CN111432463B - 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 application number 201280056765.6, entitled "SRS optimization for coordinated multipoint transmission and reception", having application date of 2012, 10/6.

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 OPTIMIZATION FOR COORDINATED MULTI-POINT TRANSMISSION AND RECEPTION," filed on 3.10.2011, which is assigned to the assignee of the present application and is hereby expressly incorporated by reference herein.

Technical Field

Certain aspects of the present disclosure generally relate to wireless communications, and more particularly, 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). The UE may communicate with the 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.

The base station may transmit data and control information to the UE on the downlink and/or may receive data and control information from the 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. The interference may degrade performance on both the downlink and uplink.

Disclosure of Invention

Certain aspects of the present disclosure provide methods for wireless communication by a User Equipment (UE). The method generally comprises: a method includes 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 power of the first SRS and the second SRS with separate power control schemes.

Certain aspects of the present disclosure provide methods for wireless communication by a Base Station (BS). The method generally comprises: 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 SRS and the second SRS using separate power control schemes.

Certain aspects of the present disclosure provide apparatus for wireless communication by a User Equipment (UE). The device generally comprises: at least one processor configured 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, transmit a second SRS intended for one or more second base stations associated with a second cell identifier, and adjust transmit power of the first SRS and the second SRS with separate power control schemes; and a memory coupled to 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 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 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 SRS and the second SRS with separate power control schemes; and a memory coupled to 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 power 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 to configure 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, configure the UE to transmit a second SRS intended for one or more second base stations associated with a second cell identifier, and transmit one or more Transmit Power Control (TPC) commands for the UE to adjust transmit powers of the first SRS and the 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 an uplink in Long Term Evolution (LTE) in accordance with certain aspects of the present disclosure.

Fig. 3 illustrates a block diagram conceptually illustrating 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 an example partitioning of resources 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, according to 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 a Remote Radio Head (RRH) in accordance with certain aspects of the present disclosure.

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

Fig. 10 is a diagram illustrating another example Sounding Reference Signal (SRS) enhancement according to aspects of the present disclosure.

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

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

Detailed Description

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

The techniques described herein may 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 wireless technologies such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variations 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, for example, evolved UTRA (E-UTRA), ultra Mobile Broadband (UMB), IEEE802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20,Etc. UTRA and E-UTRA are components of Universal Mobile Telecommunications System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-advanced (LTE-A) are new versions of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-a and GSM are described in documents from an organization named "third generation partnership project" (3 GPP). CDMA2000 and UMB are described in documents from an organization named "third generation partnership project 2" (3 GPP 2). The techniques described herein may be used for the wireless networks and wireless technologies mentioned above as well as other wireless networks and wireless technologies. For clarity, certain aspects of the technology are described below with respect to LTE, and LTE terminology is used in many of the descriptions below.

Example Wireless network

Fig. 1 illustrates a wireless communication network 100, which may be an LTE 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 a user equipment device (UE), and may also be referred to as a base station, a node B, an access point, etc. Each eNB 110 may 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 the coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macrocell, a picocell, a femtocell, and/or other type 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. The 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 residence) and may allow limited access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group, UEs of users in a residence, 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., pico base station). An eNB for a femto cell may be referred to as a femto eNB (i.e., 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. eNB 110x may be a pico eNB for pico cell 102 x. enbs 110y and 110z may be femto enbs for femto cells 102y and 102z, respectively. An eNB may support one or more (e.g., three) cells.

The 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). The 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 eNB 110a and UE 120r to facilitate communications between eNB 110a and UE 120 r. A relay station may also be referred to as a relay eNB, a relay, etc.

Wireless network 100 can be a heterogeneous network (HetNet) that includes different types of enbs (e.g., macro eNB, pico eNB, femto eNB, repeater, etc.). These different types of enbs may have different transmit power levels, different coverage areas, and different impact on interference in the 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).

The wireless network 100 may support synchronous operation 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 operation.

The network controller 130 may be coupled to a set of enbs and provide coordination and control for these enbs. The network controller 130 may communicate with the enbs 110 via a backhaul. enbs 110 may also communicate with each other, such as directly or indirectly via a wireless or wired backhaul.

