CN104243106A - Codebook construction method based of 3D (three dimensional) cross polarization channel based massive multiple input multiple output (MIMO) system - Google Patents

Abstract

The invention discloses a codebook construction method suitable for an MU (multi-user) massive multiple input multiple output (MIMO) system and belongs to the technical field of wireless communication. The codebook construction method includes that massive MIMO precoding codebooks are generated according to BD-DFT expansion and coexist in a base station terminal and a user terminal, users select precoding codewords capable of enabling the users to obtain maximized channel gains according to corresponding channel state information (CSI), an precoding matrix index (PMI) corresponding to the optimal codeword is fed back to the base station terminal, the base station terminal restores the corresponding precoding codeword according to received feedback information, and data sent by the users can be subjected to precoding processing. By the codebook construction method and a homogeneous array system of a cross polarized antenna, channel spaces are more matched, co-channel interference (CCI) of multiple users can be effectively restricted, and a simple and efficient implementation scheme is provided for the massive MU-MIMO system.

Description

A kind of codebook construction method based on the extensive mimo system of 3D cross polarization channel

Technical field

The present invention relates to mobile communication Long Term Evolution (LTE-Advanced) technical field.Specifically a kind of codebook construction method based on the extensive mimo system of 3D cross polarization channel.

Background technology

Along with the fast development of intelligent terminal, people also become more and more higher to the data demand of two-forty.Now, along with going deep into of multi-antenna technology research, although MIMO technology can improve reliability and the power system capacity of system to a certain extent, but this can not meet the requirement of user to higher and faster message transmission rate, and be also limited along with terminal equipment increases the effect that its interference mitigation technology reaches.In general, the number of antennas of sending and receiving end is more, and the degree of freedom that transmission channel provides is larger, then system provides transmission rate also just higher, and therefore, base station end adopts the extensive MIMO of a large amount of active antenna to become the study hotspot of academia and industrial circle gradually.Extensive MIMO expands on traditional MIMO basis, compare traditional MIMO, the sharply increase of extensive mimo antenna number, consider the factor such as requirement and good looking appearance of array structure, traditional even linear array (Uniform Linear Array, ULA) is no longer applicable, therefore, the present invention proposes the extensive mimo system based on 3D cross polarization channel, base station end configuration N _h× N _vuniform surface battle array (the Uniform Planar Array of dimension cross polarization (-/+45 °) antenna, UPA), not only solve the spatial limitation that in extensive mimo system, number of antennas is brought too much like this, simultaneously owing to adding a new degree of freedom (vertical dimension), make it can carry out interference coordination and AF panel more neatly, thus make the transmission rate of whole system and bit error rate performance obtain promoting more significantly.

In descending multi-user mimo system, multiple user shares same running time-frequency resource, common-channel interference (Co-Channel Interference will inevitably be caused, CCI) existence, meanwhile, usually mutually cannot cooperate between each terminal and communicate, therefore, carry out preliminary treatment in base station end to each subscriber signal for multi-user MIMO system and just seem most important, wherein multi-user pre-coding technology is exactly the most effective a kind of preconditioning technique.In current existing various precoding technique, one class is the precoding technique based on Real-time Channel process, as channel reversion, block of channels diagonalization etc., but transmitting terminal needs to know channel condition information completely, obviously, because the too large this kind of precoding technique in systems in practice of feedback quantity is difficult to realize; An other class is the precoding technique based on code book, concrete methods of realizing is exactly by the code book designed in advance and coexists in transmitting-receiving two-end, receiving terminal estimates channel information, and from the code book designed, the code word of current channel condition can be represented according to certain criterion, and feed back this code word pre-coding matrix index number (Precoding Matrix Index corresponding in the codebook, PMI), because such technology feedback quantity is limited, the main flow of precoding technique is therefore developed into gradually.

In extensive mimo system, the precoding technique key based on code book is the design of code book, and academic circles at present and industrial circle are all in the Primary Study stage.Because base station adopts two-dimentional UPA to be configured with cross polarised antenna simultaneously, therefore the design of code book not only will consider horizontal dimensions channel information and vertical dimension channel information simultaneously, also needs to consider that 3D cross polarization channel sends the diagonal angle character of correlation matrix.

