CN111432463A - SRS optimization for coordinated multipoint transmission and reception - Google Patents

Abstract

Certain aspects of the present disclosure relate to techniques for power control and SRS multiplexing for coordinated multipoint (CoMP) transmission and reception in heterogeneous networks (hetnets). Multiple SRS processes are supported with different physical and/or virtual cell IDs. Different power control offsets and procedures are associated with different SRS procedures.

Description

SRS optimization for coordinated multipoint transmission and reception

The present application is a divisional application of an application having an application date of 2012/10/6/10, an application number of 201280056765.6, entitled "SRS optimization for coordinated multipoint transmission and reception".

Claiming priority based on 35 U.S.C. § 119

This patent application claims the benefit of U.S. provisional application No.61/542,669 entitled "SRS timing for reliable timing MU L TI-POINT TRANSMISSION AND timing", filed on 3.10.2011, which is assigned to the assignee of the present application AND is hereby expressly incorporated herein by reference.

Technical Field

Certain aspects of the present disclosure generally relate to wireless communications, and more specifically to techniques for power control and user multiplexing for coordinated multipoint (CoMP) transmission and reception in heterogeneous networks (hetnets).

Background

Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and so on. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, orthogonal FDMA (ofdma) networks, and single carrier FDMA (SC-FDMA) networks.

A wireless communication network may include a plurality of Base Stations (BSs) that support communication for a plurality 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 stations to the UEs, and the uplink (or reverse link) refers to the communication link from the UEs to the base stations.

A base station may transmit data and control information to a UE on the downlink and/or may receive data and control information from a UE on the uplink. On the downlink, transmissions from a base station may observe interference due to transmissions from neighboring base stations. On the uplink, transmissions from a UE may cause interference to transmissions from other UEs communicating with neighboring base stations. This interference can degrade performance on both the downlink and uplink.

Disclosure of Invention

Certain aspects of the present disclosure provide methods for wireless communications by a User Equipment (UE). The method generally comprises: transmitting a first Sounding Reference Signal (SRS) intended for one or more first base stations currently serving the UE and associated with a first cell identifier, transmitting a second SRS intended for one or more second base stations associated with a second cell identifier, and adjusting transmit powers of the first and second SRSs with separate power control schemes.

Certain aspects of the present disclosure provide methods for wireless communications by a Base Station (BS). The method generally comprises: configuring a User Equipment (UE) to transmit a first Sounding Reference Signal (SRS), the first SRS intended for one or more first base stations currently serving the UE and associated with a first cell identifier, configuring the UE to transmit a second SRS intended for one or more second base stations associated with a second cell identifier, and transmitting one or more Transmit Power Control (TPC) commands for the UE to adjust transmit powers of the first and second SRSs with separate power control schemes.

Certain aspects of the present disclosure provide an apparatus for wireless communications by a User Equipment (UE). The apparatus generally comprises: at least one processor configured to transmit a first Sounding Reference Signal (SRS) intended to transmit a second SRS intended for one or more first base stations currently serving the UE and associated with a first cell identifier, the second SRS intended for one or more second base stations associated with a second cell identifier, and to adjust transmit powers of the first and second SRSs with separate power control schemes; and a memory coupled with the at least one processor.

Certain aspects of the present disclosure provide an apparatus for wireless communication by a first base station. The apparatus generally includes at least one processor configured to configure a User Equipment (UE) to transmit a first Sounding Reference Signal (SRS), the first SRS intended for one or more first base stations currently serving the UE and associated with a first cell identifier, configure the UE to transmit a second SRS intended for one or more second base stations associated with a second cell identifier; and transmitting one or more Transmit Power Control (TPC) commands for the UE to adjust transmit powers of the first and second SRS with separate power control schemes; and a memory coupled with the at least one processor.

Certain aspects of the present disclosure provide a computer program product comprising a computer-readable medium having instructions stored thereon. The instructions are generally executable by one or more processors for transmitting a first Sounding Reference Signal (SRS) intended for a currently serving UE and one or more first base stations associated with a first cell identifier, transmitting a second SRS intended for one or more second base stations associated with a second cell identifier, and adjusting transmit powers of the first SRS and the second SRS with separate power control schemes.

Certain aspects of the present disclosure provide a computer program product comprising a computer-readable medium having instructions stored thereon. The instructions are generally executable by one or more processors for configuring a User Equipment (UE) to transmit a first Sounding Reference Signal (SRS) intended for one or more first base stations currently serving the UE and associated with a first cell identifier, configuring the UE to transmit a second SRS intended for one or more second base stations associated with a second cell identifier, and transmitting one or more Transmit Power Control (TPC) commands for the UE to adjust transmit powers of the first and second SRS with separate power control schemes.

Drawings

Fig. 1 is a block diagram conceptually illustrating an example of a wireless communication network in accordance with certain aspects of the present disclosure.

Fig. 2 is a block diagram conceptually illustrating an example of a frame structure in a wireless communication network, in accordance with certain aspects of the present disclosure.

Fig. 2A illustrates an example format for uplink in long term evolution (L TE), in accordance with certain aspects of the present disclosure.

Fig. 3 illustrates a block diagram conceptually showing an example of a node B communicating with a user equipment device (UE) in a wireless communication network, in accordance with certain aspects of the present disclosure.

Fig. 4 illustrates an example heterogeneous network (HetNet) in accordance with certain aspects of the present disclosure.

Fig. 5 illustrates example resource partitioning in a heterogeneous network, in accordance with certain aspects of the present disclosure.

Fig. 6 illustrates an example collaborative partitioning of subframes in a heterogeneous network, in accordance with certain aspects of the present disclosure.

Fig. 7 is a schematic diagram illustrating a range extended cellular region in a heterogeneous network.

Fig. 8 is a schematic diagram illustrating a network with a macro eNB and Remote Radio Heads (RRHs) in accordance with certain aspects of the present disclosure.

Fig. 9 is a schematic diagram illustrating an example Sounding Reference Signal (SRS) enhancement, in accordance with aspects of the present disclosure.

Fig. 10 is a schematic diagram illustrating another example Sounding Reference Signal (SRS) enhancement in accordance with aspects of the present disclosure.

