CN114584249B - Interference elimination method for wireless full duplex system - Google Patents
Interference elimination method for wireless full duplex system Download PDFInfo
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- 238000006386 neutralization reaction Methods 0.000 claims abstract description 13
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
- H04J11/0023—Interference mitigation or co-ordination
- H04J11/005—Interference mitigation or co-ordination of intercell interference
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
- H04J11/0023—Interference mitigation or co-ordination
- H04J11/0026—Interference mitigation or co-ordination of multi-user interference
- H04J11/0036—Interference mitigation or co-ordination of multi-user interference at the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/14—Two-way operation using the same type of signal, i.e. duplex
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
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- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention provides an interference elimination method of a wireless full duplex system, which mainly solves the problem of poor interference elimination effect in the prior art. The scheme is as follows: setting system parameters of a full duplex network; the base station and the uplink user equipment respectively transmit data signals; the base station and the downlink user equipment acquire a receiving signal according to the transmitted data signal; aiming at interference in signals received by user equipment and a base station, self-interference is directly eliminated through local information of the base station, and a precoding matrix and a decoding matrix of the base station and the user equipment are solved for other types of interference through combined interference neutralization and interference alignment conditions; and the base station and the uplink user equipment decode the received signals according to the solved decoding matrix to eliminate the interference in the system. Simulation results show that compared with the existing interference alignment method, the method has a better interference elimination effect, and can be used for improving the network freedom degree of a wireless full duplex system.
Description
Technical Field
The invention belongs to the technical field of communication, and particularly relates to an interference elimination method which can be used for improving the network freedom degree of a wireless full duplex system.
Background
In the next five years, the mobile application market has increasingly demanded large-flow services such as network games, high-definition videos and the like, so that the mobile data traffic in hot spots is increased. As shown by the cisco global mobile data traffic prediction report, mobile data traffic will increase from 2017 to 2022 at a composite annual growth rate of 46%, and global mobile data traffic will increase 7 times by 2022 compared to 2017. To cope with such huge data floods, new architectures and technologies have to be explored to increase the load-bearing capacity of wireless networks.
The current 5G age has the characteristics of multiple access, modulation, duplexing, high frequency and networking, so that the capacity of an access network is increased by 1000 times from the initial 2G age. The common-frequency and full-duplex technology is widely applied to the 5G communication radio frequency technology due to the adoption of the uplink and downlink common frequency bands. Entering the 5G era, many application scenarios, such as enhanced mobile broadband, high-capacity hotspots, etc. Aiming at the situation that the use of frequency/time resources by cell uplink and downlink services in the scenes is dynamically changed and asymmetric along with time, flexible duplex setting or adjustment of the proportion of uplink and downlink frequency spectrums and time frames is needed to meet the requirements of different uplink and downlink service bandwidths. Conventional half-duplex radio transceivers can only use orthogonal channels, i.e., time division duplex, TDD, or frequency division duplex, FDD, to enable two-way communication. However, full duplex FD can realize two-way communication at the same time under the same frequency, and this two-way communication can double the spectrum efficiency of the physical layer, but can cause the increase of accumulated interference in the network, thereby preventing the improvement of the system capacity and affecting the system performance. Meanwhile, as the FD operation can generate new network topology property, the traditional interference alignment IA technology cannot be directly applied to the interference generated in the network, and the application of IA to eliminate the interference is not researched by a system, so that the research on the use of the interference alignment technology in a full duplex scene has practical significance.
The biggest obstacle to implementation of full duplex FD technology has long been the enormous interference of the transmitting circuit to the receiving circuit, commonly referred to as self-interference SIC. FD technology can only exert its potential to double the spectral efficiency of point-to-point radio links if self-interference is effectively eliminated. In order to solve this problem, a great deal of research for exploring a self-interference cancellation technique has been conducted in recent years.
