CN112260739B - Information transmission method for beam forming based on intelligent reflection surface - Google Patents

Information transmission method for beam forming based on intelligent reflection surface Download PDF

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CN112260739B
CN112260739B CN202010985106.7A CN202010985106A CN112260739B CN 112260739 B CN112260739 B CN 112260739B CN 202010985106 A CN202010985106 A CN 202010985106A CN 112260739 B CN112260739 B CN 112260739B
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intelligent
reflection
phase shift
reflection surface
information
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CN112260739A (en
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温淼文
林少娥
齐晓敏
郑倍雄
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South China University of Technology SCUT
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/04013—Intelligent reflective surfaces
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
    • H04B7/0842—Weighted combining
    • H04B7/086—Weighted combining using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/36—Modulator circuits; Transmitter circuits
    • H04L27/361—Modulation using a single or unspecified number of carriers, e.g. with separate stages of phase and amplitude modulation

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Abstract

The invention discloses an information transmission method for beam forming based on an intelligent reflection surface, which is applied to a wireless communication system with the assistance of orthogonal reflection modulation of the intelligent reflection surface and comprises the following steps: s1, carrying out orthogonal reflection modulation on information by element unit grouping of the intelligent reflection surface; s2, introducing a beam forming technology at a transmitting end; s3, jointly optimizing a beam forming coefficient of a transmitting end and reflection phase shift of an intelligent reflection surface; s4, analyzing the whole wireless communication system and optimizing the detection performance of the system; and S5, demodulating the information sent by the sending terminal and the intelligent reflection surface modulation information at the receiving terminal. The technology for grouping the intelligent reflection surface element units to perform orthogonal reflection modulation and shaping the signal beam at the sending end can additionally transmit certain bit information and improve the spectrum efficiency of a wireless communication system.

