includes an SRS.

The trigger transmission component 1330 may transmit a trigger to initiate a random access procedure on the second carrier. The reference signal reception component 1335 may receive the reference signal from the UE according to the adjusted transmission timing offset. In some cases, the reference signal includes an SRS.

The preamble transmission component 1340 may transmit an indication of a random access preamble for the UE to use for the random access procedure on the second carrier. In some examples, the preamble transmission component 1340 may receive a random access preamble message on the second carrier according to the random access preamble. In some cases, the random access preamble is indicated based on a PDCCH order or radio resource control signaling.

FIG. 14 shows a diagram of a system 1400 including a device 1405 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The device 1405 may be an example of or include the components of device 1105, device 1205, or a base station 105 as described herein. The device 1405 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1410, a network communications manager 1415, a transceiver 1420, an antenna 1425, memory 1430, a processor 1440, and an inter-station communications manager 1445. These components may be in electronic communication via one or more buses (e.g., bus 1450) .

The communications manager 1410 may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, receive a DDTR report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier, and transmit a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR report.

The communications manager 1410 may also configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration and transmit a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.

The communications manager 1410 may also configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration, transmit a trigger to initiate a random access procedure on the second carrier, transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, and receive the reference signal from the UE according to the adjusted transmission timing offset.

The network communications manager 1415 may manage communications with the core network (e.g., via one or more wired backhaul links) . For example, the network communications manager 1415 may manage the transfer of data communications for client devices, such as one or more UEs 115.

The transceiver 1420 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1420 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1420 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1425. However, in some cases the device may have more than one antenna 1425, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 1430 may include RAM, ROM, or a combination thereof. The memory 1430 may store computer-readable code 1435 including instructions that, when executed by a processor (e.g., the processor 1440) cause the device to perform various functions described herein. In some cases, the memory 1430 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 1440 may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 1440 may be configured to operate a memory array using a memory controller. In some cases, a memory controller may be integrated into processor 1440. The processor 1440 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1430) to cause the device 1405 to perform various functions (e.g., functions or tasks supporting TA adjustment for downlink carrier aggregation) .

The inter-station communications manager 1445 may manage communications with other base station 105, and may include a controller or scheduler for controlling communications with UEs 115 in cooperation with other base stations 105. For example, the inter-station communications manager 1445 may coordinate scheduling for transmissions to UEs 115 for various interference mitigation techniques such as beamforming or joint transmission. In some examples, the inter-station communications manager 1445 may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between base stations 105.

The code 1435 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1435 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1435 may not be directly executable by the processor 1440 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 15 shows a flowchart illustrating a method 1500 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 1500 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1500 may be performed by a communications manager as described with reference to FIGs. 7 through 10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1505, the UE may identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration. The operations of 1505 may be performed according to the methods described herein. In some examples, aspects of the operations of 1505 may be performed by a carrier identification component as described with reference to FIGs. 7 through 10.

At 1510, the UE may identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 1510 may be performed according to the methods described herein. In some examples, aspects of the operations of 1510 may be performed by a secondary carrier identification component as described with reference to FIGs. 7 through 10.

At 1515, the UE may determine a difference between the first transmission timing offset and the second transmission timing offset. The operations of 1515 may be performed according to the methods described herein. In some examples, aspects of the operations of 1515 may be performed by a timing difference component as described with reference to FIGs. 7 through 10.

At 1520, the UE may transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset. The operations of 1520 may be performed according to the methods described herein. In some examples, aspects of the operations of 1520 may be performed by a reference signal transmission component as described with reference to FIGs. 7 through 10.

FIG. 16 shows a flowchart illustrating a method 1600 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 1600 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1600 may be performed by a communications manager as described with reference to FIGs. 7 through 10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1605, the UE may identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration. The operations of 1605 may be performed according to the methods described herein. In some examples, aspects of the operations of 1605 may be performed by a carrier identification component as described with reference to FIGs. 7 through 10.

At 1610, the UE may identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 1610 may be performed according to the methods described herein. In some examples, aspects of the operations of 1610 may be performed by a secondary carrier identification component as described with reference to FIGs. 7 through 10.