Fig. 11 illustrates example operations 1100 performed at a User Equipment (UE), in accordance with certain aspects of the present disclosure.

Fig. 12 illustrates example operations 1200 performed at a base station (e.g., and eNB) in accordance with certain aspects of the present disclosure.

Detailed Description

Aspects of the present disclosure provide methods that may enhance Sounding Reference Signal (SRS) procedures for coordinated multipoint (CoMP) systems. As will be described in more detail below, a UE participating in CoMP operations may be configured to: two different sets of SRS signals are transmitted. For example, a first set of SRS may be intended for only the serving cell, while a second set of SRS may be intended for joint reception of multiple cells.

Techniques described hereinMay be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SD-FDMA and other networks. The terms "network" and "system" are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes wideband CDMA (wcdma) and other variants of CDMA. CDMA2000 covers IS-2000, IS-95 and IS-856 standards. TDMA networks may implement wireless technologies such as global system for mobile communications (GSM). OFDMA networks may implement methods such as evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE802.11(Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, and,

UTRA, E-UTRA, UMTS, L TE, L TE-a, and gsm are described in documents from an organization named "third generation partnership project" (3GPP) in documents from the organization named "third generation partnership project 2" (3GPP 2-CDMA 2000 and umb are described.

Example Wireless network

Fig. 1 illustrates a wireless communication network 100, which may be an L TE network, the wireless network 100 may include a plurality of evolved node bs (enbs) 110 and other network entities, an eNB may be a station that communicates with user equipment devices (UEs) and may also be referred to as a base station, a node B, an access point, etc., each eNB110 may provide communication coverage for a particular geographic area in 3GPP, the term "cell" may refer to a coverage area of an eNB and/or an eNB subsystem serving that coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, pico cell, femto cell, and/or other types of cells. 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 subscriptions. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscriptions. A femto cell may cover a relatively small geographic area (e.g., a home), and may allow restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group, UEs of users in the home, etc.). An eNB for a macro cell may be referred to as a macro eNB (i.e., a macro base station). An eNB for a pico cell may be referred to as a pico eNB (i.e., a pico base station). An eNB for a femto cell may be referred to as a femto eNB (i.e., a femto base station) or a home eNB. In the example shown in fig. 1, enbs 110a, 110b and 110c may be macro enbs for macro cells 102a, 102b and 102c, respectively. eNB110 x may be a pico eNB for pico cell 102 x. enbs 110y and 110z may be femto enbs for femtocells 102y and 102z, respectively. An eNB may support one or more (e.g., three) cells.

Wireless network 100 may also include relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB or UE) and sends a transmission of data and/or other information to a downstream station (e.g., a UE or eNB). A relay station may also be a UE that relays transmissions for other UEs. In the example shown in fig. 1, relay 110r may communicate with eNB110 a and UE 120r to facilitate communication between eNB110 a and UE 120 r. A relay station may also be referred to as a relay eNB, a relay, etc.

Wireless network 100 may be a heterogeneous network (HetNet) including different types of enbs (e.g., macro enbs, pico enbs, femto enbs, relays, etc.). These different types of enbs may have different transmit power levels, different coverage areas, and different effects on interference in wireless network 100. For example, macro enbs may have a high transmit power level (e.g., 20 watts), while pico enbs, femto enbs, and relays may have a lower transmit power level (e.g., 1 watt).

Wireless network 100 may support synchronous or asynchronous operation. For synchronous operation, enbs may have similar frame timing, and transmissions from different enbs may be approximately aligned in time. For asynchronous operation, enbs may have different frame timing, and transmissions from different enbs may not be aligned in time. The techniques described herein may be used for both synchronous and asynchronous operations.

Network controller 130 may couple to a set of enbs and provide coordination and control for these enbs. Network controller 130 may communicate with enbs 110 via a backhaul. The enbs 110 may also communicate with each other, e.g., directly or indirectly via a wireless or wired backhaul.

The UEs 120 may be dispersed throughout the wireless network 100, and each UE may be fixed or mobile, UEs may also be referred to as terminals, mobile stations, subscriber units, stations, etc. UEs may be cellular phones, Personal Digital Assistants (PDAs), wireless modems, wireless communication devices, handheld devices, laptops, cordless phones, wireless local loop (W LL) stations, tablets, etc. the UEs are capable of communicating with macro eNBs, pico eNBs, femto eNBs, relays, etc. in FIG. 1, the solid line with double arrows represents a desired transmission between a UE and a serving eNB, which is a designated to serve the UE on the downlink and/or uplink.

L TE utilizes Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink OFDM and SC-FDM divide the system bandwidth into multiple (K) orthogonal subcarriers, also commonly referred to as tones, bins, etc. each subcarrier may be modulated with data.

Each radio frame may include 20 slots with indices of 0 through 19 each slot may include L symbol periods, e.g., L-7 symbol periods for a normal cyclic prefix (as shown in fig. 2) or L-6 symbol periods for an extended cyclic prefix.

In L TE, the eNB may transmit a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) for each cell in the eNB As shown in FIG. 2, in each of subframe 0 and subframe 5 of each radio frame with a normal cyclic prefix, the primary and secondary synchronization signals may be transmitted in symbol periods 6 and 5, respectively.

As shown in fig. 2, the eNB may transmit a Physical Control Format Indicator Channel (PCFICH) in the first symbol period of each subframe, the PCFICH may convey the number of symbol periods (M) for the control channel, where M may be equal to 1, 2, or 3, and may vary from frame to frame, for small system bandwidths, e.g., with less than 10 resource blocks, M may also be equal to 4. the eNB may transmit a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) (not shown in fig. 2) in the first M symbol periods of each subframe, the PHICH may carry information for supporting hybrid automatic repeat request (HARQ), the PDCCH may carry information regarding resource allocation for the UE and control information for the downlink channel, the eNB may transmit a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe, the PDSCH may carry data for UEs scheduled for transmission on the downlink, various common Terrestrial evolution Channels (GPP) L, and various common Terrestrial evolution (GPP) signals.

