BR112017007104B1 - REFERENCE SIGNAL DESIGN FOR WIRELESS COMMUNICATIONS - Google Patents

Abstract

REFERENCE SIGNAL DESIGN FOR WIRELESS COMMUNICATIONS. A reference signal design in wireless systems is described. A base station may select a reference signal density scheme from a set of available density schemes associated with a port count. The reference signal density scheme may also be selected based on the category of the mobile device receiving the reference signal transmissions. The reference signal density scheme may be a higher density reference signal scheme or a lower density reference signal scheme, wherein the higher density reference signal density scheme includes more signal elements. reference signal features per subframe. The mobile device may determine the reference signal density scheme based on the characteristics of a channel. The higher density reference signal density scheme can provide additional channel estimation opportunities for the mobile device. In some cases, the mobile device sends the estimated channel based on the received reference signals to the base station.

Description

Cross References

[0001] The present application claims priority to U.S. Patent Application No. 14/876,678 to Chen et al., entitled “REFERENCE SIGNAL DESIGN FOR WIRELESS COMMUNICATIONS”, filed on October 6, 2015, and to the Application US Patent Provisional No. 62/061,634 to Chen et al., entitled “REFERENCE SIGNAL DESIGN FOR WIRELESS COMMUNICATIONS”, filed October 8, 2014, each of which is hereby assigned to the assignee.

FUNDAMENTALS Description Field

[0002] The present description relates to reference signal design for wireless communications and, more particularly, for improved machine-type communications in Long Term Evolution wireless communications.

Description of Related Technique

[0003] Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, message exchange, broadcast, and so on. These systems may be multiple access systems capable of supporting communication with multiple users by sharing available system resources (e.g., time, frequency, and power). Examples of such multiple access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and frequency division multiple access (FDMA) systems. orthogonal frequency (OFDMA).

[0004] By way of example, a multiple access wireless communication system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, otherwise known as user equipment (UE). A base station can communicate with UEs on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station). ).

[0005] UEs may be of different categories, including categories that have limited or reduced resources relative to other categories, such as when configured to use reduced communication resources compared to other categories. UEs can also operate in restricted environments, such as basements, equipment closets, and the like. And UEs may be limited by certain narrow bandwidth operations. Machine-type communication (MTC) devices, for example, may be affected by these considerations. Certain coverage enhancement (CE) techniques can, however, provide greater operational flexibility for UEs, such as MTC devices.

SUMMARY

[0006] The described characteristics generally refer to one or more improved systems, methods and/or apparatus for reference signal design in wireless communications. In general, reference signal (RS) design can provide a denser RS scheme, for example, additional reference signals (RSs) for UEs of a given type to enable additional channel estimation feedback opportunities. In some examples, a base station may determine that it is communicating with a type of UE or a UE that is operating in a category with reduced communication capabilities compared to other types of UEs or other categories. The base station may also determine the number of antenna ports available to the base station to send the RSs to the UE. The base station can then select and send RSs to the UE according to an RS density scheme that provides sufficient opportunities for the UE to measure channel conditions, and provide channel estimation feedback, to ensure that coverage requirements are met. satisfied. The base station may receive channel estimation feedback from the UE and, based on channel conditions, take appropriate action to provide the required coverage. In some examples, the base station may signal to the UE an indication of the RS density scheme being used. In some examples, the base station may receive a message from the UE including information indicating a request for improved coverage, for a particular mode of transmission, etc., which may benefit from a denser RS density scheme than a commonly used RS density scheme or otherwise a less dense RS density scheme and therefore configure the additional RSs to be used.

[0007] In one example, a method for wireless communication is described. The method may comprise selecting a reference signal (RS) density scheme from a set of RS density schemes and transmitting a reference signal to the mobile device in accordance with the selected RS density scheme.

[0008] In one example, an apparatus for wireless communication is described. The apparatus may comprise a processor, a memory in electronic communication with the processor, and instructions stored in the memory. Instructions may be executable by the processor to select a reference signal (RS) density scheme from a set of RS density schemes and transmit a reference signal to the mobile device in accordance with the RS density scheme. selected.

[0009] In one example, an apparatus for wireless communication is described. The apparatus may comprise means for selecting a reference signal (RS) density scheme from a set of RS density schemes and means for transmitting a reference signal to the mobile device in accordance with the selected RS density scheme.

[0010] In one example, a non-transitory computer-readable medium is described that stores computer-executable code for wireless communication. The code may be executable by a processor to select a reference signal (RS) density scheme from a set of RS density schemes and transmit a reference signal to the mobile device in accordance with the reference signal (RS) density scheme. RS determined.

[0011] Some examples of a non-transitory method, apparatus or computer-readable medium may comprise processes, resources, means or instructions for identifying a mobile device category or a mobile device capability. Some examples of a non-transitory method, apparatus, or computer-readable medium may comprise processes, resources, means, or instructions for identifying one or more parameters associated with a channel, which in some examples may comprise port counting of a mobile device. Some examples of a method, apparatus, or non-transitory computer-readable medium may comprise processes, resources, means, or instructions for selecting the RS density scheme from the set of RS density schemes based, at least in part, on the identified category. of the mobile device, the identified capability of the mobile device, the one or more parameters associated with the channel, or any combination thereof.

[0012] Some examples of method, apparatus or non-transitory computer readable medium may comprise processes, resources, means or instructions for receiving a channel quality indication from the mobile device, the channel quality indication based, at least on part of the transmitted reference signal. Transmitting the reference signal may comprise processes, resources, means or instructions for transmitting at least one of a cell specific reference signal (CRS) or one of a demodulation reference signal (DM-RS) or a combination thereof to the mobile device. Some examples of non-transitory method, apparatus or computer-readable medium may comprise processes, resources, means or instructions for identifying a coverage improvement for the mobile device, and selecting the RS density scheme based, at least in part, on the improvement in coverage identified.

[0013] Some examples of non-transitory method, apparatus or computer-readable medium may comprise processes, resources, means or instructions for identifying a transmission mode for the mobile device, and selecting the RS density scheme based on at least part, in the identified transmission mode. The transmission mode may comprise a broadcast mode or a unicast mode, and the transmission may utilize a broadcast channel or a unicast channel. In some examples of the non-transitory method, apparatus, or computer-readable medium, the transmission may utilize a control channel or a data channel, which may be a physical downlink control channel (PDCCH) or a physical downlink shared channel ( PDSCH). Some examples of non-transitory method, apparatus or computer-readable medium may comprise processes, resources, means or instructions for increasing a number of reference signals transmitted to the mobile device in accordance with the RS density scheme based on the identified category of the device mobile. The set of RS density schemes may comprise a lower density RS density scheme and a higher density RS density scheme. The mobile device category or mobile device capability may comprise at least one of a machine-type communications (MTC) device, a narrowband MTC device, a user equipment (UE) operating in a narrowband, a UE which supports multiple RS density schemes, or combinations thereof. The mobile device category may be Category 0. In some examples a mobile device capability may refer to an ability to operate in a mobile device category during a first period of time, which may not be the same mobile device category in a second period of time. Therefore, in some examples mobile device capability may refer to an ability to be selectively configured to operate in a category based on various parameters.

[0014] Some examples of a method, apparatus or non-transitory computer-readable medium may comprise processes, resources, means or instructions for transmitting a message to the mobile device, the message comprising an indication of the RS density scheme. The message may comprise an indication as to whether a cell specific reference signal (CRS) or a demodulation reference signal (DM-RS) or a combination thereof is included in the RS density scheme. In some examples of a non-transitory method, apparatus, or computer-readable medium, the indication of an RS density scheme may be transmitted in dedicated signaling or broadcast information. The port count can be at least one of one port or two ports. The RS density scheme may comprise twenty (20) resource elements per subframe.

[0015] In one example, a method for wireless communication is described. The method may comprise receiving a reference signal transmitted according to a reference signal (RS) density scheme, the RS density scheme selected from a set of RS density schemes, identifying the RS density scheme based, at least in part, on a channel type associated with the reference signal or a coverage enhancement for the channel associated with the reference signal, and communicating using the reference signal in accordance with the data density scheme RS identified.

[0016] In one example, an apparatus for wireless communication is described. The apparatus may comprise a processor; memory in electronic communication with the processor; and instructions stored in memory. Instructions may be executable by the processor to receive a reference signal transmitted according to a reference signal (RS) density scheme, the RS density scheme selected from a set of RS density schemes, identify the RS density scheme based, at least in part, on a channel type associated with the reference signal or on a coverage enhancement for the channel associated with the reference signal, and communicating using the reference signal in accordance with the RS density scheme identified.

[0017] In one example, an apparatus for wireless communication is described. The apparatus may comprise means for receiving a reference signal transmitted in accordance with a reference signal (RS) density scheme, the RS density scheme selected from a set of RS density schemes, identifying the RS density based, at least in part, on a channel type associated with the reference signal or on a coverage enhancement for the channel associated with the reference signal and communicating using the reference signal in accordance with the identified RS density.

[0018] In one example, a non-transitory computer-readable medium is described that stores computer-executable code for wireless communication. The code may be executable by a processor to receive a reference signal transmitted according to a reference signal (RS) density scheme, the RS density scheme selected from a set of RS density schemes, identify the RS density scheme based, at least in part, on a channel type associated with the reference signal or on a coverage enhancement for the channel associated with the reference signal, and communicate using the reference signal in accordance with the identified RS density scheme.

[0019] Some examples of a method, apparatus or non-transitory computer-readable medium may comprise processes, resources, means or instructions for receiving an indication of an RS density scheme, wherein the RS density scheme is identified based on the least in part, in the indication, and where the indication is received in dedicated signaling or broadcast information. In some examples of the method, apparatus or non-transitory computer readable medium, receiving the reference signal comprises processes, resources, means or instructions for receiving at least one of a cell specific reference signal (CRS) or a reference signal demodulation module (DM-RS) or a combination thereof.

[0020] Some examples of a method, apparatus or non-transitory computer readable medium may comprise processes, resources, means or instructions for receiving a set of reference signals, which may be an increased number of reference signals, in accordance with the scheme of RS density and based, at least in part, on a mobile device category or mobile device capability. In some examples of the non-transitory method, apparatus or computer-readable medium, the mobile device category comprises at least one of a machine-type communications (MTC) device, a narrowband MTC device, a UE operating in a narrow, a UE that supports multiple RS density schemes, or a Category 0 device.

[0021] In some examples of the method, apparatus, or non-transitory computer-readable medium, the RS density scheme is selected from the set of RS density schemes based, at least in part, on one or more associated parameters with the channel, which in some examples, may be associated with a port count of the mobile device.

[0022] In some examples of a method, apparatus or non-transitory computer readable medium, the channel type comprises at least one of a broadcast channel or a unicast channel. In some examples of the non-transitory method, apparatus, or computer-readable medium, the channel type comprises at least one of a control channel or a data channel. In some examples, the channel type may be a physical downlink control channel (PDCCH) or a physical downlink shared channel (PDSCH).

[0023] In some examples of the method, apparatus or non-transitory computer readable medium, the channel coverage enhancement comprises a repetition of the channel, and the RS density scheme is identified based, at least in part, on a number of channel repeats. In some examples the RS density scheme is identified by a first number of repetitions and another RS density scheme is identified by a second number of repetitions greater than the first number of repetitions, wherein the other RS density scheme has a higher RS density than the RS density scheme.

