CN111818533A - A Design Method of Wireless Communication System Based on Smart Reflector - Google Patents

Abstract

The invention discloses a design method of a wireless communication system based on an intelligent reflecting surface, which comprises the steps that the wireless communication system comprises a base station, the intelligent reflecting surface and a user, and the design method of the wireless communication system comprises the following steps: the base station is provided with M antennas, and signals are transmitted to users after being precoded by using the channel state information of the antennas; the intelligent reflecting surface is provided with N reflecting units, and signals from the base station are reflected to a user after phase coding is carried out on the signals by utilizing channel state information of the reflecting units; and jointly designing the signal precoding of the base station and the phase coding of the intelligent reflecting surface, and optimally updating a precoding vector and a diagonal phase shift matrix to determine a user receiving signal by taking the maximum traversal capacity as a target. Therefore, the communication quality of the wireless communication system when the line-of-sight path is lost or bad can be greatly improved, and the defect of high energy consumption of the traditional relay is overcome.

Description

A Design Method of Wireless Communication System Based on Smart Reflector

technical field

The invention relates to the field of wireless communication, in particular to a method for designing a wireless communication system based on an intelligent reflective surface.

Background technique

Current fifth-generation mobile communication technologies, such as large-scale antenna technology, have enabled wireless communication systems to achieve extremely high spectral efficiency and throughput. However, the existence of obstacles on the signal propagation path will still greatly degrade the communication quality, especially for millimeter wave communication, because the path loss and penetration loss of millimeter wave are large. Aiming at this problem, the traditional solution is to add relays in places with poor signals to forward the signals. However, because the relays will digitally process the received signals, it has higher data processing capacity requirements and higher requirements. power consumption.

In recent years, the smart reflective surface technology has received extensive attention in the industry. It envisions a future scenario in which man-made buildings will become more and more intelligent, with electronic technology integrated on their surfaces for wire-free communication. Smart reflectors are relatively inexpensive artificial artifacts that reflect electromagnetic waves and modulate the phase of incident electromagnetic waves in the process, resulting in better communication performance. It is worth mentioning that the small passive reflective unit in the smart reflective surface will only adjust the phase of the incident signal without encoding, decoding and forwarding it. In the absence of line-of-sight paths, the communication quality can be greatly improved, and the coverage of millimeter-wave signals can be improved.

Existing communication systems using smart reflectors include: Patent Application Publication No. CN110830097A discloses a reflector-based active-passive reciprocal symbiosis transmission communication system, including a single-antenna transmitting base station, a plurality of independently controllable reflectors The intelligent reflector of the unit and the single-antenna active and passive cooperative receiver, the intelligent reflector is connected with the sensor; the single-antenna transmitting base station and the intelligent reflector constitute the transmitting part of the reciprocal symbiosis communication system, respectively transmitting active signals and passive signals; the single-antenna cooperative receiver Receive active and passive signals at the same time, and demodulate the active information from the base station and the passive information from the sensor connected to the smart reflective surface, wherein the passive information is indicated by the time extension of the wireless channel.

Another example is a multi-cell wireless communication method based on an intelligent reflection surface disclosed in the patent application with the application publication number of CN111181615A. The system targeted by the method includes a plurality of cooperative cells, and an intelligent reflection surface is set in the cooperative cells. There are base stations and user terminals in each cell; the method includes: the user terminal transmits pilot signals to base stations in each cooperative cell, each base station estimates and shares channel state information, acquires global channel state information, and formulates a transmit beamforming model; The intelligent reflector formulates a reflection beamforming model, and obtains the coefficients of transmit beamforming and reflection beamforming by modeling and solving, so as to form a signal that suppresses interference.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for designing a wireless communication system based on an intelligent reflective surface, aiming at the deficiencies of the prior art.

The present invention adopts following technical scheme:

A method for designing a wireless communication system based on an intelligent reflective surface, comprising the following steps:

Equipping the base station with M antennas, using the channel state information of the antennas to precode the signal and then transmitting it to the user;

The intelligent reflective surface is equipped with N reflective units, and the signal from the base station is phase-coded by using the channel state information of the reflective units and then reflected to the user;

Jointly design the signal precoding of the base station and the phase coding of the smart reflector. The design method is as follows:

The base station sends the signal s, and the user receives the signal r as:

