CN104219703A - Two-stage interference aligning method in downlink communication of heterogeneous cellular network - Google Patents

Abstract

The invention discloses a two-stage interference alignment method in downlink communication of a heterogeneous cellular network, which mainly solves the problem of downlink interference in the heterogeneous cellular network. The implementation steps are: (1) base stations select their own service users; (2) users measure the channel state information from each base station to themselves and feed back to the base station serving them; (3) smallcell base stations send channel state information to macro base stations , (4) The macro base station constructs two-stage interference alignment according to this information; (5) The macro base station sends the transmit precoding matrix and the user's receive filter to each smallcell base station; (6) The base station sends the user's receive filter to the user And send data to the respective users; (7) The users receive the data using the received receiving filter. According to the characteristics of the heterogeneous cellular network, the invention designs a new interference alignment method, increases the number of data streams transmitted simultaneously in the network, and improves the network capacity.

Description

A Two-Stage Interference Alignment Method in Downlink Communication of Heterogeneous Cellular Networks

technical field

The invention relates to the field of wireless communication, in particular to a two-stage interference alignment method in downlink communication of heterogeneous cellular networks, which can be used for downlink interference management in heterogeneous cellular networks.

Background technique

The rapid development of wireless services makes the expansion of wireless communication networks an urgent problem to be solved. Studies have shown that by deploying small cells, such as relays, picocells, and femtocells, in existing macrocells, the capacity of the network can be economically and effectively increased. However, since smallcells and macrocells reuse the same spectrum resources, the interference problem in heterogeneous cellular networks is very serious.

Due to the introduction of smallcell, two new types of interference appear in heterogeneous cellular networks: interlayer interference and intralayer interference. Intra-layer interference refers to interference between cells of the same layer in a heterogeneous cellular network, such as interference between picocells; inter-layer interference refers to interference between cells of different layers in a heterogeneous cellular network, such as interference between macro cells and picocells. Existing interference management methods are mainly implemented through resource division. Interference avoidance is achieved by allocating orthogonal resources to mutually interfering cells. However, this method cannot realize full frequency multiplexing, so the utilization efficiency of spectrum is greatly reduced.

Interference alignment method is considered to be an effective method to solve network interference. The basic idea of interference alignment is to align multiple interference signals to the same subspace by designing the transmission precoding matrix so that other subspaces can be transmitted without interference. The method of interference alignment can effectively increase the number of data streams transmitted in parallel in the system, thereby increasing the capacity of the system. Due to the large number of small cells in the heterogeneous cellular network and the limited number of antennas of the base station and user equipment, if perfect interference alignment is to be achieved, only a small number of links can transmit simultaneously, thus limiting the capacity of the network.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention aims to provide a two-stage interference alignment method in the downlink communication of the heterogeneous cellular network, and propose a new interference alignment method by making full use of the characteristics of the heterogeneous cellular network to solve the heterogeneous Downlink interference problems in cellular networks.

In order to achieve the above object, the present invention adopts the following technical solutions:

A two-stage interference alignment method in downlink communication of a heterogeneous cellular network, comprising the following steps:

Step 1, the macro base station selects S macro users to serve, and each smallcell base station selects one user to serve, wherein S≤M ₀ , M ₀ is the number of antennas of the macro base station;

Step 2, the selected user measures the channel state information (CSI) from all base stations to itself, and feeds back to the base station serving itself;

Step 3, each smallcell base station sends the received CSI information to the macro base station;

Step 4, mark the macro base station as 0, and mark the S macro users selected by the macro base station as {k ₁ , k ₂ , ..., k _S }; since each smallcell base station only selects one user to serve, the smallcell The number of the base station is used to mark the users it serves; at the same time, since each cell has only one base station, the number of the smallcell base station is also used to mark the smallcell; smallcell base stations {1, 2, ..., L} form a group A, Smallcell base stations {L+1, L+2, ..., L+J} form a group B, where:

Δ=M+N-(S+1)d, M is the number of transmitting antennas of each smallcell base station, and all smallcell base stations have the same number of transmitting antennas; N is the number of receiving antennas of each user, and all users in the network have the same The number of receiving antennas; d is the number of data streams received by each macro user and each smallcell user in group A, that is, the macro base station sends d data streams to each macro user, and each smallcell base station in group A Also send d data streams to the users of its services;

