Enhanced positioning reference signal transmission in wireless communication network

Methods and apparatus for determining a PRS configuration in a dynamic TDD configuration adaptation are described. One example method generally includes determining a first PRS configuration for receiving PRS when communicating according to a first subframe configuration that defines one or more uplink subframes and one or more downlink subframes, receiving an indication of a switch from the first subframe configuration to a second subframe configuration, and determining a second PRS configuration for receiving PRS when communicating according to the second subframe configuration.

BACKGROUND

The present disclosure relates generally to wireless communications, and more specifically, to techniques for transmitting positioning reference signals (PRSs) in a wireless communication network.

A wireless communication network may include a number of base stations that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via the downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

A wireless communication network may support operation on multiple component carriers (CCs). A CC may refer to a range of frequencies used for communication and may be associated with certain characteristics. For example, a CC may be associated with system information describing operation on the CC. A CC may also be referred to as a carrier, a frequency channel, a cell, etc. A base station may send data and downlink control information (DCI) on one or more CCs to a UE. The UE may send data and uplink control information (UCI) on one or more CCs to the base station.

SUMMARY

In an aspect of the disclosure, a method for wireless communications by a user equipment (UE) is provided. The method generally includes determining a first positioning reference signal (PRS) configuration for receiving PRS when communicating according to a first subframe configuration that defines one or more uplink subframes and one or more downlink subframes, receiving an indication of a switch from the first subframe configuration to a second subframe configuration, and determining a second PRS configuration for receiving PRS when communicating according to the second subframe configuration.

In an aspect of the disclosure, an apparatus for wireless communications by a UE is provided. The apparatus generally includes means for determining a first positioning reference signal (PRS) configuration for receiving PRS when communicating according to a first subframe configuration that defines one or more uplink subframes and one or more downlink subframes, means for receiving an indication of a switch from the first subframe configuration to a second subframe configuration, and means for determining a second PRS configuration for receiving PRS when communicating according to the second subframe configuration.

In an aspect of the disclosure, an apparatus for wireless communications by a UE is provided. The apparatus generally includes at least one processor and a memory coupled to the at least one processor. The at least one processor is generally configured to determine a first positioning reference signal (PRS) configuration for receiving PRS when communicating according to a first subframe configuration that defines one or more uplink subframes and one or more downlink subframes, receive an indication of a switch from the first subframe configuration to a second subframe configuration, and determine a second PRS configuration for receiving PRS when communicating according to the second subframe configuration.

In an aspect of the disclosure, a computer-program product for wireless communications by a UE is provided. The computer-program product generally includes a computer-readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions generally including instructions for determining a first positioning reference signal (PRS) configuration for receiving PRS when communicating according to a first subframe configuration that defines one or more uplink subframes and one or more downlink subframes, instructions for receiving an indication of a switch from the first subframe configuration to a second subframe configuration, and instructions for determining a second PRS configuration for receiving PRS when communicating according to the second subframe configuration.

In an aspect of the disclosure, a method for wireless communications by a user equipment (UE) is provided. The method generally includes determining a first positioning reference signal (PRS) configuration for a first cell, wherein the first PRS configuration is for receiving PRS from the first cell when communicating according to a first subframe configuration, the first subframe configuration indicating one or more uplink subframes and one or more downlink subframes, determining a second PRS configuration for a second cell, wherein the second PRS configuration is for receiving PRS from the second cell when communicating according to a second subframe configuration, and defining the first PRS configuration and the second PRS configuration based on one or more common downlink subframes between the first subframe configuration and the second subframe configuration.

In an aspect of the disclosure, an apparatus for wireless communications by a UE is provided. The apparatus generally includes means for determining a first positioning reference signal (PRS) configuration for a first cell, wherein the first PRS configuration is for receiving PRS from the first cell when communicating according to a first subframe configuration, the first subframe configuration indicating one or more uplink subframes and one or more downlink subframes, means for determining a second PRS configuration for a second cell, wherein the second PRS configuration is for receiving PRS from the second cell when communicating according to a second subframe configuration, and means for defining the first PRS configuration and the second PRS configuration based on one or more common downlink subframes between the first subframe configuration and the second subframe configuration.