是智能反射面的对角相移矩阵，φ_n∈[0,2π)是第n个反射单元引入的相位偏移；

是复高斯噪声，σ为高斯噪声的方差；上标H代表共轭转置；H₁，h₂，g均为莱斯信道；Among them, P is the transmit power of the signal s; f∈C ^1×M is the precoding vector of the base station, satisfying ||f|| ² =1; g∈C ^1×M is the channel between the base station and the user; H ₁ ∈C ^N×M is the channel between the base station and the smart reflector; h ₂ ∈C ^1×N is the channel between the smart reflector and the user;

is the diagonal phase shift matrix of the smart reflection surface, φ _n ∈ [0,2π) is the phase shift introduced by the nth reflection unit;

is the complex Gaussian noise, σ is the variance of the Gaussian noise; the superscript H represents the conjugate transpose; H ₁ , h ₂ , and g are all Rice channels;

For the purpose of maximum ergodic capacity, the precoding vector f and the diagonal phase shift matrix Φ are optimized and updated to determine the user received signal r.

Among them, H ₁ , h ₂ , g satisfy:

为视距路径分量，

为非视距路径分量，视距路径分量用均匀线性阵列的信道表示，令a_N(θ)＝[1,e^{j θ},…,e^j(N-1)θ]，a_M(θ)＝[1,e^jθ,…,e^j(M-1)θ]，N和M为自然数，则

θ_AoA,1表示智能反射面处天线的等效入射角，θ_AoD,1表示基站到智能反射面的等效发射角，θ_AoD,2表示智能反射面到用户的等效发射角，θ_AoD,3表示基站到用户的等效发射角，

中的每个元素均服从均值为0，方差为1的高斯分布，且相互独立。Among them, α ₁ , β ₁ , α ₂ , β ₂ , α ₃ , β ₃ are all parameters of the Rice channel,

is the line-of-sight path component,

is the non-line-of-sight path component, the line-of-sight path component is represented by a channel of a uniform linear array, let a _N (θ)=[1,e ^{j θ} ,...,e ^j(N-1)θ ], a _M (θ) =[1,e ^jθ ,...,e ^j(M-1)θ ], N and M are natural numbers, then

θ _AoA,1 represents the equivalent incident angle of the antenna at the smart reflector, θ _AoD,1 represents the equivalent emission angle from the base station to the smart reflector, θ _AoD,2 represents the equivalent emission angle from the smart reflector to the user, θ _{AoD , 3} represents the equivalent launch angle from the base station to the user,

Each element in is subject to a Gaussian distribution with mean 0 and variance 1, and is independent of each other.

Among them, in order to maximize the traversal capacity, the following optimization problems need to be solved:

||f|| ² = 1

为which traverse capacity

for

The optimization method is:

V is obtained by the singular value decomposition of matrix H, H=U∑V ^H , where

Compared with the prior art, the beneficial effects of the present invention at least include:

The method for designing a wireless communication system based on an intelligent reflecting surface provided by the present invention optimizes the precoding vector and the diagonal phase shift matrix for the purpose of maximizing the traversal capacity by jointly designing the signal precoding of the base station and the phase encoding of the intelligent reflecting surface, to determine that the user receives the signal. This can greatly improve the communication quality of the wireless communication system when the line-of-sight path is missing or poor, and overcome the disadvantage of high energy consumption of traditional relays.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative efforts.

Fig. 1 is the wireless communication system based on the intelligent reflecting surface of the present invention;

Fig. 2 is the algorithm convergence speed diagram of the embodiment of the present invention;

FIG. 3 is a performance comparison diagram of an algorithm optimization design and a random design according to an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and do not limit the protection scope of the present invention.

Figure 1 shows a wireless communication system based on an intelligent reflective surface. The wireless communication system based on an intelligent reflective surface is composed of a base station Bs, an intelligent reflective surface LIS and a user User. The base station Bs is equipped with a large-scale uniform linear array containing M antenna elements to serve a single-antenna user. Between the base station Bs and the user, User sets up an intelligent reflector containing N reflectors. The reflectors are uniform Linear array arrangement. In Figure 1, f∈C ^1×M is the beamforming vector of the base station, satisfying |f| ² =1; g∈C ^1×M is the direct channel between the base station and the user, which may be blocked by obstacles; H ₁ ∈C ^N×M is the channel between the base station and the smart reflector; h ₂ ∈C ^1×N is the channel between the smart reflector and the user; the transmitted signal is s, which satisfies E{|s| ² }=1 . Therefore, the signal r received by the user is:

是智能反射面的对角相移矩阵，φ_n∈[0,2π)是第n个反射单元引入的相位偏移；

是复高斯噪声；(·)^H代表共轭转置；where P is the transmit power;

is the diagonal phase shift matrix of the smart reflection surface, φ _n ∈ [0,2π) is the phase shift introduced by the nth reflection unit;

is complex Gaussian noise; (·) ^H stands for conjugate transpose;

