CN104052697A - Interference alignment method based on two-layer pre-coding structure in MIMO-IBC system - Google Patents

Abstract

The invention belongs to the technical field of communication, and discloses an interference alignment method based on a two-layer pre-coding structure and suitable for a multiple input multiple output-interference broadcast channel (MIMO-IBC) system. In the MIMO-IBC system, interference among communities and interference among users are main factors for limiting channel capacity. The method includes the steps of firstly, aligning ICI signals through base station outer layer pre-coding, eliminating the ICI signals through a receiving matrix, and finally eliminating IUI signals through base station inner layer pre-coding. According to the method, when the number of antennas of a base station meets the condition, the ICI signals can be aligned in a low-dimensional interference signal sub-space through closed solution, and otherwise, the ICI signals are aligned in or gets close to the low-dimensional interference signal sub-space through loop iteration. By means of the method, the ICI signals and the IUI signals can be effectively eliminated, the system capacity can be remarkably improved; the zero-forcing technology can be adopted at a receiving end, and therefore receiving is simplified, and meanwhile the requirement for the number of antennas at the receiving end is low.

Description

Interference alignment method based on two-layer precoding structure in MIMO-IBC system

Technical Field

The present invention relates to the field of communications technologies, and in particular, to an Interference Alignment (IA) method based on a two-layer precoding structure in an Interference Broadcast Channel (IBC) system.

Background

In a MIMO system, ICI is a major constraint in obtaining high frequency spectrum utilization. Inter-Cell Interference (ICI) and Inter-user Interference (IUI) are major factors that limit channel capacity. In recent years, a new idea for managing ICI signals in MIMO Interference Channels (ICs) is proposed in the Interference Alignment (IA) technology: the receiving end aligns the ICI signal within a specific interference subspace, while the orthogonal subspace of the interference subspace is used for the transmission of the desired signal. Studies have shown that in MIMO-IC, using IA technology, 1/2 Degrees of Freedom are available per cell (Degrees of Freedom, DoF).

In early research, the IA technology was mostly used for interference channels, and the main research focuses on the problems of the IA technology, such as the optimal DoF obtained, the upper and lower limits of the system capacity, and the number of transmit/receive antennas required to implement IA. However, in the multi-cell MIMO-IBC system, one base station corresponds to multiple users, so that the users not only receive ICI signals but also IUI signals, which is much more complicated than simple MIMO-IC, and currently, the research on IA technology in the multi-cell MIMO-IBC system is not much.

In a multi-cell multi-user scenario, IA techniques can effectively cancel ICI signals and IUI signals, thereby significantly increasing channel capacity. Currently, the research on IA algorithm in multi-cell and multi-user environment can be roughly divided into two categories: iterative algorithms and direct algorithms. The iterative algorithm implements IA by continuously loop iterating the precoding matrix and the receive matrix, whereas the direct algorithm uses a closed-form solution. Iterative algorithms tend to achieve higher channel capacity, especially under low signal-to-noise conditions; however, the iterative algorithm has high complexity and slow convergence speed. The direct algorithm mainly aims at the MIMO-IBC system of 2 cells, interference alignment is realized by jointly designing a precoding matrix and a receiving matrix, and the number of receiving and transmitting antennas is required to meet specific conditions.

Disclosure of Invention

In view of the above, the technical problem to be solved by the present invention is that, for a multi-cell MIMO-IBC system, an iterative algorithm is adopted with high complexity and low convergence rate; interference alignment is realized by jointly designing a precoding matrix and a receiving matrix by adopting a direct algorithm, and the number of receiving and transmitting antennas is required to meet specific conditions. According to the characteristics of a multi-cell MIMO-IBC system, an interference alignment method based on a two-layer precoding structure is provided.

The technical scheme for solving the technical problems is to design an interference alignment method based on a two-layer precoding structure. The system scenario is set as follows: the number of cells is G, the number of users in the cell is K, each user corresponds to d data streams, and the number of antennas of base stations in all the cells is N_tThe number of the user antennas is N_rAnd use of (G, N)_t)×(K,N_r) To identify, the user k uses the symbol g in cell g_kThat is, the base station transmits signals only to users in the own cell. Constructing any Kd order nonsingular matrix (Q)_glAnd (G ≠ l; G, l ═ 1.. G), designing an outer-layer precoding matrix of the base stationAligning all ICI signals in a low-dimensional interference subspace; receiving end design receiving matrixTo cancel the ICI signal; designing inner pre-coding matrix of base stationTo eliminate the IUI signal. Wherein,with a representation dimension of N_tA complex matrix of x Kd,with a representation dimension of dXN_rThe complex matrix of (a) is then formed,a complex matrix with dimensions Kd × d is represented. ()^HIndicating the conjugate transpose of the matrix being solved for. The method specifically comprises the following steps:

designing outer precoding matrix of base stationAligning all ICI signals in a low-dimensional interference subspace; receiving matrix designed for ICI signal eliminationTherefore, the temperature of the molten metal is controlled,is the null space of the ICI signal.

