CN114040444A - Interference suppression method based on ultra-dense cellular network - Google Patents

Interference suppression method based on ultra-dense cellular network Download PDF

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CN114040444A
CN114040444A CN202111446769.2A CN202111446769A CN114040444A CN 114040444 A CN114040444 A CN 114040444A CN 202111446769 A CN202111446769 A CN 202111446769A CN 114040444 A CN114040444 A CN 114040444A
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CN114040444B (en
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张博为
陶亚雄
王彬
赵阔
王国仲
滕林
叶波
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Chongqing College of Electronic Engineering
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Abstract

The invention relates to an interference suppression technology of an ultra-dense network in the field of 5G communication, and discloses an interference suppression method based on an ultra-dense cellular network, which comprises the following steps: s1: a single AAU transmits signals to users in a single cell served by the single AAU, meanwhile, the rest AAUs keep silent, and users in all cells receive first transmission signals; s2: a single AAU in S1 receives the CSIT delayed by the user feedback; building a pre-coding matrix by the BBU pool through time delay CSIT; the precoding matrix is used for aligning interference signals and obtaining precoding signals; all AAUs transmit pre-coded signals to all cell users simultaneously; all cell users receive and obtain a third transmission signal; s3: and subtracting the first transmission signal from the third transmission signal to obtain a non-interference decoding signal. The invention can effectively reduce the dimensionality of interval interference and inter-user interference in the ultra-dense network under the time delay CSIT, and simultaneously can ensure higher system freedom.

Description

Interference suppression method based on ultra-dense cellular network
Technical Field
The invention relates to an interference suppression technology of a super-dense network in the field of 5G communication, in particular to an interference suppression method based on a super-dense cellular network.
Background
An Ultra Dense Network (UDN) is a novel Network architecture in fifth-generation mobile communication, and can shorten the distance between a user and a low-power base station and improve the spectrum efficiency of a system. In 5G technology, an ultra-dense network is very critical, and can meet the demand of people for data traffic in the future. However, after introducing the ultra-dense network, the next-generation cellular mobile communication network such as 5G, etc., with the high reuse of resources and the more dense network deployment, the distribution of users and low-power base stations is very dense, the network architecture, service scenario and requirements become more complex, the interference problem is very prominent, so that the interference management and control of the network are very difficult, and the performance of the ultra-dense network is greatly restricted.
In order to effectively suppress or eliminate interference, the conventional interference alignment technology compresses the receiving end interference to the minimum by precoding at the transmitting end, each user can obtain a degree of Freedom (DoF) of K/2, and the problem that the capacity of a multi-user interference network is limited by interference is theoretically broken through, but the technology requires that the transmitting end has perfect Channel State Information (CSIT), and the influence of factors such as Channel time variation and feedback delay cannot be ignored in practice. For this reason, in an existing retrospective interference alignment scheme, partial interference is aligned to a lower dimension by using delayed channel state information, and the requirement on the channel state information is lower, but the degree of freedom that can be obtained is relatively lower. In the actual communication process, the requirement on the degree of freedom is higher, that is, the more the channel degree of freedom, the better the channel degree of freedom is, so as to improve the capacity of the communication channel, thereby improving the system throughput and meeting the high-speed communication requirement of the current user. Therefore, how to guarantee a higher degree of freedom of the system while suppressing or eliminating interference in the case of delaying the channel state information is still an urgent problem to be solved.
Disclosure of Invention
The invention aims to provide an interference suppression method based on an ultra-dense cellular network, which can effectively reduce the dimensionality of interval interference and inter-user interference in the ultra-dense network under the time delay CSIT and can ensure higher system freedom.
The basic scheme provided by the invention is as follows: the interference suppression method based on the ultra-dense cellular network comprises the following steps:
s1: a non-cooperative transmission phase; equally dividing the stage into L time slots, in the ith time slot, transmitting a first transmission signal to users in a single cell served by a single AAU by the single AAU, simultaneously keeping the rest AAUs silent, and receiving the first transmission signal by the users in all the cells; wherein i belongs to L;
s2: interference alignment stage; equally dividing the stage into A time slots, and in the t time slot, receiving the CSIT of the user feedback delay by a single AAU in S1; meanwhile, a single AAU in S1 transmits a second transmission signal to users in the single cell it serves, while the remaining AAUs remain silent and users in all cells receive the second transmission signal; wherein t belongs to [ L +1, L + A ];
building a pre-coding matrix by the BBU pool through time delay CSIT; the precoding matrix is used for aligning an interference signal in the first transmission signal and an interference signal in the second transmission signal and obtaining a precoding signal;
after the BBU pool constructs a precoding matrix, all AAUs transmit precoding signals to all cell users at the same time; all cell users receive and obtain a third transmission signal;
s3: a user decoding stage; in this stage, the first transmission signal is subtracted from the third transmission signal to obtain a non-interfering decoded signal.