H ₁ , h ₂ , and g are all Rice channels, satisfying:

为视距路径分量，

为非视距路径分量。视距路径分量用均匀线性阵列的信道表示，令a_N(θ)＝[1,e^jθ,…,e^j(N-1)θ]，则

中的每个元素均服从均值为0，方差为1的高斯分布，且相互独立。where α _i , β _i are the parameters of the Rice channel,

is the line-of-sight path component,

is the non-line-of-sight path component. The line-of-sight path component is represented by a channel of a uniform linear array, let a _N (θ)=[1,e ^jθ ,...,e ^j(N-1)θ ], then

Each element in is subject to a Gaussian distribution with mean 0 and variance 1, and is independent of each other.

In order to maximize the traversal capacity, the following optimization problems need to be solved [1]:

||f|| ² = 1

为which traverse capacity

for

So the problem [1] can be approximated as the following problem [2]:

||f|| ² = 1

For the problem [2], first

和

中的元素期望均为0，并且相互独立，可以得出：where x ₁ is a constant; E{x _i }=0 for i=2, 3, 4, 5. also because

and

The elements in are expected to be 0 and independent of each other, we can get:

It can be inferred:

Adding the above, we get:

Therefore, problem [2] is now equivalent to the following problem [3]:

||f|| ² = 1

which can be found

Therefore, problem [3] is equivalent to problem [4]:

||f|| ² = 1

Next, the problem is solved by the alternate iteration method [4], that is, Φ and f are optimized alternately in the iterative process until convergence.

Optimization of Φ: When f is fixed, the problem [4] becomes the following problem:

是复常数，where a _M (θ _AoD,1 )f ^H and

is a complex constant,

有相同的相位：Therefore, z(Φ) is a phase-adjustable complex number whose modulus has a maximum value of Nα ₂ α ₁ . So it is necessary to find a Φ to maximize the modulus of z(Φ), and at the same time let z(Φ)a _M (θ _{AoD, 1} )f ^H and

have the same phase:

Optimization of f: When Φ is fixed, the problem [4] becomes the following problem:

st||f|| ² = 1

which is equivalent to

st||f|| ² = 1

in

This problem can be solved by singular value decomposition, H = UΣV ^H (singular values in Σ are in descending order), then one can get

f _opt = V(:, 1) ^H

where V(:, 1) represents the first column of matrix V.

Joint optimization of Φ and f: Since the optimization of Φ and f are both optimal, the general problem [3] can be solved by an alternate iteration method, and the specific steps are as follows:

The performance effect of the wireless communication system design method based on the smart reflective surface of the present invention is proved by the simulation results below. The technical effect achieved by the embodiment is:

K₁＝K₂＝K_g＝2,M＝32,N＝16,SNR＝0dB，用10,000次蒙特卡洛结果进行统计平均。可以看出，算法在在5个迭代之内就能达到收敛，效率很高。Figure 2 shows the convergence speed of the alternate iterative algorithm proposed by the invention, and the simulation conditions are:

K ₁ =K ₂ =K _g =2, M=32, N=16, SNR=0 dB, statistically averaged with 10,000 Monte Carlo results. It can be seen that the algorithm can achieve convergence within 5 iterations, and the efficiency is very high.

K₁＝K₂＝K_g＝2,M＝64,SNR＝0dB。可以看出，所提出的交替迭代设计方法具有很高的性能增益。Figure 3 is a performance comparison diagram between the alternate iterative algorithm design and the random design. The simulation conditions are:

K ₁ =K ₂ =K _g =2, M=64, SNR=0dB. It can be seen that the proposed alternate iterative design method has a high performance gain.

The smart reflector-based wireless communication system design method optimizes the precoding vector and the diagonal phase shift matrix for the purpose of maximizing the ergodic capacity through the joint design of the signal precoding of the base station and the phase coding of the smart reflector to determine the user receive signal. This can greatly improve the communication quality of the wireless communication system when the line-of-sight path is missing or poor, and overcome the disadvantage of high energy consumption of traditional relays.

The above-mentioned specific embodiments describe in detail the technical solutions and beneficial effects of the present invention. It should be understood that the above-mentioned embodiments are only the most preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, additions and equivalent substitutions made within the scope shall be included within the protection scope of the present invention.