Designing inner layer precoding matrix of base stationFor cancelling the IUI signal, B_gkIs the null space of the IUI signal, i.e.: <math> <mrow> <msub> <mi>B</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>&Subset;</mo> <mi>null</mi> <mrow> <mo>(</mo> <msup> <mrow> <mo>[</mo> <msup> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mn>1</mn> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mn>1</mn> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>H</mi> </msup> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <msup> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mrow> <mi>k</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mrow> <mi>k</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>H</mi> </msup> <mo>,</mo> <msup> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>H</mi> </msup> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <msup> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>H</mi> </msup> <mo>]</mo> </mrow> <mi>H</mi> </msup> <mo>)</mo> </mrow> </mrow> </math> whereinA reception matrix is represented by a matrix of symbols,represents a flat rayleigh fading channel from the base station to the user in the cell, and null () represents a null space for obtaining a matrix.

Base station outer layer pre-weavingCode matrixIt is desirable to align or approximate the interference signals from different base stations to a low-dimensional subspace, e.g., for users in cell g, the ICI signal is aligned or approximated to the interference signal subspace from the g +1 th cell. In the whole system, the outer layer precoding matrix of the base stationSatisfies the following formula:

$\tilde{H}p=0$

$p=\left[\begin{array}{c}\mathrm{vec}\left(P_1\right)\\ \mathrm{vec}\left(P_2\right)\\ .\\ .\\ .\\ \mathrm{vec}\left(P_G\right)\end{array}\right]$

wherein I is and { Q_glA unit matrix of the same order as (G ≠ l; G, l ═ 1.. G),representing a flat rayleigh fading channel from base station l to cell g,denotes the outer precoding matrix of the base station g, O denotes KdkN_r×KdN_tZero matrix, matrix of dimensions()^TRepresenting the transpose of the solved matrix, vec () representing the column vectorization function of the solved matrix.

The receiving matrix divides the signal space into an interference signal subspace and an expected signal subspace at a receiving end, interference signals among users and interference signals among cells are aligned to the interference signal subspace, the expected signals are aligned to the expected signal subspace, and the dimensionality of the expected signal subspace is larger than or equal to the number d of data streams to be transmitted. When N is present_t＞(G-2)KN_rWhen, { Q }_glG is any Kd order nonsingular matrix or any nonzero constant, and p has a nonzero solution; when N is present_t≤(G-2)KN_rWhile, iterating the matrix { Q over the loop_glG ≠ l; G, l ═ 1.. G) and vector p, such thatOrIs close to 0. In addition, when N is_t＝(G-2)KN_rIn time, from the properties of the block matrix, { Q ] is known by matrix operation_glG ≠ l; G, l ═ 1.. G) is a series of nonzero constants such thatIf true, p has a non-zero solution. Wherein rank () represents the rank of the matrix, and | | represents the 2-norm of the vector.

When aligning the interference signal from g +1 cell in the subspace formed by the interference signals from the rest cells, the outer layer precoding matrix of the base stationThen the formula needs to be satisfied:

to this end, for user k in cell g, the IUI signal is aligned atIs also aligned or approximated toSo that the interference signal in the multi-cell MIMO-IBC system can be eliminated using this method. Where span () represents the subspace spanned by the column vectors of the matrix. As can be seen from the design process of the invention, the receiving matrixIs a matrixThe orthogonal matrix of column vectors, therefore, the invention can effectively reduce the number of antennas at the receiving end and the processing complexity, thereby reducing the mobile deviceAnd (4) preparing design cost.

Drawings

FIG. 1 is a schematic diagram of a MIMO-IBC system;

FIG. 2 is a schematic diagram of a method for implementing interference alignment according to the present invention;

FIG. 3 is a flow chart of an implementation of the present invention;

FIG. 4 is a schematic diagram illustrating the interference alignment effect of the present invention;

fig. 5 is a system capacity comparison graph.

Detailed Description

The general multi-cell MIMO-IBC system scenario is: the number of cells is G, each cell only comprises one base station, the base station serves a plurality of users simultaneously, and the G cells have K in total_gEach user, base station and user k is equipped with M_gAndroot antenna, base station transmitting to user kA data stream ofMarking the MIMO-IBC system under the general scene.

