CN115314087A - Phase shift modulation and performance analysis method for intelligent reflector active information transmission - Google Patents

Abstract

The invention discloses a phase deviation modulation and performance analysis method for active information transmission of an intelligent reflector, which comprises the following steps: firstly, establishing a phase offset modulation system model for active information transmission of an intelligent reflecting surface; then calculating the optimal passive beam forming scheme under a given channel; then, on the basis of the optimal phase, superposing specific phase offset to transmit additional information; then, demodulating signals sent by the base station and signals sent by the RIS by using a maximum likelihood criterion at a receiving end; the performance analysis method comprises the following steps: and approximating an equivalent channel by using a central limit theorem, then calculating a moment mother function of demodulation errors under the maximum likelihood criterion, and finally calculating average paired error probability and bit error rate by using the approximation of a Q function. The invention can realize the error-free transmission of more bit information and realize higher spectral efficiency by utilizing the phase shift modulation and performance analysis method based on the intelligent reflecting surface.

Description

Phase shift modulation and performance analysis of an intelligent reflector for active information transmission method

technical field

The invention relates to the technical field of communication based on an intelligent transmitting surface, in particular to a phase offset modulation and performance analysis method for active information transmission on an intelligent reflecting surface.

Background technique

Intelligent reflective surface (RIS) technology is an emerging technology with broad application prospects and facing the future sixth generation mobile communication (6G). By using a large number of integrated low-cost passive reflection units, the phase of the incident signal is dynamically adjusted, the channel environment is reshaped, and the existing communication system is assisted to achieve low-energy, high-speed data transmission. Because it has no energy for sending and receiving signals and further signal processing, a large number of existing researches mainly use RIS as a passive device to enhance the signal-to-noise ratio of the receiving end, while ignoring the ability of using RIS for active information transmission.

The use of RIS for active information transmission can achieve higher data transmission rates and support the needs of future networks. Some existing schemes propose to achieve additional information transmission through the switch of the RIS reflection unit, or select the phase of the reflection unit orthogonal to each other, but it seriously affects the energy of the received signal, and the number of information transmitted at the same time is limited, and the RIS cannot be fully stimulated. Potential for deployment. Therefore, it is necessary to consider a better RIS information modulation method to obtain a higher rate and channel capacity.

Contents of the invention

In view of this, the purpose of the present invention is to provide a phase offset modulation and performance analysis method for active information transmission on an intelligent reflective surface, to achieve reliable transmission of more information through RIS, and to improve the communication rate of the system in practical applications. technical problem.

In order to achieve the above object, the present invention adopts the following technical solutions:

A phase offset modulation and performance analysis method for active information transmission on an intelligent reflective surface, the method comprising:

Step S1, for a downlink communication system, establish a phase shift modulation system model based on the active information transmission of the smart reflective surface, the downlink communication system includes: a base station side and a receiving side, and a smart reflective surface for auxiliary communication, wherein , the smart reflector superimposes a phase offset on the signal sent by the base station side, so as to improve the spectral efficiency of the system;

Step S2. For the phase shift modulation system model constructed in step S1, construct an optimal passive beamforming scheme under the condition of maximizing the signal-to-noise ratio at the receiving side;

Step S3, using the phase offset to modulate additional information at the smart reflector, which includes: keeping the precoding vector at the base station side unchanged, changing the phase shift configured at the RIS, and superimposing the phase offset on the original phase to realize the transmission of additional information ;

Step S4, according to the acquired signal, the receiving side uses the maximum likelihood criterion to demodulate the symbol sent by the base station side and the additional information transmitted by the smart reflector to obtain an equivalent symbol vector, wherein the expression of the equivalent symbol vector including equivalent channels;

Step S5, using the central limit theorem to approximate the equivalent channel with a Gaussian random variable;

Step S6, calculating the moment generating function of the demodulation error;

Step S7, using the approximate expression of the moment generating function and the Q function to calculate the average pairwise error probability, and calculate the approximate expression of the bit error rate.