The working principle and the advantages of the invention are as follows: a pre-coding matrix can be constructed according to the CSIT of the user feedback delay, interference signals in signals received by the user at different time slots are aligned through the pre-coding matrix, the pre-coding signals are obtained, the dimension of interference in the ultra-dense network is effectively reduced, and then the non-interference decoding signals can be obtained through simple calculation in S3. The scheme has low requirement on the channel state information of the transmitting terminal, accords with the condition that delayed channel state information exists in the actual communication environment, can fully utilize properly delayed channel state information to finish more interference information alignment, realizes more interference-free symbol stream transmission, removes interference signals to a greater extent, and can ensure higher system freedom degree.
In addition, compared with an interference alignment scheme which requires perfect channel state information and is adopted in the prior art, the scheme does not require perfect channel state information, can fully utilize delayed CSIT to perform interference alignment, and has stronger practicability; compared with a backtracking interference alignment scheme adopted in the prior art, the number of the transmitted interference-free symbol streams is relatively small, and the interference suppression method provided by the scheme can output more interference-free symbol streams and has higher degree of freedom. Meanwhile, the scheme is designed based on the ultra-dense cellular network, compared with a common cellular network, the ultra-dense cellular network is more dense in network deployment, higher in frequency spectrum reuse rate of a system, and more complex and various in interference problem, the existing interference suppression method cannot well deal with the ultra-dense cellular network, and the method provided by the scheme can deal with the complex interference situation.
Wherein, AAU (active Antenna Unit) refers to the active Antenna unit; bbu (building Base band unit) refers to a baseband processing unit; csit (channel State Information) refers to channel State Information.
Further, in S1, the first transmission signal includes a desired signal and an interference signal, and the desired signal and the interference signal are linearly combined to form the first transmission signal; the interference signal includes an inter-zone interference signal and an inter-user interference signal.
By the arrangement, the composition of the first transmission signal is determined, and meanwhile, the expected signal and the interference signal are linearly combined, so that a precoding matrix is conveniently constructed subsequently.
Further, in S1, the number of symbol streams of the desired signal is M; the total number of receiving antennas configured by all users in each cell is N, wherein N is less than M.
The setting accords with the actual communication environment, and the scheme has more practical application value.
Further, in S2, the
Figure BDA0003385020680000034
Wherein A is a positive integer.
With this arrangement, according to the range of a slots in S2, which is clearly defined by the M, N value, the slots in S1 and S2 are guaranteed to correspond to each other, so as to guarantee the accuracy of precoding matrix construction.
Further, in S1, the calculation expression of the first transmission signal transmitted by the single AAU is:
ai(ti)=a[i,1]+a[i,2]+…+a[i,K]
wherein :
Figure BDA0003385020680000031
indicating AAU to send to user [ i, k ]]The symbol vector of (a), comprising NA symbols and M-NA zero elements; user [ i, k ]]The number K of users in the cell i is pointed, and K is the total number of users in the cell; k belongs to K;
the computational expression of the first transmission signal received by a single user is:
Figure BDA0003385020680000032
wherein ,
Figure BDA0003385020680000033
express the ith AAU to the user [ l, k ]]The N × M-dimensional channel matrix of (1) includes NA symbols; user [ i, k ]]Refers to the kth user in cell 1; l belongs to L; in S1, each user receives K-1 inter-user interference signals and (LK-1) inter-zone interference signals.
By the arrangement, the signals transmitted by the AAU and the first transmission signals received by the user can be accurately calculated, and data preparation is made for subsequently constructing the precoding matrix.
