Abstract:
This invention concerns multiplexing in Long Term Evolution (LTE) and Long Term Evolution-Advanced (LTE-A) in Evolved Universal Terrestrial Radio Access Network (E-UTRAN) wireless telephony. Joint processing down link coordinated multi-point reference signaling includes combining resource signal types at a user equipment, determining conflicts between resource signals of plural user equipment, puncturing resource signals of other cell upon determining conflicts between resource signals of plural user equipment and transmitting non-punctured combined resource signals from a user equipment.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. 119(e)(1) to U.S. Provisional Application No. 61/149,126 filed Feb. 2, 2009. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The technical field of this invention is signaling in wireless telephony. 
       BACKGROUND OF THE INVENTION 
       [0003]      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 . 
         [0004]    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 
       [0005]    This invention concerns multiplexing in Long Term Evolution (LTE) and Long Term Evolution-Advanced (LTE-A) in Evolved Universal Terrestrial Radio Access Network (E-UTRAN) wireless telephony. Joint processing down link coordinated multi-point reference signaling includes combining resource signal types at a user equipment, determining conflicts between resource signals of plural user equipment, puncturing resource signals of other cell upon determining conflicts between resource signals of plural user equipment and transmitting non-punctured combined resource signals from a user equipment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other aspects of this invention are illustrated in the drawings, in which: 
           [0007]      FIG. 1  is a diagram of a communication system of the prior art related to this invention having three cells; and 
           [0008]      FIG. 2  is a flow chart illustrating the decision path of this invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0009]    This invention concerns multiplexing in Long Term Evolution (LTE) and Long Term Evolution-Advanced (LTE-A) in Evolved Universal Terrestrial Radio Access Network (E-UTRAN) wireless telephony. If we assume that the component carrier is configured to be E-UTRAN Rel. 8 (R8) compatible, then in all subframes R8 cell-specific reference signals (CRS) for antenna ports 0 to 3 shall be present for at least in the first 2 Orthogonal Frequency Division Multiplexing (OFDM) symbols (the first slot). Additionally, the system will be used for R8 channel estimation, measurements, etc. Under these conditions all LTE-A UEs are assumed to be configured for down link (DL) joint processing (JP) coordinated multi-point (COMP) transmission. 
         [0010]    Multiplexing between LTE and LTE-A UEs for R8-compatible carrier require the following. For Frequency Division Multiplexing (FDM) LTE and LTE-A transmission are allowed to co-exist in a subframe. LTE-A UEs are allocated a set of Radio Bearers (RBs). LTE-A specific features should be transparent to LTE UEs. For Time Division Multiplexing (TDM) there can be LTE-only subframes and LTE-A-only subframes. LTE and LTE-A transmissions cannot co-exist within a single subframe. This separation is supported by subframe identification. LTE-A-only subframes appear as Multimedia Broadcast Multicast Service Single Frequency Network (MBSFN) subframes to R8 UEs. Thus this multiplexing includes three types of subframes: LTE-only subframes; LTE-A-only subframes; and mixed subframes. 
         [0011]    There are several types of DL Reference Signals (RS) for COMP. Assume that DL COMP has up to 4 transmitting antennas per cell. There are three categories of DL RS for COMP. The first category is Channel Quality Indicator (CQI) RS including measurement and CQI/Precoding Matrix Indicator (PMI)/Rank Indicator (RI) computation. These are cell-specific, wideband and non-precoded. The second category is Demod-RS for DL control including channel estimation for DL control demodulation such as Physical Control Format Indicator CHannel (PCFICH), Physical Hybrid Automatic Repeat Request (ARQ) Indicator CHannel (PHICH) and Physical Downlink Control CHannel (PDCCH). These are cell-specific and wideband because DL control spans the entire component carrier bandwidth. This case can simply reuse the R8 CRS and DL control transmission mechanism. The third category is Demod-RS for Physical Downlink Shared CHannel (PDSCH) including channel estimation for data demodulation. A first alternative in this category uses R8 CRS in the first and second slots, and is wideband and non-precoded. A second alternative in this category uses additional UE-specific RS (URS) only in scheduled RB(s) and is precoded. 
         [0012]    For JP DL COMP there are two types of combining at the UE. The first type of combining is coherent combining including symbol-level combining before equalization and demodulation. The second type of combining is non-coherent combining including soft bit (LLR) combining after equalization/demodulation, preferably before FEC decoding which is analogous to Hybrid Automatic Repeat Request (HARQ) combining. This is an implementation issue, but it affects the signaling support design for DL COMP. Table 1 compares various aspects of coherent and non-coherent combining. 
         [0000]                            TABLE 1                       Non-coherent       Aspect   Coherent combining   combining                   Active set   Depending on the   Decoding is required       awareness/   demod-RS PDSCH type:   to be done       knowledge   R8 CRS is   cell-by-cell           required,   R8 CRS is more           URS may not be   suitable           required       CQI/PMI/RI   Typically suited   Disjoint reporting       reporting   with joint reporting       Transmission   Identical signal   Identical SFNs can       from multiple   System Frame Number   be from different       points   (SFN) combining gain   sets of REs or           must be in the same   different MCSs           set of resource           elements (REs) with           the same Modulation           and Coding Scheme           (MCS)       PDSCH REs and   Potential conflict   No conflict       CRS location   between PDSCH REs           and CRS location           among cells in the           active COMP set due           to frequency shift                    
The level of conflict for coherent combining depends on the following: whether using LTE or LTE-A COMP configured multiplexing in TDM or FDM; the type of demod-RS for PDSCH; and the DL control length.
