KR100888061B1 - Transmission Power Allocation Method for Improving Bit Error Rate Performance of Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing Systems - Google Patents

Abstract

The present invention relates to a transmission power allocation method that can improve bit error rate performance of an orthogonal frequency division multiplexing (OFDM) based system using spatial multiplexing. More specifically, in (1) a receiver, A first step of measuring channel quality information for each channel and transmitting the measured channel quality information to the transmitting end; and (2) the transmitting end for each antenna using the channel quality information transmitted by the first step. And a third step of calculating a transmission power to be allocated to a subcarrier, and (3) a third step of assigning, at the transmitting end, the transmission power calculated by the second step to the subcarriers for each antenna. Features of the jacket. In particular, in the present invention, the first step of measuring and transmitting channel quality information for each channel to a transmitting end, the signal state interference in the signal detection process of the receiving end of the channel state corresponding to each subcarrier of each antenna And a second step of calculating the transmission power to be allocated to each subcarrier for each antenna, comprising: (a) calculating the bit error rate of each subcarrier for each antenna as a function of the measured signal to interference noise ratio; And calculating (b) the total bit error rate by arithmetic averaging, and (b) obtaining the transmit power of each subcarrier for each antenna that minimizes the obtained total bit error rate using the Lagrange multiplier method. Features of the jacket. On the other hand, the present invention provides a method comprising the steps of: (1) grouping subchannels according to a similar characteristic bandwidth of a channel; and (2) at a receiving end, channel quality for each subchannel grouped by the first step. A second step of measuring information and transmitting it to the transmitting end; and (3) calculating a transmission power to be allocated to each of the subchannels grouped using the channel quality information transmitted by the second step in the transmitting end. And (4) a fourth step of assigning, at the transmitting end, the transmission power calculated by the third step to each of the grouped subchannels. do.

According to the transmission power allocation method of the present invention, the bit error rate performance of the spatial multiplexed OFDM system can be improved by allocating the transmission power calculated according to the state of the channel to each subcarrier of the transmission antenna. On the other hand, by grouping the subchannels corresponding to the similar characteristic bandwidth of the wireless channel and then assigning transmission power to each of the subchannels, the bit error rate performance is improved compared to the conventional method, thereby enabling stable transmission of data while simultaneously transmitting. The amount of computation for power allocation can be greatly reduced.

Orthogonal Frequency Division Multiplexing (OFDM), spatial multiplexing technology, Multi Input Multi Output (MIMO), signal-to-interference noise ratio, bit error rate, channel quality information, transmit power Allocation, subcarrier, total bit error rate, Lagrange multiplier, subchannel, grouping, computation

Description

Transmit Power Allocation Method for Improving Bit Error Rate Performance of Multi-Input Multiple Output Orthogonal Frequency Division Multiplexing System {A TRANSMIT POWER ALLOCATION METHOD FOR BIT ERROR RATE PERFORMANCE IMPROVEMENT IN MIMO OFDM SYSTEMS}

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a transmission / reception structure of a spatial multiplexing orthogonal frequency division multiplexing (OFDM) system according to an embodiment of the present invention.

2 is a view showing the experimental results of the Zero Focusing (ZF) detection method according to an embodiment of the present invention.

3 is a view showing an experimental result of a method for detecting a minimum mean square error (MMSE) according to an embodiment of the present invention.

4 is a diagram illustrating a structure grouped into subchannels corresponding to similar characteristic bandwidths according to an embodiment of the present invention.

5 is a diagram illustrating an experimental result of a ZF detection method of transmission power allocation grouped into subchannels according to an embodiment of the present invention.

6 is a diagram illustrating an experimental result of a method of detecting MMSE of transmission power allocation grouped into subchannels according to an embodiment of the present invention.

<Explanation of symbols for main parts of the drawings>

100 : system in which an embodiment of the present invention is implemented

101: part of converting serial data to parallel data

102: calculating and allocating transmit power

103: Inverse FFT (IFFT)

104: transmit antenna

105: receiving antenna

106: Fast Fourier Transform (FFT)

107: part for detecting subcarrier signal of each transmit antenna

108: channel quality information transmission part

The present invention relates to a transmission power allocation method, and more particularly, to a transmission power allocation method capable of improving bit error rate performance of an orthogonal frequency division multiplexing (OFDM) based system using a spatial multiplexing technique.

