CN103929274A - A Coordinated Multipoint 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 Coordinated Multipoint Transmission Precoding Method

technical field

The invention belongs to the field of wireless communication, and in particular relates to a cooperative communication system in a time division duplex (Time Division Duplex, TDD) mode using Orthogonal Frequency Division Multiplexing (OFDM) technology.

Background technique

In recent years, in order to further improve spectrum efficiency and improve cell edge user throughput, Coordinated Multi-point Transmission (CoMP) has become a research hotspot in the field of communication. Researchers have designed and improved a large number of precoding algorithms to completely eliminate or greatly reduce the interference between multiple users and inter-frequency cells. Since most precoding algorithms are based on ideal channel information (Channel Side Information, CSI) assumptions, the accuracy of CSI becomes the key to ensuring the performance of joint precoding algorithms. In CoMP, the TDD mode is based on the channel reciprocity feature, and obtains the CSI of the downlink channel through uplink pilot estimation, thereby avoiding the large-scale quantization feedback overhead and errors of the Frequency Division Duplex (FDD) mode. Therefore, the TDD mode is considered to be an important development direction of CoMP.

In practical applications, the uplink and downlink equivalent channels include not only the transmission channel in the hole, but also the baseband and radio frequency parts of the transmitting end and the receiving end. Therefore, the uplink and downlink equivalent channels in the TDD mode are usually non-ideal reciprocity, which greatly reduces the performance of precoding.

Contents of the invention

The purpose of the present invention is to provide a cooperative multi-point transmission precoding method for channel non-ideal reciprocity error caused by synchronization time offset.

For the convenience of description, first explain the symbols:

(·) ^H and (·) ^-1 represent conjugate transposition and matrix inverse respectively, || is the Kronecker product, diag{·} is a diagonal matrix, E{·} represents the expected value, and I _x represents the identity matrix with rank x.

The present invention adopts the CoMP system under the TDD mode of OFDM. There are B cooperative base stations in the system, each base station office is equipped with n _t antennas, and there are M users in the system, and each user is equipped with a single antenna. The system uses OFDM to divide the channel into N sub-channels in the frequency domain, that is, N sub-carriers. The k-th sub-channel, the equivalent uplink and downlink channel from the cooperative base station to user m can be expressed as:

Among them, h _{mb_UL} (k) represents the equivalent uplink channel between the cooperative base station b and user m, Represents the equivalent downlink channel between cooperative base station b and user m, H _{m_UL} represents the uplink channel matrix from user m to all base stations, and H _{n_UL} represents the uplink channel matrix from user n to all base stations. The total transmission power p is evenly distributed to each user, then the received signal of user m at the kth word channel can be expressed as $r_m=\sqrt{\frac{p}{m}}{h}_{m\_\mathrm{DL}}{v}_m{\mathrm{the\; s}}_m+\underset{j=1,j\≠m}{\overset{m}{\mathrm{\Σ}}}\sqrt{\frac{p}{m}}{h}_{m\_\mathrm{DL}}{v}_j{\mathrm{the\; s}}_j+{\mathrm{no}}_{\mathrm{noise}},$ Among them, s _m is the signal sent to user m, s _j is the signal sent to user j, v _m is the precoding vector of user m, v _j is the precoding vector of user j, n _noise is additive complex Gaussian white noise. For the convenience of expression, the formulas in this patent omit the sub-channel index k.

The starting point of the Fast Fourier Transformation (FFT) window of OFDM is located within the cyclic prefix (Cyclic Prefix, CP) without intersymbol interference, that is, the timing synchronization error d satisfies LN _CP ≤d≤0, where L represents the maximum Multipath delay, N _CP indicates CP length. The timing synchronization error d causes a phase rotation exp(-j2πkd/N).

The k-th subchannel, the uplink and downlink equivalent channel from cooperative base station b to user m can be expressed as $\begin{array}{c}{h}_{\mathrm{mb}\_\mathrm{UL}}=h_{\mathrm{mb}}\×e^{-j2\mathrm{\π}{\mathrm{kd}}_{\mathrm{mb}.\mathrm{UL}}/N}\\ h_{\mathrm{mb}\_\mathrm{DL}}=h_{\mathrm{mb}}\×e^{-j2\mathrm{\π}{\mathrm{kd}}_{\mathrm{mb}.\mathrm{DL}}/N}\end{array},$ Among them, d _mb.UL represents the timing synchronization error of the uplink, d _mb.DL represents the timing synchronization error of the downlink, Represents the transmission channel in the hole between the cooperative base station b and the user m, which satisfies ideal reciprocity. Ignoring the path fading and shadow fading of the channel, and only considering Rayleigh fading, each element in h _mb is independent of each other and obeys the standard complex Gaussian distribution CN(0,1). Therefore, the uplink and downlink equivalent channel relationship between cooperative base station b and users can be expressed as $h_{\mathrm{mb}\_\mathrm{DL}}=h_{\mathrm{mb}\_\mathrm{UL}}{e}^{-j2\mathrm{\π}{k}_{(d_{\mathrm{mb}.\mathrm{DL}}-d_{\mathrm{mb}.\mathrm{UL}})/N}}.$

