KR102107296B1 - Method for aligning interference of multi-user multi-cell mimo channel - Google Patents

Abstract

We propose a switching pattern matrix and a beamforming matrix in which some of the interference signals are naturally aligned in the same direction using an antenna switching pattern (reconfigurable antenna) method. The signal transmission method according to an embodiment includes 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 transmitting symbol vectors and a beamforming matrix. And beamforming the signal using the method, and transmitting the beamformed signal to each of the receivers.

Description

{METHOD FOR ALIGNING INTERFERENCE OF MULTI-USER MULTI-CELL MIMO CHANNEL}

The following embodiments relate to a joint interference alignment method for a K-user multi-cell multi-input multiple-output (MIMO) Gaussian interference channel, and more specifically, when channel state information is unknown, a part using a reconfigurable multi-mode antenna It relates to a method of aligning interference signals into spaces.

Interference Alignment (IA) is one of the most prominent technologies in wireless communication systems. Because of the broadcast nature of wireless networks, interference is an important constraint on the achievable data rate. Overcoming interference is an important problem in wireless networks. When an interference alignment technique is used, the signal is transmitted in a carefully selected 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 a multi-input and multi-output (MIMO) interference channel is characterized based on an independent channel matrix and an arbitrary number of antennas at each independent user node. The achievable degree of freedom (DoF) can be determined based on the total number of independent interference-free signal sizes. This arrangement can be categorized into multi-user and multi-cell network settings. Interference alignment technology can increase the total capacity and degree of freedom (DoF) of the wireless network by aligning the interference signals. Interference alignment (IA) may be the best approach for time-varying multiple-input and multiple-output (MIMO) interference 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, spatio-temporal interference alignment (STIA) technology can be used to align and reconstruct interference signals in unintended receivers by generating beamforming matrices for multiple input and multiple output (MIMO) relay channels. Joint interference alignment and power allocation strategies for orthogonal frequency division multiplexing-interleaving division multiple access wireless sensor networks 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 practical system models.

The embodiments to be described below propose a joint interference alignment and power allocation scheme for multi-user multi-cell MIMO channels through staggered antenna switching.

According to an embodiment of the present invention, a communication method using a blind interference alignment technique capable of aligning an interference signal 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 the interference signals are naturally aligned in the same direction using an antenna switching pattern (reconfigurable antenna) method.

The signal transmission method according to an aspect 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 Based on the step of 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 Includes 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 reconstructed antenna having two operating modes.

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

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,

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 transmitting the first transmission symbol to receiver k,

May indicate a beamforming vector selected when the second transmission symbol is transmitted to the k-th receiver.

The signal reception method according to the other side includes: receiving a beamformed signal from a transmitter, obtaining a beamforming matrix previously shared with the transmitter, and a receiver including the receiver and peripheral receivers Generating a channel matrix based on a switching pattern matrix controlling the antenna modes of the channel, separating a desired signal and an interference signal from the beamformed signal based on the channel matrix and the beamforming matrix, and 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 reconstructed antenna having two operating modes.

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

를 포함할 수 있다.

It may include.

Each of the transmission symbols includes one of the first transmission symbol and the second transmission symbol,

The beamforming vectors,

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 transmitting the first transmission symbol to receiver k,

May indicate a beamforming vector selected when the second transmission symbol is transmitted to the k-th receiver.

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

A base station according to the other side includes a processor connected to the transmitter and transmitting a signal, the processor obtaining a transmission symbol vector including transmission symbols to be transmitted to receivers, and a switching pattern matrix controlling antenna modes of the receivers Based on the beamforming vectors determined based on, and the transmission symbol vector, a beamforming matrix is determined, and the transmission symbol vector is beamformed using the beamforming matrix to generate a transmission signal, and the transmitter is multiplexed. The transmission signal is transmitted to the receivers using an antenna, and 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.

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

1 is a diagram of a multiple input and multiple output (MIMO) Gaussian interference channel model for 5 users per cell (L = 1) (K = 5).
FIG. 2 is a diagram illustrating interference alignment of receivers 1, 3, and 5 in multiple input and multiple output (MIMO) for five users (K = 5) per cell (L = 1) according to an embodiment. .
FIG. 3 illustrates multiple inputs and multiple outputs (MIMO) for 5 users (K = 5) per cell (L = 3) according to an embodiment, wherein 3 users per cell are multiple inputs located at a cell edge. And Multiple Output (MIMO) Gaussian Interference Channel Model.
FIG. 4 is a view showing a user divided according to an embodiment into three basic groups: cell center users (CCUs), cell intermediate users (CMUs), and cell edge users (CEUs).
5 is a graph illustrating the signal-to-interference noise ratio performance according to the distance of a cell edge user according to the presence or absence of inter-cell interference according to an embodiment.
6 is a graph illustrating a signal-to-interference noise ratio (SINR) versus capacity according to an embodiment depending on whether or not cooperation is performed between cell edge users.

