CN111756666A - A working method of equal gain combining system based on constellation rotation - Google Patents

Abstract

A working method of an equal gain combining system based on constellation rotation belongs to the technical field of wireless communication. First, the equal-gain combined receiving method is used. The equal-gain combined receiving method does not need to adaptively adjust the weighting coefficient according to the signal-to-noise ratio of each channel, so the equipment is simple, the complexity is low, and accurate channel estimation is not required; secondly, the introduction of Constellation rotation, that is, the in-phase and quadrature components are obtained through the rotation of the constellation diagram, and then the in-phase and quadrature components are sent through different antennas to eliminate the correlation between the two components, so that the transmitted signals independently fade in their respective transmission on the channel. The method proposed in the present invention can significantly improve the performance of the modulation system based on equal gain combining, and the introduction of constellation rotation can obtain modulation diversity gain without sacrificing the bandwidth and power of the frequency band. The interleaver and deinterleaver can reduce the complexity of the system implementation.

Description

A working method of equal gain combining system based on constellation rotation

technical field

The invention relates to a working method of an equal gain combining system based on constellation rotation, and belongs to the technical field of wireless communication.

Background technique

Signal Space Diversity (SSD, Signal Space Diversity) is an effective improvement scheme for dealing with fading. It has the advantages of high diversity gain and does not need to occupy additional time and frequency band resources, and can effectively improve the performance impact caused by fading. , and has been widely used in wireless communication. The combination of constellation rotation and component interleaving is the key technology of SSD. We use the degree of diversity to define the minimum number of distinguishable components in a multi-dimensional symbol set, and constellation rotation can maximize the degree of diversity between any two constellation points, resulting in improved performance. Component interleaving can eliminate the correlation between components, so that the transmitted signals are independently transmitted on fading channels, so even if one component experiences severe fading, the receiver can restore the signal through only one component.

It is well known that in mobile communication, equal gain combining (EGC, Equal Gain Combining) and maximum ratio combining (MRC, Maximal-ratio Combining) receiving technologies are the two most commonly used diversity combining technologies. In the article "Component-Interleaved Receive MRC with Rotated Constellation for Signal Space Diversity" published by scholar Sungho Jeon in 2009, he studied the performance of the combination of constellation rotation and component interleaving in the maximum ratio combining system under the condition of single-input antenna and multiple-output antenna. However, MRC performs in-phase weighted combination of multi-channel signals, and the weight is determined by the signal-to-noise ratio corresponding to each branch signal. The output signal-to-noise ratio of MRC is equal to the sum of the signal-to-noise ratio of each branch. It is estimated that the signals of each branch can be processed according to the specific conditions of the channel, so its performance is the best, but its implementation is also the most complicated. However, EGC does not need to weight the signal. The signals of each branch are added with equal gain. Compared with the maximum ratio combining, EGC does not need channel estimation, which simplifies the calculation of the weighting value. The circuit is simple and easy to implement, but the performance is slightly worse than the maximum ratio. than merge. Therefore, we propose a working method of an equal-gain combining system based on constellation rotation under the condition of multiple input antennas and multiple output antennas to improve the performance of EGC. According to the literature search, no one has studied this aspect.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the present invention provides a working method of an equal-gain combining system based on constellation rotation under the condition of multiple input antennas and multiple output antennas, which can save hardware resources and reduce the complexity of system implementation. The rotating equal-gain combining system achieves better anti-fading performance.

The technical scheme of the present invention is as follows:

A working method of an equal-gain combining system based on constellation rotation, the steps are as follows:

(1) First, the input symbol stream is Gray-mapped to the complex frequency domain; let the transmitted signal vector be s=[s ₀ ,s ₁ ,...,s _n ,...,s _N-1 ], and N is the input symbol The length of the stream, where s _n represents the constellation point corresponding to the nth signal sent, and its value is s _n =s _I,n +js _Q,n , where s _I,n and s _Q,n are respectively The real and imaginary parts of s _n represent the in-phase and quadrature components of the constellation diagram, respectively, and j represents the imaginary unit;

