KR20190137390A - Method for aligning interference of multi-user multi-cell mimo channel - Google Patents

Abstract

The present invention proposes a switching pattern matrix and a beamforming matrix which allow some of interference signals to be naturally aligned in the same direction using an antenna switching pattern (reconfigurable antenna) scheme. According to an embodiment of the present invention, a signal transmission method comprises the steps of: determining a transmission symbol vector based on a receiver; determining a beamforming matrix based on a switching pattern matrix of an antenna included in the receiver; and beamforming a signal using the transmission symbol vector and the beam forming matrix, and then transmitting the beamformed signal to each receiver.

Description

Interference alignment method for multi-user multi-cell MIMO channel {METHOD FOR ALIGNING INTERFERENCE OF MULTI-USER MULTI-CELL MIMO CHANNEL}

The embodiments below relate to a joint interference alignment method for a K-user multi-cell multi-input multiple-output (MIMO) Gaussian interfering channel, and more particularly, using a reconfigurable multi-mode antenna when channel state information is unknown. A method of aligning an interference signal in space.

Interference Alignment (IA) is one of the most prominent technologies in wireless communication systems. Because of the broadcast nature in wireless networks, interference is an important constraint on the data rate that can be achieved. Overcoming interference is an important problem in wireless networks. When an interference alignment technique is used, the signal is transmitted in a carefully chosen direction so that it can be decoded at the destination while occupying as little dimension as possible at the unintended destination.

The exact channel capacity region of the Multi Input-Multi Output (MIMO) interference channel is characterized by an independent channel matrix and an arbitrary number of antennas at each independent user node. Degree of Freedom (DoF) can be determined based on the total number of signal magnitudes without independent interference. This sort can be classified into multi-user and multi-cell network settings. Interference alignment techniques can increase the total capacity and degree of freedom (DoF) of a wireless network by aligning interference signals. Interference Alignment (IA) may be the best approach for time varying multiple input and multiple output (MIMO) interfering networks because it requires limited resources such as time, frequency and number of users.

In some special cases, global channel knowledge, such as complete and incomplete channel information, is required for interference alignment. For example, space-time interference alignment (STIA) techniques can be used to align and reconstruct interference signals at unintended receivers by generating beamforming matrices for multiple input and multiple output (MIMO) relay channels. Orthogonal Frequency Division Multiplexing-Interleaving Division Joint interference alignment and power allocation strategies for a multi-access wireless sensor network can improve overall system performance. However, this interference alignment method requires global channel knowledge, such as incomplete and complete channel state information (CSI), which is not always available in a practical system model.

Embodiments to be described below propose a joint interference alignment and power allocation scheme of a multi-user multi-cell MIMO channel with staggered antenna switching.

According to an embodiment of the present invention, a communication method using blind interference alignment technology capable of aligning interference signals without knowledge of channel state information (CSI) is proposed. In particular, a switching pattern matrix and a beamforming matrix are proposed in which some of interference signals are naturally aligned in the same direction using an antenna switching pattern (reconfigurable antenna) scheme.

According to one or more exemplary embodiments, a signal transmission method includes: obtaining a transmission symbol vector including transmission symbols to be transmitted to receivers, beamforming vectors determined based on a switching pattern matrix controlling antenna modes of the receivers, and the transmission symbol vector Determining a beamforming matrix, generating a transmission signal by beamforming the transmission symbol vector using the beamforming matrix, and transmitting the transmission signal to the receivers using multiple antennas. Steps.

The switching pattern matrix may have a predetermined value such that at least some of the interference signals generated by the receivers are naturally aligned in the same direction.

The determining of the beamforming matrix may include selecting a beamforming vector for a corresponding transmission symbol among the beamforming vectors, corresponding to each of the transmission symbols included in the transmission symbol vector.

The antenna included in the receiver may include a reconstruction antenna having two operating modes.

The switching pattern matrix P, wherein component '1' and component '2' included in the switching pattern matrix represent a first operating mode and a second operating mode, respectively,

를 포함할 수 있다.

It may include.

Each of the transmission symbols includes one of a first transmission symbol and a second transmission symbol, and the beamforming vectors are:

를 포함하고,

Including,

는 k번 수신기로 상기 제1 송신 심볼을 전송하는 경우 선택되는 빔포밍 벡터를 나타내고,

는 k번 수신기로 상기 제2 송신 심볼을 전송하는 경우 선택되는 빔포밍 벡터를 나타낼 수 있다.

Denotes a beamforming vector selected when the first transmission symbol is transmitted to receiver k,

Denotes a beamforming vector that is selected when the second transmission symbol is transmitted to receiver k.