The multi-cell MIMO-IBC system scene is set as follows: the number of cells is G, the number of users in the cell is K, each user corresponds to d degrees of freedom, and the number of antennas of base stations in all the cells is N_tThe number of the user antennas is N_rAnd use of (G, N)_t)×(K,N_r) To identify, the user k uses the symbol g in cell g_kThat is, the base station transmits signals only to users in the own cell.

FIG. 1 showsA MIMO-IBC system of G cells, in each cell, one base station serves a plurality of users. There is a total of K in g cells_gEach user, base station and user k is equipped with M_gAndroot antenna, base station transmitting to user kThe number of data streams to be transmitted is,symbol g for user k in cell g_kTo indicate. Channel State Information (CSI) is shared between base stations, and data Information is not shared. By usingRepresenting a MIMO-IBC system in a general scenario. When receiving the expected signal, the user also receives the interference signal between users in the local cell and the interference signal of the adjacent cell, at this time, the user g_kThe received signal may be expressed as:

<math> <mrow> <msub> <mi>y</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>=</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>V</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <msub> <mi>s</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>+</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mi>i</mi> <mo>&NotEqual;</mo> <mi>k</mi> </mrow> <msub> <mi>K</mi> <mi>g</mi> </msub> </munderover> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>V</mi> <msub> <mi>g</mi> <mi>i</mi> </msub> </msub> <msub> <mi>s</mi> <msub> <mi>g</mi> <mi>i</mi> </msub> </msub> <mo>+</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>l</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mi>l</mi> <mo>&NotEqual;</mo> <mi>g</mi> </mrow> <mi>G</mi> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <msub> <mi>K</mi> <mi>l</mi> </msub> </munderover> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>l</mi> </mrow> </msub> <msub> <mi>V</mi> <msub> <mi>l</mi> <mi>i</mi> </msub> </msub> <msub> <mi>s</mi> <msub> <mi>l</mi> <mi>i</mi> </msub> </msub> <mo>+</mo> <msub> <mi>n</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>,</mo> </mrow> </math>

wherein,representing base station l to user g_kA flat rayleigh fading channel;indicating transmission by base station g to user g_kThe signal of (a);representation for signalsThe precoding matrix of (2) satisfies the power constraint condition:represents a user g_kThe received noise is an independent and identically distributed complex Gaussian vector satisfyingEach user decodes the desired signal by means of a reception matrix, assuming user g_kBy means of a receiving matrixThe processed signal is represented as:corresponding user g_kThe data rate of (d) can then be expressed as:

<math> <mrow> <msub> <mi>R</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>=</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mo>{</mo> <mi>det</mi> <mo>[</mo> <mi>I</mi> <mo>+</mo> <mfrac> <mrow> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>V</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <msubsup> <mi>V</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msubsup> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> <mi>H</mi> </msubsup> <msub> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> </mrow> <mrow> <munder> <mi>&Sigma;</mi> <mrow> <mrow> <mo>(</mo> <mi>g</mi> <mo>,</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>&NotEqual;</mo> <mrow> <mo>(</mo> <mi>l</mi> <mo>,</mo> <mi>i</mi> <mo>)</mo> </mrow> </mrow> </munder> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>l</mi> </mrow> </msub> <msub> <mi>V</mi> <msub> <mi>l</mi> <mi>i</mi> </msub> </msub> <msubsup> <mi>V</mi> <msub> <mi>l</mi> <mi>i</mi> </msub> <mi>H</mi> </msubsup> <msubsup> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>l</mi> </mrow> <mi>H</mi> </msubsup> <msub> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>+</mo> <msubsup> <mi>&sigma;</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mn>2</mn> </msubsup> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> </mrow> </mfrac> <mo>]</mo> <mo>}</mo> </mrow> </math>

wherein, | | | | represents solving the 2-norm of the vector, E { } represents solving the expected operation, det { } represents solving the determinant value of the matrix.