In an aspect of the disclosure, an apparatus for wireless communications by a UE is provided. The apparatus generally includes at least one processor and a memory coupled to the at least one processor. The at least one processor is generally configured to determine a first positioning reference signal (PRS) configuration for a first cell, wherein the first PRS configuration is for receiving PRS from the first cell when communicating according to a first subframe configuration, the first subframe configuration indicating one or more uplink subframes and one or more downlink subframes, determine a second PRS configuration for a second cell, wherein the second PRS configuration is for receiving PRS from the second cell when communicating according to a second subframe configuration, and define the first PRS configuration and the second PRS configuration based on one or more common downlink subframes between the first subframe configuration and the second subframe configuration.

In an aspect of the disclosure, a computer-program product for wireless communications by a UE is provided. The computer-program product generally includes a computer-readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions generally including instructions for determining a first positioning reference signal (PRS) configuration for a first cell, wherein the first PRS configuration is for receiving PRS from the first cell when communicating according to a first subframe configuration, the first subframe configuration indicating one or more uplink subframes and one or more downlink subframes, instructions for determining a second PRS configuration for a second cell, wherein the second PRS configuration is for receiving PRS from the second cell when communicating according to a second subframe configuration, and instructions for defining the first PRS configuration and the second PRS configuration based on one or more common downlink subframes between the first subframe configuration and the second subframe configuration.

DETAILED DESCRIPTION

Techniques and apparatus are provided herein for transmitting positioning reference signals (PRSs) in a wireless communication network. According to aspects a user equipment (UE) determines PRS configuration according to a subframe configuration that defines uplink and downlink subframes. If the subframe configuration changes, the UE determines a new PRS configuration according to the new changed subframe configuration

The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts. Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from the context, the phrase, for example, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, for example the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form.

FIG. 1is a block diagram conceptually illustrating an example of a wireless communication network, which may be an LTE network or some other wireless network, in accordance with certain aspects of the present disclosure. Wireless network100may include a number of evolved Node Bs (eNBs)110and other network entities. An eNB may be an entity that communicates with the UEs and may also be referred to as a base station, a Node B, an access point, etc. Each eNB110may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of an eNB and/or an eNB subsystem serving this coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG)). In the example shown inFIG. 1, eNBs110a,110band110cmay be macro eNBs for macro cells102a,102band102c, respectively. An eNB110xmay be a pico eNB for a pico cell102x. eNBs110yand110zmay be home eNBs for femto cells102yand102z, respectively. An eNB may support one or multiple (e.g., three) cells.

Wireless network100may also include relays. A relay may be an entity that receives a transmission of data from an upstream station (e.g., an eNB or a UE) and sends a transmission of the data to a downstream station (e.g., a UE or an eNB). A relay may also be a UE that relays transmissions for other UEs. In the example shown inFIG. 1, a relay110rmay communicate with eNB110aand a UE120rin order to facilitate communication between eNB110aand UE120r.

A network controller130may couple to a set of eNBs and provide coordination and control for these eNBs. Network controller130may communicate with the eNBs via a backhaul. The eNBs may also communicate with one another, e.g., directly or indirectly via wireless or wireline backhaul.

UEs120(e.g.,120x,120y, etc.) may be dispersed throughout wireless network100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone, a smartphone, a tablet, a netbook, a smart book, an ultrabook, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, etc. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, other UEs, etc.