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

The terms used in the examples are for illustrative purposes only and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the embodiment belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

In addition, in the description with reference to the accompanying drawings, the same reference numerals are assigned to the same components regardless of reference numerals, and redundant descriptions thereof will be omitted. In describing the embodiments, when it is determined that detailed descriptions of related known technologies may unnecessarily obscure the subject matter of the embodiments, detailed descriptions thereof will be omitted.

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

Referring to FIG. 1, in a multi-input and multi-output (MIMO) system according to an embodiment, the transmitter 110 and the receiver may have a plurality of antennas. 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, a reconstructed antenna). The reconstructed antenna may operate in two modes using a receiver switch. For example, the receiver 130 may operate in two modes by selecting the antenna 131 or the antenna 132 using a receiver switch. The transmitter 110 according to an embodiment may be a base station and a receiver may be a terminal.

The antenna 110 of the transmitter 110 may transmit a desired signal to the receiver 130. The signal transmitted by the antenna 1 111 may act as an interference signal to the receivers 140 to 5 and the receiver 170. Similarly, the antenna 2 112 can transmit a desired signal to the receiver 2 140, and this signal can act as an interference signal to the remaining receivers except the receiver 2 140.

Each receiver can receive a plurality of interference signals as well as a desired signal. Interference alignment may be performed in order to reduce the effect of interference on each receiver of each antenna of the transmitter 110. The interference alignment divides the signal vector space into a plurality of subspaces, so that signals from the desired transmitting end antenna are present in the signal subspace, and signals from the unwanted transmitting end antennas are present in the interference subspace, so that the desired signal at the receiving end It may be to enable detection without interference.

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

Beamforming according to an embodiment may be download beamforming that a base station transmits to terminals in a mobile communication system. In the downlink beamforming, the base station may transmit x = ws multiplied by the beamforming vector w to s, which is signal information to be transmitted to terminals, through multiple antennas. By using multiple beams, signals can be transmitted to multiple users simultaneously as well as one user. A method of communicating with multiple users while reducing interference between users through a beam is called spatial division multiple access (SDMA). In spatial division multiple access, x = W s obtained by multiplying s, which is a signal information vector (transmission symbol vector) to be transmitted, by W, which is a beamforming matrix, can be transmitted through 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 an M × 1 vector. After beamforming a signal based on a transmission symbol vector and a beamforming matrix, a beamformed signal may be transmitted to each receiver.

The beamforming vector according to the conventional method may be determined according to channel conditions of each transmitter antenna and receivers. Since each transmitter antenna determines the beamforming vector in consideration of the channel state, it has a large amount of computation, and it takes a long time for the beamforming vector to converge, and if each antenna transmits data using an unconverged beamforming vector, data Transmission efficiency 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.The beamforming vector according to an embodiment may be determined based on the switching pattern matrix of the antenna included in the receiver.

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

May indicate a beamforming vector selected when the second transmission symbol is transmitted to the k-th receiver. 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 for determining the switching pattern matrix will be described later.

Each receiver can receive a desired signal and an 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 a 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 acquire a transmission symbol transmitted to itself from a desired signal. A detailed method of 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 in Equation 1 is

May have the same dimension as having the entire column rank. Considering a multi-user multi-input and multi-output (MU MIMO) Gaussian interference channel with a fully independent number of users (K) of 5, each independent user spans multiple (e.g., 5) interference time slots. Multiple (eg 2) independent symbols

And

Since it transmits, one of the reconfigurable multi-mode antenna patterns P that can be given may be given as in Equation 2.