Step 5, the macro base station designs the transmission precoding matrix of itself and the smallcell base stations in the group A;

Step 6, the macro base station designs the transmission precoding matrix of the smallcell base stations in the group B;

Step 7, the macro base station sends the obtained transmission precoding matrix of each smallcell base station and the receiving filter of the corresponding user to the corresponding smallcell base station through the backhaul link;

Step 8, the macro base station and each smallcell base station send the receiving filters of their users to the corresponding users, and use the transmission precoding matrix obtained in steps 5 and 6 to send data to the users served by them;

Step 9, each user uses the received receiving filter to eliminate interference and receive data.

It should be noted that in step 4, the smallcell base stations in the group A and the smallcell base stations in the group B have the following characteristics:

First, there is serious interference among the smallcells in the group A, that is, the smallcell i (i∈{1,...,L}) satisfies at least one of the following conditions:

(1) The base station of smallcell i causes serious interference to at least one of the users served by other smallcell base stations in group A, namely P _j is the transmit power of smallcell base station j, P _i is the transmit power of smallcell base station i, H _j,i represents the channel matrix from smallcell base station i to user j, and H _j,j is the direct channel from base station j to served user j Matrix, ‖·‖ _F represents the F-norm of the matrix, α is a threshold value, the value is given when configuring the system parameters;

(2) Users in smallcell i are severely interfered by at least one base station of other smallcell base stations in group A, that is H _{i, j} represents the interference channel matrix from smallcell base station j to user i; H _{i, j} is the direct channel matrix from base station i to served user i;

Secondly, the smallcell base stations in the group B cause very weak interference to the smallcell users in the group A, namely β is a threshold value, the value is given when configuring the system parameters, and the smallcell base station in group A causes very weak interference to the smallcell users in group B, namely At the same time, the smallcell base stations in the group B cause very weak interference to users of other smallcells in the group B, namely i∈{L+1,...,L+J}.

It should be noted that the step 5 specifically includes the following steps:

In step 5.1, the macro base station calculates the following matrix:

in, H _{L+x, 0} represents the channel matrix from the macro base station to the user L+x in group B, x=1, 2, ..., q, Indicates the conjugate transpose operation of the matrix, and null( ) means to find the null space of the matrix;

Step 5.2, the macro base station calculates the transmit precoding matrix of the macro base station and the smallcell base station in group A using the layered interference alignment scheme, and the macro base station uses the following equivalent channel matrix during this process

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ;</span>$

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; ;</span>$

The layered interference alignment scheme specifically includes the following process:

Step 5.2.1, the smallcell base station in the group A generates a random precoding matrix V _j , and V _j satisfies the condition Be the conjugate transpose of V _j , j=1,2,...,L, I _d is the identity matrix of d×d;

Step 5.2.2, let j=1,2,...,L;

Step 5.2.3, according to the transmission precoding matrix in step 5.2.2 Compute the interference covariance matrix: Wherein, H _{i, j} is the channel matrix from base station j to user i, P _j is the transmit power of base station j, i∈{k ₁ ,...,k _S ,1,...,L};

Step 5.2.4, judge whether the interference leakage I _f is less than the interference leakage threshold ε, if yes, the transmission precoding matrix in step 5.2.2 That is, the transmission precoding matrix required by base station j, so that And go to step 5.2.7; otherwise, go to step 5.2.5; where, interference leakage Tr[IF _i ] is the trace of the interference covariance matrix IF _i described in step 5.2.3, ε is a given interference leakage threshold, which is given when configuring system parameters; ε is an empirical value, which determines the The number of iterations of the layer interference alignment algorithm, if ε is relatively small, the number of iterations of the algorithm is more, the effect is better, otherwise, the number of iterations is less, the effect is poor. In practice, it is necessary to take an appropriate value, taking into account the number of iterations and performance;

Step 5.2.5, based on the interference covariance matrix IF _i obtained in step 5.2.3, calculate the user's receiving filter: U _i =v _d [IF _i ], i∈{k ₁ ,..., k _S ,1,...,L}, where U _i is the receiving filter of user i, v _d [IF _i ] is composed of eigenvectors corresponding to the smallest d eigenvalues of the interference covariance matrix IF _i matrix;