[0024] In some examples of the method, apparatus or non-transitory computer readable medium, the communicate comprises processes, resources, means or instructions for performing at least one of a channel estimate or an interference estimate using the reference signal, and decode the channel based on at least one of a channel estimate or an interference estimate. In some examples of the method, apparatus, or non-transitory computer-readable medium, the RS density scheme comprises twenty (20) resource elements per subframe.

[0025] The foregoing has very broadly outlined the characteristics and technical advantages of the examples in accordance with the description so that the detailed description that follows can be more easily understood. Additional features and advantages will be described below. The specific design and examples described can be readily used as a basis for modifying or designing other structures to accomplish the same purposes as the present description. These equivalent constructions do not depart from the scope of the appended claims. The characteristics of the concepts described in this document, both their organization and method of operation, together with the associated advantages will be more easily understood from the description that follows when considered in connection with the accompanying figures. Each of the figures is provided for purposes of illustration and description only and not as a definition of the limits of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] A greater understanding of the nature and advantages of the present invention can be perceived by reference to the following drawings and Appendix. In attached figures, similar components or features may have the same reference legend. Furthermore, multiple components of the same type can be distinguished by following the reference label by a dash and a second label that distinguishes between similar components. If only the first reference caption is used in the specification, the description is applicable to any of the similar components having the same first reference caption independently of the second reference caption.

[0027] FIG. 1 illustrates an example of a wireless communication system, in accordance with aspects of the present description;

[0028] FIG. 2 shows a message flowchart illustrating aspects of reference signal design in wireless communications, in accordance with aspects of the present disclosure;

[0029] FIGS. 3A to 3E show diagrams illustrating aspects of example reference signal density schemes in accordance with aspects of the present description;

[0030] FIG. 4 shows a message flow diagram illustrating aspects of reference signal design in wireless communications, in accordance with aspects of the present description;

[0031] FIG. 5 shows a message flow diagram illustrating aspects of reference signal design in wireless communications, in accordance with aspects of the present description;

[0032] FIG. 6 shows a block diagram of a device configured for use in wireless communication, in accordance with aspects of the present description;

[0033] FIG. 7 shows a block diagram of a device configured for use in wireless communication, in accordance with aspects of the present description;

[0034] FIG. 8 shows a system for use in wireless communication, in accordance with aspects of the present description;

[0035] FIG. 9 shows a block diagram of an apparatus for use in wireless communication, in accordance with aspects of the present description;

[0036] FIG. 10 shows a block diagram of an apparatus for use in wireless communication, in accordance with aspects of the present description;

[0037] FIG. 11 shows a block diagram of a base station (e.g., a base station forming part or all of an eNB) for use in wireless communication, in accordance with aspects of the present description;

[0038] FIG. 12 is a flowchart illustrating an example of a method for wireless communication in accordance with aspects of the present description;

[0039] FIG. 13 is a flowchart illustrating an example of a method for wireless communication in accordance with aspects of the present description; It is

[0040] FIG. 14 is a flowchart illustrating an example of a method for wireless communication in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

[0041] Wireless communication systems can be configured to support operation of devices at greater system bandwidths and with coverage enhancements (CEs) for limited coverage devices. System improvements can allow devices, which may have been designed to operate within a narrow bandwidth, to operate effectively over a wider bandwidth. For example, system enhancements may allow devices that are configured to operate within a 1.4 MHz bandwidth (e.g., six (6) resource blocks (RBs)) to operate, for example, in 3 MHz bands. , 5, 10, 15 or 20 MHz. And this improvement can allow coverage improvements of around 15 dB.

[0042] In some examples one or more devices of a wireless communication system may be a machine-type communication device (MTC), or may otherwise be operating in an MTC category. For example, a device may be configured to operate as a Category 5 device during one period of time, and configured to operate as an MTC device during a different period of time. In some cases, a system may utilize a wideband carrier (e.g., 3-20 MHz). Multiple MTC devices can communicate simultaneously on control and downlink channels within the bandwidth. For example, each MTC device may monitor, transmit, or receive with a restriction of six (6) physical RBs (PRB) at any given time; and different MTC devices can be served in different 6-PRB blocks. In other words, multiple MTC devices can communicate via frequency division multiplexed (FDM) resources of a single transmission time slot (TTI) (e.g., a subframe).

[0043] To support system enhancements, an MTC control or data channel may be frequency division multiplexed with control or data channels for other UEs, which may not be MTC devices. These MTC control and data channels can be referred to as an MTC physical downlink control channel (MPDCCH) and an MTC physical downlink shared channel (MPDSCH), respectively. In some examples, MTC devices capable of such FDM operation may be referred to as improved or evolved MTC (eMTC) devices.

[0044] The MPDCCH and MPDSCH can operate consistently, or beneficially with enhanced/evolved PDCCH (EPDCCH), which can provide uplink and downlink concessions to other UEs. For example, an MPDCCH or an MPDSCH with an EPDCCH can be frequency division multiplexed into a single TTI. In some examples, an EPDCCH is implemented by relying on a demodulation reference signal (DM-RS), as opposed to a cell-specific reference signal (CRS), which may allow the EPDCCH to be specifically configured for the UE. That is, each UE within a cell can be configured to monitor a different set of resources and therefore a different EPDCCH. Enhanced or evolved MTC devices can be similarly configured to monitor the MPDCCH or the MPDSCH, or both.

[0045] To support these improvements, reference signals for control or data channels, or both, may be modified with respect to other systems, such as previous Long Term Evolution (LTE) systems. These improvements can provide reference signals that produce a number of desirable properties for various devices such as MTC devices or eMTC devices. For example, reference signals in an improved system may provide both broadcast (e.g., MTC system information) and unicast transmission. They can even support coverage enhancements, including TTI bundling and non-aggregation scenarios. Additionally, they can support both normal and extended cyclic prefix (CP) implementations. And, in view of the need for backward compatibility and flexible deployment, they can support both legacy and new carrier types (e.g., LTE in an unlicensed spectrum).

[0046] An eMTC device can operate beneficially with knowledge of certain aspects of system improvement, and reference signal design, which can be conducted for eMTCs in broadcast information. For example, an eMTC device may determine the number of antenna ports (e.g., CRS ports) used by a base station by decoding a physical broadcast channel (PBCH) and, in some examples, determining a frequency offset. from CRS. Additionally, an eMTC device can determine system bandwidth (e.g., for a wideband carrier) by decoding the PBCH.

[0047] In some examples, a reference signal for eMTC devices may be based on CRS resource elements (REs) in a 6-PRB band assigned to, and monitored by, a group of eMTC devices, for example. The reference signal may also be based on DM-RS REs within the assigned PRBs. A DM-RS may be transmitted in whole, in a subset, or in none of the six assigned PRBs, however, depending on the PRB assignment. In some examples the reference signal may be based on a combination of CRS REs and DM-RS REs.

[0048] Various RS density schemes using different combinations of CRS REs and DM-RS REs can be employed to facilitate the operation of the eMTC. For example, eMTC devices may benefit from a higher density of RS transmissions than a commonly used RS density scheme, or, alternatively, a lower RS density scheme, where the higher RS density scheme high includes a set of CRS REs and DM-RS REs within a given PRB, which may be an increased number of reference signals, which may provide additional channel condition measurement and feedback opportunities. Additionally or alternatively, higher density RS density schemes may provide for MPDCCH or MPDSCH operation.

[0049] In accordance with aspects of the present description, the base station may select an RS density scheme to be used for a particular category of UE, or a UE otherwise operating in a particular category. For example, a UE may have a mobile device capability that refers to an ability to be selectively configured to operate in a category based on various parameters. The RS density scheme can also be based on one or more parameters associated with the channel. In some examples the RS density scheme may be based on the number of antenna ports being used to transmit the RS to the UE.

[0050] The RS density scheme can, for certain UEs or port counts, increase the number of resource elements (REs) used for reference signal transmissions within a PRB and, consequently, provide additional opportunities for the UE measure and report channel conditions. Channel conditions may comprise, but are not limited to, such conditions as signal phase, signal amplitude, signal strength, signal interference, signal distortion, signal-to-noise ratio (SNR), signal-to-noise plus interference ratio (SINR ), signal-to-noise plus distortion ratio (SNDR), channel coefficients, and the like. In some aspects, the RS density scheme may be based, at least in part, on a coverage improvement (e.g., a 15dB coverage improvement) for the UE, in a transmission mode (e.g., transmission over unicast, broadcast transmission, etc.) and so on to the UE. In some examples, the added REs (e.g., increased RS density) may also be increased in power — for example, certain REs may be transmitted at a higher power than other REs.

[0051] The following description provides examples, and is not limiting the scope, applicability or examples set forth in the claims. Changes can be made to the function and arrangement of the elements discussed without departing from the scope of the description. Various examples may omit, replace, or add various procedures or components when appropriate. For example, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Also, the features described in relation to some examples may be combined in other examples.

[0052] FIG. 1 illustrates an example of a wireless communication system 100 in accordance with aspects of the present description. The wireless communication system 100 includes base stations 105, UEs 115, and a core network 130. The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access. routing or mobility functions. The base stations 105 interface with the core network 130 via backhaul links 132 (e.g., S1, etc.) and may perform radio configuration and programming for communication with the UEs 115 or may operate under the control of a base station controller (not shown). In various examples, base stations 105 may communicate, either directly or indirectly (e.g., via core network 130), with other backhaul links 134 (e.g., X1, etc.), which may be wired or wireless communication links.

[0053] The base stations 105 may communicate wirelessly with the UEs 115 via one or more base station antennas. Each of the base station sites 105 may provide communications coverage for a respective geographic coverage area 110. In some examples, the base stations 105 may be referred to as a transceiver base station, a radio base station, a access, a radio transceiver, a NodeB, an eNodeB (eNB), a Home Node, a Home eNode, or some other appropriate terminology. The geographic coverage area 110 for a base station 105 may be divided into sectors that constitute a portion of the coverage area (not shown). The wireless communication system 100 may comprise base stations 105 of different types (e.g., macro and/or small cell base stations). Base stations 105 may be configured to communicate with one or more communication technologies, where each communication technology may have an associated geographic coverage area 110. The geographic coverage area 110 for a first communication technology may overlap with the geographic coverage area 110 for a second communication technology, and the first and second communication technologies may be associated with the same base station 105, or with different base stations 105.

[0054] In some examples, the wireless communication system 100 is an LTE/LTE-A network. In LTE/LTE-A networks, the terms Evolved NodeB or Enhanced NodeB (eNB) may be used generally to describe the base stations 105. The wireless communication system 100 may be a heterogeneous LTE/LTE-A network, in which different types of eNBs provide coverage for multiple geographic regions. For example, each eNB or base station 105 may provide communications coverage for a macro cell, a small cell, and/or other types of cells. The term "cell" is a 3GPP term that may be used to describe a base station, a carrier or component carrier associated with a base station, or a coverage area (e.g. sector, etc.) of a carrier or from a base station, depending on the context.

[0055] A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell is a lower power base station, compared to a macro cell, which can operate in the same band or different frequency bands (e.g. licensed, unlicensed, etc.) as macro cells. Small cells may comprise pico cells, femto cells and micro cells according to various examples. A pico cell can cover a relatively smaller geographic area and can allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell may also cover a relatively small geographic area (e.g., a home) and may provide restricted access by UEs with association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for home users and similar). An eNB for a macro cell can be referred to as a macro eNB. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB may support one or multiple (e.g., two, three, four, and the like) cells (e.g., component carriers).