When the Multi Input Multi Output (MIMO) technique using multiple antennas is applied to an OFDM-based system, it is possible to obtain stable transmission of data by improving data rate or improving bit error rate performance. In the OFDM-based system, MIMO techniques such as Space-Time Block Coding or Space-Frequency Block Coding can be applied to obtain stability of data transmission through transmit / receive diversity gain. Spatial multiplexing technology can increase the data rate. In addition, the technique of allocating the modulation-coded data or the transmission power according to the channel state to the data transmitted through each antenna may improve the transmission rate or the bit error rate performance of the multi-antenna system. The method of allocating the modulation-coded data to the transmitting end in the receiving end can improve the data transmission rate, allocate more transmission power to the bad channel and reduce the power to the good channel. The transmission power allocation method to allocate can improve bit error rate performance. However, in a system such as a wireless LAN (WLAN) and a wireless personal area network (WPAN), it is difficult to allocate modulated coded data corresponding to the state of each channel to OFDM subcarriers of each antenna. Therefore, there is a need to improve bit error rate performance by applying a transmission power allocation method according to channel conditions to subcarriers of each antenna.

In the conventional transmission power allocation method, a transmission power is allocated for each antenna according to a channel state in a spatial multiplexing system using a single carrier, and transmission power information calculated at a receiving end in a system using an OFDM multiple subcarrier is used. There is a method of assigning each subcarrier. In a spatial multiplexing system using a single carrier, a method of allocating transmission powers according to channel conditions for each antenna is a method of allocating transmission powers for each antenna in a MIMO system using a spatial multiplexing technique, and a system using multiple subcarriers of OFDM. In the method of allocating transmission power information calculated at a receiving end for each subcarrier, a subcarrier allocation method in a single transmission antenna in which multiple transmission antennas using spatial multiplexing is not considered. By combining these existing transmission power allocation methods, that is, the conventional method of allocating transmission power for each antenna and the conventional method of allocating transmission power only to each OFDM subcarrier, the spatial multiplexing technique is not applied. There is a need to improve the bit error rate performance for the OFDM-based system.

The present invention is proposed for recognizing the necessity and solving the problems as described above, and by assigning the transmission power calculated according to the channel state to each subcarrier of the transmission antenna, orthogonal frequency division multiplexing (OFDM) based on spatial multiplexing technology. The purpose of the present invention is to propose a transmission power allocation method that can improve the bit error rate performance of the system.

In addition, the present invention, by grouping the sub-channel corresponding to the similar characteristic bandwidth of the wireless channel, and then allocates the transmission power for each of the sub-channel grouping, thereby improving the bit error rate performance than the conventional method to enable stable transmission of data It is another object of the present invention to propose a transmission power allocation method capable of greatly reducing the amount of computation for transmission power allocation.

In accordance with a feature of the present invention for achieving the above object, a transmission power allocation method,

In Orthogonal Frequency Division Multiplexing (OFDM) based System Using Spatial Multiplexing Technique,

(1) a first step of, at the receiving end, measuring channel quality information for each channel and transmitting the measured channel quality information to the transmitting end;

(2) a second step of calculating, at the transmitting end, transmission power to be allocated to subcarriers for each antenna by using the channel quality information transmitted by the first step; And

(3) In the transmitting end, it comprises a third step of allocating the transmission power calculated by the second step to the subcarriers for each antenna.

Preferably, the first step of measuring the channel quality information for each channel and transmitting to the transmitting end, the channel state corresponding to each subcarrier of each antenna as a signal to interference noise ratio in the signal detection process of the receiving end Measuring,

The second step of calculating the transmission power to be allocated to each subcarrier for each antenna,

(a) expressing a bit error rate of each subcarrier for each antenna as a function of the measured signal-to-interference noise ratio, and calculating the total bit error rate by arithmetically averaging it; And

(b) using the Lagrange multiplier method, the method may further include obtaining transmission power of each subcarrier for each antenna to minimize the obtained total bit error rate.