Step 5.2.6, according to the user receiving filter in step 5.2.5, according to the following formula Calculate the transmit precoding matrix of base station j and return to step 5.2.2; wherein, U _i is the receiving filter of user i in step 5.2.5, j=1, 2, ..., L;

Step 5.2.7, based on the interference covariance matrix IF _i obtained in step 5.2.3, calculate the receiving filter of the user: U _i =v _d [IF _i ], i∈{k ₁ ,..., k _S ,1,...,L};

Step 5.2.8, calculate the precoding matrix of the macro base station:

Where s=1, 2..., S, then the transmit precoding matrix of the macro base station is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; .</span>$

It should be noted that the step 6 includes the following specific steps:

Step 6.1, design the transmission precoding matrix of the smallcell base station {L+1, L+2, ..., L+q}, specifically:

In step 6.1.1, the macro base station calculates the following matrix:

In step 6.1.2, the macro base station performs singular value decomposition on the following matrix:

Among them, the diagonal elements of matrix Λ _j are matrix The singular value of , the transmission precoding matrix of smallcell base station j is j=L+1,...,L+q, the receiving filter of user j served by it is j=L+1,...,L+q;

Step 6.2. Design the transmission precoding matrix of the smallcell base station {L+q, ..., L+J}, specifically:

In step 6.2.1, the macro base station calculates the following matrix

In step 6.2.2, the macro base station performs singular value decomposition on the following matrix

The transmit precoding matrix of Smallcell base station j is j=L+q,...,L+J, the receiving filter of user j served by it is j=L+q, . . . , L+J.

The beneficial effects of the present invention are:

1. According to the low power characteristics of smallcell base stations in a heterogeneous cellular network, the present invention makes full use of geographical space resources, so that more smallcell base stations can transmit data at the same time, increasing the throughput of the network.

2. The present invention makes full use of the heterogeneous characteristics of the heterogeneous cellular network, that is, the macro base station has more transmitting antennas: by making full use of the antennas of the macro base station, the interference of the macro base station to the smallcell base station is reduced, thereby increasing the throughput of the network .

3. The present invention not only enables the macro base station to transmit simultaneously with more smallcell base stations by designing the transmission precoding matrix, but also simultaneously eliminates inter-layer interference and intra-layer interference in the heterogeneous cellular network.

Description of drawings

Fig. 1 is the realization overall flowchart of the present invention;

Figure 2 is a flow chart of building the two-stage interference alignment in Figure 1.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings, but it should be noted that this embodiment is based on the technical solution and provides detailed implementation methods and implementation steps, but is not limited to this embodiment.

With reference to Fig. 1, concrete implementation steps of the present invention are as follows:

Step 1, the macro base station selects S macro users to serve, and each smallcell base station selects one user to serve, wherein S≤M ₀ , M ₀ is the number of antennas of the macro base station;

In step 2, the selected user measures channel state information (CSI) from all base stations to itself, and feeds back to the base station serving itself.

The channel state information CSI is a channel matrix H _{i, j} , i∈{k ₁ ,..., k _S , 1,..., L, L+1,..., L+J}, j∈ {1,...,L,L+1,...,L+J}.

Step 3: Each smallcell base station sends the received CSI information to the macro base station.

Step 4: For the sake of simplicity, we mark the macro base station as 0, and mark the S macro users selected by the macro base station as {k ₁ , k ₂ , . . . , k _S }. The smallcell base stations in group A are {1, 2, ..., L}, and the smallcell base stations in group B are {L+1, L+2, ..., L+J}, where:

Δ=M+N-(S+1)d, M is the number of transmitting antennas of each smallcell base station, and all smallcell base stations have the same number of transmitting antennas; N is the number of receiving antennas of each user, and all users in the network have the same The number of receiving antennas; d is the number of data streams received by each macro user and each smallcell user in group A, that is, the macro base station sends d data streams to each macro user, and each smallcell base station in group A It also sends d data streams to the users it serves; since each smallcell base station only selects one user service, the same number as the smallcell base station is used here to mark the users served by each base station; at the same time, since each cell has only one base station, so The number of the smallcell base station is also used to mark the smallcell.

