Abstract:
The invention discloses a TDM scheduling method for scheduling Start uplink transmission in a cellular radio communication system, comprising: obtaining relevant parameters including an Uplink pilot quality for each TDM User Equipment in a cell and an available TDM load for TDM UEs in the cell; determining a TDM group size as a number of TDM UEs to be scheduled to transmit simultaneously in a Transmission Time Interval, TTI, by using the obtained relevant parameters; and scheduling the TDM UEs according to the determined TDM group size. The TDM UEs refer to the UEs to be scheduled according to the TDM scheduling method of the present invention in the cell. With the solution of the invention, the UL system performance can be improved. The proposed solution is easy to be implemented.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to cellular radio communications, in particular to a Time Division Multiplexing (TDM) scheduling method and device for scheduling Uplink transmissions in a cellular radio communication system. 
       BACKGROUND 
       [0002]    In the cellular radio communication system, such as an Enhanced Uplink (EUL) system, User Equipments (UE) share the interference in uplink. In order to keep the stability as well as the uplink coverage of the system, there is an upper limit of uplink interference for each cell, which is usually in term of Rise over Thermal (RoT) target or Received Total Wideband Power (RTWP) target. The general EUL description is given in 3GPP specification, “3GPP TS 25.309 v6.6.0, FDD enhanced uplink; Overall description; Stage 2”. 
         [0003]    The uplink scheduler allocates the uplink interference among the UEs within the given interference limit by sending grants to UEs. With the current 3GPP specification, there are 2-ms and 10-ms Transmission Time Interval (TTI) lengths. For 10-ms TTI length, there are 4 Hybrid Automatic Repeat Request (HARQ) processes in a HARQ round trip, where the absolute grant is applied to all HARQ processes when it is received. For the 2-ms length, there are 8 HARQ processes in a HARQ round trip, where one absolute grant can be used to set the grant for all HARQ processes or one specific HARQ process. For both 2-ms and 10-ms TTI length, a serving or non-serving relative grant is used to adjust the grant for a HARQ process individually.  FIG. 1  illustrates how a relative grant adjusts the serving grant of a HARQ process. A serving or non-serving relative grant is interpreted relative to the UE power ratio in the previous TTI for the same hybrid ARQ process as the transmission which the relative grant will affect. Using the grant mechanism specified in the above 3GPP specification, the HARQ process specific grant setting is doable, which means that a UE can be scheduled to transmit by configuring non-zero grants in some HARQ processes and not to transmit by configuring zero grant in the rest HARQ processes. 
         [0004]    According to whether the HARQ process specific grant allocation is used or not, the uplink scheduling strategy can be divided into two types: Code Division Multiplexing (CDM) and TDM.  FIG. 2  illustrates a CDM scheduling example. With CDM scheduling scheme, all UEs are scheduled to transmit in each TTI.  FIG. 3  illustrates a 4-UE TDM scheduling example where only one UE are allowed to transmit in each TTI. 
         [0005]    As more advanced features, such as multiple receiver antennas, advanced receivers and Continuous Packet Connectivity (CPC), are introduced into the EUL system, the Uplink interface capability is improved. It is possible that the Uplink Uu capability is even larger than the UE capability as the evolving of the EUL system. In order to efficiently utilize the UL capability of Uu interface and serve more UEs, one or multiple rather than always single UE may be scheduled to transmit simultaneously in one TTI with TDM scheduling. 
         [0006]    In other words, a group of UEs may be allowed to transmit for each HARQ process instead of that always single UE is allowed to transmit in one TTI with TDM scheduling in order to maximize the system performance. In Patent No. U.S. Pat. No. 7,047,016, Method and Apparatus for Allocating Uplink Resources in a MIMO Communication System, the UEs are grouped based on the channel response by estimating the performance of all sub-hypothesis and channel response and a particular order is selected to process the received signals of these UEs for better Successive Interference Cancellation (SIC) effect. 
         [0007]    The existing scheduling proposals in MU-MIMO area rely too much on the channel response measurement which means the high cost to use them in the real product because: 
         [0008]      1 ) The channel response measurement should be introduced in physical layer and the channel correlation between different UEs should be estimated, which not only means a high implementation complexity but also a high computation complexity; 
         [0009]    2) The interaction between Media Access Control (MAC) scheduler and physical layer is increased which results in the flexibility loss of MAC scheduler. 
         [0010]    Another problem is that since the channels of all UEs are changing very fast, the channel measurement accuracy and delay weaken the gain by to such kinds of complex solutions. 
       SUMMARY 
       [0011]    This invention proposes a TDM scheduling method of low complexity for scheduling of TDM UEs in a cell, wherein the TDM UEs refer to the UEs to be scheduled according to the TDM scheduling method of the present invention in the cell. Instead of scheduling based on using the explicit channel response as shown in the prior arts, this invention uses scheduling parameters, such as, the UL pilot quality (e.g. one or more of DPCCH CINR, DPCCH SINR, DPCCH RSCP or DPCCH SNR) to estimate the number of TDM UEs that may be scheduled to transmit simultaneously in one TTI together with other inputs such as the available TDM load, the UL receiver capability and quality of service (QoS). 
         [0012]    In one aspect of the invention, a TDM scheduling method for scheduling uplink transmission in a cellular radio communication system is provided, which includes: obtaining relevant parameters including an Uplink pilot quality for each TDM UE in a cell and an available TDM load, for TDM UEs in the cell; determining a TDM group size as a number of TDM UEs to be scheduled to transmit simultaneously in a TTI by using the obtained relevant parameters; and scheduling the TDM UEs according to the determined TDM group size. 
