KR101683389B1 - Method and System for Beam Forming in Femto Base Station for Improving Frequency Efficiency - Google Patents

Abstract

Disclosed are a method and a system for beam forming in a femto base station for improving frequency efficiency. The disclosed system include a signal detecting unit that detects a signal from a macro base station user in a first section that a section of a signal transmission section of a user of the macro base station and performs a soft detection for the signal; a signal processing unit that generates a beam forming vector based on the soft detection by the signal detecting unit; and a signal transmitting/receiving antenna unit that transmits a signal by applying the generated beam forming vector, and the signal transmitting/receiving antenna unit applies the beam forming vector to a second section, of the signal transmission section of the user of the macro base station, except for the second section. According to the disclosed method and system, interference may be minimized and frequency efficiency may be improved by applying a recognition wireless communication technology in a network in which a macro base station and a femto base station coexist.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beamforming method and apparatus for a femto base station for improving frequency efficiency,

Embodiments of the present invention relate to a method and apparatus for forging in a base station, and more particularly, to a method and apparatus for beam fobbling a femto base station in a network in which a macro base station and a femto base station coexist.

As smart phones become more popular, there is a problem of traffic overload due to the surge of data demand in the base station. As a result, small cell base stations start to be installed in a conventional cellular network centering on a macro cell base station, resulting in a heterogeneous cellular network.

The macro cell base station and the small cell base station are mixed in the heterogeneous cellular network, while the macro cell base station transmits with a relatively large transmission power, while the small cell base station transmits with a relatively small transmission power.

The addition of the femto base station can reduce the average distance between the user and the base station, thereby greatly increasing the frequency efficiency of the system. Generally, unlike a macro base station, a femto base station can be arbitrarily installed by a user and has a small installation cost. However, since the femto base station and the macro base station are difficult to adjust the interference to reduce the interference between them, the femto base station has a disadvantage in that the random installation position can cause great interference to the macro base station.

Meanwhile, the beam-forming technique is a technique for greatly increasing a signal experienced by a receiving end using a plurality of antennas at a transmitting end of a signal. In particular, when the beamforming is used in the femto base station, not only the size of the signal experienced by the femto user but also the amount of interference to the macro base station can be greatly reduced. Therefore, there is a need for a technique for optimizing the frequency efficiency of the system while restricting the interference that the femto base station gives to the macro base station through beamforming in a situation where the macro base station and the femto base station coexist.

One aspect of the present invention provides a method and apparatus for improving frequency efficiency of a femto base station in a network in which a macro base station and a femto base station coexist.

Another aspect of the present invention provides a method and apparatus for improving frequency efficiency while minimizing interference by applying a technique of cognitive radio communication in a network in which a macro base station and a femto base station coexist.

According to an aspect of the present invention, there is provided a macro base station including: a signal sensing unit for sensing a signal from a user of the macro base station in a first section, which is a section of a signal transmission interval of a macro base station user; A signal processing unit for generating a beamforming vector based on a soft decision result in the signal sensing unit; And a transmission / reception antenna unit for transmitting a signal by applying the generated beamforming vector, wherein the transmission / reception antenna unit is configured to transmit a signal having a beamforming vector applied to a second section of the signal transmission interval of the macro base station user except for the first section, A beamforming apparatus of a femto base station for improving the frequency efficiency of transmitting a beam.

The beamforming vector based on the softband is set by a linear combination of the channel h between the femto users in the direction perpendicular to the g and g interference channels of the macro base station.

The beamforming vector has the form of the following equation.

로 정의되며, a(v)와 b(v)는

와

에 할당할 최적의 송신 전력 파워이다. In the above equation, v is a soft decision value,

, And a (v) and b (v) are defined as

Wow

Is the optimum transmission power to be allocated to the base station.

The a (v) and b (v) are determined such that the average of the maximum transmission rate to the femto user is maximized while the transmission power is smaller than a predetermined threshold and the interference to the macro base station is smaller than the predetermined threshold interference.

The a (v) and b (v) are determined by an iterative operation.

According to another aspect of the present invention, there is provided a macro base station including: a signal sensing unit for sensing a signal from a user of the macro base station in a first section, which is a section of a signal transmission interval of a macro base station user; A signal processing unit for generating a beamforming vector based on a soft decision result in the signal sensing unit; And a transmission / reception antenna unit for transmitting a signal by applying the generated beamforming vector, wherein the beamforming vector based on the softband definition is a channel between the femto users in a direction perpendicular to g and g, there is provided a beamforming apparatus of a femto base station for improving the frequency efficiency set by a linear combination of h and fading directions.