Antonio-rodi guez E proposes an adaptive analog domain SIC method capable of tracking the time-dependent changes of FD decoding-forwarding MIMO relay interference channels, with the remaining self-interference power being much lower than the noise power. The most advanced SIC techniques known so far are reported to provide performance of overall cancellation of over 100 db in real environments. Goyal demonstrates that a small-scale cell environment is more suitable for full duplex FD operation, because in practice, in a small-scale cell with a radius of about 40 meters, the average received signal-to-noise ratio for a cell suffering from 100 db SIC can be as high as 33 db. Domestic scholars Meng Tao design a circuit for directly detecting self-interference cancellation of a radio frequency domain so as to better strengthen the application of the circuit in the 5G communication radio frequency technology and continuously optimize and perfect the self-interference cancellation effect. In addition, in full duplex networks, additional intra-cell and inter-cell interference may also occur.
How to cancel intra-cell and inter-cell interference in a full duplex network becomes a troublesome problem. The interference alignment technique is an interference management method proposed in recent years. The interference alignment IA adopts the degree of freedom as the approximation of the system reachable capacity, and by designing the precoding matrix of each transmitting end and the decoding matrix of each receiving end, the interference signals received by each receiving end are aligned to subspaces with lower dimensionalities as much as possible, so that the subspaces of the signals which are not occupied by the interference remain with higher dimensionalities for useful signal transmission. However, since full duplex FD operation generates new network topology properties, conventional interference alignment techniques cannot be directly applied. Jafar first investigated the conditions of interference alignment feasibility and explicitly considered the symmetric K-users' interference channels. But FD-based networks are always asymmetric for bi-directional communication and thus have no effect. Kim K establishes a feasibility condition for IA in FD single-cell cellular networks, whereas the progress of IA performance studies for FD-based multi-cell networks is very small, in fact the interference in multi-cell networks is much more severe than in single-cell networks. Liu Qiong in the paper "study of interference alignment algorithm of full duplex base station", for the scenario of a multi-antenna full duplex base station and multiple single-antenna half duplex user equipment, it is proposed to use interference alignment technology to design precoding matrix to eliminate interference, and further obtain system degree of freedom, but because the user equipment is single antenna, there is a limitation. Li Gongyan in the paper On Feasibility of Interference Alignment in Full-Duplex-Based Small Cell Networks, a feasibility condition of establishing interference alignment in a full Duplex multi-cell network is proposed, wherein a cell base station is full Duplex, a user equipment is half Duplex, all interference in the network is eliminated by adopting an interference alignment technology to jointly design a precoding matrix and a decoding matrix, and a feasibility condition of eliminating all the interference is deduced based on the Bezout theorem, namely the number of equations in the interference elimination process is required to be not more than a variable number, and finally, a result that the system degree of freedom in the full Duplex scene is higher than that in the half Duplex scene is obtained, so that all the interference in the full Duplex system is eliminated. However, because the number of precoding matrixes in the system is limited, the number of interference eliminated by the method by using the interference alignment technology is very limited, and more antennas are needed to be adopted at the receiving end to eliminate interference signals so as to obtain the desired signals. In practice, antenna resources are often limited, and in order to fully utilize the antenna resources, interference needs to be eliminated by designing a precoding matrix and a decoding matrix, where more antennas are used to receive the desired signal. In order to eliminate interference, the precoding matrix may be designed to eliminate interference by using the interference alignment technology, but because the number of precoding matrices in the system is smaller, the number of interference eliminated by designing the precoding matrix is smaller, the receiving end also receives a lot of interference, and the decoding matrix of the receiving end needs to be designed to eliminate the rest interference, which will require the receiving end to use more antennas for processing interference, so that the received expected signal is reduced, and the interference elimination effect is affected.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides an interference elimination method of a wireless full duplex system, so that more antennas at a receiving end are used for receiving expected signals, and the interference elimination performance of the system is improved.
