KR101546380B1 - A Method for power allocation Base Stations which transmits signals with cooperative in a wireless communication system and a system thereof - Google Patents

Abstract

The present invention relates to a power allocation scheme of a wireless communication network for transmitting signals according to a cooperative transmission scheme, and a system therefor. The present invention relates to a power allocation scheme for a wireless communication network in which a first base station and a second base station Wherein the first and second base stations transmit a power when a sum of symbol error rates of signals transmitted to the first and second base stations becomes minimum, 1 and a transmission power of a second base station according to a cooperative transmission scheme. The present invention provides a power allocation method and a system therefor of a wireless communication network for transmitting signals according to a cooperative transmission scheme.

SER, SNR

Description

TECHNICAL FIELD [0001] The present invention relates to a power allocation scheme for a wireless communication network for transmitting signals according to a cooperative transmission scheme, and a system for the same.

The present invention relates to a method of allocating power to a base station and a system therefor, and more particularly, to a method of allocating power to a base station performing communication according to a cooperative transmission technique and a system therefor.

In an MIMO (Multiple Input Multiple Output) wireless communication system, efforts have been made to reduce inter-cell interference, but techniques for more aggressively reducing interference through cooperation among base stations have been studied.

MIMO technology has been developed by inheriting SISO (Single Input Single Output) technology and method. Recently, new communication technologies are being extended based on MIMO as shown in the figure. Expansion techniques include smart antenna technology that extends MIMO, communication technology based on the use of MIMO, and extended application of MIMO concept to expand capacity using multiple devices.

MIMO-OFDM-based mobile communication standards such as 3GPP LTE (Release 8) and WiMAX Evolution (SDD step progress) standardize the use of MIMO including SU-MIMO and MU-MIMO. Here, SU-MIMO allocates all the antenna resources of a base station to one user, and MU-MIMO allocates antenna resources or wireless spatial resources to a plurality of users. MU-MIMO is compatible with SU-MIMO and includes PU2RC method which requires minimum feedback resources. Although various other schemes have been proposed in 3GPP LTE Release 8, it is possible to use PU2RC because it can reduce terminal complexity and improve performance without requiring much signaling. In the future, the MU-MIMO scheme is predicted to be a driving force for the next generation mobile communication capacity surpassing the MIMO-OFDM scheme in combination with the advanced spatial signal processing techniques.

The present invention relates to a wireless communication network for efficiently operating interference reduction through cooperation between such base stations. In general, power allocation in a downlink cellular environment has been performed in such a manner as to maximize the processing capacity (Achievable throughput (capacity), or to minimize the bit error rate (BER) . This method does not consider the symbol error rate (SER) of each terminal, and a power allocation method for reducing the symbol error rate of each terminal is required.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a power allocation scheme of a wireless communication network for transmitting a signal according to a cooperative transmission scheme capable of reducing a symbol error rate .

According to another aspect of the present invention, there is provided a method of allocating power in a wireless communication network for transmitting signals according to a cooperative transmission scheme, the method comprising: A power allocation method of a wireless communication network for transmitting a signal in accordance with a transmission scheme includes the steps of calculating a power when a sum of symbol error rates of signals transmitted to the first and second base stations by the first and second base stations becomes minimum To the first and second base stations.

The allocation process is characterized in that the sum of transmission powers of the allocated first and second base stations is constant.

Wherein the allocating step allocates the power when the minimum reception SNR of a signal transmitted from the first and second base stations to the first and second base stations is maximized as the transmission power of the first and second base stations .

According to an aspect of the present invention, there is provided a system for allocating power in a wireless communication network for transmitting a signal according to a cooperative transmission scheme, the system including a first and a second base station, The system of claim 1, wherein the first and second terminals are connected to a first terminal and a second terminal, respectively, for power allocation in a wireless communication network for transmitting signals according to a cooperative transmission scheme, And a first base station and a second base station for allocating transmission power of the first base station and transmission power of the second base station.

And the one base station allocates power so that the sum of the transmission power of the first and second base stations is constant.

Wherein one of the first and second base stations allocates the power when the minimum reception SNR of a signal transmitted from the first and second base stations to each of the first and second terminals is maximized as the transmission power of the first and second base stations .

