WO2018085762A1

WO2018085762A1 - Methods for controlling rach-less mobility procedures

Info

Publication number: WO2018085762A1
Application number: PCT/US2017/060142
Authority: WO
Inventors: David Comstock
Original assignee: Kyocera Corporation
Priority date: 2016-11-04
Filing date: 2017-11-06
Publication date: 2018-05-11

Abstract

Various techniques for performing RACH-less mobility procedures are disclosed. An uplink grant is provided to the UE device so the UE device can transmit an uplink message to a target base station. In response to receiving the uplink message, the target base station transmits a radio resource allocation to the UE device via the PDCCH. The radio resource allocation can be a downlink assignment or an uplink grant. Upon receipt of the radio resource allocation, an indication that the radio resource allocation has been received is sent from a Media Access Control (MAC) protocol layer of the UE device to a protocol layer that is higher than the MAC protocol layer. The higher protocol layer of the UE device determines when the RACH-less mobility procedure has been completed, based at least partially on when the radio resource allocation is received from the target base station.

Description

METHODS FOR CONTROLLING RACH-LESS MOBILITY PROCEDURES

CLAIM OF PRIORITY

[0001] The present application claims priority to Provisional Application No.

62/417,507, entitled "METHODS FOR TRIGGERING AN ENB TO TRANSMIT A MAC MESSAGE", filed November 4, 2016 and to Provisional Application No. 62/455,432, entitled "METHODS FOR CONTROLLING RACH-LESS MOBILITY PROCEDURES", filed February 6, 2017, both assigned to the assignee hereof and hereby expressly incorporated by reference in their entirety.

FIELD

[0002] This invention generally relates to wireless communications and more particularly to controlling mobility procedures within wireless systems.

BACKGROUND

[0003] In conventional systems, a handover of a user equipment (UE) device from a source base station (e.g., source eNB) to a target base station (e.g., target eNB) involves the source base station transmitting a Handover Request message to the target base station (e.g., to initiate a handover) and the target base station transmitting a message in response. The source base station signals target base station uplink resources to the UE device, which utilizes the uplink resources for a Random-Access Channel (RACH) procedure. After the UE device is handed over to the target base station, the UE device transmits an uplink signal to the target base station as part of the RACH procedure. The target base station uses the uplink signal received from the UE device to calculate a Timing Advance (TA), which is needed in order for the UE device's uplink transmissions to be synchronized to the target base station after handover. The target base station signals the TA in the Random Access Response (RAR) message, along with uplink resources needed for the UE device to obtain uplink access to the target base station as part of the handover procedure. The UE device determines when the handover procedure is completed for the UE device, based upon when the UE device receives the RAR message. In conventional systems configured to provide Dual Connectivity, a Secondary Base Station (SeNB) Change of a UE device from a source SeNB to a target SeNB makes use of a similar RACH procedure.

SUMMARY

[0004] Various techniques for performing RACH-less mobility procedures are disclosed. An uplink grant is provided to the UE device so the UE device can transmit an uplink message to a target base station. In response to receiving the uplink message, the target base station transmits a radio resource allocation to the UE device via the PDCCH. The radio resource allocation can be a downlink assignment or an uplink grant. Upon receipt of the radio resource allocation, an indication that the radio resource allocation has been received is sent from a Media Access Control (MAC) protocol layer of the UE device to a protocol layer that is higher than the MAC protocol layer. The higher protocol layer of the UE device determines when the RACH-less mobility procedure has been completed, based at least partially on when the radio resource allocation is received from the target base station and whether the allocation is an uplink grant or a downlink assignment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 A is a block diagram of an example of a communication system configured to execute a RACH-less handover of a UE device from a source base station to a target base station.

[0006] FIG. 1 B is a block diagram of an example of a communication system configured to execute a RACH-less SeNB Change procedure, transferring a UE device from a source SeNB to a target SeNB.

[0007] FIG. 2A is a block diagram of an example of the base stations shown in FIGS. 1A and 1 B. [0008] FIG. 2B is a block diagram of an example of the UE devices shown in FIGS. 1A and 1 B.

[0009] FIG. 3 is a messaging diagram of an example of the messages exchanged between the various system components shown in FIG. 1A.

[0010] FIG. 4 is a messaging diagram of an example of the messages exchanged between the various system components shown in FIG. 1 B.

[0011] FIG. 5 is a flowchart of an example of a method in which a RACH-less mobility procedure is used to transfer a UE device to a target base station.

DETAILED DESCRIPTION

[0012] The Timing Advance (TA) provided by a target base station to a UE device during a handover in conventional systems is needed in order for the UE device's uplink transmissions to be synchronized to the target base station after handover. If the uplink transmissions are not properly synchronized to the target base station, the target base station will not be able to detect and decode the transmissions. However, one drawback of conventional systems is that the TA determination step increases the amount of time required to complete the handover procedure in examples when the TA may not need to be determined during a handover.