According to another aspect of the present invention, there is provided a method for controlling a macro base station, the method comprising the steps of: (a) detecting a signal from a user of the macro base station during a first section of a signal transmission interval of a macro base station user; (B) generating a beamforming vector based on the soft decision result in the step (a); And a step (c) of transmitting a signal by applying the generated beamforming vector, wherein the step (c) includes the step of, during a signal transmission period of the macro base station user, There is provided a beamforming method of a femto base station for improving frequency efficiency of transmitting a vector-applied signal.

According to another aspect of the present invention, there is provided a method for controlling a macro base station, the method comprising the steps of: (a) detecting a signal from a user of the macro base station during a first section of a signal transmission interval of a macro base station user; (B) generating a beamforming vector based on the soft decision result of step (a); And a step (c) of transmitting a signal by applying the generated beamforming vector, wherein the beamforming vector based on the softband definition is used as an interference channel between the femto users A beamforming method of the femto base station is provided for improving the frequency efficiency set by the linear combination of the channel h of the femto base station and the direction of the fading.

According to embodiments of the present invention, there is an advantage that frequency efficiency can be improved while minimizing interference by applying a technique of cognitive radio communication in a network in which a macro base station and a femto base station coexist.

1 illustrates a structure of a mobile communication network to which the present invention is applied.
2 illustrates a frame structure of a macro base station and a femto base station according to an exemplary embodiment of the present invention.
3 is a block diagram illustrating a structure of a femto base station according to an embodiment of the present invention;
4 is a flowchart of a method for determining a beamforming vector in accordance with an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a structure of a mobile communication network to which the present invention is applied.

Referring to FIG. 1, a mobile communication network to which the present invention is applied includes a macro base station 220, a macro user 210, a femto base station 230, and a femto user 240.

The macro base station 220 is a base station with relatively wide coverage and communicates with the macro users 210 within the coverage. The femto base station 230 communicates with the femto users 240 within coverage with less coverage than the macro base station 220. 1, a macro user 210, a femto base station 230, and a femto user 240 are illustrated for convenience of description, but a plurality of users 210 and 240 and a femto base station 230 may exist in an actual network will be.

1, a macro BS 220 and a plurality of femto BS 230 coexist in a mobile communication network to which the present invention is applied, and interference between the macro BS 220 and the femto BS 230 is necessarily interfered And the present invention relates to a method and an apparatus for appropriately determining transmission power and beamforming in a femto base station to maximize the frequency efficiency while minimizing the interference thereof.

Before examining the configuration of the femto base station, the frame structure of the macro base station and the femto base station will be described. 2 is a diagram for explaining a frame structure of a macro base station and a femto base station according to an embodiment of the present invention.

 Referring to FIG. 2, the macro user 210 transmits data to be transmitted to the macro base station 220 during a signal transmission period having a period of T (T). When there is data to be transmitted to the macro base station 220, the data transmission of the macro user 210 is activated during the transmission period of T. [ However, if there is no data to send to the user, data transmission is disabled during the transmission interval of T.

의 구간 동안을 신호 감지 구간으로 이용하고

의 구간을 신호 전송 구간으로 이용한다.

의 구간 동안 펨토 기지국(230)은 매크로 사용자(210)가 데이터를 전송하는지 여부를 감지한다. 또한, 펨토 기지국(230)은

의 구간에는 펨토 사용자에게 데이터를 전송한다. In contrast, the femto base station 230

Is used as a signal detection interval

Is used as a signal transmission section.

The femto base station 230 detects whether the macro user 210 transmits data. In addition, the femto base station 230

Lt; RTI ID = 0.0 > femto < / RTI >

The femto base station 230 determines whether to transmit data to the femto user 240 during a signal detection period and to what transmission power and beamforming vector data to transmit when transmitting data.

In the embodiment of the present invention, the femto base station 230 operates similar to the cognitive radio communication in which the femto base station 230 detects whether a macro user uses a channel.

Specifically, when the macro user 210 transmits data, the femto base station 230 determines the state of the macro user based on the received signal, based on a soft decision (Sofe Decision). That is, the femto base station 230 divides a signal level received by the femto base station 230 into a plurality of signal levels to determine the state of the macro user.

The femto base station 230 determines the transmission power and beamforming vector of the signal to be transmitted to the femto user based on the soft decision state.

3 is a block diagram illustrating a structure of a femto base station according to an embodiment of the present invention.