Further, in the step S1, the phase shift modulation system model is obtained as follows:

For the downlink communication system, the following definitions and settings are made, specifically including:

h _r ＝[h _r,1 ,…,h _r,N ] ^T represents the channel between the smart reflector and the user;

G represents the channel between the smart reflector and the base station. Due to the existing obstacles, the direct link between the user and the base station is ignored;

The channel between the smart reflector and the base station is expressed as:

G=ab ^H

In this formula, vectors a and b are known array steering vectors respectively, and the modulus of the vector elements is 1, and ( ) ^H represents the conjugate transposition of the vector;

The channel between the smart reflector and the user is modeled as a Rayleigh channel due to the existence of abundant scattering, the elements of h _r are independent of each other, and the nth element h _r,n obeys a circular symmetric complex Gaussian distribution with a mean of 0 and a variance of 1 ;

The symbol sent by the base station is s, using M-order quadrature amplitude modulation, satisfying that the average transmit power is P, the noise of the system is z, and obeys a circular symmetric complex Gaussian distribution with a mean value of 0 and a variance of ^σ2 .

Further, the step S2 includes:

和最优预编码w^*，如下所示：Configure the phase θ _n at the nth reflective unit of the smart reflector and the precoding vector w at the base station as the optimal phase

and the optimal precoding w ^* as follows:

为对角线元素的对角阵,[·]_n表示向量的第n个元素，||·||₂表示向量2范数。In the above two formulas, the phase shift matrix Θ ^* is given by

is a diagonal matrix of diagonal elements, [·] _n represents the nth element of the vector, and ||·|| ₂ represents the 2-norm of the vector.

Further, in the step S3, at the nth reflective unit of the smart reflective surface, the phase after superimposing the phase offset is expressed as:

In this formula, k is the RIS modulation information, which is selected from {0,1...,K} according to the required modulation information, K is the modulation order, and Δθ is the minimum step size of the fixed phase offset;

Wherein, the RIS is divided into L sub-blocks, each sub-block has the same number of reflection units, and the reflection units therein adopt the same phase offset.

Further, in the step S4, at the receiving side, the received signal of the user is expressed as:

k_l表示在第l个子块处所调制的信息，h为等价信道，定义为

为RIS的第l个子块；In this formula, x is the equivalent sending symbol vector, defined as

k _l represents the information modulated at the lth sub-block, h is the equivalent channel, defined as

is the lth sub-block of RIS;

为：The equivalent sign vector obtained by demodulation using the maximum likelihood criterion

for:

Further, the step S5 includes:

能够近似服从正态分布

则中均值μ_h和方差

分别计算为：because

Can approximately obey the normal distribution

Then mean μ _h and variance

are calculated as:

Further, the step S6 specifically includes:

再定义符号误差为

分别定义其实部δ_r和虚部δ_i为：The demodulation error λ is defined as

Redefine the sign error as

Define the real part δ _r and the imaginary part δ _i respectively as:

的实部和虚部；In the above two formulas, d _{l, r} and d _{l, i} are respectively

The real and imaginary parts of ;

The real part δ _r and the imaginary part δ _i are approximated by a normal distribution, respectively subject to:

将λ表征为高斯变量Δ的二次型，即λ＝Δ^TΔ；Define signed error extension vector

Characterize λ as the quadratic form of Gaussian variable Δ, that is, λ=Δ ^T Δ;

Calculate the mean vector m and covariance matrix C of the Gaussian variable Δ as:

表示为：in,

Expressed as:

为：When det(C)≠0, det( ) is the determinant of the matrix, and the moment generating function calculated separately

for:

Among them, I is the identity matrix, and t is the independent variable of the moment generating function.

