KR20130041717A - Cooperative multi-cell mimo beamforming method based on relaxed zero-forcing - Google Patents

Abstract

PURPOSE: A cooperative multiple cell MIMO(Multiple Input Multiple Output) beam forming and transmitting method based on modified zero forcing is provided to suggest an effective cooperative beam design method in a multi-cell environment including a plurality of antennas. CONSTITUTION: A beam transmitted to user terminals through a modified zero forcing beams forming method is designed(S210). The designed beam is transmitted(S220). The maximum allowable value of interference is set in user terminals in advance. The set maximum allowable value is bigger than 0 or is similar to 0. The allowable value of the interference is set by considering a thermal noise level of the user terminals. [Reference numerals] (S210) Step of designing beams to be transmitted to user terminals through a modified zero forcing beam forming method; (S220) Step of transmitting the designed beams;

Description

Cooperative MULTI-CELL MIMO BEAMFORMING METHOD BASED ON RELAXED ZERO-FORCING

The need for high data rates and frequency efficiencies in wireless mobile communications is increasing rapidly. To meet this need, the density of the cellular network must be high and the cell size must be small. In such a situation, interference between adjacent base stations and receivers (terminals) in a cellular network is inevitable, and it is very important to deal with such interference.

Among the methods of dealing with the interference, the cooperation between the base station and using the Multiple Input Multiple Output (MIMO) antenna technology at the same time has attracted attention as a key technology to solve the interference problem. Among them, the zero-forcing technique among the coordinated beamforming techniques has been widely used and studied because it is simple and practical. The zero forcing beamforming method causes the column space of the beamforming matrix of each base station to enter the null space of the channel to the receivers that do not want to transmit, thus having no interference with receivers that do not want to transmit. It is a technique of transmitting information only to a desired receiver.

Although this method effectively eliminates interference, there is a significant disadvantage in the degree of freedom of the beam design because the beamforming matrix is created within the zero space of a matrix. Therefore, in the present patent, a multi-cell multi-input method for mitigating zero-forcing beam formation in which a transmission beam is designed by determining an amount of interference in a multiple-input single-output (MIS) interference channel (IC) in advance We propose a beamforming design algorithm that increases the total data rate of the system compared to the existing zero-forcing method by extending and applying it to a multi-output network (reduced, multi-cell MIMO network) environment.

In addition, we propose an algorithm to increase the total data rate of a system using a mitigation zero forcing beamforming method in a cooperative multi-cell multi-input / output network environment.

The effective solution of interference effects in mobile communication systems has been studied for a long time, and the importance of interference management technology has recently increased. A representative interference management technique that is widely studied recently is an interference alignment technique.

The interference alignment technique divides the space occupied by the interference from the receiver and the space occupied by the desired signal through the transmission beamforming in the situation where each transmitter knows all the channel information. Through interference alignment, the interference signals are gathered in the limited interference space at the receiver, and the space of the desired signal and the space occupied by the interference are linearly independent, so that the desired signal can be extracted without the influence of the interference through a simple reception beam. have.

There are several ways to design a transmission beam for interference alignment. Prior patents (Registration No .: 10-2009-0108145) proposed a beam design method based on a least-squares approach. When the number of transmission data is 1, this method has low complexity and almost the same performance at the total data rate compared to other methods.

Prior patents (application number: 10-2010-0140497) proposed an adaptive beam design method using the conjugate gradient method in a time-varying channel environment based on the beam design technique introduced above. The adaptive beam design technique significantly reduced the calculation amount compared to the result of newly calculating the beam for every channel change in the time-varying channel, but the overall data rate was not significantly different.

The interference alignment technique proposed in the above patent has a limitation in that interference is eliminated only when both receivers know the channel matrix and the transmission beamforming matrix information and design an appropriate reception beam accordingly. In addition, the interference alignment technique is useful in a high signal to noise ratio (SNR) environment. In an actual communication environment, the terminals at the edge of a cell that receive a lot of interference from other cells operate at a low signal-to-noise ratio. It is not appropriate to use technology.

The problem to be solved by the present invention is to propose a new cooperative beam design method that is effective when the number of antennas of the base station is greater than the number of antennas of all users in a multi-cell environment where each transceiver has multiple antennas. The cooperative beam design method, which is based on the well-known zero forcing, has a low degree of freedom in beam design due to the constraint of eliminating interference completely, and the low overall data rate makes it possible to cope with such a weak zero forcing. A multi-cell MIMO beamforming transmission method is provided.