The eNB may transmit the PSS, SSS, and PBCH in the center 1.08MHz of the system bandwidth used by the eNB. In each symbol period in which these channels are transmitted, the eNB may transmit the PCFICH and PHICH across the entire system bandwidth. The eNB may transmit the PDCCH to the group of UEs in some portion of the system bandwidth. The eNB may transmit the PDSCH to a particular UE in a particular portion of the system bandwidth. The eNB may transmit PSS, SSS, PBCH, PCFICH, and PHICH to all UEs in a broadcast manner, and may transmit PDCCH to a specific UE in a unicast manner, and may also transmit PDSCH to a specific UE in a unicast manner.

In each symbol period, multiple resource elements may be available. Each resource element may cover one subcarrier in one symbol period and may be used to transmit one modulation symbol, which may be real or complex valued. Resource elements in each symbol period that are not used for reference signals may be arranged into Resource Element Groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs approximately equally spaced across frequency in symbol period 0. The PHICH may occupy three REGs spread across frequency in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong to symbol period 0 or may be spread in symbol periods 0, 1, and 2. The PDCCH may occupy 9, 18, 32, or 64 REGs selected from available REGs in the first M symbol periods. Only certain REG combinations may be allowed for PDCCH.

The UE may know specific REGs for PHICH and PCFICH. The UE may search for different REG combinations for the PDCCH. The number of combinations searched is typically smaller than the number of combinations allowed for PDCCH. The eNB may transmit the PDCCH to the UE in any one of the combinations in which the UE will search.

Fig. 2A illustrates an example format 200a for the uplink in L TE the available resource blocks for the uplink may be divided into a data portion and a control portion the control portion may be formed at both edges of the system bandwidth and may have a configurable size.

The resource blocks in the control portion may be allocated to the UE to transmit control information to the eNB. The resource blocks in the data portion may also be allocated to the UE to transmit data to the eNB. The UE may send control information on resource blocks in the allocated control portion in a Physical Uplink Control Channel (PUCCH)210a, 210 b. The UE may transmit only data or both data and control information on resource blocks in the allocated data portion in a Physical Uplink Shared Channel (PUSCH)220a, 220 b. As shown in fig. 2A, the uplink transmission may hop across two slots of a subframe and across frequency.

The UE may be within coverage of multiple enbs. One of the enbs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received power, path loss, signal-to-noise ratio (SNR), etc.

The UE may operate in a dominant interference scenario, where the UE may observe high interference from one or more interfering enbs. A significant interference scenario may occur due to restricted association. For example, in fig. 1, UE 120 may be close to femto eNB110y and may have high received power for eNB110 y. However, UE 120y may not be able to access femto eNB110y due to the restricted association and may then connect to macro eNB110 c (as shown in fig. 1) having a lower received power or to femto eNB110 z (not shown in fig. 1) also having a lower received power. UE 120y may then observe high interference from femto eNB110y on the downlink and may also cause high interference to eNB110y on the uplink.

A dominant interference scenario may also occur due to range extension, which is a scenario where the UE is connected to an eNB with lower path loss and lower SNR among all enbs detected by the UE. For example, in fig. 1, UE 120x may detect macro eNB110 b and pico eNB110 x and may have a lower received power for eNB110 x (lower than the received power for eNB110 b). However, if the path loss for eNB110 x is lower than the path loss for macro eNB110 b, UE 120x may desire to connect to pico eNB110 x. This may result in less interference to the wireless network for a given data rate for UE 120 x.

In an aspect, communication in a dominant interference scenario may be supported by having different enbs operate on different frequency bands. A frequency band is a range of frequencies that may be used for communication and may be given by (i) a center frequency and a bandwidth, or (ii) a lower frequency and a higher frequency. A frequency band may also be referred to as a band, a frequency channel, etc. The frequency bands for the different enbs may be selected so that a UE may communicate with a weaker eNB in a dominant interference scenario while allowing a strong eNB to communicate with its UEs. An eNB may be classified as a "weak" eNB or a "strong" eNB based on the received power of signals from the eNB received at the UE (rather than based on the transmit power level of the eNB).

Fig. 3 is a block diagram of a design of a base station or eNB110 and a UE 120, where the base station or eNB110 may be one of the base stations/enbs in fig. 1, and the UE 120 may be one of the UEs in fig. 1. For the restricted association scenario, eNB110 may be macro eNB110 c in fig. 1, and UE 120 may be UE 120 y. The eNB110 may also be some other type of base station. The eNB110 may be equipped with T antennas 334a through 334T and the UE 120 may be equipped with R antennas 352a through 352R, where generally T ≧ 1 and R ≧ 1.

At eNB110, a transmit processor 320 may receive data from a data source 312 and control information from a controller/processor 340. The control information may be for PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for PDSCH, etc. Transmit processor 320 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. Transmit processor 320 may also generate reference symbols (e.g., for PSS, SSS) and cell-specific reference signals. A Transmit (TX) multiple-input multiple-output (MIMO) processor 330 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide T output symbol streams to T Modulators (MODs) 332a through 332T. Each modulator 332 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 332 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. T downlink signals from modulators 332a through 332T may be transmitted via T antennas 334a through 334T, respectively.

At UE 120, antennas 352a through 352r may receive downlink signals from eNB110 and may provide received signals to demodulators (DEMODs) 354a through 354r, respectively. Each demodulator 354 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 354 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 356 may obtain received symbols from all R demodulators 354a through 354R, perform MIMO detection on the received symbols (if applicable), and provide detected symbols. A receive processor 358 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for UE 120 to a data sink 360, and provide decoded control information to a controller/processor 380.

On the uplink, at UE 120, a transmit processor 364 may receive and process data from a data source 362 (e.g., for the PUSCH) and control information from a controller/processor 380 (e.g., for the PUCCH). Transmit processor 364 may also generate reference symbols for a reference signal. The symbols from transmit processor 364 may be precoded by a TX MIMO processor 366 if applicable, further processed by modulators 354a through 354r (e.g., for SC-FDM, etc.), and transmitted to eNB 110. At eNB110, the uplink signals from UE 120 may be received by antennas 334, processed by demodulators 332, detected by a MIMO detector 336 (if applicable), and further processed by a receive processor 338 to obtain decoded data and control information sent by UE 120. Receive processor 338 may provide the decoded data to a data sink 339 and the decoded control information to controller/processor 340.