Wireless network100may support hybrid automatic retransmission (HARQ) in order to improve reliability of data transmission. For HARQ, a transmitter (e.g., an eNB) may send a transmission of a transport block and may send one or more additional transmissions, if needed, until the transport block is decoded correctly by a receiver (e.g., a UE), or the maximum number of transmissions has been sent, or some other termination condition is encountered. A transport block may also be referred to as a packet, a codeword, etc. For synchronous HARQ, all transmissions of the transport block may be sent in subframes of a single HARQ interlace, which may include evenly spaced subframes. For asynchronous HARQ, each transmission of the transport block may be sent in any subframe.

Wireless network100may utilize frequency-division duplex (FDD) and/or time-division duplex (TDD). For FDD, the downlink and uplink may be allocated separate frequency channels, and downlink transmissions and uplink transmissions may be sent concurrently on the separate frequency channels. For TDD, the downlink and uplink may share the same frequency channel, and downlink and uplink transmissions may be sent on the same frequency channel in different time periods. In the description herein, an FDD CC is a CC utilizing FDD, and a TDD CC is a CC utilizing TDD.

FIG. 2shows a block diagram conceptually illustrating an example of a base station/eNB210in communication with a UE220, which may be one of the base stations/eNBs and one of the UEs inFIG. 1, in a wireless communications network, in accordance with certain aspects of the present disclosure. Base station210may be equipped with T antennas234athrough234t, and UE220may be equipped with R antennas252athrough252r, where in general T≧1 and R≧1.

At base station210, a transmit processor213may receive data from a data source212for transmission to one or more UEs on one or more CCs, process (e.g., encode and modulate) the data for each UE based on one or more modulation and coding schemes selected for that UE, and provide data symbols for all UEs. Transmit processor213may also process DCI (e.g., downlink grants, uplink grants, ACK/NACK, configuration messages, etc.) and provide control symbols. Processor213may also generate reference symbols for reference signals. A transmit (TX) multiple-input multiple-output (MIMO) processor230may precode the data symbols, the control symbols, and/or the reference symbols (if applicable) and may provide T output symbol streams to T modulators (MOD)232athrough232t. Each modulator232may process its output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator232may further condition (e.g., convert to analog, amplify, filter, and upconvert) its output sample stream to obtain a downlink signal. T downlink signals from modulators232athrough232tmay be transmitted via T antennas234athrough234t, respectively.

On the uplink, at UE220, a transmit processor264may receive and process data from a data source262and UCI (e.g., ACK/NACK, CSI, etc.) from controller/processor260. Processor264may also generate reference symbols for one or more reference signals. The symbols from transmit processor264may be precoded by a TX MIMO processor266if applicable, further processed by modulators254athrough254r(e.g., for SC-FDM, OFDM, etc.), and transmitted to base station210. At base station210, the uplink signals from UE220and other UEs may be received by antennas234, processed by demodulators232, detected by a MIMO detector236if applicable, and further processed by a receive processor238to obtain decoded data and control information sent by UE220and other UEs. Processor238may provide the decoded data to a data sink239and the decoded UCI to controller/processor240.

Controllers/processors240and280may direct the operation at base station210and UE220, respectively. Processor280and/or other processors and modules at UE220may perform or direct process500inFIG. 5, process600inFIG. 6, and/or other processes for the techniques described herein. Memories242and282may store data and program codes for base station210and UE220, respectively. A scheduler244may schedule UEs for data transmissions on the downlink and/or uplink.

FIG. 3is a block diagram conceptually illustrating an example of a frame structure in a wireless communications network, in accordance with certain aspects of the present disclosure. The transmission timeline for the downlink and uplink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each subframe may include two slots. Each radio frame may thus include 20 slots with indices of 0 through 19. Each slot may include L symbol periods, e.g., seven symbol periods for a normal cyclic prefix (as shown inFIG. 3) or six symbol periods for an extended cyclic prefix. The 2L symbol periods in each subframe may be assigned indices of 0 through 2L−1. The available time frequency resources may be partitioned into resource blocks. Each resource block may cover12subcarriers in one slot.