Another problem to be solved by the present invention is to allow a little interference at the receiving end in order to overcome the conventional low overall data rate, but the radio communication system and the predetermined level of interference to be set in advance in consideration of the thermal noise of each receiver There is provided a cooperative multi-cell MIMO beamforming transmission method based on relaxed zero forcing that can design a transmission beam.

In addition, another problem to be solved by the present invention is based on a relaxed zero forcing that can be applied to the cooperative transmission beam technology described above even when each base station shares a message for all users through a protocol method for the cooperative beam design method To provide a cooperative multi-cell MIMO beamforming transmission method.

According to an aspect of the present disclosure, a relaxed zero forcing based MIMO beamforming transmission method includes: designing a beam to be transmitted to user terminals through a relaxed zero forcing beamforming method; And transmitting the designed beam.

The designing may include setting in advance a maximum allowable amount of interference affecting the benefit user terminals and setting the preset maximum allowable value to be greater than or equal to zero.

The allowance of the interference is set in consideration of the thermal noise level of each of the user terminals.

The thermal noise level is estimated by the base station through the signal-to-noise ratio and the interference-to-noise ratio received through the channel formed between the user terminal and the base station.

The signal-to-noise ratio or the interference-to-noise ratio is defined as a thermal noise level relative to the square of the channel size.

The designing step may be a step of designing a beam that satisfies the following conditional expression using Equation 4 described below.

&Quot; (4) "

는 간섭의 허용치를 나타낸다.Where H _ji denotes a matrix of size M × N between the j th transmitter and the i th receiver, and V _i denotes a beam forming matrix of size N × d,

Represents the tolerance of the interference.

[Conditional expression]

이며, here,

Is,

,

로 나타내며, 여기서, vi=vec(Vi) 이고,

이며,

이다.(C.1) and (C.2) are each set

,

Where vi = vec (Vi),

Is,

to be.

는 크로네커곱(Kronecker product)을 뜻한다.)
(vec (·) is an operator that creates a column vector by stacking down from the first column vector to the last column vector in the matrix.

Means Kronecker product.)

는, 아래에 기재된 수학식 7을 이용하여 계산되는 것을 특징으로 한다.remind

Is calculated using Equation 7 described below.

[Equation 7]

인데,

는 입력 값을 볼록 집합 C로 보내는 메트릭 사영(metric projection) 함수이고,

와

는 각각 목적 함수와 그것에 대한 기울기(gradient)를 나타내며,

은 (0,2) 사이의 양의 실수로 스텝 사이즈를 (step size)를 나타낸다.
here,

However,

Is a metric projection function that sends the input value to convex set C,

Wow

Respectively represent the objective function and its gradient,

Denotes a step size with a positive real number between (0, 2).

The designing step includes two or more base stations cooperatively sharing a message to be transmitted to two or more user terminals by a central management base station and the two or more user terminals through a relaxed zero-forcing beamforming method. Designing a beam to be transmitted to the devices.

The designing step may include: pre-setting a maximum allowable amount of interference affecting the two or more user terminals, and setting the preset maximum allowable value as a relaxed zero forcing condition. It characterized in that it comprises the step of designing a beam to be transmitted to the two or more user terminals through.

(여기서,

는 크기가 M×N이며 기지국 j에서 수신기 i로의 채널을 나타내고,

는 기지국 j에서 수신기 i로 정보를 전송할 때 사용하는 크기가 N×d인 송신 빔 행렬을 나타낸다.

는 기지국 m에서 수신기 i를 위한 메시지를 송신할 때, 이 신호가 수신기 j에 허용할 수 있는 최대 간섭의 세기를 말한다.)에 해당하는 것을 특징으로 한다.
The relaxed zero forcing condition is

(here,

Represents a channel from base station j to receiver i, of size M × N,

Denotes a transmission beam matrix having a size of N × d used when transmitting information from the base station j to the receiver i.

When the base station m transmits a message for the receiver i, this signal refers to the maximum strength of the interference that can be allowed to the receiver j).

According to the cooperative multi-cell MIMO beamforming method based on the relaxed zero forcing of the present invention, the receiver does not need to know both the channel and the transmission beam information, and has the effect of guaranteeing the freedom when designing the transmission beam.

In addition, according to the cooperative multi-cell MIMO beamforming method based on the relaxed zero forcing of the present invention, the performance of the total data rate is improved by increasing the degree of freedom of the beam, which is a disadvantage of the zero forcing.