Controllers/ processors 340 and 380 may direct operations at eNB110 and UE 120, respectively. The controller/processor 340, the receive processor 338, and/or other processors and modules located at the eNB110 may perform or direct operations and/or processes for the techniques described herein. Memories 342 and 382 may store data and program codes for eNB110 and UE 120, respectively. A scheduler 344 may schedule UEs for data transmission on the downlink and/or uplink.

Example resource partitioning

According to certain aspects of the present disclosure, when a network supports enhanced inter-cell interference coordination (elcic), base stations may negotiate with each other to coordinate resources in order to reduce or eliminate interference by interfering cells relinquishing a portion of their resources. According to the interference coordination, the UE can access the serving cell even in case of severe interference by using resources yielded by the interfering cell.

For example, a femto cell having a closed access mode in the coverage area of an open macro cell (i.e., a mode in which only member femto UEs can access the cell) can create a "coverage hole" for the macro cell (in the coverage area of the femto cell) by yielding resources and effectively removing interference. By negotiating for femto cell relinquishing resources, macro UEs in the femto cell coverage area can still use these relinquished resources to access the UE's serving macro cell.

In a wireless access system using OFDM, such as an evolved universal terrestrial radio access network (E-UTRAN), the yielded resources may be time-based, frequency-based, or a combination of both. When the coordinated resource partitioning is time-based, the interfering cell may simply not use some of the subframes in the time domain. When coordinated resource partitioning is frequency-based, the interfering cell may yield subcarriers in the frequency domain. In the case of a combination of both frequency and time, the interfering cell may yield frequency and time resources.

Fig. 4 illustrates an example scenario in which eICIC may allow an eICIC-enabled macro UE 120y (e.g., a release 10 macro UE as shown in fig. 4) to access a macro cell 110c (as shown by uninterrupted wireless link 402) even when the macro UE 120y is experiencing severe interference from femto cell y. A legacy macro UE 120u (e.g., a release 8 macro UE as shown in fig. 4) cannot access the macro cell 110c (as shown by the broken radio link 404) in the event of severe interference from the femto cell 110 y. Femto UE 120v (e.g., a release 8 femto UE as shown in fig. 4) may access femto cell 110y without any interference issues from macro cell 110 c.

According to certain aspects, a network may support eICIC, where there may be different sets of partitioning information. The first of these sets may be referred to as semi-Static Resource Partitioning Information (SRPI). The second of these sets may be referred to as Adaptive Resource Partitioning Information (ARPI). As the name implies, the SRPI typically does not change frequently and may be sent to the UE so that the UE may use the resource partitioning information for its own operation.

For example, the resource division may be implemented with a periodicity of 8ms (8 subframes) or a periodicity of 40ms (40 subframes). According to certain aspects, it may be assumed that Frequency Division Duplexing (FDD) may also be applied, and thus the frequency resources may also be divided. For communication via the downlink (e.g., from a cell node B to a UE), the partitioning pattern may be mapped to known subframes (e.g., the first subframe of each radio frame having a System Frame Number (SFN) value that is a multiple of an integer N (e.g., 4)). Such mapping may be applied in order to determine Resource Partitioning Information (RPI) for a particular subframe. For example, subframes subject to coordinated resource partitioning (e.g., yielded by an interfering cell) for the downlink may be identified by the following index:

index SRPI _ D L ═ (SFN × 10+ subframe number) mod 8

For the uplink, the SRPI map may be moved (e.g., moved for 4 ms). Thus, an example for the uplink may be:

the index SRPI _ D L ═ (SFN × 10+ subframe number +4) mod 8

The SRPI may use the following three values for each entry:

u (use): the value indicates that the subframe has been cleared from significant interference to be used by the cell (i.e., the primary interfering cell does not use the subframe);

n (unused): the value indicates that the subframe is not to be used; and

x (unknown): the value indicates that the subframe is not statically partitioned. The details of resource usage negotiation between base stations are not known to the UE.

Another possible set of parameters for SRPI may be as follows:

u (use): the value indicates that the subframe has been cleared from significant interference to be used by the cell (i.e., the primary interfering cell does not use the subframe);

n (unused): the value indicates that the subframe is not to be used;

x (unknown): this value indicates that the subframes are not statically partitioned (and the details of resource usage negotiation between base stations are not known to the UE); and

c (common): the value may indicate that all cells may use the subframe without resource partitioning. The subframe may be subject to interference so that the base station may choose to use the subframe only for UEs that are not subject to severe interference.

The SRPI of the serving cell may be broadcast over the air. In the E-UTRAN, the SRPI of the serving cell may be transmitted in a Master Information Block (MIB), or one of System Information Blocks (SIBs). The predefined SRPI may be defined based on characteristics of the cell, such as a macro cell, a pico cell (with open access), and a femto cell (with closed access). In this case, encoding the SRPI in the overhead message may result in a more efficient broadcast over the air.

The base station may also broadcast the SRPI of the neighboring cell in one of the SIBs. To this end, the SRPI may be transmitted with a corresponding range of SRPIs of Physical Cell Identifiers (PCIs).

The ARPI may represent further resource partitioning information with detailed information for 'X' subframes in the SRPI. As noted above, the detailed information for the 'X' subframe is typically known only to the base station and not to the UE.

Fig. 5 and 6 show examples of SRPI allocation in a scenario with macro cells and femto cells. U, N, X or C subframe is a subframe corresponding to U, N, X or C SRPI allocation.

Fig. 7 is a diagram 700 illustrating a range extended cellular region in a heterogeneous network. An eNB of a lower power class, such as RRH 710b, may have a range extended cellular region 703, the region 703 being extended from the cellular region 702 by enhanced inter-cell interference coordination between the RRH 710b and the macro eNB 710a, and by interference cancellation performed by the UE 720. The RRH 710b receives information about the interference situation of the UE720 from the macro eNB 710a in enhanced inter-cell interference coordination. This information allows the RRH 710b to serve the UE720 in the extended-range cellular region 703 and accept handover of the UE720 from the macro eNB 710a when the UE720 enters the extended-range cellular region 703.