(2) Rotate the signal constellation, and set the rotated transmitted signal vector to be x=[x ₀ , x ₁ ,...,x _n ,...,x _N-1 ], where x _n is the rotated The constellation point corresponding to the nth signal, its value is x _n =x _I,n +jx _Q,n . Similarly, x _I,n and x _Q,n are the real and imaginary parts of x _n , respectively. Represents the in-phase and quadrature components of the rotated constellation diagram, j represents the imaginary unit; and x _I,n and x _Q,n can be represented by s _I,n and s _Q,n , that is, x _I,n =s _I,n cosθ +s _Q,n sinθ,x _Q,n =-s _I,n sinθ+s _Q,n cosθ, θ is the rotation angle that optimizes the system bit error rate performance, the value range is [0,π/2] ;

矩阵的第1、2行表示两路发送信号，显然，优选的，发送天线数为2；(3) In order to eliminate the correlation between the two components, the two components can be subjected to independent fading, that is, the in-phase components x _I =[x _I,0 ,x _I,1 ,... ,x _I,n ,...,x _I,N-1 ] and the quadrature components x _Q =[x _Q,0 ,x _Q,1 ,...,x _Q,n ,...,x _{Q ,N-1} ]; for a more concise representation, the transmitted signal is represented by a matrix here as

The 1st and 2nd rows of the matrix represent two transmission signals, obviously, preferably, the number of transmission antennas is 2;

的第1、2行分别表示第k对接收的信号，

的第1、2行分别为第k对信号经历的独立衰落下的独立同分布随机变量，而

是第k对信号所加的加性高斯白噪声，这里的"·"表示矩阵的点乘；计算第k对信号的加权系数

这里的"*"表示共轭，得到归一化的接收信号矢量为

那么，可以得到等增益合并器的输出信号为

(4) The receiving mode of equal gain combining is adopted at the receiving end of the signal. When the system is applied to a flat fading channel, let the number of receiving antennas be _MR , and each antenna needs to receive in-phase and quadrature parts, which can be regarded as a pair. _MR also means that the in-phase and quadrature components are respectively The number of diversity branches when the gain is combined; then the k-th pair of received signals can be expressed as Y _k =H _k ·X+N _k , where

The 1st and 2nd lines of , respectively represent the received signal of the kth pair,

The first and second lines of are the independent and identically distributed random variables under the independent fading experienced by the k-th pair of signals, and

is the additive white Gaussian noise added to the k-th pair of signals, where "·" represents the dot product of the matrix; calculate the weighting coefficient of the k-th pair of signals

Here "*" represents conjugation, and the normalized received signal vector is

Then, the output signal of the equal gain combiner can be obtained as

采用最小欧式距离准则来进行判决，判决后得到最终的输出符号流，即恢复的输入符号流。(5) Finally, combine the output signal of the equal gain combiner

The minimum Euclidean distance criterion is used to make a decision, and the final output symbol stream, that is, the restored input symbol stream, is obtained after the decision.

和

Preferably, in step (1), for QPSK modulation and 8PSK modulation, the respective value ranges of s _I,n and s _Q,n are respectively

and

Preferably, in step (2), the optimal rotation angle θ for QPSK modulation is θ=30.3°, and the optimal rotation angle θ for 8PSK modulation is θ=9.5°.

Preferably, in step (4), the flat fading channel includes a flat Rayleigh fading channel.

Preferably, in step (5), the bit error rate can be obtained by comparing the final output symbol stream obtained after the judgment with the input symbol stream, and the bit error rate at the optimal rotation angle θ should be lower than the bit error rate when not rotated rate value.

r_I,n和r_Q,n为接收到的第n个r_I和r_Q信号，其中

h_k,I,n和h_k,Q,n分别表示第n个h_k,I和h_k,Q值，而

和

分别表示旋转后各星座点的横纵坐标。Preferably, in step (5), the calculation method of Euclidean distance is

r _I,n and r _Q,n are the nth received r _I and r _Q signals, where

h _k,I,n and h _k,Q,n represent the nth h _k,I and h _k,Q values, respectively, and

and

respectively represent the horizontal and vertical coordinates of each constellation point after rotation.

