Abstract:
This invention is a method and an apparatus to up link transmission of data from a user equipment to a base station for single user multiple input, multiple output. This invention includes receiving at least one codeword, permuting the received codewords, precoding the permuted codewords and transmitting the predecoded codewords on plural antennas. The codewords may be permuted by layer permutation or by codeword permutation.

Description:
CLAIM OF PRIORITY 
     This application claims priority under 35 U.S.C. 119(e)(1) to U.S. Provisional Application No. 61/146,834 filed Jan. 23, 2009. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The technical field of this invention is data transmission in wireless telephony. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  shows an exemplary wireless telecommunications network  100 . The illustrative telecommunications network includes base stations  101 ,  102  and  103 , though in operation, a telecommunications network necessarily includes many more base stations. Each of base stations  101 ,  102  and  103  are operable over corresponding coverage areas  104 ,  105  and  106 . Each base station&#39;s coverage area is further divided into cells. In the illustrated network, each base station&#39;s coverage area is divided into three cells. Handset or other user equipment (UE)  109  is shown in Cell A  108 . Cell A  108  is within coverage area  104  of base station  101 . Base station  101  transmits to and receives transmissions from UE  109 . As UE  109  moves out of Cell A  108  and into Cell B  107 , UE  109  may be handed over to base station  102 . Because UE  109  is synchronized with base station  101 , UE  109  can employ non-synchronized random access to initiate handover to base station  102 . 
     Non-synchronized UE  109  also employs non-synchronous random access to request allocation of up link  111  time or frequency or code resources. If UE  109  has data ready for transmission, which may be traffic data, measurements report, tracking area update, UE  109  can transmit a random access signal on up link  111 . The random access signal notifies base station  101  that UE  109  requires up link resources to transmit the UEs data. Base station  101  responds by transmitting to UE  109  via down link  110 , a message containing the parameters of the resources allocated for UE  109  up link transmission along with a possible timing error correction. After receiving the resource allocation and a possible timing advance message transmitted on down link  110  by base station  101 , UE  109  optionally adjusts its transmit timing and transmits the data on up link  111  employing the allotted resources during the prescribed time interval. 
     SUMMARY OF THE INVENTION 
     This invention is a method and an apparatus for up link transmission of data from a user equipment to a base station for single user multiple input, multiple output. This invention includes receiving at least one codeword, permuting the received codewords, precoding the permuted codewords and transmitting the predecoded codewords on plural antennas. The codewords may be permuted by layer permutation or by codeword permutation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of this invention are illustrated in the drawings, in which: 
         FIG. 1  is a diagram of a communication system of the prior art related to this invention having three cells; 
         FIG. 2  illustrates a high-level description of the up link single user multiple input multiple output of this invention (prior art); 
         FIG. 3  illustrates a prior art codeword-to-layer mapping scheme for the up link single user multiple input multiple output of this invention; and 
         FIG. 4  illustrates some examples of layer/codeword diversity according to this invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The current Evolved Universal Terrestrial Radio Access (E-UTRA) Long Term Evolution (LTE) Rel. 8 specification only supports single antenna transmission on the uplink (UL). All the signaling aspects are designed with this restriction in mind. As the enhancement for LTE is coming due to the IMT-Advanced call-of-proposal for yet another generation of upgrade in cellular technology, different aspects of LTE need to be reevaluated and improved. Of a particular interest is to increase the UL peak data rate by at least a factor of 2 and increase the UL spectral efficiency to meet the IMT-Advanced requirements. Since 64 Quadrature Amplitude Modulation (QAM) has already been supported for LTE Rel. 8, the support of UL Single-User Multiple Input, Multiple Output (SU-MIMO) including spatial multiplexing is inevitable. 
       FIG. 2  illustrates a high-level description of UL SU-MIMO operation for LTE. Base station eNB  210  including plural antennas  211  communicates with both UE 1   220  and UE 2   230 . UE 1   220  includes antennas  221 . UE 2   230  includes antennas  231 . eNB  210  communicates with UE 1   220  including up link communication  223  and down link communications  225 . eNB  210  communicates with UE 1   230  including up link communication  233  and down link communications  235 . Up link communications  223  and  233  include data on a Physical Uplink Shared CHannel (PUSCH), Sounding Reference Signals (SRS) and Demodulation Reference Signal Sequence (DMRS). Down link communications  225  and  235  include control via UL grant such as Precoding Matrix Indicator (PMI), Rank Indicator (RI) via Physical Downlink Control CHannel (PDCCH) and DL acknowledge (ACK)/not acknowledge (NAK) via Physical Hybrid Automatic Repeat Request (ARQ) Indicator CHannel (PHICH). 
     There are some challenges supporting UL SU-MIMO for LTE. This new technique needs to be backward compatible with LTE Rel. 8 and introduce minimum impact on the current LTE specification. This is particularly true for control signaling. This technique needs to support both 2 and 4 transmit antennas at the UE. 