Fig. 8 is a schematic diagram illustrating a network 800 including a macro node and a plurality of Remote Radio Heads (RRHs), in accordance with certain aspects of the present disclosure. The macro node 802 is connected to RRHs 804, 806, 808, and 810 using optical fibers. In some aspects, the network 800 may be a homogeneous or heterogeneous network, and the RRHs 804 and 810 may be low-power or high-power RRHs. In one aspect, the macro node 802 handles all scheduling for itself and RRHs within the cell. The RRHs may be configured to have the same cell Identifier (ID) as the macro node 802 or to have different cell IDs. The macro node 802 and the RRHs may operate substantially as one cell controlled by the macro node 802 if the RRHs are configured to have the same cell ID. On the other hand, if the RRHs and the macro node 802 are configured to have different cell IDs, then the macro node 802 and RRHs may appear to the UE as different cells, although all control and scheduling may still utilize the macro node 802. It should also be appreciated that the processing for the macro node 802 and the RRHs 804, 806, 808, 810 may not necessarily be located at the macro node. This may also be performed in a centralized manner at some other network device or entity connected with the macro and RRHs.

As used herein, the term transmit/receive point ("TxP") generally refers to: geographically separated transmitting/receiving nodes controlled by at least one central entity (e.g., eNodeB), which may have the same or different cell IDs.

In certain aspects, the control information may be transmitted using CRSs from the macro node 802, or both the macro node 802 and all of the RRHs, when each of the RRHs shares the same cell ID with the macro node 802. The CRS is typically transmitted from each of the transmission points using the same resource elements, and thus the signals collide. When each of the transmission points has the same cell ID, the CRSs transmitted from each of the transmission points may not be distinguished. In certain aspects, CRSs transmitted from each of the txps using the same resource elements may or may not collide when the RRHs have different cell IDs. Even in the case when the RRHs have different cell IDs and the CRSs collide, the improved UE may use interference cancellation techniques and improved receiver processing to distinguish the CRSs transmitted from each of the txps.

In certain aspects, when all transmission points are configured to have the same cell ID and CRS is transmitted from all transmission points, appropriate antenna virtualization is required if there are an unequal number of physical antennas at the transmitting macro node and/or RRH. That is, the CRS is to be transmitted with an equal number of CRS antenna ports. For example, if node 802 and RRHs 804, 806, 808 each have four physical antennas and RRH 810 has two physical antennas, then a first antenna of RRH 810 may be configured to transmit using two CRS ports and a second antenna of RRH 810 may be configured to transmit using two different CRS ports. Alternatively, for the same deployment, the macro 802 and RRHs 804, 806, 808 may transmit only two CRS antenna ports from two transmit antennas selected from the four transmit antennas per transmission point. Based on these examples, it should be appreciated that the number of antenna ports may be increased or decreased in relation to the number of physical antennas.

As discussed above, the macro node 802 and RRHs 804 and 810 may both transmit CRS when all transmission points are configured to have the same cell ID. However, if only the macro node 802 transmits the CRS, an interruption may occur near the RRH due to an Automatic Gain Control (AGC) problem. In such a scenario, CRS based transmissions from the macro 802 may be received at low received power, while other transmissions originating from nearby RRHs may be received at much higher power. This power imbalance can lead to the aforementioned AGC problems.

In general, the differences between the same/different cell ID setups relate to control and legacy issues, as well as other potential CRS-dependent operations. Scenarios with different cell IDs but with colliding CRS configurations may have similarities to the same cell ID establishment by defining CRS with collisions. Compared to the same cell ID case, scenarios with different cell IDs and with colliding CRSs generally have the following advantages: system characteristics/components that depend on cell ID (e.g., scrambling sequence, etc.) can be more easily distinguished.

Exemplary configurations may be applicable to macro/RRH establishment with the same or different cell IDs. In case of different cell IDs, the CRS may be configured to be colliding, which may result in a similar situation as the same cell ID, but with the following advantages: the UE can more easily distinguish system characteristics (e.g., scrambling code sequence, etc.) that depend on the cell ID.

In certain aspects, an exemplary macro/RRH entity may provide separation of control/data transmissions within the transmission point established by the macro/RRH. When the cell IDs for each transmission point are the same, the PDCCH may be transmitted using CRSs from the macro node 802, or both the macro node 802 and RRH804 and 810, while the PDSCH may be transmitted using channel state information reference signals (CSI-RS) and demodulation reference signals (DM-RS) from a subset of transmission points. When the cell IDs of some of the transmission points are different, the PDCCH may be transmitted using the CRS of each cell ID group. The CRSs transmitted from each cell ID group may or may not collide. The UE may not distinguish CRSs transmitted from multiple transmission points with the same cell ID, but may distinguish CRSs transmitted from multiple transmission points with different cell IDs (e.g., using interference cancellation or similar techniques).

In certain aspects, where all transmission points are configured to have the same cell ID, the separation of control data/transmissions enables the UE to associate the UE with at least one transmission point for data transmission using a transparent manner, while control is sent based on CRS transmissions from all transmission points. This enables the cell to be split across different transmission points for data transmission, while keeping the control channel common. The term "associated" above means a configuration of antenna ports for data transmission for a specific UE. This is different from the association performed in the context of handover. Control may be transmitted based on CRS as discussed above. Separating control and data may allow for faster reconfiguration of antenna ports for data transmission by the UE than would be necessary through a handover procedure. In certain aspects, feedback across transmission points is possible by configuring antenna ports of the UE to correspond to physical antennas of different transmission points.

In certain aspects, UE-specific reference signals enable this (e.g., in L TE-A, Rel-10 and above contexts.) CSI-RS and DM-RS are reference signals used in the L TE-A context.

SRS problem in CoMP scenarios

In CoMP design, one challenging part is to identify and group transmission points participating in CoMP operations (into the U L and/or D L CoMP sets) with minimal overhead SRS channels are mainly used for U L channel sounding, in the context of CoMP, SRS is often used to identify the closest cell to the UE.

Aspects of the present disclosure provide techniques that may enhance Sounding Reference Signal (SRS) procedures for use in a coordinated multipoint (CoMP) system. As will be described in more detail below, UEs involved in CoMP operations may be configured to: two different sets of SRS signals are transmitted. For example, a first set of SRS may be intended for only the serving cell, while a second set of SRS may be intended for joint reception of multiple cells.