LTE supports a number of uplink-downlink configurations for TDD. Subframes0and5are used for the downlink and subframe2is used for the uplink for all uplink-downlink configurations. Subframes3,4,7,8and9may each be used for the downlink or uplink depending on the uplink-downlink configuration. Subframe1includes three special fields composed of (i) a Downlink Pilot Time Slot (DwPTS) used for downlink control channels as well as data transmissions, (ii) a Guard Period (GP) of no transmission, and (iii) an Uplink Pilot Time Slot (UpPTS) used for either a Random Access Channel (RACH) or sounding reference signals (SRS). Subframe6may include only the DwPTS, or all three special fields, or a downlink subframe depending on the uplink-downlink configuration. The DwPTS, GP and UpPTS may have different durations for different subframe configurations. A subframe used for the downlink may be referred to as a downlink subframe, and a subframe used for the uplink may be referred to as an uplink subframe.

Table 1 lists seven uplink-downlink configurations supported by LTE for TDD. Each uplink-downlink configuration indicates whether each subframe is a downlink subframe (denoted as “D” in Table 1), or an uplink subframe (denoted as “U” in Table 1), or a special subframe (denoted as “S” in Table 1). As shown in Table 1, for example, uplink-downlink configurations2through5are downlink heavy, which means that there are more downlink subframes than uplink subframes in each radio frame. For example, uplink-downlink configuration6is uplink heavy, which means that there is more uplink subframes than downlink subframes in each radio frame.

As shown inFIG. 3, a downlink subframe may include a control region time division multiplexed (TDM) with a data region. The control region may occupy the first M symbol periods of a subframe, where M may be1,2,3or4and may change from subframe to subframe. The data region may occupy the remaining symbol periods of a subframe.

An uplink subframe may include a control region frequency division multiplexed (FDM) with a data region. The control region may occupy resource blocks near the two edges of the system bandwidth. The data region may occupy the remaining resource blocks in the middle of the system bandwidth.

As shown inFIG. 3, on the downlink in LTE, an eNB may transmit a Physical Control Format Indicator Channel (PCFICH), a Physical HARQ Indicator Channel (PHICH), a Physical Downlink Control Channel (PDCCH), and/or other physical channels in the control region of a subframe. The PCFICH may convey the size of the control region. The PHICH may carry ACK/NACK for data transmission sent on the uplink with HARQ. The PDCCH may carry downlink control information (DCI) such as downlink grants, uplink grants, etc. The eNB may transmit a Physical Downlink Shared Channel (PDSCH) and/or other physical channels in the data region of a subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink.

As also shown inFIG. 3, on the uplink in LTE, a UE may transmit a Physical Uplink Control Channel (PUCCH) in the control region of a subframe or a Physical Uplink Shared Channel (PUSCH) in the data region of the subframe. The PUCCH may carry uplink control information (UCI) such as ACK/NACK for data transmission sent on the downlink with HARQ, channel state information (CSI) to support data transmission on the downlink, etc. The PUSCH may carry only data or both data and UCI.

The various signals and channels in LTE are described in 3GPP TS 36.211, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation,” which is publicly available.

In LTE Release 9 and later, positioning reference signals (PRS) are supported. PRS may be used for estimating the position of a UE (e.g., as a distance from a transmitting base station). The estimated position may be used for various purposes, for example, location services usage. PRS, along with other reference signals, such as cell-specific reference signals (CRS), may be used for various purposes such as channel estimation, channel measurement, channel feedback reporting, etc. Referring back toFIG. 3, a cell may transmit PRS and/or CRS in certain symbol periods of each subframe (not illustrated). The CRS and PRS may be specific for the cell and may be generated based on a cell identity (ID) of the cell.

FIGS. 4A-4Billustrate a legacy PRS pattern for one and two CRS ports and four CRS ports, in accordance with certain aspects of the present disclosure. In certain aspects, for both normal cyclic prefix (CP) and extended CP types, PRS is present in all symbols except those for legacy control and common reference signal (CRS). The pattern of PRS generally exhibits a “diagonal” property, but omits the symbols containing CRS. For example, as shown inFIG. 4A, for the one and two CRS ports case, PRS is not present in symbol4of the first slot and symbols0and4in the second slot. As another example, as shown inFIG. 4B, for the four CRS ports case, PRS is not present in symbol1of the second slot.