UEs 120 may be dispersed throughout wireless network 100 and each UE may be fixed or mobile. A UE may also be called a terminal, mobile station, subscriber unit, station, etc. The UE may be a cellular telephone, a Personal Digital Assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless telephone, a Wireless Local Loop (WLL) station, a tablet computer, etc. The UE may be capable of communicating with macro enbs, pico enbs, femto enbs, relays, etc. In fig. 1, the solid lines with double arrows represent the desired transmissions between the UE and the serving eNB designated as serving eNB for the UE on the downlink and/or uplink. The dashed lines with double arrows represent the transmission of interference between the UE and the eNB. For certain aspects, the UE may comprise an LTE release 10UE.

LTE 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 a plurality (K) of orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. Typically, the modulation symbols are transmitted in the frequency domain using OFDM and in the time domain using SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may depend on the system bandwidth. For example, K may be equal to 128, 256, 512, 1024 or 2048 for a system bandwidth of 1.25, 2.5, 5, 10 or 20 megahertz (MHz), respectively. The system bandwidth may also be divided into sub-bands. For example, a subband may cover 1.08MHz, and there may be 1,2, 4, 8, or 16 subbands for a system bandwidth of 1.25, 2.5, 5, 10, or 20MHz, respectively.

Fig. 2 shows a frame structure used in LTE. The transmission time axis for the downlink may be divided into a plurality of units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)), and may be divided into 10 subframes having indexes of 0 to 9. Each subframe may include two slots. Thus, 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. An index of 0 to 2L-1 may be allocated to 2L symbol periods in each subframe. The available time-frequency resources may be divided into resource blocks. Each resource block may cover N subcarriers (e.g., 12 subcarriers) in one slot.

In LTE, an 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 having a normal cyclic prefix, a primary synchronization signal and a secondary synchronization signal may be transmitted in symbol periods 6 and 5, respectively. The synchronization signal may be used by the UE for cell detection and acquisition. The eNB may transmit a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carry certain system information.

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 transmit 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 about resource allocation for the UE and control information for a downlink channel. The eNB may transmit a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. PDSCH may carry data for UEs scheduled for data transmission on the downlink. The title "Evolved Universal Terrestrial Radio Access (E-UTRA) is available to the public; various signals and channels in LTE are described in 3gpp TS 36.211 for PHYSICAL CHANNELS AND Modulation (evolved universal terrestrial radio access; physical channel and Modulation).

The eNB may transmit 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 send PDCCH to the UE group in some portion of the system bandwidth. The eNB may transmit 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, 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 a real or complex value. The resource elements in each symbol period that are not used for the reference signal 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 in symbol period 0 that are approximately equally spaced across frequency. The PHICH may occupy three REGs spread across frequency in one or more configurable symbol periods. For example, three REGs for PHICH may all belong to symbol period 0 or may be interspersed 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 searched combinations 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 shows an exemplary format 200A for the uplink in LTE. The available resource blocks for the uplink may be divided into a data part and a control part. 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 UEs for transmission of control information. The data portion may include all resource blocks not included in the control portion. The design in fig. 2A results in the data portion including contiguous subcarriers, which may allow all contiguous subcarriers in the data portion to be allocated to a single UE.

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 UEs to transmit data to the eNB. The UE may transmit 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 span both slots of a subframe and may hop across frequency.

The UE may be within the 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 in which the UE may observe high interference from one or more interfering enbs. A dominant interference scenario may occur due to limited associations. 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 (shown in fig. 1) with lower received power or to femto eNB110 z (not shown in fig. 1) also with 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 significant interference scenario, which is a scenario in which a UE connects to an eNB having lower path loss and lower SNR among all enbs detected by the UE, may also occur due to range extension. For example, in fig. 1, UE 120x may detect macro eNB 110b and pico eNB 110x and may have a lower received power for eNB 110x (lower than the received power for eNB 110 b). However, if the path loss for eNB 110x is lower than the path loss for macro eNB 110b, UE 120x may desire to connect to pico eNB 110x. This may result in less interference to the wireless network for a given data rate for UE 120 x.