 
         [0013]    Table 2 list the parameters of JP COMP RE conflict for coherent combining. 
         [0000]                                              TABLE 2                       TDM for COMP capable               transmission   FDM (Mixed)                                    PDSCH demod-RS   Opt 1: conflict in 4   Opt 3 (R8 CRS) and       with R8 CRS   symbols per subframe   Opt 4 (URS) for:       PDSCH demod-RS   Opt 2: No conflict   n = 1: conflict in 5       with new URS       symbols per subframe               n &gt; 1: conflict in 4               symbols per subframe                    
In the second column, the TDM for COMP capable transmission includes UEs with 1-cell active set. In the third column, n is the length of DL control region in OFDM symbols. In Table 2 MBSFN subframes (TDM) for 4 transmitting antennas always use 2-symbol DL control.
 
         [0014]    There are two basic solutions when conflict occurs. The first solution ignores inter-cell CRS interference. This creates interference and rate matching error which is risky. In the second solution RE punctures on CRS locations in other cells. This causes increased overhead but is preferred. For 4 transmitting antennas and 2-symbol DL control and normal Cyclic Prefix (CP), the CRS overhead increases from 11% to 33%. Puncturing can be tailored to the active COMP set, for example dependent on the cell IDs of the member cells, to reduce overhead. This does increase the number of options. 
         [0015]    Assuming using the second solution when conflict occurs, all options noted in Table 2 incur overhead. For options Opt1 and Opt3 this overhead is RE puncturing in PDSCH. For option Opt2 this overhead is a new URS. For option Opt4 this overhead is a combination of RE puncturing and new URS. This option is not preferred. It is expected that that option Opt2 incurs less overhead than options Opt1 and Opt3. In option Opt2 the URS overhead depends on the number of layers and can be designed more efficiently. In addition in option Opt2 the same URS frequency shift is used across cells within the active COMP set. 
         [0016]    The following notes the parameters of the preferred setup according to this invention. Note that coherent combining with TDM transmission is preferred as it is believed to be the cleanest setup. For coherent combining and TDM for COMP transmission PDSCH RE puncturing is not required. Thus the UE is not required to be aware of active COMP set. In this case UE-specific RS, which is identical for all members of active COMP cell and has same frequency shift for all cells in active set, is used for PDSCH demod-RS. For coherent combining and FDM transmission PDSCH RE puncturing is required to avoid CRS interference. The UE may be required to be aware of active COMP set depending on the PDSCH RE puncturing scheme. Reuse of R8 cell-specific RS for PDSCH demod-RS seems more suitable in terms of overhead. TPMI is required for DL grant. For non-coherent combining PDSCH RE puncturing is required to avoid CRS interference. The UE must be aware of active COMP set. For non-coherent combining and TDM transmission either reusing R8 CRS or UE-specific RS with cell-specific frequency shift is reasonable. For non-coherent combining and FDM transmission reuse of R8 cell-specific RS for PDSCH demod-RS seems more suitable in terms of overhead. 
         [0017]    UE awareness of active COMP set for coherent combining with FDM does not require fixed RE puncturing corresponding to the other 2 CRS frequency shifts. This awareness can be made UE-specific for only UEs configured for COMP or cell-specific. Active-set-dependent RE puncturing corresponding to the interfering CRS frequency shifts only is required and must be UE specific. 
         [0018]    Generally the active COMP set can be cell-specific or UE-specific. If cell-specific some UEs are configured for COMP with the same active set and some are not. If UE-specific the members of the active COMP set are UE-specific. 
         [0019]      FIG. 2  is a flow chart  200  illustrating the decision path of this invention. Flow chart  200  begins with start block  201 . Test block  202  determines whether coherent combining is selected. If coherent combining is selected (Yes at test block  202 ), then test block  203  determines if Time Division Multiplexing is selected. If Time Division Multiplexing is selected (Yes at test block  203 ), then in block  204  PDSCH RE is not required, in block  205  the UE need not be aware of the COMP set and in block  206  the transmission uses a UE specific RS for PDSCH demod-RS. Flow chart  200  then ends at end block  215 . If Frequency Division Multiplexing is selected (No at test block  203 ), then in block  207  PDSCH RE is required, in block  208  the UE must be aware of the COMP set and in block  208  the transmission reuses a Cell specific RS for PDSCH demod-RS. Flow chart  200  then ends at end block  215 . 
         [0020]    If non-coherent combining is selected (No at test block  202 ), then in block  210  PDSCH RE is required and in block  211  the UE must be aware of the COMP set. Test block  212  determines if Time Division Multiplexing is selected. If Time Division Multiplexing is selected (Yes at test block  212 ), then in block  213  the transmission use an R8 cell-specific reference signal of a UE specific RS. Flow chart  200  then ends at end block  215 . If Frequency Division Multiplexing is selected (No at test block  212 ), then in block  214  the transmission reuses a Cell specific RS for PDSCH demod-RS. Flow chart  200  then ends at end block  215 .