PRS is transmitted only in resource blocks (RB) of downlink subframes configured for PRS transmission. Generally, the periodicity (e.g., 160, 320, 640, or 1280 ms) TPRSand subframe offset ΔPRSfor PRS subframes are configurable on a per cell basis. Further, positioning reference signals are transmitted in NPRSconsecutive downlink subframes, where NPRSis configured by higher layers (e.g., 1, 2, 4 or 6 subframes). In certain aspects, the first subframe of the NPRSdownlink subframes for PRS transmission instances satisfies the following equation:
(10×nf+└ns/2┘−ΔPRS)modTPRS=0,
where nfis the frame index and nsis the slot index.

In certain aspects, PRS may be in both Multimedia Broadcast Single Frequency Network (MBSFN) and/or non-MBSFN (normal) subframes. PRS may not be transmitted in special subframes in TDD. Further, PRS may not be mapped to resource elements allocated to PBCH, PSS or SSS.

Bandwidth for PRS is configurable, and may be the same or less than downlink system bandwidth. If both normal and MBSFN subframes are configured as positioning subframes within a cell, the OFDM symbols in a MBSFN subframe configured for positioning reference signal transmission may use the same cyclic prefix as used for subframe0. If only MBSFN subframes are configured as positioning subframes within a cell, the OFDM symbols configured for positioning reference signals in the MBSFN region of these subframes may use extended cyclic prefix length.

For certain aspects, the TDD DL (downlink)/UL (uplink) subframe configuration may be dynamically adapted, based on the actual traffic needs. For example, if during a short duration a large data burst on downlink is needed, the configuration may be changed from configuration #1to configuration #5. The adaptation of TDD configuration is expected to be no slower than 640 ms. However, the adaptation of TDD configuration may be as fast as 10 ms, although not desirable.

A PRS configured in a cell for a first TDD downlink/uplink subframe configuration may not be consistent with a second TDD downlink/uplink subframe configuration when dynamic TDD downlink/uplink subframe configuration is enabled by the cell. For example, an original downlink subframe carrying PRS may now become an uplink subframe after a TDD DL/UL subframe configuration change.

Therefore, certain aspects of the present disclosure provide techniques for determining a PRS configuration in a dynamic TDD configuration adaptation.

FIG. 5illustrates example operations500for determining a PRS configuration when switching between subframe configurations, in accordance with certain aspects of the present disclosure. The operations500may be performed, for example, by a UE. At502, the UE may determine a first PRS configuration for receiving PRS when communicating according to a first subframe configuration that defines one or more uplink subframes and one or more downlink subframes.

At504, the UE may receive an indication of a switch from the first subframe configuration to a second subframe configuration. Alternatively, for example, the UE may determine a switch from the first subframe configuration to a second subframe configuration based on a blind detection.

At506, the UE may determine a second PRS configuration for receiving PRS when communicating according to the second subframe configuration. For certain aspects, the first and second PRS configurations may be defined based on one or more common downlink subframes between the first and second subframe configurations, and the UE may determine the second PRS configuration by receiving signaling indicating the one or more common downlink subframes. For certain aspects, the first PRS configuration may be defined based on downlink subframes associated with the first subframe configuration, and the second PRS configuration may be defined based on downlink subframes associated with the second subframe configuration. The first and second PRS configurations may be different if one or more of the downlink subframes associated with the first subframe configuration that are configured for PRS correspond to uplink subframes associated with the second subframe configuration.

Across different cells, a PRS configured for a first cell of a first TDD downlink/uplink subframe configuration may not be consistent with a second cell of a second TDD downlink/uplink subframe configuration. For example, a downlink subframe in a first cell carrying PRS may be interfered by uplink transmission in an uplink subframe of a second cell.