Claims (8)

1. a wireless communication system design method based on an intelligent reflection surface, comprising that the wireless communication system includes a base station, an intelligent reflection surface and a user, it is characterized in that, the wireless communication system design method comprises the following steps: Equipping the base station with M antennas, using the channel state information of the antennas to precode the signal and then transmitting it to the user; The intelligent reflective surface is equipped with N reflective units, and the signal from the base station is phase-coded by using the channel state information of the reflective units and then reflected to the user; Jointly design the signal precoding of the base station and the phase coding of the smart reflector. The design method is as follows: The base station sends the signal s, and the user receives the signal r as:

Among them, P is the transmit power of the signal s; f∈C ^1×M is the precoding vector of the base station, satisfying ||f|| ² =1; g∈C ^1×M is the channel between the base station and the user; H ₁ ∈C ^N×M is the channel between the base station and the smart reflector; h ₂ ∈C ^1×N is the channel between the smart reflector and the user;

is the diagonal phase shift matrix of the smart reflection surface, φ _n ∈ [0,2π) is the phase shift introduced by the nth reflection unit;

is the complex Gaussian noise, σ is the variance of the Gaussian noise; the superscript H represents the conjugate transpose; H ₁ , h ₂ , and g are all Rice channels; For the purpose of maximum ergodic capacity, the precoding vector f and the diagonal phase shift matrix Φ are optimized and updated to determine the user received signal r. 2. The method for designing a wireless communication system based on an intelligent reflecting surface as claimed in claim 1, wherein H ₁ , h ₂ , g satisfy:

Among them, α ₁ , β ₁ , α ₂ , β ₂ , α ₃ , β ₃ are all parameters of the Rice channel,

is the line-of-sight path component,

is the non-line-of-sight path component, the line-of-sight path component is represented by a channel of a uniform linear array, let a _N (θ)=[1,e ^jθ ,...,e ^{j(N -1)θ} ], a _M (θ)= [1,e ^jθ ,…,e ^j(M-1)θ ], N and M are natural numbers, then

θ _AoA,1 represents the equivalent incident angle of the antenna at the smart reflector, θ _AoD,1 represents the equivalent emission angle from the base station to the smart reflector, θ _AoD,2 represents the equivalent emission angle from the smart reflector to the user, θ _{AoD , 3} represents the equivalent launch angle from the base station to the user,

Each element in is subject to a Gaussian distribution with mean 0 and variance 1, and is independent of each other. 3. The method for designing a wireless communication system based on an intelligent reflective surface as claimed in claim 1, characterized in that, for the purpose of maximum traversal capacity, the following optimization problem needs to be solved [1]:

||f|| ² = 1 which traverse capacity

for

4. The method for designing a wireless communication system based on an intelligent reflective surface as claimed in claim 3, wherein the problem [1] can be approximated as the following problem [2]:

||f|| ² = 1 For the problem [2], first

where x ₁ is a constant; for i=2, 3, 4, 5, E{x _i }=0, and because

and

The elements in are expected to be 0 and independent of each other, we can get:

It can be inferred:

Adding the above, we get:

5. The method for designing a wireless communication system based on an intelligent reflective surface as claimed in claim 4, wherein the current problem [2] is equivalent to the following problem [3]:

||f|| ² = 1 which found

6. The method for designing a wireless communication system based on an intelligent reflective surface as claimed in claim 5, wherein the problem [3] is equivalent to the problem [4]:

||f|| ² = 1 Next, the problem is solved by the alternate iteration method [4], that is, Φ and f are optimized alternately in the iterative process until convergence. 7. The method for designing a wireless communication system based on an intelligent reflective surface as claimed in claim 6, wherein the optimization of Φ: when f is fixed, the problem [4] becomes the following problem:

where a _M (θ _AoD,1 )f ^H and

is a complex constant,

Therefore, z(Φ) is a complex number with adjustable phase, and the maximum value of its modulus is Nα ₂ α ₁ , so it is necessary to find a Φ to maximize the modulus of z(Φ), and at the same time let z(Φ)a _M (θ _{AoD ,1} )f ^H and

have the same phase:

Optimization of f: When Φ is fixed, the problem [4] becomes the following problem:

st||f|| ² = 1 which is equivalent to

st||f|| ² = 1 in

This problem can be solved by singular value decomposition, H = U∑V ^H (singular values in ∑ are in descending order), then one can get f _opt = V(:, 1) ^H where V(:,1) represents the first column of matrix V. 8. the wireless communication system design method based on intelligent reflecting surface as claimed in claim 7 is characterized in that, the concrete steps of the joint optimization of Φ and f are as follows:

V is obtained by the singular value decomposition of matrix H, H=U∑V ^H , where

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