[0013] RACH-less handovers can be used in examples when the TA does not need to be determined during a handover, in order to reduce the time required to complete the handover procedure. As used herein, the term "RACH-less handover" refers to skipping the transmission of the Random-Access Channel (RACH) by the user equipment (UE) device to the target base station (e.g., target eNB) during handover, which significantly improves the delay for the handover procedure since the RACH procedure is a substantial part of the handover delay. However, if the RACH procedure is not performed, an alternative method must provide a way for the UE device to be able to determine when a handover of the UE device has been successfully completed, which is determined by receiving the RAR message in conventional systems. [0014] Besides the foregoing requirements, a RACH-less handover procedure performed in a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system that is configured to provide Dual Connectivity to UE devices requires similar considerations. For example, Dual Connectivity (DC) allows UE devices to exchange data simultaneously from different base stations, also referred to as eNodeBs (eNBs), in order to boost the performance in a heterogeneous network with dedicated carrier deployment. Dual Connectivity in an LTE network can significantly improve per-user throughput and mobility robustness by allowing users to be connected simultaneously to a master cell group (MCG) and a secondary cell group (SCG) via a Master eNB (MeNB) and Secondary eNB (SeNB), respectively. In such a system, as a UE device moves or radio conditions change, the UE device may maintain a primary connection with the same MeNB but may have a secondary connection that is handed over from a first SeNB (e.g., Source SeNB) to a second SeNB (e.g., Target SeNB). This type of handover in a system that provides Dual Connectivity is known as a Secondary base station (SeNB) Change procedure.

[0015] The examples described herein illustrate various techniques for performing RACH-less mobility procedures, including RACH-less handovers and RACH-less SeNB Change procedures. As part of a RACH-less handover procedure, a source base station can transmit a semi-permanent uplink grant to the UE device in a Radio

Resource Control (RRC) Connection Reconfiguration message. Alternatively, a target base station can transmit an uplink grant to the UE device on the Physical Downlink Control Channel (PDCCH). Regardless of the manner in which the uplink grant is provided to the UE device, the uplink grant provides the resources for the UE device to transmit an uplink transmission to the target base station and is the first uplink grant received from the target base station for the handover procedure. The higher layer stores an indication that the first uplink grant has been received. The UE device transmits an RRC Connection Reconfiguration Complete message using the uplink grant received either in the RRC Connection Reconfiguration message or via the PDCCH. [0016] Upon receipt of the RRC Connection Reconfiguration Complete message, the target base station can begin exchanging data with the UE according to normal operation and will transmit a radio resource allocation to the UE device via the PDCCH. The radio resource allocation can be a downlink assignment or an uplink grant, according to the available traffic. The UE device determines when the handover procedure has been completed, based at least partially on when this radio resource allocation is received from the target base station and the stored indication of the first uplink grant.

[0017] As part of a RACH-less SeNB Change procedure in systems configured to provide Dual Connectivity, the MeNB can transmit a semi-permanent uplink grant to the UE device in a Radio Resource Control (RRC) Connection Reconfiguration message. Alternatively, a Target SeNB can transmit an uplink grant to the UE device on the PDCCH. Regardless of the manner in which the uplink grant is provided to the UE device, the uplink grant provides the resources for the UE device to transmit an uplink transmission to the Target SeNB and is the first uplink grant received for the SeNB Change procedure. The higher layer stores an indication that the first uplink grant has been received. Upon receipt of the uplink grant, the UE device generates an

unspecified message to send to the Target SeNB. In some examples, the message comprises only a MAC message. In other examples, the message may also contain data and/or control information. The UE device transmits the message using the uplink grant received either in the RRC Connection Reconfiguration message or via the PDCCH.

[0018] Upon receipt of the message, the Target SeNB can begin exchanging data with the UE according to normal operation and will transmit a radio resource allocation to the UE device via the PDCCH. The radio resource allocation can be a downlink assignment or an uplink grant, according to the available traffic. The UE device determines when the SeNB Change procedure has been completed, based at least partially on when the radio resource allocation is received from the Target SeNB and the stored indication of the first uplink grant. [0019] FIG. 1 A is a block diagram of an example of a communication system configured to execute a RACH-less handover of a UE device from a source base station to a target base station. The communication system 100 is part of a radio access network (not shown) that provides various wireless services to UE devices that are located within the respective service areas of the various base stations that are part of the radio access network.

[0020] In the interest of clarity and brevity, communication system 100 is shown as having only source base station 101 and target base station 103. However, in other examples, communication system 100 could have any suitable number of base stations. In the example of FIG. 1A, at least a portion of the service areas (cells) for base stations 101 , 103 are represented by cells 107, 1 1 1 , respectively. Cells 107, 1 1 1 are

represented by ovals, but a typical communication system 100 would have a plurality of cells, each having variously shaped geographical service areas. Moreover, although cells 107, 1 1 1 are shown as only partially overlapping in the example of FIG. 1A, one of the cells 107, 1 1 1 may be located entirely within the other cell 107, 1 1 1 in other examples.

[0021] Base stations 101 , 103, sometimes referred to as eNodeBs or eNBs, communicate with the wireless user equipment (UE) device 105 by respectively transmitting downlink signals 109, 1 13 when connected to UE device 105. Base stations 101 , 103 respectively receive uplink signals 1 17, 1 19 transmitted from the UE device 105 when connected to UE device 105. The UE device 105 is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone, for example.