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

According to one embodiment, the antenna included in the receiver may use a low-cost reconfigurable antenna operating 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.When the second time slot ends, the first receiver may switch the antenna from the first operation mode to the second operation mode. The switching pattern of receiver 1 is

The channel matrix designed based on the antenna k and the receiver 1 of the transmitter 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.For the second receiver, the antenna mode can be switched three times. At the end of the first time slot, the antenna is switched from the second operation mode to the first operation mode, and at the end of the second time slot, the antenna is switched from the first operation mode to the second operation mode, and at the end of the fourth time slot In the antenna can be switched from the second operation mode to the first operation mode. The switching pattern of receiver 2 is

The channel matrix designed based on the antenna k and the receiver 2 of the transmitter is 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 case of receiver 3, the antenna mode can be switched twice. At the end of the first time slot, the antenna can be switched from the first operating mode to the second operating mode, and the antenna can be switched back to the first operating mode at the end of the fourth time slot. The switching pattern of receiver 3 is

The channel matrix designed based on the antenna k and the receiver 3 of the transmitter is 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.After the third time slot, the receiver 4 may switch the antenna to the first operation mode and the second operation mode. The switching pattern of receiver 4 is

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

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 case of receiver 5, the antenna mode can be switched three times. At the end of the first time slot, the antenna is switched from the second operation mode to the first operation mode, and at the end of the second time slot, the antenna is switched from the first operation mode to the second operation mode, and at the end of the third time slot In the antenna can be switched from the second operation mode to the first operation mode. The switching pattern of receiver 5 is

The channel matrix designed based on the antenna k and the receiver 3 of the transmitter may be equal to 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.Each user according to an embodiment has two symbols

Wow

Can send. The beamforming vector may be given by Equation 3.

FIG. 2 is a diagram illustrating interference alignment of receivers 1, 3, and 5 in multiple input and multiple output (MIMO) for five users (K = 5) per cell (L = 1) according to an embodiment. to be.

Referring to FIG. 2, the transmitting end 210 according to an embodiment includes the first transmitter 211, the second transmitter 212, the third transmitter 213, the fourth transmitter 214, and the fifth transmitter 215. It may include. The receiver 220 according to an embodiment may include a receiver 1 221, a receiver 2 222, a receiver 3 223, a receiver 4 224, and a receiver 5 225.

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, 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 an interference signal as well as a desired signal. For example, the first receiver 221 is a signal transmitted from the first transmitter 211

,

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

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

As described below, the receiver 1 according to an embodiment can observe that two desired symbols and eight interfering symbols can be decoded by multiplying the corresponding beamforming vector and channel vector, respectively.

If the signal received by the receiver 1 according to an embodiment is y ₁ , and the noise (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 W, which is a beamforming matrix. The product of the channel matrix and the transmission signal can 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 can 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 ), (h ₁₄ and h ₁₅ ) can be naturally aligned in the same direction. In the first receiver, the transmitter signal is aligned in the interference signal subspace, and the interference signal aligned in the same dimension subspace can 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 × 7 (full-rank) matrix, which may include a 2-dimensional desired signal subspace and a 5-dimensional interfering signal subspace. By removing the 3D interfering signals aligned in the same dimensional subspace, receiver 1 can achieve 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 equal to Equation (9).

The received signal y ₃ of the receiver 3 according to an embodiment may be obtained in the same manner as the receiver 1. The signals (h ₃₃ and h ₃₂ ), (h ₃₁ and h ₃₂ ), and (h ₃₄ and h ₃₅ ) can be naturally aligned in the same direction. In receiver 3, the transmitter signal is aligned in the interfering signal subspace, and the interference signal aligned in the same dimension subspace can 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 (Noise) at that time is Z ₅ , y ₅ may be equal to Equation (11).

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

According to the interference alignment method according to an embodiment, in order to generate a 2-dimensional desired signal subspace, an 8-dimensional subspace may be aligned and an interference subspace signal having a similar dimension may be removed. The matrix R _-n includes a desired signal and an interference symbol, and interference symbols aligned in the same order subspace can be canceled. By using this, the desired signal can be interference-aligned with less overhead without channel state information (CSI).

FIG. 3 illustrates multiple inputs and multiple outputs (MIMO) for 5 users (K = 5) per cell (L = 3) according to an embodiment, wherein 3 users per cell are multiple inputs located at a cell edge. And a multiple output (MIMO) Gaussian interference 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 it focuses on cell edge cooperation, it can be considered that the frequency reuse technology uses the same frequency after a certain distance in the wireless system.

In an environment in which interference between a plurality of adjacent cells occurs, it can be applied in a manner of detecting a user located at a cell edge and performing cooperative communication using the above-described indirect alignment technique only for the corresponding user.

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

In order to improve cell-edge user (CEU) performance 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 speed of each terminal user (MU). For example, consider partial cooperative transmission between cell edge users (CEUs) for three base stations (L = 3) to improve signal-to-interference noise ratio (SINR) by co-transmitting one user at a time. You can.