In another embodiment, a signal receiving method includes: receiving a beamformed signal from a transmitter, obtaining a beamforming matrix pre-shared with the transmitter, and the receiver and peripheral receivers Generating a channel matrix based on a switching pattern matrix controlling antenna modes of the antennas, separating a desired signal and an interference signal from the beamformed signal, based on the channel matrix and the beamforming matrix, and Obtaining a transmission symbol for the receiver from a desired signal.

The switching pattern matrix may have a predetermined value such that at least some of the interference signals are naturally aligned in the same direction.

The antenna included in the receiver may include a reconstruction antenna having two operating modes.

The switching pattern matrix P, wherein component '1' and component '2' included in the switching pattern matrix represent a first operating mode and a second operating mode, respectively,

를 포함할 수 있다.

It may include.

Each of the transmission symbols comprises one of a first transmission symbol and a second transmission symbol,

The beamforming vectors are

를 포함하고,

는 k번 수신기로 상기 제1 송신 심볼을 전송하는 경우 선택되는 빔포밍 벡터를 나타내고,

는 k번 수신기로 상기 제2 송신 심볼을 전송하는 경우 선택되는 빔포밍 벡터를 나타낼 수 있다.

Including,

Denotes a beamforming vector selected when the first transmission symbol is transmitted to receiver k,

Denotes a beamforming vector that is selected when the second transmission symbol is transmitted to receiver k.

Receiving the beamformed signal may include receiving a signal transmitted from the transmitter while switching an antenna mode of the receiver based on the switching pattern matrix.

The base station according to the other side includes a processor connected to the transmitter for transmitting a signal, the processor obtains a transmission symbol vector containing transmission symbols to be transmitted to the receivers, and switching pattern matrix for controlling the antenna modes of the receivers Based on the beamforming vectors determined based on the transmission symbol vector, and determining a beamforming matrix, and generating a transmission signal by beamforming the transmission symbol vector using the beamforming matrix, wherein the transmitter is multiplexed. The antenna transmits the transmission signal to the receivers, and the switching pattern matrix may have a predetermined value so that at least some of the interference signals generated by the receivers are naturally aligned in the same direction.

According to an embodiment of the present invention, the interference signal may be aligned without knowledge of the channel state information (CSI). In particular, by using the proposed switching pattern matrix and the beamforming matrix, some of the interference signals can be naturally aligned in the same direction so that the interference signals can be more easily removed.

1 is a diagram of a multiple input and multiple output (MIMO) Gaussian interference channel model for five users (K = 5) per cell (L = 1).
FIG. 2 illustrates interference arrangements of receivers 1, 3, and 5 in multiple input and multiple output (MIMO) for five users (K = 5) per cell (L = 1) according to one embodiment. .
FIG. 3 shows a multiple input and multiple output (MIMO) for five users (K = 5) per cell (L = 3), where three users per cell are multiple inputs located at the cell edge And a diagram for a multiple output (MIMO) Gaussian interfering channel model.
4 is a diagram illustrating a user segmentation into three basic groups of cell center users (CCUs), cell intermediate users (CMUs), and cell edge users (CEUs), according to an embodiment.
FIG. 5 is a graph illustrating signal-to-interference noise ratio performance according to distance of a cell edge user according to an embodiment, with or without inter-cell interference; FIG.
FIG. 6 is a graph illustrating signal-to-interference noise ratio (SINR) versus capacity between cell edge users according to one embodiment. FIG.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. However, various changes may be made to the embodiments so that the scope of the patent application is not limited or limited by these embodiments. It is to be understood that all changes, equivalents, and substitutes for the embodiments are included in the scope of rights.

The terminology used herein is for the purpose of description and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

In addition, in the description with reference to the accompanying drawings, the same components regardless of reference numerals will be given the same reference numerals and duplicate description thereof will be omitted. In the following description of the embodiment, when it is determined that the detailed description of the related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted.

1 is a diagram of a multiple input and multiple output (MIMO) Gaussian interference channel model for five users (K = 5) per cell (L = 1).

Referring to FIG. 1, a transmitter 110 and a receiver may have a plurality of antennas in a multiple input and multiple output (MIMO) system according to an embodiment. For example, the transmitter 110 may have five antennas. The antenna included in the receiver according to an embodiment may be a reconfigurable multi-mode antenna (hereinafter, referred to as a reconstruction antenna). The reconstruction antenna can operate in two modes using a receiver switch. For example, the first receiver 130 may operate in two modes by selecting the antenna 131 or the antenna 132 by using a receiver switch. According to an embodiment, the transmitter 110 may be a base station and a receiver may be a terminal.