[0022] Base stations 101 , 103 are connected to the network through backhaul 1 15 in accordance with known techniques. As shown in FIG. 2A, source base station 101 comprises controller 204, transmitter 206, and receiver 208, as well as other electronics, hardware, and code. Although FIG. 2A specifically depicts the circuitry and

configuration of source base station 101 , the same base station circuitry and

configuration that is shown and described in connection with source base station 101 is also utilized for base station 103, in the example shown in FIG. 1A, and for base stations 102, 104, 106 in the example shown in FIG. 1 B. In other examples, any of the base stations may have circuitry and/or a configuration that differs from that of the source base station 101 shown in FIG. 2A.

[0023] The source base station 101 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to the source base station 101 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

[0024] For the example shown in FIG. 2A, the source base station 101 may be a fixed device or apparatus that is installed at a particular location at the time of system deployment. Examples of such equipment include fixed base stations or fixed transceiver stations. In some situations, the source base station 101 may be mobile equipment that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generating equipment such as electric generators, solar panels, and/or batteries. Larger and heavier versions of such equipment may be transported by trailer. In still other situations, the source base station 101 may be a portable device that is not fixed to any particular location.

[0025] The controller 204 includes any combination of hardware, software, and/or firmware for executing the functions described herein as well as facilitating the overall functionality of the source base station 101 . An example of a suitable controller 204 includes code running on a microprocessor or processor arrangement connected to memory. The transmitter 206 includes electronics configured to transmit wireless signals. In some situations, the transmitter 206 may include multiple transmitters. The receiver 208 includes electronics configured to receive wireless signals. In some situations, the receiver 208 may include multiple receivers. The receiver 208 and transmitter 206 receive and transmit signals, respectively, through an antenna 210. The antenna 210 may include separate transmit and receive antennas. In some

circumstances, the antenna 210 may include multiple transmit and receive antennas. [0026] The transmitter 206 and receiver 208 in the example of FIG. 2A perform radio frequency (RF) processing including modulation and demodulation. The receiver 208, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 206 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the base station functions. The required components may depend on the particular functionality required by the base station.

[0027] The transmitter 206 includes a modulator (not shown), and the receiver 208 includes a demodulator (not shown). The modulator modulates the signals to be transmitted as part of the downlink signals 109 and can apply any one of a plurality of modulation orders. The demodulator demodulates any uplink signals 1 17 received at the source base station 101 in accordance with one of a plurality of modulation orders. Returning to FIG. 1A, the communication system 100 provides various wireless services to UE device 105 via base stations 101 , 103. For the examples herein, the

communication system 100 operates in accordance with at least one revision of the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) communication specification. UE device 105 is initially served by source base station 101 . Thus, UE device 105 receives downlink signals 109 via antenna 212 and receiver 214, as shown in FIG. 2B. Besides antenna 212 and receiver 214, UE device 105 further comprises controller 216 and transmitter 218, as well as other electronics, hardware, and code. UE device 105 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to UE device 105 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

[0028] The controller 216 includes any combination of hardware, software, and/or firmware for executing the functions described herein as well as facilitating the overall functionality of a UE device. An example of a suitable controller 216 includes code running on a microprocessor or processor arrangement connected to memory. The transmitter 218 includes electronics configured to transmit wireless signals. In some situations, the transmitter 218 may include multiple transmitters. The receiver 214 includes electronics configured to receive wireless signals. In some situations, the receiver 214 may include multiple receivers. The receiver 214 and transmitter 218 receive and transmit signals, respectively, through antenna 212. The antenna 212 may include separate transmit and receive antennas. In some circumstances, the antenna 212 may include multiple transmit and receive antennas.

[0029] The transmitter 218 and receiver 214 in the example of FIG. 2B perform radio frequency (RF) processing including modulation and demodulation. The receiver 214, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 218 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in

combination or cooperation with other components perform the UE device functions. The required components may depend on the particular functionality required by the UE device.

[0030] The transmitter 218 includes a modulator (not shown), and the receiver 214 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as part of the uplink signals 1 17, 1 19, which are shown in FIG. 1 A. The demodulator demodulates the downlink signals 109, 1 13 in accordance with one of a plurality of modulation orders.

[0031] At the beginning of operation of the example shown in FIG. 1 A, the UE device 105 is being served by source base station 101 . Thus, upon receipt of the downlink signals 109, the UE device 105 demodulates the downlink signals 109, which yields encoded data packets that contain data pertaining to at least one of the wireless services that the source base station 101 is providing to the UE device 105. The UE device 105 decodes the encoded data packets, using controller 216, to obtain the data.

[0032] When any one or more criteria are met for source base station 101 to hand the UE device 105 over to target base station 103, source base station 101 transmits a handover request, via communication link 1 15, to target base station 103. The

handover criteria may include, for example, radio congestion at source base station 101 , poor/deteriorating signal quality for the uplink/downlink signals for UE device 105, and/or underutilization of available resources by target base station 103. However, any other suitable criteria could be used.

[0033] Regardless of the criteria used, the source base station 101 can transmit the handover request to target base station 103 via a wired (e.g., X2) or a wireless communication link. If the transmission is wireless, source base station 101 uses transmitter 206 and antenna 210 to transmit the handover request, and target base station 103 receives the wireless transmission of the handover request via antenna 210 and receiver 208. The transmission of the handover request to the target base station 103 is represented in FIG. 3 by signal 302.