[0056] The wireless communication system 100 may support synchronous or asynchronous operations. For synchronous operations, base stations can have similar frame timing, and transmissions from different base stations can be approximately aligned in time. For asynchronous operations, base stations may have different frame timing, and transmissions from different base stations may not be time aligned. The techniques described in this document can be used for synchronous or asynchronous operations.

[0057] Communication networks that can accommodate some of the various examples described can be packet-based networks that operate according to a layered protocol stack. At the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer can be IP-based. A Radio Link Control (RLC) layer can perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer can perform priority manipulation and multiplexing of logical channels within transport channels. The MAC layer can also use hybrid ARQ (HARQ) to provide retransmission at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide for the establishment, configuration, and maintenance of an RRC connection between a UE 115 and base stations 105 or the core network 130 supporting radio bearers for data on the user plan. At the Physical layer (PHY), transport channels can be mapped to Physical channels.

[0058] The UEs 115 may be dispersed throughout the wireless communication system 100, and each UE 115 may be stationary or mobile. A UE 115 may also comprise or be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device , a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a telephone handset, a user agent, a mobile client, a customer or some other appropriate terminology. A UE 115 may be a cellular telephone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a portable computer, a cordless telephone, a loop station wireless location (WLL), or similar. A UE 115 may be, or may otherwise be, operating as a machine-type communication device (MTC), an improved or evolved MTC device (eMTC), etc., which may comprise automated meters, sensors, and the like. which may have relatively low throughput applications, etc. A UE may be capable of communicating with various types of base stations and network equipment including macro eNBs, small cell eNBs, relay base stations, and the like.

[0059] In some examples, UEs 115 are MTC or eMTC devices located in areas that inhibit communications with a base station 105. An MTC may be located in a basement or equipment closet, for example, which may limit the ability of the MTC device to effectively receive transmissions from a base station 105. A base station 105 may therefore employ coverage enhancement (CE) techniques to improve or increase the likelihood of successful communications with the MTC device. Coverage enhancement techniques may comprise a number of transmission strategies that increase the effective transmission power of a signal.

[0060] By way of example, CE techniques may comprise repeated transmissions, TTI grouping, HARQ retransmission, uplink shared physical channel hopping (PUSCH), beamforming, power boosting or other techniques. The CE techniques used may depend on the specific needs of devices in different circumstances. For example, TTI grouping may involve sending multiple copies of the same information in a group of consecutive TTIs rather than waiting for a NACK before retransmitting redundant versions. This can be effective for users involved in VoLTE or voice over IP (VOIP) communications. In other cases, the number of HARQ retransmissions can also be increased. Uplink data transmissions can be transmitted using frequency hopping to achieve frequency diversity. Beamforming can be used to increase the strength of a signal in a certain direction, or the transmission power can simply be increased. In some cases, one or more CE options may be combined and CE levels may be set based on a number of decibels the techniques are expected to enhance a signal (e.g., no CE, 5dB CE, 10dB CE , 15dB CE, etc.). Additionally or alternatively, coverage improvement techniques may include a selection of a higher density RS scheme.

[0061] The communication links 125 shown in the wireless communication system 100 may include uplink transmissions (UL) from a UE 115 to a base station 105, and/or downlink transmissions (DL) from a base station 105 to a UE 115. Downlink transmissions may also be called forward link transmissions while uplink transmissions may also be called reverse link transmissions. Each communication link 125 may include one or more carriers, where each carrier may be a signal composed of multiple subcarriers (e.g., waveform signals of different frequencies) modulated in accordance with the various radio technologies described above. Each modulated signal can be sent on a different subcarrier and can carry control information (e.g. reference signals, control channels, etc.), overhead information, user data, etc. Communication links 125 may transmit bidirectional communications using frequency division duplexing (FDD) (e.g., utilizing paired spectrum resources) or time division duplexing (TDD) operation (e.g., utilizing unpaired spectrum resources). . Frame structures for FDD (e.g. frame structure type 1) and TDD (e.g. frame structure type 2) can be defined.

[0062] In some examples of the wireless communication system 100, the base stations 105 or the UEs 115 may include multiple antennas to employ antenna diversity schemes to improve the quality and reliability of communication between the base stations 105 and the UEs. 115. Additionally or alternatively, base stations 105 and/or UEs 115 may employ multiple-input multiple-output (MIMO) techniques that can take advantage of multipath environments to transmit multiple spatial layers carrying the same or different encoded data. .

[0063] The wireless communication system 100 may support operations on multiple cells or carriers, a feature that may be referred to as carrier aggregation (CA) or multicarrier operation. A carrier may also be referred to as a component carrier (CC), a layer, a channel, etc. The terms "carrier," "component carrier," "cell" and "channel" may be used interchangeably in this document. A UE 115 may be configured with multiple downlink CCs and one or more uplink CCs for carrier aggregation. Carrier aggregation can be used with both FDD and TDD component carriers.

[0064] In some examples, a base station 105 may select an RS density scheme from a set of available RS density schemes. In some examples, the selection of an RS density scheme may be based on the number of available antenna ports used to transmit RSs, as well as the mobile device category or mobile device capability of the UE 115 to which the RSs are located. being transmitted. For some categories or capabilities of UEs 115, the base station may select an increase in the density of RSs being transmitted within a PRB to provide additional channel measurement, interference measurement, and estimation support. For example, a UE 115 may be an eMTC that utilizes the increased RS density within the PRB to take additional RS measurements to provide clearer and more definitive feedback information about the channel condition. Consequently, the base station 105 may have more information to base transmission characteristic decisions on, e.g., modulation and coding scheme (MCS), transmission capacity, data rate, transmission power, etc. Accordingly, base station 105 may adjust the RS density scheme to provide additional channel measurement and report opportunities to support UEs 115 associated with or otherwise operate in a certain category. In some examples, the base station 105 may send a message to the UE 115 indicating the selected RS density scheme. The base station 105 may, for example, transmit a downlink control information element (DCI) on a control channel, and the DCI may indicate a particular RS density scheme.

[0065] FIG. 2 shows a message flow diagram 200 illustrating aspects of reference signal design in wireless communications, in accordance with aspects of the present disclosure. Message flow diagram 200 may illustrate aspects of wireless communication system 100 described with reference to FIG. 1. Message flow diagram 200 includes a source cell 205 and a mobile device 210. Source cell 205 may be an example of aspects of one or more of the base stations 105 described with reference to FIG. 1. The mobile device 210 may be an example of aspects of one or more of the UEs 115 described with reference to FIG. 1. Generally, message flow diagram 200 illustrates design implementation aspects of reference signal density scheme in wireless communication systems. In some examples, a system device, such as one of the UEs 115 or the base stations 105 described with reference to FIG. 1 may execute a set of codes to control functional elements of the device to perform some or all of the functions described below.

[0066] In block 215, source cell 205 may identify a mobile device category or a mobile device capability of mobile device 210. In various examples, mobile device 210 may be associated with, or otherwise be operating in, the identified category. . For example, mobile device 210 may have a mobile device capability that refers to an ability to be selectively configured to operate in a category based on various parameters. In some examples, the mobile device category or mobile device capability may be related to a configuration of the mobile device 210 to use reduced communication resources, e.g., reduced data rate, reduced bandwidth, etc., than otherwise available through the source cell 205. The mobile device 210 may be a low-cost UE, an MTC device, an eMTC device, etc. Additionally or alternatively, the mobile device category or mobile device capability for the mobile device 210 may be associated with a mobile device 210 that may benefit from coverage enhancements from communication configurations selected to support a transmission mode. private, etc.

[0067] In block 220, source cell 205 may identify one or more parameters associated with a channel. For example, source cell 205 may identify the number of antenna ports, or simply "ports," available to source cell 205 for RS transmission on the channel. In various examples, the source cell 205 may have one port, two ports, three ports, and so on, available to transmit an RS to the mobile device 210. The port count may be determined based, at least in part, on the configuration of the source cell 205, the available (or free) ports of the source cell 205, and the like. In some examples, the mobile device 210 may be aware of the port count for the source cell 205, for example, by decoding a physical broadcast channel (PBCH) and an associated RS frequency offset. Additionally or alternatively, the mobile device 210 may be aware of the supported system bandwidth of the source cell 205 by decoding the PBCH.

[0068] In block 225, source cell 205 may select an RS density scheme from a set of RS density schemes available for RS transmissions. In some examples the selection of an RS density scheme may be based, at least in part, on parameters associated with the channel, and additionally or alternatively be based, at least in part, on the mobile device category or device capability. mobile device 210. In some examples, the selected RS density scheme may provide additional instances of RSs (e.g., REs) within a given PRB. The RS(s) transmitted according to the selected RS density scheme may comprise a cell specific reference signal (CRS), a demodulation reference signal (DM-RS), which may be referred to as a UE-specific reference signal, or combinations thereof.

[0069] In some aspects, the selected RS density scheme may support broadcast transmissions, unicast transmissions, or both. For example, an MTC system information block (SIB) can provide an indication of the selected RS density scheme. The selected RS density scheme can support transmission time slot (TTI) grouping as well as non-TTI grouping. The selected RS density scheme can support standard length CPs as well as extended length CPs. In some examples, the selected RS density scheme may support heterogeneous networks, for example, LTE systems utilizing licensed or unlicensed spectrum.

[0070] At 230, the source cell 205 may optionally send a signal to the mobile device 210 that includes an indication about the selected RS density scheme, which may be transmitted by dedicated signaling or broadcast transmission. For example, source cell 205 may send a DCI element over a control channel to inform mobile device 210 of the selected RS density scheme. Alternatively, the source cell 205 may not send some or all of the selected RS density scheme indications to the mobile device 210. Instead, the mobile device 210 may attempt to monitor the REs associated with the RS transmissions and, if so, successful, determine that the RSs are intended for channel measurements or interference measurements, i.e., they are RSs according to the selected RS density scheme. As an example, the mobile device 210 may attempt to blindly decode the RSs using a cyclic redundancy check (CRC) and, if the CRC is successful, determine that the RS is intended for channel estimation and measurement in accordance with the selected RS density.

[0071] At 235, the source cell 205 may send the RSs to the mobile device 210 according to the selected RS density scheme. In various examples, the source cell 205 may send a CRS, a DM-RS, or combinations of the two, on the PRB/subframe resource elements as defined by the RS density scheme.

[0072] FIGS. 3A to 3E show diagrams 300-a to 300-e, respectively, illustrating example aspects of RS density schemes, in accordance with aspects of the present description. Diagrams 300 may illustrate aspects of wireless communication system 100 described with reference to FIG. 1. One or more of the base stations 105 described above in connection with FIGS. 1 or 2 may implement aspects of the diagrams 300. For example, the diagrams 300 may collectively illustrate a set of RS density schemes, and any one or more of the RS density schemes may be associated with any one or more than one parameter associated with a channel, which, in some examples, could be a port count, a mobile device category, or a mobile device capability. A base station 105 may select one of the RS density schemes for RS transmissions to a UE 115. In some examples, a system device such as one of the UEs 115 or one of the base stations 105 may execute code sets to control the functional elements of the device to perform some or all of the functions illustrated with respect to the diagrams 300 described with reference to FIGs. 3A to 3E.