计算

为：When det(C)=0, one of δ _r and δ _i is 0, or two random variables are linearly correlated; if one of δ _r and δ _i is not 0, it is δ _x ≠ 0, another ratio to δ _x is recorded as c, and its mean and variance are recorded as μ _x and

calculate

for:

Further, in the step S7, the average pairwise error probability is calculated as follows:

The approximate formula of the Q function is:

计算为：The average pairwise error probability

Calculated as:

Further, in the step S7, the calculated approximate bit error rate is:

为将等价符号x估计为

出现错误的比特数。In this formula,

To estimate the equivalent symbol x as

The number of bits in error occurred.

The beneficial effects of the present invention are:

By superimposing a specific phase offset on the optimal passive beamforming phase, the present invention realizes the transmission of additional information while ensuring the gain of passive beamforming, and realizes high-order modulation, which can transmit more information . For the proposed modulation scheme, the present invention proposes an approximation method based on the central limit theorem, which can concisely obtain the approximate expression of the bit error rate, can accurately approximate the actual bit error rate, and has guiding significance for actual parameter selection, etc. .

The invention proposes an efficient information modulation scheme and an effective bit error rate analysis method to obtain higher spectrum efficiency.

Description of drawings

FIG. 1 is a schematic diagram of an actual application scenario of the downlink communication system in Embodiment 1;

FIG. 2 is a schematic flowchart of a phase offset modulation and performance analysis method for active information transmission on an intelligent reflective surface provided in Embodiment 1;

FIG. 3 is a schematic diagram of the bit error rate performance of the modulation method provided by the embodiment 1 and the approximation of the bit error rate proposed by the embodiment 1.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

Referring to Figures 1-3, this embodiment provides a phase offset modulation and performance analysis method for active information transmission on a smart reflector. In this method, a specific phase offset is superimposed on the optimal passive beamforming phase, The transmission of additional information is realized while ensuring the passive beamforming gain; the bit error rate is approximated with the help of the central limit theorem and the approximation of the Q function. Before explaining the method in detail, the following explanation is given:

RIS: Smart Reflective Surface;

BER: bit error rate;

QAM: Quadrature Amplitude Modulation.

The specific flow of the method is shown in Figure 1, and specifically includes the following steps:

Step S1, for a downlink communication system, establish a phase shift modulation system model based on the active information transmission of the smart reflective surface, the downlink communication system includes: a base station side and a receiving side, and a smart reflective surface for auxiliary communication, wherein , the smart reflector superimposes a phase offset on the signal sent by the base station side, so as to improve the spectral efficiency of the system;

Specifically, in this embodiment, the step S1 includes:

First, as shown in Figure 1, consider a downlink communication system, which includes: a base station equipped with N _t antennas, a user equipped with a single antenna, and a smart phone with N reflection units for auxiliary communication Reflective surface.

Then, the following definitions and settings are made for the downlink communication system, specifically including:

h _r ＝[h _r,1 ,…,h _r,N ] ^T represents the channel between the smart reflector and the user;

G represents the channel between the smart reflector and the base station. Due to the existing obstacles, the direct link between the user and the base station is ignored;

The smart reflective surface is deployed within a range with a strong line-of-sight link with the base station, and the channel between the smart reflective surface and the base station can be expressed as:

G=ab ^H

In this formula, the vectors a and b are known array steering vectors respectively, and the modulus of the vector elements is 1, and (·) ^H represents the conjugate transposition of the vector.

The channel between the smart reflector and the user is modeled as a Rayleigh channel due to the existence of abundant scattering, the elements of h _r are independent of each other, and the nth element h _r,n obeys a circular symmetric complex Gaussian distribution with a mean of 0 and a variance of 1 .

The symbol sent by the base station is s, and the M-order quadrature amplitude modulation (QAM) is adopted to meet the requirement that the average transmit power is P. The noise of the system is z, which obeys a circular symmetric complex Gaussian distribution with mean 0 and variance σ ² .