According to yet another aspect of the present invention, a transmission power allocation method includes

In Orthogonal Frequency Division Multiplexing (OFDM) based System Using Spatial Multiplexing Technique,

(1) grouping subchannels according to the similar characteristic bandwidth of the channel;

(2) a second step of measuring, at a receiving end, channel quality information of each subchannel grouped by the first step and transmitting the measured channel quality information to the transmitting end;

(3) a third step of calculating, at the transmitting end, transmission power to be allocated to each of the subchannels grouped using the channel quality information transmitted by the second step; And

(4) characterized in that at the transmitting end, assigning the transmission power calculated by the third step to each of the grouped subchannels.

Preferably, the second step of measuring and transmitting channel quality information for each of the grouped subchannels to the transmitting end, the channel state corresponding to each of the grouped subchannels, during the signal detection process of the receiving end Measuring with a signal to interference noise ratio,

The third step of calculating the transmission power to be allocated to each of the grouped subchannels,

(a) at the transmitting end, expressing the bit error rates of each subchannel grouped as a function of the transmitted signal to interference noise ratio, and then calculating the total bit error rate by arithmetically averaging them; And

(b) using the Lagrange multiplier method, the method may further include obtaining the transmit power of each of the grouped subchannels to minimize the obtained overall bit error rate.

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

이다. 여기서, [ ]^T는 전치(Transpose) 연산을 의미한다. 송신 안테나에서 송신되어, 채널을 통과한 후, M_r개의 수신 안테나에서 수신된 신호는 다음 수학식 1과 같이 표현할 수 있다.In order to understand the transmission power allocation method according to the present invention, the reception stage detection process of the OFDM system to which the conventional spatial multiplexing is applied will be described first. If the number of transmitting antennas is M _t , the number of receiving antennas is M _r, and the number of OFDM subcarriers is K, then the signal transmitted to the kth subcarrier of each transmitting antenna is

to be. Here, [] ^T means a transpose operation. After being transmitted by the transmitting antenna and passing through the channel, the signals received by the M _r receiving antennas can be expressed by Equation 1 below.

는 k번째 부반송파에 해당하는 수신 신호 벡터를, 채널 H _k는 k번째 부반송파에서

크기를 갖는 채널 행렬을 각각 의미한다. 즉, H _k(i,j)는 j번째 송신 안테나에서 i번째 수신 안테나로의 채널을 의미한다. n _k는 평균이 0이고 분산이

인 복소 가우시안 랜덤 잡음 벡터를 의미한다.here,

Is the received signal vector corresponding to the k th subcarrier, and channel H _k is the k th subcarrier.

Each means a channel matrix having a size. That is, H _k (i, j) means a channel from the j th transmit antenna to the i th receive antenna. n _k has a mean of 0 and its variance

It means a complex Gaussian random noise vector.

In order to determine the transmitted signal x _k from a received signal y _k of Equation 1, ZF (Zero Forcing) may take into account the shape and MMSE (Minimum Mean Square Error) type spatial multiplexing MIMO detection methods.

First, the ZF-type detection method may be described using Equations 2 to 4 below.

i = 1

Here, () ⁺ denotes a pseudo inverse matrix operation, () _j denotes a j th row vector of the matrix, and ∥∥ denotes a norm operation.

In order to detect the transmission signal x _k , first, a pseudo inverse of a channel is obtained as shown in Equation 3, and an order of removing components of the transmitted signal is obtained as shown in Equation 4 above. Equations 2 to 4 are initial values for detecting signals at the receiving end, and original data may be detected by repeatedly performing Equations 5 to 11 below.

i = i + 1

로 정의하고, 이를, 상기 수학식 6과 같이, 수신 신호 y _{i ,k}에 곱해

을 얻는다. 얻어진

을, 상기 수학식 7과 같이, 변조 방식에 따른 결정 함수 Q( )에 대입함으로써 송신 신호 x _k의 s_i번째 신호 성분에 대한 추정치

을 얻을 수 있다. 여기서, x _k의 s_i번째 신호 성분이 완벽히 추정되었다고 가정하고, i번째 단계에서의 수신 신호 벡터 y _{i ,k}에서 s_i번째 검출된 간섭 신호 성분을 제거한다. 상기 수학식 8을 통해 (i+1)번째 단계에서의 연산을 위한 수신 신호 벡터 y _{i +1,k}을 결정한다. 상기 수학식 8에서,

는 행렬의 s_i번째 열 벡터를 의미하고, 상기 수학식 9의

는 행렬의 s_i번째 열 벡터 성분을 모두 0으로 널링한 행렬을 의미한다. 나머지 간섭 신호 성분 검출을 위하여 채널의 의사 역행렬 Z _{i +1,k}을 상기 수학식 9에서 구하고, 상기 수학식 10에서 다음 단계를 위한 최적의 검출 순서를 결정한다. 위와 같은 과정을 K개의 모든 부반송파에 대하여 적용하면, 수신 신호로부터 원래의 송신 데이터를 검출해 낼 수 있다.Nulling vector of the s _i th row vector of the matrix Z _{i , k} as shown in Equation 5 above.