At 1615, the UE may determine a difference between the first transmission timing offset and the second transmission timing offset. The operations of 1615 may be performed according to the methods described herein. In some examples, aspects of the operations of 1615 may be performed by a timing difference component as described with reference to FIGs. 7 through 10.

At 1620, the UE may transmit a DDTR report to the PCell that indicates the difference between the first transmission timing offset and the second transmission timing offset. The operations of 1620 may be performed according to the methods described herein. In some examples, aspects of the operations of 1620 may be performed by a DDTR report component as described with reference to FIGs. 7 through 10.

At 1625, the UE may receive a TA command indicating the adjusted transmission timing offset. The operations of 1625 may be performed according to the methods described herein. In some examples, aspects of the operations of 1625 may be performed by a TA command reception component as described with reference to FIGs. 7 through 10.

At 1630, the UE may transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset. The operations of 1630 may be performed according to the methods described herein. In some examples, aspects of the operations of 1630 may be performed by a reference signal transmission component as described with reference to FIGs. 7 through 10.

FIG. 17 shows a flowchart illustrating a method 1700 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 1700 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1700 may be performed by a communications manager as described with reference to FIGs. 7 through 10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1705, the UE may receive a TA command from the PCell that includes an indication for the UE to autonomously apply the adjusted transmission timing offset. The operations of 1705 may be performed according to the methods described herein. In some examples, aspects of the operations of 1705 may be performed by an autonomous adjustment component as described with reference to FIGs. 7 through 10.

At 1710, the UE may identify a first transmission timing offset for a first carrier of a PCell of a downlink carrier aggregation configuration. The operations of 1710 may be performed according to the methods described herein. In some examples, aspects of the operations of 1710 may be performed by a carrier identification component as described with reference to FIGs. 7 through 10.

At 1715, the UE may identify a second transmission timing offset for a second carrier of an SCell of the downlink carrier aggregation configuration, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 1715 may be performed according to the methods described herein. In some examples, aspects of the operations of 1715 may be performed by a secondary carrier identification component as described with reference to FIGs. 7 through 10.

At 1720, the UE may determine a difference between the first transmission timing offset and the second transmission timing offset. The operations of 1720 may be performed according to the methods described herein. In some examples, aspects of the operations of 1720 may be performed by a timing difference component as described with reference to FIGs. 7 through 10.

At 1725, the UE may adjust, at the UE, the second transmission timing offset to the adjusted transmission timing offset based on receiving the TA command from the PCell, the difference between the first transmission timing offset and the second transmission timing offset, or both. The operations of 1725 may be performed according to the methods described herein. In some examples, aspects of the operations of 1725 may be performed by an autonomous adjustment component as described with reference to FIGs. 7 through 10.

At 1730, the UE may transmit a reference signal to the SCell using an adjusted transmission timing offset based on the difference between the first transmission timing offset and the second transmission timing offset. The operations of 1730 may be performed according to the methods described herein. In some examples, aspects of the operations of 1730 may be performed by a reference signal transmission component as described with reference to FIGs. 7 through 10.

FIG. 18 shows a flowchart illustrating a method 1800 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 1800 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1800 may be performed by a communications manager as described with reference to FIGs. 7 through 10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1805, the UE may configure a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 1805 may be performed according to the methods described herein. In some examples, aspects of the operations of 1805 may be performed by a carrier aggregation configuration component as described with reference to FIGs. 7 through 10.

At 1810, the UE may receive a trigger to initiate a random access procedure on the second carrier. The operations of 1810 may be performed according to the methods described herein. In some examples, aspects of the operations of 1810 may be performed by a trigger reception component as described with reference to FIGs. 7 through 10.

At 1815, the UE may receive, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset. The operations of 1815 may be performed according to the methods described herein. In some examples, aspects of the operations of 1815 may be performed by a TA command reception component as described with reference to FIGs. 7 through 10.

At 1820, the UE may transmit a reference signal on the second carrier using the adjusted transmission timing offset. The operations of 1820 may be performed according to the methods described herein. In some examples, aspects of the operations of 1820 may be performed by a reference signal transmission component as described with reference to FIGs. 7 through 10.