As described above, according to the present invention, two base stations transmitting a signal to the cooperative transmission scheme among the downlink transmission schemes apply an Alamouti Space Time Block Code, The performance of the wireless communication system can be improved by obtaining a diversity gain without interfering with each other and by allocating power that minimizes the sum of symbol error rates (SER) between the terminals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same configurations of the drawings denote the same reference numerals as far as possible.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, I will do it. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

First, a configuration of a wireless communication network according to an embodiment of the present invention will be described. 1 is a diagram illustrating a structure of a wireless communication network for cooperative base station transmission according to an embodiment of the present invention.

First and second base stations _{(BS 0, BS 1) (} 101, 102) and first and second terminal _{(MS 0, MS 1) (} 201, 202) in Figure 1 is shown. Here, the first and second base stations 101 and 102 transmit signals to the respective mobile stations 201 and 202 according to the cooperative transmission scheme to the cooperative base stations.

The first and second base stations (BS ₀ , BS ₁ ) 101 and 102 each have one antenna and are located adjacent to each other. The first and second MSs (MS ₀ and MS ₁ ) 201 and 202 are connected to the first and second base stations 101 and 102, respectively, Is located at the edge of the cell (Cell Edge).

In addition, the transmission symbol S ₀ is for the first terminal 201 located in the service area of the first base station (BS ₀ ) 101 and the symbol S ₁ is for the service area of the second base station (BS ₁ ) (MS ₁ ) 202 located in the second terminal (MS ₁ ) 202.

Meanwhile, Alamouti code is used as a cooperation method between the base stations for minimizing the interference between the two base stations S ₀ and S ₁ , and the information between the two symbols is shared through the backhaul between the base stations .

Here, when a symbol is transmitted to the first MS 201 according to the cooperative transmission scheme in consideration of the power allocation values of the first and second BSs 101 and 102, the downlink transmission is expressed as Equation (1) .

: 제1 기지국

: First base station

: 제2 기지국

: Second base station

In Equation (1), s ₀ and s ₁ are transmission symbols of the first and second base stations 101 and 102, respectively, and P ₀ and P ₁ are power of the first and second base stations 101 and 102, respectively Quotient.

Here, according to the embodiment of the present invention, the sum of the power allocation values of the two base stations is constant. This can be expressed as Equation (2) below.

for i=0,1 : sum power constraints

for i = 0,1: sum power constraints

As shown in Equation (2), since the sum of the power allocation values of the two base stations is the same, the power allocated to each of the base stations 101 and 102 is always adjusted at a constant power. Where P _T is the maximum power that can be allocated to the two base stations 101 and 102, and i is the base station index.

Meanwhile, as shown in FIG. 1, the channel state is expressed as h _xy , x is the index of the base station, and y is the index of the terminal.

For example, the channel power gain from the first base station 101 to the second terminal 202 is expressed as h ₀₁ . On the other hand, as in the basic assumption of Alamouti codes in symbol transmission, the channel state h _xy is assumed to be constant during two symbol transmission periods.

As described above, the signal received by the first terminal in consideration of the channel state can be expressed as Equation (3) below.

의 인덱스 m과 n는 각기 단말기와 심벌(시간)을 나타낸다. 그리고 n ₀₀ 과 n ₀₁ 는

분산을 가진 노이즈(independent zero-mean additive white Gaussian noise)이고, s^*는 심벌 s의 콘주게이트(conjugate) 표현식이다. In Equation (3)

The indices m and n represent the terminal and the symbol (time), respectively. And n ₀₀ and n ₀₁ are

Is an independent zero-mean additive white Gaussian noise, and s ^* is a conjugate expression of the symbol s.

In addition, the signal received from the first terminal 201 can be expressed as a vector form as shown in Equation (4).

If it is assumed that the MS extracts symbols according to the MRC reception technique, the MS can extract each symbol according to Equation (5) below.

In Equation (5), H ^H is a hermitian expression of H. That is, Equation (5) assumes MRC reception considering the "effective channel" type of H.

In the case of receiving a symbol according to this method, the diversity gain obtained by the symbol at each terminal is expressed by Equation (6).

= + : 제1 단말

= +: First terminal

=

+

: 제2 단말

=

+

: Second terminal

In accordance with Equation (6), the received SNR according to each symbol can be expressed as Equation (7).

= : 제1 단말

=: First terminal

=

: 제2 단말

=

: Second terminal

이다. 여기서, E(.) 는 "expectation operation"을 나타낸다. 또한, N_o는 "Noise variance"를 나타낸다. In Equation (6) and Equation (7), symbol power, E _s =

to be. Here, E (.) Denotes an "expectation operation ". Also, N _o represents "Noise variance".