Define φ _mb =-2πkΔd _mb /N as the timing synchronization heterogeneity error of the uplink and downlink equivalent channels between the cooperative base station b and user m, where Δd _mb =(d _mb.DL -d _mb.UL ). The downlink equivalent channel between the cooperative base station and user m can be expressed as the product of the uplink channel and the timing synchronization reciprocity error, that is, H _{m_DL} = H _{m_UL} Φ _m , where, Indicates the actual channel reciprocal error matrix between user m and all base stations.

For a multipoint-to-multipoint CoMP system, the timing synchronization reciprocity error will cause the traditional precoding performance to be greatly degraded. Aiming at timing synchronization reciprocity error characteristics, this patent proposes a cooperative multi-point transmission precoding method. Based on two different CoMP system application scenarios, the cooperative multi-point transmission precoding method can be divided into precoding methods based on estimation compensation and error distribution based precoding methods.

The object of the present invention is achieved through the following steps:

S1. According to the channel conditions between the transmitting and receiving antennas, select the antenna p of the user m and the antenna q of the base station b as a reference antenna pair;

S2. Select n subcarriers as reference subcarriers, where 1≤n≤N;

S3. For subchannel k, estimate the uplink channel through the uplink pilot Obtain downlink channel through user quantization feedback in, Indicates the uplink channel between antenna p of user m and antenna q of base station b on the kth subcarrier, Indicates the downlink channel between antenna p of user m and antenna q of base station b on the kth subcarrier;

S4. Using the linear relationship of the timing synchronization reciprocity error on each reference subchannel, obtain the distance between subchannel k user m and base station b from n uplink and downlink reference subchannels by least squares (Least Squares, LS) Timing Synchronization Reciprocity Error Estimated as follows:

S41. Assume that the channel between the antenna of user m and the antenna of base station b is Among them, 1≤a≤m;

S42. When , select the antenna p of the base station b as the calibration antenna, as described in S31 is the calibration channel, where, 1≤p≤n, q≠p;

S43. For the standard carrier Q _k , the base station obtains the downlink equivalent channel between the user m and the antenna p of the base station b through the minimum mean square error estimation based on the uplink pilot, and feeds back to the base station b through RVQ to obtain n calibration carriers The uplink and downlink equivalent channels of : ${\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p=[{\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\left(a_1\right)...{\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\left(a_{\mathrm{no}}\right)],{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p=[{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\left(a_1\right)...{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\left(a_{\mathrm{no}}\right)],$ then you can get ${\mathrm{\Φ}}_{\mathrm{mb}}^p=\mathrm{diag}\left({\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\right)\mathrm{diag}{\left({\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\right)}^{-1};$

S44, take out the described in S43 The phase of the mid-diagonal elements Then D _mb = diag(Φ _mb (a ₁ )...Φ _mb (a _m ))·diag(-2πa ₁ /N...-2πa _m /N) ^-1 ;

S45, can be obtained according to S44 For subcarrier k, the synchronization reciprocity estimation between user m and base station b can be obtained

S46. Obtain subcarrier k, timing synchronization reciprocity error estimation between user m and other base stations in, Denotes the channel reciprocity error estimation matrix representing user m and all base stations, represents the identity matrix with rank n _t , and n _t represents the number of antennas of each base station, is the Kronecker product;