FIG. 19 shows a flowchart illustrating a method 1900 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 1900 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1900 may be performed by a communications manager as described with reference to FIGs. 7 through 10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1905, the UE may configure a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 1905 may be performed according to the methods described herein. In some examples, aspects of the operations of 1905 may be performed by a carrier aggregation configuration component as described with reference to FIGs. 7 through 10.

At 1910, the UE may receive a trigger to initiate a random access procedure on the second carrier. The operations of 1910 may be performed according to the methods described herein. In some examples, aspects of the operations of 1910 may be performed by a trigger reception component as described with reference to FIGs. 7 through 10.

At 1915, the UE may receive an indication of a random access preamble for the UE to use for the random access procedure on the second carrier. The operations of 1915 may be performed according to the methods described herein. In some examples, aspects of the operations of 1915 may be performed by a preamble identification component as described with reference to FIGs. 7 through 10.

At 1920, the UE may transmit a random access preamble message on the second carrier according to the random access preamble. The operations of 1920 may be performed according to the methods described herein. In some examples, aspects of the operations of 1920 may be performed by a preamble identification component as described with reference to FIGs. 7 through 10.

At 1925, the UE may receive, from the SCell, a TA command in a random access response message that indicates an adjusted transmission timing offset. The operations of 1925 may be performed according to the methods described herein. In some examples, aspects of the operations of 1925 may be performed by a TA command reception component as described with reference to FIGs. 7 through 10.

At 1930, the UE may transmit a reference signal on the second carrier using the adjusted transmission timing offset. The operations of 1930 may be performed according to the methods described herein. In some examples, aspects of the operations of 1930 may be performed by a reference signal transmission component as described with reference to FIGs. 7 through 10.

FIG. 20 shows a flowchart illustrating a method 2000 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 2000 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2000 may be performed by a communications manager as described with reference to FIGs. 11 through 14. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 2005, the base station may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 2005 may be performed according to the methods described herein. In some examples, aspects of the operations of 2005 may be performed by a carrier aggregation component as described with reference to FIGs. 11 through 14.

At 2010, the base station may receive a DDTR report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier. The operations of 2010 may be performed according to the methods described herein. In some examples, aspects of the operations of 2010 may be performed by a DDTR report manager as described with reference to FIGs. 11 through 14.

At 2015, the base station may transmit a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR report. The operations of 2015 may be performed according to the methods described herein. In some examples, aspects of the operations of 2015 may be performed by a TA command transmission component as described with reference to FIGs. 11 through 14.

FIG. 21 shows a flowchart illustrating a method 2100 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 2100 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2100 may be performed by a communications manager as described with reference to FIGs. 11 through 14. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 2105, the base station may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 2105 may be performed according to the methods described herein. In some examples, aspects of the operations of 2105 may be performed by a carrier aggregation component as described with reference to FIGs. 11 through 14.

At 2110, the base station may transmit a configuration for the DDTR report. The operations of 2110 may be performed according to the methods described herein. In some examples, aspects of the operations of 2110 may be performed by a DDTR report manager as described with reference to FIGs. 11 through 14.

At 2115, the base station may receive a DDTR report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier. The operations of 2115 may be performed according to the methods described herein. In some examples, aspects of the operations of 2115 may be performed by a DDTR report manager as described with reference to FIGs. 11 through 14.

At 2120, the base station may transmit a TA command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on the DDTR report. The operations of 2120 may be performed according to the methods described herein. In some examples, aspects of the operations of 2120 may be performed by a TA command transmission component as described with reference to FIGs. 11 through 14.

FIG. 22 shows a flowchart illustrating a method 2200 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 2200 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2200 may be performed by a communications manager as described with reference to FIGs. 11 through 14. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 2205, the base station may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 2205 may be performed according to the methods described herein. In some examples, aspects of the operations of 2205 may be performed by a carrier aggregation component as described with reference to FIGs. 11 through 14.

At 2210, the base station may transmit a TA command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell, where the adjusted transmission timing offset is based on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier. The operations of 2210 may be performed according to the methods described herein. In some examples, aspects of the operations of 2210 may be performed by an autonomous adjustment manager as described with reference to FIGs. 11 through 14.