     The codeword-to-layer mapping which includes the number of codewords for a given number of transmission layers is important. Keeping the impact on the specification to a minimum while maintaining competitive performance is desirable. Reusing the codeword-to-layer mapping for DL SU-MIMO is hence preferred. It is also desirable to minimize the DL control overhead, for example PHICH and UL grant. 
       FIG. 3  illustrates a prior art codeword-to-layer mapping scheme for the DL SU-MIMO. There are at most 2 codewords for a given number of layers. Each codeword is associated with a transport block (TB). There are at most 2 TBs for a given number of layers. This should be distinguished from a codeblock where one TB can be segmented into multiple codeblocks. Each TB is associated with one Hybrid Automatic Repeat Request (HARQ) process including the associated ACK/NAK, redundancy version (RV) and new data indicator (NDI) as well as one Modulation and Coding Scheme (MCS). Alternatively, in case of spatial multiplexing with 2 TBs, both TBs can be associated with the same HARQ process but with different ACK/NAK, RV, NDI and MCS. 
       FIG. 3  illustrates Rank  1  and Rank  2  cases for two transmit antennas and Rank  1 , Rank  2 , Rank  3  and Rank  4  for four transmit antennas. In the two transmit antenna, Rank  1  case codeword CW 1  supplies predecoding  310  which connects to two transmit antennas  315 . In the two transmit antenna, Rank  2  case codewords CW 1  and CW 2  supply predecoding  320  which connects to two transmit antennas  325 . In the four transmit antenna, Rank  1  case codeword CW 1  supplies predecoding  330  which connects to four transmit antennas  335 . In the four transmit antenna, Rank  2  case codewords CW 1  and CW 2  supply predecoding  340  which connects to four transmit antennas  345 . In the four transmit antenna, Rank  3  case codeword CW 1  directly supplies predecoding  350  and codeword CW 2  supplies predecoding  350  via two outputs of serial to parallel converter  353 . Predecoding  350  connects to four transmit antennas  355 . In the four transmit antenna, Rank  4  case codeword CW 1  supplies serial to parallel converter  361  and codeword CW 2  supplies serial to parallel converter  363 . Serial to parallel converters  361  and  363  each supply two outputs to predecoding  360 . Predecoding  360  connects to four transmit antennas  365 . 
       FIG. 4  illustrates some examples of layer/codeword diversity according to this invention.  FIG. 4  only illustrates examples for the four transmit antenna case. This is illustrative only. Embodiments for the two transmit antenna case are simple to deduce from these examples.  FIG. 4  illustrates illustrative permutation patterns only. Other permutation patterns are also feasible. 
       FIG. 4  illustrates 2 layer, 3 layer and 4 layer exampled for four transmit antennas. In the 2 layer case, codewords CW 1  and CW 2  supply permuter  411 . Permuter  411  performs the function k=mod(m+d,2) in supplying two outputs to predecoding  410  which connects to four transmit antennas  415 . In a 3 layer, layer permutation case, codeword CW 1  supplies one signal to permuter  421 . Codeword CW 2  supplies serial to parallel converter  423  which supplies two signals to permuter  421 . Permuter  421  performs the function k=mod(n+d,3) in supplying three signals to predecoding  420  which connects to four transmit antennas  425 . In a an alternative 3 layer, codeword permutation case, codewords CW 1  and CW 2  each supply one signal to permuter  431 . Permuter  431  performs the function n′=mod(m+d,2) in generating two outputs. Permuter  431  supplies one signal directly to predecoding  430  and one signal to serial to parallel converter  433  which supplies two signals to predecoding  430 . Predecoding  430  connects to four transmit antennas  435 . In a 4 layer, layer permutation case, codeword CW 1  supplies serial to parallel converter  443  which supplies two signals to permuter  441 . Codeword CW 2  supplies serial to parallel converter  443  which supplies two signals to permuter  441 . Permuter  441  performs the function k=mod(n+d,4) in generating four outputs. Permuter  441  supplies four signals to predecoding  440  which connects to four transmit antennas  445 . In a an alternative layer, codeword permutation case, codewords CW 1  and CW 2  each supply one signal to permuter  451 . Permuter  451  performs the function n′=mod(m+d,2) in generating two outputs. Permuter  451  supplies one signal to serial to parallel converter  453  and one signal to serial to parallel converter  433 . Serial to parallel converters  453  and  457  each supply two signals to predecoding  450 . Predecoding  450  connects to four transmit antennas  455 . Note in  FIG. 4 : m is an index of input code words; k is an index of inputs to the predecoding; n is an index of intermediate signals before permutation; and n′ is an index of intermediate signals after permutation. 