On the other hand, assuming ML detection (maximum likelihood detection), the sum of the symbol error rates obtained in each MS (MS _0, MS ₁ ) 201 and 202 is expressed by Equation (8).

for x

0:

for x

0

According to the embodiment of the present invention, the power for each base station is allocated such that the sum of the symbol error rates is minimized in each of the terminals 101 and 102 as shown in Equation (9).

As a first method for allocating power, all the elements in the allocable set are expressed by Equation (10), which represents the sum of symbol error rates (SER) of signals received by each terminal There is a method of substituting the power for each base station and finding the minimum value among the values that are substituted, which is referred to as a full search method.

의 모든 집합은,

= {(0, P_T), (

, P_T-

), (2

, P_T-2

),…,(P_T-

,

), (P_T, 0)}와 같이 나타낼 수 있다. 여기서,

은 각 기지국에 할당할 수 있는 단위 전력(power step size)이다. 따라서 각 기지국에 전력을 할당하기 위하여 단위 전력(power step size) 만큼 변화시켜 그 할당하는 전력을 변화시킨다. The power of the first and second base stations that can be allocated in Equation (10)

All sets of,

= {(0, P _T ), (

, P _T -

), (2

, P _T -2

), ... , (P _T -

,

), (P _T , 0)}. here,

Is a power step size that can be assigned to each base station. Therefore, in order to allocate the power to each base station, the power allocated to the base station is changed by the power step size to change the allocated power.

Meanwhile, according to another embodiment of the present invention, a method of using a signal-to-noise ratio (SNR) to minimize the symbol error rate (SER) will be described. 2A to 2C are diagrams for explaining a power allocation method according to another embodiment of the present invention.

According to another embodiment of the present invention, the SNR, which is the factor that has the greatest effect on the change of the symbol error rate, is used. Accordingly, when the minimum reception SNR of the signal transmitted to each of the first and second base stations 101 and 102 is maximized, the first and second base stations 101 and 102 transmit the power, As shown in FIG. This method will be referred to as a max-min method.

Therefore, according to another embodiment of the present invention, the discrimination equation for minimizing the symbol error rate sum of the received signals at each terminal as shown in Equation (10) can be expressed as Equation (11) You can consider this by changing to the minimum (max-min) expression.

)하며, 전력 할당을 위한 구간 [0,P_T]에서, 수신 SNR은 다음의 <수학식 12>와 같이 나타낼 수 있다. The sum of the power allocated to the two base stations is constant (

), And in a section [0, P _T ] for power allocation, the received SNR can be expressed as Equation (12).

=

=

=

=

=

:

=

,

), 전력 할당 가능한 구간의 양 끝점[0,P_T] 및 그 구간에서 직선들 간의 서로 만나는 점(crossing-point)을 고려해서 해결할 수 있다. On the other hand, the general max-min problem is a straight line obtained by discrimination for resource allocation (

,

), The end points [0, P _T ] of the power allocatable section, and the crossing-points between the straight lines in the section.

,

)이 만나는 점(crossing-point)이 존재하지 않는 경우를 가정한다.FIG. 2A is a graph showing the relationship between the two straight lines (0, P _T ) in the section [0, P _T ] for power allocation as shown in graphs (A) and

,

) Crossing-point does not exist.

및

를 비교 했을 때, 최소 SNR을 가지는 직선은

이며,

에서 최대 값을 가지는 점은 점 x이다. 따라서 이때의 전력 할당을 최적 값으로 선택한다. 즉, x 축인 P₀가 0 및 P_T값을 가질 때의 점 x 및 점 y 중 최대값인 점 x를 전력 할당을 위한 최적 값(

)으로 선택한다. In graph (A), in the section for power allocation [0, P _T ], two straight lines

And

, The straight line with the minimum SNR is

Lt;

The point having the maximum value at point x is point x. Therefore, the power allocation at this time is selected as the optimum value. That is, the point x, which is the maximum value among the points x and y when the x-axis P ₀ has values of 0 and P _T ,

).