In order to achieve the above purpose, the technical scheme of the invention comprises the following steps:
(1) Setting parameter configuration of full duplex network
Setting the number of a full duplex base station, half duplex uplink user equipment and half duplex downlink user equipment in a network as P, setting M base station antennas and N user antennas, setting an uplink channel as an interference channel, setting a downlink channel as an X channel, and receiving expected signals and different types of interference by the downlink user equipment and the base station;
(2) The base station and the uplink user equipment respectively transmit data signals;
(3) The base station and the downlink user equipment obtain different receiving signals according to the transmitting signals:
downlink user equipmentReceived signal->The method comprises the following steps:
the base station is in an uplink stateWhen it receives signal->The method comprises the following steps:
wherein ,for j-th base station in downlink state +.>To the i-th downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b); />For j-th uplink user equipment +.>To the i-th upstream user equipment +.>Is a channel matrix of (a) a channel matrix of (b);is->When the base station is in the uplink state +.>Is a channel matrix of (a) a channel matrix of (b); />Is->To->Is a channel matrix of (a) a channel matrix of (b); />Is->Send to->Is a data signal of (a); />Is->Is a precoding matrix of (a); />Is->A transmitted data signal;is->Is a precoding matrix of (a); /> and />Respectively-> and />Received noise;
(4) Canceling interference in a received signal:
4a) Designing a precoding matrix for eliminating interference between a base station and a user:
4a1) Setting downlink user equipmentInterference cancellation is performed by adopting an interference neutralization technology and an interference alignment technology, and the conditions which need to be satisfied are as follows:
interference neutralization conditions:
interference alignment condition 1:
interference alignment condition 2:
4a2) According to 4a 1), respectively obtaining precoding matrixes of the base station and the user:
through type<1>Base station precoding matrix for solving data signal transmitted from ith base station to jth downlink user equipmentAnd the base station precoding matrix of the data signal transmitted to the jth downlink user equipment by the (P+1) -i) th base station
Through type<2>Base station precoding matrix for solving data signal transmitted from ith base station to 1 st downlink user equipment
Through type<3>User precoding matrix for solving data signal transmitted by ith uplink user equipment
Where i e { 1..p }, j e { 2..p },is to solve the base station precoding matrix +.>The space is opened and closed>Is to solve the user precoding matrix>The set space is the matrix space formed by the spread of all column vectors of the matrix,
4b) Designing a decoding matrix for eliminating residual interference of a base station and a user according to the precoding matrix:
4b1) Based on the precoding matrix of the base station and the user obtained in (4 a), two sets of conditions required to be satisfied for eliminating all remaining interference are designed:
the first group is three conditions that the kth downlink ue needs to meet to cancel all interference,
the second set is three conditions that the kth base station needs to satisfy to cancel all interference:
where H represents the conjugate transpose of the matrix, rank represents the rank of the matrix, d s For the length of one data signal, x is the downlink user equipmentIs a desired signal number of (a);
4b2) Decoding matrix of user from first set of conditionsDecoding matrix of base station from second set of conditions
4c) The base station obtains the precoding matrix of the base station according to the above solutionTransmitting signals and according to the decoding matrix->Decoding the signal it receives; the uplink user equipment solves the user precoding matrix according to the above>Transmitting signals, and the downlink user equipment obtains a user decoding matrix according to the above>To the signals it receivesDecoding to eliminate interference in the received signal.
Compared with the prior art, the invention has the following advantages:
1. the invention determines the precoding matrix and the decoding matrix of the base station, the precoding matrix of the uplink user equipment and the decoding matrix of the downlink user equipment by combining the conditions of the interference neutralization and the interference alignment technology so as to eliminate the interference signals of an interference link, improve the interference elimination effect and improve the degree of freedom of the wireless full duplex network.
2. In the invention, the solution of the precoding matrix is directly solved after the space expression is converted into the matrix form, so that iterative calculation is not needed, and the calculation complexity is reduced.
Drawings
Fig. 1 is a diagram of a conventional two-base station, four-user equipment full duplex system.
FIG. 2 is a flow chart of an implementation of the present invention for interference cancellation of FIG. 1;
fig. 3 is a diagram of simulation results of degrees of freedom obtained after interference cancellation of fig. 1 using the present invention.
Detailed Description
Embodiments and effects of the present invention are described in further detail below with reference to the accompanying drawings.
