Power control for devices having multiple antennas

Power control for devices having multiple transmit antennas are disclosed, including power control methods for Physical Uplink Control Channel (PUCCH) and Sounding Reference Signal (SRS) transmissions for a wireless transmit/receive unit (WTRU). The PUCCH and SRS power control methods include selecting a multiple input multiple output (MIMO) mode and changing the power of the PUCCH or SRS transmission based on the selected MIMO mode. Another power control method estimates an antenna gain imbalance (AGI) for a WTRU having at least two transmit antennas. The AGI is based on measuring a Reference Signal Received Power (RSRP) on each transmit antenna. Each transmit antenna is then scaled by an AGI scaling factor based on the estimated AGI.

FIELD OF THE INVENTION

This application is related to wireless communications.

BACKGROUND

In Third Generation Partnership Project (3GPP) long term evolution (LTE) Release 8 (R8) uplink (UL), wireless transmit/receive units (WTRUs) may transmit their data (and sometimes their control information) on the physical uplink shared channel (PUSCH). The evolved Node B (eNB) may schedule and control PUSCH transmission from each WTRU using an UL scheduling grant, which may be carried on a physical downlink control channel (PDCCH) format 0. As part of the uplink scheduling grant, the WTRU may receive control information on the modulation and coding set (MCS), the transmit power control (TPC) command, uplink resource allocation (e.g., the indices of allocated resource blocks), and the like. The WTRU may then transmit its PUSCH on the allocated UL resources using the corresponding MCS at a transmit power set by the TPC command.

The UL may also need to signal certain control signaling such as, but not limited to, acknowledgement/negative acknowledgement (ACK/NACK), Channel Quality Indicator (CQI), scheduling request (SR), and sounding reference signal (SRS) to support transmission of downlink (DL) and UL transport channels. If the WTRU has not been assigned an UL resource for data transmission, e.g., PUSCH, then the control information may be transmitted in an UL resource specially assigned for UL control signals on the PUCCH. These resources may be located at the edges of the total available cell bandwidth (BW). The transmit power for PUCCH may be controlled to ensure that the PUCCH is received at the cell site at an appropriate power.

In LTE R8, PUSCH and PUCCH transmissions of a given WTRU are scheduled to occur at different times. LTE-Advanced (LTE-A) may support simultaneous transmissions of PUSCH and PUCCH. Additionally, the LTE-A UL may support multiple transmit antennas (e.g., up to 4 antennas) with a possible maximum of two code words (transport blocks) for data transmission per UL component carrier. Multiple transmit antennas may be used for PUCCH and SRS transmissions, respectively. An antenna gain imbalance (AGI) may occur when using multiple antenna transmissions in the UL.

SUMMARY

Power control methods for devices using multiple transmit antennas for transmission in the uplink (UL) are disclosed herein. Methods include changing the power of a physical uplink control channel (PUCCH) transmission to a new level, the new level depending at least in part on a multiple input multiple output (MIMO) mode (a transmission mode configuration). Another method describes changing the power of sounding reference signal (SRS) transmission to a new level, the new level depending at least in part on a selected MIMO mode (or a transmission mode configuration). A method is provided to estimate an antenna gain imbalance (AGI) for transmit antennas based on measured Reference Signal Received Power (RSRPs) and each transmit antenna is scaled by an AGI scaling factor that is based on the estimated AGIs. The estimated AGIs may be expressed in terms of scaled relative AGIs with regard to a reference transmit antenna.

DETAILED DESCRIPTION

FIG. 1Cis a system diagram of the RAN104and the core network106according to an embodiment. As noted above, the RAN104may employ an E-UTRA radio technology to communicate with the WTRUs102a,102b,102cover the air interface116. Though WTRUs102a,102b, and102care shown inFIG. 1C, the disclosed embodiments and examples may contemplate any number of WTRUs. The RAN104may also be in communication with the core network106.

The serving gateway144may also be connected to the PDN gateway146, which may provide the WTRUs102a,102b,102cwith access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs102a,102b,102cand IP-enabled devices.