Summary of the invention

For above deficiency of the prior art, the object of the present invention is to provide a kind of cross polarization channel space more to mate, and effectively can suppress the codebook construction method based on the extensive mimo system of 3D cross polarization channel of multi-user's common-channel interference.Technical scheme of the present invention is as follows:

Based on a codebook construction method for the extensive mimo system of 3D cross polarization channel, it comprises the following steps:

101, at base station end configuration N _h× N _vthe uniform surface battle array UPA of dimension cross polarization (-/+45 °) antenna, wherein N _hfor the horizontal dimension number of transmit antennas of uniform surface battle array UPA, N _vfor the line number of the antenna of uniform surface battle array UPA, adopt block diagonal angle-discrete Fourier transform method to carry out conversion to uniform surface battle array UPA and produce basic code book W ₁ ^g, wherein W ₁ ^gfor block diagonal arrangement;

102, then according to the N in step 101 _h× N _vphase difference between dimension cross polarised antenna uniform surface battle array produces code book W ₂ ^l, pass through W ₁ ^gw ₂ ^lstructure adopts the code book that the channel of cross polarised antenna even linear array is corresponding;

103, last according to the correlation between vertical dimension antenna, generate the steering vector W of vertical dimension _v, utilize formula produce precoding codebook, and be kept at base station end and user side, each user of user side selects to make this user obtain the code word of maximum channel gain according to current channel condition information CSI from the precoding codebook designed, the pre-encoding codeword call number PMI of its correspondence is fed back to base station, base station recovers corresponding code word according to PMI from identical code book, and then carries out precoding processing to different user data and then go out from Base Transmitter.

Further, the concrete formula adopting block diagonal angle-discrete Fourier transform method to convert uniform surface battle array UPA in step 101 is as follows:

$w_g(m,n)=\frac{1}{\sqrt{N}}{e}^{j\frac{2\mathrm{\π}}{N}m(n+\frac{g}{G})},m=\mathrm{0,1},\·\·\·,N_h/2-1;n=\mathrm{0,1},\·\·\·,N_h/2-1;g=\mathrm{0,1},\·\·\·,G-1$

Wherein w _g(m, n) represents pre-coding matrix the element of capable n-th row of m, N represents reception antenna number, N _hfor the horizontal dimension number of transmit antennas of UPA, G represents the number of full rank DFT matrix, then generates block diagonal arrangement code book W according to following formula ₁ ^g, concrete form is as follows:

${W_1}^g=\left[\begin{array}{cc}{\tilde{W}}^g& 0\\ 0& {\tilde{W}}^g\end{array}\right]$

Wherein corresponding one group is uniformly distributed and the channel of same polarization antenna formation respectively.

Further, to the code book corresponding to the channel of cross polarization (-/+45 °) even linear array ULA in step 102, close series structure W according to two groups of co-polarization antenna phase differences ₂ ^l:

Wherein e _lrepresent that the n-th element is 1, other elements are the N of 0 _hthe vector of/2 × 1, represent the phase difference between two groups of co-polarization antennas.

Further, in step 103 according to the interactive design steering vector W of vertical dimension antenna _vformula be:

$W_V=\frac{1}{\sqrt{N_v}}{\left[\begin{array}{cccc}{e}^{-j(\mathrm{Nv}-1)\mathrm{\ψ}}& \·\·\·& e^{-\mathrm{j\ψ}}& 1\end{array}\right]}^T$

Wherein ψ represents the phase difference that the wave path-difference that caused by vertical dimension antenna distance is corresponding.

Further, the user in step 103 obtains current channel matrix according to channel estimating singular value decomposition is carried out to it

${\tilde{H}}_{N_r\×(N_h/2\×N_v)}^{3D}=\mathrm{U\Σ}{V}^H$

Wherein unitary matrice U is current channel matrix left singular vector matrix, Σ is current channel matrix the matrix that forms by descending order of characteristic value, unitary matrice V is current channel matrix right singular vector matrix, if according to current channel matrix the optimum pre-encoding codeword selected is w=[V] ₁, [V] ₁the first row of representing matrix V, then equivalent channel is: ${{\left|\right|{\tilde{H}}^{3D}w\left|\right|}_2}^2={{\left|\right|{\tilde{H}}^{3D}{\left[V\right]}_1\left|\right|}_2}^2={\left({\mathrm{\λ}}_{\max }\right)}^2{\left|\right|{\left[U\right]}_1\left|\right|}^2={\left({\mathrm{\λ}}_{\max }\right)}^2,$ Wherein λ ^maxfor current channel matrix maximum singular value, can find out from above formula, as w=[V] ₁time, user obtains maximum channel gain.