Referring to fig. 1, the existing full duplex system of two base stations and four user equipments includes two full duplex base stations, two half duplex uplink user equipments and two half duplex downlink user equipments, wherein the uplink channel is an interference channel, and the downlink channel is an X channel. Wherein:
in the X channel: the 1 st base station is in the downlink stateThe 2 nd base station is in the downlink state +.>Both base stations give 1 st downlink user equipment +.>And 2 nd downlink user equipment +.>Transmitting data;
in the interference channel: 1 st uplink user equipmentFor the 1 st base station in uplink state +.>Transmitting a data signal; 2 nd uplink user equipment +.>For base station 2 in uplink state +.>Transmitting data;
in fig. 1, a solid line indicates that a desired signal is transmitted through the channel, and a broken line indicates that an interference signal is transmitted through the channel.
Referring to fig. 2, the implementation steps of the interference cancellation for the full duplex system in this example are as follows:
and step 1, setting system parameters of a full duplex network.
In the system of the full duplex network of the two full duplex base stations, the two half duplex uplink user equipment and the two half duplex downlink user equipment, the number of the antennas at the uplink user equipment and the downlink user equipment is set to be N=10, and the number of the antennas at the base stations is M epsilon [10,15].
When the base station is in a downlink state, a data signal is sent to the downlink user equipment, and the downlink user equipment receives a desired signal and interference sent by the base station and is also interfered by the uplink user equipment.
When the base station is in an uplink state, the base station receives the expected signals sent by the corresponding uplink user equipment, and meanwhile, the base station is interfered by other uplink user equipment, and the self-interference of the base station and the mutual interference caused by other base stations are also received.
And 2, setting the transmitting data signals of the base station and the uplink user equipment.
The data signals sent by the base station and the uplink user equipment are all carried out through an X channel and an interference channel, and the transmitted data are different, wherein:
in the X channel:
the 1 st base station is in the downlink stateWhich is sent to the 1 st downlink user equipment +.>Is +.>Send to the 2 nd downlink user equipment +.>Is +.>
The 2 nd base station is in the downlink stateWhich is sent to the 1 st downlink user equipment +.>Is the data signal of (a)Send to the 2 nd downlink user equipment +.>Is also +.>I.e. < -> and />The two base stations cooperatively transmit
In the interference channel:
1 st uplink user equipmentIt is sent only to the 1 st base station in uplink state +.>Is marked as->
2 nd uplink user equipmentWhich is sent only to the 2 nd base station in uplink state +.>Is marked as->
And step 3, the base station and the downlink user equipment obtain different receiving signals according to the transmitting signals.
3.1 For the 1 st downlink user equipmentAnd receives the expected signal sent by the base station, and also receives the interference sent by the base station to other downlink user equipment, and also receives the interference of uplink user equipment,the signal it receives->The form is expressed as follows:
wherein ：for the 1 st base station in downlink state +.>To 1 st downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 2 nd base station in downlink state +.>To 1 st downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 1 st uplink user equipment +.>To 1 st uplink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 2 nd uplink user equipment +.>To 1 st uplink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
is->Send to->Is a data signal of (a);
is->Send to->Is a data signal of (a);
is->Send to->Is a data signal of (a);
is->Send->Is a precoding matrix of (a);
is->Send->Is a precoding matrix of (a);
is->Send->Is a precoding matrix of (a);
is->Send->Is a precoding matrix of (a);
is->A transmitted data signal;
is->A transmitted data signal;
is->Is a precoding matrix of (a);
is->Is a precoding matrix of (a);
is->Received noise;
3.2 For the 2 nd downlink user equipmentReceiving a desired signal transmitted from a base station, receiving interference from the base station to other downlink user equipments, and receiving interference from uplink user equipments, the received signal +.>The form is expressed as follows:
wherein ：for the 1 st base station in downlink state +.>To the 2 nd downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 2 nd base station in downlink state +.>To the 2 nd downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 1 st uplink user equipment +.>To the 2 nd upstream user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 2 nd uplink user equipment +.>To the 2 nd upstream user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
is->Received noise;
3.3 For the 1 st base station in the uplink state)When it receives the expected signal sent by the corresponding uplink user equipment, and at the same time, it also receives the interference of other uplink user equipment, the self-interference of the base station and the mutual interference between base stations caused by other base stations, and the received signal->The form is expressed as follows:
wherein ：is->When the base station is in the uplink state +.>Is a channel matrix of (a) a channel matrix of (b);
is->When the base station is in the uplink state +.>Is a channel matrix of (a) a channel matrix of (b);
is->To->Is a channel matrix of (a) a channel matrix of (b);
is->To->Is a channel matrix of (a) a channel matrix of (b);
is->Received noise;
3.4 For the 2 nd base station in the uplink state)When receiving the expected signal sent by the corresponding uplink user equipment, the interference of other uplink user equipment, the self-interference of the base station and the mutual interference between the base stations caused by other base stations are also received, and the received signal is received>The form is expressed as follows:
wherein ：is->When the base station is in the uplink state +.>Is a channel matrix of (a) a channel matrix of (b);
is->When the base station is in the uplink state +.>Is a channel matrix of (a) a channel matrix of (b);
is->To->Is a channel matrix of (a) a channel matrix of (b);
is->To->Is a channel matrix of (a) a channel matrix of (b);
is->Received noise;
and 4, eliminating interference in the received signal.
