CN103929274A - Coordinated multi-point transmission precoding method - Google Patents

Abstract

The invention discloses a coordinated multi-point transmission downlink precoding algorithm for timing synchronous reciprocity errors. In the application scene where the timing synchronous reciprocity errors are approximately constant, the errors can be supplemented by the algorithm when precoding vectors or matrixes are designed through MMSE channel estimation, RVQ quantized feedback, LS error estimation and linear interpolation. In the application scene where the timing synchronous reciprocity errors change in real time, the lower bound of SLNR can be averaged to the maximum degree by the algorithm through a probability density function of the errors, and then robust precoding vectors or matrixes are acquired. In a coordinated multi-point transmission system in a TDD mode, compared with a traditional precoding algorithm, the algorithm can avoid the influence of the timing synchronous reciprocity errors on the orthogonality between the precoding vectors or matrixes, better eliminate interference between users or cells, and increase the capacity of the system.

Description

A kind of cooperative multipoint transmission method for precoding

Technical field

The invention belongs to wireless communication field, relate in particular to and adopt OFDM (Orthogonal Frequency Division Multiplexing, OFDM) cooperation communication system of the time division duplex of technology (Time Division Duplex, TDD) pattern.

Background technology

In recent years, in order further to improve spectrum efficiency, to improve Cell Edge User throughput, cooperative multipoint transmission (Coordinated Multi-point Transmission, CoMP) becomes the study hotspot of the communications field.Researcher design and improved a large amount of precoding algorithms, to eliminate completely or to reduce by a relatively large margin the interference between multi-user and between co-frequency cell.Because most of precoding algorithm is supposed based on ideal communication channel information (Channel Side Information, CSI), therefore the accuracy of CSI becomes the key that ensures associating precoding algorithm performance.In CoMP, tdd mode, based on channel reciprocity feature, is estimated to obtain the CSI of down channel by ascending pilot frequency, thereby has avoided extensive quantification feedback overhead and the error of Frequency Division Duplexing (FDD) (Frequency Division Duplex, FDD) pattern.Therefore, tdd mode is considered to the important development direction of CoMP.

In actual application, up-downgoing equivalent channel, except comprising the transmission channel in hole, also comprises base band and the radio frequency part of transmitting terminal and receiving terminal.Therefore, the up-downgoing equivalent channel of tdd mode is generally imperfect reciprocity, thereby the performance of precoding is significantly reduced.

Summary of the invention

The imperfect reciprocity error of channel that the object of the invention is partially to cause when synchronous provides a kind of cooperative multipoint transmission method for precoding.

For convenience of description, first symbol is made an explanation:

() ^hwith () ^-1represent respectively conjugate transpose and matrix inversion, || with || || represent to get respectively the 2-norm of the modulus of complex number and amount of orientation, for Kronecker product (Kronecker product), diag{} is diagonal matrix, and E{} represents to get desired value, I _xrepresent the unit matrix that order is x.

The present invention adopts the CoMP system under the tdd mode of OFDM, has B cooperative base station in system, the individual base station assembling n of office _troot antenna, has M user in system, each with assembling per family single antenna.System adopts OFDM channel to be divided on frequency domain to N sub-channels, i.e. N subcarrier.At k sub-channels, cooperative base station can be expressed as to the equivalent up-downgoing channel of user m:

wherein, h _{mb_UL}(k) represent the equivalent up channel between cooperative base station b and user m, represent the equivalent down channel between cooperative base station b and user m, H _{m_UL}represent the up channel matrix of user m to all base stations, H _{n_UL}represent the up channel matrix of user n to all base stations.Total emission power p is averagely allocated to each user, and user m can be expressed as at the reception signal of k word channel $r_m=\sqrt{\frac{p}{M}}{H}_{m\_\mathrm{DL}}{v}_m{s}_m+\underset{j=1,j\≠m}{\overset{M}{\mathrm{\Σ}}}\sqrt{\frac{p}{M}}{H}_{m\_\mathrm{DL}}{v}_j{s}_j+n_{\mathrm{noise}},$ Wherein, s _mfor sending to the signal of user m, s _jfor sending to the signal of user j, v _mfor the precoding vector of user m, v _jfor the precoding vector of user j, n _noisefor additivity white complex gaussian noise.For expressing conveniently, in this patent, formula all omits sub-channel index k.