In order to decode the desired signal efficiently, the receiving matrix divides the signal space into an interference signal subspace and a desired signal subspace at the receiving end, the inter-user interference signal and the inter-cell interference signal are aligned to the interference signal subspace, and the desired signal is aligned to the desired signal subspace, so that the dimension of the desired signal subspace cannot be smaller than the number of data streams to be transmittedFor this reason, the condition for linear IA can be expressed as:

<math> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>l</mi> </mrow> </msub> <msub> <mi>V</mi> <msub> <mi>l</mi> <mi>i</mi> </msub> </msub> <mo>=</mo> <mn>0</mn> <mo>,</mo> <mo>&ForAll;</mo> <mi>l</mi> <mo>&NotEqual;</mo> <mi>g</mi> <mo>,</mo> <mi>i</mi> <mo>&Element;</mo> <mo>{</mo> <mn>1,2</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <msub> <mi>K</mi> <mi>l</mi> </msub> <mo>}</mo> </mtd> </mtr> <mtr> <mtd> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>V</mi> <msub> <mi>g</mi> <mi>i</mi> </msub> </msub> <mo>=</mo> <mn>0</mn> <mo>,</mo> <mo>&ForAll;</mo> <mi>i</mi> <mo>&NotEqual;</mo> <mi>k</mi> </mtd> </mtr> <mtr> <mtd> <mi>rank</mi> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>V</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>d</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>,</mo> <mo>&ForAll;</mo> <mi>g</mi> <mo>,</mo> <mi>k</mi> </mtd> </mtr> </mtable> </mfenced> </math>

here, rank () represents the rank of the matrix.

Fig. 2 is a schematic diagram of an IA implementation based on a two-layer precoding structure proposed by the present invention, assuming that a system has symmetric antenna numbers, each cell has one base station and K users, each user corresponds to d data streams, and all base station antenna numbers are N_t＝M_gG, the number of user antennas is 1For this system (G, N)_t)×(K,N_r) Marked, user k in cell g uses symbol g_kThat is, the base station transmits signals only to users in the own cell. The base station is provided with two layers of precoding, and the inner layer precoding is recorded asFor cancelling the IUI signal; the outer layer precoding is recorded asFor aligning ICI signals. User g_kBy means of a receiving matrixThe processed signal is represented as:

<math> <mrow> <mover> <msub> <mi>s</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>^</mo> </mover> <mo>=</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <msub> <mi>B</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <msub> <mi>s</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>+</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mi>i</mi> <mo>&NotEqual;</mo> <mi>k</mi> </mrow> <mi>K</mi> </munderover> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <msub> <mi>B</mi> <msub> <mi>g</mi> <mi>i</mi> </msub> </msub> <msub> <mi>s</mi> <msub> <mi>g</mi> <mi>i</mi> </msub> </msub> <mo>+</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <munderover> <mi>&Sigma;</mi> <mrow> <mi>l</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mi>l</mi> <mo>&NotEqual;</mo> <mi>g</mi> </mrow> <mi>G</mi> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>K</mi> </munderover> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>l</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>l</mi> </msub> <msub> <mi>B</mi> <msub> <mi>l</mi> <mi>i</mi> </msub> </msub> <msub> <mi>s</mi> <msub> <mi>l</mi> <mi>i</mi> </msub> </msub> <mo>+</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>n</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> </mrow> </math>

wherein,representing base station l to user g_kThe flat rayleigh fading channel of (1),indicating transmission by base station g to user g_kThe signal of (a) is received,represents a user g_kThe received noise is an independent and identically distributed complex Gaussian vector satisfyingA complex matrix with dimensions Kd x d is represented,with a representation dimension of N_tA complex matrix of x Kd,with a representation dimension of dXN_rA complex matrix of (a);

fig. 3 is a flow chart showing an implementation of the present invention, which specifically includes the following steps:

step 301, designing inner layer precoding of base stationMatrix arrayThe ICI signal is aligned in a low dimensional subspace. Thus, the interfering signals from other cells can be expressed as:

the receiving end uses zero forcing technique to eliminate ICI signal, therefore, in order to receive d non-interference data streams, the number of receiving end antennas N is needed_rNot less than (G-1) Kd + d. The scheme passes through a precoding matrixAligning interference signals from different base stations in the same low-dimensional subspace, and for a user k in a cell g, aligning the interference from other cells to the interference signal subspace from a g +1 cell one by oneNamely: $\mathrm{span}\left(G_{g_k,g+1}\right)=\mathrm{span}\left(H_{g_k,1}{P}_1\right)=...=\mathrm{span}\left(H_{g_k,g-1}{P}_{g-1}\right)=\mathrm{span}\left(H_{g_k,g+2}{P}_{g+2}\right)=...=\mathrm{span}\left(H_{g_k,G}{P}_G\right)$ where span () represents the subspace spanned by the column vectors of the matrix.