The interference in the received signal is of a different type for the user equipment and the base station, wherein:
for downlink user equipment, the interference transmitted by the base station to other downlink user equipment and the interference transmitted by the uplink user equipment are included.
When the base station is in the uplink state, the interference of non-corresponding uplink user equipment, the self-interference of the base station and the mutual interference among base stations caused by other base stations are included.
Aiming at the interference, the method comprises the following steps:
4.1 For self-interference of the base station, the local information of the base station is stored, and the local information comprises a channel matrix, a data signal transmitted by the base station and a precoding matrix of the data signal transmitted by the base station, so that the self-interference of the base station can be directly eliminated by utilizing the local information of the base station;
4.2 For other types of interference received by the downlink user equipment and the base station, a precoding matrix and a decoding matrix of the base station, a precoding matrix of the uplink user equipment and a decoding matrix of the downlink user equipment are designed through a combined interference neutralization and interference alignment technology:
4.2.1 Setting up downlink user equipmentInterference neutralization technology and downlink User Equipment (UE)>By using a dry processThe conditions that need to be met for interference cancellation by the interference alignment technique are as follows:
interference neutralization conditions:
interference alignment condition 1:
interference alignment condition 2:
wherein ,for the 1 st base station in downlink state +.>To 1 st downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 2 nd base station in downlink state +.>To 1 st downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 1 st base station in downlink state +.>To the 2 nd downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 2 nd base station in downlink state +.>To the 2 nd downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 1 st uplink user equipment +.>To the 2 nd upstream user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
for the 2 nd uplink user equipment +.>To the 2 nd upstream user equipment +.>Is a channel matrix of (a) a channel matrix of (b);
is->Send->Is a precoding matrix of (a);
is->Send->Is a precoding matrix of (a);
is->Send->Is a precoding matrix of (a);
is->Send->Is a precoding matrix of (a);
is->Is a precoding matrix of (a);
is->Is a precoding matrix of (a);
is to solve the base station precoding matrix +.> and />The space is formed by the arranged sheet;
is to solve the user precoding matrix> and />The space is formed by the arranged sheet;
span is the matrix space into which all column vectors of the matrix are spread.