In step 4, the small cells in group A and the small cells in group B have the following characteristics:

First, there is serious interference among the smallcells in the group A, that is, the smallcell i (i∈{1,...,L}) satisfies at least one of the following conditions:

(1) The base station of smallcell i causes serious interference to at least one of the users served by other smallcell base stations in group A, namely P _j is the transmit power of smallcell base station j, P _i is the transmit power of smallcell base station i, H _j,i represents the channel matrix from smallcell base station i to user j, and H _j,j is the direct channel from base station j to served user j Matrix, ||·|| _F represents the F-norm of the matrix, α is a threshold value, and the value is given when configuring the system parameters;

(2) The users in smallcell i are severely interfered by at least one base station of other smallcell base stations in group A, namely H _{i, j} represents the interference channel matrix from smallcell base station j to user i; H _{i, j} is the direct channel matrix from base station i to served user i;

Secondly, the smallcell base stations in the group B cause very weak interference to the smallcell users in the group A, namely β is a threshold value, the value is given when configuring the system parameters, and the smallcell base station in group A causes very weak interference to the smallcell users in group B, namely At the same time, the smallcell base stations in the group B cause very weak interference to users of other smallcells in the group B, namely i∈{L+1,...,L+J}.

As shown in Figure 2, the process of constructing a two-stage interference alignment scheme is as follows:

Step 5: Realize the first stage of constructing two-stage interference alignment, that is, the macro base station designs itself and the precoding matrix of the samllcell base station in group A;

Step 5.1, the macro base station calculates the following matrix:

in, H _{L+x, 0} represents the channel matrix from the macro base station to user L+x in group B, where x=1, 2, . . . , q. Indicates the conjugate transpose operation of the matrix, and null( ) means to find the null space of the matrix;

In step 5.2, the macro base station calculates the precoding matrix of the macro base station and the smallcell base stations in group A by using the layered interference alignment scheme. In this process, the macro base station uses the following equivalent channel matrix

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ;</span>$

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; ;</span>$

The implementation steps of the layered interference alignment scheme are as follows:

Step 5.2.1, the smallcell base station in group A generates a random precoding matrix V _j , and V _j satisfies the condition Be the conjugate transpose of V _j , j=1,2,...,L, I _d is the identity matrix of d×d;

Step 5.2.2, let j=1,2,...,L;

Step 5.2.3, according to the transmission precoding matrix in step 5.2.2 Compute the interference covariance matrix:

Wherein, H _{i, j} is the channel matrix from base station j to user i, P _j is the transmit power of base station j, i∈{k ₁ ,...,k _S ,1,...,L};

Step 5.2.4, judge whether the interference leakage I _f is less than the interference leakage threshold ε, if yes, the transmission precoding matrix in step 5.2.2 That is, the transmission precoding matrix required by base station j, so that And go to step 5.2.7; otherwise, go to step 5.2.5. Among them, interference leakage Tr[IF _i ], Tr[IF _i ] is the trace of the interference covariance matrix IF _i in step 5.2.3, and ε is a given interference leakage threshold, which is given when configuring system parameters;

Step 5.2.5, based on the interference covariance matrix IF _i , calculate the user's receiving filter:

U _i =v _d [IF _i ], i∈{k ₁ ,...,k _S ,1,...,L};

Among them, U _i is the receiving filter of user i, and v _d [IF _i ] is a matrix composed of eigenvectors corresponding to the smallest d eigenvalues of the interference covariance matrix IF _i ;

Step 5.2.6, according to the user receiving filter obtained in step 5.2.5, according to the formula Calculate the transmit precoding matrix of base station j, and return to step 5.2.2, wherein U _i is the receiving filter of user i obtained in step 5.2.5, j=1, 2, ..., L;

Step 5.2.7, based on the interference covariance matrix IF _i in step 5.2.3, calculate the user's receiving filter: U _i =v _d [IF _i ], i∈{k ₁ ,..., k _S , 1 ,...,L};

Step 5.2.8, calculate the transmit precoding matrix of the macro base station:

First calculate the following matrix:

where s=1, 2, . . . , S.

Then the transmission precoding matrix of the macro base station is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ;</span>$

Step 6: Realize the second stage of constructing the two-stage interference alignment, that is, the transmit precoding matrix of the smallcell base station in the macro base station design group B.