Since the elementary column transformations do not change the column space of a matrix, by enhancing the constraint, the above equation can be written as:

$G_{g_k,g+1}=H_{g_k,1}{P}_1{Q}_{g1}=...=H_{g_k,g-1}{P}_{g-1}{Q}_{g(g-1)}=H_{g_k,g+2}{P}_{g+2}{Q}_{g(g+2)}=...=H_{g_k,G}{P}_G{Q}_{\mathrm{gG}},$

wherein, { Q_glThe Kd order nonsingular square matrix can be used, and the Kd order nonsingular square matrix can also be used as a nonzero constant.

According to the Cronck product propertyThe above formula can be further written as: <math> <mrow> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <mrow> <mo>(</mo> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mrow> <mi>g</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mo>=</mo> <mrow> <mo>(</mo> <msub> <mi>Q</mi> <mrow> <mi>g</mi> <mn>1</mn> </mrow> </msub> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mn>1</mn> </msub> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mo>.</mo> </mtd> </mtr> <mtr> <mtd> <mo>.</mo> </mtd> </mtr> <mtr> <mtd> <mo>.</mo> </mtd> </mtr> <mtr> <mtd> <mrow> <mo>(</mo> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mrow> <mi>g</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mo>=</mo> <mrow> <mo>(</mo> <msub> <mi>Q</mi> <mrow> <mi>g</mi> <mrow> <mo>(</mo> <mi>g</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </msub> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mrow> <mi>g</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mo>(</mo> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mrow> <mi>g</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mo>=</mo> <mrow> <mo>(</mo> <msub> <mi>Q</mi> <mrow> <mi>g</mi> <mrow> <mo>(</mo> <mi>g</mi> <mo>+</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </msub> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> <mo>+</mo> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mrow> <mi>g</mi> <mo>+</mo> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mo>.</mo> </mtd> </mtr> <mtr> <mtd> <mo>.</mo> </mtd> </mtr> <mtr> <mtd> <mo>.</mo> </mtd> </mtr> <mtr> <mtd> <mrow> <mo>(</mo> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mrow> <mi>g</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> <mo>=</mo> <mrow> <mo>(</mo> <msub> <mi>Q</mi> <mi>gG</mi> </msub> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>G</mi> </mrow> </msub> <mo>)</mo> </mrow> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mi>G</mi> </msub> <mo>)</mo> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>,</mo> </mrow> </math> wherein I is and { Q_glThe unit arrays of the same order; ()^TRepresenting the transpose of the solved matrix, vec () representing the column vectorization function of the solved matrix. At this time, an inter-cell interference signalTherefore, it is understood that the number of user antennas can be effectively reduced by the above processing.

For the whole system, the interference signals between cells are aligned in the interference subspace from the next cell, and the outer layer precoding matrix of the base stationThe following equation is satisfied:

$\tilde{H}p=0$

$p=\left[\begin{array}{c}\mathrm{vec}\left(P_1\right)\\ \mathrm{vec}\left(P_2\right)\\ .\\ .\\ .\\ \mathrm{vec}\left(P_G\right)\end{array}\right]$

wherein I is and { Q_glA unit matrix of the same order of (G ≠ l; G, l ═ 1,. G);

representing a flat rayleigh fading channel from base station l to cell g, representing the outer precoding matrix, P, of the base station g₁Representing the outer precoding matrix of the base station 1, i.e. P₂Denotes the outer precoding matrix of the base station 2, O denotes KdkN_r×KdN_tA zero matrix of dimensions; matrix array

Matrix arrayEach matrix block (e.g., O,) All are matrixes with the same dimension, and if each matrix block is viewedInto an element, then a matrixThere are (G-2) G rows, G columns, each row having only 2 elements other than O, the first (G-2) row being for aligning ICI signals received by users in cell 1, the second (G-2) row being for aligning ICI signals received by users in cell 2, and so on.

To illustrate the outer precoding matrix specifically and simplyTaking the example of G-3 as an analysis, the alignment of inter-cell interference signals needs to satisfy

The following formula:

<math> <mrow> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <mi>O</mi> </mtd> <mtd> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>12</mn> </msub> </mtd> <mtd> <mo>-</mo> <msubsup> <mi>Q</mi> <mn>13</mn> <mi>T</mi> </msubsup> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>13</mn> </msub> </mtd> </mtr> <mtr> <mtd> <mo>-</mo> <msubsup> <mi>Q</mi> <mn>21</mn> <mi>T</mi> </msubsup> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>21</mn> </msub> </mtd> <mtd> <mi>O</mi> </mtd> <mtd> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>23</mn> </msub> </mtd> </mtr> <mtr> <mtd> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>31</mn> </msub> </mtd> <mtd> <mo>-</mo> <msubsup> <mi>Q</mi> <mn>32</mn> <mi>T</mi> </msubsup> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>32</mn> </msub> </mtd> <mtd> <mi>O</mi> </mtd> </mtr> </mtable> </mfenced> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mn>1</mn> </msub> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mi>vec</mi> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mn>3</mn> </msub> <mo>)</mo> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>=</mo> <mover> <mi>H</mi> <mo>~</mo> </mover> <mi>p</mi> <mo>=</mo> <mn>0</mn> </mrow> </math>