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

Fig. 3 is a block diagram of a design of a base station or eNB 110 and a UE 120, where the base station or eNB 110 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 a restricted association scenario, eNB 110 may be macro eNB 110c in fig. 1 and UE 120 may be UE 120y. The eNB 110 may also be some other type of base station. eNB 110 may be equipped with T antennas 334a through 334T, and UE 120 may be equipped with R antennas 352a through 352R, where typically T is.

At eNB 110, transmit processor 320 may receive data from data source 312 and control information from controller/processor 340. The control information may be for PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for PDSCH or the like. The transmit processor 320 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The 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 the downlink signals from eNB 110 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. 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 PUSCH) and control information from a controller/processor 380 (e.g., for PUCCH). The 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 eNB 110, 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. The receive processor 338 may provide the decoded data to a data sink 339 and the decoded control information to the controller/processor 340.

Controllers/processors 340 and 380 may direct the operation at eNB 110 and UE 120, respectively. The controller/processor 340, receive processor 338, and/or other processors and modules located at the eNB 110 may perform or direct operations and/or processes for the techniques described herein. Memories 342 and 382 may store data and program codes for eNB 110 and UE 120, respectively. The scheduler 344 may schedule UEs for data transmission on the downlink and/or uplink.

Example resource partitioning

In accordance with certain aspects of the present disclosure, when the network supports enhanced inter-cell interference coordination (eICIC), the base stations may negotiate with each other to coordinate resources so that interference is reduced or eliminated 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 with a closed access mode in the coverage area of an open macro cell (i.e., where 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 relinquish resources, macro UEs in the femto cell coverage area can still use these relinquished resources to access the UE's serving macro cell.

In wireless access systems using OFDM, such as the 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 the coordinated resource partitioning is frequency-based, the interfering cell may yield subcarriers in the frequency domain. In 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 an eICIC may allow a eICICC-capable macro UE 120y (e.g., a release 10 macro UE as shown in fig. 4) to access macro cell 110c (as shown by uninterrupted wireless link 402) even when macro UE 120y is experiencing severe interference from femto cell y. Legacy macro UE 120u (e.g., release 8 macro UE as shown in fig. 4) cannot access macro cell 110c (as shown by broken wireless link 404) in the event of severe interference from femto cell 110y. Femto UE 120v (e.g., 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, the network may support eICIC, where there may be different sets of partitioning information. A first of these sets may be referred to as semi-Static Resource Partitioning Information (SRPI). A second of these sets may be referred to as Adaptive Resource Partitioning Information (ARPI). As the name implies, SRPI typically does not change frequently, and SRPI may be sent to the UE so that the UE may use the resource partitioning information for its own operation.

By way of example, the resource partitioning 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, such that frequency resources may also be partitioned. For communication via the downlink (e.g., from the cell node B to the UE), the partitioning pattern may be mapped to a known subframe (e.g., a 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 a mapping may be applied in order to determine Resource Partitioning Information (RPI) for a particular subframe. For example, subframes subjected to coordinated resource partitioning (e.g., yielded by the interfering cell) for the downlink may be identified by the following index:

index srpi_dl= (SFN x 10+ subframe number) mod 8

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

Index srpi_dl= (SFN x 10+ subframe number + 4) mod 8

SRPI may use the following three values for each entry:

U (use): the value indicates that a 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): this value indicates that the subframe is not to be used; and

X (not known): the value indicates that the subframe is not statically partitioned. The details of the 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 a 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): this value indicates that the subframe is not to be used;

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

C (public): 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 E-UTRAN, the SRPI of the serving cell may be transmitted in a Master Information Block (MIB), or one of System Information Blocks (SIB). The predefined SRPI may be defined based on characteristics of the cell, such as a macrocell, a picocell (with open access), and a femtocell (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 neighbor cell in one of the SIBs. To this end, the SRPI may be transmitted in a corresponding range of SRPIs of a Physical Cell Identifier (PCI).

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' subframes is typically known only to the base station, which is not known to the UE.

Fig. 5 and 6 show examples of SRPI allocation in a scenario with a macrocell and a femtocell. U, N, X or C subframes are subframes corresponding to U, N, X or C SRPI allocations.