3, a femto base station according to an exemplary embodiment of the present invention may include a transmission / reception antenna unit 250, a transmission / reception changeover switch 260, a signal detection unit 270, and a signal processing unit 280.

The transmission / reception antenna unit 250 may include a plurality of antennas and performs signal transmission / reception. In the transmission mode, the transmission / reception antenna unit 250 transmits a signal to femto users, and in the reception mode, the transmission / reception antenna unit 250 receives signals transmitted by femto users or other base stations and users.

The transmission / reception changeover switch 260 functions to control the switching of the transmission mode or the reception mode.

The signal detection unit 270 analyzes the received signal and estimates the state of the macro user.

번의 빈도로 표본 추출한다. 본 명세서에서, i번째로 표본 추출된 신호를

로 정의한다. Specifically, the signal sensing unit 270 receives the reception signal through the transmission / reception antenna unit 260 every second

Sampling frequency. In the present specification, the i-th sampled signal

.

는 다음의 수학식 1과 같이 정의될 수 있다. As the signal transmission of the macro user 210 is activated or deactivated,

Can be defined as the following equation (1).

는 i번째 표본에 대한 잡음 벡터를 의미하고, C는 매크로 사용자(210)와 펨토 기지국(230) 사이의 채널을 의미하며, q는 매크로 사용자가 사용하는 빔 포밍 벡터를 의미하고,

는 매크로 사용자가 송신하고자 하는 심볼의 i번째 표본을 의미한다. In Equation (1) above,

C denotes a channel between the macro user 210 and the femto base station 230, q denotes a beamforming vector used by a macro user,

Denotes an i-th sample of a symbol to be transmitted by a macro user.

When the macro user is inactivated, the sample detection signal detected by the signal detection unit 270 includes only the noise signal. However, when the macro user is activated, the sample detection signal includes both the signal transmitted by the macro user and the noise together.

인 AWGN(Additive White Gaussian Noise)일 수 있으며,

는 평균값이 0이고 파워가

일 수 있다. For example, the noise vector has a mean value of zero and power

Lt; / RTI > may be AWGN (additive white Gaussian noise)

The average value is 0 and the power is

Lt; / RTI >

개의 표본 벡터들은 송수신 전환 스위치(260)를 통해 신호 감지부(270)로 전달되고, 신호 감지부(270)는 매크로 사용자의 신호 상태에 대해 연판정 v를 구한다. The transmission / reception antenna unit 250 receives

The sample vectors are transmitted to the signal sensing unit 270 through the transmission / reception changeover switch 260, and the signal sensing unit 270 obtains a soft decision v for the signal state of the macro user.

For example, the soft decision performed by the signal sensing unit may be expressed as Equation 2 below.

The soft decision value v obtained by the signal sensing unit is transmitted to the signal processing unit 280. [ The signal processing unit 280 determines the beamforming vector p (v) to be used by the femto base station 230 in the signal transmission period using the soft decision value v.

를 곱하여 송신 신호

를 생성한다. In addition, the signal processing unit 280 may determine the beamforming vector p (v) to be transmitted to the femto base station 230,

≪ / RTI >

.

는 송수신 안테나부(250)를 통해 펨토 사용자(240)에게 송신된다. 펨토 사용자(240)가 수신하는 신호는 매크로 사용자(210)의 신호 전송이 활성화 되어있을 경우와 비활성화 되어있을 경우에 따라 각각 상이하다. The transmission signal generated in the signal processing unit 280

Is transmitted to the femto user (240) through the transmission / reception antenna unit (250). The signals received by the femto user 240 are different depending on whether the signal transmission of the macro user 210 is active or inactive.

The received signal r received by the femto user 240 can be expressed by the following equation (3).

은 매크로 사용자(210)와 펨토 사용자(240) 사이의 채널을 의미하며, h는 펨토 사용자(240)와 펨토 기지국(230) 사이의 채널을 의미하고,

은 매크로 사용자(210)가 매크로 기지국(220)에 전송하는 심볼을 의미한다. In Equation (3), w denotes noise in the femto user,

Denotes a channel between the macro user 210 and the femto user 240, h denotes a channel between the femto user 240 and the femto base station 230,

Means a symbol transmitted from the macro user 210 to the macro base station 220. [

인 AWGN일 수 있으며,

은 평균값이 0이고 파워가

일 수 있다. The noise w has a mean value of 0 and power

Can be an AWGN,

The average value is 0 and the power is

Lt; / RTI >

When the transmission of the macro user is deactivated, the femto user receives only the signal from the femto base station, but when the transmission of the macro user is activated, the macro user and the femto base station receive the signal together.