Fast Fourier transform (Fast Fourier Transformation, FFT) the window starting point of OFDM is positioned at the Cyclic Prefix (Cyclic Prefix, CP) without intersymbol interference, and Timing Synchronization error d meets L-N _cP≤ d≤0, wherein, L represents maximum multipath time delay, N _cPrepresent CP length.Described Timing Synchronization error d causes phase rotating exp (j2 π kd/N).

At k sub-channels, cooperative base station b can be expressed as to the up-downgoing equivalent channel of user m $\begin{array}{c}{h}_{\mathrm{mb}\_\mathrm{UL}}=h_{\mathrm{mb}}\×e^{-j2\mathrm{\π}{\mathrm{kd}}_{\mathrm{mb}.\mathrm{UL}}/N}\\ h_{\mathrm{mb}\_\mathrm{DL}}=H_{\mathrm{mb}}\×e^{-j2\mathrm{\π}{\mathrm{kd}}_{\mathrm{mb}.\mathrm{DL}}/N}\end{array},$ Wherein, d _mb.ULrepresent up Timing Synchronization error, d _mb.DLrepresent descending Timing Synchronization error, represent that cooperative base station b, to transmission channel in the hole between user m, meets desirable reciprocity.Ignore path fading and the shadow fading of channel, only consider Rayleigh fading, h _mbin the separate and equal multiple Gaussian Profile CN (0,1) of obedience standard of each element.So the up-downgoing equivalent channel relation between cooperative base station b and user can be expressed as $h_{\mathrm{mb}\_\mathrm{DL}}=h_{\mathrm{mb}\_\mathrm{UL}}{e}^{-j2\mathrm{\π}{k}_{(d_{\mathrm{mb}.\mathrm{DL}}-d_{\mathrm{mb}.\mathrm{UL}})/N}}.$

Definition φ _mb=-2 π k Δ d _mb/ N is the Timing Synchronization heterogeneite error of up-downgoing equivalent channel between cooperative base station b and user m, wherein, and Δ d _mb=(d _mb.DL-d _mb.UL).Descending equivalent channel between cooperative base station and user m can be expressed as the product of up channel and Timing Synchronization reciprocity error, i.e. H _{m_DL}=H _{m_UL}Φ _m, wherein, represent the actual channel reciprocity error matrix of user m and all base stations.

For multi-multipoint CoMP system, Timing Synchronization reciprocity error can cause traditional precoding performance significantly to reduce.For Timing Synchronization reciprocity error characteristics, this patent has proposed cooperative multipoint transmission method for precoding, based on the different CoMP system applies scene of two classes, the method for precoding that described cooperative multipoint transmission method for precoding can be divided into the method for precoding based on estimation compensation and distribute based on error.

Object of the present invention realizes as follows:

S1, according to the channel condition between send and receive antenna, choose the antenna p of user m and the antenna q of base station b as with reference to antenna pair;

S2, choose n subcarrier as with reference to subcarrier, wherein, 1≤n≤N;

S3, for subchannel k, estimate up channel by ascending pilot frequency quantize feedback by user and obtain down channel wherein, represent the up channel between the antenna p of user m and the antenna q of base station b on k subcarrier, represent the down channel between the antenna p of user m and the antenna q of base station b on k subcarrier;

S4, utilize Timing Synchronization reciprocity error each with reference to the linear relationship on subchannel, by least square (Least Squares, LS) from n up-downgoing with reference to the Timing Synchronization reciprocity error obtaining subchannel between subchannel k user m and base station b estimate, specific as follows:

Channel between antenna and the antenna of base station b of S41, supposition user m is wherein, 1≤a≤m;

S42, when time, select the antenna p of base station b as boresight antenna, described in S31 for calibration channel, wherein, 1≤p≤n, q ≠ p;

S43, for standard carrier Q _k, base station is estimated to obtain the descending equivalent channel between user m and the antenna p of base station b by the Minimum Mean Square Error based on ascending pilot frequency, and feeds back to base station b by RVQ, obtains the up-downgoing equivalent channel of n calibration carrier wave: ${\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p=[{\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\left(a_1\right)...{\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\left(a_n\right)],{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p=[{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\left(a_1\right)...{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\left(a_n\right)],$ Can obtain ${\mathrm{\Φ}}_{\mathrm{mb}}^p=\mathrm{diag}\left({\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\right)\mathrm{diag}{\left({\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\right)}^{-1};$