The beneficial effects of the present invention are:

The present invention introduces constellation rotation into the equal-gain combining system, that is, the in-phase (I channel) and quadrature (Q channel) components are obtained through the rotation of the constellation diagram, and then the in-phase and quadrature components are sent through different antennas to eliminate the two The correlation between the channel components enables the transmitted signals to be independently transmitted on their respective fading channels. The method proposed in the present invention can significantly improve the performance of the modulation system based on equal gain combining, and the introduction of constellation rotation can obtain modulation diversity gain without sacrificing the bandwidth and power of the frequency band. The correlation between components, so the interleaver and deinterleaver are not needed, which can save hardware resources and reduce the complexity of system implementation. From a technical point of view, the present invention has a concise idea and is easy to implement.

Description of drawings

FIG. 1 is a block diagram of an equal gain combining system based on constellation rotation proposed by the present invention.

FIG. 2 is a comparison diagram of the bit error rate of a QPSK modulation equal-gain combining system based on constellation rotation. In the two curves in Figure 2, from top to bottom are ① the bit error rate curves of the QPSK modulation system with equal gain combining and the constellation not rotated (θ=0°); ② using equal gain combining, constellation rotation (the most The bit error rate curve of the QPSK modulation system with the optimal rotation angle θ=30.3°).

FIG. 3 is a comparison diagram of the bit error rate of the 8PSK modulation equal-gain combining system based on constellation rotation. In the two curves in Figure 3, from top to bottom are ① the bit error rate curves of the 8PSK modulation system with equal gain combining and the constellation not rotated (θ=0°); ② using equal gain combining, constellation rotation (the most The bit error rate curve of the 8PSK modulation system with the optimal rotation angle θ=9.5°).

Detailed ways

The present invention will be further described below with reference to the embodiments and the accompanying drawings, but is not limited thereto.

Example 1:

A working method of an equal-gain combining system based on constellation rotation, the present invention is introduced by taking the equal-gain combining system based on constellation rotation with the number of antennas at the receiving end being _MR = 2 as an example. The system block diagram is shown in Figure 1: First, the input data sequence is Gray-mapped to the complex frequency domain to obtain in-phase and quadrature components, namely s _I , s _Q ; then, constellation rotation is performed to obtain x _I , x _Q , and they are They are respectively transmitted through different antennas; after passing through the flat Rayleigh fading channel, the signals r _I and r _Q are obtained by equal gain combining, and finally the minimum Euclidean distance judgment is performed to obtain the output sequence.

Specific steps are as follows:

和

(1) First, the input symbol stream is Gray-mapped to the complex frequency domain; let the transmitted signal vector be s=[s ₀ ,s ₁ ,...,s _n ,...,s _N-1 ], and N is the input symbol The length of the stream, where s _n represents the constellation point corresponding to the nth signal sent, and its value is s _n =s _I,n +js _Q,n , where s _I,n and s _Q,n are respectively The real and imaginary parts of s _n represent the in-phase and quadrature components of the constellation diagram, respectively, and j represents the imaginary unit; for QPSK modulation and 8PSK modulation, the respective value ranges of s _{I, n} and s _{Q, n} are

and

(2) Rotate the signal constellation, and set the rotated transmitted signal vector to be x=[x ₀ , x ₁ ,...,x _n ,...,x _N-1 ], where x _n is the rotated The constellation point corresponding to the nth signal, its value is x _n =x _I,n +jx _Q,n . Similarly, x _I,n and x _Q,n are the real and imaginary parts of x _n , respectively. Represents the in-phase and quadrature components of the rotated constellation diagram, j represents the imaginary unit; and x _I,n and x _Q,n can be represented by s _I,n and s _Q,n , that is, x _I,n =s _I,n cosθ +s _Q,n sinθ,x _Q,n =-s _I,n sinθ+s _Q,n cosθ, θ is the rotation angle that optimizes the system bit error rate performance, the value range is [0,π/2] ; The value of the optimal rotation angle θ of QPSK modulation is θ=30.3°, and the value of the optimal rotation angle θ of 8PSK modulation is θ=9.5°.