[0073] The exemplary RS density schemes shown in diagrams 300 are generally represented in a subframe that includes two PRBs, e.g., each PRB includes 12 subcarriers (labeled Tone Index 0-11) and seven symbols (labeled Index of Symbols 0-6 and 7-13 for the two PRBs, respectively). Consequently, each PRB includes 84 resource elements (REs) (12 subcarriers per 7 symbols) and the subframe includes a total of 168 REs available for transmitting data or control information. A base station 105 may transmit an RS into a number of REs, depending on a particular RS density scheme, for channel estimation or interference measurements on the UE. As previously discussed, a parameter associated with the channel, such as port count for base station 105, can be used to determine, at least to some extent, the number or location of REs for RS transmission.

[0074] For example, and as illustrated in FIG. 3A, the RS density scheme shown in diagram 300-a may be associated with a one-port RS transmission and may be selected for the RS density schemes that are applicable for a UE 115 associated with, or otherwise , operating in any category. In some examples, the RS density scheme shown in diagram 300-a may be referred to as a lower density RS density scheme. As shown in FIG. 3A, a base station 105 may transmit 16 RSs (8 RSs per PRB) through the antenna of a port (identified as antenna port "0") during the REs corresponding to Tone Indices 0, 3, 6, and 9 and the Symbol Indexes 0, 4, 7 and 11, respectively. That is, base station 105 may transmit an RS at Tone Index 0, Symbol Index 0, another RS at Tone Index 3, Symbol Index 0, and so on, until all 16 RSs are transmitted. In some aspects, the RS density scheme shown in diagram 300-a may be applicable to a UE 115 associated with a mobile device category or a mobile device capability, e.g., an MTC or other device that communicates using the total capacity of the associated base station 105. Consequently, the base station 105 may, in some aspects, avoid signaling overhead of indicating the RS density scheme to the UEs 115.

[0075] As another example, and as illustrated in FIG. 3B, the RS density scheme shown in diagram 300-b may also be associated with a one-port RS transmission and may be selected for RS density schemes that are advantageous to the UEs 115 associated with, or otherwise form, operating in certain categories. The RS density scheme shown in diagram 300-b may be a higher density RS scheme, at least in comparison to the lower density RS density scheme shown in diagram 300-a. In some examples, the RS density scheme shown in diagram 300-b may be selected by a base station 105 based on communications with a UE 115 associated with, or otherwise operating in, a mobile device category or device capability. predefined mobile devices, for example, a narrowband UE, an MTC device, an eMTC device, and the like. In some aspects, the category of UE 115 associated with the RS communication and density scheme may correspond to lower functional requirements, e.g., narrow bandwidth, low data rate, etc. In other words, the UE category can indicate to a base station the capabilities of UEs with respect to UL and DL communications. Generally, the RS density scheme shown in diagram 300-b includes additional RSs per PRB or per subframe compared, for example, to the RS density scheme illustrated in FIG. 3A. As shown in FIG. 3B, the base station may transmit four additional RS instances (e.g., REs) at Symbol Index 8 and Tone Indexes 0, 3, 6, and 9, for a total of 20 REs (or 20 RS instances) per subframe. Consequently, the UE 115 may have four additional channel measurement, estimation, and reporting opportunities for the subframe.

[0076] In some examples, the RSs transmitted in the lower density RS density scheme of diagram 300-a may be CRS and the extra REs transmitted in the higher density RS density scheme shown in diagram 300-b may be be CRS, DM-RS, or combinations of the two. In some examples, the REs can be programmed for DM-RS transmission where the DM-RS signal can be used for channel estimation, in a manner similar to a CRS transmission. Consequently, transmission of CRS-type RSs during DM-RS REs can provide increased RS design considerations. Additionally or alternatively, the base station 105 may transmit DM-RS during the added REs. DM-RS REs can be encoded with a known precoder, or they can be unpredicted. A UE 115 receiving the DM-RS may perform various combination functions to determine channel estimation, e.g., weighting, averaging, etc. For example, the UE 115 may measure channel conditions using the CRS REs and then perform channel measurement or interference measurement from the DM-RS REs and, based on both sets of measurements, determine an index of channel conditions. to report the channel estimate or interference estimate.

[0077] In some examples, the selection of DM-RS REs for use in an RS density scheme may be based on coverage needs of the UE 115. For example, a UE 115 that does not have an enhanced coverage need from of base station 105 may be programmed to receive CRS REs. As another example, DM-RS REs may be selected for inclusion in the RS density scheme depending on the transmission mode of the UE 115, e.g., DM-RS REs may be associated with other DM-RS REs to improve reporting. channel estimate or interference estimate. In other examples, the selection of DM-RS REs to be included in the RS density scheme may be the same, or different for a control channel or a data channel, for example, a physical downlink control channel (PDCCH ) and a shared physical downlink channel (PDSCH).

[0078] With reference to FIGS. 3C and 3D, examples of RS density schemes for two-port RS transmission are shown in accordance with various aspects of the present disclosure. Generally, the RS density scheme shown in diagram 300-c may be a lower density RS density scheme and may be selected for a UE 115 associated with, or otherwise operating in, any category, while the RS density scheme of RS density shown in diagram 300-d, which may be a higher density RS density scheme, may be selected for a UE 115 associated with, or otherwise operating in a particular category, e.g., a device eMTC using reduced communication resources. A base station 105 can transmit an RS through two-port antenna (identified as port "0" and "1") according to the selected RS density scheme. The RS density scheme shown in diagram 300-c may comprise 16 REs being transmitted within the subframe. In contrast, the RS density scheme shown in diagram 300-d may comprise four additional REs being transmitted, for a total of twenty RS REs. This provides additional opportunities for UEs 115 operating in a given category to measure and report channel conditions, which can be used to improve coverage for the UE 115.

[0079] In some cases, the higher density RS density schemes shown in diagrams 300-b and 300-d are backwards compatible. For example, the higher density RS density schemes of diagrams 300-b and 300-d include RS being transmitted in accordance with the lower density RS density schemes of diagrams 300-a and 300-c, respectively. Therefore, a UE 115 that does not support the higher density RS density schemes, for example, may still be able to perform channel estimation or interference estimation procedures based on the known location of the RS. A UE 115 that supports the presently described RS density scheme, however, may be able to utilize additional REs from the RS density schemes shown in diagrams 300-b and 300-d for added channel measurement, interference measurement, and reporting of opportunities.

[0080] As another example, and as illustrated in FIG. 3E, four-port RS transmission may be employed in accordance with various aspects of the present disclosure. In some examples, the RS density scheme shown in diagram 300-e may be selected for a UE 115 associated with, or otherwise operating in, any category. A base station 105 can transmit 24 instances of an RS in REs associated with Tone Indices 0, 3, 6 and 9 and Symbol Indices 0, 1, 4, 7, 8 and 11. The base station 105 can transmit the 24 RSs using the four-port antenna (labeled ports "0", "1", "2", and "3"). Consequently, a UE 115 may have sufficient opportunities for channel estimation and reporting.

[0081] FIG. 4 shows a message flow diagram 400 illustrating aspects of reference signal design in wireless communications, in accordance with aspects of the present disclosure. Message flow diagram 400 may illustrate aspects of wireless communication system 100 described with reference to FIG. 1. Message flow diagram 400 includes a source cell 405 and a mobile device 410. Source cell 405 may be an example of aspects of one or more of the base stations 105 described with reference to FIGs. 1 or 3, or the source cell 205 described with reference to FIG. 2. The mobile device 410 may be an example of aspects of one or more of the UEs 115 described above with reference to FIGS. 1 or 3, or the mobile device 210 described with reference to FIG. 2. Generally, message flow diagram 400 illustrates aspects of implementing reference signal density scheme design in wireless communication systems. In some examples, a system device, such as one of the UEs 115 or one of the base stations 105 described with reference to FIGs. 1 or 3, or the source cell 205 or mobile device 210 described with reference to FIG. 2 may execute sets of codes to control functional elements of the device to perform some or all of the functions described below.

[0082] In block 415, source cell 405 may identify a mobile device category or a mobile device capability of mobile device 410. In some examples the category may be related to a configuration of mobile device 410 to use reduced communication capabilities , e.g., reduced data rate, reduced bandwidth, etc., that are otherwise available through the source cell 405, e.g., an eMTC device. Additionally or alternatively, the mobile device category or mobile device capability for mobile device 410 may be associated with a mobile device 410 that may benefit from coverage enhancements, communication configurations selected to support a particular mode of transmission, etc.

[0083] In block 420, source cell 405 can identify parameters associated with a channel. For example, in some examples, the source cell 405 may identify a number of ports available to the source cell 405 for RS transmission. In various examples, the source cell 405 may have one port, two ports, three ports, and so on, available to transmit the RSs to the mobile device 410. The port count may be determined based, at least in part, on the configuration of the source cell 405, the available (or free) ports of the source cell 405 and the like. In some examples, the mobile device 410 may be aware of the port count for the source cell 405, for example, by decoding a physical broadcast channel (PBCH) and an associated RS frequency offset. Additionally or alternatively, the mobile device 410 may be aware of the supported system bandwidth of the source cell 405 by decoding the PBCH.

[0084] In block 425, source cell 405 may select an RS density scheme from a set of RS density schemes available for RS transmissions, e.g., any one of the RS density schemes illustrated in diagrams 300. For example, the RS density scheme may be based, at least in part, on the port count of the source cell 405, and additionally or alternatively, may be based, at least in part, on the category of the mobile device or in the mobile device capability of the mobile device 410, or in the category in which the mobile device 410 is otherwise operating. In some examples, the RS density scheme may provide additional RSs within a given PRB, e.g., the RS density schemes illustrated in diagrams 300-b or 300-d. The RS transmitted according to the selected RS density scheme may comprise a cell-specific reference signal (CRS), a demodulation reference signal (DM-RS), which may be referred to as a UE-specific reference signal , or a combination of the two.

[0085] In some aspects, the RS density scheme can support both broadcast and unicast transmissions. For example, an MTC system information block (SIB) can provide an indication of RS density schema. The RS density scheme can support TTI clustering as well as non-TTI clustering. The RS density scheme can support standard-length as well as CP-extended-length cyclic prefixes (CP). In some examples, the RS density regime may support heterogeneous networks, for example, LTE systems using licensed or unlicensed spectrum.

[0086] At 430, the source cell 405 may send a signal to the mobile device 410 that includes an indication about the selected RS density scheme, which may be transmitted in dedicated signaling or broadcast transmission. For example, source cell 405 may send a DCI element over a control channel to inform mobile device 410 of the selected RS density scheme. In some examples, the source cell 405 may also send, via the DCI element, an indication as to whether the DM-RS REs are being used in the selected RS density scheme. The mobile device 410 may, however, determine aspects of the selected RS density scheme based on its available knowledge of the port count and/or its category, for example, through PBCH decoding.

[0087] At 435, the source cell 405 may send the RSs to the mobile device 410 according to the selected RS density scheme. In various examples, the source cell 405 may send a CRS, a DM-RS, or combinations thereof, in the REs of the PRB/subframe as defined by the RS density scheme.

[0088] In block 440, the mobile device 410 may determine at least one of a channel estimate or an interference estimate for the transmitted RS REs. For example, the mobile device 410 may determine various channel condition parameters, e.g., signal-to-noise ratio, signal-to-interference-plus-noise ratio, etc., based on measuring the transmitted RSs according to the RS density scheme. selected. In some examples where the RS density scheme includes CRS and DM-RS, the mobile device 410 may perform various combination functions to determine the channel estimate or interference estimate.