FIG. 23 shows a flowchart illustrating a method 2300 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 2300 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2300 may be performed by a communications manager as described with reference to FIGs. 11 through 14. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 2305, the base station may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 2305 may be performed according to the methods described herein. In some examples, aspects of the operations of 2305 may be performed by a carrier aggregation component as described with reference to FIGs. 11 through 14.

At 2310, the base station may transmit a trigger to initiate a random access procedure on the second carrier. The operations of 2310 may be performed according to the methods described herein. In some examples, aspects of the operations of 2310 may be performed by a trigger transmission component as described with reference to FIGs. 11 through 14.

At 2315, the base station may transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell. The operations of 2315 may be performed according to the methods described herein. In some examples, aspects of the operations of 2315 may be performed by a TA command transmission component as described with reference to FIGs. 11 through 14.

At 2320, the base station may receive the reference signal from the UE according to the adjusted transmission timing offset. The operations of 2320 may be performed according to the methods described herein. In some examples, aspects of the operations of 2320 may be performed by a reference signal reception component as described with reference to FIGs. 11 through 14.

FIG. 24 shows a flowchart illustrating a method 2400 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 2400 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2400 may be performed by a communications manager as described with reference to FIGs. 11 through 14. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 2405, the base station may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 2405 may be performed according to the methods described herein. In some examples, aspects of the operations of 2405 may be performed by a carrier aggregation component as described with reference to FIGs. 11 through 14.

At 2410, the base station may transmit a trigger to initiate a random access procedure on the second carrier. The operations of 2410 may be performed according to the methods described herein. In some examples, aspects of the operations of 2410 may be performed by a trigger transmission component as described with reference to FIGs. 11 through 14.

At 2415, the base station may transmit an indication of a random access preamble for the UE to use for the random access procedure on the second carrier. The operations of 2415 may be performed according to the methods described herein. In some examples, aspects of the operations of 2415 may be performed by a preamble transmission component as described with reference to FIGs. 11 through 14.

At 2420, the base station may receive a random access preamble message on the second carrier according to the random access preamble. The operations of 2420 may be performed according to the methods described herein. In some examples, aspects of the operations of 2420 may be performed by a preamble transmission component as described with reference to FIGs. 11 through 14.

At 2425, the base station may transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell. The operations of 2425 may be performed according to the methods described herein. In some examples, aspects of the operations of 2425 may be performed by a TA command transmission component as described with reference to FIGs. 11 through 14.

At 2430, the base station may receive the reference signal from the UE according to the adjusted transmission timing offset. The operations of 2430 may be performed according to the methods described herein. In some examples, aspects of the operations of 2430 may be performed by a reference signal reception component as described with reference to FIGs. 11 through 14.

FIG. 25 shows a flowchart illustrating a method 2500 that supports TA adjustment for downlink carrier aggregation in accordance with aspects of the present disclosure. The operations of method 2500 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2500 may be performed by a communications manager as described with reference to FIGs. 11 through 14. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 2505, the base station may configure a UE with a first carrier of a PCell and a second carrier of an SCell for downlink carrier aggregation, where uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration. The operations of 2505 may be performed according to the methods described herein. In some examples, aspects of the operations of 2505 may be performed by a carrier aggregation component as described with reference to FIGs. 11 through 14.

At 2510, the base station may transmit a trigger to initiate a random access procedure on the second carrier. The operations of 2510 may be performed according to the methods described herein. In some examples, aspects of the operations of 2510 may be performed by a trigger transmission component as described with reference to FIGs. 11 through 14.

At 2515, the base station may transmit a TA command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the SCell. The operations of 2515 may be performed according to the methods described herein. In some examples, aspects of the operations of 2515 may be performed by a TA command transmission component as described with reference to FIGs. 11 through 14.

At 2520, the base station may receive the reference signal from the UE according to the adjusted transmission timing offset. The operations of 2520 may be performed according to the methods described herein. In some examples, aspects of the operations of 2520 may be performed by a reference signal reception component as described with reference to FIGs. 11 through 14.

At 2525, the base station may transmit a subsequent TA command in a random access response message, a MAC CE, or both, that indicates a further adjusted transmission timing offset. The operations of 2525 may be performed according to the methods described herein. In some examples, aspects of the operations of 2525 may be performed by a TA command transmission component as described with reference to FIGs. 11 through 14.