FIG. 6illustrates example operations600for determining a PRS configuration for multiple cells, in accordance with certain aspects of the present disclosure. The operations600may be performed, for example, by a UE. At602, the UE may determine a first PRS configuration for a first cell, wherein the first PRS configuration is for receiving PRS from the first cell when communicating according to a first subframe configuration, the first subframe configuration indicating one or more uplink subframes and one or more downlink subframes.

At604, the UE may determine a second PRS configuration for a second cell, wherein the second PRS configuration is for receiving PRS from the second cell when communicating according to a second subframe configuration.

At606, the UE may define the first PRS configuration and the second PRS configuration based on one or more common downlink subframes between the first subframe configuration and the second subframe configuration. For certain aspects, the first and second PRS configurations may be the same. For certain aspects, the first PRS configuration may be defined based on downlink subframes associated with the first subframe configuration, and the second PRS configuration may be defined based on downlink subframes associated with the second subframe configuration. The first and second PRS configurations may be different if one or more of the downlink subframes associated with the first subframe configuration that are configured for PRS correspond to uplink subframes associated with the second subframe configuration. For certain aspects, the second PRS configuration may correspond to other downlink subframes associated with the first subframe configuration that are configured for PRS, wherein the other downlink subframes correspond to downlink subframes associated with the second subframe configuration.

In some embodiments, the UE may receive an indication of the frequency locations of PRSs that are transmitted in downlink subframes. For certain aspects, the UE may receive a list of PRS configurations corresponding to different subframe configurations

For certain aspects, PRS subframes may be defined based on a set of downlink subframes, independent of the actual TDD DL/UL subframe configuration in a given frame. As an example, since for all TDD DL/UL subframe configurations, subframe #0and subframe #5are always downlink subframes, PRS may be defined based on these two subframes, and not based on other downlink subframes that are associated with a given TDD DL/UL subframe configurations. However, if only subframe #0and subframe #5are for PRS, CP for PRS may have to be the same as that of subframe #0. Extended CP for PRS may not be supported if subframe #0is normal CP. In such a case, the PRS configuration may further indicate whether the CP type for PRS is normal CP or extended CP.

As another example, if a cell switches between configuration #1(e.g., DSUUDDSUUD) and configuration #2(e.g., DSUDDDSUDD), the PRS subframes may be defined based on the common downlink subframes between the two configurations, (e.g., subframes #0, #4, #5, and #9). More downlink subframes may potentially be used for PRS. As another example, if a first cell uses configuration #1(e.g., DSUUDDSUUD) and a second cell uses configuration #2(e.g., DSUDDDSUDD), the PRS subframes may be defined based on the common downlink subframes between the two cells (e.g., subframes #0, #4, #5, and #9). The set of subframes may be signaled to a UE via broadcast or unicast signaling.

For certain aspects, PRS subframes may be defined based on the actual available DL subframes associated with an active TDD DL/UL subframe configuration in a given frame. PRS transmission subframes may be updated if a TDD DL/UL subframe configuration is updated. For example, assuming NPRSis 6, for a cell originally configured according to subframe configuration #1(e.g., DSUUDDSUUD), PRS may start transmitting from subframe #0and is transmitted four times (e.g., subframes #0, #4, #5, #9) in the frame. In the next frame, if the cell switches to subframe configuration #2(e.g., DSUDDDSUDD), PRS may continue transmitting in subframes #0and subframe #3.

As another example, assuming NPRSis 2, for a cell originally configured according to the second subframe configuration (e.g., DSUDDDSUDD), PRS may be transmitted in subframes #0and #3every 160 ms. If the cell later switches to configuration #0(e.g., DSUUUDSUUU), PRS may be transmitted in subframes #0and #5every 160 ms.