Fig. 7 is a schematic diagram 700 illustrating a range-expanded cellular region in a heterogeneous network. An eNB of 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. RRH 710b receives information about the interference situation of UE 720 from macro eNB 710a in enhanced inter-cell interference coordination. This information allows RRH 710b to serve UE 720 in range-extended cellular region 703 and to accept handover of UE 720 from macro eNB 710a when UE 720 enters range-extended 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 certain aspects, the network 800 may be a homogeneous network or a heterogeneous network, and the RRHs 804-810 may be low power or high power RRHs. In one aspect, the macro node 802 handles all scheduling within a cell for itself and RRHs. The RRH can be configured to have the same cell Identifier (ID) as the macro node 802 or to have a different cell ID. The macro node 802 and the RRH may operate basically as one cell controlled by the macro node 802 if the RRH are configured to have the same cell ID. On the other hand, if the RRH and macro node 802 are configured with different cell IDs, then the macro node 802 and RRH 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 RRHs 804, 806, 808, 810 may not necessarily be at the macro node. This may also be performed in a centralized manner at some other network device or entity connected to the macro and RRH.

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

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

In certain aspects, when all transmission points are configured to have the same cell ID and CRS is transmitted from all transmission points, proper antenna virtualization is required if there are an unequal number of physical antennas at the transmitting macro node and/or RRH. That is, CRSs are 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 can be configured to transmit using two CRS ports, and a second antenna of RRH 810 can be configured to transmit using two different CRS ports. Or for the same deployment, the macro 802 and RRHs 804, 806, 808 may send only two CRS antenna ports from two transmit antennas selected from 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, macro node 802 and RRHs 804-810 may both transmit CRS when all transmission points are configured to have the same cell ID. However, if only macro node 802 transmits CRS, an interruption may occur near the RRH due to Automatic Gain Control (AGC) problems. In such a scenario, CRS based transmissions from macro 802 may be received at low received power, while other transmissions from nearby RRHs may be received at much higher power. Such power imbalance can lead to the AGC problems described previously.

In general, the differences between the same/different cell ID setups relate to control and carryover issues, as well as other potential CRS-dependent operations. A scenario with different cell IDs but with conflicting CRS configurations may establish a similarity with the same cell ID by defining CRSs with conflicts. Compared to the same cell ID case, a scenario with different cell IDs and with conflicting CRSs generally has the following advantages: system characteristics/components that depend on a cell ID (e.g., scrambling sequence, etc.) can be more easily distinguished.

The exemplary configuration may be applicable to macro/RRH establishment with the same or different cell IDs. In case of different cell IDs, CRSs may be configured to collide, which may lead to a similar situation as the same cell ID, but with the following advantages: the UE may more easily distinguish system characteristics (e.g., scrambling sequences, etc.) that depend on the cell ID.

In certain aspects, an exemplary macro/RRH entity can provide separation of control/data transmissions within a transmission point established by the macro/RRH. When the cell IDs for each transmission point are the same, PDCCH may be transmitted with CRS from macro node 802, or both macro node 802 and RRHs 804-810, while PDSCH may be transmitted with channel state information reference signals (CSI-RS) and demodulation reference signals (DM-RS) from a subset of transmission points. When cell IDs of some of the transmission points are different, a PDCCH may be transmitted with 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 transmitting control based on CRS transmissions from all transmission points. This enables the cell to split across different transmission points for data transmission while keeping the control channels 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 a handover. The 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 the antenna ports of the UE to correspond to physical antennas of different transmission points.

In certain aspects, the UE-specific reference signals enable this operation (e.g., in LTE-A, rel-10 and above background). CSI-RS and DM-RS are reference signals used in the context of LTE-a. The interference estimation may be performed based on or facilitated by CSI-RS muting. When the control channel is common to all transmission points in the case of the same cell ID establishment, there may be a capacity problem because the capacity of the PDCCH may be limited. The control capacity may be extended by using FDM control channels. The relay PDCCH (R-PDCCH) or an extension thereof, such as enhanced PDCCH (ePDCCH), may be used in addition to, or in place of the PDCCH control channel.