And multiply the received signals y _{i and k} as in Equation 6 above.

Get Obtained

, Equation (7), by substituting the decision function Q () according to the modulation scheme for the s _i th signal component of the transmission signal x _k

Can be obtained. Here, it is assumed that the s _i th signal component of x _k is perfectly estimated _, and the s _i th detected interference signal component is removed from the received signal vectors y _{i , k} in the i th stage. Equation 8 determines the received signal vector y _{i + 1, k} for the operation in the (i + 1) th step. In Equation 8,

Denotes the s _i th column vector of the matrix,

Denotes a matrix in which all of the s _i- th column vector components of the matrix are nulled. In order to detect the remaining interference signal components, the pseudo inverse Z _{i + 1, k} of the channel is obtained from Equation 9, and the optimal detection order for the next step is determined in Equation 10. If the above process is applied to all K subcarriers, the original transmission data can be detected from the received signal.

The ZF detection method described above has the disadvantage that the influence of noise is increased by completely removing the interference component. In order to solve this problem, a MMSE type spatial multiplexed MIMO detection method has been proposed that provides a good compromise between interference suppression and noise enhancement. The MMSE detection method exhibits better performance than the ZF detection method by minimizing the mean square error between the transmitted signal and the signal estimated at the receiving end. In the MMSE detection method, the pseudo inverse of the channel obtained in Equations 3 and 9 of the ZF detection method can be obtained as in Equations 12 and 13.

Here, () ^H means conjugate transpose operation.

Equations 4 and 10 of the ZF detection method for determining the detection order of the signal are replaced by the following equations (14) and (15).

Here, () _ij means the elements of the i th row and j th column of the matrix. Except for determining the pseudo inverse matrix operation and the detection order of the channels of Equations 12 to 15, the remaining processes are the same as the above ZF detection method.

Based on the above description, the embodiment of the present invention will be described in detail.

An embodiment of the present invention may be implemented to allocate transmission power to subcarriers for each transmission antenna for an OFDM based system using a spatial multiplexing technique as shown in FIG. 1. The transmitting end of the system 100 in which an embodiment of the present invention is implemented includes a portion 101 for converting serial data into parallel data so as to transmit different data for each antenna, and calculating transmission power for subcarriers for each antenna. And a transmit power calculation and allocation portion 102, an inverse fast Fourier transformer (IFFT) 103 for OFDM, and M _t transmit antennas 104. The receiving end of the system 100 in which an embodiment of the present invention is implemented includes M _r receiving antennas 105 and a fast Fourier transformer (FFT) for receiving a signal transmitted from the transmitting antenna 104 and having passed through a wireless channel. 106, a portion 107 for detecting a subcarrier signal of each transmit antenna, and a channel quality information transmission portion 108 for transmitting the measured signal-to-interference noise ratio as channel quality information to the transmitting end.

As shown in FIG. 1, the quality information of the channel measured in the form of a signal-to-interference noise ratio at the receiving end is transmitted to the transmitting end by the channel quality information transmitting part 108. In relation to the transmission of such channel quality information, the present invention is based on a method of transmitting from a receiving end to a transmitting end through a frame of a time division duplexing (TDD) system.

의 송신 전력을 할당하면 수신 신호는 다음 수학식 16과 같다.The present invention, unlike the conventional spatial multiplexing OFDM system that allocates the same transmission power to all subcarriers, transmits the channel quality information to the transmitter in the form of signal-to-interference noise ratio during the receiver-side signal detection process. It is configured to calculate the transmission power using the channel quality information and assign it to subcarriers for each antenna of the transmitting end. The data detection order of a spatial multiplexed OFDM system is determined based on the signal to interference plus noise ratio of the transmission signal. Using the determined detection order, the state of the channel is determined, and the transmit power that minimizes the overall bit error rate is calculated by the Lagrange multiplier method and allocated to the subcarriers of each transmit antenna. To the kth subcarrier of each transmit antenna

When the transmission power of is allocated, the received signal is given by the following equation (16).

