An Orthogonal Frequency Division Multiplexing (OFDM) technology is a multi-carrier modulation communication technology in essence and is one of the core technologies for the 4th generation mobile communication. In the frequency domain, the multi-path channel of OFDM is characterized by frequency selective fading. To overcome such fading, a channel is divided into multiple sub-channels in the frequency domain, the characteristic of the frequency spectrum of every sub-channel is approximately flat, and every sub-channel of OFDM is orthogonal with each other. Therefore, the overlap of frequency spectrums of sub-channels is allowed, so that the frequency spectrum resource can be used to the greatest extent.
A Long Term Evolution (LTE) system is an important program of the 3rd Generation Partner Organization. FIG. 1 shows a frame structure under a Frequency Division Duplex (FDD) mode in an LTE system. As shown in FIG. 1, a 10 ms radio frame comprises twenty slots of a length of 0.5 ms, which are numbered #0-#19. A slot 2i and slot 2i+1 comprise a subframe i of a length of 1 ms. When the LTE system uses a subframe with a normal cyclic prefix, a slot includes 7 uplink/downlink signals and has a length of 7 uplink/downlink signals; when the LTE system uses a subframe with an extended cyclic prefix, a slot includes 6 uplink/downlink signals and has a length of 6 uplink/downlink signals. A Resource Element (RE) is a subcarrier in an OFDM symbol. If the LTE system uses a subframe with a normal cyclic prefix, then 12 contiguous subcarriers and 7 contiguous OFDM symbols constitute a downlink Resource Block (RB); if the LTE system uses a subframe with an extended cyclic prefix, then 12 contiguous subcarriers and 6 contiguous OFDM symbols constitute an RB which is 180 kHz in the frequency domain and has a time length of a normal slot in the time domain, as shown in FIG. 2. In terms of resource allocation, the resource is allocated by a unit of a resource block.
The LTE system supports the application of a 4-antenna Multiple-Input Multiple-Output (MIMO) system, and a corresponding antenna port #0, antenna port #1, antenna port #2 and antenna port #3 use full-bandwidth Cell-Specific Reference Signals (CRSs). When the cyclic prefix of a subframe is a normal cyclic prefix, the position of a CRS in a physical resource block is shown as in FIG. 3a; when the cyclic prefix of a subframe is an extended cyclic prefix, the position of the CRS in a physical resource block is shown as in FIG. 3b. In addition, there is also a UE-specific reference signal, which is only transmitted at the time and frequency domain position where a UE-specific physical downlink shared channel (PDSCH) is located, wherein the functions of the CRS include the measurement of the downlink channel quality and estimation (demodulation) of the downlink channel.
A base station needs to measure the position of a UE in a cell, so that it can perform configuration and scheduling for the UE effectively. At present, the CRS is configured to measure the UE, but due to the semi-static configuration of the power of the CRS, the UE positioning performance is limited.
At present, the solution to the above problem is to perform positioning by is transmitting a position reference signal (PRSs), thus to ensure the positioning precision of the UE. The transmitting cycles of the PRS are 160 ms, 320 ms, 640 ms and 1280 ms, and the numbers of contiguous subframes transmitted with the PRS are 1, 2, 4 and 6. The PRS sequence rl,ns(m) is defined as per the following formula:
                    r                  l          ,                      n            s                              ⁡              (        m        )              =                            1                      2                          ⁢                  (                      1            -                          2              ·                              c                ⁡                                  (                                      2                    ⁢                    m                                    )                                                              )                    +              j        ⁢                  1                      2                          ⁢                  (                      1            -                          2              ·                              c                ⁡                                  (                                                            2                      ⁢                      m                                        +                    1                                    )                                                              )                      ,          ⁢      m    =    0    ,  1  ,  …  ⁢          ,                    2        ⁢                  N          RB          PRS                    -      1        ;  
wherein ns is an index of a slot in a radio frame, l is the index of an OFDM symbol in a slot, and NRBPRS is the PRS bandwidth configured by high layer signaling. The formula for generating a pseudorandom sequence c(i) is defined as follows:c(i)=(x1(i+Nc)+x2(i+Nc))mod 2x1(i+31)=(x1(i+3)+x1(i))mod 2x2(i+31)=(x2(i+3)+x2(i+2)+x2(i+1)+x2(i))mod 2;
wherein Nc=1600,x1(0)=1, x1(n)=0, n=1,2, . . . , 30
x2 is generated according to the initial value of a pseudorandom sequence which is cinit=Σn=030x2(n)·2n,
cinit calculated according to the following formula generates a pseudorandom sequence c(i) of every OFDM symbol:
                    c        init            =                                    2            10                    ·                      (                                          7                ·                                  (                                                            n                      s                                        +                    1                                    )                                            +              l              +              1                        )                    ·                      (                                          2                ·                                  N                  ID                  cell                                            +              1                        )                          +                  2          ·                      N            ID            cell                          +                  N          CP                      ,                  ⁢    wherein              N      CP        =          {                                    1                                              when              ⁢                                                          ⁢              the              ⁢                                                          ⁢              cyclic              ⁢                                                          ⁢              prefix              ⁢                                                          ⁢              is              ⁢                                                          ⁢              a              ⁢                                                          ⁢              normal              ⁢                                                          ⁢              cyclic              ⁢                                                          ⁢              prefix                                                            0                                              when              ⁢                                                          ⁢              the              ⁢                                                          ⁢              cyclic              ⁢                                                          ⁢              prefix              ⁢                                                          ⁢              is              ⁢                                                          ⁢              an              ⁢                                                          ⁢              extended              ⁢                                                          ⁢              cyclic              ⁢                                                          ⁢                              prefix                .                                                        
The PRS sequence rl,ns(m) is mapped to the complex modulation symbol ak,l(p) at the antenna port p of the slot ns as per the following formula, ak,l(p)=rl,ns(m′), wherein k is the index of a subcarrier on the OFDM symbol l.