Third Generation Partnership Project (3GPP) long term evolution (LTE) Release 8 (R8) uplink (UL) wireless transmit/receive units (WTRUs) may include single antennas and, therefore, UL power control functionality in LTE R8 is applied to single transmissions from single transmit antennas. UL power control is applied to physical uplink shared channel (PUSCH) transmissions, physical uplink control channel (PUCCH) transmissions, and Sounding Reference Signals (SRSs) for a single transmit antenna.

LTE-Advanced (LTE-A) may support multiple WTRU transmit antennas (e.g., up to 4). For LTE-A PUSCH transmissions, several single user (SU) MIMO modes (also referred to herein as transmission modes or transmission schemes) may be applicable, including precoding spatial multiplexing (SM) MIMO, transmit diversity and single antenna port transmission. The eNB may configure the WTRU to use a particular MIMO mode (or transmission scheme) for PUSCH transmission. Similarly, for PUCCH transmissions in LTE-A, it may be expected that the eNB may configure the MIMO mode (or transmission scheme) via higher layer signaling. For example, when a LTE-A WTRU with multiple transmit antennas operates in a R8 network, the WTRU may need to revert to a fallback configuration (e.g., single antenna port transmission).

Typically, different MIMO modes have different MIMO (antenna) gains. For example, the MIMO gain (or transmit diversity gain) of space time transmit diversity (STTD) is about 3 dB (as compared with single antenna transmission) while the (Rank-1) beamforming (BF) MIMO mode may have more gain on average than STTD. For a given transmit power level, the received power levels may be different among various MIMO modes. Power control methods may be utilized to adapt to different MIMO gains in LTE-A UL MIMO transmissions as described herein.

Use of multiple transmit antennas for transmission in the UL may cause antenna gain imbalance (AGI) issues for MIMO. AGI may, for example, create link inefficiency due to the multiple antennas receiving different average received signal-to-noise ratios (SNRs) or the multiple antennas transmitting at different antenna gains. For example, pathloss measurements over different antennas may be different due to the position of each transmit antenna in a WTRU (for example, an antenna may be blocked in a hand-held WTRU). The AGI may, however, be compensated using power control methods as described herein.

When an R10 WTRU operates in an R8 network, and the R8 network is not aware that the WTRU has multiple transmit antennas, single antenna port transmission (single antenna transmission or any comparable transparent transmission) may be used for the R10 WTRU due to backward compatibility. That is, the R10 WTRU may be configured to revert to a fallback mode (e.g., transparent transmission mode), such as precoding vector switching (PVS), cyclic delay diversity (CDD), transmit antenna switching/selection, or single antenna port transmission (e.g., transmit beamforming), which are transparent to the R8 network. The power control for the R10 WTRU may be configured as described herein.

Power control methods are described herein that address WTRUs having multiple transmit antennas. One example method is directed to power control for PUCCH transmissions when using different UL MIMO modes. This method accounts for the different antenna gains associated with PUCCH transmissions in different MIMO modes (or transmission schemes). Another example method is directed to power control for SRS transmissions when using different UL MIMO modes (or transmission schemes). This method accounts for the fact that SRS and PUSCH transmissions may be independently configured for MIMO transmission. Another example method provides AGI compensation for multiple transmit antenna configurations. This example method addresses the effects caused by AGI resulting in differences in average received SNR between the received signals from the multiple antennas. Another example method provides a power control method for fallback transmission modes.

Although the example methods are described with respect to UL MIMO, the example methods may be extended to include support for carrier aggregation.