의 검출 후 각 부반송파의 신호 대 간섭 잡음 비(

)를 구하면, 다음 수학식 17의 널링 벡터를 통해 다음 수학식 18로 구할 수 있다.At the receiving end, estimated through the ZF detection process

Signal-to-interference noise ratio of each subcarrier after

) Can be obtained by the following equation (18) through the nulling vector of the following equation (17).

는 동일한 전력이 할당되었을 경우의 널링 벡터를 의미하며, 상기 수학식으로부터, 각 부반송파의 신호 대 잡음 비(

)는 널링 벡터

와 송신 전력

로 구성됨을 확인할 수 있다.here,

Denotes a nulling vector when the same power is allocated, and from the above equation, the signal-to-noise ratio of each subcarrier (

Knurled vector

And transmit power

You can see that it consists of.

As can be seen from Equations 17 and 18, in the case of the ZF detection method, the interference component is removed and not considered, whereas in the case of the MMSE detection method, not only the s _i th transmission signal but also the transmission power of other transmission signals are not considered. Consideration should be given. Reflecting this, using Equation 19, a signal-to-interference noise ratio for the MMSE detection method can be obtained.

)을 송신 전력(

)의 함수로 표현해야 한다. 이전 검출 단계에서 추정된 송신 신호가 완벽히 제거되었다고 가정하면, 주어진 채널 상태에서 k번째 부반송파의 s_i번째 송신 신호의 비트 오류율(

)은 다음 수학식 20과 같이 신호 대 간섭 잡음 비의 함수로 표현할 수 있다.Using the obtained signal-to-interference noise ratio, the transmission power is allocated according to the state of the channel, and the Lagrange multiplier method is used to calculate the optimal transmission power to minimize the overall bit error rate. To calculate the transmit power for improving the bit error rate performance, the bit error rate (

Transmit power (

Must be expressed as a function of Assuming that the transmitted signal estimated in the previous detection phase has been completely removed, the bit error rate of the s _i th transmitted signal of the k th subcarrier in a given channel state (

) Can be expressed as a function of signal-to-interference noise ratio, as shown in Equation 20 below.

이며, Q-함수는

로 정의된다. 각 안테나별 부반송파에 실린 데이터는 서로 독립이기 때문에, 전체 비트 오류율(

)은 다음 수학식 21과 같이 각 안테나별 부반송파의 비트 오류율(

)에 대한 산술 평균으로 구할 수 있다.Here, f () is a function determined according to a specific modulation scheme. For example, in the case of the QPSK scheme,

And the Q-function is

Is defined as Since the data on the subcarriers of each antenna are independent of each other, the overall bit error rate (

) Is the bit error rate of the subcarrier for each antenna as shown in Equation 21 below.

Can be calculated as the arithmetic mean of

)을 찾기 위해서는, 다음 수학식 22와 같은 전체 송신 전력 제한 조건(Power Constraint) 하에서, 라그랑지 승수법을 이용할 수 있다. 라그랑지 승수법의 비용 함수(Cost Function)는, 상기 수학식 20 및 21을 대입한 다음 수학식 23의 형태가 된다.Transmit power to minimize overall bit error rate

), The Lagrange multiplier method can be used under an overall transmit power constraint (Equation 22). The cost function of the Lagrange multiplier method becomes the form of Equation 23 after substituting Equations 20 and 21 above.

는 각 안테나별 송신 전력이 K개의 부반 송파에 균등하게 분포되어 있을 때 각 부반송파의 평균 송신 전력을 의미한다.Where λ is the Lagrange multiplier,

Denotes the average transmit power of each subcarrier when the transmit power of each antenna is evenly distributed among the K subcarriers.

에 대해 미분한 값이 0이 되도록 두면, 다음 수학식 24 및 25와 같다.Equation 23, which is a cost function of the Lagrange multiplier, is transmitted

If the derivative value for is set to 0, the following equations (24) and (25) are given.