矩阵的第1、2行表示两路发送信号，显然，发送天线数为2；(3) In order to eliminate the correlation between the two components, the two components can be subjected to independent fading, that is, the in-phase components x _I =[x _I,0 ,x _I,1 ,... ,x _I,n ,...,x _I,N-1 ] and the quadrature components x _Q =[x _Q,0 ,x _Q,1 ,...,x _Q,n ,...,x _{Q ,N-1} ]; for a more concise representation, the transmitted signal is represented by a matrix here as

The 1st and 2nd rows of the matrix represent two transmission signals. Obviously, the number of transmission antennas is 2;

的第1、2行分别表示第k对接收的信号，

的第1、2行分别为第k对信号经历的独立瑞利衰落下的独立同分布随机变量，而

是第k对信号所加的加性高斯白噪声，这里的"·"表示矩阵的点乘；计算第k对信号的加权系数

这里的"*"表示共轭，得到归一化的接收信号矢量为

那么，可以得到等增益合并器的输出信号为

(4) The receiving mode of equal gain combining is adopted at the receiving end of the signal. The steps are the same when the system applies any flat fading channel, and this embodiment takes a flat Rayleigh fading channel as an example. When the system is applied to a flat Rayleigh fading channel, let the number of receiving antennas be _MR , and each antenna needs to receive in-phase and quadrature components, which can be regarded as a pair. _MR also represents the in-phase and quadrature components, respectively. The number of diversity branches when equal-gain combining is performed; then the k-th pair of received signals can be expressed as Y _k =H _k ·X+N _k , where

The 1st and 2nd lines of , respectively represent the received signal of the kth pair,

The first and second lines of are the independent and identically distributed random variables under the independent Rayleigh fading experienced by the k-th pair of signals, and

is the additive white Gaussian noise added to the k-th pair of signals, where "·" represents the dot product of the matrix; calculate the weighting coefficient of the k-th pair of signals

Here "*" represents conjugation, and the normalized received signal vector is

Then, the output signal of the equal gain combiner can be obtained as

采用最小欧式距离准则来进行判决，判决后得到最终的输出符号流，即恢复的输入符号流。将判决后得到最终的输出符号流与输入符号流对比就可以得到误码率，在最佳旋转角度θ处的误码率应低于未旋转时的误码率值。(5) Finally, combine the output signal of the equal gain combiner

The minimum Euclidean distance criterion is used to make a decision, and the final output symbol stream, that is, the restored input symbol stream, is obtained after the decision. The bit error rate can be obtained by comparing the final output symbol stream obtained after the judgment with the input symbol stream. The bit error rate at the optimal rotation angle θ should be lower than the bit error rate value when it is not rotated.

r_I,n和r_Q,n为接收到的第n个r_I和r_Q信号，其中

h_k,I,n和h_k,Q,n分别表示第n个h_k,I和h_k,Q值，而

和

分别表示旋转后各星座点的横纵坐标。The Euclidean distance is calculated as

r _I,n and r _Q,n are the nth received r _I and r _Q signals, where

h _k,I,n and h _k,Q,n represent the nth h _k,I and h _k,Q values, respectively, and

and

respectively represent the horizontal and vertical coordinates of each constellation point after rotation.

The present invention uses the bit error rate as an index to measure system performance, and compares the method proposed by the present invention with the method without constellation rotation, and the comparison results are shown in FIGS. 2 and 3 .

In Figures 2 and 3, the method of the present invention has 2 antennas at the receiving end. It can be clearly seen that in QPSK modulation and 8PSK modulation, at the optimal rotation angle, the obtained EGC system performance is better than when the constellation is not rotated. EGC system performance.