Described herein is a power control method for PUCCH transmission using a designated UL MIMO mode. In LTE-A, multiple MIMO mode options may be considered for PUCCH transmission, including, for example, single antenna port transmission and transmit diversity (e.g., spatial orthogonal resource transmit diversity (SORTD) for multiple resource PUCCH transmission with 2 transmit antennas). The transmit power levels for the individual MIMO modes may be different because, for example, different MIMO modes may have different antenna/beamforming/transmit diversity gains. Accordingly, the LTE power control formula may be modified for LTE-A PUCCH transmissions, according to equation (1):
PPUCCH(i)=min {PCMAX,c,PO—PUCCH+PL+h(nCQI,nHARQ)+ΔF—PUCCH(F)+g(i)+ΔPUCCH—MIMO}  (1)
where certain terms in equation (1) are summarized below:
PCMAX,cis used to represent the CC (serving cell) specific maximum transmit power value for the primary cell (noting that PUCCH is transmitted only on the primary cell in LTE-A), which may take into account one or more of the signalled maximum power value, PMax,cfor the serving cell, c, the maximum power of the WTRU power class, maximum power reduction (MPR) allowances, tolerances, and the like. PCMAX,cmay be referred to as the configured maximum power (or configured maximum transmit power) for the CC; PO—PUCCHis a parameter composed of the sum of a (cell specific) parameter PO—NOMINAL—PUCCHprovided by higher layers and a (WTRU specific) component PO—WTRU—PUCCHprovided by higher layers; PL is the downlink pathloss estimate calculated in the WTRU in dB; h(nCQI,nHARQ) is a PUCCH format dependent value, where nCQIcorresponds to the number of information bits for the channel quality information (CQI) and nHARQis the number of HARQ acknowledge/negative acknowledge (ACK/NACK) bits; ΔF—PUCCH(F) is provided by higher layers, where each ΔF—PUCCH(F) value corresponds to a PUCCH format (F) relative to PUCCH format 1a, where each PUCCH format (F) is defined; and

g⁡(i)=g⁡(i-1)+∑m=0M-1⁢δPUCCH⁡(i-km)
where g(i) is the current PUCCH power control adjustment state and where g(0) is the first value after reset and where δPUCCHis a WTRU specific correction value, also referred to as a transmit power command (TPC) command, included in a physical downlink control channel (PDCCH) with, for example, downlink control information (DCI) format 1A/1B/1D/1/2A/2/2B (for the primary cell) or sent jointly coded with other WTRU specific PUCCH correction values on a PDCCH with, for example, DCI format 3/3A whose cyclic redundancy check (CRC) parity bits are scrambled with a TPC-PUCCH-radio network temporary identifier (TPC-PUCCH-RNTI).

The term ΔPUCCH—MIMOis a MIMO power offset for PUCCH, which is WTRU specific, and depends on the MIMO mode applied for PUCCH. Once the transmission mode for PUCCH is indicated to the WTRU, the PUCCH MIMO power offset may be determined by the WTRU. Alternatively, the PUCCH MIMO power offset may be provided to the WTRU.

The WTRU may determine the PUCCH MIMO power offset using a variety of methods. In one example method, the ΔPUCCH—MIMOmay be provided by higher layers, such as by using a look up table (LUT) via semi static signaling. Alternatively, the ΔPUCCH—MIMOmay be a pre-defined value (and, therefore may not need any signaling). Table 1 is an illustrative example of a LUT, which may be used to obtain the ΔPUCCH—MIMO. The variables may be replaced with values, which may be different for different embodiments. For example, Δ1and Δ2may be −3 dB and −6 dB, respectively, and both Δ5and Δ6may be 0 dB (or 0<=Δ5<3 dB, 0<=Δ5<3 dB).

If a look up table (LUT) is used for ΔPUCCH—MIMO, the LUT may be the same for all WTRUs and, therefore, may be broadcast. The WTRU may select from the table a value of ΔPUCCH—MIMO, corresponding to the MIMO mode in use.

According to another embodiment, the eNB may signal a value of ΔPUCCH—MIMOto the WTRU. Here, the value may be WTRU-specific and may be signaled, for example, via dedicated signaling.

According to another embodiment, the value of ΔPUCCH—MIMOmay be absorbed in an existing power control parameter such as PO—PUCCH(e.g., in PO—UE—PUCCH) or ΔF—PUCCH(F). In this case, ΔPUCCH—MIMOmay be removed from the PUCCH power control in equation (1). The range of PO—UE—PUCCH(or ΔF—PUCCH(F)) may also need to be revised accordingly as ΔPUCCH—MIMOis now added to PO—PUCCH(or ΔF—PUCCH(F)).