The first antenna 111 of the transmitter 110 may transmit a desired signal to the first receiver 130. The signal transmitted by the first antenna 111 may act as an interference signal to the second receiver 140 to the fifth receiver 170. Similarly, antenna 112 may transmit a desired signal to receiver 140, which may act as an interference signal to receivers other than receiver 140.

Each receiver may receive not only a desired signal but also a plurality of interference signals. Interference alignment may be made to reduce the effect of interference on each of the antennas of the transmitter 110 on the respective receivers. The interference alignment separates the signal vector space into a plurality of subspaces so that signals from the desired transmit antenna are present in the signal subspace and signals from the unwanted transmit antenna are present in the interference subspace, thereby allowing the desired signal at the receiving end. Can be detected without the influence of interference.

There are many ways to create signal vector space to align interference. According to an embodiment, a signal vector space in which interference signals are aligned using a switching pattern and a beamforming vector of an antenna included in a receiver may be created.

Beamforming according to an embodiment may be download beamforming transmitted by a base station to terminals in a mobile communication system. In downlink beamforming, a base station may export x = ws multiplied by s, which is signal information to be transmitted to terminals, w, which is a beamforming vector, through multiple antennas. Multiple beams allow simultaneous transmission of signals to multiple users as well as one user. The method of communicating with multiple users while reducing interference between users through a beam is called SDMA. In the spatial division multiple access, x = W s obtained by multiplying the signal information vector (transmission symbol vector) s by the beamforming matrix W may be exported through the multiple antennas. Beamforming matrix W = [w ₁ , w ₂ ,... , w _M ] is the M × L matrix, and the transmission symbol vector s = [s _1, s ₂ ,... , s _M ] T may be M × 1 vectors. After beamforming the signal based on the transmission symbol vector and the beamforming matrix, the beamformed signal may be transmitted to each receiver.

The beamforming vector according to the conventional method may be determined according to channel states of each transmitter antenna and receivers. Since each transmitter antenna determines the beamforming vector in consideration of the channel condition, it is computationally expensive, it takes a long time for the beamforming vector to converge, and if each antenna transmits data using the unconverged beamforming vector, The efficiency of the transmission may be low.

는 k번 수신기로 상기 제1 송신 심볼을 전송하는 경우 선택되는 빔포밍 벡터를 나타내고,

는 k번 수신기로 상기 제2 송신 심볼을 전송하는 경우 선택되는 빔포밍 벡터를 나타낼 수 있다. 스위칭 패턴 매트릭스는 간섭 신호 중 적어도 일부가 자연적으로 동일한 방향으로 정렬되도록 미리 정해진 값을 가질 수 있다. 스위칭 패턴 매트릭스를 결정하는 자세한 방법은 후술하겠다.According to an embodiment, the beamforming vector may be determined based on a switching pattern matrix of the antenna included in the receiver.

Denotes a beamforming vector selected when the first transmission symbol is transmitted to receiver k,

Denotes a beamforming vector that is selected when the second transmission symbol is transmitted to receiver k. The switching pattern matrix may have a predetermined value such that at least some of the interference signals are naturally aligned in the same direction. A detailed method of determining the switching pattern matrix will be described later.

Each receiver can receive the desired signal and the interference signal together. The receiver may receive a beamformed signal from the transmitter 110 and obtain a beamforming matrix previously shared with the transmitter 110. The receiver may generate a channel matrix based on a switching pattern matrix that controls antenna modes of the plurality of receivers. The plurality of receivers may include itself and surrounding receivers. The receiver may separate a desired signal and an interference signal from the beamforming signal based on the channel matrix and the beamforming matrix. The receiver can obtain the transmitted symbol sent to itself from the desired signal. Detailed methods for this will be described later.

The reconfigurable multi-mode antenna switching pattern according to an embodiment may satisfy Equation 1.

가 전체 컬럼 랭크(Rank)를 갖는 것과 동일한 차원(Dimension)을 가질 수 있다. 완전히 독립적인 사용자 수(K)가 5인 다중 사용자 다중 입력 및 다중 출력(MU MIMO) 가우시안 간섭 채널을 고려하면, 각각의 독립적인 사용자는 복수(예를 들어, 5 개)의 간섭 시간 슬롯에 걸쳐 복수(예를 들어, 2개)의 독립적인 심볼

및

를 송신하기 때문에 가능한 재구성 가능한 다중 모드 안테나 패턴(P) 중 하나가 수학식 2와 같이 주어질 수 있다.The matrix P _K column vector of Equation 1 is

May have the same dimension as having the full column rank. Considering a multi-user multi-input and multi-output (MU MIMO) Gaussian interference channel with a totally independent number of users (K) of 5, each independent user spans multiple (e.g., five) interference time slots. Multiple (eg two) independent symbols

And

Since one of the possible reconfigurable multi-mode antenna patterns (P) can be given by Equation (2).