4.2.2 Through type)<1>Base station precoding matrix for resolving data signal transmitted from 1 st base station to 2 nd downlink user equipmentAnd a base station precoding matrix of a data signal transmitted from the 2 nd base station to the 2 nd downlink user equipment>
Conditions for interference neutralizationThe arrangement is opened as a space->Make the following steps
Will be stretched into spatial expressionsIs converted into the following matrix form:
wherein Is a unitary matrix->From the definition of the matrix null space, F 1 Is a matrix of (n+2m) × (2M-N), +.>When meeting F 1 Is used for solving matrix X by zero space ratio 1 When the space of (a) is large, X can be solved 1 Namely, the constraint condition 2M-N is more than or equal to d is required to be satisfied s ；
According to constraint condition 2M-N is greater than or equal to d s From the above matrix<4>Solving for X 1 Take out X 1 M-th to 2-th rows of the base station precoding matrix of data signals transmitted from the 1 st base station to the 2 nd downlink user equipmentTake out X 1 2 nd M row to 3 rd M row data signal transmitted from 2 nd base station to 2 nd downlink user equipmentIs>
4.2.3 Through type)<2>Base station precoding matrix for resolving data signal sent by 1 st base station to 1 st downlink user equipmentAnd a base station precoding matrix of a data signal transmitted from the 2 nd base station to the 1 st downlink user equipment>
Sheet space for setting interference alignment condition 1Make->
Will be stretched into spatial expressionsConverting into a matrix form:
wherein Is a unitary matrix->From the definition of the matrix null space, F 2 Is a matrix of (n+2m) × (2M-N), +.>When meeting F 2 Is used for solving matrix X by zero space ratio 2 When the space of (a) is large, X can be solved 2 Namely, the constraint condition 2M-N is more than or equal to d is required to be satisfied s ；
According to constraint condition 2M-N is greater than or equal to d s From the matrix<5>Solving for X 2 Take out X 2 M-th to 2-th rows of the base station precoding matrix of data signals transmitted from the 1 st base station to the 1 st downlink user equipmentTake out X 2 2M-th to 3M-th rows of the base station precoding matrix of data signals transmitted from the 2 nd base station to the 1 st downlink user equipment>
4.2.4 Through type)<3>User precoding matrix for solving 1 st uplink user equipment transmitting data signalAnd user precoding matrix of 2 nd uplink user equipment transmitting data signal +.>
Space-wise arrangement of interference alignment conditions 2Make->
Will be stretched into spatial expressionsConverting into a matrix form:
wherein Is a unitary matrix->From the definition of the matrix null space, F 3 Is a matrix of (n+2n) ×n, < >>When meeting F 3 Is used for solving matrix X by zero space ratio 3 When the space of (a) is large, X can be solved 3 Namely, the constraint condition that N is more than or equal to d is required to be satisfied s ；
According to constraint condition N is greater than or equal to d s From the matrix<6>Solving for X 3 Take out X 3 User precoding matrix for transmitting data signals by 1 st uplink user equipment from nth to 2nthTake out X 3 2N-th to 3N-th rows of a user precoding matrix for transmitting data signals by 2 nd uplink user equipments->
4.2.5 Designing a decoding matrix for eliminating residual interference of the base station and the user according to the precoding matrix:
firstly, based on the precoding matrix of the base station and the user obtained in the above process, four groups of conditions required to be satisfied for eliminating all residual interference are designed:
the first group is the 1 st downlink user equipmentThree conditions that need to be met to cancel all interference:
the second group is2 nd downlink user equipmentThree conditions that need to be met to cancel all interference:
the third group is the 1 st base stationThree conditions that need to be met to cancel all interference:
the fourth group is the 2 nd base stationThree conditions that need to be met to cancel all interference:
where H represents the conjugate transpose of the matrix, rank represents the rank of the matrix, d s Is the length of one data signal;
then, decoding matrix of 1 st downlink user equipment is solved by the first set of conditionsDecoding matrix of the 2 nd downlink user equipment is solved by the second set of conditions>Decoding matrix of 1 st base station is solved by third group of conditions>From a fourth group of stripsDecoding matrix of 2 nd base station is solved>
4.3 The base station and the user equipment respectively transmit data signals according to the respective precoding matrixes and decode the received signals according to the decoding matrixes so as to eliminate interference:
4.3.1 1 st base station according to the above-mentioned solved precoding matrix of base stationTransmitting a signal to the 1 st downlink user equipment +.>According to precoding matrix->Transmitting a signal to the 2 nd downlink user equipment +.>And according to the decoding matrixDecoding the signal it receives to obtain the desired signal +.>
4.3.2 2 nd base station according to the above-mentioned solved precoding matrix of base stationTransmitting a signal to the 1 st downlink user equipment +.>According to precoding matrix->To the 2 ndDownlink user equipment transmit signal +.>And according to the decoding matrixDecoding the signal it receives to obtain the desired signal +.>
4.3.3 1 st uplink user equipment according to the above solved user precoding matrixTransmitting signal +.>The 1 st downlink user equipment solves the user decoding matrix according to the above>Decoding the signal it receives to obtain the desired signal +.> and />
4.3.4 2 nd uplink user equipment according to the above-mentioned solved user precoding matrixTransmitting signal +.>The 1 st downlink user equipment solves the user decoding matrix according to the above>Decoding the signal it receives to obtain the desired signal +.>
The step 4.3) can realize the complete elimination of interference at the receiving end of the user equipment and the receiving end of the base station, and obtain the expected signal.