[0034] If the target base station 103 agrees to the handover, the target base station 103 sends a handover request acknowledgement message to the source base station 101 via communication link 1 15, which can be a wired connection or a wireless connection. The handover request acknowledgement message includes configuration information to be sent to the UE device 105 to be used for accessing the target base station 103. The transmission of the handover request acknowledgement is represented in FIG. 3 by signal 304.

[0035] Upon receipt of the handover request acknowledgement, the source base station 101 transmits a Radio Resource Control (RRC) Connection Reconfiguration message, using transmitter 206 and antenna 210, to the UE device 105. The UE device 105 receives the RRC Connection Reconfiguration message via antenna 212 and receiver 214. The RRC Connection Reconfiguration message includes an information element that indicates that a RACH-less handover procedure is to be performed and which also specifies that the UE device 105 should operate in a mobility configuration associated with the RACH-less handover procedure. In some examples, the RRC Connection Reconfiguration message also includes, from the target base station, a semi-permanent uplink grant, which recurs periodically but is configured once with a single signaling message to the UE device 105. The semi-permanent uplink grant is the first uplink grant received from the target base station 103 for the handover procedure. The higher layer stores an indication that the first uplink grant has been received. Transmission of the RRC Connection Reconfiguration message is represented in FIG. 3 by signal 306.

[0036] In other examples, the target base station 103 transmits the first uplink grant for the handover procedure, using transmitter 206 and antenna 210, to the UE device 105 on the Physical Downlink Control Channel (PDCCH). The UE device 105 receives the uplink grant via antenna 212 and receiver 214. Upon receipt of the first uplink grant, the controller 216 of the UE device 105 sends an indication, from a Media Access Control (MAC) protocol layer to a protocol layer that is higher than the MAC protocol layer, that an uplink grant has been received. The higher layer stores an indication that the first uplink grant has been received. Transmission of the uplink grant via the

PDCCH is represented in FIG. 3 by signal 307.

[0037] Regardless of how the first uplink grant for the handover procedure is provided to the UE device 105, the UE device 105 utilizes the uplink grant to send an RRC Connection Reconfiguration Complete message, using transmitter 218 and antenna 212, to the target base station 103 once the RRC Connection Reconfiguration is complete. The target base station 103 receives the RRC Connection Reconfiguration Complete message via antenna 210 and receiver 208. The transmission of the RRC Connection Reconfiguration Complete message is represented in FIG. 3 by signal 308.

[0038] Upon receipt of the RRC Connection Reconfiguration Complete message, the target base station 103 can begin exchanging data with the UE according to normal operation and will transmit, via transmitter 206 and antenna 210, a radio resource allocation message to the UE device 105, according to the available traffic. The UE device 105 receives the radio resource allocation message via antenna 212 and receiver 214. In some examples, the radio resource allocation is a downlink assignment. In other examples, the radio resource allocation is an uplink grant.

[0039] Upon receipt of the radio resource allocation message, the controller 216 of the UE device 105 sends an indication, from a Media Access Control (MAC) protocol layer to a protocol layer that is higher than the MAC protocol layer, that the radio resource allocation message has been received. For the examples described herein, MAC messages contain control information that originates and terminates in peer MAC layer (Layer 2) protocol entities, such as specified in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) MAC specification, for example, and includes MAC messages, such as the Random Access Response (RAR) message, as well as MAC Control Elements. Radio Resource Control (RRC) messages contain control information that originates and terminates in peer RRC layer (Layer 3) protocol entities. RRC layer messages are higher protocol layer messages with respect to MAC protocol layer messages.

[0040] Based on the indication that the radio resource allocation message has been received and the stored indication of the first uplink grant, the higher protocol layer (e.g., RRC protocol layer) of the UE device 105 determines that the mobility procedure (e.g., RACH-less handover) has been completed. If the indication is for a downlink

assignment, the higher protocol layer of the UE device 105 determines that the mobility procedure has been completed. If the indication is for an uplink grant and a first uplink grant has previously been received, the higher protocol layer of the UE device 105 determines that the mobility procedure has been completed. In addition, upon receipt of the radio resource allocation message (e.g., uplink grant or downlink assignment), the controller 216 of the UE device 105 can stop a timer associated with the mobility procedure (e.g., RACH-less handover), which indicates that the mobility procedure has been completed. Moreover, reception of the radio resource allocation message (e.g., uplink grant or downlink assignment) will trigger the controller 216 of the UE device 105 to release the mobility configuration associated with the RACH-less handover.

Furthermore, in examples in which a semi-permanent uplink grant was transmitted to the UE device 105 in the RRC Connection Reconfiguration message, reception of the radio resource allocation message (e.g., uplink grant or downlink assignment) will trigger the controller 216 of the UE device 105 to clear the semi-permanent uplink grant.

[0041] FIG. 1 B is a block diagram of an example of a communication system configured to provide Dual Connectivity in which a RACH-less SeNB Change procedure is executed so that the secondary connection of a UE device is handed over from a first SeNB (e.g., Source SeNB) to a second SeNB (e.g., Target SeNB). The communication system 200 is part of a radio access network (not shown) that provides various wireless services to UE devices that are located within the respective service areas of the various base stations that are part of the radio access network. More specifically, the communication system 200 provides various wireless services to UE device 105 via base stations 102, 104, 106.