을 구할 수 있다. MMSE 검출 방법의 경우, 위와 같은 방법으로 송신 전력을 계산하기 위해서는 신호 대 간섭 잡음 비의 근사화가 필요하다. MMSE 검출 방법의 각 검출 과정을 통한 신호 대 잡음 비는, 다음 수학식 26과 같이, 송신 전력

와 각 안테나별 부반송파에 같은 전력이 할당되었을 경우의 신호 대 간섭 잡음 비의 곱으로 근사화할 수 있다.By calculating the equation (25), the transmission power of the sub-carrier for each antenna to minimize the overall bit error rate

Can be obtained. In the case of the MMSE detection method, an approximation of the signal-to-interference noise ratio is required to calculate the transmission power in the above manner. The signal-to-noise ratio through each detection process of the MMSE detection method is represented by Equation 26 below.

It can be approximated by the product of the signal-to-interference noise ratio when the same power is allocated to each subcarrier and each antenna.

Similar to the ZF detection method, in the case of the MMSE detection method, the transmission power can be obtained by the Lagrange multiplier method using the approximated signal-to-noise ratio.

가 할당된 경우, 수신 단에서 신호를 검출하는 방법은 종래의 공간 다중화 OFDM 시스템의 검출 과정과 동일하다. 다만, 기존의 수학식 3 및 9에 송신 전력 행렬 P _k가 추가되어 다음과 같은 수학식 27 및 28의 형태가 된다.Transmit power to subcarriers of each transmit antenna

If is assigned, the method of detecting a signal at the receiving end is the same as the detection process of the conventional spatial multiplexing OFDM system. However, the transmission power matrix P _k is added to the existing equations (3) and (9) to form the following equations (27) and (28).

Similarly, in the case of the MMSE detection method, Equations 12 and 13 are replaced by Equations 29 and 30 as follows.

Equation 8, which removes the detected interference signal and creates a new reception vector for the next step, is changed to Equation 31 as follows.

Meanwhile, according to the transmission power allocation method according to the present invention, as the number of transmission antennas and subcarriers in an OFDM system to which spatial multiplexing is applied increases, the amount of computation for transmission power allocation increases. In order to solve this problem, in another embodiment of the transmission power allocation method of the present invention, the total bandwidth of the wireless channel is grouped into subchannels corresponding to similar characteristic bandwidths, and the transmission power is allocated to each of the grouped subchannels. In addition, we propose a method that can significantly reduce the amount of computation for calculating transmit power while improving bit error rate performance compared to the existing transmit power allocation method. By dividing the total bandwidth B by obtaining the similar characteristic bandwidth B _c of the wireless channel, the C grouped subchannels can be obtained as in Equation 32 below.

By allocating transmit power for each C subchannel corresponding to the similar characteristic bandwidth B _c instead of the K subcarriers for each antenna, the transmission power calculation amount can be greatly reduced from KM _t to CM _t .

Next, the effect of improving the bit error rate performance of the embodiments of the present invention described so far will be described through concrete experiments.

)은 다음 수학식 33과 같이 Q-함수(Q-Function)를 사용하여 표현할 수 있다.First, as an experimental condition, an OFDM based Ultra WideBand (UWB) system having two transmit antennas and two receive antennas of a spatial multiplexing technique is assumed. UWB channel CM1 (3.1 to 3.628 GHz) of IEEE 802.15.3a was used as the wireless channel, and the number of OFDM subcarriers of the UWB system was 128. Uncoded quadrature phase shift keying (QPSK) was performed on the data of each subcarrier. For QPSK, the bit error rate of the s _i th transmit signal of the k th subcarrier (

) Can be expressed using a Q-Function as shown in Equation 33 below.

는 검출 과정에서의 잡음에 대한 간섭 부분으로서, 다음 수학식 34와 같이 ZF 방법과 MMSE 방법에 따라 다르게 정의가 된다.here,

Is an interference part for noise during the detection process, and is defined differently according to the ZF method and the MMSE method as shown in Equation 34 below.

에 대해 미분한 값이 0이 되도록 하면, 다음과 같은 수학식 35를 얻을 수 있다.After substituting the equation 33 for the bit error rate into the Lagrange multiplier method of equation 23 for calculating the transmission power, the transmission power

If the derivative is 0, the following equation (35) can be obtained.

)을 1이라고 가정을 하고, 상기 수학식 35를 계산하면, 채널 상태에 따른 송신 전력을 다음 수학식 36 및 수학식 37과 같이 얻을 수 있다.Average transmit power allocated to each subcarrier (

Assuming that 1) is 1 and the equation 35 is calculated, the transmission power according to the channel state can be obtained as shown in Equations 36 and 37.

