WO2013078743A1 - Precoding method and matrix generation device for coordinated multiple point multiple user mimo system - Google Patents

Abstract

A precoding method and matrix generation device for a coordinated multiple point (CoMP) multiple user MIMO (MU-MIMO) system, the method comprising the following steps: S1, a central control station acquires from each cell base station n (n=1,...,T) a base station transmission power Pn (n=1,...,T), the channel information Hn,i between the base station n and a user i, and a signal-to-noise ratio SNRn,i (i=1,...K), wherein T is the number of cooperative cells, and K is the number of users in the system, and further obtains the channel information Hi and the noise power sigmai 2 of each user; S2, acquiring the complementary channel H̅ i of each user on the basis of the channel information Hi of each user, and conducting channel expansion for each complementary channel H̅ i to obtain a matrix H̿={ H̅ i,sigmai/}, wherein / is the unit matrix of formula I, and Mk represents the number of the receiving aerial of the user k; S3, conducting LQ decomposition for the matrix H̅ i to obtain a unitary matrix Qi; S4, conducting conjugate transposition for the submatrix Q̅ i of the unitary matrix Qi, and multiplying the transposed submatrix by Hi to obtain the equivalent channel Hi equ of each user; S5, conducting SVD decomposition for the equivalent channel Hi equ to obtain the precoding matrix Wi (i=1,...,K) of each user; and S6, obtaining the precoding matrix Wn base (n=1,...T) of each base station according to the precoding matrix Wi (i=1,...,K) of each user, and transmitting the precoding matrix Wn base (n=1,...T) to the corresponding cell base station for precoding.

Description

 Co-coding method and matrix generation device for cooperative multi-point multi-user MIMO system

 The present invention relates to the field of wireless mobile communication technologies, and in particular, to a precoding method and a matrix generation method for a coordinated multi-point user MIMO system. Background technique

 Multiple-Input Multiple-Output (MIMO) technology is a major breakthrough in wireless mobile communications technology. MIMO technology refers to the use of multiple antennas for data transmission and reception. Studies have shown that the use of MIMO technology can increase the capacity of wireless communication systems. With the deepening of multi-antenna technology research, MIMO technology has expanded from point-to-point single-user MIMO technology to point-to-multipoint multi-user MIMO (Multi-User MIMO, MU-MIMO). In MU-MIMO technology, multi-antenna diversity gain can effectively reduce the system error rate, and multi-antenna multiplexing gain expands the capacity area of multi-user systems. MU-MIMO usually uses the transmitter precoding technology to transmit information of multiple users on the same time and frequency resources by using Spatial Division Multiple Access (SDMA) technology.

 In order to meet the requirements of LTE-A system in terms of peak bandwidth average rate of bandwidth, 3GPP proposed Coordinated Multipoint (CoMP) technology in LTE-A system. CoMP technology can be divided into Coordinated beamf orming (CB) and Joint processing (JP) technology. The JP technology can effectively improve the performance of the system by co-precoding of the coordinated cell. However, for CoMP MU-MIMO, since each cell base station simultaneously transmits data to multiple clients, multiple users share the same time-frequency resource, and there must be inter-user interference in the system, including inter-cell interference and intra-cell interference. Therefore, user interference and noise are the same, which greatly affects the performance of the system.

The Zero forcing channel inversion (ZF-CI) technique is proposed to eliminate multi-user interference, but it does not consider the influence of noise, and it is only applicable to one antenna for each user at the receiving end. Minimum mean-squared error channel inversion (MMSE-CI) considers the effect of noise and multi-user interference on system performance, but compared with ZF-CI, it is only suitable for each user at the receiving end. Receive antenna. The Block Diagonolization (BD) precoding technique is proposed to completely eliminate interference between users, and each user at the receiving end can have more than one antenna. However, the BD technology must satisfy the case where the number of antennas at the transmitting end is greater than or equal to the sum of the number of receiving antennas of all users. Therefore, the BD technology is not suitable for the case where each user at the receiving end has an arbitrary receiving antenna. Moreover, BD technology It only eliminates the interference between users, and does not consider the influence of noise on system performance. Therefore, when the signal-to-noise ratio is reduced, its performance is relatively poor. Summary of the invention

 (1) Technical problems to be solved

 The object of the present invention is to enable each user of a CoMP MU-MIMO system to have an arbitrary root receiving antenna, and to reduce the influence of interference and noise between users on the system, and to improve system performance, especially when the noise is large.