wherein, $p=\left[\begin{array}{c}\mathrm{vec}\left(P_1\right)\\ \mathrm{vec}\left(P_2\right)\\ \mathrm{vec}\left(P_3\right)\end{array}\right]=\left[\begin{array}{c}{p}_1\\ p_2\\ p_3\end{array}\right].$

3011: in N_t＞KN_rWhen, { Q }_glG is any Kd order nonsingular matrix or any nonzero constant, and p has a nonzero solution.

3012: in N_t≤KN_rWhen the above equation has a non-zero solution, the matrix { Q }_glG (G ≠ l; G, l ═ 1.. G) needs to be satisfied, so thatOr makeClose to 0, eventually solving for p. At this time, the rank limitation problem can be changed to the following optimization problem:in the known { Q_glIn the case of (G ≠ l; G, l ═ 1.. G), the optimal solution p of the equation is a matrixThe minimum eigenvalue of (2) corresponds to the eigenvector. In addition to this, the present invention is, <math> <mrow> <munder> <mi>min</mi> <mrow> <mi>p</mi> <mo>,</mo> <mo>{</mo> <msub> <mi>Q</mi> <mi>gl</mi> </msub> <mo>}</mo> </mrow> </munder> <msup> <mrow> <mo>|</mo> <mo>|</mo> <mover> <mi>H</mi> <mo>~</mo> </mover> <mi>p</mi> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>=</mo> <munder> <mi>min</mi> <mrow> <mi>p</mi> <mo>,</mo> <mo>{</mo> <msub> <mi>Q</mi> <mi>gl</mi> </msub> <mo>}</mo> </mrow> </munder> <mrow> <mo>(</mo> <msup> <mrow> <mo>|</mo> <mo>|</mo> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>12</mn> </msub> <msub> <mi>p</mi> <mn>2</mn> </msub> <mo>-</mo> <msubsup> <mi>Q</mi> <mn>13</mn> <mi>T</mi> </msubsup> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>13</mn> </msub> <msub> <mi>p</mi> <mn>3</mn> </msub> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup> <mrow> <mo>|</mo> <mo>|</mo> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>23</mn> </msub> <msub> <mi>p</mi> <mn>3</mn> </msub> <mo>-</mo> <msubsup> <mi>Q</mi> <mn>21</mn> <mi>T</mi> </msubsup> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>21</mn> </msub> <msub> <mi>p</mi> <mn>1</mn> </msub> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup> <mrow> <mo>|</mo> <mo>|</mo> <mi>I</mi> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>31</mn> </msub> <msub> <mi>p</mi> <mn>1</mn> </msub> <mo>-</mo> <msubsup> <mi>Q</mi> <mn>32</mn> <mi>T</mi> </msubsup> <mo>&CircleTimes;</mo> <msub> <mi>H</mi> <mn>32</mn> </msub> <msub> <mi>p</mi> <mn>2</mn> </msub> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>)</mo> </mrow> </mrow> </math> from the least squares solution, Q is known₁₃＝((H₁₃p₃)^HH₁₃p₃)^-1(H₁₃p₃)^H(H₁₂p₂)，Q₂₁,Q₃₂Is also similar to Q₁₃. Next, the vector p and the matrix { Q ] are iterated through a loop_glG ≠ l; G, l ═ 1.. G), resulting in an optimal solution. Wherein rank () represents the rank of the matrix, and | | represents the 2-norm of the vector.

The steps of this round robin algorithm are summarized as follows: 1) initializing arbitrary Kd order nonsingular square matrix Q_glG ≠ l; G, l ═ 1.. G); 2) solving the matrixThe feature vector p corresponding to the minimum feature value of (a); 3) solving for { Q) from a least squares solution_glG ≠ l; G, l ═ 1.. G); 4) repeating the steps 2) and 3) untilε is a non-negative number.