[0042] For the examples herein, the communication system 200, which operates in accordance with at least one revision of the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) communication specification, is configured to provide Dual Connectivity to UE devices. Dual Connectivity (DC) allows UE devices to exchange data simultaneously from different base stations, also referred to as eNodeBs (eNBs), in order to boost the performance in a heterogeneous network with dedicated carrier deployment. Dual Connectivity in an LTE network can significantly improve per-user throughput and mobility robustness by allowing users to be connected simultaneously to a master cell group (MCG) and a secondary cell group (SCG) via a Master eNB (MeNB) and Secondary eNB (SeNB), respectively. In such a system, as a UE device moves or radio conditions change, the UE device may maintain a primary connection with the same MeNB but may have a secondary connection that is handed over from a first SeNB (e.g., Source SeNB) to a second SeNB (e.g., Target SeNB). This type of handover in a system that provides Dual Connectivity is known as a Secondary base station (SeNB) Change procedure.

[0043] In the interest of clarity and brevity, communication system 200 is shown as having only one Master base station (MeNB) 102 and only two Secondary base stations (SeNBs) 104, 106. However, in other examples, communication system 200 could have any suitable number of Master base stations and Secondary base stations. In the example of FIG. 1 B, at least a portion of the service area (cell) for Master base station 102 is represented by cell 108. At least a portion of the respective service areas (cells) for Secondary base stations 104, 106 are represented by cells 1 12, 1 16. Cells 108, 1 12, 1 16 are represented by ovals, but a typical communication system 200 would have a plurality of cells, each having variously shaped geographical service areas. Moreover, although cell 108 is shown as only partially overlapping cells 1 12, 1 16 in the example of FIG. 1 B, one, or both, of cells 1 12, 1 16 may be located entirely within cell 108, in other examples.

[0044] Base stations 102, 104, 106, sometimes referred to as eNodeBs or eNBs, communicate with the wireless user equipment (UE) device 105 by respectively transmitting downlink signals 1 10, 1 14, 122 when connected to UE device 105. Base stations 102, 104, 106 respectively receive uplink signals 1 18, 120, 124 transmitted from the UE device 105 when connected to UE device 105. The UE device 105 is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone, for example.

[0045] Base stations 102, 104, 106 are connected to the network through a backhaul (not shown) in accordance with known techniques. As described above, base stations 102, 104, 106 comprise the circuitry and configuration shown in FIG. 2A and have the characteristics and features described in connection with source base station 101 of FIG. 1A. However, in other examples, any of the base stations 102, 104, 106 may have circuitry, a configuration, characteristics, and/or features that differ from that shown in FIG. 2A and described in connection with source base station 101 of FIG. 1A.

[0046] UE device 105 is initially served by Master base station 102 and by Source SeNB (S-SeNB) 104. As described above, UE device 105 comprises the circuitry and configuration shown in FIG. 2B and has the characteristics and features described in connection with FIG. 1A. However, in other examples, UE device 105 may have circuitry, a configuration, characteristics, and/or features that differ from that shown in FIG. 2B and described in connection with FIG. 1A.

[0047] At the beginning of operation of the example shown in FIG. 1 B, the UE device 105 is being served by Master base station 102 and Source SeNB 104. Thus, upon receipt of the downlink signals 1 10, 1 14, the UE device 105 demodulates the downlink signals 1 10, 1 14, which yields encoded data packets that contain data pertaining to at least one of the wireless services that the Master base station 102 and the Source SeNB 104 are providing to the UE device 105. The UE device 105 decodes the encoded data packets, using controller 216, to obtain the data. [0048] When the Secondary base station (SeNB) Change procedure criteria are met, the SeNB Change procedure is initiated. The SeNB Change procedure criteria may include, for example, radio congestion at Source SeNB 104, poor/deteriorating signal quality for the uplink/downlink signals for UE device 105, and/or underutilization of available resources by Target SeNB 106. However, any other suitable criteria could be used. As mentioned above, when performing the SeNB Change procedure, the UE device 105 maintains its primary connection with the Master base station 102 but hands over its secondary connection from the Source SeNB 104 to the Target SeNB 106.

[0049] To initiate the SeNB Change procedure, the Master base station 102 transmits an SeNB Addition Request to Target SeNB 106 via a wired (e.g., X2) or a wireless communication link. If the transmission is wireless, Master base station 102 uses transmitter 206 and antenna 210 to transmit the SeNB Addition Request, and Target SeNB 106 receives the wireless transmission of the SeNB Addition Request via its antenna 210 and receiver 208. The transmission of the SeNB Addition Request to the Target SeNB 106 is represented in FIG. 4 by signal 402.

[0050] If the Target SeNB 106 agrees to serve as the SeNB for UE device 105, the Target SeNB 106 sends an SeNB Addition Request Acknowledgement message to the Master base station 102 via a wired connection or a wireless connection. The transmission of the SeNB Addition Request Acknowledgement is represented in FIG. 4 by signal 404. Upon receipt of the SeNB Addition Request Acknowledgement, the

Master base station 102 transmits an SeNB Release Request to Source SeNB 104 via a wired (e.g., X2) or a wireless communication link, which informs the Source SeNB 104 that the secondary connection of the UE device 105 is being handed over to Target SeNB 106. The transmission of the SeNB Release Request message is represented in FIG. 4 by signal 406.