It should be noted that the methods described herein describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined.

Although aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR networks. For example, the described techniques may be applicable to various other wireless communications systems such as Ultra Mobile Broadband (UMB) , Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Flash-OFDM, as well as other systems and radio technologies not explicitly mentioned herein.

Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, a CPU, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration) .

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include random-access memory (RAM) , read-only memory (ROM) , electrically erasable programmable ROM (EEPROM) , flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that may be used to carry or store desired program code means in the form of instructions or data structures and that may be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) , or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of computer-readable medium. Disk and disc, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD) , floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of” or “one or more of” ) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) . Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an example step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on. ”

In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label.

The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “example” used herein means “serving as an example, instance, or illustration, ” and not “preferred” or “advantageous over other examples. ” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

The description herein is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein, but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

A method for wireless communications at a user equipment (UE), comprising:

identifying a first transmission timing offset for a first carrier of a primary cell of a downlink carrier aggregation configuration;

identifying a second transmission timing offset for a second carrier of a secondary cell of the downlink carrier aggregation configuration, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

determining a difference between the first transmission timing offset and the second transmission timing offset; and

transmitting a reference signal to the secondary cell using an adjusted transmission timing offset based at least in part on the difference between the first transmission timing offset and the second transmission timing offset.
The method of claim 1, further comprising:

transmitting a differential downlink timing reference reporting report to the primary cell that indicates the difference between the first transmission timing offset and the second transmission timing offset.
The method of claim 2, further comprising:

receiving a configuration for the differential downlink timing reference reporting report.
The method of claim 3, wherein the differential downlink timing reference reporting report is configured as aperiodic, periodic, semi-persistent, or a combination thereof.
The method of claim 3, wherein the configuration is received via radio resource control signaling.
The method of claim 2, wherein the differential downlink timing reference reporting report is transmitted via a physical uplink shared channel, a physical uplink control channel, or both.
The method of claim 2, further comprising:

receiving an indication of an identification of the second carrier via radio resource control signaling or downlink control information.
The method of claim 2, further comprising:

receiving a timing advance command indicating the adjusted transmission timing offset.
The method of claim 8, wherein the timing advance command indicating the adjusted transmission timing offset is based at least in part on the differential downlink timing reference reporting report, the reference signal transmitted to the secondary cell, or both.
The method of claim 1, further comprising:

receiving a timing advance command from the primary cell that includes an indication for the UE to autonomously apply the adjusted transmission timing offset.
The method of claim 10, further comprising:

adjusting, at the UE, the second transmission timing offset to the adjusted transmission timing offset based at least in part on receiving the timing advance command from the primary cell, the difference between the first transmission timing offset and the second transmission timing offset, or both.
The method of claim 1, further comprising:

transmitting the reference signal or a data signal to the primary cell using the first transmission timing offset for the primary cell; and

switching to the secondary cell to transmit the reference signal to the secondary cell using the adjusted transmission timing offset.
The method of claim 1, wherein the primary cell and the secondary cell comprise different radio frequency bands.
The method of claim 13, wherein a radio frequency band of the primary cell is lower than a radio frequency band of the secondary cell.
The method of claim 1, wherein the primary cell and the secondary cell are non-collocated cells.
The method of claim 1, wherein the reference signal comprises a sounding reference signal.
A method for wireless communications at a user equipment (UE), comprising:

configuring a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

receiving a trigger to initiate a random access procedure on the second carrier;

receiving, from the secondary cell, a timing advance command in a random access response message that indicates an adjusted transmission timing offset; and

transmitting a reference signal on the second carrier using the adjusted transmission timing offset.
The method of claim 17, further comprising:

receiving an indication of a random access preamble for the UE to use for the random access procedure on the second carrier; and

transmitting a random access preamble message on the second carrier according to the random access preamble.
The method of claim 18, wherein the random access preamble is indicated based at least in part on a physical downlink control channel order or radio resource control signaling.
The method of claim 17, further comprising:

receiving a subsequent timing advance command in a random access response message, a medium access control layer control element, or both, that indicates a further adjusted transmission timing offset.
The method of claim 17, wherein the primary cell and the secondary cell comprise different radio frequency bands.
The method of claim 21, wherein a radio frequency band of the primary cell is lower than a radio frequency band of the secondary cell.
The method of claim 17, wherein the primary cell and the secondary cell are non-collocated cells.
The method of claim 17, wherein the reference signal comprises a sounding reference signal.
A method for wireless communications, comprising:

configuring a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

receiving a differential downlink timing reference reporting report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier; and

transmitting a timing advance command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell, wherein the adjusted transmission timing offset is based at least in part on the differential downlink timing reference reporting report.
The method of claim 25, further comprising:

transmitting a configuration for the differential downlink timing reference reporting report.
The method of claim 26, wherein the differential downlink timing reference reporting report is configured as aperiodic, periodic, semi-persistent, or a combination thereof.
The method of claim 26, wherein the configuration is transmitted via radio resource control signaling.
The method of claim 25, wherein the differential downlink timing reference reporting report is received via a physical uplink shared channel, a physical uplink control channel, or both.
The method of claim 25, further comprising:

transmitting an indication of an identification of the second carrier via radio resource control signaling or downlink control information.
The method of claim 25, wherein the primary cell and the secondary cell comprise different radio frequency bands.
The method of claim 31, wherein a radio frequency band of the primary cell is lower than a radio frequency band of the secondary cell.
The method of claim 25, wherein the primary cell and the secondary cell are non-collocated cells.
The method of claim 25, wherein the reference signal comprises a sounding reference signal.
A method for wireless communications, comprising:

configuring a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration; and

transmitting a timing advance command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell, wherein the adjusted transmission timing offset is based at least in part on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.
The method of claim 35, wherein the timing advance command is transmitted via a random access response message or a medium access control layer control element.
The method of claim 35, wherein the primary cell and the secondary cell comprise different radio frequency bands.
The method of claim 37, wherein a radio frequency band of the primary cell is lower than a radio frequency band of the secondary cell.
The method of claim 35, wherein the primary cell and the secondary cell are non-collocated cells.
The method of claim 35, wherein the reference signal comprises a sounding reference signal.
A method for wireless communications, comprising:

configuring a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

transmitting a trigger to initiate a random access procedure on the second carrier;

transmitting a timing advance command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell; and

receiving the reference signal from the UE according to the adjusted transmission timing offset.
The method of claim 41, further comprising:

transmitting an indication of a random access preamble for the UE to use for the random access procedure on the second carrier; and

receiving a random access preamble message on the second carrier according to the random access preamble.
The method of claim 42, wherein the random access preamble is indicated based at least in part on a physical downlink control channel order or radio resource control signaling.
The method of claim 41, further comprising:

transmitting a subsequent timing advance command in a random access response message, a medium access control layer control element, or both, that indicates a further adjusted transmission timing offset.
The method of claim 41, wherein the primary cell and the secondary cell comprise different radio frequency bands.
The method of claim 45, wherein a radio frequency band of the primary cell is lower than a radio frequency band of the secondary cell.
The method of claim 41, wherein the primary cell and the secondary cell are non-collocated cells.
The method of claim 41, wherein the reference signal comprises a sounding reference signal.
An apparatus for wireless communications at a user equipment (UE), comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

identify a first transmission timing offset for a first carrier of a primary cell of a downlink carrier aggregation configuration;

identify a second transmission timing offset for a second carrier of a secondary cell of the downlink carrier aggregation configuration, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

determine a difference between the first transmission timing offset and the second transmission timing offset; and

transmit a reference signal to the secondary cell using an adjusted transmission timing offset based at least in part on the difference between the first transmission timing offset and the second transmission timing offset.
An apparatus for wireless communications at a user equipment (UE), comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

configure a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

receive a trigger to initiate a random access procedure on the second carrier;

receive, from the secondary cell, a timing advance command in a random access response message that indicates an adjusted transmission timing offset; and

transmit a reference signal on the second carrier using the adjusted transmission timing offset.
An apparatus for wireless communications, comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

configure a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

receive a differential downlink timing reference reporting report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier; and