Described in S44, taking-up S43 the phase place of middle diagonal element d _mb=diag (Φ _mb(a ₁) ... Φ _mb(a _m)) diag (2 π a ₁/ N...-2 π a _m/ N) ^-1;

S45, according to obtaining described in S44 for subcarrier k, user m estimates to obtain with the reciprocity of synchronizeing of base station b

S46, obtain subcarrier k, the Timing Synchronization reciprocity estimation error of user m and other base stations wherein, represent the channel reciprocity estimation error matrix of user m and all base stations, expression order is n _tunit matrix, n _trepresent each antenna for base station number, for Kronecker product;

S5, at precoding vector place, Timing Synchronization reciprocity error is compensated, the precoding vector of subchannel k user m can be expressed as $w_m~\max .\mathrm{eigenvector}\left({({\mathrm{\σ}}_{\mathrm{noise}}^{2}I+\underset{n=1,n\≠m}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\Ω}}_n)}^{-1}{\mathrm{\Ω}}_m\right),$ Wherein, ${\mathrm{\Ω}}_n={\widehat{\mathrm{\Φ}}}_n^H{H}_{n\_\mathrm{UL}}^H{H}_{n\_\mathrm{UL}}{\widehat{\mathrm{\Φ}}}_n,$ ${\mathrm{\Ω}}_m={\widehat{\mathrm{\Φ}}}_m^H{H}_{m\_\mathrm{UL}}^H{H}_{m\_\mathrm{UL}}{\widehat{\mathrm{\Φ}}}_m,$ h _{m_UL}represent the up channel matrix of user m to all base stations, H _{n_UL}represent the up channel matrix of user n to all base stations;

S6, as Timing Synchronization reciprocity error φ in CoMP system _mbchange rapidly in time domain, be difficult to estimate and follow the trail of, adopt the precoding algorithm distributing based on error, specific as follows: the k sub-channels precoding vector of user m can be expressed as: v _m～max.eigenvector (E{M _m} ^-1e{Q _m),

w _m＝v _m/||v _m||

Wherein, $E\left\{M_m\right\}={\mathrm{\σ}}_{\mathrm{noise}}^{2}I+\underset{n=1,n\≠m}{\overset{M}{\mathrm{\Σ}}}E\left\{Q_n\right\},$

$E\left\{Q_m\right\}=E\left\{H_{m\_\mathrm{DL}}^H{H}_{m\_\mathrm{DL}}\right\}=E\left\{{\mathrm{\Φ}}_m^H{H}_{m\_\mathrm{UL}}^H{H}_{m\_\mathrm{UL}}{\mathrm{\Φ}}_m\right\},$ H _{m_UL}can estimate to obtain by ascending pilot frequency, pilot tone estimates to adopt MMSE, $E\left\{{\mathrm{\Φ}}_m^H{H}_{m\_\mathrm{UL}}^H{H}_{m\_\mathrm{UL}}{\mathrm{\Φ}}_m\right\}\≈E\left\{{\mathrm{\Φ}}_m^H\right\}{H}_{m\_\mathrm{UL}}^H{H}_{m\_\mathrm{UL}}E\left\{{\mathrm{\Φ}}_m\right\}$ Wherein, $E\left\{{\mathrm{\Φ}}_m\right\}=\mathrm{diag}\left\{E\right\{e^{j{\mathrm{\φ}}_{m,1}}\},...E\{e^{j{\mathrm{\φ}}_{m,B}}\left\}\right\}\⊗I_{n_t},E\left\{e^{j{\mathrm{\φ}}_{m,b}}\right\}=E\left\{{\cos \mathrm{\φ}}_{m,b}\right\}+\mathrm{jE}\left\{{\sin \mathrm{\φ}}_{m,b}\right\},$ According to the probability distribution of the Timing Synchronization heterogeneite error of user m, just can pass through φ _m,bprobability density function and functional integration obtain E{ Φ _m.