For certain aspects, there may be PRS configuration inconsistencies after switching TDD DL/UL subframe configurations in a cell. As an example, a cell starts with configuration #2(e.g., DSUDDDSUDD), and PRS is transmitted in subframe #3every 160 ms. If the cell later switches to configuration #0(e.g., DSUUUDSUUU) subframe #3is now an uplink subframe, leading to PRS configuration inconsistencies. In an effort to resolve this issue, PRS subframes can be adjusted accordingly, e.g., by looking for the next available DL subframe. In some embodiments, a new PRS configuration may be issued after switching if there is a PRS inconsistency. However, this may not desirable due to overhead and latency. As another option, the eNB may ensure consistent PRS configuration before and after switching. From the UE perspective, a UE may discard an inconsistent PRS configuration after switching.

For certain aspects, the PRS configuration may be updated based on the current TDD DL/UL subframe configuration. As an example, for each possible TDD DL/UL subframe configuration that a cell may use, a PRS configuration may be signaled (e.g., broadcast or unicast). Then for a given TDD DL/UL subframe configuration in use, the UE may select the corresponding PRS configuration.

As another example, the UE may autonomously update PRS configuration based on DL subframe availability. For example, for a cell starting with configuration #2(e.g., DSUDDDSUDD), PRS may be transmitted in subframe #3every 160 ms. If the cell later switches to configuration #0(e.g., DSUUUDSUUU) where subframe #3is now an uplink subframe, the UE may determine that PRS is now transmitted in subframe #5(e.g., the first downlink subframe after downlink subframe #3in the current DL/UL subframe configuration) every 160 ms.

As a further example of potential PRS configuration inconsistencies, there may be issues with CP length change during a subframe configuration switch. As an example, a cell starts with the configuration #2(e.g., DSUDDDSUDD), subframe #3is an MBSFN subframe, and PRS is transmitted in subframe #3every 160 ms (as a result, the CP for PRS is extended CP). Later, the cell switches to configuration #0(e.g., DSUUUDSUUU), and the PRS may be determined to be transmitted in subframes #5(e.g., a non-MBSFN subframe) every 160 ms. As a result, the PRS may need to be changed from extended CP to normal CP, if subframe #0is normal CP. In other words, the CP length for PRS may be determined based on the current DL/UL subframe configuration, and the CP length may change after TDD DL/UL subframe configuration switching, with or without explicit signaling involved.

For certain aspects, PRS may not be transmitted if there is a subframe mismatch. As an example, if a cell starts with configuration #2(e.g., DSUDDDSUDD), PRS may be transmitted in subframe #3every 160 ms. If the cell later switches to configuration #0(e.g., DSUUUDSUUU) where subframe #3is now an uplink subframe, PRS may not be transmitted. As another example, if a cell starts with configuration #2(e.g., DSUDDDSUDD), PRS may be transmitted in subframes #0and #3(e.g., NPRS=2) every 160 ms. If the cell later switches to configuration #0(DSUUUDSUUU) where subframe #3is now an uplink subframe, PRS may only be transmitted in subframe #0, although NPRS=2. This same design can also be applied to MBSFN subframes. For example, if a MBSFN subframe in a first TDD DL/UL subframe configuration becomes an uplink subframe in a second TDD DL/UL subframe configuration, the MBSFN subframe may skipped (e.g., MBMS is not transmitted).

In addition, the location of PRS may not necessarily be in the center. Currently, PRS may be transmitted in the center of downlink system bandwidth—although PRS bandwidth may be the same or less than downlink system bandwidth. It may be beneficial for a narrowband PRS (e.g., less than DL system bandwidth) to be transmitted in a non-center region (e.g., to avoid collision with PSS/SSS/PBCH). The location of PRS may be informed to the UEs or predetermined (e.g., the location explicitly in the specification).

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software/firmware module executed by a processor, or combinations thereof. A software/firmware module may reside in random access memory (RAM), flash memory, read only memory (ROM), erasable programmable ROM (EPROM), electrically EPROM (EEPROM), phase change memory (PCM), registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.