At the RIS, by superimposing a specific phase offset on the basis of the original optimal phase, the transmission of additional information is realized and the spectral efficiency of the system is improved.

Step S2, for the phase shift modulation system model constructed in step S1, under the condition of maximizing the signal-to-noise ratio at the receiving side, select the optimal RIS reflection phase shift and the optimal precoding vector at the base station side, and construct the optimal Excellent passive beamforming scheme.

Specifically, in this embodiment, the step S2 includes:

和最优预编码w^*，如下所示：Configure the phase θ _n at the nth reflection unit of the RIS and the precoding vector w at the base station to configure the optimal phase

and the optimal precoding w ^* as follows:

为对角线元素的对角阵,[·]_n表示向量的第n个元素，||·||₂表示向量2范数；In the above two formulas, the phase shift matrix Θ ^* is given by

is a diagonal matrix of diagonal elements, [·] _n represents the nth element of the vector, ||·|| ₂ represents the vector 2 norm;

Step S3, using the phase offset to modulate the additional information at the RIS, which includes: keeping the precoding vector at the base station side unchanged, changing the phase shift configured at the RIS, and superimposing the phase offset on the original phase to realize the transmission of additional information.

Specifically, in this embodiment, at the nth reflective unit of the RIS, the phase after superimposing the phase offset is expressed as:

In this formula, k is the RIS modulation information, which is selected from {0,1...,K} according to the required modulation information, K is the modulation order, and Δθ is the minimum step size of the fixed phase offset. Consider dividing the RIS into L sub-blocks, each sub-block has the same number of reflection units, and the reflection units in it adopt the same phase offset.

Step S4, according to the acquired signal, the receiving side uses the maximum likelihood criterion to demodulate the symbols sent by the base station and the additional information transmitted by the RIS to obtain an equivalent symbol vector, wherein the expression of the equivalent symbol vector includes price channel;

Specifically, in this embodiment, the signal received by the user is expressed as:

k_l表示在第l个子块处所调制的信息，h为等价信道，定义为

为RIS的第l个子块；In this formula, x is the equivalent sending symbol vector, defined as

k _l represents the information modulated at the lth sub-block, h is the equivalent channel, defined as

is the lth sub-block of RIS;

为：The equivalent sign vector obtained by demodulation using the maximum likelihood criterion

for:

Step S5, using the central limit theorem to approximate the equivalent channel with Gaussian random variables.

Specifically, in this embodiment, the step S5 includes:

可以近似服从正态分布

则中均值μ_h和方差

分别计算为：because

Can approximately obey the normal distribution

Then mean μ _h and variance

are calculated as:

Step S6, calculating the moment generating function of the demodulation error.

Specifically, in this embodiment, the above step S6 includes:

再定义符号误差为

分别定义其实部δ_r和虚部δ_i为：The demodulation error λ is defined as

Redefine the sign error as

Define the real part δ _r and the imaginary part δ _i respectively as:

的实部和虚部；将实部δ_r和虚部δ_i用正态分布近似，分别服从：In the above two formulas, d _{l, r} and d _{l, i} are respectively

The real part and the imaginary part; the real part δ _r and the imaginary part δ _i are approximated by normal distribution, respectively obeying:

将λ表征为高斯变量Δ的二次型，即λ＝Δ^TΔ。计算高斯变量Δ的均值向量m和协方差矩阵C为：Define signed error extension vector

Characterize λ as the quadratic form of the Gaussian variable Δ, ie λ=Δ ^T Δ. Calculate the mean vector m and covariance matrix C of the Gaussian variable Δ as:

表示为：in,

Expressed as:

为：When det(C)≠0, det( ) is the determinant of the matrix, and the moment generation function that can be calculated separately

for:

In this formula, I is the identity matrix, and t is the independent variable of the moment generating function.