[0051] The Master base station 102 transmits a Radio Resource Control (RRC) Connection Reconfiguration message, using transmitter 206 and antenna 210, to the UE device 105. The UE device 105 receives the RRC Connection Reconfiguration message via antenna 212 and receiver 214. The RRC Connection Reconfiguration message includes an information element that indicates that a RACH-less SeNB Change procedure is to be performed and which also specifies that the UE device 105 should operate in a mobility configuration associated with the RACH-less SeNB Change procedure. In some examples, the RRC Connection Reconfiguration message also includes, from the Target SeNB 106, a semi-permanent uplink grant, which recurs periodically but is configured once with a single signaling message to the UE device 105. The semi-permanent uplink grant is the first uplink grant received from the Target SeNB 106 for the SeNB Change procedure. The higher layer stores an indication that the first uplink grant has been received. Transmission of the RRC Connection Reconfiguration message is represented in FIG. 4 by signal 408.

[0052] In other examples, the Target SeNB 106 transmits the first uplink grant for the SeNB Change procedure, using transmitter 206 and antenna 210, to the UE device 105 on the Physical Downlink Control Channel (PDCCH) at a later time. The UE device 105 receives the uplink grant via antenna 212 and receiver 214. Upon receipt of the first uplink grant, the controller 216 of the UE device 105 sends an indication, from a Media Access Control (MAC) protocol layer to a protocol layer that is higher than the MAC protocol layer, that an uplink grant has been received. The higher layer stores an indication that the first uplink grant has been received. Transmission of the uplink grant via the PDCCH is represented in FIG. 4 by signal 414. Although FIG. 4 shows that signal 414 is transmitted after transmission of the SeNB Reconfiguration Complete signal 412, signal 414 can be transmitted at any time before transmission of the MAC message 416.

[0053] Once the RRC Connection is reconfigured, the UE device 105 transmits an RRC Connection Reconfiguration Complete message to the Master base station 102. The RRC Connection Reconfiguration Complete message is represented in FIG. 4 by signal 410. Upon receipt of the RRC Connection Reconfiguration Complete message, the Master base station 102 transmits an SeNB Reconfiguration Complete message to Target SeNB 106 to inform Target SeNB 106 that UE device 105 has been reconfigured to switch its secondary connection from Source SeNB 104 to Target SeNB 106. The SeNB Reconfiguration Complete message is represented in FIG. 4 by signal 412. [0054] Utilizing the uplink grant provided by the RRC Connection Reconfiguration message 408 or the PDCCH via signal 414, the UE device 105 sends an uplink transmission to the Target SeNB 106. For example, upon receipt of the uplink grant, the UE device 105 generates an unspecified message to send to the Target SeNB 106. In some examples, the message comprises only a MAC message. In other examples, the message may also contain data and/or control information.

[0055] The UE device 105 transmits, via transmitter 218 and antenna 212, the unspecified message (e.g., MAC message) to the Target SeNB 106 in an uplink transmission 124. The Target SeNB 106 receives the unspecified message via antenna 210 and receiver 208. The transmission of the unspecified message to the Target SeNB 106 is represented in FIG. 4 by signal 416.

[0056] Upon receipt of the unspecified message, the Target SeNB 106 can begin exchanging data with the UE device 105 according to normal operation and will transmit, via transmitter 206 and antenna 210, a radio resource allocation message to the UE device 105 on the PDCCH, according to the available traffic. The UE device 105 receives the radio resource allocation message via antenna 212 and receiver 214. The transmission of the radio resource allocation message is represented in FIG. 4 by signal 418. In some examples, the radio resource allocation is a downlink assignment. In other examples, the radio resource allocation is an uplink grant.

[0057] Upon receipt of the radio resource allocation message, the controller 216 of the UE device 105 sends an indication, from a Media Access Control (MAC) protocol layer to a protocol layer that is higher than the MAC protocol layer, that the radio resource allocation message has been received. For the examples described herein, MAC messages contain control information that originates and terminates in peer MAC layer (Layer 2) protocol entities, such as specified in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) MAC specification, for example, and includes MAC messages, such as the Random Access Response (RAR) message, as well as MAC Control Elements. Radio Resource Control (RRC) messages contain control information that originates and terminates in peer RRC layer (Layer 3) protocol entities. RRC layer messages are higher protocol layer messages with respect to MAC protocol layer messages.