In addition, through this scheme, we propose a new cooperative beam system that cooperates while controlling the amount of interference on an undesired terminal, and allows each base station to adjust the amount of interference caused to a terminal that does not want to transmit information, while simultaneously controlling the data rate of the desired terminal. Has the effect of optimizing

1 is an exemplary diagram illustrating a cooperative multi-cell MIMO communication network based on relaxed zero forcing according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating a relaxed zero forcing based MIMO beamforming transmission method according to an embodiment of the present invention through the communication network shown in FIG. 1.
FIG. 3 is a flow chart more specifically illustrating the design steps shown in FIG. 2.
FIG. 4 is a graph showing the total data rate obtained when the relaxation zero forcing beam is obtained through Equation 11 in the same condition as in Equation 4. FIG.
FIG. 5 is a graph of the total data rate obtained when the relaxation zero forcing beam is obtained through Equation 11 in the same condition as in [Condition 4]. FIG.
6 is an exemplary diagram illustrating a cooperative multi-cell MIMO communication network based on relaxed zero forcing according to another embodiment of the present invention.
FIG. 7 is a flowchart illustrating a relaxed zero forcing based MIMO beamforming transmission method according to another embodiment of the present invention through the communication network shown in FIG. 6.
FIG. 8 is an exemplary diagram illustrating the total data rate that can be obtained through a relaxed zero forcing transmission beam and the total data rate that can be obtained when using a zero forcing transmission beam in a cooperative multi-input multi-output multi-cellular network.
FIG. 9 is an exemplary diagram illustrating the total data rate that can be obtained through a relaxed zero forcing transmission beam and the total data rate that can be obtained when using a zero forcing transmission beam in a cooperative multi-input multi-output multi-cellular network.

Specific structural to functional descriptions of embodiments according to the inventive concept disclosed in the specification or the application are only illustrated for the purpose of describing embodiments according to the inventive concept, and according to the inventive concept. The examples may be embodied in various forms and should not be construed as limited to the embodiments set forth herein or in the application.

Embodiments in accordance with the concepts of the present invention can make various changes and have various forms, so that specific embodiments are illustrated in the drawings and described in detail in this specification or application. However, this is not intended to limit the embodiments in accordance with the concept of the present invention to a particular disclosed form, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The terms first and / or second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are intended to distinguish one element from another, for example, without departing from the scope of the invention in accordance with the concepts of the present invention, the first element may be termed the second element, The second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between. Other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "comprises ",or" having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

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 to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as ideal or overly formal in the sense of the art unless explicitly defined herein Do not.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the accompanying drawings, wherein like characters have the same meanings.

1 is an exemplary diagram illustrating a cooperative multi-cell MIMO communication network based on the relaxed zero forcing of the present invention.

Referring to FIG. 1, the communication system 200 of the present invention includes a plurality of base stations 210, 220, and 230 and a plurality of user terminals 240, 250, and 260.

In this case, it is assumed that each base station has K receivers providing services to other base stations, and each base station and receivers have N and M antennas, respectively, where N and M are natural numbers.

In particular, the present invention assumes a situation where the number of antennas satisfies N ≧ KM (K is a natural number).

For example, each base station 210, 220, 230 pairs with one receiver and transmits information to the receiver paired with it.

First, each base station (210, 220, 230) is a situation where other base stations do not know what information to send (this situation is called a MIMO IC), the signal received by the receiver i (e.g., a receiver belonging to the base station i) is [ Equation 1] is given. (In the future, the base station is mixed with the transmitter.)

)를 따른다고 가정한다.Here, H _ij denotes a channel matrix having a size M × N between base stations j and i, and s _i and V _i denote a transmission beamforming matrix having a size of N × d whose d × 1 data vector transmitted from the base station i is N × d. The data vector s _i and the noise vector n _i (size: M × 1) are circulary symmetric complex normal distributions CN (0, I _d ) and CN (0,

Assume that

은 수신기 i에서 열잡음 레벨이다. 여기서, [수학식 1]의 우변에서 첫째 항은 수신기가 원하는 신호를, 둘째와 셋째 항은 각각 간섭 신호와 잡음 신호를 나타낸다.

Is the thermal noise level at receiver i. Here, in the right side of Equation 1, the first term represents a signal desired by the receiver, and the second and third terms represent an interference signal and a noise signal, respectively.

A zero forcing transmit beam that avoids interference from base station i to a receiver belonging to another base station (a receiver that does not want to transmit information) is determined in a matrix satisfying Equation 2.