Components '1' and '2' of the switching pattern matrix of Equation 2 according to an embodiment may indicate that the first operating mode and the second operating mode operate, respectively.

According to an embodiment, the antenna included in the receiver may use a low-cost reconfigurable antenna that operates only in two switching modes. The antenna switching pattern for receiver K can be designed as follows.

와 같고, 송신기의 k번 안테나 및 1번 수신기에 기초하여 설계된 채널 매트릭스는 H_1k=diag([h_1k(1) h_1k(1) h_1k(2) h_1k(2) h_1k(2)])와 같을 수 있다.The first receiver may switch the antenna from the first operation mode to the second operation mode at the end of the second time slot. The switching pattern of receiver 1 is

Channel matrix designed based on transmitter k antenna and receiver # 1 is H _1k = diag ((h _1k (1) h _1k (1) h _1k (2) h _1k (2) h _1k (2) ])

와 같고, 송신기의 k번 안테나 및 2번 수신기에 기초하여 설계된 채널 매트릭스는 H_2k=diag([h_2k(2) h_2k(1) h_2k(2) h_2k(2) h_2k(1)])와 같을 수 있다.In the case of receiver 2, the antenna mode can be switched three times. Switch the antenna from the second mode of operation to the first mode of operation at the end of the first time slot, switch the antenna from the first mode of operation to the second mode of operation at the end of the second time slot, and end of the fourth time slot The antenna may switch from the second operating mode to the first operating mode at. The switching pattern of receiver 2 is

Channel matrix designed based on transmitter k antenna and receiver 2 is given by H _2k = diag ([h _2k (2) h _2k (1) h _2k (2) h _2k (2) h _2k (1) ])

와 같고, 송신기의 k번 안테나 및 3번 수신기에 기초하여 설계된 채널 매트릭스는 H_3k=diag([h_3k(1) h_3k(2) h_3k(2) h_3k(2) h_3k(1)])와 같을 수 있다.In the case of receiver 3, the antenna mode can be switched twice. At the end of the first time slot, the antenna may be switched from the first mode of operation to the second mode of operation, and at the end of the fourth time slot, the antenna may be switched back to the first mode of operation. The switching pattern of receiver 3 is

Channel matrix designed based on the transmitter k antenna and receiver 3 is given by H _3k = diag ([h _3k (1) h _3k (2) h _3k (2) h _3k (2) h _3k (1) ])

와 같고, 송신기의 k번 안테나 및 4번 수신기에 기초하여 설계된 채널 매트릭스는 H_4k=diag([h_4k(2) h_4k(2) h_4k(2) h_4k(1) h_4k(1))와 같을 수 있다.The fourth receiver may switch the antenna to the first operation mode and the second operation mode after the third time slot ends. The switching pattern of receiver 4 is

The channel matrix designed based on the transmitter k and receiver 4 is equal to H _4k = diag ([h _4k (2) h _4k (2) h _4k (2) h _4k (1) h _4k (1) May be equal to).

와 같고, 송신기의 k번 안테나 및 3번 수신기에 기초하여 설계된 채널 매트릭스는 H5k=diag([h5k(2)h5k(1)h5k(2)h5k(1)h5k(1)])와 같을 수 있다.In the case of receiver 5, the antenna mode can be switched three times. Switch the antenna from the second mode of operation to the first mode of operation at the end of the first time slot, switch the antenna from the first mode of operation to the second mode of operation at the end of the second time slot, and end of the third time slot The antenna may switch from the second operating mode to the first operating mode at. The switching pattern of receiver 5 is

And a channel matrix designed based on antenna k and receiver 3 of the transmitter may be H5k = diag ([h5k (2) h5k (1) h5k (2) h5k (1) h5k (1)]) .

와

를 전송할 수 있다. 빔포밍 벡터는 수학식 3과 같이 주어질 수 있다.According to one embodiment each user has two symbols

Wow

Can be transmitted. The beamforming vector may be given by Equation 3 below.

FIG. 2 illustrates interference arrangements of receivers 1, 3, and 5 in multiple input and multiple output (MIMO) for five users (K = 5) per cell (L = 1) according to one embodiment. to be.

Referring to FIG. 2, the transmitter 210 according to an embodiment of the present invention is a transmitter 211, a transmitter 212, a transmitter 3, 213, a transmitter 4, and a transmitter 215. It may include. The receiver 220 according to an embodiment may include the first receiver 221, the second receiver 222, the third receiver 223, the fourth receiver 224, and the fifth receiver 225.

과, 제2 동작 모드에 따른 신호

를 송신할 수 있다.Each transmitter according to an embodiment may transmit two signals according to a switching mode. For example, the first transmitter 211 signals the first receiver 221 according to the first operation mode.