The specific design method is as follows:

Step 1: Design the transmit precoding matrix of the smallcell base station {L+1, L+2, ..., L+q}

The macro base station calculates the following matrix:

Then the macro base station performs singular value decomposition on the following matrix:

Among them, the diagonal elements of matrix Λ _j are matrix singular value of . The transmit precoding matrix of Smallcell base station j is j=L+1,...,L+q, the receiving filter of user j served by it is j=L+1,...,L+q;

Step 2: Design the transmit precoding matrix of the smallcell base station {L+q,...,L+J}:

The macro base station calculates the following matrix:

Then the macro base station performs singular value decomposition on the following matrix:

The transmit precoding matrix of Smallcell base station j is j=L+q,...,L+J, the receiving filter of user j served by it is j=L+q, . . . , L+J.

Step 7: The macro base station sends the calculated transmit precoding matrix of the smallcell base station and the receive filter of the corresponding user to each smallcell base station through the backhaul link.

Step 8: The macro base station and the smallcell base station send the receiving filters of their users to the users, and use the transmission precoding matrices obtained in steps 5 and 6 to send data to the users they serve;

Step 9: Each user takes the conjugate transpose of the received receiving filter matrix, and multiplies the received signal to realize the elimination of interference, and successfully receives its own signal.

For those skilled in the art, various corresponding changes and modifications can be made according to the above technical solutions and concepts, and all these changes and modifications should be included in the protection scope of the claims of the present invention.

Claims (4)