Λ of Equation 37 may be obtained through Equation 22 for the total transmission power limit. In the process of calculating the transmission power using the Lagrange multiplier, some values of the transmission power may be negative. In this case, we assign a negative transmit power of zero and recalculate the Lagrange multiplier method with the remaining values. When the calculations are made until all the values are negative, the transmission power values by the Lagrange multiplier method are as shown in Equations 38 and 39.

보다 작으면 k번째 부반송파의 s_i번째 송신 신호에 송신 전력을 할당하지 않음을 의미한다.In Equation 38, a state of a channel is

If smaller, it means that no transmit power is allocated to the s _i th transmission signal of the k th subcarrier.

2 shows the bit error rate performance of the ZF detection method when the same transmission power is allocated to 128 subcarriers for each antenna (the existing method) and when the transmission power is allocated according to the channel condition (the method according to the present invention). This is a diagram showing the comparison. From FIG. 2, when the method according to the present invention is applied to the ZF detection method, a signal-to-noise ratio gain of about 5.5 dB occurs at a 10 ^-2 bit error rate compared to the conventional method in which the same transmission power is allocated to subcarriers for each antenna. You can see that.

Fig. 3 shows the bit error rate performance of the MMSE detection method when the same transmission power is allocated to 128 subcarriers for each antenna (the existing method) and when the transmission power is allocated according to the channel condition (the method according to the present invention). This is a diagram showing the comparison. 3 shows that, when the method according to the present invention is applied to the MMSE detection method, a signal-to-noise ratio gain of about 5 dB occurs at a 10 ^-2 bit error rate compared to the conventional method in which the same transmission power is allocated to subcarriers for each antenna. You can check it. Also, by comparing FIG. 3 with FIG. 2, it can be seen that the MMSE detection method is superior in performance to the ZF method in which the noise increase effect occurs.

On the other hand, according to the transmission power allocation method proposed in the present invention, since the transmission power is allocated to all subcarriers of each transmission antenna, there is a problem in that the amount of calculation for the transmission power becomes very large. As a method for solving this problem, the amount of computation can be reduced by allocating the same transmission power for each subchannel corresponding to the similar characteristic bandwidth of the UWB channel. That is, after grouping by subchannels corresponding to the similar characteristic bandwidth and obtaining the average signal-to-interference noise ratio of the grouped subchannels, Equation 36 and 37 calculates transmission power for C subchannels instead of K subcarriers. By doing so, the amount of calculation can be greatly reduced. The pseudo characteristic bandwidth of the IEEE UWB channel can be roughly obtained using Equation 40 using the root mean square delay of the channel.

은 약 5.28ns이고, 이를 상기 수학식 40에 대입하면 유사 특성 대역폭(B_c)은 약 33MHz로 근사화할 수 있다. 이는 전체 528MHz 대역폭을 16개의 33MHz의 부채널로 그룹화할 수 있다는 것을 의미한다. 그룹화된 부채널별로 할당된 송신 전력은, 상기 수학식 36 및 37로부터 다음 수학식 41 및 42와 같이 구할 수 있다.Square root mean square delay of CM1 channel

Is about 5.28 ns. Substituting this in Equation 40, the pseudo characteristic bandwidth B _c can be approximated to about 33 MHz. This means that the entire 528MHz bandwidth can be grouped into 16 33MHz subchannels. The transmission power allocated to each of the grouped subchannels can be obtained from Equations 36 and 37 as shown in Equations 41 and 42.

In the over the same way, each antenna by calculating only the number of subcarriers the transmission power that corresponds to the place of each antenna sub-channel to the allocated transmission power by assigned, 128 the amount of computation KM _t * 2 = CM _t at 256 It can be greatly reduced to 16 * 2 = 32.

Fig. 4 shows the same bit error rate performance for the ZF detection method when the transmission power is allocated to all 128 subcarriers and when the transmission power is allocated to only 16 subchannels. The figure shows the comparison with the case where electric power was allocated (the existing method). From FIG. 4, when the transmission power is allocated to only 16 subchannels, there is a performance degradation of about 1.5 dB compared to the case where the transmission power is allocated to all 128 subcarriers for each antenna. If instead it can be confirmed that the signal-to-noise ratio gain of about 4dB generated from ^10-2 bit error rate. That is, in case of allocating transmit power only to grouped subchannels, there is a slight performance degradation compared to allocating transmit power to all subcarriers, but the computation amount for allocating transmit power can be greatly reduced, and the same power is allocated. The results show that the bit error rate performance can be significantly improved over the conventional method.