SRS problem in CoMP scenarios

In CoMP design, one challenging part is to identify and group (into UL and/or DL CoMP sets) transmission points involved in CoMP operations with minimal overhead. The SRS channel is mainly used for UL channel sounding. In the context of CoMP, SRS is often used to identify the cell closest to the UE. The current LTE SRS channel in release 8-10 was designed without much consideration of CoMP operation. As a result, existing CoMP designs may result in size limitations or design complexity for various CoMP scenarios.

Aspects of the present disclosure provide techniques that may enhance a Sounding Reference Signal (SRS) procedure 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 SRS signal sets are transmitted. For example, the first SRS set may be intended for only the serving cell, while the second SRS set may be intended for joint reception for multiple cells.

A Sounding Reference Signal (SRS) is transmitted by the UE on the uplink and allows the receiving node to estimate the quality of the channel at different frequencies. In CoMP systems, SRS may allow a receiving node to determine the nearest transmission point and, for example, dynamically switch the transmission point of a serving 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., a 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 the particular UE. The measurements cannot be obtained with Demodulation Reference Signals (DRSs) 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 the DRS associated with the physical uplink control channel and the shared channel, the 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 estimate is used to schedule uplink transmissions on resource blocks of good quality.

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

The pico eNB may have its own Physical Cell Identity (PCI) or cell ID with an X2 connection with the macro eNB. The pico eNB has its own scheduler operation and may be linked to multiple macro enbs. The RRH may or may not have the same PCI as the macro eNB and have a fiber connection with the macro eNB, providing a better backhaul. For RRHs, the scheduler operations may be performed only on the macro eNB side. Femto enbs may have limited associations and are not considered much in CoMP schemes.

The SRS techniques presented herein may be applied to a number of different Downlink (DL) CoMP scenarios. For example, in a first scenario (scenario 1), there may be a homogeneous deployment with intra-site CoMP. In a second scenario (scenario 2), there may be a homogeneous deployment with high power RRHs connected by fiber.

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 macro and pico enbs. In this scenario, cell splitting gain can be easily achieved by scheduling different users to different RRHs, however, DL CoMP transmission based on CSI-RS or CRS requires enhanced feedback from the UE.

In the 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 the PBCH, while in another case, both the macro eNB and RRH may transmit CRS, PSS, SSS and the 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 obtained but cell split gain cannot be obtained. The SRS channel may be used to identify the nearest RRH and based thereon, cell splitting may be performed by transmitting only from nearby RRHs to the UE.

In scenario 3, where each RRH has a different PCI, the SRS channel from each RRH will have a different configuration, sequence, etc. For DL CoMP and Uplink (UL) CoMP, each RRH will need to attempt SRS transmitted from other RRHs. Or in scenario 4, in case the RRHs have the same PCI, all RRHs will attempt to decode the SRS transmission of the same UE. Depending on the received signal strength, DL and UL CoMP sets may be formed. However, a design difficulty is in the dimension of the SRS channel, i.e., more UEs may stress the limits of the SRS channel.

As noted above, aspects of the present disclosure provide methods that may enhance a Sounding Reference Signal (SRS) procedure 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 SRS signal sets are transmitted. For example, the first SRS set may be intended for only the serving cell, while the second SRS set may be intended for joint reception for multiple cells.

For example, one possible enhancement for scene 3 is: one eNB (macro eNB, RRH, pico eNB, femto eNB, etc.) allocates SRS transmission using a PCI different from itself. The PCI may be a virtual or group PCI that may be signaled or exchanged between all participating nodes over an optical fiber or X2 connection. All nodes that can receive the SRS can participate in DL or UL CoMP with the UE. For non-CoMP operation, all of these nodes may receive SRS belonging to their own PCI. Further, for DL or UL CoMP operations, each node may receive SRS belonging to virtual or group PCIs.

Fig. 9 shows an example of transmitting SRS using group PCI. In an example, the UE is served by RRH2 for non-CoMP operation. Thus, the UE transmits the first SRS using the PCI of RRH 2. However, the UE also transmits 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 eNB (eNB 0), 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 scenario 4). In this case, the UE may transmit the PCI (PCI 1) of the neighboring node in addition to the UE's own PCI (PCI 0). Macro eNB0 may schedule UEs for transmitting SRS according to PCI0 and PCI 1. Macro eNB1 and eNB0 may jointly transmit or receive for a UE.