Further, the right selection standard of reference antenna is that channel condition between antenna pair is better than other antennas pair described in S1, wherein, s _mrepresent the pilot signal that user m sends, air traffic channel between antenna p and the antenna q of base station b of expression user m, represent that the antenna p of user m is to the reception noise of the antenna q of base station b, represent by the air traffic channel between antenna j and the antenna l of base station b of user m, represent that the antenna j of user m is to the reception noise of the antenna l of base station b.

Further, described in S3, pilot tone estimation adopts least mean-square error (Minimum Mean Square Error, MMSE) estimation, described quantification feedback employing random vector quantification (Random Vector Quantization, RVQ).

The invention has the beneficial effects as follows:

By the cumulative distribution function curve of power system capacity, can find that traditional SLNR is very responsive to Timing Synchronization reciprocity error, be subject to it to affect power system capacity and significantly reduce, and the precoding algorithm that this patent proposes slows down the performance loss that this error causes, and has promoted precoding performance.

Brief description of the drawings

Fig. 1 is tdd mode cooperative multicast system, is practical application scene of the present invention.In Fig. 1, also comprise the equivalent up-downgoing channel architecture of base station b and user m.

Fig. 2 be under desirable channel reciprocity condition and Timing Synchronization reciprocity error condition under the simulation result of the average achievable rate of user and its theory lower-bound.

Fig. 3 is the multi-base station cooperative downlink transfer structured flowchart that adopts this patent precoding algorithm.

Fig. 4 is 2 base station 2 users' cooperative multicast system scene, and the Performance Ratio of the precoding that traditional SLNR precoding algorithm and this patent propose.

Fig. 5 is 3 base station 3 users' cooperative multicast system scene, and the Performance Ratio of the precoding that traditional SLNR precoding algorithm and this patent propose.

Embodiment

Below in conjunction with accompanying drawing and example, the invention will be further described, and embodiments of the present invention include but not limited to following example.

The cooperative multicast system of tdd mode of the present invention, it is characterized by and adopt OFDM with opposing multipath fading, OFDM symbol cyclic prefix length is greater than maximum multipath time delay, and the FFT starting point of OFDM is positioned at the Cyclic Prefix without intersymbol interference, i.e. Timing Synchronization error residue sampling d=" τ/T _s", meet " L/T _s"-N _cP≤ d≤0, the remaining d of this Timing Synchronization only causes phase rotating exp (j2 π kd/N), and wherein, τ represents actual Timing Synchronization error residue, and d represents the sampling of Timing Synchronization error residue, T _srepresent sampling period, L represents maximum multipath time delay, N _cPrepresent circulating prefix-length, k represents k subcarrier, the total sub-carrier number of N.

As shown in Figure 1, make cooperative base station number B=2, number of users M=2, cooperative base station antenna number n _t=2, user is single antenna.The sub-carrier number of OFDM is N=1024, and circulating prefix-length is N _cp=144, maximum path time delay is L=(N _cp/ 2).

User, to the up channel of cooperative base station, carries out MMSE by the block pilot tone in the detection reference signal (Sounding ReferenceSignal, SRS) that user is sent and estimates to obtain.Cooperative base station, to user's down channel, supposes that user can obtain desirable down channel, quantizes (Random Vector Quantization, RVQ) simultaneously down channel is quantized to feedback by random vector.With cooperative base station 1,, 2 to user 1 down channels for example, quantize code book C by 2 ^tthe multiple unit vector of individual 4 dimension forms wherein T is for quantizing number of bits of feedback, and T is larger, and quantification feedback error is less, conventionally makes T=8.Quantize feedback vector selection based on

${\hat{H}}_{1\_\mathrm{DL}}~\arg \underset{j=1,...,2^T}{\max }\left|H_{1\_\mathrm{DL}}{\hat{H}}_j^H\right|.$

Cooperative base station is being obtained after up-downgoing channel, just can calculate the situation of change of channel reciprocity error phase in time domain.As shown in Figure 4, if its error at time domain approximately constant, adopts the precoding algorithm based on estimation compensation, if its error in time domain real-time change, adopts the precoding algorithm distributing based on error.