The effect of this example can be further illustrated by the following simulations:
first, simulation conditions
The full duplex system of two full duplex base stations, two half duplex uplink user equipment and two downlink user equipment is used as a simulation scene, wherein the number of antennas at the uplink user equipment and the downlink user equipment is set to be N=10, and the number of antennas at the base stations is changed to be M epsilon [10,15].
Second, simulation content
The invention eliminates the interference in the full duplex system under the simulation condition to obtain the expected signal number obtained by the base station and the user equipment under different antenna numbers, and further obtain the degree of freedom of the system, and the result is shown in figure 3.
As can be seen from fig. 3, under the same simulation scenario, as the number of base station antennas increases, the present invention can obtain a higher degree of freedom, and compared with the existing method for eliminating interference in a full duplex system by only using an interference alignment technique, the present invention has a better effect of eliminating interference by using a combined interference neutralization technique and an interference alignment technique.
Claims (3)
1. An interference cancellation method for a wireless full duplex system, comprising:
(1) Setting parameter configuration of full duplex network
Setting the number of a full duplex base station, half duplex uplink user equipment and half duplex downlink user equipment in a network as P, setting M base station antennas and N user antennas, setting an uplink channel as an interference channel, setting a downlink channel as an X channel, and receiving expected signals and different types of interference by the downlink user equipment and the base station;
(2) The base station and the uplink user equipment respectively transmit data signals;
(3) The base station and the downlink user equipment obtain different receiving signals according to the transmitting signals:
downlink user equipmentReceived signal->The method comprises the following steps:
the base station is in an uplink stateWhen it receives signal->The method comprises the following steps:
wherein ,for j-th base station in downlink state +.>To the i-th downlink user equipment +.>Is a channel matrix of (a) a channel matrix of (b); />For j-th uplink user equipment +.>To the i-th upstream user equipment +.>Is a channel matrix of (a) a channel matrix of (b);is->When the base station is in the uplink state +.>Is a channel matrix of (a) a channel matrix of (b); />Is->To->Is a channel matrix of (a) a channel matrix of (b); />Is->Send to->Is a data signal of (a); />Is->Is a precoding matrix of (a); />Is->A transmitted data signal; />Is->Is a precoding matrix of (a); /> and />Respectively-> and />Received noise;
(4) Canceling interference in a received signal:
4a) Designing a precoding matrix for eliminating interference between a base station and a user:
4a1) Setting downlink user equipmentInterference cancellation is performed by adopting an interference neutralization technology and an interference alignment technology, and the conditions which need to be satisfied are as follows:
interference neutralization conditions:
interference alignment condition 1:
interference alignment condition 2:
4a2) According to 4a 1), respectively obtaining precoding matrixes of the base station and the user:
through type<1>Base station precoding matrix for solving data signal transmitted from ith base station to jth downlink user equipmentAnd the base station precoding matrix of the data signal transmitted from the (P+1) -i-th base station to the (j) -th downlink user equipment>Through type<2>Base station precoding matrix for solving data signal transmitted from ith base station to 1 st downlink user equipment>Through type<3>Solving user precoding matrix of data signal transmitted by ith uplink user equipment>
Where i e { 1..p }, j e { 2..p },is to solve the base station precoding matrix +.>The space is formed by the arrangement of the plates,is to solve the user precoding matrix>The set tense space, span is the matrix space formed by tense all column vectors of the matrix;
the base station precoding matrix of the data signal sent to the jth downlink user equipment by the ith base station is solved from the interference neutralization conditionAnd the base station precoding matrix of the data signal transmitted from the (P+1) -i-th base station to the (j) -th downlink user equipment>The realization is as follows:
conditions for interference neutralizationThe arrangement is opened as a space->Make the following steps