을 제로 포싱 송신 빔이라 정하고, 제로 포싱 송신 빔은 [조건식 1]와 같은 최적화 조건식를 얻을 수 있다.
Of these zero forcing beams, the beam having the largest data rate between base station i and receiver i

Is defined as a zero forcing transmission beam, and the zero forcing transmission beam can obtain an optimization conditional expression as shown in [Condition 1].

[Conditional expression 1]

Where I _M is a unit matrix of size M × M. When using a zero forcing transmission beam, the total data rate of the system can be expressed as Equation 3 below.

The zero forcing transmission technique can completely eliminate the inter-cell interference, but since the transmission beam is determined while satisfying Equation 2, it is not an optimal method in terms of total data rate.

In a conventional MISO IC study, a transmission beam having the largest data rate when two users is used is a beam that eliminates interference to an unwanted receiver (i.e., a zero forcing beam) and a matching filter that maximizes the data rate of a desired receiver. It is known that it is made by linear combination of matched filter.

In view of this, a linear transmit / receive beam structure that maximizes the total data rate of the MIMO IC at a finite signal-to-noise ratio is not yet known, but it can be expected to have a structure similar to the optimal beam of the MISO interference channel.

Accordingly, the present invention intends to propose a beam design method that extends the results known from the MISO IC to the MIMO system to slightly interfere with the unwanted receiver when designing the transmission beam.

2 is a flow chart illustrating a method of relaxed zero forcing based MIMO beamforming transmission according to an embodiment of the present invention.

As shown in FIG. 2, the MIMO beamforming transmission method S200 includes a design step S210 and a transmission step S220.

The design step S210 is a step of designing a beam to be transmitted to user terminals through a relaxed zero forcing beamforming method.

The transmitting step (S220) is a step of transmitting the designed beam to each terminal.

More specifically, the design step S210 may be a step of setting a maximum allowable amount of interference affecting the user terminals in advance and setting the preset maximum allowable value to be greater than or equal to zero.

The allowance of the interference is set in consideration of the thermal noise level of each of the user terminals, and the thermal noise level is estimated by the base station through the signal-to-noise ratio and the interference-to-noise ratio received through the channel formed between the user terminal and the base station.

The signal-to-noise ratio or the interference-to-noise ratio may be defined as a thermal noise level relative to the square of the channel size.

Hereinafter, to describe the design step S210 in more detail, it will be described through a number of equations and conditional expressions.

The design step (S210) is a step of designing a beam in a range that satisfies Equation 4 described below, but satisfies [condition 2] below.

를 작은 양수로 설정,

=0으로 설정하는 단계(S211),

로 하고

를 [수학식 9]를 사용하여 계산하는 단계(S212), [수학식 7]을 이용하여

을 갱신하는 단계(S213),

일 경우, 초기 단계로 피드백되며, 그렇지 않을 경우 다음 단계로 진행하는 단계(S214) 및 Vi를 기지국 i의 완화 제로 포싱 송신 빔 형성 행렬을 생성하는 단계(S215)를 포함할 수 있다.
In the design step 210, when the base station i is 1 to K, the threshold value is initialized to the zero forcing transmission beam, and then the threshold value.

Set to a small positive number,

Setting to = 0 (S211),

With

Calculating using [Equation 9] (S212), using [Equation 7]

Updating the step (S213),

In one case, the method may include feeding back to the initial stage, otherwise proceeding to the next stage (S214), and generating Vi as a mitigation-forcing transmission beamforming matrix of the base station i (S215).

Hereinafter, the design step will be described in more detail.

For example, a constraint used in each base station i may be expressed as shown in [Equation 4].

This condition will be called a relaxed zero-forcing (RZF) condition. (Or I will call it an RZF constraint.)

일 경우 기존 제로 포싱 송신 빔이 만족시켜야 하는 조건과 같음을 알 수 있다. 특히 RZF 제약 조건에서는 간섭의 허용치

를 0 보다 크거나 같게 정하되 간섭의 허용치를 정할 때 각 수신기에 존재하는 열잡음의 세기를 고려하여 정하도록 한다.If at all receiver j

In this case, it can be seen that the existing zero forcing transmission beam is equal to a condition to be satisfied. Especially allowance of interference in RZF constraints

Is set to be greater than or equal to 0, but considering the strength of thermal noise present in each receiver when determining the tolerance.