transmit a timing advance command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell, wherein the adjusted transmission timing offset is based at least in part on the differential downlink timing reference reporting report.
An apparatus for wireless communications, comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

configure a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration; and

transmit a timing advance command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell, wherein the adjusted transmission timing offset is based at least in part on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.
An apparatus for wireless communications, comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

configure a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

transmit a trigger to initiate a random access procedure on the second carrier;

transmit a timing advance command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell; and

receive the reference signal from the UE according to the adjusted transmission timing offset.
An apparatus for wireless communications at a user equipment (UE), comprising:

means for identifying a first transmission timing offset for a first carrier of a primary cell of a downlink carrier aggregation configuration;

means for identifying a second transmission timing offset for a second carrier of a secondary cell of the downlink carrier aggregation configuration, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

means for determining a difference between the first transmission timing offset and the second transmission timing offset; and

means for transmitting a reference signal to the secondary cell using an adjusted transmission timing offset based at least in part on the difference between the first transmission timing offset and the second transmission timing offset.
An apparatus for wireless communications at a user equipment (UE), comprising:

means for configuring a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

means for receiving a trigger to initiate a random access procedure on the second carrier;

means for receiving, from the secondary cell, a timing advance command in a random access response message that indicates an adjusted transmission timing offset; and

means for transmitting a reference signal on the second carrier using the adjusted transmission timing offset.
An apparatus for wireless communications, comprising:

means for configuring a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

means for receiving a differential downlink timing reference reporting report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier; and

means for transmitting a timing advance command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell, wherein the adjusted transmission timing offset is based at least in part on the differential downlink timing reference reporting report.
An apparatus for wireless communications, comprising:

means for configuring a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration; and

means for transmitting a timing advance command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell, wherein the adjusted transmission timing offset is based at least in part on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.
An apparatus for wireless communications, comprising:

means for configuring a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

means for transmitting a trigger to initiate a random access procedure on the second carrier;

means for transmitting a timing advance command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell; and

means for receiving the reference signal from the UE according to the adjusted transmission timing offset.
A non-transitory computer-readable medium storing code for wireless communications at a user equipment (UE), the code comprising instructions executable by a processor to:

identify a first transmission timing offset for a first carrier of a primary cell of a downlink carrier aggregation configuration;

identify a second transmission timing offset for a second carrier of a secondary cell of the downlink carrier aggregation configuration, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

determine a difference between the first transmission timing offset and the second transmission timing offset; and

transmit a reference signal to the secondary cell using an adjusted transmission timing offset based at least in part on the difference between the first transmission timing offset and the second transmission timing offset.
A non-transitory computer-readable medium storing code for wireless communications at a user equipment (UE), the code comprising instructions executable by a processor to:

configure a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

receive a trigger to initiate a random access procedure on the second carrier;

receive, from the secondary cell, a timing advance command in a random access response message that indicates an adjusted transmission timing offset; and

transmit a reference signal on the second carrier using the adjusted transmission timing offset.
A non-transitory computer-readable medium storing code for wireless communications, the code comprising instructions executable by a processor to:

configure a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

receive a differential downlink timing reference reporting report that indicates a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier; and

transmit a timing advance command indicating an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell, wherein the adjusted transmission timing offset is based at least in part on the differential downlink timing reference reporting report.
A non-transitory computer-readable medium storing code for wireless communications, the code comprising instructions executable by a processor to:

configure a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration; and

transmit a timing advance command that includes an indication for the UE to autonomously apply an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell, wherein the adjusted transmission timing offset is based at least in part on a difference between a first transmission timing offset for the first carrier and a second transmission timing offset for the second carrier.
A non-transitory computer-readable medium storing code for wireless communications, the code comprising instructions executable by a processor to:

configure a user equipment (UE) with a first carrier of a primary cell and a second carrier of a secondary cell for downlink carrier aggregation, wherein uplink transmission resources for the second carrier are reserved for reference signal transmissions according to a reference signal carrier switching configuration;

transmit a trigger to initiate a random access procedure on the second carrier;

transmit a timing advance command in a random access response message that indicates an adjusted transmission timing offset for transmitting a reference signal from the UE to the secondary cell; and

receive the reference signal from the UE according to the adjusted transmission timing offset.