Further, at S2, the precoding matrix is V[l,k](tn),V[l,k](tn) The calculation expression of (a) is:
Figure BDA0003385020680000041
wherein ,V[l,k](tn) Represents the user [ l, k [ ]]At tnThe pre-coding matrix of the slot is,
Figure BDA0003385020680000042
by the arrangement, the precoding matrix is accurately defined, and the interference dimension received by each user can be effectively reduced through the precoding matrix.
Further, the method also comprises the step of S4: calculating the degree of freedom of the system; the following formula is adopted when calculating the degree of freedom:
Figure BDA0003385020680000043
wherein, B is a transmission time slot; alpha is a transmission efficiency factor; alpha is A/TIA;TIATo use the number of time slots, TIAL + a; q is the number of AAU clusters, and each AAU cluster comprises L AAUs; each AAU serves one cell.
By the arrangement, the degree of freedom value which can be achieved by the scheme can be accurately obtained, and the method is guaranteed to operate effectively.
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Fig. 1 is a schematic diagram of an interference suppression method based on an ultra-dense cellular network according to an embodiment of the present invention.
Detailed Description
The following is further detailed by the specific embodiments:
the embodiment is basically as shown in the attached figure 1: the interference suppression method based on the ultra-dense cellular network comprises the following steps:
s1: a non-cooperative transmission phase; equally dividing the stage into L time slots, in the ith time slot, transmitting a first transmission signal to users in a single cell served by a single AAU by the single AAU, simultaneously keeping the rest AAUs silent, and receiving the first transmission signal by the users in all the cells; wherein i ∈ L.
The first transmission signal comprises a desired signal and an interference signal, and the desired signal and the interference signal are linearly combined to form the first transmission signal; the interference signal includes an inter-zone interference signal and an inter-user interference signal. The number of symbol streams of the desired signal is M; the total number of receiving antennas configured by all users in each cell is N, wherein N is less than M.
Specifically, in this embodiment, a multi-cluster multi-cell multi-user communication environment is taken as an example, and includes Q AAU clusters, where each AAU cluster includes L AAUs; each AAU serves one cell.
L time slots in total, i.e. t e { t ∈ { t } in S11,t2,...,tLAt time slot ti(i e L), the ith AAU sends a new symbol stream, transmitting signals to users in the i cell it serves, while the remaining AAUs remain silent.
The computational expression of the ith AAU transmitted signal is:
ai(ti)=a[i,1]+a[i,2]+…+a[i,K]
wherein :
Figure BDA0003385020680000051
indicating AAU to send to user [ i, k ]]A symbol vector of (a symbol stream) containing NA symbols and M-NA zero elements; user [ i, k ]]The number K of users in the cell i is pointed, and K is the total number of users in the cell; k belongs to K;
the computational expression of the first transmission signal received by user [ l, k ] is:
Figure BDA0003385020680000052
wherein ,
Figure BDA0003385020680000053
express the ith AAU to the user [ l, k ]]The N × M-dimensional channel matrix of (1) includes NA symbols; user [ i, k ]]The kth user in the l cell; l belongs to L; in S1, each user receives K-1 inter-user interference signals and (LK-1) inter-zone interference signals.
S2: interference alignment stage; this phase is equally divided into A time slots, i.e. t e { t ∈L+1,tL+2,…,tL+A}; in the t-th time slot, i.e. ti(ti∈{tL+1,tL+2,…,tL+A}), a single AAU in S1 receives CSIT delayed by user feedback; meanwhile, a single AAU in S1 transmits a second transmission signal to users in the single cell it serves, while the remaining AAUs remain silent and users in all cells receive the second transmission signal; wherein t is ∈ [ L +1, L + A];
Figure BDA0003385020680000054
Wherein A is a positive integer.
Building a pre-coding matrix by the BBU pool through time delay CSIT; the precoding matrix is used for aligning an interference signal in the first transmission signal and an interference signal in the second transmission signal and obtaining a precoding signal;
after the BBU pool constructs a precoding matrix, all AAUs transmit precoding signals to all cell users at the same time; all cell users receive and obtain a third transmission signal;
wherein, the pre-coding signals sent simultaneously are:
ai(t)=V[i,1](t)a[i,1]+V[i,2](t)a[i,2]+…+V[i,K](t)a[i,K],t∈{tL+1,tL+2,…,tL+A};
the third transmission signal received by the user is:
Figure BDA0003385020680000061
precoding matrix is V[l,k](tn) Said V is[l,k](tn) The calculation expression of (a) is:
Figure BDA0003385020680000062
wherein ,V[l,k](tn) Represents the user [ l, k [ ]]At tnThe pre-coding matrix of the slot is,
Figure BDA0003385020680000063
when M is more than or equal to (LK-1) N and each element of the channel matrix is continuously distributed and mutually independent, the inverse or pseudo-inverse of the matrix C exists, then V[l,k](tn) Exists with a probability of 1. Therefore, after S2 is completed, the inter-cell interference and the inter-user interference dimension received by each user are effectively reduced, so that all interference can be cancelled in S3.