[0089] At 445, the mobile device 410 may send a message to the source cell 405 that includes an indication of channel measurements and estimates or interference measurements and estimates. In examples where a higher density RS scheme with additional REs has been selected, reporting the channel estimate or interference estimate may provide an improved and/or more accurate condition determination. Therefore, the source cell 405 can have improved information regarding channel conditions and therefore make more informed decisions regarding MCS selection, transmission capacity, data rate, transmission power, etc.

[0090] FIG. 5 shows a message flow diagram 500 illustrating reference signal design aspects in wireless communication, in accordance with aspects of the present disclosure. Message flow diagram 500 may illustrate aspects of wireless communication system 100 described with reference to FIG. 1. Message flow diagram 500 includes a source cell 505 and a mobile device 510. The source cell 505 may be an example of aspects of one or more of the base stations 105 described with reference to FIGs. 1 or 3, or source cells 205 or 405 described with reference to FIGS. 2 or 4. The mobile device 510 may be an example of aspects of one or more of the UEs 115 described with reference to FIGs. 1 or 3, or mobile devices 210 or 410 described with reference to FIGS. 2 or 4. Generally, message flow diagram 500 illustrates aspects of reference signal density scheme design implementation in wireless communication systems. In some examples, a system device, such as one of UEs 115, base stations 105, source cells 205 or 405, or mobile devices 210 or 410 may execute sets of codes to control functional elements of the device to perform some or all the functions described below.

[0091] At 515, the source cell 505 may send a signal to the mobile device 510 that includes an indication of an RS density scheme selected from a set of RS density schemes. The RS density scheme may be selected based, at least in part, on any one or more of the mobile device categories or mobile device capabilities of the mobile device 510, or one or more parameters associated with a channel, which, in some examples, it may be related to a port count of the source cell 505. For example, the source cell 505 may send a DCI element over a control channel to inform the mobile device 510 of the selected RS density scheme. In some examples, the source cell 505 may also send, via the DCI element, an indication as to whether the DM-RS REs are being used in the selected RS density scheme.

[0092] At 520, the source cell 505 may send the RSs to the mobile device 510 according to the selected RS density scheme. In various examples, the source cell 505 may send a CRS, a DM-RS, or combinations thereof, in the REs of the PRB/subframe as defined by the RS density scheme.

[0093] In block 525, the mobile device 510 may determine at least one of a channel estimate or an interference estimate for the transmitted RS REs. For example, the mobile device 510 may determine various channel conditions or interference conditions, e.g., signal-to-noise ratio, signal-to-interference-plus-noise ratio, etc., based on measuring the transmitted RSs according to the density scheme. selected RS. In some examples where the RS density scheme includes CRS and DM-RS, the mobile device 510 may perform various combination functions to determine the channel estimate or interference estimate.

[0094] At 530, the mobile device 510 may send a message to the source cell 505 that includes an indication of channel estimates and measurements. In examples where a higher density RS scheme with additional REs has been selected, channel estimation reporting may provide improved and/or more accurate condition determination. Therefore, the source cell 505 can have improved information regarding channel conditions and therefore make more informed decisions regarding MCS selection, transmission capacity, data rate, transmission power, etc.

[0095] FIG. 6 shows a block diagram 600 of a device 605 configured for use in wireless communication in accordance with aspects of the present description. The device 605 may be an example of aspects of one or more of the UEs 115 described with reference to FIGS. 1 or 3, or mobile devices 210, 410 or 510 described with reference to FIGS. 2, 4 or 5, respectively. Device 605 may comprise a receiver module 610, a channel/interference estimation module 615, and a transmitter module 620. Device 605 may also be or include a processor (not shown). Each of these modules can be in communication with each other.

[0096] The components of device 605 may, individually or collectively, be implemented using one or more application-specific integrated circuits (ASICs) adapted to perform some or all of the applicable hardware functions. Additionally or alternatively, the functions may be performed by one or more processing units (or cores), in one or more integrated circuits. In other examples, other types of integrated circuits may be used (e.g., structured/platform ASICs, field-programmable gate arrays (FPGAs), and other semi-custom ICs), which may be programmed in any manner known in the art. The functions of each module can be implemented, in whole or in part, with instructions embedded in a memory, formatted to be executed by one or more general or application-specific processors.

[0097] The receiver module 610 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, etc.). The receiver module 610 may be configured to receive an indication of an RS density scheme from a base station 105, as well as receive RSs that are being transmitted in accordance with the RS density schemes. The information may be received in dedicated signaling or broadcast transmission and may include one or more of an SCR or a DM-RS or a combination thereof. The information may be passed to the channel/interference estimation module 615, and to other components of the device 605.

[0098] The channel/interference estimation module 615 may determine a channel quality indication based on the receipt and measurement of an RS and transmit the channel quality indication to a base station 105. The channel/interference estimation module interference 615 may receive, via the receiver module 610, an indication from the base station 105 of an RS density scheme selected for use by the device 605. In some examples the channel/interference estimation module 615 may identify the scheme of RS density based, at least in part, on one of a type of a channel coverage or a coverage enhancement for the channel.

[0099] In some examples, the RS density scheme may have been selected by the base station 105 based, at least in part, on the mobile device category or mobile device capability of the device 605, e.g., based on the device 605 being or otherwise operating as an MTC device or an eMTC device. Additionally alternatively, the RS density scheme may have been selected by the base station 105 based, at least in part, on one or more parameters associated with a channel, which in some examples may be associated with the base station port measurement. 105, for example, the antenna ports available to the base station 105 for RS transmissions. Therefore, the channel/interference estimation module 615 can receive the RS transmitted according to the indicated RS density scheme and perform channel measurements based on the RS. The channel/interference estimate module 615 may subsequently pass the indication of at least one of the channel estimate or the interference estimate to the transmitter module 620 for transmission to base station 105.

[0100] In some examples, a higher density RS density scheme may be selected to provide additional RS REs for the device 605, e.g., to provide more opportunities for the channel/interference estimation module 615 to measure and report current channel conditions. Consequently, the base station can have improved information regarding channel conditions and therefore make more informed decisions regarding MCS selection, transmission capacity, data rate, transmission power, etc.

[0101] The transmitter module 620 may transmit one or more signals received from other components of the device 605. The transmitter module 620 may transmit an indication of channel estimation information to the base station 105. In some examples, the transmitter module 620 may be placed with the receiver module 610 in a transceiver module.

[0102] FIG. 7 shows a block diagram 700 of a device 605-a configured for use in wireless communication in accordance with aspects of the present description. Device 605-a may be exemplary of aspects of one or more of the UEs 115 described with reference to FIGS. 1 or 3, the mobile devices 210, 410 or 510 described with reference to FIGS. 2, 4 or 5, or device 605 described with reference to FIG. 6. Device 605-a may comprise a receiver module 610-a, a channel/interference estimation module 615-a, and a transmitter module 620-a, which may be examples of corresponding modules of device 605. Device 605-a may also include a processor (not shown). Each of these components can be in communication with the other. The channel/interference estimation module 615-a may comprise an RS density scheme determination module 705, a channel/interference estimation determination module 710, and a coverage/transmission enhancement mode module 715. receiver module 610-a and transmitter module 620-a may perform the functions of receiver module 610 and transmitter module 620 as described with reference to FIG. 6, respectively.

[0103] The RS density scheme determination module 705 may receive, via the receiver module 610-a, one or more messages, for example, a DCI element on a control channel, from a base station 105 which includes an indication of an RS density scheme selected by the base station 105. The RS density scheme determination module 705 may, based on the indication, determine which REs within a PRB, a group of PRBs, a subframe, a group of subframes, or combinations thereof, may include RSs for channel estimation. In some examples the RS density scheme determination module 705 may identify the RS density scheme based, at least in part, on one of a type of a channel or a coverage enhancement for the channel. In some examples, the channel type may include at least one of a broadcast channel or a unicast channel. In some examples, the channel type may include at least one of a control data channel or a data channel, which in some examples may be a PDCCH or a PDSCH. In some RS density schemes, additional RS REs may be allocated to at least one of the channel estimation measurements or the interference estimation measurements to support at least one of the mobile device category of mobile device 605-a, a mobile device capability of device 605-a, or one or more channel parameters, which in some examples may be associated with port count for base station 105, etc. Additionally or alternatively, the message(s) may include an indication as to whether the selected RS density scheme may include CRS, DM-RS, or combinations thereof.

[0104] The channel/interference estimation determination module 710 may, in cooperation with the receiver module 610-a or the RS density scheme determination module 705, receive the RSs in the REs associated with the density scheme of RS and measure the RSs to determine channel conditions. For example, the channel/interference estimation determination module 710 may, for one or more of the channels, determine interference levels, received signal strength, etc., to identify the operating conditions of the channel. In the case where the indicated RS density scheme includes DM-RS, the channel/interference estimation determination module 710 may exercise various combinations of characteristics to determine channel estimates or interference estimates, e.g., weighting, calculation of average, etc., for CRS and DM-RS transmissions. In some aspects, DM-RS can be included in the RS density scheme to provide improved channel measurements and estimates or improved interference measurements and estimates.

[0105] The coverage enhancement/transmission mode module 715 may determine, for the device 605-a, whether one or more of a coverage enhancement or a particular transmission mode is applicable. For example, device 605-a may be or otherwise operate as an MTC device, a narrowband MTC device, a narrowband UE, a category 0 UE, etc., which may be associated with requirements reduced communication capabilities, e.g. reduced data rate, limited data transmission, lower bandwidth, etc. Accordingly, the device 605-a may be of a mobile device category or of a mobile device capability that may benefit from a coverage enhancement from the base station 105. In another example, the device 605-a may wish to use a transmission mode that would benefit from additional channel estimation or interference estimation measurements and reporting, for example, broadcast transmissions which may be bursty transmissions. Accordingly, the coverage/transmission enhancement mode module 715 may send a signal to the base station 105 indicating its category and/or requirements. The base station 105 may select an RS density scheme that considers the category/capability/need of the device 605-a and therefore selects an RS density scheme that provides sufficient channel estimation or interference estimation opportunities.

[0106] FIG. 8 shows a system 800 for use in wireless communication, in accordance with aspects of the present description. System 800 may include a UE 115-a, which may be exemplary of aspects of one or more of the UEs 115 described with reference to FIGS. 1 or 3, mobile devices, 210, 410 or 510 described with reference to FIGS. 2, 4 and 5 or devices 605 described with reference to FIGS. 6 and 7.

[0107] The UE 115-a generally may comprise components for two-way voice and/or data communications including components for transmitting communications and components for receiving communications. The UE 115-a may comprise one or more antennas 840, a transceiver module 835, a processor module 805, and memory 815 (including code 820), which may communicate, directly or indirectly, with each other (e.g., through of one or more buses 845). The transceiver module 835 may be configured to communicate bidirectionally, through the one or more antennas 840 or one or more wired or wireless links, with one or more networks, as described above. For example, transceiver module 835 may be configured to communicate bidirectionally with any one or more of base stations 105 described with reference to FIGS. 1 and 3, and source cells 205, 405, or 505 described with reference to FIGS. 2, 4 and 5. The transceiver module 835 may include a modem configured to modulate packets and provide the modulated packets to one or more antennas 840 for transmission, and demodulate packets received from one or more antennas 840. The UE 115, one may have one or more antennas 840 capable of simultaneously transmitting and/or receiving multiple wireless transmissions. The transceiver module 835 may be capable of communicating simultaneously with one or more base stations 105 via multiple carrier components.

