CN101969366B - Pre-coding method for MIMO system of 8 transmitting antennas - Google Patents

Abstract

The present invention proposes a precoding method for an MIMO system with 8 transmitting antennas. The method adopts a double codebook, and the double codebook is determined by selectively inheriting part of LTE codewords and then performing certain expansion. The present invention uses the double codebook for precoding, reduces system feedback overhead, and obtains good performance gain, and is suitable for multi-user-multiple-input multiple-output (MU-MIMO) systems.

Description

The method for precoding that is used for 8 transmitting antenna MIMO systems

Technical field

The present invention relates to multiple-input and multiple-output (MIMO) communication technical field, particularly relate to a kind of method for precoding that is used for 8 transmitting antenna MIMO systems.

Background technology

In the closed-loop MIMO transmission, receiving terminal is to the transmitting terminal feeding back channel state information, and transmitting terminal carries out precoding processing based on feedback information before the emission data, effectively the elevator system performance.

Long Term Evolution (Long Term Evolution LTE) in the space division multiplexing of closed-loop fashion, adopts the linear predictive coding technology, promptly utilizes known spatial channel information to carry out precoding processing at transmitting terminal, thus raising system and user's throughput.The linear predictive coding operation can be expressed as:

y＝HWx+n (1)

Y is that receiving terminal receives vector, and x is that transmitting terminal sends vector, and H is a spatial channel matrix; N is a noise vector; W is a pre-coding matrix, pre-coding matrix index (Precoding Matrix Indicator, PMI) index of pre-coding matrix W in corresponding code book of expression selection.

In LTE-A R10, promote the performance gain of multi-user's multiple-input, multiple-output MU-MIMO and guarantee that low feedback overhead is an important goal.So proposed dicode form originally: W=W ₁W ₂Perhaps W=W ₂W ₁, matrix W wherein ₁Reflection long-term channel information, matrix W ₂Reflect instantaneous frequency selectivity characteristic, W ₁And W ₂Respectively from two different code book C ₁And C ₂Middle selection, W ₁And W ₂Corresponding index PMI ₁And PMI ₂Common final decision pre-coding matrix.

Based on W=W ₂W ₁The rotation difference code book of structure need satisfy following requirement:

W is a N _tThe unitary pre-coding matrix of * R, N _tBe number of transmit antennas, R representes the value of the order that the user selects

W ₁∈ C ₁The expression broadband is the long-term channel characteristic, is a N _tThe unitary matrice of * R

W ₂∈ C ₂The expression frequency selectivity is instantaneous channel characteristics, is a N _t* N _tDiagonal matrix

Based on top design criterion, Samsung has designed a cover code book, but C in this code book ₂The granularity of code book is selected improper, makes code book poor performance when MU-MIMO.

Summary of the invention

The objective of the invention is to propose a kind of code book that is used for 8 transmitting antenna MIMO systems, reduced the system feedback expense, and obtain good performance gain.

The method for precoding that is used for 8 transmitting antenna MIMO systems all has code book C at transmitting terminal and receiving terminal _{1_8Tx}And C _{2_8Tx}, this method may further comprise the steps:

(1) transmitting terminal sends pilot tone;

(2) receiving terminal is estimated channel H according to pilot tone;

(3) receiving terminal calculates first code word W ₁Index PMI ₁: counting statistics information at first

With the current time is that timing point is counted H forward _iRepresent i channel estimation value constantly,

Expression H _iConjugate transpose, the N equivalence is in W ₁Feedback cycle in the channel estimating number of times, at code book C _{1_8Tx}In find code word near the main right singular vector of R, the corresponding index of this code word then is PMI ₁

(4) receiving terminal calculates second code word W ₂Index PMI ₂: calculate second code word

At code book C _{2_8Tx}Middle inquiry W ₂Corresponding index PMI ₂

(5) receiving terminal feedback index PMI ₁And PMI ₂Give transmitting terminal;

(6) transmitting terminal is according to the index PMI of feedback ₁And PMI ₂, from code book C _{1_8Tx}And C _{2_8Tx}Middle its corresponding code word of selecting is formed pre-coding matrix;

(7) transmitting terminal utilizes pre-coding matrix to carry out precoding;

Said code book C _{1_8Tx}And C _{2_8Tx}As shown in table 2 like table 1 respectively:

Table 1

Table 2

Wherein, T representes transposition, and diag{} is expressed as diagonal matrix.

Technique effect of the present invention is embodied in: pre-coding matrix is to be target to approach the channel matrix H right singular matrix in theory, in the present invention is based on the difference code book of rotation, and W ₁Directly approached the right singular matrix of channel, W ₂Be one the tenth of the twelve Earthly Branches diagonal matrix, be reflected in W ₁On be a low-angle increment of rotation, be in order to follow the trail of W ₁Fluctuation.Owing to adopted this this structure of dicode, W ₁What reflect is long-term channel information, and feedback cycle is long, W ₂The short-term channel information of reflection, feedback cycle is short, W ₁Feedback needs 4bits, and W ₂Feedback only needs 2bits, can effectively reduce feedback overhead.Reasonably select W simultaneously ₂Granularity θ also be code book key for design part, through numerical simulation,, obtained W used in the present invention based on the consideration of best performance ₂Granularity.