         [0013]    In a further aspect of the invention, a TDM scheduling device for scheduling uplink transmission in a cellular radio communication system is provided, which includes: an obtaining module for obtaining relevant parameters including an Uplink pilot quality for each TDM UE in a cell and an available TDM load for TDM UEs in the cell; a determining module for determining a TDM group size as a number of TDM UEs to be scheduled to transmit simultaneously in a TTI by using the obtained relevant parameters; and a scheduling module for scheduling the TDM UEs according to the determined TDM group size. 
         [0014]    The invention also proposes a computer program product containing a computer readable medium having thereon computer program code means adapted, when the program is loaded onto a computing apparatus, to make the computing apparatus execute the TDM scheduling method according to the invention. Meanwhile, the invention proposes a computer program, distributable by electronic data transmission, containing computer program code means adapted, when the program is loaded onto a computing apparatus, to make the computing apparatus execute the TDM scheduling method according to the invention. 
         [0015]    With the solution of the invention, the UL system performance can be improved. And the proposed solution is easy to be implemented. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    In the following section, the invention will be described with reference to exemplary embodiments illustrated in the drawings, in which: 
           [0017]      FIG. 1  illustrates Timing relation for Relative Grant (10-ms TTI) in prior art; 
           [0018]      FIG. 2  illustrates a CDM scheduling example with 4 UEs (2-ms TTI) in prior art; 
           [0019]      FIG. 3  illustrates a 4-UEs TDM scheduling example with singe UE per TTI in prior art; 
           [0020]      FIG. 4  illustrates a TDM scheduling method in EUL system of the present invention; 
           [0021]      FIG. 5  illustrates an exemplary embodiment for performing the step of determining a TDM group size; 
           [0022]      FIG. 6  illustrates a schematic diagram of a cellular radio communication system; 
           [0023]      FIG. 7  illustrates a structural block diagram of a TDM scheduling device in the present invention; and 
           [0024]      FIG. 8  illustrates a structural block diagram of the determining module in the TDM scheduling device shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Embodiments of the present invention will be described by referring to the accompanying drawings. 
         [0026]      FIG. 4  illustrates a TDM scheduling method in a EUL system of the present invention. As illustrated in step  11 , relevant parameters for a certain cell are obtained. The relevant parameters include an Uplink pilot quality for each TDM UE in the cell, such as one or more of DPCCH CINR, DPCCH SINR, DPCCH RSCP or DPCCH SNR, and an available 
         [0027]    TDM load for TDM UEs in the cell. In step  12 , a TDM group size is determined by using the relevant parameters obtained in step  11 . The TDM group size is defined as the number of TDM UEs to be scheduled to transmit simultaneously in a certain TTI. In step  13 , the TDM UEs are scheduled according to the TDM group size determined in step  12 . 
         [0028]      FIG. 5  illustrates an exemplary embodiment for performing the step of determining a TDM group size. In step  21 , a group size range is determined according to the uplink Uu capability and the TDM UEs are distributed into different groups with the group sizes within the group size range, wherein a certain UE can be distributed in multiple groups; In step  22 , for each group, the available TDM load is tentatively allocated to each TDM UE in the group according to a given load allocation strategy, and then the maximum reachable rate of each group is estimated using Uplink pilot quality for each TDM UE in the group and a given Transport Format Table; in step  23 , an average maximum reachable rate for all groups with same TDM group size is calculated based on the estimated maximum reachable rate for each group; and in step  24 , the TDM group size is determined as the group size of the group with a maximal average maximum reachable rate. 
         [0029]    In particular, an example is illustrated as follows. Assume there are N TDM UEs in a certain cell. The number of TDM UEs that should be scheduled to transmit in , a TTI is referred as TDM group size in the following. The TDM group size can be estimated by the following steps: 
         [0030]    Step 1: List a part of or all possible TDM UE groups with the groupSize=1, 2, 3, . . . , M (M≦N) , where M is the maximum TDM group size based on the UL network capability, which should be a constant value for a given network. 
         [0031]    Step 2: Estimate the maximum reachable rate for each group. 
         [0032]    a. For a certain group, assume the available TDM load for a TDM UE in this group is L TDM /groupSize, where groupSize is the number of TDM UEs in this group. 
         [0033]    b. Estimate the maximum reachable rate for each TDM UE in this group and the maximum reachable rate of this group by summing up the maximum reachable rates of all TDM UEs in this group, based on the algorithm described hereinafter. 
         [0034]    Step 3: For all groups with the same groupSize, calculate the average maximum reachable rate based on the estimated maximum reachable rate according to Step 2. 
         [0035]    Step 4: Determine the TDM group size. The TDM group size is equal to the group size with a maximal average maximum reachable rate calculated from Step 3. 
         [0036]    The TDM scheduler should schedule the number of TDM UEs to transmit simultaneously in the TTI according to the group size determined in step 4. 
         [0037]    The TDM group size may be updated in various ways. For example, the TDM group size is updated by repeating the above steps as the available TDM load varies. Alternatively, the TDM group size is updated periodically by repeating the above steps. 
         [0038]    The following descriptions give an illustration for the algorithm that may be used during the implementation. The available TDM load for TDM UEs in a certain cell can be estimated in the following formula (1): 
         [0000]        L   TDM   =L   MAX   −L   dch   −L   edch,CDM −L hsdpcch   −L   other    (1)
 