및

를 비교 했을 때, 최소 SNR을 가지는 직선은

이며,

에서 최대 값을 가지는 점은 점 y이다. 따라서 이때의 전력 할당을 최적 값으로 선택한다. 즉, P₀가 P_T 값을 가진 점 y를 전력 할당을 위한 최적값(

)으로 선택한다. In graph (B), in the section for power allocation [0, P _T ], two straight lines

And

, The straight line with the minimum SNR is

Lt;

The point having the maximum value at the point is the point y. Therefore, the power allocation at this time is selected as the optimum value. That is, the point y with P ₀ having the value P _T is the optimum value for power allocation (

).

The above process can be summarized by the following Equation (13).

및

이 만나는 점(crossing-point)이 존재하는 경우를 가정한다. FIG. 2B is a graph showing the relationship between the two straight lines in the section [0, P _T ] for power allocation as shown in graphs (A) and (B)

And

And a crossing-point exists.

및

가 구간 [0,P_T]에서 서로 만나는 점(crossing-point)은 두 단말(MS₀, MS₁)에서의 SNR이 동일하다. 이때, "

=

"라고 놓음으로써, 다음의 <수학식 14>와 같은 "closed-form" 형태 식을 얻을 수 있다. Two straight lines

And

The crossing-points of the MSs ₀ and MS ₁ in the interval [0, P _T ] are the same at the two MSs (MS ₀ and MS ₁ ). At this time, "

=

Quot; closed-form "form expression such as the following Equation (14) can be obtained.

및

가 만나는 점(crossing-point)이 존재하는 경우에 대해서 설명한다. As shown in the graph (C) and the graph (D) in FIG. 2B, in the allocable section [0, P _T ]

And

(Crossing-point) exists.

및

을 비교했을 때, 점 x 내지 점 z의 구간에서, 최소 SNR을 가지는 직선은

이며, 점 z 내지 점 y의 구간에서, 최소 SNR을 가지는 직선은

이다. 이와 같이 최 소 SNR을 가지는 직선의 값들 중, 최대 값을 가지는 점은 점 x이다. 따라서 점 x에서의 전력 할당을 최적 값으로 선택한다. Referring to the graph (C) of FIG. 2B, in the section [0, P _T ] for power allocation,

And

, A straight line having the minimum SNR in the interval of the point x to the point z

, A straight line having the minimum SNR in the interval of the point z to the point y

to be. Among the values of the straight line having the minimum SNR, the point having the maximum value is the point x. Therefore, the power allocation at the point x is selected as the optimum value.

및

가 만나는 점(crossing-point)인 점 z 중 최대값인 P₀가 0 값을 갖는 점 x를 전력 할당의 최적값(

)으로 선택한다. That is, each point x and y when the x-axis P ₀ has a value of 0 and P _T ,

And

A point x having a maximum value P ₀ of 0, which is a crossing-point of a point z,

).

및

을 비교했을 때, 점 x 내지 점 z의 구간에서, 최소 SNR을 가지는 직선은

이며, 점 z 내지 점 y의 구간에서, 최소 SNR을 가지는 직선은

이다. 이와 같이 최소 SNR을 가지는 직선의 값들 중, 최대값을 가지는 점은 점 x이다. 따라서 점 x에서의 전력 할당을 최적 값으로 선택한다. Referring to graph (D), in the section [0, P _T ] for power allocation,

And

, A straight line having the minimum SNR in the interval of the point x to the point z

, A straight line having the minimum SNR in the interval of the point z to the point y

to be. Among the values of the straight line having the minimum SNR, the point having the maximum value is the point x. Therefore, the power allocation at the point x is selected as the optimum value.

및

가 만나는 점(crossing-point)인 점 z 중 최대값인 점 z를 전력 할당의 최적값(

)으로 선택한다. That is, each point x and y when the x-axis P ₀ has a value of 0 and P _T ,

And

The point z which is the maximum value of the point z which is a crossing-point of the power allocation,

).

및

의 기울기가 다른 부호를 가지는 경우, 두 직선

및

가 만나는 점(crossing-point)을 최적의 값으로 선택한다. According to the above procedure, in graph (D), point z is chosen as the optimal value of the power allocation,

And

The slope of the two straight lines &lt; RTI ID = 0.0 &gt;

And

The crossing-point is selected as the optimum value.

The above process can be summarized in the following Equation (15).

는 <수학식 14>의

를

또는

에 적용했을 때의 임의 값이다. In Equation (15)

&Lt; EMI ID = 14.0 >

To

or

Is an arbitrary value.

A power allocation method according to an embodiment of the present invention will now be described. 3 is a diagram for explaining a power allocation method according to an embodiment of the present invention.