And a signal according to the second operation mode

Can be sent.

,

뿐만 아니라, 나머지 송신기(212, 213, 214, 215)에서 송신한 신호도 간섭 신호로 수신하여 총 10개의 신호를 수신할 수 있다.Each receiver according to an embodiment may receive not only a desired signal but also an interference signal. For example, the first receiver 221 transmits a signal transmitted by the first transmitter 211.

,

In addition, signals transmitted from the remaining transmitters 212, 213, 214, and 215 may also be received as interference signals to receive a total of 10 signals.

Each receiver according to an embodiment may obtain a transmission symbol vector by spatially separating an interference signal and a desired signal through interference alignment and decoding only a desired signal. For example, referring to FIG. 2, the first receiver 221 may spatially separate 10 signals received through interference alignment. The interference alignment method is described in detail below.

Receiver 1 according to an embodiment can observe that it is possible to decode two desired symbols and eight interference symbols by multiplying the corresponding beamforming vector and the channel vector, respectively, as described below.

If the signal received by the first receiver according to an embodiment is y ₁ and the noise at that time is Z ₁ , y ₁ may be equal to Equation 4.

The transmission signal x may be x = W s obtained by multiplying the transmission symbol vector s by the beamforming matrix W. The product of the channel matrix and the transmission signal may be represented by the product of the channel matrix, the beamforming matrix and the transmission symbol vector. The product of the channel matrix and the beamforming matrix may be represented as shown in Table 1 below.

Referring to Table 1, Equation 4 may be expressed as Equation 5.

If Equation 5 is simplified, it can be expressed as Equation 6.

The matrix multiplied by the transmission symbol vector of Equation 6 may be referred to as R ₁ . From R ₁ , the signals h ₁₁ and h ₁₂ , h ₁₂ and h ₁₃ , and h ₁₄ and h ₁₅ can be naturally aligned in the same direction. In receiver 1, the transmitter signal is aligned in the interference signal subspace, and the interference signal aligned in the subspace of the same dimension may be canceled as shown in Equation (7).

When the interference signal is removed according to Equation 7, R ₁ may be expressed as Equation 8.

R ₁ is a 5 x 7 (full-rank) matrix, which may include a two-dimensional desired signal subspace and a five-dimensional interfering signal subspace. By eliminating three-dimensional interference signals aligned in subspaces of the same dimension, receiver # 1 can achieve a 2/7 normalized DoF.

If the signal received by the receiver 3 according to an embodiment is y ₃ and the noise at that time is Z ₃ , y ₃ may be represented by Equation 9.

The received signal y ₃ of the third receiver according to an embodiment may be obtained by the same method as the first receiver. The signals h ₃₃ and h ₃₂ , (h ₃₁ and h ₃₂ ), and (h ₃₄ and h ₃₅ ) can naturally be aligned in the same direction. In receiver 3, the transmitter signal is aligned in the interference signal subspace, and the interference signal aligned in the subspace of the same dimension may be canceled as shown in Equation 10.

If the signal received by the receiver 5 according to an embodiment is y ₅ and the noise at that time is Z ₅ , y ₅ may be represented by Equation 11 below.

The reception signal y ₃ of the receiver 5 according to an embodiment may be obtained by the same method as the receiver 1. The signals h ₅₅ and h ₅₄ , h ₅₁ and h ₅₂ , and h ₅₂ and h ₅₃ can naturally be aligned in the same direction. In receiver 5, the transmitter signal is aligned in the interference signal subspace, and the interference signal aligned in the subspace of the same dimension may be canceled as shown in Equation 12.

According to the interference alignment method according to an embodiment, in order to generate a two-dimensional desired signal subspace, the eight-dimensional subspace may be aligned and the interference subspace signal having a similar dimension may be removed. The matrix R _−n contains the desired signal and interference symbols, and interference symbols aligned in subspace of the same order can be canceled. By using this, the desired signal can be interference aligned with less overhead without channel state information (CSI).

FIG. 3 shows a multiple input and multiple output (MIMO) for five users (K = 5) per cell (L = 3), where three users per cell are multiple inputs located at the cell edge And multiple output (MIMO) Gaussian interfering channel model.

Referring to FIG. 3, a multi-cell multi-input and multi-output (MIMO) network may be performed in consideration of partial cooperation between cell edge mobile users. Because the focus is on cell edge cooperation, frequency reuse techniques can be considered to use the same frequency after a certain distance in a wireless system.

In an environment in which interference between a plurality of adjacent cells occurs, the present invention may be applied by detecting a user located at a cell edge and performing cooperative communication using only the indirect alignment technique described above with respect to the corresponding user.