Will be stretched into spatial expressionsIs converted into the following matrix form:
wherein Is a unitary matrix->From the definition of the matrix null space, F 1 Is a matrix of (n+2m) × (2M-N), +.>When meeting F 1 Is used for solving matrix X by zero space ratio 1 When the space of (a) is large, namely the constraint condition is satisfied, 2M-N is more than or equal to d s ；
According to constraint condition 2M-N is greater than or equal to d s Solving for X from the matrix 1 Obtaining a base station precoding matrix of a data signal sent to the jth downlink user equipment by the ith base stationAnd the base station precoding matrix of the data signal transmitted from the (P+1) -i-th base station to the (j) -th downlink user equipment>
The base station precoding matrix for solving the data signal sent by the ith station to the 1 st downlink user equipment from the interference alignment condition 1The realization is as follows:
for the interference alignment condition 1, the arrangement is made spaceMake the following steps
Will be stretched into spatial expressionsConverting into a matrix form: />
wherein Is a unitary matrix->From the definition of the matrix null space, F k Is (N+PM) x [ PM- (P-1) N]Matrix of->When meeting F k Is used for solving matrix X by zero space ratio k When the space of (a) is large, namely meeting the constraint condition PM- (P-1) N is more than or equal to d s ；
According to constraint condition PM- (P-1) N is greater than or equal to d s Solving X from the matrix k Obtaining a base station precoding matrix of a data signal sent to the ith downlink user equipment by the 1 st base stationWhere i e {1,., P };
the user precoding matrix of the data signal sent by the ith uplink user equipment is solved from the interference alignment condition 2The realization is as follows:
for the interference alignment condition 2, the arrangement is made spaceMake the following steps
Will be stretched into spatial expressionsConverting into a matrix form: />
wherein Is a unitary matrix->From the definition of the matrix null space, F 2 Is a matrix of (N+PN) ×N, +.>When meeting F k Is used for solving matrix X by zero space ratio k When the space of (a) is large, namely meeting the constraint condition N is more than or equal to d s ；
According to constraint condition N is greater than or equal to d s Solving X from the matrix k Obtaining a precoding matrix of the ith uplink user equipmentWhere i e {1,., P };
4b) Designing a decoding matrix for eliminating residual interference of a base station and a user according to the precoding matrix:
4b1) Based on the precoding matrix of the base station and the user obtained in (4 a), two sets of conditions required to be satisfied for eliminating all remaining interference are designed:
the first group is three conditions that the kth downlink user equipment needs to satisfy to eliminate all interference:
the second set is three conditions that the kth base station needs to satisfy to cancel all interference:
where H represents the conjugate transpose of the matrix, rank represents the rank of the matrix, d s For the length of one data signal, x is the downlink user equipmentIs a desired signal number of (a);
4b2) Decoding matrix of user from first set of conditionsDecoding matrix of base station from second set of conditions4c) The base station solves the precoding matrix of the base station according to the above>Transmitting signals and according to the decoding matrix->Decoding the signal it receives; the uplink user equipment solves the user precoding matrix according to the above>Transmitting signals, and the downlink user equipment obtains a user decoding matrix according to the above>The signal it receives is decoded to cancel the interference in the received signal.
2. The method of claim 1, wherein the data signals transmitted by the base station in (2) are represented as follows:
wherein For j-th base station in downlink state +.>Transmitting to the i-th downlink user equipment +.>Is used for the data signal of the (c),representation->Send to->Is the ith data stream, d s For the length of the data signal transmitted by the base station, T represents the transpose of the matrix.
3. The method of claim 1, wherein the data signals transmitted by the uplink user equipment in (2) are represented as follows:
wherein For j-th uplink user equipment +.>Transmitting to the jth base station in uplink state +.>Is used for the data signal of the (c),representation->Send to->Is the ith data stream, d s For the length of the data signal sent by the upstream user equipment, T represents the transpose of the matrix.
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