[0108] The UE 115-a may comprise a channel/interference estimation module 615-b, which may perform the functions described above for the channel/interference estimation modules 615 described with reference to FIGs. 6 and 7. The UE 115-a may also comprise an RS receive control module 825 and a communication optimization module 830. The RS receive control module 825 may control aspects of the UE 115-a by performing estimates channel or interference estimates based on reception of RSs according to an RS density scheme for the UE 115-a. The RS density scheme may be selected based on the UE 115-a being or otherwise operating as an MTC device, a narrowband MTC device, etc., and may be a higher density RS density scheme. high having additional RS REs. Additional RS REs can provide increased channel estimation, interference estimation, and reporting opportunities for the UE 115-a.

[0109] The communication optimization module 830 may provide improved communication functionality for the UE 115-a. For example, the communication optimization module 830 may determine and report at least one of a category of the UE 115-a, a category in which the UE 115-a is operating, or a communication parameter for the UE 115-a to a base station 105 to enable selection of an RS density scheme that supports the requirements of UE 115-a.

[0110] Memory 815 may comprise random access memory (RAM) and read-only memory (ROM). Memory 815 may store computer-executable and computer-readable firmware/software code 820 containing instructions that are configured to, when executed, cause processor module 805 to perform various functions described in this document (e.g., perform channel estimation and reports based on RS REs associated with an RS density scheme, etc.). Alternatively, the computer-executable and computer-readable software/firmware code 820 may not be directly executable by the processor module 805 but be configured to cause a computer (e.g., when compiled and executed) to perform the functions described herein. The processor module 805 may comprise an intelligent hardware device, e.g., a central processing unit (CPU), a microcontroller, an application-specific integrated circuit (ASIC), etc.

[0111] FIG. 9 shows a block diagram 900 of an apparatus 905 for use in wireless communication, in accordance with aspects of the present description. In some examples, the apparatus 905 may exemplify aspects of one or more of the base stations 105 described with reference to FIGS. 1 or 3, or source cells 205, 405 or 505 described with reference to FIGS. 2, 4 and 5. In some examples, the apparatus 905 may be part of or comprise an LTE/LTE-A eNB and/or an LTE/LTE-A base station. The apparatus 905 may also be a processor. Apparatus 905 may comprise a receiver module 910, an RS density scheme module 915, and a transmitter module 920. Each of these modules may be in communication with one another.

[0112] The components of apparatus 905 may, individually or collectively, be implemented using one or more ASICs adapted to perform some or all of the applicable hardware functions. Additionally or alternatively, the functions may be performed by one or more processing units (or cores), in one or more integrated circuits. In other examples, other types of integrated circuits (e.g., structured/platform ASICs, FPGAs, and other semi-custom ICs) may be used that may be programmed in any manner known in the art. The functions of each component can also be implemented, in whole or in part, with instructions embedded in a memory, formatted to be executed by one or more general or application-specific processors.

[0113] In some examples, the receiver module 910 may comprise at least one radio frequency (RF) receiver, such as an RF receiver operable to receive signals reporting at least one of the channel estimate or interference estimate from the UEs 115 associated with apparatus 905. Receiver module 910 may be used to receive various types of data or control signals (e.g., transmissions) on one or more communication links of a wireless communication system, such as one or more communication links. communication of the wireless communication system 100 described with reference to FIG. 1.

[0114] In some examples, transmitter module 920 may comprise at least one RF transmitter, such as at least one RF transmitter operable to transmit RSs, e.g., CRS, DM-RS, or combinations thereof. Transmitter module 920 may be used to transmit various types of data and/or control signals (e.g., transmissions) on one or more communication links of a wireless communication system, such as one or more communication links of the wireless communication system. wireless communication 100 described with reference to FIG. 1. Transmitter module 920 can be configured to transmit RSs over one type of unicast or broadcast channel, and can be configured to transmit over more than one type of control channel or one type of data channel, such as a PDCCH or a PDSCH channel type.

[0115] In some examples, the RS density scheme module 915 may select an RS density scheme from a set of RS density schemes available for RS transmissions. Selection of an RS density scheme may be based, at least in part, on any one or more of one parameter associated with a channel, which in some examples may be associated with a port count of apparatus 905, a category of mobile device of a UE 115 receiving the RS transmissions, or a mobile device capable of a UE 115 receiving the RS transmissions. For example, the RS 915 density scheme module may identify any one or more of the category of UE, the category of the UE 115 that is otherwise operating, or the port count and select a density scheme. RS from a set of RS density schemes available for selection. The set of available RS density schemes may include a higher density RS density scheme that provides additional channel estimation and measurement opportunities or interference estimation and measurement opportunities for the UE 115. The density scheme module of RS 915 can, through the transmitter module 920, transmit the RS to the UE 115 according to the determined RS density scheme. In some examples, the transmission of RSs may include one or more of a CSR or a DM-RS or a combination thereof. The RS density scheme module 915 may also transmit an indication of an RS density scheme to a UE 115.

[0116] FIG. 10 shows a block diagram 1000 of an apparatus 905-a for use in wireless communication, in accordance with aspects of the present description. In some examples, apparatus 905-a may be an example of aspects of one or more of base stations 105 described with reference to FIGS. 1 and 3, source cells 205, 405 or 505 described with reference to FIGS. 2, 4 and 5, or apparatus 905 described with reference to FIG. 9. In some examples, apparatus 905-a may be part of or include an LTE/LTE-A eNB or an LTE/LTE-A base station. Apparatus 905-a may also be a processor. The apparatus 905-a may comprise a receiver module 910-a, an RS density scheme module 915-a, and/or a transmitter module 920-a. Each of these modules can be in communication with each other.

[0117] The components of apparatus 905-a may, individually or collectively, be implemented using one or more ASICs adapted to perform some or all of the applicable hardware functions. Additionally or alternatively, the functions may be performed by one or more processing units (or cores), in one or more integrated circuits. In other examples, other types of integrated circuits (e.g., structured/platform ASICs, FPGAs, and other semi-custom ICs) may be used that may be programmed in any manner known in the art. The functions of each component can also be implemented, in whole or in part, with instructions embedded in a memory, formatted to be executed by one or more general or application-specific processors.

[0118] In some examples, the receiver module 910-a may be an example of one or more aspects of the receiver module 910 described with reference to FIG. 9. In some examples, the receiver module 910-a may comprise at least one radio frequency (RF) receiver, such as an RF receiver operable to receive signals reporting at least one of channel estimation or interference estimation from the UEs 115 associated with apparatus 905. Receiver module 910-a may be used to receive various types of data or control signals (e.g., transmissions) on one or more communication links of a wireless communication system, such as one or more communication links of the wireless communication system 100 described with reference to FIG. 1.

[0119] In some examples, the transmitter module 920-a may be an example of one or more aspects of the transmitter module 920 described with reference to FIG. 9. In some examples, the transmitter module 920-a may comprise at least one RF transmitter, such as at least one RF transmitter operable to transmit RSs in the REs in accordance with a selected RS density scheme. Transmitter module 920-a may be used to transmit various types of data and/or control signals (e.g., transmissions) on one or more communication links of a wireless communication system, such as one or more communication links of the wireless communication system 100 described with reference to FIG. 1. Transmitter module 920-a can be configured to transmit RSs over one type of unicast or broadcast channel, and can be configured to transmit over more than one type of control channel or one type of data channel, such as a PDCCH or a PDSCH channel type.

[0120] In some examples, the RS density scheme module 915-a may comprise a mobile device category/capability identification module 1005, a channel parameter identification module 1010, and a capacity identification scheme selection module. RS density scheme selection module 1015. The RS density scheme selection module 1015 may include a channel/interference estimation selection module 1020. The mobile device category/capability identification module 1005 may identify at least one of a category associated with a mobile device or a category of a mobile device that is otherwise operating. The mobile device category may be an MTC device, a narrowband MTC device, a narrowband UE, or combinations thereof. In some examples, the mobile device category is Category 0.

[0121] In some aspects, the mobile device category/capability identification module 1005 may identify a coverage enhancement for a mobile device and select an RS density scheme based, at least in part, on the identified coverage enhancement. . For example, the mobile device category/capability identification module 1005 may receive, via the receiver module 910-a, a message from a mobile device, indicating an operational capability for the mobile device. The operational capability may include an indication that the mobile device can benefit from an improved coverage area provided by the apparatus 905-a, e.g., an increase of 10 dB, 15dB, 20dB, etc., of the coverage provided by the apparatus 905 - The. A higher density RS scheme can be selected to provide channel estimation to support improved coverage.

[0122] In some aspects, the mobile device category/capability identification module 1005 may identify a transmission mode for the mobile device and select the RS density scheme based, at least in part, on the identified transmission mode. . For example, the transmission mode may be a broadcast transmission mode and the selected RS density scheme may be a higher density RS density scheme having more RS REs within the PRB/subframe. In contrast, a unicast transmission mode may comprise selecting a lower density RS REs scheme that includes fewer RS REs.

[0123] The channel parameter identification module 1010 may, in some examples, determine which antenna ports are available to the apparatus 905-a for transmitting RSs. For example, apparatus 905-a may comprise or otherwise have available one port, two ports, three ports, etc., for transmitting RSs. The available antenna ports may determine the port count for the 905-a device.

[0124] The RS density scheme selection module 1015 can select an RS density scheme from a set of RS density schemes available for RS transmission. An RS density scheme may be selected based on one or more parameters associated with a channel, the mobile device category associated with the mobile device, and/or the mobile device capability associated with the mobile device. The set of RS density schemes may comprise a lower density RS density scheme and a higher density RS density scheme. The higher density RS density scheme may include more RS REs than the lower density RS density scheme. In some examples, the higher density RS density scheme may be compatible with the lower density RS density scheme, e.g., include at least the same RS REs as the lower density RS density scheme in addition to of the new RS REs. The selected RS density scheme may include a cell specific reference signal (CRS) or a demodulation reference signal (DM-RS) or a combination of the two being transmitted to one or more mobile devices.

[0125] In some aspects, the RS density scheme selection module 1015 may comprise an increasing number of RSs transmitted to the mobile device based, at least in part, on the identified mobile device category or mobile device capability. of the mobile device. For example, the RS density scheme may comprise twenty (20) RS REs within a subframe.

[0126] In some aspects, the RS density scheme selection module 1015 may, via the transmitter module 920-a, transmit a message to the mobile device that includes an indication of the selected RS density scheme. For example, the message may be a DCI element in a control channel transmitted to the mobile device. The message may also include an indication as to whether a DM-RS is included in the selected RS density scheme.

[0127] The channel/interference estimation selection module 1020 may determine at least one of a channel estimation requirement or an interference estimation requirement, which may be used to select an RS density scheme. In some examples, the channel/interference estimation selection module 1020 may receive a channel quality indication from a mobile device that is based on a transmitted reference signal. Depending on one or more of the UE's mobile device category, the UE's mobile device capability, one or more parameters associated with a channel such as a port count, the UE's communication mode, etc., the selection module channel/interference estimation system 1020 may determine and release information indicating that channel estimation, interference estimation, or additional reporting may be required and therefore a higher density RS density scheme may be selected. In some examples, the channel/interference estimation selection module 1020 may affect the selected RS density scheme based on channel feedback from the mobile device upon receipt of one or more non-acknowledgement (NACK) signals from of the mobile device, and the like.