S3: a user decoding stage; in this stage, the first transmission signal is subtracted from the third transmission signal to obtain a non-interfering decoded signal.
Specifically, in S3, each user can obtain NA equations containing only the desired signal, i.e., interference-free decoded signals, by subtracting the signal received in S1 from the signal received in S2. Taking user [1, 1] as an example, the expected signals received at S1 and S2 form an input-output relationship as follows:
Figure BDA0003385020680000064
among others, because of the equivalent channel matrix
Figure BDA0003385020680000065
Is a channel matrix of dimension NA × M (M ≧ NA). As can be seen from the above formula, for the user [1, 1]In other words, the interference between users and the inter-interval interference are eliminated, and the scheme effectively eliminates the interference.
S4: calculating the degree of freedom; the following formula is adopted in the calculation of the degree of freedom:
Figure BDA0003385020680000071
wherein, B is a transmission time slot; alpha is a transmission efficiency factor; alpha is A/TIA;TIATo use the number of time slots, TIA=L+A。
Compared with the system degree of freedom LKN/3 that can be achieved by the conventional backtracking interference alignment scheme using fully delayed CSIT, the degree of freedom of the scheme is significantly higher than that of the conventional scheme, and the system degree of freedom upper limit QLKN under the configuration of the embodiment can be approximated to a greater extent.
For the convenience of understanding, specifically, taking a communication environment of two cells as an example, the communication environment is set to include 1 AAU cluster, that is, the Q value is 1; each AAU cluster comprises 2 AAUs, namely the L value is 2; each AAU correspondingly serves a cell, the total number of people in each cell is K and is 2, and the number M of symbol streams of expected signals is 6; the total number N of receiving antennas configured by all users in each cell is 2. The overall system configuration is (Q, L, K, N, M) ═ 1, 2, 2, 2, 6.
The method specifically comprises the following steps:
s1: this phase contains 2 slots, slot 1 and slot 3. In time slot 1, AAU sends signal a1(1) AAU two remains silent, and the transmitted signal for AAU one is: a1(1) ═ a[1,1]+a[1,2]
wherein ,
Figure BDA0003385020680000072
and
Figure BDA0003385020680000073
respectively representing a number AAU to a user [1, 1]]And users [1, 2]]Symbol stream of (c) ()TRepresenting a transpose of a vector or matrix. In slot 1, the received first transmission signal for each user is:
Figure BDA0003385020680000074
i,k∈{1,2}
wherein ,
Figure BDA0003385020680000075
is a 2 × 6 dimensional signal matrix of NxM[i,k](1) Is a 2 x 1 dimensional vector. From the above formula, user [1, 1]]And users [1, 2]]A symbol stream of 6 desired signals and 6 inter-user interference symbol streams are received, respectively. User [2, 1]]And users [2, 2]Then 12 inter-sector interference symbol streams from AAU number one are received, respectively. Similarly, in slot 3, AAU number one remains silent, and AAU number two transmits the following signals: a is2(3)=a[2,1]+a[2,2]
In time slot 3, the received first transmission signal for each user is:
Figure BDA0003385020680000076
as can be seen from the above formula, the users [2, 1] and [2, 2] receive the symbol streams of 6 desired signals and the symbol streams of 6 inter-user interference, respectively. User [1, 1] and user [1, 2] respectively receive 12 inter-sector interference symbol streams from AAU number one. Thus, for each user [ i, k ], it is necessary to cancel 12 inter-cell interference symbol streams and 6 inter-user interference symbol streams and provide 6 linearly independent equations containing only the desired signal symbol stream to be able to decode the desired signal.
S2: this phase contains 3 time slots, namely slots 6, 8 and 10. And aligning the interval interference and the user interference by using the time slot t epsilon {6, 8, 10 }.