1. a two-stage interference alignment method in heterogeneous cellular network downlink communication, is characterized in that, described method comprises the steps: Step 1, the macro base station selects S macro users to serve, where S≤M ₀ , M ₀ is the number of antennas of the macro base station; each smallcell base station selects one user to serve; Step 2, the selected user measures the channel state information (CSI) from all base stations to itself, and feeds back to the base station serving itself; Step 3, each smallcell base station sends the received CSI information to the macro base station; Step 4, mark the macro base station as 0, and mark the S macro users selected by the macro base station as {k ₁ , k ₂ , ..., k _S }; since each smallcell base station only selects one user to serve, the smallcell The number of the base station is used to mark the users it serves; at the same time, since each cell has only one base station, the number of the smallcell base station is also used to mark the corresponding smallcell; smallcell base stations {1, 2, ..., L} form a group A, smallcell base stations {L+1, L+2, ..., L+J} form a group B, where: Δ=M+N-(S+1)d, M is the number of transmitting antennas of each smallcell base station, all smallcell base stations have the same number of transmitting antennas; N is the number of receiving antennas of each user, all users in the network All have the same number of receiving antennas; d is the number of data streams received by each macro user and each smallcell user in group A, that is, the macro base station sends d data streams to each macro user, and each user in group A receives d data streams. A smallcell base station also sends d data streams to the users it serves; Step 5, the macro base station designs and transmits a precoding matrix for itself and the smallcell base stations in the group A; Step 6, the macro base station designs the transmission precoding matrix of the smallcell base stations in the group B; Step 7, the macro base station sends the obtained transmission precoding matrix of each smallcell base station and the receiving filter of the corresponding user to the corresponding smallcell base station through the backhaul link; Step 8, the macro base station and each smallcell base station send the receiving filters of their users to the corresponding users, and use the transmission precoding matrix obtained in steps 5 and 6 to send data to the users served by them; Step 9, each user uses the received receiving filter to eliminate interference and receive data. 2. The two-stage interference alignment method in a heterogeneous cellular network downlink communication according to claim 1, wherein in step 4, the smallcell in the group A and the smallcell in the group B have the following characteristic: First, there is serious interference among the smallcells in the group A, that is, the smallcelli (i∈{1,...,L}) satisfy at least one of the following conditions: (1) The base station of smallcell i causes serious interference to at least one of the users served by other smallcell base stations in group A, namely P _j is the transmit power of smallcell base station j, P _i is the transmit power of smallcell base station i, H _j,i represents the interference channel matrix from smallcell base station i to user j, and H _j,j is the transmission power from base station j to user j it serves Direct channel matrix, ||·|| _F represents the F-norm of the matrix, α is a threshold value, which is given when configuring the system parameters; (2) Users in smallcell i are severely interfered by at least one base station of other smallcell base stations in group A, that is H _{i, j} represents the interference channel matrix from smallcell base station j to user i; H _{i, i} is the direct channel matrix from base station i to served user i; Secondly, the smallcell base stations in the group B cause very weak interference to the smallcell users in the group A, namely β is a threshold value, which is given when configuring system parameters; and the smallcell base stations in group A cause very weak interference to smallcell users in group B, namely At the same time, the smallcell base stations in the group B cause very weak interference to users of other smallcells in the group B, namely i∈{L+1,...,L+J}. 3. The two-stage interference alignment method in a heterogeneous cellular network downlink communication according to claim 1, wherein said step 5 specifically comprises the following steps: In step 5.1, the macro base station calculates the following matrix: in, H _{L+x, 0} represents the channel matrix from the macro base station to the user L+x in group B, x=1, 2, ..., q, Indicates the conjugate transpose operation of the matrix, and null( ) means to find the null space of the matrix; Step 5.2, the macro base station uses layered interference alignment to calculate the transmit precoding matrix of the macro base station and the smallcell base station in group A, and the macro base station uses the following equivalent channel matrix during this process ${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ;</span>$ ${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; ;</span>$ The hierarchical interference alignment specifically includes the following process: Step 5.2.1, the smallcell base station in the group A generates a random precoding matrix V _j , and V _j satisfies the condition Be the conjugate transpose of V _j , j=1,2,...,L, I _d is the identity matrix of d×d; Step 5.2.2, let j=1,2,...,L; Step 5.2.3, according to the transmission precoding matrix in step 5.2.2 Compute the interference covariance matrix: Among them, H _{i, j} is the interference channel matrix from base station j to user i, P _j is the transmit power of base station j, i∈{k ₁ ,...,k _S ,1,...,L}; Step 5.2.4, judge whether the interference leakage I _f is less than the interference leakage threshold ε, if yes, the transmission precoding matrix in step 5.2.2 That is, the transmission precoding matrix required by base station j, so that And go to step 5.2.7; otherwise, go to step 5.2.5; where, interference leakage Tr[IF _i ] is the trace of the interference covariance matrix IF _i described in step 5.2.3, and ε is a given interference leakage threshold, which is given when configuring the system parameters; Step 5.2.5, based on the interference covariance matrix IF _i obtained in step 5.2.3, calculate the user's receiving filter: U _i =v _d [IF _i ], i∈{k ₁ ,..., k _S ,1,...,L}, where U _i is the receiving filter of user i, v _d [IF _i ] is composed of eigenvectors corresponding to the smallest d eigenvalues of the interference covariance matrix IF _i matrix; Step 5.2.6, according to the user receiving filter in step 5.2.5, according to the formula Calculate the transmit precoding matrix of base station j and return to step 5.2.2; wherein, U _i is the receiving filter of user i in step 5.2.5, j=1, 2, ..., L; Step 5.2.7, based on the interference covariance matrix IF _i obtained in step 5.2.3, calculate the receiving filter of the user: U _i =v _d [IF _i ], i∈{k ₁ ,..., k _S ,1,...,L}; Step 5.2.8, calculate the transmit precoding matrix of the macro base station: First calculate the following matrix: Where s=1, 2..., S, then the transmit precoding matrix of the macro base station is: ${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; .</span>$ 4. The two-stage interference alignment method in a heterogeneous cellular network downlink communication according to claim 1 or 3, wherein said step 6 comprises the following specific steps: Step 6.1, design the transmission precoding matrix of the smallcell base station {L+1, L+2, ..., L+q}, specifically: In step 6.1.1, the macro base station calculates the following matrix: In step 6.1.2, the macro base station performs singular value decomposition on the following matrix: Among them, the diagonal elements of matrix Λ _j are matrix The singular value of , the transmission precoding matrix V _j of smallcell base station j can be calculated as j=L+1,...,L+q, the receiving filter of user j served by it is j=L+1,...,L+q; Step 6.2. Design the transmission precoding matrix of the smallcell base station {L+q, ..., L+J}, specifically: In step 6.2.1, the macro base station calculates the following matrix In step 6.2.2, the macro base station performs singular value decomposition on the following matrix The transmit precoding matrix of Smallcell base station j is The receiving filter of user j served by it is j=L+q, . . . , L+J.