In either case, the calculated WTRU transmit power may be distributed evenly among the active antennas (or antenna ports) in the WTRU.

Referring toFIG. 2, there is shown an example power control flowchart200for physical uplink channel transmissions when using uplink (UL) multiple input multiple output (MIMO) as described herein. Initially, a WTRU may receive an UL MIMO mode selection from the base station or eNB (210). The WTRU may then determine the MIMO offset based on the selected UL MIMO mode (220). The WTRU may then calculate the PUCCH transmit power based, in part, on the MIMO offset (230). The PUCCH transmit power may then be distributed evenly amongst the transmit antennas (240). For example, the PUCCH transmit power may be distributed amongst active transmit antennas (or antenna ports). The WTRU transmits information over the PUCCH using the calculated transmit power (250).

Described herein is a power control method for SRS transmission using a designated UL MIMO mode.

In LTE R8, the WTRU transmit power, PSRS, for the SRS transmitted on subframe i, may be defined as set forth in equation (2):
PSRS(i)=min {PCMAX,PSRS—OFFSET+10 log10(MSRS)+PO—PUSCH(j)+α(j)·PL+f(i)}[dBm]  (2)
where certain terms in equation (2) are summarized below:
PCMAXis the configured maximum WTRU power;
For KS=1.25, PSRS—OFFSETis a 4-bit WTRU specific parameter semi-statically configured by higher layers with 1 dB step size in the range [−3, 12] dB and for KS=0, PSRS—OFFSETis a 4-bit WTRU specific parameter semi-statically configured by higher layers with 1.5 dB step size in the range [−10.5, 12] dB; KSis given by the WTRU specific parameter deltaMCS-Enabled provided by higher layers; MSRSis the bandwidth of the SRS transmission in subframe i expressed in number of resource blocks; PO—PUSCH(j) is a parameter composed of the sum of a (cell specific nominal) component PO—NOMINAL—PUSCH(j) provided from higher layers for j=1 and a (WTRU specific) component PO—WTRU—PUSCH(j) provided by higher layers for j=1, where j=1 for PUSCH (re)transmissions corresponding to a dynamic scheduled grant; For α(j) where j=1 αε{0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} is a 3-bit cell specific parameter provided by higher layers; PL is the downlink pathloss estimate calculated in the WTRU in dB; and f(i) is the current power control adjustment state for the PUSCH.

The LTE UL power control may be limited to, for example, only one carrier and one transmit antenna (e.g., LTE UL may not support single user MIMO (SU-MIMO)). In LTE-A, UL SU-MIMO and carrier aggregation may be supported and the power control formula for SRS may be modified as described herein.

For both LTE-A and LTE, the same TPC command for a UL serving cell (component carrier) may be used for both PUSCH and SRS transmissions on the serving cell. Further, PUSCH and SRS transmissions may be independently configured with a MIMO mode, e.g., PUSCH with precoding MIMO but SRS with single antenna port transmission.

Considering the above two aspects, an example power control method includes modifying the LTE UL power control formula such that setting the WTRU transmit power for the SRS transmitted in the n-th antenna port (or layer) in subframe on serving cell, c, may be defined as shown in equation (3):
PSRS,c(i,n)=min {PCMAX,c,PSRS—OFFSET,c+10 log10(MSRS,c(i,n))+PO—PUSCH,c(j)+αc(j)·PLc(n)+fc(i)+ΔSRS—MIMO}  (3)
where n is the antenna port (or layer) index and i is the sub-frame number. The term PCMAX,cis used to represent the CC (serving cell) specific maximum transmit power value for serving cell, c, which may take into account one or more of the signaled maximum power value, PMax,cfor the serving cell, c, the maximum power of the WTRU power class, maximum power reduction (MPR) allowances, tolerances, and the like. PCMAX,cmay be referred to as the configured maximum power (or configured maximum transmit power) for the serving cell, c, and f(i) is the current power control adjustment state for the PUSCH for the serving cell, c.