Advantage of the present invention and beneficial effect as follows:

First the present invention considers the diagonal angle feature that cross polarization channel sends correlation matrix, codebook design method based on BD-DFT is proposed, by DFT code book is combined structure code book with block diagonalization structure, the characteristic of channel of cross-polarized antenna set can be mated so well, and can effectively transmitting power be loaded in polarised direction, then utilize the correlation structure steering vector between vertical dimension antenna, and expanded to the code book mated with UPA by steering vector.The code book based on the extensive mimo system of 3D cross polarization channel that the present invention proposes, not only more mate with cross polarization channel space, and can effectively suppress multi-user CCI, thus, the precoding that this invention is the extensive mimo system of descending 3D multi-user provides one implementation simply and efficiently.

Accompanying drawing explanation

Figure 1 shows that the system block diagram of the extensive mimo system precoding based on 3D cross polarization channel that the present invention proposes, comprise the calculating of chnnel coding, modulation, precoding and channel estimating and feedback information;

Fig. 2 is the uniform surface battle array schematic diagram of the 3D cross polarised antenna that base station adopts;

Fig. 3 is the precoding basic operation flow chart based on code book;

Fig. 4 is the precoding flow chart based on code book of the present invention;

Fig. 5 is the codebook design operation chart based on 3D cross polarization channel of the present invention;

Fig. 6 is the codebook design method flow chart based on the extensive mimo system of 3D cross polarization channel of the present invention.

Embodiment

The invention will be further elaborated to provide an infinite embodiment below in conjunction with accompanying drawing.But should be appreciated that, these describe just example, and do not really want to limit the scope of the invention.In addition, in the following description, the description to known features and technology is eliminated, to avoid unnecessarily obscuring concept of the present invention.

As shown in Figure 1, Fig. 1 is the system block diagram of the extensive mimo system precoding based on 3D cross polarization channel that the present invention proposes.The N of base station end configuration cross polarised antenna _h/ 2 × N _vdimension UPA, wherein N _hrepresent UPA horizontal dimension antenna number, N _vrepresent the line number of UPA antenna, require that each transmit antennas can both information simultaneously in processing horizontal dimension and vertical dimensions, receiving terminal has K user, each user's reception antenna number N _rrepresent, after user side receives signal, carry out channel estimating and obtain 3D channel matrix ${H^{3D}}_{N_r\×(N_h/2\×N_v)}.$

For simplifying the analysis, suppose that channel fading is smooth, then the signal that a kth user receives can be expressed as:

$y_k=\sqrt{p_k}{H}_k{W}_k{X}_k+\sqrt{p_i}{H}_k\underset{i=1,i\≠k}{\overset{K}{\mathrm{\Σ}}}{W}_i{X}_i+n_k$

Wherein represent the desired signal of a kth receiving terminal, represent the interference from other subscriber signals that a kth user receives, H _kand W _krepresent channel matrix and the pre-coding matrix of user k respectively, for the transmitted power of user k, meet p ₀for the transmitting power that system is total, n _krepresent noise signal, for obeying CN (0, N ₀) probability distribution white Gauss noise.

Fig. 2 is the uniform surface battle array model of the 3D cross polarised antenna that the present invention proposes, this model adopts UPA structure as shown in the figure, consider the restriction of antenna physical size, antenna adopts cross polarization (-/+45 °) configuration, in Fig. 2 (a), each round dot represents one group of cross dipole antenna, in order to intuitive and convenient, Fig. 2 (a) two-dimensional array structure diagram can be changed into as shown in Fig. 2 (b) plane.