For the precoding algorithm based on estimation compensation, first antenna of selecting collaboration base station is reference antenna, choose n sub-channels as with reference to channel, by least-squares estimation (Least quare, LS) at frequency domain the reciprocity error by other subchannel of reciprocity estimation error with reference to subchannel.If with reference to number of subchannels n=2, the Timing Synchronization reciprocity error of k subcarrier between user 1 and base station 1 can be expressed as

$e^{j{\widehat{\mathrm{\φ}}}_{11}}={\left(\frac{{\hat{h}}_{11\_\mathrm{DL}}\left(c_2\right)h_{11\_\mathrm{UL}}\left(c_1\right)}{h_{11\_\mathrm{UL}}\left(c_2\right){\hat{h}}_{11\_\mathrm{DL}}\left(c\right)1}\right)}^{k/(c_2-c_1)},$

User 1 can be expressed as at the precoding vector of subchannel k

$w_1~\max .\mathrm{eigenvector}\left({({\mathrm{\σ}}_{\mathrm{noise}}^{2}I+{\mathrm{\Ω}}_2)}^{-1}{\mathrm{\Ω}}_1\right),$

Wherein, ${\mathrm{\Ω}}_2={\widehat{\mathrm{\Φ}}}_2^H{H}_{2\_\mathrm{UL}}^H{H}_{2\_\mathrm{UL}}{\widehat{\mathrm{\Φ}}}_2,$ ${\mathrm{\Ω}}_1={\widehat{\mathrm{\Φ}}}_1^H{H}_{1\_\mathrm{UL}}^H{H}_{1\_\mathrm{UL}}{\widehat{\mathrm{\Φ}}}_1,$

${\widehat{\mathrm{\Φ}}}_1=\mathrm{diag}\{e^{j{\widehat{\mathrm{\φ}}}_{11}},...e^{j{\widehat{\mathrm{\φ}}}_{12}}\}\⊗I_2,$ ${\widehat{\mathrm{\Φ}}}_2=\mathrm{diag}\{e^{j{\widehat{\mathrm{\φ}}}_{21}},...e^{j{\widehat{\mathrm{\φ}}}_{22}}\}\⊗I_2,$

For the precoding algorithm distributing based on error, suppose the Timing Synchronization error of the up-downgoing equivalent channel between cooperative base station b and user m obedience is uniformly distributed U (Z _mb, 0), wherein Z _mb=N _cP-L _mb.By deriving, the Timing Synchronization reciprocity error phase φ between base station b and user m _mbprobability density function can be expressed as:

$f\left({\mathrm{\&phi;}}_{\mathrm{mb}}\right)=\left\{\begin{array}{cc}\mathrm{\&rho;}\frac{-{\mathrm{\&rho;\&phi;}}_{\mathrm{mb}}+Z_{\mathrm{mb}}}{Z_{\mathrm{mb}}^2}& \mathrm{if}0<{\mathrm{\&phi;}}_{\mathrm{mb}}\&le;\frac{Z_{\mathrm{mb}}}{\mathrm{\&rho;}}\\ \mathrm{\&rho;}\frac{{\mathrm{\&rho;\&phi;}}_{\mathrm{mb}}+Z_{\mathrm{mb}}}{Z_{\mathrm{mb}}^2}& \mathrm{if}\frac{Z_{\mathrm{mb}}}{\mathrm{\&rho;}}<{\mathrm{\&Delta;d}}_{\mathrm{mb}}\&le;\end{array}\right.,$ Wherein, ρ=N/2 π k.

Distribute according to this error, user 1 k sub-channels precoding vector can be expressed as:

$\begin{array}{c}{v}_1~\max .\mathrm{eigenvector}\left(E\right\{M_1{\}}^{-1}E\left\{Q_1\right\})\\ w_1=v_1/\left|\right|v_1\left|\right|\end{array},$

Wherein, $E\left\{M_1\right\}={\mathrm{\&sigma;}}_{\mathrm{noise}}^{2}I+E\left\{Q_2\right\}$