Therefore, the beam design conditional equation that maximizes the total data rate under relaxed zero forcing condition can be written as

[Conditional expression 2]

이다. 다른 기지국들로부터 오는 간섭이 0이 아니므로, [조건식 1]에 견주어 간섭에 관련된 항

가 [조건식 2]에 목적 함수에 추가된 것을 알 수 있고, RZF 제약 조건이 (C.1)에 사용되었다. here

to be. Since the interference from other base stations is not zero, the terms related to the interference in comparison to [Condition 1]

Is added to the objective function in [Condition 2], and the RZF constraint is used in (C.1).

배가 되는 안에서 송신 빔을 정할 수 있음을 뜻한다. (C.1) of [Condition 2] shows the RZF constraint of the base station i. The maximum power of the interference that the base station i has on the receiver j is compared with the thermal noise of the receiver j.

It means that the transmission beam can be determined in a double.

배가 됨을 알 수 있다. (C.2)는 각 기지국의 송신 빔 행렬이 가진 파워 제한을 나타낸다.
Base station i designs the transmit beam with RZF constraints on every unwanted receiver, and on the contrary, looking at any receiver j, the maximum amount of interference power that can be received from all unwanted base stations is

It can be seen that the ship is doubled. (C.2) shows the power limitation of the transmission beam matrix of each base station.

Since the objective function of [Condition 2] includes the interference covariance matrix B _i according to the beams of other base stations, it is very difficult to solve the conditional equation for designing a transmission beam that maximizes the total data rate in [Condition 2]. However, using the RZF constraint, the upper bound of the interference power to each receiver can be taken as shown in Equation 5 below.

는 positive semi-definite 행렬이 되는 것을 알 수 있다. 따라서 간섭과 잡음의 총 파워가

가 되고 여기서 다음과 같이 [조건식 2]의 목적 함수의 하계(lower bound)를 [수학식 6]과 같이 얻을 수 있다. (여기서 tr(A)는 어떤 행렬 A의 대각합(trace)이다.)
then

It can be seen that becomes a positive semi-definite matrix. Therefore, the total power of the interference and noise

Here, the lower bound of the objective function of [Condition 2] can be obtained as shown in [Equation 6] as follows. (Where tr (A) is the trace of some matrix A.)

In Equation 6, since the transmission beamforming matrix used by other base stations does not appear, the transmission beams can be designed independently at each base station. Therefore, the transmission beam design conditional expression for maximizing the overall data rate with the RZF constraint in the multi-input multiple output interference channel becomes the same distributed beam design conditional expression.

Therefore, the optimal beam can be obtained by solving the following equation under the RZF constraint in base station i.

[Condition 3]

.here,

.

,

로 나타낼 수 있다. Looking at how to find the optimal V _i in [Condition 3], constraints (C.1) and (C.2) of [Condition 3] are set respectively.

,

.

이고,

이며,

이다.here,

ego,

Is,

to be.

는 크로네커곱(Kronecker product)을 뜻한다.) (vec (·) is an operator that creates a column vector by stacking down from the first column vector to the last column vector in the matrix.

Means Kronecker product.)

에 속해 있어야 한다. 여기서 E_ji와 B_i는 각각 타원체와 구를 의미하므로 블록 집합(convex set)이 되고, 그것의 교집합인 C_i 역시 볼로 집합이 된다. 그리고 최적화 하고자 하는 함수

는 아래로 볼록인 함수(convex function)이므로 [조건식 3]은 볼록 함수를 볼록 집합 내에서의 최적화하는 조건식로, 따라서 convex 최적화 조건식이다.
Therefore, the transmission beam obtained in [Condition 3] is set

Must belong to Here, E _ji and B _i are ellipsoids and spheres, respectively, and thus become a convex set, and its intersection C _i is also a bolo set. And the function you want to optimize

Is a convex function, so [Condition 3] is a conditional expression that optimizes the convex function within a convex set, and thus a convex optimization conditional expression.

The solution of convex optimization conditional equations such as [Condition 3] is well known and one of several known methods can be used to obtain the optimal transmission beam. The transmission beam obtained by solving [Condition 3] will be called a relaxation zero forcing beam.

The Adaptive Projected Subgradient Method (APSM) is widely used as an example of how to solve convex optimization conditional expressions such as [Condition 3]. Using APSM, an iterative algorithm for solving [Condition 3] can be written as Equation 7 below.

인데,

는 입력 값을 볼록 집합 C로 보내는 메트릭 사영(metric projection) 함수이고,

와

는 각각 목적 함수와 그것의

에 대한 기울기(gradient)를 말하며,

은 (0,2) 사이의 양의 실수로 스텝 사이즈를 (step size)를 뜻한다.here,

However,

Is a metric projection function that sends the input value to convex set C,

Wow

Are the objective function and its

Is the gradient of,

Means the step size is a positive real number between (0,2).