Fig. 3 is the precoding basic operation flow chart based on code book.According to Fig. 3, based on the precoding technique of code book, first offline design code book, and it is all coexisted in base station end and user side, then each user travels through each code word in off-line code book according to its instant CSI, select to make this user terminal obtain the code word of maximum channel gain, and the PMI that this code word is corresponding is in the codebook fed back to base station end, base station end recovers the code word making this user terminal obtain maximum channel gain according to the feedback information received, thus realizes carrying out precoding processing to different user data.

Fig. 4 is the precoding flow chart based on code book that the present invention proposes.

Step 41: the N of base station end configuration cross polarised antenna _h/ 2 × N _vdimension UPA, wherein N _hrepresent UPA horizontal dimension antenna number, N _vrepresent the line number of UPA antenna, require that each transmit antennas can both information simultaneously in processing horizontal dimension and vertical dimensions, receiving terminal has K user, each user's reception antenna number N _rrepresent;

Step 42: the design of code book, according to channel characteristic design and the code book adopting the UPA of cross polarised antenna to match, and is coexisted in transmitting-receiving two-end;

Step 43: each user is according to the channel information estimating to obtain select respectively to make it obtain the code word of maximum channel gain from the code book designed, and the call number that this code word is corresponding is in the codebook fed back to base station end;

Detailed process is as follows:

A () obtains current channel matrix according to channel estimating singular value decomposition is carried out to it

${\tilde{H}}_{N_r\×(N_h/2\×N_v)}^{3D}=\mathrm{U\Σ}{V}^H$

Wherein unitary matrice U is current channel matrix left singular vector matrix, Σ is current channel matrix the matrix that forms by descending order of characteristic value, unitary matrice V is current channel matrix right singular vector matrix, if according to current channel matrix the optimum pre-encoding codeword selected is w=[V] ₁([V] ₁the first row of representing matrix V), then equivalent channel is: ${{\left|\right|{\tilde{H}}^{3D}w\left|\right|}_2}^2={{\left|\right|{\tilde{H}}^{3D}{\left[V\right]}_1\left|\right|}_2}^2={\left({\mathrm{\λ}}_{\max }\right)}^2{\left|\right|{\left[U\right]}_1\left|\right|}^2={\left({\mathrm{\λ}}_{\max }\right)}^2,$ Wherein λ ^maxfor current channel matrix maximum singular value, can find out from above formula, as w=[V] ₁time, user can obtain maximum channel gain, and the pre-encoding codeword criterion that the present invention selects is exactly approach optimum pre-encoding codeword as far as possible, to obtain maximum channel gain.

B () the present invention adopts minimum chordal distance criterion to approach maximum channel gain, according to current channel matrix from the code book of offline design select in (B represents the bit number of this system feedback) to make each user obtain the optimum pre-encoding codeword W of maximum channel gain ^opt=W _n, specific as follows:

To a kth user, the optimum pre-coding matrix of selection is as follows:

Make W ^opt=W _n

$n=\underset{i=\mathrm{1,2}\·\·\·2^B}{\arg \min }{d}_{\mathrm{chord}}({\left[V\right]}_1,W_i)$

Wherein W _i, W _nrepresent the i-th row and n-th row of V respectively, chordal distance d _chord(X, Y) is defined as follows:

$d_{\mathrm{chord}}(X,Y)=\frac{1}{\sqrt{2}}{\left|\right|{\mathrm{XX}}^H-{\mathrm{YY}}^H\left|\right|}_F$

Wherein X, Y are all the column vectors with same dimension, [] ^hrepresent the conjugate transpose of vector, ‖ ‖ _frepresent F norm.

Step 44: base station end recovers with it corresponding optimum pre-encoding codeword according to the PMI received, thus realize that data are sent to each user and carry out precoding processing.

Fig. 5 is the codebook design operation chart based on 3D cross polarization channel of the present invention.

ULA based on cross polarised antenna can be divided into two groups of like-polarized even linear arrays according to the polarised direction of antenna, and each its channel relevancy of group antenna is very high, and simultaneously orthogonal based on the polarised direction between difference group antenna, its correlation is almost nil.Therefore, can the code book of design block diagonal arrangement match according to this character of channel.Meanwhile, according to the correlation between UPA vertical dimension antenna, the code book that can be matched with UPA by steering vector structure.