The maximum transmission rate that the femto user 240 can transmit can be expressed by Equation (4). The maximum transmission rate that the femto user 240 can send is different from that when the signal transmission of the macro user 210 is activated and deactivated.

The average of the maximum data rates that the femto user 240 can send from Equation (4) is given by Equation (5)

는 전체 프레임 길이 T 중에서 펨토셀의 신호 전송 구간(130)이 차지하는 비율을 의미하고,

는 매크로 사용자의 신호 전송이 비활성화되었을 경우 v의 확률 밀도 함수이며,

는 매크로 사용자의 신호 전송이 비활성화되었을 경우 v의 확률 밀도 함수를 의미한다. here,

Denotes a ratio of the signal transmission interval 130 of the femtocell to the total frame length T,

Is a probability density function of v when the macro user's signal transmission is inactive,

Means a probability density function of v when signal transmission of a macro user is inactivated.

Meanwhile, during the signal transmission period of the femto base station 230, the average transmission power transmitted by the femto base station 230 and the average interference caused by the femto base station 230 to the macro base station 220 are expressed by Equation (6) Can be expressed as in Equation 7.

In Equation (7), g denotes a channel between the femto base station 230 and the macro base station 220.

보다 작아지도록 빔 포밍 벡터를 결정한다. 또한, 수학식 7에 표현된 펨토 기지국(230)이 매크로 기지국(220)에게 미치는 평균 간섭이 미리 설정된 임게 간섭치인

보다 작아지도록 신호 처리부(280)는 빔 포밍 벡터 p(v)를 결정한다. 또한, 빔 포밍 벡터는 수학식 5의 펨토 사용자의 최대 전송률의 평균이 최대화되도록 결정될 수 있다. When the signal processing unit 280 determines the beamforming vector p (v), the average transmission power of Equation (6) is a predetermined threshold transmission power

The beamforming vector is determined to be smaller. Also, if the mean interference of the femto base station 230 expressed in Equation (7) to the macro base station 220 is a predetermined interference

The signal processing unit 280 determines the beam forming vector p (v). Also, the beamforming vector may be determined such that the average of the maximum transmission rate of the femto user of Equation (5) is maximized.

It is preferable to set the beamforming vector p (v) to a linear combination in the direction closest to the channel h between the femto base station 230 and the femto user 240 among the directions perpendicular to the g and g interference channels to the macro base station Do. At this time, the beamforming vector p (v) can be expressed by the following equation (8).

로 정의된다. 본 발명의 바람직한 실시예에 따르면, 빔 포밍 벡터를 결정하는 과정은 벡터

와

에 할당할 최적의 송신 전력 파워인 a(v)와 b(v)를 얻는 과정으로 정의할 수 있다. In Equation (8) above,

. According to a preferred embodiment of the present invention, the process of determining the beamforming vector comprises the steps of:

Wow

(V) and b (v), which are optimal transmission power powers to be allocated to the transmission power of the mobile station.

Hereinafter, a process of determining the beamforming vector in the signal processor 280 will be described in detail.

4 is a flowchart of a method for determining a beamforming vector according to an embodiment of the present invention.

및

를 모두

로 설정한다(단계 400). 위 첨자는 루프 반복수를 의미한다. l번째 루프에서의

,

,

,

를 구한다(단계 402). Referring to FIG. 4, the variables used for the a (v) and b (v) operations and corresponding to the Lagrangian multipliers

And

All

(Step 400). Superscripts indicate the number of loop iterations. In the lth loop

,

,

,

(Step 402).

는 max(0,x)를 의미하고, 수학식 9와 10에서 사용된 변수들은 다음의 수학식 11을 통해 계산한다. In the above equations (9) and (10)

Means max (0, x), and the variables used in Equations (9) and (10) are calculated by the following Equation (11).

,

와

,

및 다음의 수학식 12를 이용하여

과

를 계산한다(단계 404). Calculated from Equations (9) and (10)

,

Wow

,

And using the following equation (12)

and

(Step 404).

와

를 계산한다(단계 406). Using Equations (9), (10), (12) and (13)

Wow

(Step 406).

는

를 의미하고, 1 또는 2의 값을 가진다.

는

를 의미한다.here,

The

And has a value of 1 or 2.

The

.