By repeating [Equation 7], the fixed point theory proves that we can find a solution that optimizes the objective function within the constraints of [Equation 3].

에 대한 기울기와 각 볼록 집합으로의 메트릭 사영 함수를 구하여야 한다. 본 발명에서 필요로하는 메트릭 사영은 타원체와 구에 대한 메트릭 사영으로, 구 집합으로의 메트릭 사영은 [수학식 8]로 나타낼 수 있다.Therefore, to solve Equation 7

We need to find the slope for and the metric projection function for each convex set. The metric projection required by the present invention may be a metric projection on an ellipsoid and a sphere, and the metric projection on a sphere set may be represented by Equation 8.

에 대한 기울기는 [수학식 9]로 나타낼 수 있다.
Projections to ellipsoids are difficult to obtain in closed form, but algorithms are known to find them numerically. Function of the objective function

The slope with respect to Equation 9 can be expressed.

이다. here,

to be.

By configuring the slope of the objective function with respect to Equation 9 and the function T required by the metric projection function, the algorithm represented by Equation 7 can be implemented. By repeatedly performing the process shown in [Equation 7], the optimal solution of [Condition 3] can be finally obtained. Fig. 2 summarizes the operation process of the algorithm for designing a zero-forcing beam with an adaptive projection quasi-slope method.

각 수신기가 허용할 수 있는 총 간섭의 최대 파워를 결정하는 변수도 같다고 하였을 때,

[수학식 4]에 나타나는 K-1 개의 RZF 제약 조건을 다음 [수학식 10]와 같이 간단히 한 개의 RZF 제약 조건으로 표현할 수 있다.
In particular, all receivers have the same thermal noise,

Assuming that the maximum power of the total interference that each receiver can tolerate is the same,

The K-1 RZF constraints shown in [Equation 4] can be simply expressed as one RZF constraint as shown in [Equation 10] below.

(크기: (K-1)M×N)이다. [수학식 4]와 같이 K-1 개의 RZF 제약 조건을 쓰는 대신 [수학식 10]과 같이 단일한 RZF 제약 조건을 쓸 수 있는 경우 [조건식 3]과 같은 완화된 제로 포싱 빔 설계 조건식를 아래 [조건식 4]와 같이 바꿀 수 있다.
here,

(Size: (K-1) M × N). If a single RZF constraint can be used as shown in [Equation 10] instead of using K-1 RZF constraints as shown in [Equation 4], the relaxed zero forcing beam design conditional expression as shown in [Condition 3] is 4].

[Conditional expression 4]

이다. [조건식 3]에서는 제약 조건이 총 개수가 K임과 달리 [조건식 4]에서는 제약 조건이 2개로 줄어든 것을 알 수 있다. 따라서, 제약조건 (C.3)과 (C.2)을 각각 집합

와

로 나타낼 수 있으며, (여기서

이며

을 뜻한다.) 여기에 상기한 적응적 사영 준기울기 방법을 적용하면, 수학식 11과 같이 간단히 쓸 수 있다.
here,

to be. In condition 3, the total number of constraints is K, whereas in condition 4, the constraints are reduced to two. Therefore, the set of constraints (C.3) and (C.2), respectively

Wow

Can be represented by (where

And

If we apply the adaptive projection quasi-slope method to it, we can simply write

에 대한 기울기(gradient)는 수학식 12와 같이 나타낼 수 있다.
Where the objective function

The gradient with respect to can be expressed as shown in Equation 12.

이다. 결과적으로 [수학식 7]에서는 K-1 개의 타원 볼록 집합으로 메트릭 사영을 했어야 하나, [수학식 11]에서는 1개의 타원

로의 메트릭 사영만으로 충분하여 알고리즘의 실행 복잡도에서 많은 이득을 얻을 수 있다.
In [Equation 12]

to be. As a result, in Equation 7, we should have projected the metric with a set of K-1 ellipsoid convex, but in Equation 11 1 ellipse

The metric projection of the raw suffice is sufficient, which can benefit a lot from the execution complexity of the algorithm.

4 and 5 are graphs of the total data rates obtained when a relaxation forcing beam is obtained through Equation 11 in the same condition as in [Condition 4].