S5. Compensate the timing synchronization reciprocity error at the precoding vector, and the precoding vector of subchannel k and user m can be expressed as $w_m~\max .\mathrm{eigenvector}\left({({\mathrm{\σ}}_{\mathrm{noise}}^{2}I+\underset{\mathrm{no}=1,\mathrm{no}\≠m}{\overset{m}{\mathrm{\Σ}}}{\mathrm{\Ω}}_{\mathrm{no}})}^{-1}{\mathrm{\Ω}}_m\right),$ in, ${\mathrm{\Ω}}_{\mathrm{no}}={\widehat{\mathrm{\Φ}}}_{\mathrm{no}}^h{h}_{\mathrm{no}\_\mathrm{UL}}^h{h}_{\mathrm{no}\_\mathrm{UL}}{\widehat{\mathrm{\Φ}}}_{\mathrm{no}},$ ${\mathrm{\Ω}}_m={\widehat{\mathrm{\Φ}}}_m^h{h}_{m\_\mathrm{UL}}^h{h}_{m\_\mathrm{UL}}{\widehat{\mathrm{\Φ}}}_m,$ H _{m_UL} represents the uplink channel matrix from user m to all base stations, and H _{n_UL} represents the uplink channel matrix from user n to all base stations;

S6. When the timing synchronization reciprocity error φ _mb in the CoMP system changes rapidly in the time domain and is difficult to estimate and track, a precoding algorithm based on the error distribution is used, specifically as follows: the kth subchannel precoding vector of user m can be Expressed as: v _m ～max.eigenvector(E{M _m } ^-1 E{Q _m }),

w _m =v _m /||v _m ||

in, $\mathrm{E.}\left\{m_m\right\}={\mathrm{\σ}}_{\mathrm{noise}}^{2}I+\underset{\mathrm{no}=1,\mathrm{no}\≠m}{\overset{m}{\mathrm{\Σ}}}\mathrm{E.}\left\{Q_{\mathrm{no}}\right\},$

$\mathrm{E.}\left\{Q_m\right\}=\mathrm{E.}\left\{h_{m\_\mathrm{DL}}^h{h}_{m\_\mathrm{DL}}\right\}=\mathrm{E.}\left\{{\mathrm{\Φ}}_m^h{h}_{m\_\mathrm{UL}}^h{h}_{m\_\mathrm{UL}}{\mathrm{\Φ}}_m\right\},$ H _{m_UL} can be obtained through uplink pilot estimation, and the pilot estimation adopts MMSE, then $\mathrm{E.}\left\{{\mathrm{\Φ}}_m^h{h}_{m\_\mathrm{UL}}^h{h}_{m\_\mathrm{UL}}{\mathrm{\Φ}}_m\right\}\≈\mathrm{E.}\left\{{\mathrm{\Φ}}_m^h\right\}{h}_{m\_\mathrm{UL}}^h{h}_{m\_\mathrm{UL}}\mathrm{E.}\left\{{\mathrm{\Φ}}_m\right\}$ in, $\mathrm{E.}\left\{{\mathrm{\Φ}}_m\right\}=\mathrm{diag}\left\{\mathrm{E.}\right\{e^{j{\mathrm{\φ}}_{m,1}}\},...\mathrm{E.}\{e^{j{\mathrm{\φ}}_{m,B}}\left\}\right\}\⊗I_{{\mathrm{no}}_t},\mathrm{E.}\left\{e^{j{\mathrm{\φ}}_{m,b}}\right\}=\mathrm{E.}\left\{{\cos \mathrm{\φ}}_{m,b}\right\}+J\left\{{\sin \mathrm{\φ}}_{m,b}\right\},$ According to the probability distribution of the timing synchronization heterogeneity error of user m, E{Φ _m } can be obtained through the probability density function and function integral of φ _m,b .

Further, the selection criterion of the reference antenna pair in S1 is that the channel condition between the antenna pair is better than that of other antenna pairs, that is, Among them, s _m represents the pilot signal sent by user m, Denotes the air channel between antenna p of user m and antenna q of base station b, Indicates the receiving noise from antenna p of user m to antenna q of base station b, Denotes the air channel between antenna j of user m and antenna l of base station b, Indicates the received noise from antenna j of user m to antenna l of base station b.

Further, the pilot estimation in S3 adopts minimum mean square error (Minimum Mean Square Error, MMSE) estimation, and the quantization feedback adopts random vector quantization (Random Vector Quantization, RVQ).

The beneficial effects of the present invention are:

Through the cumulative distribution function curve of the system capacity, it can be found that the traditional SLNR is very sensitive to the timing synchronization reciprocity error, and the system capacity is greatly reduced by it, while the precoding algorithm proposed in this patent slows down the performance loss caused by the error and improves precoding performance.

Description of drawings

FIG. 1 is a CoMP transmission system in TDD mode, which is an actual application scenario of the present invention. Figure 1 also includes the equivalent uplink and downlink channel structures of base station b and user m.