Base station coordination according to an embodiment may include control distribution, data signal transmission, channel state information (CSI) and precoder over a wired backhaul link to synchronize transmitters and mobile users. have. The base station can use this information to adapt the environment and communication strategy to the desired channel conditions.

In order to improve the performance of cell-edge users (CEUs) according to an embodiment, multi-user partial cooperation may be investigated in a multi-cell environment scenario. The Signal-to-Interference-plus-Noise Ratio (SINR) may determine the transmission rate of each terminal user (MU). For example, consider partial cooperative transmission between cell edge users (CEU) for three base stations (L = 3) to improve the signal-to-interference noise ratio (SINR) by jointly transmitting one user at a time. Can be.

The base station cooperative methodology according to one embodiment may be reasonable because the base stations are connected via high speed wired backhaul to exchange information to maximize overall system performance. A fully cooperative downlink multiple input and multiple output (MIMO) Gaussian interfering channel network according to one embodiment may result in maximum sum rate and throughput. The overall cost may increase due to the large amount of global channel state information (CSI) exchange between the terminal users and the base station.

In a normal operation according to an embodiment, a non-cooperative transmission scheme between terminal users (MU) may be considered. The SINR _nc for the downlink multiple input and multiple output (MIMO) Gaussian interfering channel network can be expressed as Equation 13.

The bits / s / Hz capacity of the terminal users under the non-cooperative transmission scheme is expressed using the Shannon capacity formula, where λ is the determined signal-to-interference noise ratio (SINR) difference between the theoretical coding scheme and the actual coding scheme. Can be.

In general, full cooperation between users can lead to high sum rates and throughput. A user located near the cell edge CE may experience co-channel interference with adjacent cells. Full cooperation increases cost efficiency due to the large amount of information exchange between the user and the base station, such as channel state information (CSI), transmitter and pre-coding information, but perfect cooperation between users generally increases complexity and places a lot of load on the backhaul link. Can be imposed.

According to an embodiment, cost efficiency may be improved in consideration of cooperation between cell edge users (CEUs), and a lot of information and complex information may be exchanged at a base station. Cooperation with adjacent cell edge users (CEUs) may be considered. Since SINR _nc for downlink multi-input and multiple-output (MIMO) Gaussian interfering channel network will depend on the proposed cell edge users cooperation scheme, the bits of terminal users under cell edge users cooperation in bits / s / Hz The / s / Hz capacity may be as shown in Equation 14.

>

를 보다 양호하게 수행하기 위한 자원 제약에 대한 셀 엣지 사용자 협력 방식에 대한 정확한 표현은 수학식 15와 같을 수 있다.Α of Equation 14 may mean a proportion of resource sharing allocation among cell edge users to cooperate with. According to one embodiment, α = 0.5. Multiple input and multiple output (MIMO) downlink transmission schemes, i.e.

>

The exact representation of the cell edge user coordination scheme for resource constraints for better performance may be given by Equation 15.

According to an embodiment, it may be desirable for cell edge users to perform a cooperative downlink multiple input and multiple output (MIMO) transmission scheme between adjacent cell edge users.

Frequency Re-Use (FR) according to an embodiment may be to reuse the same frequency after a certain distance in a cellular wireless system. The limited frequency bandwidth is divided into a number of subgroups when identifying the user location from the base station, where each group containing several subcarriers can in turn be assigned to adjacent cells. Partial frequency reuse (FFR) and soft frequency reuse (SFR) techniques can help reduce intercell interference (ICI), intercell interference coordination (ICIC) and improve spectral efficiency for cell edge users. have.

In general, partial frequency reuse (FFR) and soft frequency reuse (SFR) techniques divide a cell into inner and outer regions, and different frequency reuse factors may be used for each region. The distance from the base station to the cell edge user can cause poor channel conditions and low quality of service (QoS). To solve this problem, it may be necessary to determine the location of the user of the cell center (CC), the cell center (CM) and the cell edge (CE). In the downlink multiple input and multiple output (MIMO) Gaussian interference channel, the signal-to-interference noise ratio (SINR) for k terminal users in L cells may be as shown in equation (16).

은 기지국에 의해 할당 된 다운링크 송신 전력이고,

은 K 번째 단말기 사용자에 대한 채널 이득이고,

은 제로 평균 부가 백색 가우스 잡음 (AWGN: additive white Gaussian noise) 전력일 수 있다.Of equation (15)

Is the downlink transmit power allocated by the base station,

Is the channel gain for the K-th terminal user,

May be zero average additive white Gaussian noise (AWGN) power.

4 is a diagram illustrating a user segmenting into three basic groups of cell center users (CCUs), cell intermediate users (CMUs), and cell edge users (CEUs), according to an exemplary embodiment.