The term PSRS—OFFSET,cis a parameter semi-statically configured for serving cell, c, by higher layers. With UL MIMO (e.g., up to four antennas) for PUSCH, there may be various MIMO modes/options (including spatial multiplexing (SM) MIMO (SM MIMO), transmit diversity, and BF/single antenna port transmission) for PUSCH transmission. However, the SRS transmission mode with multiple antennas may be deterministic (or semi-static) such as multiple antenna port transmission or single antenna port transmission. In that case, different PSRS—OFFSET,cvalues may be required for different MIMO options for PUSCH. The range of PSRS—OFFSET,cvalues may be modified appropriately.

The term MSRS,c(i,n) is the bandwidth (BW) of the SRS transmission over the n-th antenna port (or layer) in subframe i and serving cell, c, in terms of the number of resource blocks (RBs). It may be possible for each antenna port (or layer) to use a different (flexible) number of RBs (e.g., allowing different SRS densities in frequency), for example, in order to reduce SRS overhead in MIMO. Alternatively, MSRS,c(i,n) may be the same for all n. In this case, the index n may be removed.

The term PLc(n) is the pathloss estimate calculated for the n-th antenna port in the WTRU for serving cell c in dB. The same pathloss may be used for all the antenna ports. In this case, the index n may be removed such that PLc(n)=PLc.

In LTE-A, PO—PUSCH,c(j) may be extended to UL MIMO such that j represents the transmission mode and MIMO mode. For instance, j=0, 1, 2 may represent the same transmission mode as in LTE, while j=3, 4, 5, . . . , M, may represent the MIMO mode for PUSCH transmission. Alternatively, as in LTE, j is fixed to 1 for PO—PUSCH,c(j).

The term ΔSRS—MIMOis an SRS MIMO offset parameter, which represents a MIMO gain difference between the MIMO mode used for PUSCH and the MIMO mode used for SRS. Note that SRS may be precoded. For example, when PUSCH uses a single antenna port mode and SRSs are transmitted over multiple antennas (e.g., two antennas), ΔSRS—MIMOmay be set to approximately 3 dB. ΔSRS—MIMOmay be provided by higher layers, such as by using a look up table via semi static signaling. Table 2 is an illustrative LUT for ΔSRS—MIMO. The variables may be replaced with values, which may depend on the specific method.

If an LUT is used for ΔSRS—MIMO, it may be the same for all WTRUs, and it may be broadcast. In this case, the WTRU may select from the table a value of ΔSRS—MIMOthat corresponds to the MIMO mode applied for PUSCH transmission and the MIMO mode applied for SRS transmission.

Alternatively, the eNB may signal a value of ΔSRS—MIMOto a WTRU, where the value is WTRU-specific. For instance, ΔSRS—MIMOmay be signaled in a PDCCH (e.g., UL grant). Alternatively, ΔSRS—MIMOmay be signaled by higher layers (e.g., via RRC signaling).

According to another example method, the ΔSRS—MIIMOmay be absorbed in an existing power control parameter such as PO—PUSCH,c(e.g., in PO—UE—PUSCH,c) or PSRS—OFFSET,cso that the term ΔSRS—MIIMOmay be removed from equation (3). In this case, the range of PO—UE—PUSCH,cor PSRS—OFFSET,cmay need to be modified to account for ΔSRS—MIIMO.

In another embodiment, when the SRS bandwidth is the same for all the antenna ports simultaneously transmitted on serving cell c (i.e., MSRS,c(i,n)=MSRS,c(i)), the total power of SRS transmissions over the (active) antenna ports, denoted by PSRS,c(i), may be determined in subframe i on serving cell, c, as shown in equation (4):
PSRS,c(i)=min {PCMAX,c,PSRS—OFFSET,c+10 log10(MSRS,c(i))+PO—PUSCH,c(j)+αc(j)·PLc+fc(i)+ΔSRS—MIMO}  (4)
In this case, the calculated total transmit power for SRS may be distributed evenly among the active antennas (or antenna ports) in the WTRU. The variables/parameters are as defined previously.