Figure 2 shows the simulation results and theoretical lower bounds of the user's average achievable rate under ideal channel reciprocity conditions and timing synchronization reciprocity error conditions.

Fig. 3 is a structural block diagram of multi-base station cooperative downlink transmission using the patented precoding algorithm.

Fig. 4 is a scenario of a CoMP transmission system with 2 base stations and 2 users, and the performance comparison between the traditional SLNR precoding algorithm and the precoding proposed in this patent.

Fig. 5 is a scenario of a CoMP transmission system with 3 base stations and 3 users, and the performance comparison between the traditional SLNR precoding algorithm and the precoding proposed in this patent.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and examples, and the embodiments of the present invention include but are not limited to the following examples.

The coordinated multipoint transmission system of the TDD mode of the present invention is characterized in that OFDM is used to resist multipath fading, the OFDM symbol cyclic prefix length is greater than the maximum multipath delay, and the FFT starting point of OFDM is located in the cyclic prefix without intersymbol interference. That is, the timing synchronization error residual sampling d = "τ/T _s ", satisfying "L/T _s "-N _CP ≤d≤0, the timing synchronization residual d only causes phase rotation exp(-j2πkd/N), where, τ Represents the actual timing synchronization error residual, d represents the timing synchronization error residual sampling, T _s represents the sampling period, L represents the maximum multipath delay, N _CP represents the cyclic prefix length, k represents the kth subcarrier, N total number of subcarriers.

As shown in FIG. 1 , let the number of coordinated base stations B=2, the number of users M=2, the number of antennas of the coordinated base station n _t =2, and the number of users is a single antenna. The number of subcarriers of OFDM is N=1024, the length of the cyclic prefix is N _cp =144, and the maximum path delay is L=(N _cp /2).

The uplink channel from the user to the coordinated base station is obtained by performing MMSE estimation on the block pilot in the Sounding Reference Signal (SRS) sent by the user. For the downlink channel from the cooperative base station to the user, it is assumed that the user can obtain an ideal downlink channel, and the downlink channel is quantized and fed back through random vector quantization (Random Vector Quantization, RVQ). The downlink channel from cooperative base stations 1, 2 to user 1 As an example, the quantized codebook C consists of 2 ^T 4-dimensional complex unit vectors Where T is the number of quantization feedback bits, the larger T is, the smaller the quantization feedback error is, and T=8 is usually set. The selection of the quantization feedback vector is based on

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; DL</span>}}<span\; class="notranslate">\; ~</span>\mathrm{<span\; class="notranslate">\; arg</span>}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}}{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; DL</span>}}{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; .</span>$

After the cooperative base station acquires the uplink and downlink channels, it can calculate the variation of the channel reciprocity error phase in the time domain. As shown in Figure 4, if the error is approximately constant in the time domain, the precoding algorithm based on estimation compensation is used, and if the error changes in real time in the time domain, the precoding algorithm based on error distribution is used.

For the precoding algorithm based on estimation compensation, the first antenna of the cooperative base station is selected as the reference antenna, n subchannels are selected as the reference channel, and the reciprocity The reciprocity error estimates the reciprocity error of other subchannels. If the number of reference subchannels n=2, the timing synchronization reciprocity error of the kth subcarrier between user 1 and base station 1 can be expressed as

${\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\frac{{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; DL</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; UL</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; UL</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; DL</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>$

The precoding vector of user 1 in subchannel k can be expressed as

${\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ~</span>\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; eigenvector</span>}<span\; class="notranslate">\; (</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; noise</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

in, ${\mathrm{\&Omega;}}_2={\widehat{\mathrm{\&Phi;}}}_2^h{h}_{2\_\mathrm{UL}}^h{h}_{2\_\mathrm{UL}}{\widehat{\mathrm{\&Phi;}}}_2,$ ${\mathrm{\&Omega;}}_1={\widehat{\mathrm{\&Phi;}}}_1^h{h}_{1\_\mathrm{UL}}^h{h}_{1\_\mathrm{UL}}{\widehat{\mathrm{\&Phi;}}}_1,$

${\widehat{\mathrm{\&Phi;}}}_1=\mathrm{diag}\{e^{j{\widehat{\mathrm{\&phi;}}}_{11}},...e^{j{\widehat{\mathrm{\&phi;}}}_{12}}\}\&CircleTimes;I_2,$ ${\widehat{\mathrm{\&Phi;}}}_2=\mathrm{diag}\{e^{j{\widehat{\mathrm{\&phi;}}}_{\mathrm{twenty\; one}}},...e^{j{\widehat{\mathrm{\&phi;}}}_{\mathrm{twenty\; two}}}\}\&CircleTimes;I_2,$