Referring to FIG. 4, since the cell edge user is greatly affected by inter-cell interference (ICI), interference of neighboring cells may be considered. Inter-cell interference (ICI) signals may need to be identified and aligned to overcome low quality of service (QoS) and low throughput issues. Users near the base station are considered cell center users (CCUs), users with average interference are considered cell intermediate users (CMUs), and users with higher interference in adjacent cells may be considered cell edge users (CEUs). To efficiently pair users, the median can be used to divide users into three basic groups: cell center users (CCUs), cell intermediate users (CMUs), and cell edge users (CEUs). The cell middle users (CMUs) may be as shown in Equation 17.

In consideration of Equation 17, a cell edge user may be identified. Coordination between cell edge users and inter-cell interference (ICI) can help to improve overall spectral efficiency of base station and terminal user performance. For example, partial cooperation of u ₄ and w ₅ , v ₅ and w ₄ , and u ₅ and v ₄ of FIG. 3 may be considered.

When the number L of cells according to an embodiment is 3, the summation, total capacity, power distribution, and feasible conditions between cell edge users may be discussed in the following three cases.

Case 1: The partial coordination between cell edge terminal users {u ₄ and w ₅ } of cell 1 and cell 3 may be as shown in equation (18).

,

일 수 있다. 셀 엣지 사용자의 부분 협력에 의해 달성 된 총 용량은 수학식 19와 같을 수 있다.SINR _u4 and SINR _w5 may be considered for cooperation of users of Cell 1 and Cell 3 according to an embodiment. Of equation (17)

,

Can be. The total capacity achieved by the partial cooperation of the cell edge user may be as shown in Equation 19.

,

}이고 해당 채널 이득은 각각 {

,

}일 수 있다. 셀 1과 셀 3에서의 CEU 부분 협력을 위한 최적의 전력 할당 {

,

}는 수학식 20과 같을 수 있다.The optimal power allocation for CEU partial collaboration in Cell 1 and Cell 3 is {

,

} And their respective channel gains are each {

,

}. Optimal Power Allocation for CEU Partial Collaboration in Cells 1 and 3 {

,

} May be equal to (20).

를 만족할 수 있다. 나머지 케이스인 v₅와 w₄, u₅와 v₄간의 부분 협력도 마찬가지 방법으로 구할 수 있다.Equation 20 is

Can be satisfied. The same can be done with the remaining cases, v ₅ and w ₄ , and partial cooperation between u ₅ and v ₄ .

According to an embodiment, in the absence of channel state information (CSI), K-user multi-cell multi-input and multi-output (MIMO) Gaussian interference channel may be characterized by antenna switching and power analysis for a cell edge terminal user. . It is possible to limit the total number of K-user communication pairs to be smaller than the number of transmitters M and receiver antennas N. Since K independent users transmit n symbols according to an embodiment, a fully connected K-user multiple input and multiple output (MIMO) Gaussian interference channel may be considered. The antenna switching pattern can be designed assuming a randomly generated transmission strategy for the K-user. According to an embodiment, a reconfigurable multi-mode antenna switch among two preset modes may be considered. As shown in Equation 21, input and output relations for a desired signal and an interference signal can be calculated.

FIG. 5 is a graph illustrating signal-to-interference noise ratio performance according to distance of a cell edge user according to an embodiment according to the presence or absence of inter-cell interference.

Referring to FIG. 5, the case where there is partial cooperation in another inter-cell interference (ICI) in one embodiment shows that better performance is achieved than otherwise. For example, in the absence of cell-to-cell coordination, the signal-to-interference noise ratio (SINR) of 10 dB and 0 dB increases from 0.55 km to 0.9 km, while in one embodiment there is a signal-to-interference noise ratio The (SINR) value increases from 0.6 km to 1 km, with a larger width. Considering that cooperation between cell edge users from adjacent cells improves cell edge terminal user performance compared to the case without inter-cell interference (ICI), signal-to-interference noise for the proposed scheme with inter-cell interference (ICI) A drastic change in the ratio (SINR) can be expected.

FIG. 6 is a graph illustrating signal-to-interference noise ratio (SINR) versus capacity between cell edge users according to an embodiment.

Referring to FIG. 6, when the signal-to-interference noise ratio (SINR) increases from 5 [dB] to 20 [dB], the system capacity of the partially cooperative cell edge user according to an embodiment is 37.5 at 12C [bps / Hz]. Can be increased to C [bps / Hz]. In the absence of cooperation, the capacity may increase from 9.5 C [bps / Hz] to 22 C [bps / Hz]. For cooperative cell edge users, it can increase from 15C [bps / Hz] to 47.5C [bps / Hz]. This result is expected to improve the performance of the overall terminal users in consideration of the perfect cooperation between the adjacent cell edge terminal users. In the case of using partial coordination between cell edge terminal users according to an embodiment, the performance is better than that of non-cooperative cell edge terminal users, and the performance may be almost similar to that of all cooperative cell edge terminal users.