Claims (6)

1. a working method based on the equal gain combining system of constellation rotation, is characterized in that, step is as follows: (1) First, the input symbol stream is Gray-mapped to the complex frequency domain; let the transmitted signal vector be s=[s ₀ ,s ₁ ,...,s _n ,...,s _N-1 ], and N is the input symbol The length of the stream, where s _n represents the constellation point corresponding to the nth signal sent, and its value is s _n =s _I,n +js _Q,n , where s _I,n and s _Q,n are respectively The real and imaginary parts of s _n represent the in-phase and quadrature components of the constellation diagram, respectively, and j represents the imaginary unit; (2) Rotate the signal constellation, and set the rotated transmitted signal vector to be x=[x ₀ , x ₁ ,...,x _n ,...,x _N-1 ], where x _n is the rotated The constellation point corresponding to the nth signal, its value is x _n =x _I,n +jx _Q,n . Similarly, x _I,n and x _Q,n are the real and imaginary parts of x _n , respectively. Represents the in-phase and quadrature components of the rotated constellation diagram, j represents the imaginary unit; and x _I,n and x _Q,n can be represented by s _I,n and s _Q,n , that is, x _I,n =s _I,n cosθ +s _Q,n sinθ,x _Q,n =-s _I,n sinθ+s _Q,n cosθ, θ is the rotation angle that optimizes the system bit error rate performance, the value range is [0,π/2] ; (3) In order to eliminate the correlation between the two components, make the two components experience independent fading, that is, send the in-phase components x _I =[x _I,0 ,x _I,1 ,..., through different antennas respectively x _I,n ,...,x _I,N-1 ] and the quadrature components x _Q =[x _Q,0 ,x _Q,1 ,...,x _Q,n ,...,x _{Q, N-1} ]; the transmitted signal is represented by a matrix as

The first and second rows of the matrix represent two transmission signals, preferably, the number of transmission antennas is 2; (4) The receiving mode of equal gain combining is adopted at the receiving end of the signal. When the system is applied to a flat fading channel, the number of receiving antennas is set as _MR , and each antenna needs to receive two parts in phase and quadrature respectively, which can be seen as As a pair, _MR also represents the number of diversity branches when the in-phase and quadrature components are combined with equal gain respectively; then the k-th pair of received signals can be expressed as Y _k =H _k ·X+N _k , where

The 1st and 2nd lines of , respectively represent the received signal of the kth pair,

The first and second lines of are the independent and identically distributed random variables under the independent fading experienced by the k-th pair of signals, and

is the additive white Gaussian noise added to the k-th pair of signals, where "·" represents the dot product of the matrix; calculate the weighting coefficient of the k-th pair of signals

Here "*" represents conjugation, and the normalized received signal vector is

Then, the output signal of the equal gain combiner can be obtained as

(5) Finally, combine the output signal of the equal gain combiner

The minimum Euclidean distance criterion is used to make a decision, and the final output symbol stream, that is, the restored input symbol stream, is obtained after the decision. 2. the working method of the equal-gain combining system based on constellation rotation according to claim 1, is characterized in that, in step (1), for QPSK modulation and 8PSK modulation, s _{I, n} and s _{Q, the respective values of n} The value ranges are

and

3. the working method of the equal gain combining system based on constellation rotation according to claim 1, is characterized in that, in step (2), the value of QPSK modulation optimum rotation angle θ is θ=30.3 °, and 8PSK modulation is the most The optimum rotation angle θ is θ=9.5°. 4. The working method of the equal-gain combining system based on constellation rotation according to claim 1, wherein in step (4), the flat fading channel comprises a flat Rayleigh fading channel. 5. the working method of the equal-gain combining system based on constellation rotation according to claim 1, is characterized in that, in step (5), just can obtain bit error by comparing the final output symbol stream and input symbol stream after the judgment The bit error rate at the optimal rotation angle θ should be lower than the bit error rate value when it is not rotated. 6. the working method of the equal gain combining system based on constellation rotation according to claim 1, is characterized in that, in step (5), the calculation method of Euclidean distance is

r _I,n and r _Q,n are the nth received r _I and r _Q signals, where

and h _k,Q,n represent the nth h _k,I and h _k,Q values, respectively, and

and

respectively represent the horizontal and vertical coordinates of each constellation point after rotation.

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