Fig. 6 is the codebook design method flow chart that the present invention proposes.

Step 61: according to BD-DFT produce adopt based on ULA channel corresponding code book

First according to rotation DFT formula:

${\tilde{w}}_g(m,n)=\frac{1}{\sqrt{N}}{e}^{j\frac{2\mathrm{\π}}{N}m(n+\frac{g}{G})},m=\mathrm{0,1},\·\·\·,N_h/2-1;n=\mathrm{0,1},\·\·\·,N_h/2-1;g=\mathrm{0,1},\·\·\·,G-1$

Generate DFT matrix W ₁ ^g, as follows:

Wherein w _g(m, n) represents the element of capable n-th row of m in pre-coding matrix, and N represents reception antenna number, N _hfor the horizontal dimension number of transmit antennas of UPA, G represents the number of full rank DFT matrix, N _hrepresent the number of every a line poliarizing antenna.

Then BD structure structure code book W is adopted according to the correlation of cross polarised antenna emission matrix ₁ ^g, correspond to and adopt ULA cross polarization channel.Concrete form is as follows:

${W_1}^g=\left[\begin{array}{cc}{\tilde{W}}^g& 0\\ 0& {\tilde{W}}^g\end{array}\right]$

Wherein corresponding one group is uniformly distributed and the channel of same polarization antenna formation respectively.

Step 62: according to the character structure code book W of instant channel ₂, and the feature of instant channel depends on the relative phase relation of two groups of cross-polarized antennas to a great extent, can adopt following formula:

Wherein e _nrepresent that other elements are the unit vector of 0, and the span of n is (1,2LN except the n-th element is except 1 _h/ 2), represent the phase difference between two groups of co-polarization antennas.Obtained based on code book W=W corresponding to ULA cross polarization channel by above two steps ₁ ^gw ₂ ^l.

Step 63: the generation of steering vector.

Steering vector W is generated according to the correlation between vertical dimension antenna _v:

$W_V=\frac{1}{\sqrt{N_v}}{\left[\begin{array}{cccc}{e}^{-j(\mathrm{Nv}-1)\mathrm{\ψ}}& \·\·\·& e^{-\mathrm{j\ψ}}& 1\end{array}\right]}^T$

Wherein N _vrepresent UPA vertical dimension antenna line number, ψ represents the phase difference that the wave path-difference that caused by vertical dimension antenna distance is corresponding.

Step 64: construct final 3D precoding codebook.

Finally adopt following formula:

${W_k}^{3D}=W_V\⊗\left({W_1}^g{W_2}^l\right)$

Code book (the W that ULA cross polarization channel is corresponding will be adopted ₁ ^gw ₂ ^l) be extended to code book W based on the extensive mimo system of 3D cross polarization channel _k ^3D, and coexisted in base station end and user side.

Due to the code word pairwise orthogonal in DFT code book at the tenth of the twelve Earthly Branches, and meet constant modulus property, the 3D precoding codebook adopting above method to obtain is still mutually orthogonal, and still meets constant modulus property.Therefore adopt the 3D code book of the present invention's structure not only can effectively mate and adopt the feature of 3D cross polarised antenna channel but also the CCI between user can well be suppressed.

These embodiments are interpreted as only being not used in for illustration of the present invention limiting the scope of the invention above.After the content of reading record of the present invention, technical staff can make various changes or modifications the present invention, and these equivalence changes and modification fall into the inventive method claim limited range equally.