[0128] FIG. 11 shows a block diagram 1100 of a base station 105-a (e.g., a base station as part or all of an eNB) for use in wireless communication in accordance with aspects of the present description. In some examples, base station 105-a may exemplify aspects of one or more of the base stations 105 described with reference to FIGS. 1, 3 and 11, source cells 205, 405 or 505 described with reference to FIGS. 2, 4 and 5, or apparatus 905 described with reference to FIGS. 9 or 10. Base station 105-a may be configured to implement or facilitate at least some features and functions of the base station or apparatus described with reference to FIGS. 1-10.

[0129] The base station 105-a may comprise a base station processor module 1110, a base station memory module 1120, at least one base station transceiver module (represented by base station transceiver module(s) base 1150), at least one base station antenna (represented by base station antennas 1155) and an RS density scheme module 915-b. The base station 105-a may also include one or more of a base station communications module 1130 and/or a network communications module 1140. Each of these modules may be in communication with the other, directly or indirectly, through one or more 1135 buses.

[0130] Base station memory module 1120 may comprise random access memory (RAM) or read-only memory (ROM). The base station memory module 1120 may store computer-executable and computer-readable software/firmware code 1125 containing instructions that are configured to, when executed, cause the processor module 110 to perform various functions described in this document (e.g. , perform channel estimation and reporting based on RS REs associated with an RS density scheme, etc.). Alternatively, the computer-executable and computer-readable software/firmware code 1125 may not be directly executable by the processor module 1110 but be configured to cause a computer (e.g., when compiled and executed) to perform the functions described herein.

[0131] The processor module 1110 may comprise an intelligent hardware device, e.g., a central processing unit (CPU), a microcontroller, an (ASIC), etc. The base station processor module 1110 may process information received through the base station transceiver module(s) 1150, the base station communications module 1130, or the network communications module 1140. The base station processor module 1110 may also process information to be sent to the transceiver module(s) 1150 for transmission through the antenna(s) 1155, to the base station communication module 1130, for transmission to one or more other base stations 105-b and 105-c, or to the network communications module 1140 for transmission to a core network 1145, which may be an example of one or more aspects of the core network 130 described with reference to FIG. 1. The base station processor module 1110 may handle, alone or in connection with the RS density scheme module 915-b, various aspects of RS density scheme selection and, in some aspects, communication to the device. mobile.

[0132] The transceiver module(s) of the base station 1150 may include a modem configured to modulate packets and provide the modulated packets to the antennas of the base station 1155 for transmission and demodulate packets received from the station's antennas. base station 1155. The base station transceiver module(s) 1150 may, in some examples, be implemented as one or more base station transmitter modules and one or more separate base station receiver modules. The base station transceiver module(s) 1150 may support communications in a first radio frequency spectrum band or a second radio frequency spectrum band. The base station transceiver module(s) 1150 may be configured to communicate bidirectionally, via antenna(s) 1155, with one or more UEs or apparatus, such as one or more of the UEs 115 described with reference to FIGS. 110. The base station 105-a may, for example, include multiple antennas of the base station 1155 (e.g., an antenna array). Base station 105-a may communicate with core network 1145 via network communications module 1140. Base station 105-a may also communicate with other base stations, such as base stations 105-b and 105-c, using the 1130 base station communications module.

[0133] The RS 915-b density scheme module may be configured to perform or control some or all of the features or functions described with reference to FIGS. 1-10 related to RS density scheme selection. In some examples, the RS 915-b density scheme module may identify one or more of a port count, a category of a mobile device, or a category of a mobile device that is operating and select a port density scheme. RS from a set of RS density schemes available to support the mobile device. For example, certain mobile device categories may benefit from extra channel estimation opportunities and a higher density RS REs scheme having more RS REs per subframe may be selected. The RS 915-b density scheme module, or portions of the RS 915-b density scheme module, may include a processor, or some or all of the functions of the RS 915-b density scheme module may be performed by the base station processor module 1110 or in connection with the base station processor module 1110. In some examples, the RS density scheme module 915-b may be an example of the RS density scheme modules 915 or 915 -a described with reference to FIGS. 9 or 10.

[0134] In some examples, the RS density scheme module 915-b may comprise a channel/interference estimation control module 1160 and mobile device category/capacity control module 1165. The estimation control module channel/interference requirement 1160 may determine a channel estimation requirement or an interference estimation requirement for a mobile device based on various factors, e.g., a transmission mode of the mobile device, a coverage enhancement for the mobile device, etc. . Therefore, the channel/interference estimation control module 1160 may determine whether additional RS REs can be provided in the selected RS density scheme to support the added channel estimation or interference estimation opportunities.

[0135] In some examples, the mobile device category/capability control module 1165 may determine which mobile device category the mobile device is associated with or otherwise operating on, for example, an MTC device, a narrowband MTC device, a narrowband UE, a Category 0 UE, etc. Therefore, it can determine the mobile device category/capability control module 1165, based, at least in part, on the mobile device category or mobile device capacity, in an RS density scheme that provides estimation opportunities channel or interference estimate sufficient to support the mobile device.

[0136] FIG. 12 is a flowchart illustrating a method 1200 for wireless communication in accordance with aspects of the present disclosure. For clarity, method 1200 is described below with reference to aspects of one or more of base stations 105 described with reference to FIGS. 1, 3 and 11, source cells 205, 405 and 505 described with reference to FIGS. 2, 4, or 5, and/or apparatus 905 described with reference to FIGS. 9 or 10. In some examples, a base station may execute one or more sets of codes to control functional elements of the base station to perform the functions described below. Additionally or alternatively, the base station may perform one or more of the functions described below using special purpose hardware.

[0137] In block 1205, method 1200 may comprise identifying a mobile device category or a mobile device resource of a mobile device. For example, the mobile device may be a Category 0 mobile device or may otherwise be operating as a Category 0 device. In some examples, the mobile device may be associated with or otherwise operating as a Category 0 device. MTC, a narrowband MTC device, a narrowband UE, and the like. In various examples, the mobile device category or mobile device capability may be associated with a mobile device that uses reduced communication functionalities, e.g., reduced data rate, narrow bandwidth, etc. The base station may determine the category of the mobile device independently or based, at least in part, on information received from the mobile device, for example, via a mobile device capabilities announcement message. The operation(s) in block 1205 may be performed using any one or more of the RS density scheme modules 915 described with reference to FIGS. 9, 10 or 11.

[0138] In block 1210, method 1200 may comprise identifying one or more parameters associated with a channel for communicating reference signals to the mobile device. In some examples, this may comprise identifying a port count available to transmit RSs to the mobile device. The port count can be identified based on the configuration of the base station, for example, the number of antenna ports, and/or based on the base station's available ports. In some examples, the port count might be one port, two ports, three ports, and so on. Operations in block 1205 may be performed using any one or more of the RS density scheme modules 915 described with reference to FIGS. 9, 10 or 11, the channel parameter identification module 1010 described with reference to FIG. 10, or the channel/interference estimation control module 1160 described with reference to FIG. 11.

[0139] In block 1215, method 1200 may comprise selecting an RS density scheme from a set of RS density schemes. For example, for each port count a base station may have one or more RS density schemes available to transmit RS to the mobile device. The RS density scheme may be selected based, at least in part, on the mobile device category of the mobile device, or the mobile device capability of the mobile device. For example, mobile devices associated with, or otherwise operating in, a particular category of mobile device may utilize a higher density RS density scheme that includes more RS REs per subframe. Additional RS REs can provide channel plus channel measurements or interference measurement opportunities to the mobile device to enhance channel estimation or interference estimation reporting. The operation(s) in block 1205 may be performed using any one or more of the RS density scheme modules 915 described with reference to FIGS. 9, 10 or 11, the RS 1015 density scheme selection module described with reference to FIG. 10, or the channel/interference estimation control module 1160 described with reference to FIG. 11.

[0140] In block 1220, method 1200 may comprise transmitting an RS to the mobile device according to the selected RS density scheme. For example, the base station may transmit RSs into REs according to the selected RS density scheme to provide sufficient channel measurement, interference measurement, and reporting opportunities. The operation(s) in block 1205 may be performed using any one or more of the RS density scheme modules 915 described with reference to FIGS. 9, 10 or 11, the transmitter modules 920 described with reference to FIGS. 9 or 10, or the base station transceiver modules 1150 or the base station antenna(s) 1155 described with reference to FIG. 11.

[0141] Thus, method 1200 can provide wireless communication. It should be noted that method 1200 is only one implementation and that operations of method 1200 may be rearranged or otherwise modified so that other implementations are possible.

[0142] FIG. 13 is a flowchart illustrating a method 1300 for wireless communication in accordance with various aspects of the present disclosure. For clarity, method 1300 is described below with reference to aspects of one or more of the UEs 115 described with reference to FIGs. 1, 3 and 11, the mobile devices 210, 410 and 510 described with reference to FIGS. 2, 4 or 5, and/or the devices 605 described with reference to FIGS. 6 or 7. In some examples, the UE may execute one or more sets of codes to control functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may perform one or more of the functions described below using special purpose hardware.

[0143] In block 1305, method 1300 may comprise receiving an RS transmitted according to an RS density scheme. The RS density scheme can be selected from a set of available RS density schemes. The RS density scheme may also be selected based, at least in part, on the mobile device category associated with the UE, the mobile device capability associated with the UE in, or one or more parameters associated with the channel. The RS density scheme can be a higher density RS REs scheme (e.g., with 20 RS REs per subframe) or a lower density RS REs scheme having fewer RS REs than the RS REs. of higher density RS. In some examples, receiving the reference signal may comprise receiving at least one of a CRS or a DM-RS or combinations thereof. Operations in block 1305 may be performed using any one or more of the receiver modules 610 described with reference to FIGS. 6 or 7, the channel/interference estimation modules 615 described with reference to FIGS. 6, 7 or 8, or the transceiver module 835 and the antenna(s) 840 described with reference to FIGs. 8.

[0144] In block 1310, method 1300 may comprise identifying the RS density scheme based, at least in part, on a channel type associated with the reference signal or a coverage enhancement for the channel associated with the signal. of reference. In some examples, the channel type may be a broadcast channel or a unicast channel. In some examples, the channel type may be a control channel or a data channel, such as a PDCCH or a PDSCH. In some examples the channel coverage improvement may comprise a channel repetition, and the RS density scheme may be identified based, at least in part, on a number of channel repetitions. Operations in block 1310 may be performed using one or more of the channel/interference estimation modules 615 described with reference to FIGs. 6, 7 or 8 or the RS 705 density scheme determination module described with reference to FIG. 7.

[0145] In block 1315, method 1300 may comprise communicating using the reference signal in accordance with the identified RS density scheme. The communication may comprise performing at least one of a channel estimate or an interference estimate using the reference signal, and transmitting a channel estimate indication to a serving base station. Therefore, the serving base station can adjust transmissions to account for channel conditions and support UE communications. Operations on blocks 1315 may be performed using any one or more of the channel/interference estimation modules 615 described with reference to FIGs. 6, 7 or 8, the channel/interference estimation determination module 710 described with reference to FIG. 7, the coverage/transmission mode enhancement module 715 described with reference to FIG. 7, the transmitter modules 620 described with reference to FIGS. 6 or 7, or the transceiver module 835 and antenna(s) 840 described with reference to FIG. 8.

[0146] Thus, method 1300 can provide wireless communication. It should be noted that method 1300 is only one implementation and that the operations of method 1300 may be rearranged or otherwise modified such that other implementations are possible.