     This invention aims to minimize the control overhead while keeping the same codeword-to-layer mapping scheme for UL SU-MIMO. This invention uses the same codeword-to-layer mapping as depicted in  FIG. 3 . Thus there is a maximum of 2 codewords and each codeword is associated with one transport block. This invention also includes some layer or codeword diversity scheme. The layer diversity can be introduced in frequency domain across sub-carriers or resource elements or time domain across Discrete Fourier Transform Spread (DFTS) Orthogonal Frequency Division Multiplexing (OFDM) symbols. The permutation domain is indexed by d in  FIG. 4 . Introducing layer diversity amounts to equalizing the Signal to Interference plus Noise Ratio (SINR) across codewords when a linear/one-shot MIMO receiver is used such as LMMSE. 
     Large delay Cyclic Delay Diversity (CDD) could be used for LTE DL SU-MIMO. Such a large delay CDD tends to increase the Peak-to-Average Power Ratio (PAPR)/CM due to the Discrete Fourier Transform (DFT) precoding unless a fixed DFT precoding is used. 
     Simple layer permutation could be used in which each of the data streams at the output of a serial to parallel converter is spread across all layers/virtual antennas. This introduces spatial diversity within each of the data streams. 
     Codeword permutation spreads each of the data streams across all the layers, thus the two codewords are permuted. Since a codeword is mapped onto one or two layers, this also results in spreading of each data stream across layers. Note that codeword permutation is identical to layer permutation for 1-layer and 2-layer transmission since 1 codeword is associated only with 1 layer. 
     Other variations of  FIG. 4  and permutation patterns are possible. For codeword permutation, it is possible to perform another permutation after the serial to parallel conversion. For example, in 4 layer mapping the carrier  1  is layer permutation is (1, 2, 3, 4) and the carrier  2  layer permutation is (4, 3, 2, 1). For 3 layer mapping the carrier  1  layer permutation is (1, 2, 3,) and the carrier  2  layer permutation is (3, 2, 1). 
     DL ACK/NAK bundling across codewords known as spatial bundling avoids increasing PHICH overhead. In the case, both codewords and thus the TBs share the same DL ACK/NAK. Only a 1-bit DL ACK/NAK is used regardless of the number of codewords or layers. 
     There are 4 possibilities in regard of the combination of NDI, RV and Transport Block Size (TBS). The RV is jointly encoded with MCS in the UL grant in a technique known as MCS-RV field. The TBS is derived from MCS and resource allocation field which is the number of assigned resource blocks (RBs). 
     In a first alternative, there is one distinct set (NDI, RV, TBS) per codeword. Thus a TB has 2 NDI and 2 MCS-RV. This alternative provides the maximum flexibility. 
     In a second alternative, there is one distinct NDI per codeword/TB and a single set (RV, TBS) shared by all codeword(s). Thus each TB has 2 NDI and 1 MCS-RV. If the SINR for the two codewords are similar such as with LMMSE receiver, this second alternative may offer comparable performance to the first alternative if both codewords correspond to new transmission. If one of the codewords is an adaptive retransmission, then some performance degradation may occur with this second alternative relative to the first alternative. The second alternative may encounter some scheduler restrictions. For example for the adaptive retransmission codeword, the TB size shall be the same as the initial transmission of the same TB, the MCS combined with resource allocation determines the modulation order, coding rate and RV. The MCS and resource allocation also determines the TB size and modulation order for the new transmission on the other codeword. If one codeword is for new transmission and the other codeword is for adaptive retransmission, MCS from  29  to  31  may not be used for the retransmission codeword, because MCS from  29  to  31  is not meaningful to a new transmission codeword. Having a single MCS does not allow the system to reap maximum benefit with SIC receiver. 
     In a third alternative, a single NDI is shared by all codewords and TBs, and a single set (RV, TBS) is shared by all codewords. Thus each TB has one NDI and one MCS-RV. This third alternative is the most economical solution and has comparable performance to the second alternative. In this alternative, the RV corresponding to both TBs may be made the same but this is not required. 
     In a fourth alternative, a single NDI is shared by all codewords and TBs, and one distinct set (RV, TBS) is shared per codeword. Thus each TB has 1 NDI and 2 MCS-RV. In this fourth alternative, the RV corresponding to both TBs may be made the same while the MCS corresponding to the 2 TBs can be different but this is not required. This fourth alternative is consistent with DL ACK/NAK spatial bundling. Having different MCS fields for the 2 TBs allows the system to exploit the SINR gain in the second TB when SIC receiver is used. The gain of SIC receiver is more significant in the first transmission. Differential MCS can be used for the second codeword relative to the MCS of the first codeword to reduce the overhead corresponding to the second MCS. The differential MCS corresponding to the second TB is indicated by less than 5 bits such as 3 bits while the MCS associated with the first TB is indicated by 5 bits. The differential MCS is defined only relative to the MCS values of 0 to 28. If a single NDI is used, a single HARQ process may be defined for both codewords and TBs. This is possible whether the two TBs share the same MCS field or not.