The base station cooperation methodology according to an embodiment may be reasonable because the base stations are connected through a high-speed wired backhaul exchanging information to maximize overall system performance. A fully cooperative downlink multiple input and multiple output (MIMO) Gaussian interference channel network according to one embodiment may result in maximum total speed 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 method between terminal users MU may be considered. SINR _nc for a downlink multiple input and multiple output (MIMO) Gaussian interference channel network may be expressed as Equation (13).

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

In general, full collaboration between users can lead to high total ratios and throughput. A user located near the cell edge CE may experience co-channel interference with adjacent cells. Full collaboration increases cost effectiveness due to the large amount of information exchange between the user and the base station, such as channel status information (CSI), transmitter and precoding information, but seamless collaboration between users generally increases complexity and loads on the backhaul link. Can be charged.

According to an embodiment, cost efficiency may be improved by considering cooperation between cell edge users (CEUs), and a lot of information and complex information may be exchanged at a base station. Collaboration with adjacent cell edge users (CEUs) can be considered. SINR _nc for downlink multiple input and multiple output (MIMO) Gaussian interference channel network will depend on the proposed cell edge users cooperation plan, bits of terminal users under the cooperation of cell edge users in bits / s / Hz The / s / Hz capacity may be equal to Equation 14.

>

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

>

An accurate expression of a cell edge user cooperation method for resource constraints to perform better may be as shown in Equation (15).

It may be desirable for cell edge users according to an embodiment 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 plurality of sub-groups when identifying a user location from a base station, where each group including several sub-carriers can be assigned to adjacent cells in turn. Partial frequency reuse (FFR) and soft frequency reuse (SFR) technologies can help reduce intercell interference (ICI), coordination intercell interference (ICIC) and improve spectral efficiency for cell edge users. have.

In general, partial frequency reuse (FFR) and soft frequency reuse (SFR) techniques divide cells into internal and external regions, and different frequency reuse factors can be used for each region. The distance from the base station to the cell edge user can cause bad channel conditions and low quality of service (QoS). In order to solve this problem, it may be necessary to determine the location of the cell center (CC), cell center (CM), and cell edge (CE) users. In a downlink multiple input and multiple output (MIMO) Gaussian interference channel, a signal-to-interference noise ratio (SINR) for k terminal users in L cells may be expressed as 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.Equation (15)

Is the downlink transmission 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.

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

Referring to FIG. 4, since a cell edge user according to an embodiment 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 problems. 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 from neighboring cells can be considered cell edge users (CEUs). To efficiently pair users, you can use the median to divide users into three basic groups: cell center users (CCUs), cell middle users (CMUs), and cell edge users (CEUs). Cell middle users (CMUs) may be as shown in Equation (17).

The cell edge user may be identified by considering Equation 17. Coordination between cell edge users and intercell interference (ICI) can help improve the 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 , 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 can be discussed in the following three cases.

Case 1: Partial cooperation between the cell edge terminal users {u ₄ and w ₅ } of cells 1 and 3 may be expressed as 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 cells 1 and 3 according to an embodiment. Equation 17

,

Can be The total capacity achieved by partial cooperation of the cell edge user may be equal to 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 cooperation in cells 1 and 3 is {

,

} And the corresponding channel gain is {

,

}. Optimal power allocation for CEU partial cooperation in cells 1 and 3 {

,

} May be equal to Equation 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 remaining cases, v ₅ and w ₄ , and partial cooperation between u ₅ and v ₄ can be obtained in the same way.

According to an embodiment, when there is no channel state information (CSI), a K-user multi-cell multi-input and multi-output (MIMO) Gaussian interference channel may be characterized through antenna switching and power analysis for a cell edge terminal user. . The total number of K-user communication pairs can be limited to less than the number of transmitters M and N of the receiver antennas. Since K independent users transmit n symbols according to an embodiment, fully connected K-user multiple input and multiple output (MIMO) Gaussian interference channels may be considered. The antenna switching pattern can be designed by 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 of a desired signal and an interference signal can be calculated.

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

Referring to FIG. 5, it is shown that in one embodiment, when there is partial cooperation in inter-cell interference (ICI), better performance is achieved than the case where it is not. For example, in the absence of inter-cell cooperation, the signal-to-interference noise ratio (SINR) of 10 dB and 0 dB increases from 0.55 km to 0.9 km, but in one embodiment there is signal-to-interference noise ratio if there is another cell-to-cell cooperation. The (SINR) value increases from 0.6 km to 1 km, and its width is larger. Signal-to-interference noise for the proposed scheme with inter-cell interference (ICI), considering that collaboration between cell-edge users from neighboring cells improves cell-edge terminal user performance compared to the absence of inter-cell interference (ICI) A drastic change in the ratio (SINR) can be expected.