With UL MIMO (e.g., with up to four antennas), if simultaneous SRS transmissions over multiple transmit antennas occur, the transmit power density of SRS for each antenna (or antenna port) may get lower as the number of antennas (or antenna ports) increases. This may degrade channel estimation performance at the eNB. This degradation in estimation performance may be resolved using the example methods described herein. In one example method, the eNB may signal the WTRU, via higher layers, to switch to time division multiplexing (TDM) mode for SRS transmission, such as one SRS transmission in a single antenna (or at most two SRS transmissions over two antennas) in each SRS subframe.

In another example method, when the sum of the WTRU transmit powers (i.e., sum(PSRS,C(i,n)) where the summation is done over all the antenna ports n, in Equation (3)) (or total SRS transmit power before limiting to PCMAX,cin Equation (4)) for SRS transmissions simultaneously transmitted over multiple antennas exceeds a maximum WTRU power (or configured transmit power, PCMAX,cfor serving cell, c) by a predefined threshold, the WTRU may select one SRS (possibly more SRSs if transmit power is available) to be transmitted in the next SRS subframe. The selection may be based on a rotation manner.

In another example method, SRS bandwidth (BW) (i.e., MSRS(i,n) or MSRS(i)) may be adjusted (or reconfigured) appropriately by the eNB and signaled to the WTRU via higher layers. In another embodiment, when the WTRU is power limited (e.g., total SRS transmit power before limiting to PCMAX,cin Equation (4) exceeds PCMAX,c(or WTRU power class, denoted by Ppowerclass) by a threshold, the WTRU is (re)configured to switch to single antenna port transmission for SRS (from multi antenna port transmission).

Described herein are power reduction methods in the event the sum of the required transmit powers (as in Equation (3)) for simultaneous SRS transmissions over multiple antennas exceeds a maximum WTRU power (or configured transmit power, PCMAX,cfor serving cell, c). In one example method, the transmit powers for the individual SRS transmissions may be reduced evenly to meet the maximum power constraint. In another example method, PCMAX,cmay be defined per power amplifier (PA) in equation (3). In this method, the configured (WTRU) transmit power may be equally distributed among the multiple PAs. That is, Pcmax,cpa(dB)=Pcmax,c−10×log 10(Npa) where Npa is the number of active PAs in the WTRU in a given SRS subframe for serving cell c. With respect to equation (3), Pcmax,cpais substituted for Pcmax,c. In this case the Σ Pcmax,cpamay be less than or equal to Pcmax,c.

Referring toFIG. 3, there is shown an example power control flowchart300for SRS transmissions when using UL MIMO as described herein. Initially, a WTRU may receive an UL MIMO mode selection/configuration for SRS transmission from the base station or eNB (310). The WTRU may then receive from the base station a PSRS—OFFSET,c(320). The WTRU may then determine the ΔSRS—MIMOoffset based on the UL MIMO mode for PUSCH and MIMO transmission mode for SRS (330). Alternatively, as stated previously, the PSRS—OFFSET,cmay include the ΔSRS—MIMO, in which case the PSRS—OFFSET,cmay be based on the selected UL MIMO mode. A SRS transmit power is then calculated based, in part, on the PSRS—OFFSET,cand the ΔSRS—MIMOoffset (340). The WTRU may perform power reduction methods if the (total) SRS transmit power is greater than a threshold such as for example the configured WTRU maximum transmit power (360). This may happen, for example, if the WTRU may be transmitting simultaneous SRS transmissions. The WTRU transmits the SRS at the SRS transmit power (370).

Described herein are power control methods to address antenna gain imbalance (AGI). When multiple antenna transmissions are made in the UL, there may be an issue with AGI. This may create link inefficiency because it may result in differences in average received signal-to-noise (SNR) between the signals received from the multiple antennas. For example, path loss measurements over different antennas may be different due to the position of each transmit antenna in the WTRU (for example, an antenna may be blocked in a hand-held WTRU). The AGI may be compensated by employing the power control methods described herein.