$E\left\{Q_1\right\}=E\left\{H_{1\_\mathrm{DL}}^H{H}_{1\_\mathrm{DL}}\right\}=E\left\{{\mathrm{\&Phi;}}_1^H{H}_{1\_\mathrm{UL}}^H{H}_{1\_\mathrm{UL}}{\mathrm{\&Phi;}}_1\right\}\&ap;E\left\{{\mathrm{\&Phi;}}_1^H\right\}{H}_{1\_\mathrm{UL}}^H{H}_{1\_\mathrm{UL}}E\left\{{\mathrm{\&Phi;}}_1\right\}.$ Meanwhile,

$E\left\{{\mathrm{\&Phi;}}_1\right\}=\mathrm{diag}\left\{E\right\{e^{j{\mathrm{\&phi;}}_{11}}\},E\{e^{j{\mathrm{\&phi;}}_{12}}\left\}\right\}\&CircleTimes;I_2,E\left\{e^{j{\mathrm{\&phi;}}_{11}}\right\}=E\left\{\cos {\mathrm{\&phi;}}_{11}\right\}+\mathrm{jE}\left\{\sin {\mathrm{\&phi;}}_{11}\right\},$

$E\left\{e^{j{\mathrm{\&phi;}}_{12}}\right\}=E\left\{\cos {\mathrm{\&phi;}}_{12}\right\}+\mathrm{jE}\left\{\sin {\mathrm{\&phi;}}_{12}\right\}.$

Make Z ₁₁=Z ₁₂=Z,

$\begin{array}{c}E\left\{\sin {\mathrm{\&phi;}}_{11}\right\}=E\left\{\sin {\mathrm{\&phi;}}_{12}\right\}=0\\ E\left\{\cos {\mathrm{\&phi;}}_{11}\right\}=E\left\{\cos {\mathrm{\&phi;}}_{12}\right\}=\frac{{2\mathrm{\&rho;}}^2}{Z^2}(1-\cos \left(\frac{Z}{\mathrm{\&rho;}}\right))\end{array}.$

Claims (3)

1. a cooperative multipoint transmission method for precoding, is characterized in that, comprises the following steps:

S1, according to the channel condition between send and receive antenna, choose the antenna p of user m and the antenna q of base station b as with reference to antenna pair;

S2, choose n subcarrier as with reference to subcarrier, wherein, 1≤n≤N;

S3, for subchannel k, estimate up channel by ascending pilot frequency quantize feedback by user and obtain down channel wherein, represent the up channel between the antenna p of user m and the antenna q of base station b on k subcarrier, represent the down channel between the antenna p of user m and the antenna q of base station b on k subcarrier;

S4, utilize Timing Synchronization reciprocity error each with reference to the linear relationship on subchannel, by least square (Least Squares, LS) from n up-downgoing with reference to the Timing Synchronization reciprocity error obtaining subchannel between subchannel k user m and base station b estimate, specific as follows:

Channel between antenna and the antenna of base station b of S41, supposition user m is wherein, 1≤a≤m;

S42, when time, select the antenna p of base station b as boresight antenna, described in S31 for calibration channel, wherein, 1≤p≤n, q ≠ p;

S43, for standard carrier Q _k, base station is estimated to obtain the descending equivalent channel between user m and the antenna p of base station b by the Minimum Mean Square Error based on ascending pilot frequency, and feeds back to base station b by RVQ, obtains the up-downgoing equivalent channel of n calibration carrier wave: ${\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p=[{\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\left(a_1\right)...{\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\left(a_n\right)],{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p=[{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\left(a_1\right)...{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\left(a_n\right)],$ Can obtain ${\mathrm{\&Phi;}}_{\mathrm{mb}}^p=\mathrm{diag}\left({\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\right)\mathrm{diag}{\left({\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\right)}^{-1};$

Described in S44, taking-up S43 the phase place of middle diagonal element d _mb=diag (Φ _mb(a ₁) ... Φ _mb(a _m)) diag (2 π a ₁/ N...-2 π a _m/ N) ^-1;

S45, according to obtaining described in S44 for subcarrier k, user m estimates to obtain with the reciprocity of synchronizeing of base station b

S46, obtain subcarrier k, the Timing Synchronization reciprocity estimation error of user m and other base stations wherein, represent the channel reciprocity estimation error matrix of user m and all base stations, expression order is n _tunit matrix, n _trepresent each antenna for base station number, for Kronecker product;