Sounding Reference Signals (SRS) are transmitted by UEs on the uplink and allow receiving nodes to estimate the quality of the channel at different frequencies. In a CoMP system, SRS may allow a receiving node to determine the closest transmission point and, for example, dynamically switch transmission points serving a UE on the uplink or downlink. The techniques presented herein may be applied to both periodic SRS (e.g., SRS transmissions scheduled to be transmitted periodically) and aperiodic SRS (e.g., single SRS transmission triggered by a downlink transmission).

The base station uses the SRS to estimate the quality of the uplink channel for large bandwidths outside the range allocated to a particular UE. This measurement cannot be obtained with the Demodulation Reference Signal (DRS) because these are always associated with the Physical Uplink Shared Channel (PUSCH) and the Physical Uplink Control Channel (PUCCH) and are limited by the bandwidth allocated by the UE. Unlike DRSs associated with physical uplink control channels and shared channels, SRS is not necessarily transmitted together using any physical channel. If the SRS is transmitted using a physical channel, it can be spread over a larger frequency band. The information provided by the estimation is used to schedule uplink transmissions on resource blocks of good quality.

SRS is typically sent from a UE with a cell ID that can be detected by a given transmission point (e.g., PCI of the serving cell). However, as described herein, a UE may transmit two sets of SRS using different cell IDs.

A pico eNB may have its own Physical Cell Identity (PCI) or cell ID with an X2 connection with a macro eNB. A pico eNB has its own scheduler operation and may be linked to multiple macro enbs. The RRHs may or may not have the same PCI as the macro eNB and have fiber connections with the macro eNB, providing better backhaul. For RRHs, scheduler operations may be performed only on the macro eNB side. Femto enbs may have limited association and no additional consideration for it in CoMP schemes.

For example, in a first scenario (scenario 1), there may be a homogeneous deployment that utilizes intra-site CoMP, in a second scenario (scenario 2), there may be a homogeneous deployment that utilizes high-power RRHs connected by optical fibers.

In a third scenario (scenario 3), the macro eNB and RRH and/or pico eNB have different pcis-in this scenario, Common Reference Signals (CRS), Primary Synchronization Signals (PSS), Secondary Synchronization Signals (SSS) and Physical Broadcast Channels (PBCH) are all transmitted from the macro eNB and pico eNB-in this scenario, cell-splitting gains can be easily achieved by scheduling different users to different RRHs, however, CSI-RS or CRS based D L CoMP transmission requires enhanced feedback from the UE.

In a fourth scenario (scenario 4), the macro eNB and RRH have the same PCI. In one case, only the macro eNB transmits CRS, PSS, SSS, and PBCH, while in another case, both the macro eNB and RRH may transmit CRS, PSS, SSS, and PBCH. For RRHs with the same cell ID, the macro eNB and RRH effectively form a "super cell" with centralized scheduling. Single Frequency Network (SFN) gain can be achieved but cell split gain cannot be achieved. The SRS channel may be used to identify the nearest RRH and based on this, cell splitting may be performed by transmitting to the UE only from nearby RRHs.

In scenario 3, where each RRH has a different PCI, the SRS channel from each RRH will have a different configuration, sequence, etc. for D L CoMP and uplink (U L) CoMP, each RRH will need to attempt SRS transmitted from other RRHs.

As noted above, aspects of the present disclosure provide methods that may enhance Sounding Reference Signal (SRS) procedures for use in a coordinated multipoint (CoMP) system. In accordance with the techniques presented herein, a UE involved in CoMP operations may be configured to: two different sets of SRS signals are transmitted. For example, a first set of SRS may be intended for only the serving cell, while a second set of SRS may be intended for joint reception of multiple cells.

For example, one possible enhancement to scenario 3 is that one eNB (macro eNB, RRH, pico eNB, femto eNB, etc.) allocates SRS transmissions that are different from its own PCI-this PCI can be a virtual or set PCI-it can be signaled or exchanged between all participating nodes over a fiber or X2 connection all nodes that can receive this SRS can participate in D L or U L CoMP with the UE.

Fig. 9 shows an example of transmitting SRS using group PCI. In an example, the UE is served by RRH2 for non-CoMP operation. Accordingly, the UE transmits the first SRS using the PCI of the RRH 2. However, the UE also sends SRS mapped to another PCI (designated as group PCI) for possible CoMP operations from RRH1, RRH2, RRH3, and macro eNB.

Fig. 10 shows another example of transmitting SRS using group PCI. The example shows a boundary case where the UE is served by an eNB (eNB0), but is located on the boundary between eNB0 and another macro eNB (eNB 1). In this example, RRH2 has the same PCI as eNB0, while RRH3 has the same PCI as eNB1 (e.g., as in scene 4). In this case, the UE may transmit the PCI of the neighboring node (PCI1) in addition to the UE's own PCI (PCI 0). The macro eNB0 may schedule UEs for transmitting SRS according to PCI0 as well as PCI 1. Macro eNB1 and eNB0 may transmit or receive jointly for a UE.

Multiplexing for different SRSs with separate powers

When the UE is configured for at least two SRS configurations, different SRSs may be multiplexed according to different techniques. For example, the UE may be configured to switch between the two SRS configurations using Time Division Multiplexing (TDM). This TDM approach has little or no impact on the peak-to-average ratio and therefore may be a preferred solution. Alternatively, the UE may be configured to: the two SRS configurations are transmitted via Frequency Division Multiplexing (FDM) with different cyclic shifts or different combs (comb), although this approach may increase the peak-to-average ratio if the two SRS configurations are transmitted in the same subframe.

For a TDM SRS transmission occasion, one SRS may be intended for (a transmission point of) a serving cell only. Other SRSs may be intended for joint reception of (transmission points of) multiple cells. According to certain aspects, two different power control schemes may be used for different SRS configurations.

For example, the first power control scheme may be referred to as power control scheme a (PC _ a) and may be used for SRS targeting multiple reception points (e.g., four transmission points as shown in fig. 9) or different reception points. The second power control scheme may be referred to as power control scheme B (PC _ B), and may be used for SRS targeted for a reception point in a single cell.