A single AAU in S1 receives the CSIT delayed by the user feedback; meanwhile, a single AAU in S1 transmits signals to users in a single cell it serves, while the remaining AAUs remain silent and users in all cells receive the second transmission signal; wherein t is ∈ [ L +1, L + A];
Figure BDA0003385020680000085
wherein ,
Figure BDA0003385020680000086
pointing down to get the whole.
Building a pre-coding matrix by the BBU pool through time delay CSIT; the precoding matrix is used for aligning an interference signal in the first transmission signal and an interference signal in the second transmission signal and obtaining a precoding signal;
after the BBU pool constructs a precoding matrix, all AAUs transmit precoding signals to all cell users at the same time; all cell users receive and obtain a third transmission signal;
in the three time slots 6, 8 and 10, AAU number one and AAU number two transmit precoded signals as follows:
a1(t)=V[1,1](t)a[1,1]+V[1,2](t)a[1,2],t∈{6,8,10};
a2(t)=V[2,1](t)a[2,1]+V[2,2](t)a[2,2],t∈{6,8,10};
the third transmission signal received by the user is:
Figure BDA0003385020680000081
t∈{6,8,10},i,k∈{1,2}.
precoding matrix V[i,k](t) (i, k ∈ {1, 2}, and t ∈ {6, 8, 10}) is:
Figure BDA0003385020680000082
Figure BDA0003385020680000083
Figure BDA0003385020680000084
Figure BDA0003385020680000091
in the first formulaFor example, analysis V[i,k](t) presence. Because of the fact that
Figure BDA0003385020680000092
And
Figure BDA0003385020680000093
is a 3N × M ═ 6 × 6 dimensional matrix, and each element of the channel matrix obeys a continuous distribution and is independent of each other, so matrices G and F are full rank and rank is 6, therefore V[1,1](t)=G-1F. Wherein (C)-1Representing the inverse of the matrix.
In the same way, V[i,k](t) (i, k ∈ {1, 2}) exists. As can be seen from the second to fourth expressions in the above expressions, the precoding matrix V is constructed by design[i,k](t) enabling users [ i, k [ ]]The inter-zone interference and user interference at time slot t e {6, 8, 10} are aligned with the inter-zone interference and inter-user interference at time slot t e {1, 3 }.
S3: and subtracting the first transmission signal from the third transmission signal to obtain a non-interference decoding signal.
Specifically, in S3, each user can obtain NA equations containing only the desired signal, i.e., interference-free decoded signals, by subtracting the signal received in S1 from the signal received in S2. Taking user [1, 1] as an example, the signals received in S1 and S2 form an input-output relationship as follows:
Figure BDA0003385020680000094
because of V[i,k](t) constructing a channel matrix independent and each element of the channel matrix follows a continuous distribution and is independent of each other, where the matrix is in the formula
Figure BDA0003385020680000095
Full rank with probability 1 and rank 6[13 ]]. Thus, users [1, 1]]It is possible to decode 6 desired signals in 5 slots. Similarly, user [ i, k ]](i, k ∈ {1, 2}) is able to decode 6 desired signals 5 slots. In addition, it should be noted that the TDMA method is utilized when the time slot for executing the scheme is not selectedI.e. a conventional time division multiple access scheme. Since the TDMA scheme does not affect the degree of freedom as the number of time slots tends to infinity.
Therefore, the method provided by the scheme can transmit 24 interference-free symbols in 5 time slots, and 24/5 degrees of freedom are obtained. Through specific calculation, the scheme has high degree of freedom.
The interference suppression method based on the ultra-dense cellular network provided by this embodiment provides an ultra-dense network interference alignment scheme using the appropriate delay CSIT, which can effectively reduce the dimensionality of a large number of inter-interval interferences and inter-user interferences in the ultra-dense network, approach the upper bound of the system degree of freedom, ensure a higher system degree of freedom, and meet the increasing communication requirements of users. The method provided by the embodiment can solve the problem of complex interference under an ultra-dense cellular network which cannot be perfectly solved by the prior art, and can output more interference-free symbol streams compared with the existing backtracking interference alignment scheme and the like, so that the method is stronger in applicability and higher in reachable freedom.