 (2) Technical plan

 In order to solve the above technical problem, the present invention provides a precoding method for a coordinated multipoint multi-user MIMO system, comprising the following steps:

S1: The central control station obtains the base station transmit power Ρ _η η = 1, -, Γ), the channel information H „ between the base station η and the user i, and the letter from each cell base station n (n = 1, -; ; T) The noise ratio SNR „, _; ( = l, , , where T is the number of cooperative cells, ^ is the number of users in the system; and then the channel information H, and noise power of each user is obtained.

S2: The central control station obtains the complement channel ^ of each user according to the channel information H of each user, and performs channel extension to obtain a matrix ^ = { ·, ^}; where / is ∑ _k ^K = _{1 i} M _k The unit matrix of x∑ _lk≠ M _k , ^^ represents the number of receiving antennas of the user;

 S3: The central control station performs LQ decomposition on the matrix to obtain a unitary matrix;

 S4: The central control station multiplies the sub-matrix ^: conjugate transpose of β,. by H,. to obtain the equivalent letter of each user.

S5: The central control station performs SVD decomposition on the equivalent channel to obtain a precoding matrix W _t (i = !, ■■■, Κ) of each user;

 S6: The central control station obtains the precoding matrix “= 1,−, ) of each base station according to the precoding matrix ^^' = 1,··· of each user, and sends the precoding matrix to the corresponding cell base station, thereby implementing precoding.

 Preferably, the step S1 further comprises the steps of:

S11: The cell base station obtains channel information ^ _n , SNR _n . {i = \, -, K) through feedback or channel reciprocity.

S12: The central control station obtains the transmission power P„, channel information υκ·= ι,···, from each base station through the network interface; S13: The central control station obtains channel information of each user by combining according to the transmission power P„ and the channel information 11′ obtained from each base station ^=[7^! ^ ...

S14: The central control station obtains the noise power between the base station n and the user i according to the transmission power obtained from each base station, and the signal-to-noise ratio SNR, and obtains the noise power of the user i according to ^ ⁷ ^^ ,.

 Preferably, the step S14 further comprises the steps of:

S141: Obtain the power of the user i receiving the base station n according to the path loss formula == (^) ² ^

R ^C

^P - =^ PL , where c is the speed of light, f is the frequency, d is the distance between the base station and the user, indicating the path loss index; according to the received power and ^^w, the base station n and the user i are obtained.

 , P

SNR _N ,

S142: According to the noise power c^ between the base station n and the user i, the noise power of the user i is obtained=Ση=ΐ ^σ , _ί .

 Preferably, in the step S2:

 First, according to the channel information H,. of each user, the channel information of the multi-user system Η«···, Η···Η Υ, the complement channel of each user ^=( ,···, H , H ... Ύ, here Τ indicates that the step S4 further includes:

 Select the sub-matrix consisting of the elements of the first N column and the last N row of 3⁄4 and multiply the conjugate transposed matrix by H,. to obtain the equivalent channel τ"=Αα" for each user.

 Preferably, the step S5 further comprises the steps of:

 S51: Η Decompose according to the SVD decomposition formula Η = UV" = uM^f; where is the left 酉 matrix, Λ, . is the diagonal matrix, is the right 酉 matrix, consists of the front column, ·, ο by the back N - Μ, column composition, V denotes the complex conjugate transposed matrix of the matrix, , denotes the number of receiving antennas of the user, and N denotes the sum of the number of transmitting antennas of all base stations;

 S52: According to obtaining a precoding matrix of each user ^^ = 1,···, ).