PC _ a may result in: the SRS targeted for multiple cells is transmitted with a higher power offset relative to the SRS targeted only for the serving transmission point. PC _ a may also enable outer loop power control and potentially separate Transmit Power Control (TPC) commands from those of the PUSCH and PUCCH that may be used (meaning that the transmit power for SRS need not be directly linked to those for PUSCH and PUCCH).

The PC _ B power control scheme targeting the service reception point or points (e.g., RRH2 in the example shown in fig. 9) may use a different power offset than the PC _ a power control scheme. In this case, the SRS may be transmitted with a different power offset, the outer power control loop may be disabled, and/or PC _ B may use a different outer loop than PC _ a and may use the same TPC as PUSCH with a fixed power offset.

The enhanced signaling impact described above is that the eNB needs to signal multiple SRS configurations to the UE the participating nodes need to exchange information for a common SRS configuration intended for D L CoMP or U L CoMP there may also be additional signaling to support multiple power control levels for different SRS configurations, or alternatively, incremental offsets between different SRS configurations.

The impact on UE transmission is: the UE will have multiple SRS transmissions with different configurations (time, frequency, offset, comb) and possibly different power offsets. The impact on eNB reception is: the eNB may receive SRS from the same UE with multiple configurations, and the eNB may run multiple power control loops for different SRS.

In alternative embodiments, the UE and/or eNB and RRH may use more than two SRS configurations.

Fig. 11 illustrates example operations 1100 performed by a User Equipment (UE), in accordance with aspects of the present disclosure. At 1102, operations 1100 begin with a UE transmitting a first Sounding Reference Signal (SRS) intended for one or more base stations currently serving the UE and associated with a first cell identifier. At 1104, the UE transmits a second SRS intended for joint reception by one or more base stations associated with a second cell identifier. At 1106, the UE adjusts transmit power of the first and second SRS with separate power control schemes.

Fig. 12 illustrates example operations 1200 performed by a Base Station (BS), in accordance with certain aspects of the present disclosure. At 1202, operations 1200 begin with a BS configuring a User Equipment (UE) to transmit a first Sounding Reference Signal (SRS) intended for one or more base stations currently serving the UE and associated with a first cell identifier. At 1204, the BS configures the UE to transmit a second SRS intended for another base station or base stations associated with a second cell identifier. At 1206, the BS transmits one or more Transmit Power Control (TPC) commands for the UE to adjust transmit power of the first and second SRS with separate power control schemes.

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

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

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

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software modules may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, 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 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. Generally, where there are operations illustrated in the figures, those operations may have corresponding functional module components with like reference numerals.

In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof if implemented in software, the functions may be stored on or transmitted over as one or more instructions or code in a computer readable medium including a computer storage medium and a communication medium including any medium that facilitates transfer of a computer program from one place to another.

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

Claims (38)

1. A method for wireless communications by a user equipment, UE, comprising:

transmitting a first sounding reference signal, SRS, intended for one or more first base stations currently serving the UE and associated with a first cell identifier;

transmitting a second SRS intended for joint reception by one or more second base stations associated with a second cell identifier and for the one or more second base stations; and

adjusting transmit powers of the first SRS and the second SRS with separate power control schemes based on one or more Transmit Power Control (TPC) commands, wherein the TPC commands for adjusting the first SRS are not associated with a physical uplink shared channel and a physical uplink control channel and the TPC commands for adjusting the second SRS are associated with a physical uplink shared channel.

2. The method of claim 1, wherein the UE is configured to: periodically transmitting at least one of the first SRS and the second SRS.

3. The method of claim 1, wherein the UE is configured to: transmitting at least one of the first SRS and the second SRS aperiodically.

4. The method of claim 1, wherein adjusting the transmit power of the first SRS and the second SRS with separate power control schemes comprises:

adjusting the first SRS with a first power control scheme; and

adjusting the second SRS with a second power control scheme, wherein the first power control scheme is such that the first SRS is transmitted at a different transmit power than the second SRS.

5. The method of claim 4, wherein the first power control scheme uses an outer power control loop with TPC commands from a base station.

6. The method of claim 5, wherein the second power control scheme does not use an outer power control loop.

7. The method of claim 5, wherein the TPC commands of the first power control scheme are different from TPC commands applied to other physical uplink channels.

8. The method of claim 1, wherein:

the second cell identifier includes: virtual cell identifiers associated with a plurality of base stations participating in a coordinated multipoint, CoMP, operation with the UE.

9. The method of claim 1, wherein the second cell identifier comprises: a cell identifier associated with a neighboring cell.

10. A method for wireless communications by a first base station, comprising:

configuring a user equipment, UE, to transmit a first sounding reference signal, SRS, the first SRS intended for one or more first base stations currently serving the UE and associated with a first cell identifier;

configuring the UE to transmit a second SRS intended for joint reception by one or more second base stations associated with a second cell identifier and for the one or more second base stations; and

transmitting one or more Transmit Power Control (TPC) commands for the UE to adjust transmit powers of the first and second SRSs with separate power control schemes, wherein the TPC commands for adjusting the first SRS are not associated with a physical uplink shared channel and a physical uplink control channel and the TPC commands for adjusting the second SRS are associated with a physical uplink shared channel.

11. The method of claim 10, wherein the UE is configured to: periodically transmitting at least one of the first SRS and the second SRS.

12. The method of claim 10, wherein the UE is configured to: transmitting at least one of the first SRS and the second SRS aperiodically.

13. The method of claim 10, wherein the one or more TPC commands comprise: TPC commands for use in an outer power control loop of the first power control scheme.

14. The method of claim 13, wherein the one or more TPC commands further comprise: additional TPC commands for use in an outer power control loop of the second power control scheme.

15. The method of claim 13, further comprising:

transmit TPC commands applied by the UE to adjust transmit power of one or more other physical uplink channels.

16. The method of claim 10, wherein:

the second cell identifier includes: virtual cell identifiers associated with a plurality of base stations participating in a coordinated multipoint, CoMP, operation with the UE.

17. The method of claim 10, wherein the second cell identifier comprises: a cell identifier associated with a neighboring cell.