FIG. 5 shows the bit error rate performance when the transmission power is allocated to all 128 subcarriers and the transmission power is allocated only to 16 subchannels in the MMSE detection method. The transmission power is the same for all 128 subcarriers for each antenna. Is shown in comparison with the case of assigning (the conventional method). From FIG. 5, when the transmission power is allocated to only 16 subchannels, there is a performance degradation of about 1 dB compared to the case of allocating the transmission power to all 128 subcarriers for each antenna, but the conventional case in which the same transmission power is allocated Rather, we can see that a signal-to-noise ratio gain of about 4dB occurs at a 10 ^-2 bit error rate. As in the case of the ZF detection method, when the transmission power is allocated only to the grouped subchannels, there is a slight performance degradation compared to the case of allocating the transmission power to all subcarriers, but the computation amount for the transmission power allocation can be greatly reduced. In addition, the results show that the bit error rate performance can be significantly improved over the conventional method of allocating the same power.

The present invention described above may be variously modified or applied by those skilled in the art, and the scope of the technical idea according to the present invention should be defined by the following claims.

According to the transmission power allocation method of the present invention, the bit error rate performance of the spatial multiplexed OFDM system can be improved by allocating the transmission power calculated according to the state of the channel to each subcarrier of the transmission antenna.

On the other hand, by grouping the subchannels corresponding to the similar characteristic bandwidth of the wireless channel and then assigning transmission power to each of the subchannels, the bit error rate performance is improved compared to the conventional method, thereby enabling stable transmission of data while simultaneously transmitting. The amount of computation for power allocation can be greatly reduced.

Claims (4)

In Orthogonal Frequency Division Multiplexing (OFDM) based System Using Spatial Multiplexing Technique, (1) a first step of, at the receiving end, measuring channel quality information for each channel and transmitting the measured channel quality information to the transmitting end; (2) a second step of calculating, at the transmitting end, transmission power to be allocated to subcarriers for each antenna according to the state of each channel using the channel quality information transmitted by the first step; And (3) a third step of allocating, at the transmitting end, the transmission power calculated by the second step to the subcarriers for each antenna, The first step of measuring and transmitting channel quality information for each channel to a transmitting end includes measuring a channel state corresponding to each subcarrier of each antenna with a signal-to-interference noise ratio in a signal detecting process of the receiving end. and, The second step of calculating the transmission power to be allocated to each subcarrier for each antenna, (a) expressing a bit error rate of subcarriers for each antenna as a function of the measured signal-to-interference noise ratio, and calculating the total bit error rate by arithmetically averaging it; And (b) obtaining a transmission power of each subcarrier for each antenna that minimizes the obtained overall bit error rate by using a Lagrange multiplier; Transmission power allocation method further comprising. delete In Orthogonal Frequency Division Multiplexing (OFDM) based System Using Spatial Multiplexing Technique, (1) grouping subchannels according to the similar characteristic bandwidth of the channel; (2) a second step of measuring, at a receiving end, channel quality information of each subchannel grouped by the first step and transmitting the measured channel quality information to the transmitting end; (3) a third step of calculating, at the transmitting end, transmission power of grouped subchannels using the channel quality information transmitted by the second step; And (4) at the transmitting end, allocating the transmit power calculated by the third step to each of the grouped subchannels, In the second step of measuring and transmitting channel quality information of each of the grouped subchannels, the channel state corresponding to each of the grouped subchannels is determined by signal-to-interference noise in a signal detection process of the receiver. Measuring by ratio, The third step of calculating the transmission power to be allocated to each of the grouped subchannels, (a) expressing the bit error rates of each subchannel grouped as a function of the measured signal-to-interference noise ratio, and then calculating the total bit error rate by arithmetically averaging them; And (b) using the Lagrange multiplier method to obtain the transmit power of each grouped subchannel that minimizes the obtained overall bit error rate Transmission power allocation method further comprising. Transmission power allocation method comprising a. delete

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