Description of drawings

Fig. 1 is the inventive method flow chart.

Core innovative point of the present invention is the code book form, below the origin and the characteristics of main explanation code book of the present invention.

At transmitting antenna is number when being 8 (8Tx), and top-priority antenna scene when the dual polarized antenna configuration is design is mainly considered when therefore designing 8Tx+scene of the dual polarized antenna of/-45 degree.

During dual polarized antenna, emission correlation matrix H ^HH has following piece diagonal angle form:

$H^{H}H=\left[\begin{array}{cc}A& B\\ B& A\end{array}\right]---\left(1\right)$

A and B are matrix.

In the strong correlation channel, B levels off to 0 matrix, so through after the singular value decomposition (SVD), singular matrix V-arrangement formula is following:

$V=\left[\begin{array}{cc}{U}_1& U_2\\ \±U_1& m{U}_2\end{array}\right]---\left(2\right)$

U ₁And U ₂Be matrix.

Therefore, when 8Tx, can with the 8Tx equivalence be two groups independently 4Tx carry out code book design; These two groups independently the polarised direction of 4Tx is vertical each other; 4 antenna polarization directions in every group of 4Tx antenna are identical, and be compact arranged uniform linear array (Uniform Linear Array, ULA).For the ULA of 4Tx, code book C ₁The variation of employing discrete fourier (Discrete Fourier Transform, DFT) code word is optimum, generates by following expression formula:

$P_g(m,n)=\frac{1}{\sqrt{N_t}}\exp \left(j\frac{2\mathrm{\π}}{N}m(n+\frac{g}{G})\right)---\left(3\right)$

m＝O，L，N _t-1；n＝O，L，N _t-1；g＝O，L?G-1

P _g(m, n) expression generates the value of the capable n row of m of DFT matrix, N _tExpression generates the dimension of DFT matrix, promptly is N _t* N _tSquare formation, G representes the number of generator matrix.

At N _t=4, under the situation of G=2, codebook matrix is:

$D_1=\frac{1}{2}\left[\begin{array}{cccc}1& 1& 1& 1\\ 1& j& -1& -j\\ 1& -1& 1& -1\\ 1& -j& -1& j\end{array}\right],$ $D_2=\frac{1}{2}\left[\begin{array}{cccc}1& 1& 1& 1\\ \frac{1+j}{\sqrt{2}}& \frac{-1+j}{\sqrt{2}}& \frac{-1-j}{\sqrt{2}}& \frac{1-j}{\sqrt{2}}\\ j& -j& j& -j\\ \frac{-1+j}{\sqrt{2}}& \frac{1+j}{\sqrt{2}}& \frac{1-j}{\sqrt{2}}& \frac{-1-j}{\sqrt{2}}\end{array}\right]---\left(4\right)$

So precoding codebook C of 8Tx _{1_8Tx}Adopt following mode to generate:

$M=\frac{1}{8}[K\⊗D_1,K\⊗D_2]---\left(5\right)$

Here

D ₁And D ₂Be the DFT matrix in (4), Expression Kronecker (Kronecker) is long-pending.M is one 8 * 16 a matrix, and 16 column vectors choosing M are as W ₁The code word of order when being 1 (rank-1).

C during 8 transmitting antennas ₂Code book is by C _{2_8Tx}Expression, C _{2_8Tx}Be diagonal unitary, also can with its equivalence be two groups independently 4Tx design, its structure is as follows:

$W_2=\left[\begin{array}{cccccccc}{e}^{\mathrm{j\π\θ}}& & & & & & & \\ & e^{\mathrm{j\π}2\mathrm{\θ}}& & & & & & \\ & & e^{\mathrm{j\π}3\mathrm{\θ}}& & & & & \\ & & & e^{\mathrm{j\π}4\mathrm{\θ}}& & & & \\ & & & & e^{\mathrm{j\π\θ}}& & & \\ & & & & & e^{\mathrm{j\π}2\mathrm{\θ}}& & \\ & & & & & & e^{\mathrm{j\π}3\mathrm{\θ}}& \\ & & & & & & & e^{\mathrm{j\π}4\mathrm{\θ}}\end{array}\right]---\left(6\right)$

Wherein, θ is W ₂To W ₁The phase place adjustment angle of wave beam.Simplifying under code book feedback overhead (the being typically designed to 2bit) condition, suggestion θ value is 0,1/16 ,-1/16,1/8, and its corresponding code book space is:

C _{2_8Tx，0}＝diag{1，1，1，1，1，1，1，1}

$C_{2\_8\mathrm{Tx},1}=\mathrm{diag}\{e^{-j\frac{\mathrm{\π}}{16}},e^{-j\frac{2\mathrm{\π}}{16}},e^{-j\frac{3\mathrm{\π}}{16}},e^{-j\frac{4\mathrm{\π}}{16}},e^{-j\frac{\mathrm{\π}}{16}},e^{-j\frac{2\mathrm{\π}}{16}},e^{-j\frac{3\mathrm{\π}}{16}},e^{-j\frac{4\mathrm{\π}}{16}}\}$

$C_{2\_8\mathrm{Tx},2}=\mathrm{diag}\{e^{j\frac{\mathrm{\π}}{16}},e^{j\frac{2\mathrm{\π}}{16}},e^{j\frac{3\mathrm{\π}}{16}},e^{j\frac{4\mathrm{\π}}{16}},e^{j\frac{\mathrm{\π}}{16}},e^{j\frac{2\mathrm{\π}}{16}},e^{j\frac{3\mathrm{\π}}{16}},e^{j\frac{4\mathrm{\π}}{16}}\}---\left(8\right)$

$C_{2\_8\mathrm{Tx},3}=\mathrm{diag}\{e^{j\frac{\mathrm{\π}}{8}},e^{j\frac{2\mathrm{\π}}{8}},e^{j\frac{3\mathrm{\π}}{8}},e^{j\frac{4\mathrm{\π}}{8}},e^{j\frac{\mathrm{\π}}{8}},e^{j\frac{2\mathrm{\π}}{8}},e^{j\frac{3\mathrm{\π}}{8}},e^{j\frac{4\mathrm{\π}}{8}}\}$

C wherein _{2_8Tx, 0}, C _{2_8Tx, 1}, C _{2_8Tx, 2}, C _{2_8Tx, 3}Expression code book C _{2_8Tx}4 code words in the code book.

The present invention's design has provided the codebook design schemes of 8Tx, and codebook structure is:

W ₁Code book is constructed W through the long-pending mode of Kronecker ₂Be diagonal unitary.

Have following characteristics:

1. pre-coding matrix is W=W ₂W ₁Form, W ₂Be a square formation, W ₁Be a high matrix (tall matrix);

2. be the basis with the DFT vector;

3. multiplexing LTE R8 code book;

4. low feedback overhead, W ₁Be 4bits, W ₂Be 2bits.

When providing 8Tx in table 1 and the table 2, order is 1 codeword list, C _{1_8Tx}16 code words are arranged, C in the code book _{2_8Tx}4 code words are arranged in the code book.

Though this code book is under the scene of dual polarized antenna of+/-45 degree, to design, its application is not limited, can be applicable to existing any antenna configurations environment.

Pre-coding matrix is to be target to approach the channel matrix H right singular matrix in theory, in difference code book based on rotation, and W ₁Directly approached the right singular matrix of channel, W ₂Be one the tenth of the twelve Earthly Branches diagonal matrix, be reflected in W ₁On be a low-angle increment of rotation, be in order to follow the trail of W ₁Fluctuation.Owing to adopted this this structure of dicode, W ₁What reflect is long-term channel information, and feedback cycle is long, W ₂The short-term channel information of reflection, feedback cycle is short, W ₁Feedback needs 4bits, and W ₂Feedback only needs 2bits, effectively reduces feedback overhead.

Claims (1)

1. The precoding method that is used for 8 transmit antenna MIMO systems, codebook C _{1_8Tx} and C _{2_8Tx} are all stored at the transmitting end and the receiving end, and the method comprises the following steps: (1) The sender sends the pilot; (2) The receiving end estimates the channel H according to the pilot frequency; (3) The receiving end calculates the index PMI ₁ of the first codeword W ₁ : first calculate the statistical information H _i represents the estimated channel value at the i-th moment counted forward from the current moment,

Indicates the conjugate transpose of H _i , N is equivalent to the number of channel estimations in the feedback cycle of W ₁ , find the codeword of the main right singular vector closest to R in the codebook C _{1_8Tx} , the index of the codeword is _PMI1 ; (4) The receiving end calculates the index PMI ₂ of the second codeword W ₂ : calculate the second codeword

Query the index PMI ₂ of W ₂ in the codebook C _{2_8Tx} ; (5) The receiving end feeds back the indexes PMI ₁ and PMI ₂ to the sending end; (6) The sending end selects the corresponding codewords from the codebooks C _{1_8Tx} and C _{2_8Tx} according to the feedback indexes PMI ₁ and PMI ₂ to form a precoding matrix; (7) The sending end uses the precoding matrix to perform precoding; The codebook C _{1_8Tx} is shown in Table 1:

Table 1 The codebook C _{2_8Tx} is shown in Table 2:

Table 2 Among them, T represents the transpose, and diag{} is represented as a diagonal matrix.

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