 Preferably, the step S6 further comprises the steps of:

S61: According to the obtained precoding matrix ^(ζ' = 1,···, ), the matrix ^ = [^, one, ^], Gan + Λ ^ NX Υ ^Τ Ν - '甘ώ / 志it W ^ ^ 4 *r · S62: obtaining a precoding matrix w + ι of the base station according to the matrix ^ = [^,···, ^]

：∑ ,,：)表示由矩阵 w的 第∑; , +¹至第 U 行组成的子矩阵；

:∑ , ,:) represents a submatrix consisting of the ∑; , + ¹ to U lines of the matrix w;

 S63: The central control station sends the precoding matrix of each base station (" = 1, - to the base station of the corresponding cell) through the network interface.

 The invention also provides a precoding matrix generating device for a coordinated multi-point multi-user MIMO system, comprising an obtaining module, a calculating module and a generating module:

The acquiring module is configured to acquire transmit power, channel information Η^, ^^^Ι, ···, ^) from each cell base station; where Η„,,· represents channel information between the cell _η and the user i, SNR „,, represents the signal to noise ratio between cell n and user i;

 The calculating module is configured to calculate channel information H, and noise power of the user

 The generating module is configured to generate a precoding matrix of each user according to channel information H, and noise power of each user.

 Preferably, the generating module further includes:

 a channel extension module, configured to perform channel extension on a complement channel of each user to obtain a matrix; an LQ decomposition module, configured to perform LQ decomposition on the matrix, and obtain an effective zero space matrix for each user

Q ;

 The SVD decomposition module is configured to perform SVD decomposition on the equivalent channel Hr=H^T of each user, and obtain a gain matrix of each user;

 The multiplication module is used to multiply the zero space matrix ^ of each user by its gain matrix to obtain the precoding matrix ^=^^ of each user.

Preferably, the matrix after complementing the channel is expanded by ^={·, ^Π; where I is an identity matrix of ∑ί _{Ϊ ί} Μ _{≠l u≠l} M _k , where ^ represents the number of receiving antennas of user k.

 (3) Beneficial effects

In the case that the user has multiple antennas, the above precoding method and device are used to eliminate the influence of two factors such as multi-user interference and noise on the system, and the performance of the coordinated multi-point multi-user MIMO system is improved and the performance is reduced. The complexity of the sender increases the feasibility of this method in practical applications. DRAWINGS Figure 1 is a flow chart of the method of the present invention;

 2 is a schematic structural view of a device of the present invention;

 3 is a graph showing a capacity comparison of a precoding method of the present invention and a cooperative multipoint MIMO system based on the BD precoding method according to an embodiment of the present invention. detailed description

 The specific embodiments of the present invention are further described in detail below with reference to the drawings and embodiments. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

 As shown in FIG. 1, the precoding method of the present invention includes the following steps:

S1: The central control station obtains the base station transmit power from each cell base station (eNB) Ρ„(" = 1,···,Γ) (Τ is the number of cooperative cells), and the channel information between the base station η and the user i ,, and the signal-to-noise ratio SNR _ni (i = l, -, K) (which is the number of users in the system), and then obtain the channel information H of each user _; and the noise power σ, ² 0' = 1,··· , , the specific steps are:

= l,-,K) , 其中 Η„,表示小区 _n与用户 1间的信道信息， SNR 表示小 区 n与用户 i间的信噪比； Cell base station ( = 1,···,Γ) Obtain channel information through feedback or channel reciprocity

= l, -, K) , where Η „ indicates the channel information between cell _n and user 1, and SNR represents the signal-to-noise ratio between cell n and user i;

The central control station obtains transmit power from each base station through a network interface, channel information U _n ., SNR _ni (i = l, ---, K);

According to the transmission power and channel information obtained from each base station, the central control station obtains the channel information of each user by combining... V^3⁄4 _{r ;}

According to the transmission power obtained from each base station and the ^SNR _n , i , according to the path loss formula

。 PL = ^ = (^†d obtains the power of the user i receiving the base station _n = , according to the obtained received power and further obtains the noise power between the base station n and the user i, = one; according to the noise between the base station n and the user i Power ² , ·, and then get the noise power of user i

.