Claims (5)

1., based on a codebook construction method for the extensive mimo system of 3D cross polarization channel, it is characterized in that: comprise the following steps:

101, at base station end configuration N _h× N _vthe uniform surface battle array UPA of dimension cross polarization (-/+45 °) antenna, wherein N _hfor the horizontal dimension number of transmit antennas of uniform surface battle array UPA, N _vfor the line number of the antenna of uniform surface battle array UPA, adopt block diagonal angle-discrete Fourier transform method to carry out conversion to uniform surface battle array UPA and produce basic code book W ₁ ^g, wherein W ₁ ^gfor block diagonal arrangement;

102, then according to the N in step 101 _h× N _vphase difference between dimension cross polarised antenna uniform surface battle array produces code book W ₂ ^l, pass through W ₁ ^gw ₂ ^lstructure adopts the code book that the channel of cross polarised antenna even linear array is corresponding;

103, last according to the correlation between vertical dimension antenna, generate the steering vector W of vertical dimension _v, utilize formula produce precoding codebook, and be kept at base station end and user side, each user of user side selects to make this user obtain the code word of maximum channel gain according to current channel condition information CSI from the precoding codebook designed, the pre-encoding codeword call number PMI of its correspondence is fed back to base station, base station recovers corresponding code word according to PMI from identical code book, and then carries out precoding processing to different user data and then go out from Base Transmitter.

2. the codebook construction method based on the extensive mimo system of 3D cross polarization channel according to claim 1, is characterized in that: the concrete formula adopting block diagonal angle-discrete Fourier transform method to convert uniform surface battle array UPA in step 101 is as follows:

$w_g(m,n)=\frac{1}{\sqrt{N}}{e}^{j\frac{2\mathrm{\π}}{N}m(n+\frac{g}{G})},m=\mathrm{0,1},...,N_h/2-1;n=\mathrm{0,1},...,N_h/2-1;g=\mathrm{0,1},...,G-1$

Wherein w _g(m, n) represents pre-coding matrix the element of capable n-th row of m, N represents reception antenna number, N _hfor the horizontal dimension number of transmit antennas of UPA, G represents the number of full rank DFT matrix, then generates block diagonal arrangement code book W according to following formula ₁ ^g, concrete form is as follows:

${W_1}^g=\left[\begin{array}{cc}{\tilde{W}}^g& 0\\ 0& {\tilde{W}}^g\end{array}\right]$

Wherein corresponding one group is uniformly distributed and the channel of same polarization antenna formation respectively.

3. the codebook construction method based on the extensive mimo system of 3D cross polarization channel according to claim 1, it is characterized in that: to the code book corresponding to the channel of cross polarization (-/+45 °) even linear array ULA in step 102, close series structure W according to two groups of co-polarization antenna phase differences ₂ ^l:

Wherein e _lrepresent that the n-th element is 1, other elements are the N of 0 _hthe vector of/2 × 1, represent the phase difference between two groups of co-polarization antennas.

4. the codebook construction method based on the extensive mimo system of 3D cross polarization channel according to claim 1, is characterized in that: according to the interactive design steering vector W of vertical dimension antenna in step 103 _vformula be:

$W_V=\frac{1}{\sqrt{N_v}}{\left[\begin{array}{cccc}{e}^{-j(\mathrm{Nv}-1)\mathrm{\ψ}}& ...& e^{-\mathrm{j\ψ}}& 1\end{array}\right]}^T$

Wherein ψ represents the phase difference that the wave path-difference that caused by vertical dimension antenna distance is corresponding.

5. the codebook construction method based on the extensive mimo system of 3D cross polarization channel according to claim 1, is characterized in that: the user in step 103 obtains current channel matrix according to channel estimating singular value decomposition is carried out to it

${\tilde{H}}_{N_r\×(N_h/2\×N_v)}^{3D}={\mathrm{U\ΣV}}^H$

Wherein unitary matrice U is current channel matrix left singular vector matrix, Σ is current channel matrix the matrix that forms by descending order of characteristic value, unitary matrice V is current channel matrix right singular vector matrix, if according to current channel matrix the optimum pre-encoding codeword selected is w=[V] ₁, [V] ₁the first row of representing matrix V, then equivalent channel is: ${{\left|\right|{\tilde{H}}^{3D}w\left|\right|}_2}^2={{\left|\right|{\tilde{H}}^{3D}{\left[V\right]}_1\left|\right|}_2}^2={\left({\mathrm{\λ}}_{\max }\right)}^2{\left|\right|{\left[U\right]}_1\left|\right|}^2={\left({\mathrm{\λ}}_{\max }\right)}^2,$ Wherein λ ^maxfor current channel matrix maximum singular value, can find out from above formula, as w=[V] ₁time, user obtains maximum channel gain.