[0058] Based on the indication that the radio resource allocation message has been received and the stored indication of the first uplink grant, the higher protocol layer (e.g., RRC protocol layer) of the UE device 105 determines that the mobility procedure (e.g., RACH-less SeNB Change procedure) has been completed. If the indication is for a downlink assignment, the higher protocol layer of the UE device 105 determines that the mobility procedure has been completed. If the indication is for an uplink grant and a first uplink grant has previously been received, the higher protocol layer of the UE device 105 determines that the mobility procedure has been completed. In addition, upon receipt of the radio resource allocation message (e.g., uplink grant or downlink assignment), the controller 216 of the UE device 105 can stop a timer associated with the mobility procedure (e.g., RACH-less SeNB Change procedure), which indicates that the mobility procedure has been completed. Moreover, reception of the radio resource allocation message (e.g., uplink grant or downlink assignment) will trigger the controller 216 of the UE device 105 to release the mobility configuration associated with the RACH-less SeNB Change procedure. Furthermore, in examples in which a semipermanent uplink grant was transmitted to the UE device 105 in the RRC Connection Reconfiguration message, reception of the radio resource allocation message (e.g., uplink grant or downlink assignment) will trigger the controller 216 of the UE device 105 to clear the semi-permanent uplink grant.

[0059] FIG. 3 is a messaging diagram of an example of the messages exchanged between the various system components shown in FIG. 1A. In this example, the source base station 101 transmits a Handover Request to target base station 103, via signal 302. In response, target base station 103 transmits a Handover Request

Acknowledgement to the source base station 101 via signal 304.

[0060] Upon receipt of the Handover Request Acknowledgement, the source base station 101 transmits an RRC Connection Reconfiguration message to the UE device 105, which is represented by signal 306. As mentioned above, the RRC Connection Reconfiguration message may contain (1 ) a semi-permanent uplink grant for the UE device 105, and (2) an information element that indicates that a RACH-less handover procedure is to be performed and which also specifies that the UE device 105 should operate in a mobility configuration associated with the RACH-less handover procedure.

[0061] In other examples, the target base station 103 transmits an uplink grant to the UE device 105 on the Physical Downlink Control Channel (PDCCH). Transmission of the uplink grant via the PDCCH is represented in FIG. 3 by signal 307.

[0062] Once the RRC Connection is reconfigured, the UE device 105 uses the uplink grant to transmit an RRC Connection Reconfiguration Complete message to the target base station 103 via signal 308. Upon receipt of the RRC Connection Reconfiguration Complete message, the target base station 103 can begin exchanging data with the UE device 105 according to normal operation and will transmit a radio resource allocation message to the UE device 105 via the PDCCH, according to the available traffic. The transmission of the radio resource allocation message is represented in FIG. 3 by signal 310. As mentioned above, in some examples, the radio resource allocation is a downlink assignment. In other examples, the radio resource allocation is an uplink grant.

[0063] The UE device 105 utilizes the radio resource allocation message to (1 ) determine that the mobility procedure (e.g., RACH-less handover) has been completed, (2) stop a timer associated with the mobility procedure (e.g., RACH-less handover), which indicates that the mobility procedure has been completed, (3) release the mobility configuration associated with the RACH-less handover, and/or (4) clear the semipermanent uplink grant, if a semi-permanent uplink grant was transmitted to the UE device 105 in the RRC Connection Reconfiguration message.

[0064] FIG. 4 is a block diagram of an example of the messages exchanged between the various system components shown in FIG. 1 B. In this example, the Master base station 102 transmits a SeNB Addition Request to Target SeNB 106, via signal 402. In response, Target SeNB 106 transmits an SeNB Addition Request

Acknowledgement to the Master base station 102 via signal 404. Upon receipt of the SeNB Addition Request Acknowledgement, the Master base station 102 transmits an SeNB Release Request to the Source SeNB 104 via signal 406. [0065] The Master base station 102 transmits an RRC Connection Reconfiguration message to the UE device 105, which is represented by signal 408. As mentioned above, the RRC Connection Reconfiguration message may contain (1 ) a semipermanent uplink grant for the UE device 105, and (2) an information element that indicates that a RACH-less SeNB Change procedure is to be performed and which also specifies that the UE device 105 should operate in a mobility configuration associated with the RACH-less SeNB Change procedure.

[0066] In other examples, the Target SeNB 106 transmits an uplink grant to the UE device 105 on the Physical Downlink Control Channel (PDCCH) at a time before transmission of the MAC message 416. In the example shown in FIG. 4, the

transmission of the uplink grant via the PDCCH is represented by signal 414. Although FIG. 4 shows that signal 414 is transmitted after transmission of the SeNB

Reconfiguration Complete signal 412, signal 414 can be transmitted at any time before transmission of the MAC message 416.

[0067] Once the RRC Connection is reconfigured, the UE device 105 transmits an RRC Connection Reconfiguration Complete message to the Master base station 102 via signal 410. Upon receipt of the RRC Connection Reconfiguration Complete message, the Master base station 102 transmits an SeNB Reconfiguration Complete message to Target SeNB 106 to inform Target SeNB 106 that UE device 105 has been reconfigured to switch its secondary connection from Source SeNB 104 to Target SeNB 106. The SeNB Reconfiguration Complete message is represented in by signal 412.

[0068] Utilizing the uplink grant provided by the RRC Connection Reconfiguration message 408 or the PDCCH via signal 414, the UE device 105 sends an uplink transmission to the Target SeNB 106. For example, upon receipt of the uplink grant, the UE device 105 generates an unspecified message to send to the Target SeNB 106. In some examples, the message comprises a MAC message. In other examples, the message also contains data and/or control information.