을 갖는다고 두었고 각각 (N,K,M)=(6,3,2)와 (N,K,M)=(10,5,2)인 상황에서, 도 4는

을 각각 1, 0.1, 0.01로 두었을 때 완화 제로 포싱 송신 빔의 성능과 제로 포싱 송신 빔의 성능을 비교한 그래프이고, 도 5는

을 각각 6,1,0.1로 두었을 때 완화 제로 포싱 송신 빔의 성능과 제로 포싱 송신 빔의 성능을 나타낸 그래프이다.
4 and 5, each terminal is the same

4 and (N, K, M) = (6, 3, 2) and (N, K, M) = (10, 5, 2), respectively, FIG.

Is a graph comparing the performance of the relaxed forcing transmission beam and the performance of the zero forcing transmission beam when 1 is set to 1, 0.1, and 0.01, respectively.

Is a graph showing the performance of the mitigating zero-forcing transmission beam and the performance of the zero-forcing transmission beam when P is set to 6, 1, and 0.1, respectively.

FIG. 6 is an exemplary diagram illustrating a cooperative MIMO multi-cell network capable of cooperative transmission according to another embodiment of the present invention, and FIG. 7 is a multi-input multiple output multiple output shown in FIG. A block diagram illustrating a relaxed zero forcing beamforming transmission method using a cellular network.

6 and 7, in the MIMO beamforming transmission method based on the relaxed zero forcing according to another embodiment of the present invention, two or more base stations cooperate with a message to be transmitted to two or more user terminals by a central management base station. The step S110 of designing a beam to be transmitted to the two or more user terminals through the sharing step S110 and the relaxed zero forcing beamforming method is included.

Specifically, assume B base stations with N transmit antennas and K receivers with M receive antennas, and all base stations 120 and 130 are coordinated by central management base station 110 (hereinafter referred to as base station base station). Assume a situation in which information is cooperatively transmitted to receivers in all user terminals 140, 150, and 160.

The situation in which coordination and coordination by the base station 110 is performed by B base stations sharing (i.e., all known) different messages that should be delivered to the receivers of the respective user terminals 140, 150, and 160. This is a situation in which all base stations transmit a message by cooperatively processing a transmission signal.

Since each base station knows all the information to be sent to each receiver, as shown in FIG. 6, each base station can broadcast a desired message to all receivers simultaneously.

S120 may be a step of designing a relaxed zero forcing beam through the equations and conditional expressions described below.

If it is assumed that N≥MK, the received signal of the receiver i may be represented by Equation 13 below.

는 크기가 M×N 이며 기지국 j에서 수신기 i로의 채널을 나타내고,

기지국 j에서 수신기 i로 정보를 전송할 때 사용하는 크기가 N×d인 송신 빔 행렬을 나타낸다. 송신 빔의 파워

의 제약을 갖는다. here,

Denotes a channel M from base station j to receiver i,

A transmission beam matrix having a size of N × d is used when transmitting information from the base station j to the receiver i. Power of transmission beam

Has a constraint.

In Equation 13, the first term on the right side represents a desired signal at receiver i, and the second and third terms represent interference and thermal noise, respectively. As described above, the relaxed zero forcing condition is represented by Equation 14 in this example.

Equation (14) is a relaxed zero forcing condition in which, when transmitting a message for the receiver i from the base station m, the strength of the interference of the signal on the receiver j is based on the thermal noise of the terminal j.

Based on Equation 14, a method of designing a transmission beam vector design can be finally generated by using a method similar to the above example.

[Conditional expression 5]

Each base station j = 1,2,... , For B,

이다. 즉, 임의의 기지국 j에서 수신기 i를 위한 송신 빔 행렬

는 [조건식 5]를 풀어서 얻을 수 있게 되는데 [조건식 5]는 [조건식 3] 또는 [조건식 4]와 같이 적응적 사영 준기울기 방법을 이용해 해를 구한 것과 같은 일련의 과정을 거쳐 송신 빔 행렬을 얻을 수 있다.
here

to be. That is, the transmit beam matrix for receiver i at any base station j

Can be obtained by solving [Condition 5]. [Condition 5] can be obtained through the same process as the solution using the adaptive projection quasi-slope method such as [Condition 3] or [Condition 4]. Can be.

8 and 9 are exemplary diagrams showing the total data rate that can be obtained through a relaxed zero forcing transmission beam and the total data rate that can be obtained when using a zero forcing transmission beam in a cooperative multi-input multi-output multi-cellular network.

라고 두고

라고 하였으며,

라고 가정한다.At this time,

Leave

Said,

.