S2: the central control station of each user based on channel information _H;, obtained patch of each user channel ^, and obtain the matrix channel extension of its embodiments, the specific steps:

 Obtaining channel information of the multi-user MIMO system according to the channel information H,. of each user is

H = «···, Η ···ΐ ^τ , the complement channel for each user is ^ =( ,···, H , H ... Ύ, here is the table Transposed.

The channel expansion is performed on the complement channel of each user, and the matrix ^={ , σ _; / } is obtained, where / is the unit matrix of ∑^ _≠ , ><∑^ _≠ , representing the number of receiving antennas of the user. By placing σ,·/ on the right side (the usual method in the prior art is to put it below), the dimension of the matrix is changed to ∑ ^^ ^x (∑ _≠i ^ ⁺ W), obviously its number of columns is greater than its The number of rows, in turn, guarantees the dimensional requirements of the acquisition, zero space. Therefore, the present invention is suitable for a CoMP MU-MIMO precoding system in which each user at the receiving end has an arbitrary receiving antenna. It can be seen from the form of ^ that it considers the influence element and noise which cause interference between multiple users, and /, N is the number of antennas at the transmitting end. Moreover, we can see that the noise power may be different for different users, depending on the transmit power of each base station. Therefore, the present invention is also effectively applicable to a CoMP system in which base station base stations transmit power differently.

 In step S3, the LQ decomposition is performed on the matrix to obtain the lower triangular matrix ^ and the 酉 matrix. The LQ decomposition is used to obtain the triangular matrix Z^P酉 matrix, which reduces the complexity of the transmitting end.

 Step S4, multiplying the sub-matrix of the 3⁄4 with the channel information matrix to obtain an equivalent channel 各 of each user, which specifically includes the following:

The elements of the first N columns and the last N rows of 3⁄4 are selected to form the submatrix ^:, and the conjugate is transposed and right multiplied by H _; , and the equivalent channel 各 "= ^ of each user is obtained.

 Step S5: Perform an SVD decomposition operation on the equivalent channel of each user, and obtain a precoding matrix of each user, which specifically includes the following:

Decompose the H _t ^equ according to the SVD decomposition formula Hr = υ, Α, ν, " = UW _l V _lfi } ^H , where is the left 酉 matrix, Λ _; is the diagonal matrix, is the right 酉 matrix, consists of the front column , ^ff denotes the complex conjugate transposed matrix of the matrix K. The latter is composed of N minus columns, where ^ represents the number of receiving antennas of the user, and N is the number of antennas at the transmitting end.

 According to ^:^^, the precoding matrix of each user is obtained.

 S106: The central control station sends the precoding matrix of each base station obtained according to the precoding matrix to each cell base station, and then performs precoding, which specifically includes the following:

 According to the obtained precoding matrix '= ι,···· of each user, the matrix w = [^d ] can be obtained, and its size is Wx∑^N„, where ^ represents the number of transmitting antennas of the base station;

Obtaining a precoding matrix w = w(∑ N ₊ iU , _: ) of the base station ^z according to ^ W(∑" N _} + 1:∑ ^η Ν _} , :) represents a submatrix consisting of U ₊ 1 to the first row of the matrix w;

Central control station via the network interface precoding matrix ^ ^¾ each base station ( "= 1, a) issue a corresponding base station."

 2 is a schematic structural diagram of a CoMP MU-MIMO precoding matrix generating apparatus according to the present invention. The apparatus includes: an obtaining module 10, a calculating module 20, and a generating module 30:

= !,■-, K) , 其中 H„,_;表示小区 _n与用户 i间的信道信息， SNR_n„泉示 小区 n与用户 i间的信噪比；所述计算模块 20,用于计算出用户的信道信息 以 及噪声功率 所述生成模块 30, 用于根据各用户的信道信息 H_;以及噪声功率 , 生成预编码矩阵 。 The acquiring module 10 is configured to acquire transmit power C channel information from each cell base station.

= !,■-, K) , where H„, _; represents channel information between cell _n and user i, SNR _n „shows the signal-to-noise ratio between cell n and user i; said calculation module 20 is used for calculation the user channel information and the noise power generation module 30, for each user according to channel information _H; and a noise power, to generate a precoding matrix.