[0147] FIG. 14 is a flowchart illustrating a method 1400 for wireless communication in accordance with various aspects of the present disclosure. For clarity, the method 1400 is described below with reference to aspects of one or more of the base stations 105 described with reference to FIGS. 1, 3 and 11, the source cells 205, 405 or 505 described with reference to FIGS. 2, 4 or 5, and/or apparatus 905 described with reference to FIGS. 9 or 10. In some examples, a base station may execute one or more sets of codes to control functional elements of the base station to perform the functions described below. Additionally or alternatively, the base station may perform one or more of the functions described below using special purpose hardware.

[0148] In block 1405, method 1400 may comprise identifying a mobile device category or a mobile device enhancement of a mobile device. The mobile device may be a Category 0 mobile device, or may otherwise be operating as a Category 0 mobile device. In some examples, the mobile device may be, or otherwise be operating as, an MTC device. a narrowband MTC device, a narrowband UE and the like. In other examples, the mobile device category or mobile device capability may be associated with a mobile device that uses reduced communication functionalities, e.g., reduced data rate, narrow bandwidth, etc. The base station may determine the mobile device category or mobile device capability independently or based on information received from the mobile device, for example, via a mobile device capability announcement message.

[0149] In block 1410, method 1400 may comprise identifying one or more parameters associated with a channel. In some examples, the method may comprise identifying a port count for communicating RSs to the mobile device. The port count may be identified based, at least in part, on the configuration of the base station, e.g., the number of antenna ports, and/or the available ports of the base station. In some examples, the port count might be one port, two ports, three ports, and so on.

[0150] In block 1415, method 1400 may comprise determining whether a higher density RS scheme should be selected based, at least in part, on any one or more of the UE port counts, the category of the UE or the category in which the EU is operating. For example, an RS density scheme may be selected from a set of RS density schemes associated with port count, UE category, or UE capacity. In an example, the highest density RS density scheme may be selected if it is a UE, or is otherwise operating as an MTC device, a narrowband MTC device, a UE operating in a narrowband, a UE that supports multiple RS density schemes, etc. If a higher density RS density scheme is determined to be selected, method 1400 may comprise selecting the higher density RS density scheme in block 1420.

[0151] In block 1425, method 1400 may comprise determining whether a higher density RS density scheme can be selected based, at least in part, on a coverage improvement for the UE. For example, a base station may determine that the UE is experiencing reception problems (e.g., based on receiving a predetermined number of NACK messages from the UE), based on the UE's location (e.g., at a base station cell), and/or based on an indication received from the UE indicating that coverage enhancement may be necessary. The base station can improve UE coverage by selecting a higher density RS density scheme to provide additional RS REs per subframe for added channel measurement, interference measurement, and reporting. If a higher density RS scheme is selected based on coverage improvement, method 1400 moves to block 1420 where the higher density RS scheme is selected.

[0152] In block 1430, method 1400 may comprise determining whether a higher density RS density scheme should be selected based on a transmission mode of the UE. For example, the base station may determine that the UE is involved in broadcast communications, and therefore a higher density RS scheme may provide improved channel estimation, interference estimation, and reporting. The base station can provide enhanced broadcast transmission coverage based on the added channel estimate report or interference estimate.

[0153] If no higher density RS scheme is selected, method 1400 may move to block 1435 where a lower density RS scheme is selected. The lower RS density scheme can generally have fewer RS REs per subframe than the higher density RS scheme.

[0154] The operation(s) on blocks 1405, 1410, 1415, 1420, 1425, 1430 and/or 1435 may be performed using any one or more of the RS 915 density scheme modules described with reference to FIGS. 9, 10 or 11.

[0155] Thus, method 1400 can provide wireless communication. It should be noted that method 1400 is only one implementation and that operations of method 1400 may be rearranged or modified so that other implementations are possible.

[0156] In some examples, aspects between two or more methods 1200, 1300 or 1400 may be combined. It should be noted that methods 1200, 1300 and 1400 are example implementations only, and that the operations of methods 1200, 1300 or 1400 may be rearranged or modified so that other implementations are possible.

[0157] The techniques described in this document can be used for various wireless communications systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other systems. The terms "system" and "network" are often used interchangeably. A CDMA system can implement a radio technology such as CDMA2000, Universal Terrestrial Access Radio (UTRA), etc. CDMA2000 covers IS-2000, IS-95 and IS-856 standards. IS-2000 versions 0 and A are commonly referred to as CDMA2000 1X, 1X, etc. IS-856 (TIA-856) is commonly referred to as CDMA2000 1xEV-DO, High Rate Packet Data (HRPD), etc. UTRA includes broadband CDMA (WCDMA) and other CDMA variants. A TDMA system can implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA system can implement a radio technology such as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (WiFi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash -OFDM™, etc. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System (UMTS). Long Term Evolution (LTE) 3GPP and LTE-Advanced (LTE-A) are new versions of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization called the "3rd Generation Partnership Project" (3GPP). CDMA2000 and UMB are described in documents from an organization called "3rd Generation Partnership Project 2" (3GPP2). The techniques described in this document can be used for the systems and technologies mentioned above, as well as other radio systems and technologies, including cellular communications (e.g., LTE) over an unlicensed and/or shared radio bandwidth. The above description, however, describes an LTE/LTE-A system for example purposes, and the LTE terminology is used throughout much of the above description, although the techniques are applicable beyond LTE/LTE-A applications.

[0158] The detailed description presented above in connection with the attached drawings describes examples and does not represent the only examples that can be performed or that are within the scope of the claims. The terms "example" and "exemplary," when used in this description, mean "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 techniques described. These techniques, however, can be practiced without these specific details. In some cases, well-known apparatus and structures are shown in block diagram form to avoid obscuring the concepts of the examples described.

[0159] Information and signals can be represented using any of a variety of different techniques and technologies. For example, data, instructions, commands, information, signals, bits, symbols and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles or any of their combinations.

[0160] The various illustrative blocks and components described in relation to the description presented in this document can be implemented or realized with a general purpose processor, a digital signal processor (DSP), an ASIC, a Field Programmable Gate Array (FPGA) ) or other programmable logic device, discrete gate or logic transistor, discrete hardware components, or any combination thereof designed to perform the functions described in this document. A general purpose processor can be a microprocessor, the processor can be any conventional processor, controller, microcontroller or state machine. A processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other configuration.

[0161] The functions described in this document can be implemented in hardware, in software executed by a processor, firmware or any combination thereof. If implemented in software executed by a processor, functions may be stored or transmitted as one or more instructions or codes in a computer-readable medium. Other implementations and examples are within the scope and spirit of the description and the added claims. For example, depending on the nature of the software, the functions described above may be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. The resources to implement the functions may also be physically located in various positions, including being distributed so that parts of the functions are implemented in different physical locations. As used herein, including the claims, the term "and/or", when used in a list of two or more items, means that any one of the items listed may be employed by itself, or any combination of two or more of the items listed. For example, if a composition is described as containing components A, B and/or C, the composition may contain only A; only B; C only; A and B in combination; A and C in combination; B and C in combination; or A, B and C in combination. Also, as used herein, including the claims, "or" when used in a list of items (e.g., a list of items preceded by a phrase such as "at least one of" or "one or more of" indicates an inclusive list that, for example, a phrase referring to "at least one of" a list of items refers to any combination of those items, including the individual members. For example, "at least one of: A, B, or C" is intended to cover A, B, C, A-B, A-C, B-C, and A-B-C, as well as any combination with multiples of the same element (e.g., A-A-A-A-A, A-A-B, A-A-C, A-B-B, A-C- C, B-B, B-B-B, B-B-C, C-C and C-C-C or any other order of A, B and C).

[0162] The computer-readable medium comprises both the non-transitory computer storage medium and the communication medium, including any communication medium that facilitates the transfer of a computer program from one place to another. A non-transitory storage medium can be any available medium that can be accessed by a special purpose or general purpose computer. By way of example, and not limitation, non-transitory computer-readable media may comprise RAM, ROM, electrically erasable programmable read-only memory (EEPROM), compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that can be used to transport or store the desired program code means in the form of instructions or data structures and that can be accessed by a general purpose computer or special purpose, or a general purpose or special purpose processor. Also, any connection is correctly called a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and micro- waves, then coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disk, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically, while (discs) reproduce data optically with lasers. Combinations of the above are also included in the scope of computer-readable media.

[0163] The foregoing description of the disclosure is provided to enable any person skilled in the art to manufacture or use the description. Various modifications to the description 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 spirit and scope of the description. Accordingly, the description is not intended to be limited to the examples and projects described herein, but should be granted the broadest scope consistent with the principles and innovative features described in this document.

Claims (13)

1. Method for wireless communication carried out by a mobile device (510), characterized by the fact that it comprises: receiving (1305), from a source cell (505), a reference signal (520) transmitted according to a reference signal density scheme, RS, the RS density scheme selected from a set of RS density schemes; identify (1310) the RS density scheme based, at least in part, on a type of a channel associated with the reference signal (520) or a coverage enhancement for the channel associated with the reference signal (520) ; and communicating (1315) using the reference signal (520) according to the RS density scheme. 2. The method of claim 1, further comprising: receiving an indication of an RS density scheme (515), wherein the RS density scheme is identified based, at least in part , in the indication and where the indication is received in dedicated signaling or in broadcast information. 3. Method according to claim 1, characterized in that receiving the reference signal (520) comprises: receiving at least one of a cell specific reference signal (CRS) or a demodulation reference signal, DM -RS, or a combination thereof. 4. Method according to claim 1, characterized by the fact that it further comprises: receiving a set of reference signals (435) in accordance with the RS density scheme and based, at least in part, on one of mobile device category or a mobile device capability. 5. The method of claim 4, wherein the mobile device category or mobile device capability comprises at least one of a machine-type communication device, MTC, a narrowband MTC device, a user equipment, UE, operating in a narrowband, or a UE that supports multiple RS density schemes. 6. The method of claim 1, wherein the RS density scheme is further determined based on one or more parameters associated with the channel. 7. Method according to claim 1, characterized by the fact that the channel type associated with the reference signal (520) comprises at least one of a broadcast channel or a unicast channel. 8. Method according to claim 1, characterized by the fact that the type of channel associated with the reference signal (520) comprises at least one of a control channel or a data channel. 9. Method according to claim 1, characterized by the fact that the channel coverage improvement comprises a channel repetition, wherein the RS density scheme is identified based, at least in part, on a number of channel repeats. 10. Method according to claim 9, characterized by the fact that the RS density scheme is identified for a first number of repetitions and another RS density scheme is identified for a second number of repetitions greater than the first number of repetitions, where the other RS density scheme has a higher RS density than the RS density scheme. 11. Method, according to claim 1, characterized by the fact that communicating using the reference signal (520) comprises: performing at least one of a channel estimate or an interference estimate using the reference signal (520); and decoding the channel based on at least one of the channel estimate or the interference estimate. 12. Mobile device (510) for wireless communication, characterized in that it comprises: means for receiving (610), from a source cell (505), a reference signal (520) transmitted in accordance with a scheme of signal reference density, RS, the RS density scheme selected from a set of RS density schemes; means for identifying (615) the RS density scheme based, at least in part, on a type of a channel associated with the reference signal (520) or a coverage enhancement for the channel associated with the reference signal (520) 520); and means for communicating (620) using the reference signal (520) in accordance with the RS density scheme. 13. Computer readable memory, characterized by the fact that it comprises instructions stored therein, the instructions being executed by a computer to carry out the method as defined in any one of claims 1 to 11.