计算

为：When det(C)=0, one of δ _r and δ _i is 0, or one is the linear product of the other. Set any one of δ _r and δ _i that is not 0 as δ _x ≠ 0, the ratio of the other to δ _x is denoted as c, and its mean and variance are denoted as μ _x and

calculate

for:

。

.

并计算得到误比特率P_b的近似表达式。Step S7, using the approximate expression of the moment generator function and the Q function to calculate the average pairwise error probability

And calculate the approximate expression of bit error rate P _b .

Specifically, in this embodiment, the step S7 includes:

The approximate formula of the Q function is:

Then the average pairwise error probability can be calculated as:

Further, calculate the approximate bit error rate:

为将等价符号x估计为

出现错误的比特数。In this formula,

To estimate the equivalent symbol x as

The number of bits in error occurred.

As shown in Figure 2, the main process of this embodiment is to establish a model first, then obtain the optimal passive beamforming scheme, superimpose a specific phase offset on the basis of the optimal phase shift to achieve additional information transmission, and then receive The terminal uses the maximum likelihood criterion for demodulation. Further, the equivalent channel is approximated by using the central limit theorem, and then the moment generating function of the demodulation error λ is calculated, and finally the average pairwise error probability and the approximate bit error rate are obtained by combining the approximate formula of the Q function.

In order to verify the effect of this embodiment, a simulation experiment is carried out, the number of transmitting antennas is set to 8, and the number of RIS transmitting units is 128, which are divided into two sub-blocks. As shown in FIG. 3 , the modulation method proposed in this embodiment can realize effective transmission of information, and the theoretical approximation of the bit error rate proposed can effectively approximate the real bit error rate.

To sum up, the present invention uses the phase shift modulation and performance analysis method based on the intelligent reflector to realize error-free transmission of more bits of information and achieve higher spectral efficiency.

The parts of the present invention that are not described in detail are known technologies of those skilled in the art.

The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (9)

1. A phase offset modulation and performance analysis method for active information transmission on an intelligent reflector, characterized in that the method comprises: Step S1, for a downlink communication system, establish a phase shift modulation system model based on the active information transmission of the smart reflective surface, the downlink communication system includes: a base station side and a receiving side, and a smart reflective surface for auxiliary communication, wherein , the smart reflector superimposes a phase offset on the signal sent by the base station side, so as to improve the spectral efficiency of the system; Step S2. For the phase shift modulation system model constructed in step S1, construct an optimal passive beamforming scheme under the condition of maximizing the signal-to-noise ratio at the receiving side; Step S3, using the phase offset to modulate additional information at the smart reflector, which includes: keeping the precoding vector at the base station side unchanged, changing the phase shift configured at the RIS, and superimposing the phase offset on the original phase to realize the transmission of additional information ; Step S4, according to the acquired signal, the receiving side uses the maximum likelihood criterion to demodulate the symbol sent by the base station side and the additional information transmitted by the smart reflector to obtain an equivalent symbol vector, wherein the expression of the equivalent symbol vector including equivalent channels; Step S5, using the central limit theorem to approximate the equivalent channel with a Gaussian random variable; Step S6, calculating the moment generating function of the demodulation error; Step S7, using the approximate expression of the moment generating function and the Q function to calculate the average pairwise error probability, and calculate the approximate expression of the bit error rate. 2. The phase shift modulation and performance analysis method for active information transmission on an intelligent reflective surface according to claim 1, characterized in that, in the step S1, the phase shift modulation system model is obtained as follows : For the downlink communication system, the following definitions and settings are made, specifically including: h _r ＝[h _r,1 ,…,h _r,N ] ^T represents the channel between the smart reflector and the user; G represents the channel between the smart reflector and the base station. Due to the existing obstacles, the direct link between the user and the base station is ignored; The channel between the smart reflector and the base station is expressed as: G=ab ^H In this formula, vectors a and b are known array steering vectors respectively, and the modulus of the vector elements is 1, and ( ) ^H represents the conjugate transposition of the vector; The channel between the smart reflector and the user is modeled as a Rayleigh channel due to the existence of abundant scattering, the elements of h _r are independent of each other, and the nth element h _r,n obeys a circular symmetric complex Gaussian distribution with a mean of 0 and a variance of 1 ; The symbol sent by the base station is s, using M-order quadrature amplitude modulation, satisfying that the average transmit power is P, the noise of the system is z, and obeys a circular symmetric complex Gaussian distribution with a mean value of 0 and a variance of ^σ2 . 3. The phase shift modulation and performance analysis method for active information transmission on an intelligent reflective surface according to claim 2, wherein said step S2 comprises: Configure the phase θ _n at the nth reflective unit of the smart reflector and the precoding vector w at the base station as the optimal phase