The generating module 30 further includes: a channel expansion module 31, an LQ decomposition module 32, an SVD decomposition module 33, and a multiplication module 34. The channel expansion module 31 is configured to perform channel extension on the complement channel of each user, and obtain a matrix LQ decomposition module 32, configured to perform LQ decomposition on the matrix, and obtain a valid zero-space matrix SVD decomposition module 33 for each user, for each user. The equivalent channel ΗΓ = Η ^ ^Η implement SVO decomposition to obtain the gain matrix of each user ^; the multiplication module 34 is used to multiply the zero space matrix of each user by its gain matrix to obtain the precoding matrix W of each user. _t = 3⁄4.

 A comparison of the precoding method of the present invention with other existing precoding schemes will be given below to make the advantages and features of the present invention more apparent.

For a real matrix of mx«, the complexity of SVD decomposition is 1⁄2 ² + 13m ³ (flops), and the complexity of LQ decomposition is 2m ² («-m/3) (flops). Here is a real matrix as an example.

Suppose the system has a user, each user has the same number of receiving antennas _; =Μ, = 0ίΓ-1)χΜ, and assumes that the number of streams transmitted per user is 1, the precoding method of the present invention and the existing precoding The comparison of the complexity is shown in Table 1, where the instance (8, 2, 2, 4) indicates that the sum of the number of transmitting antennas at the base station of the system is ,8, the system has two cells cooperating, and the number of receiving antennas per user is 2. There are 4 users in the system.

 Table 1 Comparison of the complexity of the precoding method of the present invention and the existing precoding

Complexity expression example (8, 2, 2, 4)

 It can be seen from Table 1 that compared with the conventional CoMP MU-MIMO precoding method, such as BD, the technical solution of the present invention greatly reduces the computational complexity of the transmitting end, which will facilitate the practical application of the method of the present invention.

 In addition, as shown in FIG. 3, a capacity comparison graph of the system (8, 2, 4) based on the precoding method of the present invention and the CoMP MU-MIMO system based on the BD precoding method is shown, the system has 4 users, Each user has 2 receiving antennas, and there are 2 coordinated cells. Each cell base station has 4 transmitting antennas at the transmitting end, and the receiving end uses ZF detection. Under different SNR conditions, the multi-user based on the present invention A simulation comparison of the capacity of the precoding system and the BD multi-user precoding system. As can be seen from Fig. 3, the precoding scheme of the present invention can improve the signal to noise ratio of the system better than the BD scheme, thereby increasing the capacity of the system. Moreover, as shown in Table 1, the solution of the present invention has a lower complexity than BD. Furthermore, it shows that this scheme is better implemented than the traditional BD scheme.

 The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make several improvements and substitutions without departing from the technical principles of the present invention. It should also be considered as the scope of protection of the present invention.

Claims

Claim  A precoding method for a coordinated multi-point multi-user MIMO system, comprising the steps of: S1: The central control station obtains the base station transmit power Ρ η = 1, -, Γ), the channel information H „ between the base station η and the user i, and the letter from each cell base station η (η = 1, . . . , Γ) The noise ratio SNR ^l, , , where T is the number of cooperative cells, ^ is the number of users in the system; and then the channel information H of each user is obtained _; and the noise power S2: the central control station of each user based on channel information _H; complement obtaining each user channel ^, ^ embodiment and obtain the matrix channel extension ¾ = {¾,}; where I is ^{_{Σi ≠ i M k xΣ k K}} = _U≠l M _k parking space matrix, ₄ represents the number of receiving antennas of the user;  S3: The central control station performs LQ decomposition on the matrix to obtain a unitary matrix ft; S4: The central control station multiplies the 3⁄4 sub-matrix conjugate by H _; multiplies to obtain the equivalent letter of each user. S5: The central control station performs SVD decomposition on the equivalent channel Hr" to obtain a precoding matrix W _t (i = !, ■■■, K) of each user; S6: The central control station obtains a precoding matrix ^ ("1, -,") of each base station according to each user's precoding matrix ^^' = 1, . . . , and sends it to the corresponding cell base station, thereby implementing precoding.  2. The method of claim 1 wherein said step S1 further comprises the step of: S11: The cell base station obtains channel information ^ _n , SNR _n . {i = \, -, K) through feedback or channel reciprocity. S12: The central control station obtains transmit power, channel information U _ni , SNR _n . (i = l, -, K) from each base station through a network interface. S13: The central control station obtains channel information of each user by combining according to the transmission power obtained from each base station, and the channel information 11...