을 계산하기 위한 방향 벡터를 계산한다(단계 408). (L + 1) < th > loop using the following equation (14)

(Step 408). ≪ / RTI >

를 갱신한다(단계 410). Using the direction vector obtained from the above equation (14) and the following equation (15)

(Step 410).

은 l번째 루프에서의 스텝 사이즈로

을 이용한다. 위의 과정을

가 정해진 임계치보다 작아질 때까지 반복한다(단계 412). 일례로, 임계치는 10^-8일 수 있다. here,

Is the step size in the lth loop

. The above process

Lt; / RTI > is smaller than a predetermined threshold (step 412). For example, the threshold may be 10 ^-8 .

라 할 경우 최적의 a(v) 및 b(v)는 다음의 수학식 16을 통해 계산된다(단계 414). The number of loops when the loop is finished

The optimal a (v) and b (v) are calculated through the following equation (16) (step 414).

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (12)

A signal sensing unit for sensing a signal from the macro base station user during a first section of the signal transmission interval of the macro base station user and performing a soft decision on the signal;
A signal processing unit for generating a beamforming vector based on a soft decision result in the signal sensing unit; And
And a transmitting / receiving antenna unit for transmitting a signal by applying the generated beamforming vector,
Wherein the transmission / reception antenna unit transmits a signal to which the beamforming vector is applied in a second interval excluding the first interval in a signal transmission interval of the macro base station user,
Wherein the soft-decision-based beamforming vector is set by a linear combination of a direction perpendicular to the interference channels g and g to the macro base station and a direction closest to the channel h between the femto users. The femto base station comprising:
delete The method according to claim 1,
Wherein the beamforming vector has the form of the following equation: < EMI ID = 1.0 >

In the above equation, v is a soft decision value,

, And a (v) and b (v) are defined as

Wow

Is the optimal transmission power to be allocated to the base station. The method of claim 3,
The a (v) and b (v) are determined so as to maximize an average of a maximum transmission rate to the femto user while a transmission power is smaller than a predetermined threshold and an interference to the macro base station is smaller than a preset threshold interference Wherein the femto base station includes a beamforming unit for modulating a frequency of the femto base station. 5. The method of claim 4,
Wherein the a (v) and the b (v) are determined by an iterative operation. A signal sensing unit for sensing a signal from the macro base station user during a first section of the signal transmission interval of the macro base station user and performing a soft decision on the signal;
A signal processing unit for generating a beamforming vector based on a soft decision result in the signal sensing unit; And
And a transmitting / receiving antenna unit for transmitting a signal by applying the generated beamforming vector,
Wherein the soft-decision-based beamforming vector is set by a linear combination of a direction perpendicular to the interference channels g and g to the macro base station and a direction closest to the channel h between the femto users. The femto base station comprising: (A) detecting a signal from the macro base station user in a first section, which is a section of a signal transmission interval of a macro base station user, and performing a soft decision on the signal;
(B) generating a beamforming vector based on the soft decision result in the step (a); And
And (c) transmitting a signal by applying the generated beamforming vector,
Wherein the step (c) transmits a signal to which the beamforming vector is applied in a second period excluding the first period of the signal transmission period of the macro base station user,
Wherein the soft-decision-based beamforming vector is set by a linear combination of a direction perpendicular to the interference channels g and g to the macro base station and a direction closest to the channel h between the femto users. Wherein the femto base station includes a femto base station.
delete 8. The method of claim 7,
Wherein the beamforming vector has the form of the following equation: < EMI ID = 17.0 >

In the above equation, v is a soft decision value,

, And a (v) and b (v) are defined as

Wow

Is the optimal transmission power to be allocated to Eq. 10. The method of claim 9,
The a (v) and b (v) are determined so as to maximize an average of a maximum transmission rate to the femto user while a transmission power is smaller than a predetermined threshold and an interference to the macro base station is smaller than a preset threshold interference A method of beamforming a femto base station to improve frequency efficiency. 10. The method of claim 9,
Wherein the a (v) and the b (v) are determined by an iterative operation. (A) detecting a signal from the macro base station user in a first section, which is a section of a signal transmission interval of a macro base station user, and performing a soft decision on the signal;
(B) generating a beamforming vector based on the soft decision result of step (a); And
And (c) transmitting a signal by applying the generated beamforming vector,
Wherein the soft-decision-based beamforming vector is set by a linear combination of a direction perpendicular to the interference channels g and g to the macro base station and a direction closest to the channel h between the femto users. Wherein the femto base station includes a femto base station.

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