and the optimal precoding w ^* as follows:

In the above two formulas, the phase shift matrix Θ ^* is given by

is a diagonal matrix of diagonal elements, [·] _n represents the nth element of the vector, and ||·|| ₂ represents the 2-norm of the vector. 4. The phase shift modulation and performance analysis method for active information transmission of an intelligent reflective surface according to claim 3, characterized in that, in the step S3, at the nth reflective unit of the intelligent reflective surface, superimposed The phase after the phase offset is expressed as:

In this formula, k is the RIS modulation information, which is selected from {0,1...,K} according to the required modulation information, K is the modulation order, and Δθ is the minimum step size of the fixed phase offset; Wherein, the RIS is divided into L sub-blocks, each sub-block has the same number of reflection units, and the reflection units therein adopt the same phase offset. 5. The phase shift modulation and performance analysis method of active information transmission of a kind of intelligent reflective surface according to claim 4, characterized in that, in said step S4, at the receiving side, the user's received signal is expressed as:

In this formula, x is the equivalent sending symbol vector, defined as

k _l represents the information modulated at the lth sub-block, h is the equivalent channel, defined as

is the lth sub-block of RIS; The equivalent sign vector obtained by demodulation using the maximum likelihood criterion

for:

6. The phase shift modulation and performance analysis method for active information transmission on an intelligent reflective surface according to claim 5, wherein said step S5 comprises: because

Can approximately obey the normal distribution

Then mean μ _h and variance

are calculated as:

7. A phase shift modulation and performance analysis method for active information transmission on an intelligent reflective surface according to claim 6, wherein the step S6 specifically includes: The demodulation error λ is defined as

Redefine the sign error as

Define the real part δ _r and the imaginary part δ _i respectively as:

In the above two formulas, d _{l, r} and d _{l, i} are respectively

The real and imaginary parts of ; The real part δ _r and the imaginary part δ _i are approximated by a normal distribution, respectively subject to:

Define signed error extension vector

Characterize λ as the quadratic form of Gaussian variable Δ, that is, λ=Δ ^T Δ; Calculate the mean vector m and covariance matrix X of the Gaussian variable Δ as:

in,

Expressed as:

When det(C)≠0, det( ) is the determinant of the matrix, and the moment generating function calculated separately

for:

Among them, I is the identity matrix, and t is the independent variable of the moment generating function. When det(C)=0, one of δ _r and δ _i is 0, or two random variables are linearly correlated; if one of δ _r and δ _i is not 0, it is δ _x ≠ 0, another ratio to δ _x is recorded as c, and its mean and variance are recorded as μ _x and

calculate

for:

8. The phase offset modulation and performance analysis method for active information transmission on an intelligent reflective surface according to claim 7, wherein in the step S7, the average pairwise error probability is calculated as follows arrive: The approximate formula of the Q function is:

The average pairwise error probability

Calculated as:

9. The phase shift modulation and performance analysis method of active information transmission on a smart reflective surface according to claim 8, wherein, in the step S7, the calculated approximate bit error rate is:

In this formula,

To estimate the equivalent symbol x as

The number of bits in error occurred.

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