8 shows a case where K = 6, N = 6, M = 1, and B = 2, and FIG. 9 shows a case where K = 8 and N = 8, M = 1, and B = 2. Referring to FIGS. 8 and 9, it can be seen that the beams based on the relaxed zero forcing have much better performance than the conventional zero forcing techniques in the situations where the signal-to-noise ratios are -10 dB to 10 dB and -10 dB to 15 dB, respectively.

In particular, it can be seen that the performance increase is large when the signal to noise ratio is low.

In other words, the relaxed zero forcing-based MIMO beamforming transmission method according to the present invention provides the maximum amount of interference that each terminal can have. The transmission beamforming method maximizes the data rate.

In addition, the RZF transmission beamforming method is a transmission beamforming method in which each base station needs only a channel from itself to each terminal and does not need to know a channel between other base stations and terminals.

According to the cooperative multi-cell MIMO beamforming method based on the relaxed zero forcing of the present invention, the receiver does not need to know both the channel and the transmission beam information, and has the effect of guaranteeing the freedom when designing the transmission beam.

In addition, according to the cooperative multi-cell MIMO beamforming method based on the relaxed zero forcing of the present invention, the performance of the total data rate is improved by increasing the degree of freedom of the beam, which is a disadvantage of the zero forcing.

In addition, through this scheme, we propose a new cooperative beam system that cooperates while controlling the amount of interference on an undesired terminal, and allows each base station to adjust the amount of interference caused to a terminal that does not want to transmit information, while simultaneously controlling the data rate of the desired terminal. Has the effect of optimizing

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is to be understood that various changes and modifications may be made without departing from the scope of the appended claims.

110: central management base station
120, 130, 210, 220, 230: base station
140, 150, 160, 240, 250, 260: user terminal

Claims (10)

Designing a beam to be transmitted to user terminals through a relaxed zero forcing beamforming method; And
Transmitting the designed beam comprising: a relaxed zero forcing based MIMO beamforming transmission method.
The method of claim 1,
Wherein the designing comprises:
And presetting a maximum allowable amount of interference affecting the user terminals, and setting the preset maximum allowable value to be greater than or equal to zero.
The method of claim 2,
The allowance of the interference,
The zero-forcing-based MIMO beamforming transmission method of claim 1, wherein the user terminal is configured in consideration of the thermal noise level of each of the user terminals.
The method of claim 3,
The thermal noise level is,
And estimating at the base station based on the signal-to-noise ratio and the interference-to-noise ratio received through the channel formed between the user terminal and the base station.
5. The method of claim 4,
The signal to noise ratio or the interference to noise ratio,
And a thermal noise level relative to the square of the channel size.
The method of claim 5,
Wherein the designing comprises:
Equation 4 described below, the step of designing a beam that satisfies the relaxed zero forcing conditions below, characterized in that the relaxed zero forcing based MIMO beamforming transmission method.
&Quot; (4) "

Where H _ji denotes a matrix of size M × N between the j th transmitter and the i th receiver, and V _i denotes a beam forming matrix of size N × d,

Represents the tolerance of the interference.
[Conditional expression]

here,

Is,
(C.1) and (C.2) are sets

, Wow

. here,

ego,

Is,

to be.
(vec (·) is an operator that creates a column vector by stacking down from the first column vector to the last column vector in the matrix.

Means Kronecker product.)
The method according to claim 6,
remind

Quot;
A relaxed zero forcing based MIMO beamforming transmission method, which is calculated using Equation 7 described below.
&Quot; (7) "

here,

However,

Is a metric projection function that sends the input value to convex set C,

Wow

Are the objective function and its

Indicates the gradient to,

Denotes a step size with a positive real number between (0, 2).
The method of claim 2,
Wherein the designing comprises:
Cooperatively sharing a message to be transmitted to two or more user terminals by the central management base station by the two or more base stations; and
And designing a beam to be transmitted to the two or more user terminals through a relaxed zero-forcing beamforming method.
9. The method of claim 8,
Wherein the designing comprises:
The at least two users through a relaxed zero-forcing beamforming method which presets a maximum allowable amount of interference affecting the at least two user terminals and sets the preset maximum allowable as a relaxed zero forcing condition And designing a beam to be transmitted to the terminals.
10. The method of claim 9,
The relaxed zero forcing condition is
The following equation

(here,

Is the size

Denotes a channel from base station j to receiver i,

Is the size used when transmitting information from base station j to receiver i

Indicate the transmit beam matrix.

Is the maximum strength of interference that this signal can tolerate for receiver j when transmitting a message for receiver i at base station m).

Images