[0069] The UE device 105 transmits the unspecified message (e.g., MAC message) to the Target SeNB 106 in an uplink transmission, which is represented in FIG. 4 by signal 416. Upon receipt of the unspecified message, the Target SeNB 106 can begin exchanging data with the UE device 105 according to normal operation and will transmit a radio resource allocation message to the UE device 105 via the PDCCH, according to the available traffic. The transmission of the radio resource allocation message is represented in FIG. 4 by signal 418. As mentioned above, in some examples, the radio resource allocation is a downlink assignment. In other examples, the radio resource allocation is an uplink grant.

[0070] The UE device 105 utilizes the radio resource allocation message to (1 ) determine that the mobility procedure (e.g., RACH-less SeNB Change procedure) has been completed, (2) stop a timer associated with the mobility procedure (e.g., RACH- less SeNB Change procedure), which indicates that the mobility procedure has been completed, (3) release the mobility configuration associated with the RACH-less SeNB Change procedure, and/or (4) clear the semi-permanent uplink grant, if a semipermanent uplink grant was transmitted to the UE device 105 in the RRC Connection Reconfiguration message.

[0071] FIG. 5 is a flowchart of an example of a method in which a RACH-less mobility procedure is used to handover a UE device to a target base station. The steps of method 500 may be performed in a different order than described herein and shown in the example of FIG. 5. Furthermore, in some examples, one or more of the steps may be omitted. Moreover, in other examples, one or more additional steps may be added.

[0072] The method 500 begins at step 502 with receiving, at UE device 105, a first uplink grant. In some examples, the first uplink grant is a semi-permanent uplink grant received in an RRC Connection Reconfiguration message. In other examples, the first uplink grant is an uplink grant received from a target base station (e.g., target base station 103 or Target SeNB 106) via the PDCCH. At step 504, the UE device 105 receives a radio resource allocation message via the PDCCH during a RACH-less mobility procedure (e.g., RACH-less handover or RACH-less SeNB Change procedure). The radio resource allocation message may be an uplink grant or a downlink

assignment. At step 506, the UE device 105 sends an indication, from the MAC protocol layer to a higher protocol layer, that the radio resource allocation has been received. At step 508, the higher protocol layer of the UE device 105 determines, based on the indication, that the mobility procedure has been completed. At step 510, the UE device 105 stops a timer associated with the mobility procedure. At step 512, the UE device 105 releases a mobility configuration associated with the mobility procedure.

[0073] Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims

1 . A method comprising:

receiving a message, which includes a radio resource allocation, on a Physical Downlink Control Channel (PDCCH) during a mobility procedure, the mobility procedure not involving transmission of a Random-Access Channel (RACH) by a user equipment (UE) device to a target base station;

sending, from a Media Access Control (MAC) protocol layer to a protocol layer that is higher than the MAC protocol layer, an indication that the radio resource allocation has been received; and

determining, by the higher layer, that the mobility procedure has been completed based on the indication.

2. The method of claim 1 , wherein the mobility procedure comprises a handover.

3. The method of claim 2, wherein the message comprises a downlink assignment.

4. The method of claim 2, wherein the message comprises an uplink grant.

5. The method of claim 1 , wherein the mobility procedure comprises a Secondary base station (SeNB) Change procedure.

6. The method of claim 5, wherein the message comprises a downlink assignment.

7. The method of claim 5, wherein the message comprises an uplink grant.

8. The method of claim 1 , further comprising: upon receipt of a downlink assignment, stopping a timer associated with the mobility procedure; and

releasing a mobility configuration associated with the mobility procedure.

9. The method of claim 1 , further comprising:

receiving a first uplink grant;

upon receipt of a second uplink grant, stopping a timer associated with the mobility procedure; and

releasing a mobility configuration associated with the mobility procedure.

10. A system comprising:

a target base station; and

a user equipment (UE) device comprising:

a receiver configured to receive a message, which includes a radio resource allocation, on a Physical Downlink Control Channel (PDCCH) during a mobility procedure, the mobility procedure not involving transmission of a

Random-Access Channel (RACH) by a user equipment (UE) device to the target base station, and

a controller configured to:

send, from a Media Access Control (MAC) protocol layer to a protocol layer that is higher than the MAC protocol layer, an indication that the radio resource allocation has been received, and

determine, at the higher layer, that the mobility procedure has been completed based on the indication.

1 1 The system of claim 10, wherein the mobility procedure comprises a handover.

12. The system of claim 1 1 , wherein the message comprises a downlink assignment.

13. The system of claim 1 1 , wherein the message comprises an uplink grant.

14. The system of claim 10, wherein the mobility procedure comprises a Secondary base station (SeNB) Change procedure.

15. The system of claim 14, wherein the message comprises a downlink assignment.

16. The system of claim 14, wherein the message comprises an uplink grant.

17. The system of claim 10, wherein the controller of the UE device is further configured to:

upon receipt of a downlink assignment, stop a timer associated with the mobility procedure; and

release a mobility configuration associated with the mobility procedure.

18. The system of claim 10, wherein the receiver of the UE device is further configured to receive a first uplink grant and a second uplink grant, and wherein the controller of the UE device is further configured to:

upon receipt of the second uplink grant, stop a timer associated with the mobility procedure; and

release a mobility configuration associated with the mobility procedure.