For the precoding algorithm based on error distribution, it is assumed that the timing synchronization error of the uplink and downlink equivalent channels between the coordinated base station b and user m Obey the uniform distribution U(-Z _mb ,0), where Z _mb =N _CP -L _mb . By derivation, the probability density function of the timing synchronization reciprocity error phase φ _mb between base station b and user m can be expressed as:

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

According to the error distribution, the kth subchannel precoding vector of user 1 can be expressed as:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ~</span>\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; eigenvector</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \}</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\end{array}<span\; class="notranslate">\; ,</span>$

in, $\mathrm{E.}\left\{m_1\right\}={\mathrm{\&sigma;}}_{\mathrm{noise}}^{2}I+\mathrm{E.}\left\{Q_2\right\}$

$\mathrm{E.}\left\{Q_1\right\}=\mathrm{E.}\left\{h_{1\_\mathrm{DL}}^h{h}_{1\_\mathrm{DL}}\right\}=\mathrm{E.}\left\{{\mathrm{\&Phi;}}_1^h{h}_{1\_\mathrm{UL}}^h{h}_{1\_\mathrm{UL}}{\mathrm{\&Phi;}}_1\right\}\&ap;\mathrm{E.}\left\{{\mathrm{\&Phi;}}_1^h\right\}{h}_{1\_\mathrm{UL}}^h{h}_{1\_\mathrm{UL}}\mathrm{E.}\left\{{\mathrm{\&Phi;}}_1\right\}.$ at the same time,

$\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; diag</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; J</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>$

$\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; J</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; .</span>$

Let Z ₁₁ =Z ₁₂ =Z, then

$\begin{array}{c}\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&rho;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; Z</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\end{array}<span\; class="notranslate">\; .</span>$

Claims (3)