The foregoing is merely an example of the present invention, and common general knowledge in the field of known specific structures and characteristics is not described herein in any greater extent than that known in the art at the filing date or prior to the priority date of the application, so that those skilled in the art can now appreciate that all of the above-described techniques in this field and have the ability to apply routine experimentation before this date can be combined with one or more of the present teachings to complete and implement the present invention, and that certain typical known structures or known methods do not pose any impediments to the implementation of the present invention by those skilled in the art. It should be noted that, for those skilled in the art, without departing from the structure of the present invention, several changes and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent. The scope of the claims of the present application shall be determined by the contents of the claims, and the description of the embodiments and the like in the specification shall be used to explain the contents of the claims.

Claims (7)

1. The interference suppression method based on the ultra-dense cellular network is characterized by comprising the following steps:
s1: a non-cooperative transmission phase; equally dividing the stage into L time slots, in the ith time slot, transmitting a first transmission signal to users in a single cell served by a single AAU by the single AAU, simultaneously keeping the rest AAUs silent, and receiving the first transmission signal by the users in all the cells; wherein i belongs to L;
s2: interference alignment stage; equally dividing the stage into A time slots, and in the t time slot, receiving the CSIT of the user feedback delay by a single AAU in S1; meanwhile, a single AAU in S1 transmits a second transmission signal to users in the single cell it serves, while the remaining AAUs remain silent and users in all cells receive the second transmission signal; wherein t belongs to [ L +1, L + A ];
building a pre-coding matrix by the BBU pool through time delay CSIT; the precoding matrix is used for aligning an interference signal in the first transmission signal and an interference signal in the second transmission signal and obtaining a precoding signal;
after the BBU pool constructs a precoding matrix, all AAUs transmit precoding signals to all cell users at the same time; all cell users receive and obtain a third transmission signal;
s3: a user decoding stage; in this stage, the first transmission signal is subtracted from the third transmission signal to obtain a non-interfering decoded signal.
2. The ultra-dense cellular network-based interference suppression method according to claim 1, wherein in S1, the first transmission signal comprises a desired signal and an interference signal, and the desired signal and the interference signal are linearly combined to form the first transmission signal; the interference signal includes an inter-zone interference signal and an inter-user interference signal.
3. The ultra-dense cellular network-based interference suppression method according to claim 2, wherein in S1, the number of symbol streams of the desired signal is M; the total number of receiving antennas configured by all users in each cell is N, wherein N <.
4. The ultra-dense cellular network-based interference mitigation method of claim 3, wherein in S2, the step
Figure FDA0003385020670000011
Wherein A is a positive integer.
5. The ultra-dense cellular network-based interference mitigation method of claim 4, wherein in S1, the calculation expression of the first transmission signal transmitted by the single AAU is:
ai(ti)=a[i,1]+a[i,2]+…+a[i,K]
wherein :
Figure FDA0003385020670000012
indicating AAU to send to user [ i, k ]]The symbol vector of (a), comprising NA symbols and M-NA zero elements; user [ i, k ]]The number K of users in the cell i is pointed, and K is the total number of users in the cell; k belongs to K;
the computational expression of the first transmission signal received by a single user is:
Figure FDA0003385020670000021
wherein ,
Figure FDA0003385020670000022
express the ith AAU to the user [ l, k ]]The N × M-dimensional channel matrix of (1) includes NA symbols; user [ i, k ]]The kth user in the l cell; l belongs to L; in S1, each user receives K-1 inter-user interference signals and (LK-1) inter-zone interference signals.
6. The method of claim 5, wherein the method comprises performing interference suppression based on a very dense cellular networkThen, in S2, the precoding matrix is V[l,k](tn),V[l,k](tn) The calculation expression of (a) is:
Figure FDA0003385020670000023
wherein ,V[l,k](tn) Represents the user [ l, k [ ]]At tnThe pre-coding matrix of the slot is,
Figure FDA0003385020670000024
7. the ultra-dense cellular network-based interference mitigation method of claim 3, further comprising S4: calculating the degree of freedom; the following formula is adopted when the degree of freedom of the system is calculated:
Figure FDA0003385020670000025
wherein, B is a transmission time slot; alpha is a transmission efficiency factor; alpha is A/TIA;TIATo use the number of time slots, TIAL + a; q is the number of AAU clusters, and each AAU cluster comprises L AAUs; each AAU serves one cell.
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