Multiplexing for different SRS with separate power

When the UE is configured for at least two SRS configurations, different SRS may be multiplexed according to different technologies. 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 effect on the peak-to-average ratio and therefore may be a preferred solution. Or 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 the method may increase the peak-to-average ratio if the two SRS configurations are transmitted in the same subframe.

For TDM SRS transmission opportunities, one SRS may be intended for (the transmission point of) only the serving cell. Other SRS may be intended for joint reception for (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 a 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 targeting a reception point in a single cell.

Pc_a may result in: SRS targeting multiple cells is transmitted with a higher power offset than SRS targeting only the serving transmission point. Pc_a may also enable outer loop power control and potentially separate Transmit Power Control (TPC) commands from the transmit power control commands for PUSCH and PUCCH that may be used (meaning that transmit power for SRS does not need to be directly linked to transmit power commands 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, 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 the same TPC as PUSCH with a fixed power offset may be used.

The enhanced signaling impact described above is: 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 DL CoMP or UL 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 effect on UE transmissions is: the UE will have multiple SRS transmissions with different configurations (time, frequency, offset, comb) and possibly different power offsets. The effect on eNB reception is: the eNB may utilize a variety of configurations to receive SRS from the same UE, and the eNB may run multiple power control loops for different SRS.

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

Fig. 11 illustrates example operations 1100 performed by a User Equipment (UE) in accordance with aspects of the disclosure. At 1102, operation 1100 begins 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 for a base station or base stations associated with a second cell identifier. At 1106, the UE adjusts the transmit power of the first and second SRS using separate power control schemes.

Fig. 12 illustrates example operations 1200 performed by a Base Station (BS) in accordance with certain aspects of the disclosure. At 1202, operation 1200 begins 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 the second cell identifier. At 1206, the BS transmits one or more Transmit Power Control (TPC) commands for the UE to adjust the transmit power of the first and second SRS using 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 be located 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 shown in the figures, those operations may have corresponding functional module elements 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 on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. Storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general purpose or special purpose computer or general purpose or special purpose processor. Further, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes Compact Disc (CD), laser disc, optical disc, digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

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 communication by a user equipment, UE, comprising:

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

Transmitting a second sounding reference signal intended for one or more second base stations associated with a second cell identifier and joint reception for the one or more second base stations; and

The transmit powers of the first and second sounding reference signals are adjusted using separate power control schemes based on one or more transmit power control TPC commands, wherein TPC commands for adjusting the first sounding reference signal are not associated with a physical uplink shared channel and a physical uplink control channel, TPC commands for adjusting the second sounding reference signal are associated with a physical uplink shared channel.

2. The method of claim 1, wherein the UE is configured to: at least one of the first sounding reference signal and the second sounding reference signal is periodically transmitted.

3. The method of claim 1, wherein the UE is configured to: at least one of the first sounding reference signal and the second sounding reference signal is transmitted aperiodically.

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

Adjusting the first sounding reference signal using a first power control scheme; and

The second sounding reference signal is adjusted with a second power control scheme, wherein the first power control scheme causes the first sounding reference signal to be transmitted at a different transmit power than the second sounding reference signal.

5. The method of claim 4, wherein the first power control scheme uses an external 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 external 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 according to claim 1, wherein:

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

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

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

Configuring a user equipment, UE, to transmit a first sounding reference signal 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 sounding reference signal intended for one or more second base stations associated with a second cell identifier and joint reception for the one or more second base stations; and

One or more transmit power control, TPC, commands for the UE are sent to adjust transmit powers of the first and second sounding reference signals using separate power control schemes, wherein TPC commands for adjusting the first sounding reference signal are not associated with a physical uplink shared channel and a physical uplink control channel, TPC commands for adjusting the second sounding reference signal are associated with a physical uplink shared channel.

11. The method of claim 10, wherein the UE is configured to: at least one of the first sounding reference signal and the second sounding reference signal is periodically transmitted.

12. The method of claim 10, wherein the UE is configured to: at least one of the first sounding reference signal and the second sounding reference signal is transmitted 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 include: additional TPC commands for use in the outer power control loop of the second power control scheme.