         [0039]    Where L MAX  is the maximum available load in the cell, L DCH  is the load taken by DCH channels of all UEs, L edch,CDM  is the load taken by the EUL UEs in CDM scheduling mode, L hsdpcch  is the load taken by HS-DPCCH and L other  is the load taken by the unmonitored interference. 
         [0040]    According to the load estimation formula for the i-th UE can be estimated by Formula (2): 
         [0000]    
       
         
           
             
               
                 
                   
                     L 
                     i 
                   
                   = 
                   
                     
                       
                         γ 
                         dpcch 
                         i 
                       
                       · 
                       
                         ( 
                         
                           1 
                           + 
                           
                             Δ 
                             edpcch 
                           
                           + 
                           
                             Δ 
                             edch 
                             i 
                           
                         
                         ) 
                       
                     
                     
                       antGain 
                       + 
                       
                         
                           ( 
                           
                             1 
                             - 
                             α 
                           
                           ) 
                         
                         · 
                         
                           γ 
                           dpcch 
                           i 
                         
                         · 
                         
                           ( 
                           
                             1 
                             + 
                             
                               Δ 
                               edpcch 
                             
                             + 
                             
                               Δ 
                               edch 
                               i 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0041]    Where L i  is the allocated load for the i-th UE, γ i   dpcch  is the DPCCH CINR target or measured DPCCH CINR of the i-th UE, Δ edpcch  is the power offset of E-DPCCH UEs, Δ i   edch  is the E-DCH power offset of the i-th UE, antGain is the antenna gain and α is the orthogonality factor of this UE. 
         [0042]    When a certain TDM load is allocated for the i-th UE, the maximum E-DCH power offset for this UE can be calculated by Formula (3) : 
         [0000]    
       
         
           
             
               
                 
                   
                     Δ 
                     edch 
                     i 
                   
                   = 
                   
                     
                       
                         
                           L 
                           i 
                         
                         · 
                         antGain 
                       
                       
                         
                           γ 
                           dpcch 
                           i 
                         
                          
                         