In an example method, the WTRU performs AGI estimation followed by AGI compensation. For AGI estimation, the WTRU may perform a Reference Signal Received Power (RSRP) measurement on each antenna (or antenna port). In case of carrier aggregation, the RSRP measurement may be performed on a downlink (DL) anchor or primary component carrier (CC) (i.e., primary cell) or a reference DL CC associated with the UL serving cell (CC). Alternatively, all configured DL CCs may be used for the RSRP measurement. A filtering approach may be used for the RSRP measurement. For example, a higher layer (e.g., Layer 3) filter configuration may be used for the RSRP measurement.

Based on the RSRP measurement on each antenna (or antenna port), the WTRU may estimate the AGI among the antennas (or antenna ports) used for the UL transmission. The AGI may be expressed in terms of a scaled relative AGI with regard to a reference transmit antenna.

The WTRU performs AGI compensation on each transmit antenna after estimating the AGI on the individual transmit antennas (or antenna ports). The WTRU may scale each transmit antenna to compensate for the adverse impact of AGI. For example, assume that a WTRU includes N transmit antennas and the estimated AGI for each antenna is denoted as AGI(i) on a linear scale (and i is the antenna index). The WTRU may scale each transmit antenna by an AGI compensation scaling factor, β(i), where

β⁡(i)=1AGI⁡(i)∑mN⁢1AGI⁡(m)
and where AGI(i)<=1.

In another method, the eNB may estimate the AGI on each individual transmit antenna (or antenna port) of the WTRU and provide an AGI correction factor for the WTRU via an L1 layer (e.g., similar to providing TPC commands per antenna) or higher layers (e.g., radio resource control (RRC) signaling). For example, the above AGI compensation scaling factor, β(i), may be determined by the eNB and then signaled to the WTRU through RRC signaling.

In another method, the AGIs for each transmit antenna (or antenna port) may be compared with a threshold value, and antenna(s) with too high an AGI value may be turned off or fall-back to, for example, single antenna port transmission mode. For example, if the AGI impact from a transmit antenna is too adverse on link performance (e.g., the AGI value is too high), the WTRU may turn off the antenna(s) having the AGI values that are too high or fall-back to another mode (e.g., single antenna port transmission mode).

Referring toFIG. 4, there is shown an example power control flowchart400for AGI compensation as described herein. Initially, a WTRU may perform a RSRP measurement (410). The WTRU may then determine an AGI estimate based on the RSRP (420). The WTRU may then apply an AGI compensation scaling factor to each transmit antenna (430).

Referring toFIG. 5, there is shown another example power control flowchart500for AGI compensation as described herein. Initially, a base station may determine an AGI estimate for the WTRU (510). The WTRU may then receive an AGI compensation factor from the base station (520). The WTRU may then apply the AGI compensation factor on each transmit antenna (530).

Described herein is a power control method for fallback transmission mode. By way of example, when a WTRU (that is, for example, configured to operate with a particular network such LTE R10) operates in a network other than the one that it is configured for use with (e.g., LTE R8) and that is, for example, not aware that the WTRU has multiple transmit antennas, the WTRU may operate in another mode, such as single antenna (port) transmission mode (or comparable transparent transmission mode) to take advantage of backward compatibility. In other words, in an example embodiment, an R10 WTRU may be configured to revert to a fallback mode (e.g., transparent transmission mode), such as precoding vector switching (PVS), CDD (cyclic delay diversity), or single antenna port transmission (e.g., transmit beamforming), which is transparent to the R8 network. The WTRU may also be configured to enter a fallback transmission mode in certain other cases. For example, when the UL MIMO channels for a WTRU are highly correlated, the WTRU may use transmit beamforming. In this example, the power control for the R10 WTRU may need to be configured accordingly. In an example power control method for fallback transmission, when the WTRU is in the fallback transmission mode for a physical channel, the eNB and WTRU may operate the LTE R8 power control method (or a power control method for single antenna port transmission) for the physical channel.