S5, at precoding vector place, Timing Synchronization reciprocity error is compensated, the precoding vector of subchannel k user m can be expressed as $w_m~\max .\mathrm{eigenvector}\left({({\mathrm{\&sigma;}}_{\mathrm{noise}}^{2}I+\underset{n=1,n\&NotEqual;m}{\overset{M}{\mathrm{\&Sigma;}}}{\mathrm{\&Omega;}}_n)}^{-1}{\mathrm{\&Omega;}}_m\right),$ Wherein, ${\mathrm{\&Omega;}}_n={\widehat{\mathrm{\&Phi;}}}_n^H{H}_{n\_\mathrm{UL}}^H{H}_{n\_\mathrm{UL}}{\widehat{\mathrm{\&Phi;}}}_n,$ ${\mathrm{\&Omega;}}_m={\widehat{\mathrm{\&Phi;}}}_m^H{H}_{m\_\mathrm{UL}}^H{H}_{m\_\mathrm{UL}}{\widehat{\mathrm{\&Phi;}}}_m,$ h _{m_UL}represent the up channel matrix of user m to all base stations, H _{n_UL}represent the up channel matrix of user n to all base stations;

S6, as Timing Synchronization reciprocity error φ in CoMP system _mbchange rapidly in time domain, be difficult to estimate and follow the trail of, adopt the precoding algorithm distributing based on error, specific as follows: the k sub-channels precoding vector of user m can be expressed as: v _m～max.eigenvector (E{M _m} ^-1e{Q _m),

w _m＝v _m/||v _m||

Wherein, $E\left\{M_m\right\}={\mathrm{\&sigma;}}_{\mathrm{noise}}^{2}I+\underset{n=1,n\&NotEqual;m}{\overset{M}{\mathrm{\&Sigma;}}}E\left\{Q_n\right\},$

$E\left\{Q_m\right\}=E\left\{H_{m\_\mathrm{DL}}^H{H}_{m\_\mathrm{DL}}\right\}=E\left\{{\mathrm{\&Phi;}}_m^H{H}_{m\_\mathrm{UL}}^H{H}_{m\_\mathrm{UL}}{\mathrm{\&Phi;}}_m\right\},$ H _{m_UL}can estimate to obtain by ascending pilot frequency, pilot tone estimates to adopt MMSE, $E\left\{{\mathrm{\&Phi;}}_m^H{H}_{m\_\mathrm{UL}}^H{H}_{m\_\mathrm{UL}}{\mathrm{\&Phi;}}_m\right\}\&ap;E\left\{{\mathrm{\&Phi;}}_m^H\right\}{H}_{m\_\mathrm{UL}}^H{H}_{m\_\mathrm{UL}}E\left\{{\mathrm{\&Phi;}}_m\right\}$ Wherein, $E\left\{{\mathrm{\&Phi;}}_m\right\}=\mathrm{diag}\left\{E\right\{e^{j{\mathrm{\&phi;}}_{m,1}}\},...E\{e^{j{\mathrm{\&phi;}}_{m,B}}\left\}\right\}\&CircleTimes;I_{n_t},E\left\{e^{j{\mathrm{\&phi;}}_{m,b}}\right\}=E\left\{{\cos \mathrm{\&phi;}}_{m,b}\right\}+\mathrm{jE}\left\{{\sin \mathrm{\&phi;}}_{m,b}\right\},$ According to the probability distribution of the Timing Synchronization heterogeneite error of user m, just can pass through φ _m,bprobability density function and functional integration obtain E{ Φ _m.

2. a kind of cooperative multipoint transmission method for precoding according to claim 1, is characterized in that: described in S1, the right selection standard of reference antenna is that channel condition between antenna pair is better than other antennas pair, wherein, s _mrepresent the pilot signal that user m sends, air traffic channel between antenna p and the antenna q of base station b of expression user m, represent that the antenna p of user m is to the reception noise of the antenna q of base station b, represent by the air traffic channel between antenna j and the antenna l of base station b of user m, represent that the antenna j of user m is to the reception noise of the antenna l of base station b.

3. a kind of cooperative multipoint transmission method for precoding according to claim 1, is characterized in that: described in S3, pilot tone estimates to adopt least mean-square error to estimate, described quantification feedback adopts random vector to quantize.