18. An apparatus for wireless communications by a User Equipment (UE), comprising:

means for transmitting a first sounding reference signal, SRS, intended for one or more first base stations currently serving the UE and associated with a first cell identifier;

means for transmitting a second SRS intended for joint reception by one or more second base stations associated with a second cell identifier and for the one or more second base stations; and

means for adjusting transmit powers of the first and second SRSs with separate power control schemes based on one or more Transmit Power Control (TPC) commands, wherein the TPC commands for adjusting the first SRS are not associated with a physical uplink shared channel and a physical uplink control channel and the TPC commands for adjusting the second SRS are associated with a physical uplink shared channel.

19. The apparatus of claim 18, wherein the UE is configured to: periodically transmitting at least one of the first SRS and the second SRS.

20. The apparatus of claim 18, wherein the UE is configured to: transmitting at least one of the first SRS and the second SRS aperiodically.

21. The apparatus of claim 18, wherein adjusting the transmit power of the first and second SRS with separate power control schemes comprises:

adjusting the first SRS with a first power control scheme; and

adjusting the second SRS with a second power control scheme; wherein the first power control scheme is such that the first SRS is transmitted at a different transmit power than the second SRS.

22. The apparatus of claim 21, wherein the first power control scheme uses an outer power control loop with TPC commands from a base station.

23. The apparatus of claim 22, wherein the second power control scheme does not use an outer power control loop.

24. The apparatus of claim 22, wherein the TPC commands of the first power control scheme are different from TPC commands applied to other physical uplink channels.

25. The apparatus of claim 18, wherein,

the second cell identifier includes: virtual cell identifiers associated with a plurality of base stations participating in a coordinated multipoint, CoMP, operation with the UE.

26. The apparatus of claim 18, wherein the second cell identifier comprises: a cell identifier associated with a neighboring cell.

27. An apparatus for wireless communications by a first base station, comprising:

means for configuring a user equipment, UE, to transmit a first sounding reference signal, SRS, intended for one or more first base stations currently serving the UE and associated with a first cell identifier;

means for configuring the UE to transmit a second SRS intended for joint reception by one or more second base stations associated with a second cell identifier and for the one or more second base stations; and

means for transmitting one or more Transmit Power Control (TPC) commands for the UE to adjust transmit powers of the first and second SRSs with separate power control schemes, wherein the TPC commands for adjusting the first SRS are not associated with a physical uplink shared channel and a physical uplink control channel and the TPC commands for adjusting the second SRS are associated with a physical uplink shared channel.

28. The apparatus of claim 27, wherein the UE is configured to: periodically transmitting at least one of the first SRS and the second SRS.

29. The apparatus of claim 27, wherein the UE is configured to: transmitting at least one of the first SRS and the second SRS aperiodically.

30. The apparatus of claim 27, wherein the one or more TPC commands comprise: TPC commands for use in an outer power control loop of the first power control scheme.

31. The apparatus of claim 30, wherein the one or more TPC commands further comprise: additional TPC commands for use in an outer power control loop of the second power control scheme.

32. The apparatus of claim 30, further comprising:

means for transmitting TPC commands applied by the UE to adjust transmit power of one or more other physical uplink channels.

33. The apparatus of claim 27, wherein,

the second cell identifier includes: virtual cell identifiers associated with a plurality of base stations participating in a coordinated multipoint, CoMP, operation with the UE.

34. The apparatus of claim 27, wherein the second cell identifier comprises: a cell identifier associated with a neighboring cell.

35. An apparatus for wireless communications by a User Equipment (UE), comprising:

at least one processor configured to: transmitting a first sounding reference signal, SRS, the first SRS intended to transmit a second SRS, for one or more first base stations currently serving the UE and associated with a first cell identifier, for joint reception by one or more second base stations associated with a second cell identifier and by the one or more second base stations, and adjusting transmit powers of the first SRS and the second SRS with separate power control schemes based on one or more transmit power control, TPC, commands; and

a memory coupled with the at least one processor,

wherein the TPC commands for adjusting the first SRS are not associated with a physical uplink shared channel and a physical uplink control channel, and the TPC commands for adjusting the second SRS are associated with a physical uplink shared channel.

36. An apparatus for wireless communications by a first base station, comprising:

at least one processor configured to: configuring a user equipment, UE, to transmit a first sounding reference signal, SRS, the first SRS intended for joint reception by one or more first base stations currently serving the UE and associated with a first cell identifier, configuring the UE to transmit a second SRS intended for joint reception by one or more second base stations associated with a second cell identifier and by the one or more second base stations, and transmitting one or more transmit power control, TPC, commands for the UE to adjust transmit powers of the first and second SRSs with separate power control schemes; and

a memory coupled with the at least one processor,

wherein the TPC commands for adjusting the first SRS are not associated with a physical uplink shared channel and a physical uplink control channel, and the TPC commands for adjusting the second SRS are associated with a physical uplink shared channel.

37. A computer-readable medium having instructions stored thereon, the instructions executable by one or more processors for:

transmitting a first sounding reference signal, SRS, intended for one or more first base stations currently serving UEs and associated with a first cell identifier;

transmitting a second SRS intended for joint reception by one or more second base stations associated with a second cell identifier and for the one or more second base stations; and

adjusting transmit powers of the first SRS and the second SRS with separate power control schemes based on one or more Transmit Power Control (TPC) commands, wherein the TPC commands for adjusting the first SRS are not associated with a physical uplink shared channel and a physical uplink control channel and the TPC commands for adjusting the second SRS are associated with a physical uplink shared channel.

38. A computer-readable medium having instructions stored thereon, the instructions executable by one or more processors for:

configuring a user equipment, UE, to transmit a first sounding reference signal, SRS, the first SRS intended for one or more first base stations currently serving the UE and associated with a first cell identifier;

configuring the UE to transmit a second SRS intended for joint reception by one or more second base stations associated with a second cell identifier and for the one or more second base stations; and

transmitting one or more Transmit Power Control (TPC) commands for the UE to adjust transmit powers of the first and second SRSs with separate power control schemes, wherein the TPC commands for adjusting the first SRS are not associated with a physical uplink shared channel and a physical uplink control channel and the TPC commands for adjusting the second SRS are associated with a physical uplink shared channel.

Images