When the cyclic prefix of the system is a normal cyclic prefix:
      k    =                  6        ⁢        m            +                        (                      6            -            l            +                          v              shift                                )                ⁢        mod        ⁢                                  ⁢        6                  l    =          {                                                                                                        3                    ,                    5                    ,                    6                                                                                                              if                      ⁢                                                                                          ⁢                                              n                        s                                            ⁢                      mod                      ⁢                                                                                          ⁢                      2                                        =                    0                                                                                                                    1                    ,                    2                    ,                    3                    ,                    5                    ,                    6                                                                                                              if                      ⁢                                                                                          ⁢                                              n                        s                                            ⁢                      mod                      ⁢                                                                                          ⁢                      2                                        =                                          1                      ⁢                                                                                          ⁢                      and                      ⁢                                                                                          ⁢                                              (                                                                              p                            =                            0                                                    ,                          1                                                )                                                                                                                                                              2                    ,                    3                    ,                    5                    ,                    6                                                                                                                                      if                        ⁢                                                                                                  ⁢                                                  n                          s                                                ⁢                        mod                        ⁢                                                                                                  ⁢                        2                                            =                                              1                        ⁢                                                                                                  ⁢                        and                        ⁢                                                                                                  ⁢                                                  (                                                                                    p                              =                              0                                                        ,                            1                            ,                            2                            ,                            3                                                    )                                                                                      ;                                                                        ⁢                                                  ⁢            m                    =          0                ,        1        ,        K        ,                                            2              ·                              N                RB                PRS                                      -                          1              ⁢                                                          ⁢                              m                ′                                              =                      m            +                          N              RB                              max                ,                DL                                      -                          N              RB              PRS                                          
wherein NRBmax,DL the maximum downlink bandwidth.
When the cyclic prefix of the system is an extended cyclic prefix:
      k    =                  6        ⁢        m            +                        (                      5            -            l            +                          v              shift                                )                ⁢        mod        ⁢                                  ⁢        6                  l    =          {                                                                                                        4                    ,                    5                                                                                                              if                      ⁢                                                                                          ⁢                                              n                        s                                            ⁢                      mod                      ⁢                                                                                          ⁢                      2                                        =                    0                                                                                                                    1                    ,                    2                    ,                    4                    ,                    5                                                                                                              if                      ⁢                                                                                          ⁢                                              n                        s                                            ⁢                      mod                      ⁢                                                                                          ⁢                      2                                        =                                          1                      ⁢                                                                                          ⁢                      and                      ⁢                                                                                          ⁢                                              (                                                                              p                            =                            0                                                    ,                          1                                                )                                                                                                                                                              2                    ,                    4                    ,                    5                                                                                                              if                      ⁢                                                                                          ⁢                                              n                        s                                            ⁢                      mod                      ⁢                                                                                          ⁢                      2                                        =                                          1                      ⁢                                                                                          ⁢                      and                      ⁢                                                                                          ⁢                                              (                                                                              p                            =                            0                                                    ,                          1                          ,                          2                          ,                          3                                                )                                                                                                                  ⁢                                                  ⁢            m                    =          0                ,        1        ,        K        ,                                                            2                ·                                  N                  RB                  PRS                                            -                              1                ⁢                                                                  ⁢                                  m                  ′                                                      =                                          m                +                                  N                  RB                                      max                    ,                    DL                                                  -                                                      N                    RB                    PRS                                    ⁢                                                                          ⁢                  wherein                  ⁢                                                                          ⁢                                      v                    shift                                                              =                                                (                                                            ∑                                                                        i                          ″                                                =                        0                                            7                                        ⁢                                                                  2                                                  i                          ″                                                                    ⁢                                              c                        ⁡                                                  (                                                                                    i                              ″                                                        +                                                          8                              ⁢                                                              ⌊                                                                                                      n                                    s                                                                    2                                                                ⌋                                                                                                              )                                                                                                      )                                ⁢                mod                ⁢                                                                  ⁢                6                                              ;                    
wherein vshift is the initial frequency domain position of the PRS in a physical resource block, “└ ┘” represents rounding down. According to cinit=NCellID(NCellID represents the identity of a cell), every radio frame generates a pseudorandom sequence c(i″), and the time-frequency position of a PRS in a physical resource block is as shown in FIG. 4a and FIG. 4b. As the initial frequency domain position vshift of the PRS in the physical resource block is generated randomly, it's not good for reducing the interference of a neighboring cell through cell layout.
In addition, in the existing solutions, a sequence rl,ns(m) with the fixed length 2×NRBPRS is generated first when the PRS is transmitted, then the transmitting sequence rl,ns(m′) is acquired according to the difference of NRBmax,DL−NRBPRS. However, as m decides the length of the pre-generated sequence rl,ns(m), rl,ns(m′) represents the PRS data transmitted, and m′=m+NRBmax,DL−NRBPRS shows that rl,ns(m′) is acquired from rl,ns(m), therefore when NRBmax,DL−NRBPRS is not equal to 0, m′ will certainly go beyond the scope of values of m, and as a result, rl,ns(m′) will be meaningless and effective PRS sequence data can not be acquired.
USPTO Backgrounds
USPTO Backgrounds