S14: The central control station obtains the noise power ^ ² between the base station n and the user i according to the transmission power obtained from each base station, the signal to noise ratio SNR, and obtains the noise power of the user i according to ^ ⁷ ^. The method of claim 2, wherein the step S14 further comprises the step of: S141: obtaining the power of the user i receiving the base station n according to the path loss formula == (^ ² ^ ) ^P :=^ PLF, where c represents the speed of light, f is the frequency, d represents the distance between the base station and the user, and represents an index; and according to the obtained received power and ^ν , , ·, the base station η and the user i are obtained.

S142: Obtain the noise power of the user i=Ση=ΐ ^σ η according to the noise power σ^· between the base station n and the user i.  4. The method according to claim 1, wherein in the step S2: First, according to the channel information H,. of each user, the channel information of the multi-user system Η«····Έ,···· ί ^τ , the complement channel of each user ^ = ( ,···, ΑΚ ₊₁ ·· Λ Here Τ indicates 5. The method as claimed in claim 1, wherein the step S4 further comprises: selecting a sub-matrix consisting of elements of the first N columns and the last N rows of the 3⁄4, and multiplying the conjugate transposed matrix by the right Obtain the equivalent channel of each user at H,.  The method of claim 1 wherein said step S5 further comprises the step of: S51: Η Decompose according to the SVD decomposition formula Η = UV" = uM^f; where is the left 酉 matrix, Λ, . is the diagonal matrix, is the right 酉 matrix, consists of the front column, ·, ο by the back N - Μ, column composition, V, represents the complex conjugate transposed matrix of the matrix, represents the number of receiving antennas of the user, and N represents the sum of the number of transmitting antennas of all base stations;  S52: According to obtaining a precoding matrix of each user ^^' = 1,···, ).  The method according to claim 1, wherein the step S6 further comprises the step of: S61: obtaining a matrix according to the obtained precoding matrix ^(ζ' = 1,···, ) [^,一,^] , whose size is ^χΣ^^; where ^ represents the number of transmitting antennas of the base station;  S62: obtaining a precoding matrix of the base station according to the matrix ^ = [^,···, ^]

+ι:∑ , ,:) represents the sub-matrix consisting of the ∑; , + ¹ to the first row of the matrix w;  S63: The central control station sends the precoding matrix of each base station (" = 1, - to the base station of the corresponding cell) through the network interface. 8. A precoding matrix generating apparatus for a coordinated multi-point multi-user MIMO system, characterized in that The acquisition module (10), the calculation module (20), and the generation module (30) are included: The obtaining module (10) is configured to acquire transmit power, channel information Η^, ^^^Ι, ···, ^) from each cell base station; where Η„,,· represents a channel between the cell _η and the user i Information, SNR„,, represents the signal-to-noise ratio between cell n and user i; The calculating module (20) is configured to calculate a channel information H of the user _; and noise power The generating module (30) is configured to generate a precoding matrix of each user according to channel information H of each user _; and noise power.  9. The apparatus of claim 8, wherein the generating module (30) further comprises:  The channel expansion module (31) is configured to perform channel extension on the complement channel of each user to obtain a matrix, and the LQ decomposition module (32) is configured to perform LQ decomposition on the matrix to obtain a valid zero space matrix for each user; The SVD decomposition module (33) is configured to perform SVD decomposition on the equivalent channel Hr=H, ^{H of} each user, and obtain a gain matrix of each user^;  The multiplication module (34) is configured to multiply each user's zero space matrix ^ by its gain matrix to obtain a precoding matrix W of each user. 10. The apparatus according to claim 9, wherein the complemented channel expanded matrix H^iH^I]; wherein / is an identity matrix of ∑, _k≠i M _k ∑ _{lk ≠} M _k , where ^ represents a user The number of receiving antennas of k.