1. A coordinated multipoint transmission precoding method, comprising the following steps: S1. According to the channel conditions between the transmitting and receiving antennas, select the antenna p of the user m and the antenna q of the base station b as a reference antenna pair; S2. Select n subcarriers as reference subcarriers, where 1≤n≤N; S3. For subchannel k, estimate the uplink channel through the uplink pilot Obtain downlink channel through user quantization feedback in, Indicates the uplink channel between antenna p of user m and antenna q of base station b on the kth subcarrier, Indicates the downlink channel between antenna p of user m and antenna q of base station b on the kth subcarrier; S4. Using the linear relationship of the timing synchronization reciprocity error on each reference subchannel, obtain the distance between subchannel k user m and base station b from n uplink and downlink reference subchannels by least squares (Least Squares, LS) Timing Synchronization Reciprocity Error Estimated as follows: S41. Assume that the channel between the antenna of user m and the antenna of base station b is Among them, 1≤a≤m; S42. When , select the antenna p of the base station b as the calibration antenna, as described in S31 is the calibration channel, where, 1≤p≤n, q≠p; S43. For the standard carrier Q _k , the base station obtains the downlink equivalent channel between the user m and the antenna p of the base station b through the minimum mean square error estimation based on the uplink pilot, and feeds back to the base station b through RVQ to obtain n calibration carriers The uplink and downlink equivalent channels of : ${\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p=[{\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\left(a_1\right)...{\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\left(a_{\mathrm{no}}\right)],{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p=[{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\left(a_1\right)...{\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\left(a_{\mathrm{no}}\right)],$ then you can get ${\mathrm{\&Phi;}}_{\mathrm{mb}}^p=\mathrm{diag}\left({\hat{h}}_{\mathrm{mb}\_\mathrm{DL}}^p\right)\mathrm{diag}{\left({\hat{h}}_{\mathrm{mb}\_\mathrm{UL}}^p\right)}^{-1};$ S44, take out the described in S43 The phase of the mid-diagonal elements Then D _mb = diag(Φ _mb (a ₁ )...Φ _mb (a _m ))·diag(-2πa ₁ /N...-2πa _m /N) ^-1 ; S45, can be obtained according to S44 For subcarrier k, the synchronization reciprocity estimation between user m and base station b can be obtained S46. Obtain subcarrier k, timing synchronization reciprocity error estimation between user m and other base stations in, Denotes the channel reciprocity error estimation matrix representing user m and all base stations, represents the identity matrix with rank n _t , and n _t represents the number of antennas of each base station, is the Kronecker product; S5. Compensate the timing synchronization reciprocity error at the precoding vector, and the precoding vector of subchannel k and user m can be expressed as $w_m~\max .\mathrm{eigenvector}\left({({\mathrm{\&sigma;}}_{\mathrm{noise}}^{2}I+\underset{\mathrm{no}=1,\mathrm{no}\&NotEqual;m}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Omega;}}_{\mathrm{no}})}^{-1}{\mathrm{\&Omega;}}_m\right),$ in, ${\mathrm{\&Omega;}}_{\mathrm{no}}={\widehat{\mathrm{\&Phi;}}}_{\mathrm{no}}^h{h}_{\mathrm{no}\_\mathrm{UL}}^h{h}_{\mathrm{no}\_\mathrm{UL}}{\widehat{\mathrm{\&Phi;}}}_{\mathrm{no}},$ ${\mathrm{\&Omega;}}_m={\widehat{\mathrm{\&Phi;}}}_m^h{h}_{m\_\mathrm{UL}}^h{h}_{m\_\mathrm{UL}}{\widehat{\mathrm{\&Phi;}}}_m,$ H _{m_UL} represents the uplink channel matrix from user m to all base stations, and H _{n_UL} represents the uplink channel matrix from user n to all base stations; S6. When the timing synchronization reciprocity error φ _mb in the CoMP system changes rapidly in the time domain and is difficult to estimate and track, a precoding algorithm based on the error distribution is used, specifically as follows: the kth subchannel precoding vector of user m can be Expressed as: v _m ～max.eigenvector(E{M _m } ^-1 E{Q _m }), w _m =v _m /||v _m || in, $\mathrm{E.}\left\{m_m\right\}={\mathrm{\&sigma;}}_{\mathrm{noise}}^{2}I+\underset{\mathrm{no}=1,\mathrm{no}\&NotEqual;m}{\overset{m}{\mathrm{\&Sigma;}}}\mathrm{E.}\left\{Q_{\mathrm{no}}\right\},$ $\mathrm{E.}\left\{Q_m\right\}=\mathrm{E.}\left\{h_{m\_\mathrm{DL}}^h{h}_{m\_\mathrm{DL}}\right\}=\mathrm{E.}\left\{{\mathrm{\&Phi;}}_m^h{h}_{m\_\mathrm{UL}}^h{h}_{m\_\mathrm{UL}}{\mathrm{\&Phi;}}_m\right\},$ H _{m_UL} can be obtained through uplink pilot estimation, and the pilot estimation adopts MMSE, then $\mathrm{E.}\left\{{\mathrm{\&Phi;}}_m^h{h}_{m\_\mathrm{UL}}^h{h}_{m\_\mathrm{UL}}{\mathrm{\&Phi;}}_m\right\}\&ap;\mathrm{E.}\left\{{\mathrm{\&Phi;}}_m^h\right\}{h}_{m\_\mathrm{UL}}^h{h}_{m\_\mathrm{UL}}\mathrm{E.}\left\{{\mathrm{\&Phi;}}_m\right\}$ in, $\mathrm{E.}\left\{{\mathrm{\&Phi;}}_m\right\}=\mathrm{diag}\left\{\mathrm{E.}\right\{e^{j{\mathrm{\&phi;}}_{m,1}}\},...\mathrm{E.}\{e^{j{\mathrm{\&phi;}}_{m,B}}\left\}\right\}\&CircleTimes;I_{{\mathrm{no}}_t},\mathrm{E.}\left\{e^{j{\mathrm{\&phi;}}_{m,b}}\right\}=\mathrm{E.}\left\{{\cos \mathrm{\&phi;}}_{m,b}\right\}+J\left\{{\sin \mathrm{\&phi;}}_{m,b}\right\},$ According to the probability distribution of the timing synchronization heterogeneity error of user m, E{Φ _m } can be obtained through the probability density function and function integral of φ _m,b . 2. A kind of coordinated multi-point transmission precoding method according to claim 1, is characterized in that: the selection criterion of the reference antenna pair described in S1 is that the channel condition between the antenna pair is better than other antenna pairs, namely Among them, s _m represents the pilot signal sent by user m, Denotes the air channel between antenna p of user m and antenna q of base station b, Indicates the receiving noise from antenna p of user m to antenna q of base station b, Denotes the air channel between antenna j of user m and antenna l of base station b, Indicates the received noise from antenna j of user m to antenna l of base station b. 3. A method for precoding in coordinated multi-point transmission according to claim 1, characterized in that: said pilot estimation in S3 adopts minimum mean square error estimation, and said quantization feedback adopts random vector quantization.