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

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]. It can be increased to C [bps / Hz]. Without cooperation, the capacity can increase from 9.5C [bps / Hz] to 22C [bps / Hz]. For a cooperative cell edge user, 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 perfect cooperation between adjacent cell edge terminal users. When using partial cooperation between cell edge terminal users according to an embodiment, performance is superior to that of non-cooperative cell edge terminal users, and almost similar performance can be achieved even when compared with all of the cooperative cell edge terminal users.

The method according to the embodiment may be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer readable medium. The computer-readable medium may include program instructions, data files, data structures, or the like alone or in combination. The program instructions recorded on the medium may be specially designed and configured for the embodiments or may be known and usable by those skilled in computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROMs, DVDs, and magnetic media such as floptical disks. -Hardware devices specially configured to store and execute program instructions such as magneto-optical media, and ROM, RAM, flash memory, and the like. Examples of program instructions include high-level language code that can be executed by a computer using an interpreter, etc., as well as machine language codes produced by a compiler. 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, instruction, or a combination of one or more of these, and configure the processing device to operate as desired, or process independently or collectively You can command the device. Software and / or data may be interpreted by a processing device, or to provide instructions or data to a processing device, of any type of machine, component, physical device, virtual equipment, computer storage medium or device. , Or may be permanently or temporarily embodied in the transmitted signal wave. The software may be distributed on networked computer systems, and stored or executed in a distributed manner. Software and data may be stored in one or more computer-readable recording media.

As described above, although the embodiments have been described with limited drawings, those skilled in the art can apply various technical modifications and variations based on the above. For example, the described techniques are performed in a different order than the described method, and / or the components of the described system, structure, device, circuit, etc. are combined or combined in a different form from the described method, or other components Alternatively, even if replaced or substituted by equivalents, appropriate results can be achieved.

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

Claims (13)

Obtaining a transmission symbol vector containing transmission symbols to be transmitted to the receivers;
Determining beamforming matrices based on a switching pattern matrix that controls antenna modes of the receivers, and a beamforming matrix 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
Including,
The switching pattern matrix P-component '1' and component '2' included in the switching pattern matrix indicate a first operation mode and a second operation mode, respectively,

Signal transmission method comprising a.
According to claim 1,
The switching pattern matrix is a signal transmission method having a predetermined value such that at least some of the interference signals generated by the receivers are naturally aligned in the same direction.
According to claim 1,
Determining the beamforming matrix is
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.
According to claim 1,
The antenna included in the receiver includes a reconstructed antenna having two operating modes.
delete According to claim 1,
Each of the transmission symbols includes one of the first transmission symbol and the second transmission symbol,
The beamforming vectors,

Including,

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

Is a method of transmitting a signal indicating a beamforming vector selected when the second transmission symbol is transmitted to the k-th receiver.
In the method of receiving the signal 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 that controls 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
Including,
The switching pattern matrix P-component '1' and component '2' included in the switching pattern matrix indicate a first operation mode and a second operation mode, respectively,

Signal receiving method comprising a.
The method of claim 7,
The switching pattern matrix is a signal reception method having a predetermined value such that at least a portion of the interference signal is naturally aligned in the same direction.
The method of claim 7,
The antenna included in the receiver includes a reconstructed antenna having two operating modes.
delete The method of claim 7,
Each of the transmission symbols includes one of the first transmission symbol and the second transmission symbol,
Beamforming vectors,

Including,

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

Is a signal receiving method indicating a beamforming vector selected when the second transmission symbol is transmitted to the k-th receiver.
The method of claim 7,
The step of receiving the beamformed signal is
Receiving a signal transmitted from the transmitter while switching an antenna mode of the receiver based on the switching pattern matrix
Including, the signal receiving method.
transmitter;
And a processor connected to the transmitter to transmit a signal,
The processor
A transmission symbol vector including transmission symbols to be transmitted to receivers is obtained, and beamforming vectors determined based on a switching pattern matrix that controls antenna modes of the receivers, and a beamforming matrix is determined based on the transmission symbol vector. And generates 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 generated by the receivers are naturally aligned in the same direction,
The switching pattern matrix P-component '1' and component '2' included in the switching pattern matrix indicate a first operation mode and a second operation mode, respectively,

Base station comprising a.

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