The method according to the embodiment may be embodied in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the media may be those specially designed and constructed for the purposes of the embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

The software may include a computer program, code, instructions, or a combination of one or more of the above, and configure the processing device to operate as desired, or process it independently or collectively. You can command the device. Software and / or data may be any type of machine, component, physical device, virtual equipment, computer storage medium or device in order to be interpreted by or to provide instructions or data to the processing device. Or may be permanently or temporarily embodied in a signal wave to be transmitted. The software may be distributed over networked computer systems so that they may be stored or executed in a distributed manner. Software and data may be stored on one or more computer readable recording media.

Although the embodiments have been described with reference to the accompanying drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the described techniques may be performed in a different order than the described method, and / or components of the described systems, structures, devices, circuits, etc. may be combined or combined in a different manner than the described method, or other components. Or even if replaced or replaced by equivalents, an appropriate result can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are within the scope of the following claims.

Claims (13)

Obtaining a transmission symbol vector comprising transmission symbols to send to receivers;
Determining beamforming vectors determined based on a switching pattern matrix controlling antenna modes of the receivers, and based on the transmission symbol vector;
Generating a transmission signal by beamforming the transmission symbol vector using the beamforming matrix; And
Transmitting the transmission signal to the receivers using multiple antennas
Signal transmission method comprising a.
The method of claim 1,
And the switching pattern matrix has a predetermined value such that at least some of the interference signals occurring at the receivers are naturally aligned in the same direction.
The method of claim 1,
Determining the beamforming matrix
Selecting a beamforming vector for a corresponding transmission symbol among the beamforming vectors, corresponding to each of the transmission symbols included in the transmission symbol vector
Signal transmission method comprising a.
The method of claim 1,
The antenna included in the receiver comprises a reconstruction antenna having two modes of operation.
The method of claim 1,
The switching pattern matrix P, wherein component '1' and component '2' included in the switching pattern matrix represent a first operating mode and a second operating mode, respectively,

Signal transmission method comprising a.
The method of claim 1,
Each of the transmission symbols comprises one of a first transmission symbol and a second transmission symbol,
The beamforming vectors are

Including,

Denotes a beamforming vector selected when the first transmission symbol is transmitted to receiver k,

Is a signal transmission method indicating a beamforming vector selected when transmitting the second transmission symbol to receiver k.
In the signal receiving method of the receiver,
Receiving a beamformed signal from a transmitter;
Obtaining a beamforming matrix previously shared with the transmitter;
Generating a channel matrix based on a switching pattern matrix controlling antenna modes of receivers including the receiver and peripheral receivers;
Separating a desired signal and an interference signal from the beamformed signal based on the channel matrix and the beamforming matrix; And
Obtaining a transmission symbol for the receiver from the desired signal
Signal receiving method comprising a.
The method of claim 7, wherein
And the switching pattern matrix has a predetermined value such that at least some of the interfering signals are naturally aligned in the same direction.
The method of claim 7, wherein
The antenna included in the receiver comprises a reconstruction antenna having two modes of operation.
The method of claim 7, wherein
The switching pattern matrix P, wherein component '1' and component '2' included in the switching pattern matrix represent a first operating mode and a second operating mode, respectively,

Signal receiving method comprising a.
The method of claim 7, wherein
Each of the transmission symbols comprises one of a first transmission symbol and a second transmission symbol,
The beamforming vectors are

Including,

Denotes a beamforming vector selected when the first transmission symbol is transmitted to receiver k,

Is a signal reception method indicating a beamforming vector selected when transmitting the second transmission symbol to receiver k.
The method of claim 7, wherein
Receiving the beamformed signal
Receiving a signal transmitted from the transmitter while switching an antenna mode of the receiver based on the switching pattern matrix
Comprising a signal reception method.
transmitter;
A processor coupled to the transmitter to transmit a signal;
The processor is
Obtain a transmission symbol vector including transmission symbols to be transmitted to receivers, determine beamforming vectors determined based on a switching pattern matrix controlling antenna modes of the receivers, and based on the transmission symbol vector, determine a beamforming matrix Generate a transmission signal by beamforming the transmission symbol vector using the beamforming matrix,
The transmitter transmits the transmission signal to the receivers using multiple antennas,
The switching pattern matrix has a predetermined value such that at least some of the interference signals occurring at the receivers are naturally aligned in the same direction,
Base station.

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