3013: when N is present_t＝KN_rWhen, { Q }_glG (G ≠ l; G, l ═ 1.. G) need only be a non-zero constant, which is divided by the non-zero constant { Q for ease of distinction_glG is marked as { a ≠ l; G, l ═ 1_glAnd (G ≠ l; G, l ═ 1,. G), obtaining a precoding matrix through closed-type solvingAt this time, the matrixIs equivalent to $\det \left\{\tilde{H}\right\}=0.$ By matrix operation, we can get:wherein, $b={(-1)}^{N_t}\det \left(H_{23}{H}_{32}{H}_{13}{H}_{23}^{-1}{H}_{21}\right)$ and <math> <mrow> <mi>&Omega;</mi> <mo>=</mo> <mo>-</mo> <msubsup> <mi>H</mi> <mn>21</mn> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msubsup> <msub> <mi>H</mi> <mn>23</mn> </msub> <msubsup> <mi>H</mi> <mn>13</mn> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msubsup> <msub> <mi>H</mi> <mn>12</mn> </msub> <msubsup> <mi>H</mi> <mn>32</mn> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msubsup> <msub> <mi>H</mi> <mn>31</mn> </msub> <mo>.</mo> </mrow> </math> when-a₃₂a₁₃a₂₁When the characteristic value is equal to the characteristic value of omega,this is true. Where det { } denotes a determinant value of the matrix.

Step 302, design the receiving matrixTo cancel the ICI signal and, therefore,is the null space of ICI signal, where G is the number of cells, K is the number of users in a cell, N_rThe number of antennas configured for the users, d data streams per user,with a representation dimension of dXN_rTo (2)Matrix, ()^HIndicating the conjugate transpose of the matrix being solved for.

Step 303, designing inner layer precoding matrix of base stationTo cancel the IUI signal and, therefore,is the null space of the IUI signal. Namely:

<math> <mrow> <msub> <mi>B</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> </msub> <mo>&Subset;</mo> <mi>null</mi> <mrow> <mo>(</mo> <msup> <mrow> <mo>[</mo> <msup> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mn>1</mn> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mn>1</mn> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>H</mi> </msup> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <msup> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mrow> <mi>k</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mrow> <mi>k</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>H</mi> </msup> <mo>,</mo> <msup> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>H</mi> </msup> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <msup> <mrow> <mo>(</mo> <msubsup> <mi>U</mi> <msub> <mi>g</mi> <mi>k</mi> </msub> <mi>H</mi> </msubsup> <msub> <mi>H</mi> <mrow> <msub> <mi>g</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>g</mi> </mrow> </msub> <msub> <mi>P</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>H</mi> </msup> <mo>]</mo> </mrow> <mi>H</mi> </msup> <mo>)</mo> </mrow> </mrow> </math> . Wherein,a reception matrix is represented by a matrix of symbols,representing the flat Rayleigh fading channel, P, from the base station to the users of the cell_gRepresenting the outer precoding matrix of base station g. G is the number of cells, K is the number of users in the cell, each user corresponds to d degrees of freedom,a complex matrix with dimensions Kd x d is represented,with a representation dimension of dXN_rComplex matrix of (c) ()^HDenotes the conjugate transpose of the matrix being evaluated, null () denotes the null space of the matrix being evaluated.

To this end, the IUI signal is aligned atIs also aligned or approximated toThe interference signal of the multi-cell MIMO-IFBC system is cancelled in the orthogonal subspace, as shown in fig. 4. Where span () represents the subspace spanned by the column vectors of the matrix. Symbol in FIG. 4The numbers refer to the above.

In addition, we can also align the interference signal from g +1 th cell in the subspace formed by the interference signals from the remaining cells, i.e. the interference signal from g +1 th cell is represented as a linear combination of the interference signals from the remaining cells, when the precoding matrix { P }_gSatisfy the following equation:

at this time, the ICI signal from the neighboring cell is expressed as:

the number of required receiving-end antennas is increased compared to the above scheme, but the number of required base station antennas is decreased. Thus, under different scenarios, different ICI signal alignment schemes may be selected.

Fig. 5 is a simulation diagram of system capacity when the number d of data streams transmitted by the base station to each user is 1 and the total degree of freedom DoF is 8 in the (4,13) × (2,3), (4,12) × (2,3), and (4,11) × (2,3) system configurations. Number of antennas N of base station_tNot less than 13, namely N is satisfied_t> (G-2) KNr, the ICI signal can be aligned completely within the same low-dimensional subspace, i.e.The orthogonal subspace of (a); number of antennas N of base station_t≤(G-2)KN_rIn time, by designing the nonsingular array Q, the inter-cell interference signals can be aligned or approximated toWithin the orthogonal subspace. From the results of fig. 5, it can be seen that the number of antennas N at the base station_t12,11, a littleBelow the threshold 13, ICI signals are almost completely cancelled and the system capacity is slightly reduced, mainly due to the reduced number of base station antennas. The invention effectively reduces the number of user antennas and the processing complexity by arranging double-layer precoding in the base station, saves the design cost of the mobile equipment, and can effectively eliminate ICI signals and IUI signals in a multi-cell MIMO-IBC system.