3, the first base station 101 is a serving base station of the first terminal 201 and the second base station 102 is a cooperative base station of the first base station cooperating in transmitting a signal to the first terminal 201 do. It is also assumed that the second base station 102 is the serving base station of the second terminal 102 and the first base station 101 is the cooperative base station of the second base station cooperating in transmitting signals to the second terminal 102. [

Referring to FIG. 3, the first and second terminals 201 and 202 transmit channel state information to the first base station 101 in step S301. At this time, the channel state information may be a symbol error rate and a received SNR. Each of the terminals 201 and 202 can transmit information measured by the base stations 101 and 102 to each base station.

In step S303, the first base station 101 receives the channel status information and allocates power to the first and second base stations 101 and 102. [

Here, the first base station 101 allocates power using a method of minimizing a symbol error rate of a received signal of each terminal and a method of finding a maximum value of a minimum received SNR. Also, the first base station 101 allocates the power of each base station so that the sum of the allocated power of the first and second base stations 101 and 102 is constant.

Then, the first base station 101 transmits power allocation information, which is information on the power allocated to the second base station 102 in step S305, through a back-haul.

Accordingly, the first and second base stations 101 and 102 share the power allocation information, and accordingly, the first and second base stations 101 and 102 transmit power allocated to the first terminal 201 in step S307 And transmits signals according to the cooperative transmission scheme.

3, it is assumed that a signal is transmitted to the first terminal 201. However, in the case of transmitting a signal of the second terminal 202, it is also possible to allocate power as described in FIG. 3 Of course.

Next, the performance of the cooperative transmission scheme according to the embodiment of the present invention will be described.

4 is a diagram for explaining performance of a cooperative transmission scheme according to an embodiment of the present invention.

FIG. 4 shows a result of assuming that 1,000,000 channels are independently generated for each Es / No.

In FIG. 4, an equal power method of assigning the same power to two base stations, a full search method of searching all assignable power sets, and a max-min method And symbol error rates in the case of FIG.

The maximum-to-minimum power allocation method proposed by the present invention has a gain of about 4 dB compared to the equal power, and is close to the performance of the full search method.

On the other hand, in the actual implementation, the full search method may increase the amount of computation if the power step size becomes finer or the search interval becomes larger.

The maximum-minimum method has feedback of the instantaneous channel gain, and gains according to the power allocation can be obtained only by the simple SNR comparison of each terminal.

While the present invention has been described with reference to several preferred embodiments, these embodiments are illustrative and not restrictive. It will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.

1 is a diagram illustrating a structure of a wireless communication network for cooperative base station transmission according to an embodiment of the present invention.

2A and 2B are diagrams for explaining a power allocation method according to another embodiment of the present invention.

3 is a diagram for explaining a power allocation method according to an embodiment of the present invention.

4 illustrates performance of a cooperative transmission scheme according to an embodiment of the present invention;

Claims (6)

A method for allocating power in a wireless communication network in which first and second base stations transmit signals according to a cooperative transmission scheme to first and second terminals, And allocating, as the transmission power of the first and second base stations, the power when the sum of symbol error rates of the signals transmitted by the first and second base stations to the first and second base stations is minimized Wherein the power allocation method is a cooperative transmission scheme. The method according to claim 1, The allocating process Wherein the sum of the transmission powers allocated by the first and second base stations is constant. The method according to claim 1, The allocating process And allocates a power when the minimum reception SNR of a signal transmitted from the first and second base stations to each of the first and second base stations is maximized as the transmission power of the first and second base stations A method of allocating power in a wireless communication network for transmitting signals according to a transmission scheme. A system for power allocation of a wireless communication network in which first and second base stations transmit signals according to a cooperative transmission scheme to first and second terminals, The first base station and the second base station allocating a power when a sum of symbol error rates of signals to be transmitted to the first and second terminals becomes minimum, to transmission power of the first and second base stations; Wherein the system is configured to transmit a signal according to a cooperative transmission scheme. 5. The method of claim 4, One of the base stations Wherein power is allocated such that a sum of transmission powers allocated by the first and second base stations is constant. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; 5. The method of claim 4, One of the base stations And allocates a power when the minimum reception SNR of a signal transmitted from the first and second base stations to each of the first and second base stations is maximized as the transmission power of the first and second base stations A system for power allocation in a wireless communication network that transmits signals according to a transmission scheme.

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