                           ( 
                           
                             1 
                             - 
                             
                               L 
                               i 
                             
                             + 
                             
                               α 
                               · 
                               
                                 L 
                                 i 
                               
                             
                           
                           ) 
                         
                       
                     
                     - 
                     1 
                     - 
                     
                       Δ 
                       edpcch 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0043]    With the maximum E-DCH power offset by Formula (3), the maximum E-TFC that the UE is allowed to use can be looked up from a given E-TFC table. The relationship between the maximum E-DCH power offset and a Transport block size is defined in the E-TFC table, and then the maximum reachable rate for the i-th TDM UE in the group is calculated from the Transport block size. 
         [0044]    Because the UL pilot quality measurement is already implemented (e.g. The DPCCH CINR is measured per slot for inner loop power control) in the existing EUL system, the complex implementation and computation can be saved. 
         [0045]    As shown in  FIG. 6 , a schematic diagram of a cellular radio communication system  100  is provided, including a radio base station  101  serving a cell, which is alternatively referred to as Node B, and UEs (such as  102   a ,  102   b  and  102   c ) operating in the cell. A downlink transmission  103  generally refers to communications in a direction from the radio base station to the UEs. An uplink transmission  104  generally refers to communications in a direction from the UEs to the radio base station. The radio base station  101  contains a TDM scheduling device  200  for scheduling uplink transmissions in a cellular radio communication system. 
         [0046]      FIG. 7  illustrates a structural block diagram of a TDM scheduling device  200  according to an embodiment of the present invention. The TDM scheduling device  200  includes: an obtaining module  201  for obtaining relevant parameters including an Uplink pilot quality for each 
         [0047]    TDM UE in a cell and an available TDM load for TDM UEs in the cell; a determining module  202  for determining a TDM group size by using the obtained relevant parameters, wherein the TDM group size is defined as a number of TDM UEs to be scheduled to transmit simultaneously in one TTI; and a scheduling module  203  for scheduling the TDM UEs according to the determined TDM group size. 
         [0048]    Preferably, as  FIG. 8  shows, the determining module  202  may further include: a first determining unit  2001 , adapted to determine a group size range according to Uplink network capability and distribute the TDM UEs into different groups with various group sizes; an estimating unit  2002 , adapted to estimate a maximum reachable rate for each group by using the Uplink pilot quality for each TDM UE in the group and a E-TFC Table; a calculating unit  2003 , adapted to calculate an average maximum reachable rate for all groups with the same TDM group size based on the estimated maximum reachable rate for each group; and a second determining unit  2004 , adapted to determine the TDM group size as the group size of the group with a maximal average maximum reachable rate. 
         [0049]    Preferably, the estimating unit  2002  may further include: an allocating sub-unit, adapted to, for each group, tentatively allocate an available TDM load of the cell to each TDM UE in the group according to a given load allocation strategy; and an estimating sub-unit, adapted to estimate a maximum reachable rate for each TDM UE in each group, and a maximum reachable rate of each group by summing up the maximum reachable rates of all TDM UEs in the group. 
         [0050]    Although the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention. 
         [0051]    Abbreviation terms: 
         [0052]    DCH: Dedicated Channel 
         [0053]    E-DCH: Enhanced Dedicated Channel 
         [0054]    DPCCH: Dedicated Physical Control Channel 
         [0055]    E-DPCCH: Enhanced Dedicated Physical Control Channel 
         [0056]    CINR: Carrier to Interference plus Noise Ratio 
         [0057]    RSCP: Received Signal Code Power 
         [0058]    SNR: Signal-Noise Ratio 
         [0059]    TTI: Transmission Time Interval 
         [0060]    TDM: Time Division Multiplexing 
         [0061]    DM: Code Division Multiplexing 
         [0062]    UL: Uplink 
         [0063]    EUL: Enhanced Uplink 
         [0064]    SIC: Successive Interference Cancellation 
         [0065]    E-TFC: E-DCH Transport Format Combination 
         [0066]    CQI: Channel Quality Indicator 
         [0067]    SINR: Signal to Interference plus Noise Ratio 
         [0068]    MU-MIMO: Multi-User Multi-Input-Multi-Output 
         [0069]    UE: User Equipment 
         [0070]    HARQ: Hybrid Automatic Repeat Request 
         [0071]    RoT: Rise Over Thermal 
         [0072]    RTWP: Received Total Wideband Power 
         [0073]    CPC: Continuous Packet Connectivity