15. The method of claim 13, further comprising:

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

16. The method according to claim 10, wherein:

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

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

18. An apparatus for wireless communication by a user equipment, UE, comprising:

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

Means for transmitting a second sounding reference signal intended for joint reception by and for one or more second base stations associated with a second cell identifier; and

Means for adjusting transmit powers of the first and second sounding reference signals using separate power control schemes based on one or more transmit power control TPC commands, wherein TPC commands for adjusting the first sounding reference signal are not associated with a physical uplink shared channel and a physical uplink control channel, TPC commands for adjusting the second sounding reference signal are associated with a physical uplink shared channel.

19. The apparatus of claim 18, wherein the UE is configured to: at least one of the first sounding reference signal and the second sounding reference signal is periodically transmitted.

20. The apparatus of claim 18, wherein the UE is configured to: at least one of the first sounding reference signal and the second sounding reference signal is transmitted aperiodically.

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

Adjusting the first sounding reference signal using a first power control scheme; and

Adjusting the second sounding reference signal using a second power control scheme; wherein the first power control scheme causes the first sounding reference signal to be transmitted at a different transmit power than the second sounding reference signal.

22. The apparatus of claim 21, wherein the first power control scheme uses an external 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 external power control loop.

24. The apparatus of claim 22, wherein the TPC commands for 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 coordinated multipoint CoMP operations with the UE.

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

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

means for configuring a user equipment, UE, to transmit a first sounding reference signal 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 sounding reference signal intended for joint reception by and for one or more second base stations associated with a second cell identifier; and

Means for transmitting one or more transmit power control, TPC, commands for the UE to adjust transmit powers of the first and second sounding reference signals using separate power control schemes, wherein the TPC commands for adjusting the first sounding reference signal are not associated with a physical uplink shared channel and a physical uplink control channel and the TPC commands for adjusting the second sounding reference signal are associated with a physical uplink shared channel.

28. The apparatus of claim 27, wherein the UE is configured to: at least one of the first sounding reference signal and the second sounding reference signal is periodically transmitted.

29. The apparatus of claim 27, wherein the UE is configured to: at least one of the first sounding reference signal and the second sounding reference signal is transmitted 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 the outer power control loop of the second power control scheme.

32. The apparatus of claim 30, further comprising:

the apparatus includes 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 coordinated multipoint CoMP operations with the UE.

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

35. An apparatus for wireless communication by a user equipment, UE, comprising:

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

A memory coupled to the at least one processor,

Wherein TPC commands for adjusting the first sounding reference signal are not associated with a physical uplink shared channel and a physical uplink control channel, and TPC commands for adjusting the second sounding reference signal are associated with a physical uplink shared channel.

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

at least one processor configured to: configuring a user equipment, UE, to transmit a first sounding reference signal 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 sounding reference signal intended for joint reception for 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 sounding reference signals with separate power control schemes; and

A memory coupled to the at least one processor,

Wherein TPC commands for adjusting the first sounding reference signal are not associated with a physical uplink shared channel and a physical uplink control channel, and TPC commands for adjusting the second sounding reference signal are associated with a physical uplink shared channel.

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

Transmitting a first sounding reference signal intended for a currently serving UE and associated with one or more first base stations of a first cell identifier;

Transmitting a second sounding reference signal intended for one or more second base stations associated with a second cell identifier and joint reception for the one or more second base stations; and

The transmit powers of the first and second sounding reference signals are adjusted using separate power control schemes based on one or more transmit power control TPC commands, wherein TPC commands for adjusting the first sounding reference signal are not associated with a physical uplink shared channel and a physical uplink control channel, TPC commands for adjusting the second sounding reference signal are associated with a physical uplink shared channel.

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

Configuring a user equipment, UE, to transmit a first sounding reference signal 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 sounding reference signal intended for one or more second base stations associated with a second cell identifier and joint reception for the one or more second base stations; and

One or more transmit power control, TPC, commands for the UE are sent to adjust transmit powers of the first and second sounding reference signals using separate power control schemes, wherein TPC commands for adjusting the first sounding reference signal are not associated with a physical uplink shared channel and a physical uplink control channel, TPC commands for adjusting the second sounding reference signal are associated with a physical uplink shared channel.