Claims (7)

1. The interference alignment method based on the two-layer precoding structure in the multi-input multi-output interference broadcast channel system is characterized by comprising the following steps: constructing any Kd order nonsingular matrix (Q)_glDesigning an outer precoding matrix of the base stationAligning all ICI signals in a low-dimensional interference subspace; receiving end design receiving matrixTo cancel the ICI signal; designing inner pre-coding matrix of base stationTo cancel IUI signals, wherein l 1.. G, G1.. G; k1, K, G being the number of cells in the system, K being the number of users in each cell, N_tAnd N_rThe number of antennas configured for the base station and the user, d is the data stream corresponding to each user,with a representation dimension of N_tA complex matrix of x Kd,with a representation dimension of dXN_rThe complex matrix of (a) is then formed,complex matrix of dimension Kd × d, ()^HIndicating the conjugate transpose of the matrix being solved for.

2. The method according to claim 1, wherein aligning all ICI signals in a low-dimensional interference subspace comprises: for users in a cell g, aligning or approximating ICI signals to an interference signal subspace from a g +1 cell, and a base station outer layer precoding matrix P_gSatisfies the formula:

$\tilde{H}p=0$

$p=\left[\begin{array}{c}\mathrm{vec}\left(P_1\right)\\ \mathrm{vec}\left(P_2\right)\\ .\\ .\\ .\\ \mathrm{vec}\left(P_G\right)\end{array}\right]$

wherein Q is_glIs Kd order nonsingular matrix, I is AND Q_glUnit array of the same order, H_glRepresenting a flat Rayleigh fading channel, P, from base station l to cell g_gAn outer layer precoding matrix of a base station g is represented, and g is not equal to l; g, l ═ 1.. G, O denotes KdkN_r×KdN_tZero matrix, matrix of dimensionsThe expression dimension is (G-2) GKKDKN_r×GKdN_tComplex matrix of (c) ()^TRepresenting the transpose of the solved matrix, vec () representing the column vectorization function of the solved matrix.

3. The method of claim 1Method, characterized in that the interfering signals from g +1 cells are aligned into the subspace formed by the interfering signals from the remaining cells, the outer precoding matrix P of the base station_gSatisfies the formula:

wherein Q is_glIs Kd order nonsingular matrix, I is AND Q_glUnit array of the same order, H_glRepresenting a flat Rayleigh fading channel, P, from base station l to cell g_gDenotes the outer precoding matrix of the base station g, O denotes KdkN_r×KdN_tZero matrix, matrix of dimensionsThe expression dimension is GKdKN_r×GKdN_tComplex matrix of (c) ()^TRepresenting the transpose of the solved matrix, vec () representing the column vectorization function of the solved matrix.

4. A method according to one of claims 1-3, characterized in that the receiving matrix is a matrixIs the null space of the ICI signal, where,with a representation dimension of dXN_rThe complex matrix of (a).

5. Method according to one of claims 1 to 3, characterized in that the inner precoding matrix B of the base station is designed_gkIs the null space of the IUI signal, where, a complex matrix with dimensions Kd × d is represented.

6. A method according to one of claims 1 to 3, characterized in that the receiving matrix at the receiving end divides the signal space into an interference signal subspace to which inter-user interference signals and inter-cell interference signals are aligned and a desired signal subspace to which desired signals are aligned, the dimensions of the desired signal subspace being greater than or equal to the number of data streams to be transmitted.

7. The method of claim 2, wherein when N is_t＞(G-2)KN_rTime, matrix Q_glIs any Kd order nonsingular matrix or any nonzero constant; when N is present_t＜(G-2)KN_rWhile iterating the matrix Q through the loop_glAnd a vector p, such thatOr makeIs close to 0; when N is present_t＝(G-2)KN_rTime, matrix Q_glIs a non-zero constant. Wherein,is a dimension of (G-2) GKdkK_r×GKdN_tThe elements of the complex matrix are composed of a channel matrix and a non-singular matrix Q_glFormed by the elements of the vector P being the outer precoding matrix P of the base station_gThe rank () represents the rank of the solution matrix, and | | represents the 2-norm of the solution vector.