Description

Information transmission method for beam forming based on intelligent reflection surface
Technical Field
The invention relates to the technical field of wireless communication, in particular to a method for assisting a wireless communication system in beam forming and information transmission by using an intelligent reflection surface orthogonal reflection modulation mode.
Background
In order to further improve the data transmission rate and communication service quality of future releases of fifth generation wireless networks or future wireless networks, researchers have been exploring more flexible and competitive physical layer solutions. The intelligent reflecting surface is a promising technical scheme in the field of future wireless communication due to the fact that the intelligent reflecting surface is low in cost, low in energy consumption, convenient to deploy and capable of intelligently controlling the reflection phase shift of an incident signal.
Beamforming is a technique that uses a beamformer to control the phase and signal amplitude of each transmitting device to obtain the desired constructive and destructive interference patterns at the receiving end. The signals received by the different receivers are combined in a suitable manner to obtain the desired radiation pattern of the signals. In the wireless system assisted by the intelligent reflecting surface, when a direct channel between a sending end and a receiving end is blocked, the antenna gain from the sending end to the intelligent reflecting surface can be improved by adopting a beam forming technology at the sending end.
On the other hand, with the increase of applicable scenes of the intelligent reflection surface, information such as the ambient environment state collected by the intelligent reflection surface through a sensor of the intelligent reflection surface is continuously increased, and how to transmit the information through the intelligent reflection surface also becomes a research hotspot. In order to transmit the information collected by the intelligent reflective surface, researchers have proposed transmitting the information by controlling the switching state of the intelligent reflective surface element units, or grouping the intelligent reflective surface element units and leaving a certain number of element units in each group in an off state. In both schemes, due to the presence of the smart reflective surface element unit in the off state, the whole smart reflective surface cannot obtain the whole gain, and the energy of the received signal is weakened. And the uncertainty of the change in the switching state of the smart reflective surface element cells also increases the complexity of the wireless communication system.
Disclosure of Invention
The present invention is directed to solve the above-mentioned defects in the prior art, and provides a method for improving the spectrum efficiency of a wireless communication system in an intelligent reflection surface-assisted mimo wireless system by using an orthogonal reflection modulation scheme of an intelligent reflection surface to transmit information and combining with a beam forming technique of a transmitting end.
The purpose of the invention is achieved by adopting the following technical scheme:
an information transmission method based on intelligent reflection surface for beam forming is applied to a wireless communication system with the assistance of orthogonal reflection modulation of the intelligent reflection surface, the wireless communication system comprises at least one base station with N transmitting antennas, at least one intelligent reflection surface adopting preset grouping and a user, the intelligent reflection surface is provided with L0An element unit of L0The element units are divided into L groups, and the method for beamforming and information transmission comprises the following steps:
s1, randomly dividing the L-component elements of the intelligent reflection surface into two parts, wherein the p-component elements contained in the first part adjust the reflection phase shift to the optimal reflection phase shift, so that the phase shifts of signals reflected by the elements of the first part are consistent; the L-p group elements contained in the second part adjust the reflection phase shift to the optimal reflection phase shift and add pi/2 to ensure that the phase shift of the signals reflected by the elements of the second part is orthogonal to the phase shift of the signals reflected by the elements of the first part, and the information sensed by the intelligent reflecting surface is embedded into the group elements of the intelligent reflecting surface through orthogonal reflection modulation;
s2, introducing a beam forming technology at the transmitting end, and controlling the phase and amplitude of the transmitted signal by using a beam former at the transmitting end to enable the signal energy received by the receiving end to be maximum;
s3, jointly optimizing a beam forming coefficient of a transmitting end and reflection phase shift of an intelligent reflection surface;
s4, analyzing the whole wireless communication system, and eliminating the random rotation phase introduced by the channel from the sending end to the receiving end before detecting the received signal;
and S5, demodulating the information sent by the sending terminal and the intelligent reflection surface modulation information at the receiving terminal.
Further, given L and p, the total number of grouping schemes of the L groups of elements of the intelligent reflecting surface is calculated by a total probability formula, and the total number is
Figure GDA0003240947550000031
In a grouping manner, i.e. having at most
Figure GDA0003240947550000032
The bit information is additionally transmitted by grouping element units of the intelligent reflecting surface
Figure GDA0003240947550000033
An index representing p-group grouping elements of the first part,
Figure GDA0003240947550000034
an index representing the remaining L-p sets of elements, and the reflection phase shift of the L-th set of smart reflective surfaces is expressed as:
Figure GDA0003240947550000035
wherein, thetalExpressing the optimal reflection phase shift of the group element of the intelligent reflecting surface I, and expressing the group L of the intelligent reflecting surface LAn index of the element.
Further, in a single-input single-output wireless communication system, the process of embedding the perception information of the intelligent reflection surface into the grouping elements of the intelligent reflection surface through orthogonal reflection modulation is as follows:
the reflection phase shift of the smart reflective surface quadrature reflection modulation is expressed as:
Figure GDA0003240947550000036
wherein e is a natural constant, and the natural constant is,
Figure GDA0003240947550000037
s represents a coefficient obtained by simplifying the reflection phase shift of the orthogonal reflection modulation of the intelligent reflection surface, theta represents the optimal reflection phase shift of each group element of the intelligent reflection surface, and the value of s of the group element of the ith group of the intelligent reflection surface is expressed as:
Figure GDA0003240947550000038
after information is embedded into the grouping elements of the intelligent reflection surface, the signal from the sending end to the receiving end through the intelligent reflection surface is represented as follows:
y＝θH hx+n＝sHdiag(θH)hx+n；
wherein,hrepresenting a cascade channel from a transmitting end to a receiving end via an intelligent reflective surface, x representing symbol information transmitted by the transmitting end, n representing noise of the system, and
Figure GDA0003240947550000039
is additive white Gaussian noise, and obeys a mean value of 0 and a variance of N0Is normally distributed.
Further, the step S2 is as follows:
the signal received by the user at the receiving end is represented as:
Figure GDA0003240947550000041
wherein,
Figure GDA0003240947550000042
representing a channel from an r-th antenna of a transmitting end to an l-th component group element of the intelligent reflection surface, wherein r is 1, 2. 1,2, L,G lrepresenting the channel of the l-th group of packet elements of the intelligent reflecting surface to the receiving end,
Figure GDA0003240947550000043
indicating the channel from the transmitting end to the receiving end,
Figure GDA0003240947550000044
representing active beamforming coefficients of a transmitting end, wherein symbols
Figure GDA0003240947550000045
Representing a complex set with energy P;
the signal received by the user at the receiving end is further represented as:
Figure GDA0003240947550000046
wherein,
Figure GDA0003240947550000047
representing a cascade channel from the transmitting end to the receiving end via the l-th group of packet elements of the intelligent reflective surface,
Figure GDA0003240947550000048
representing a cascade channel from a sending end to a receiving end through an intelligent reflecting surface;
the signal-to-noise ratio of a wireless communication system is expressed as:
Figure GDA0003240947550000049
wherein it is assumed that the base station is knownHAnd
Figure GDA00032409475500000410
the channel state information of (a).
Further, in step S3, the design of the orthogonal reflection modulation of the smart reflective surface is extended to a multi-input single-output wireless communication system and is based onHAnd
Figure GDA00032409475500000411
the channel state information jointly optimizes a beam forming coefficient w of a sending end and a reflection phase shift theta of an intelligent reflection surface, the energy of signals received by a receiving end is maximized through optimization, and the optimization process is as follows:
the problem of jointly optimizing the beam forming coefficient of the transmitting end and the reflection phase shift of the intelligent reflection surface is expressed as follows:
Figure GDA0003240947550000051
from the nature of the triangle inequality, the following conclusions are drawn:
Figure GDA0003240947550000052
the above expression is only given in
Figure GDA0003240947550000053
The time equal sign is established;
fixing the beamforming coefficient w of the transmitting end, the optimization problem of the wireless communication system is expressed as:
Figure GDA0003240947550000054
obtaining an optimal solution of the reflection phase shift of the intelligent reflection surface according to the expression, namely
Figure GDA0003240947550000055
First group of Intelligent reflexesThe optimal reflected phase shift of a surface is expressed as:
Figure GDA0003240947550000056
giving an intelligent reflection surface grouping element reflection phase shift theta, and obtaining an optimal solution of a beam forming coefficient according to a maximum ratio transmission principle, wherein the expression is as follows:
Figure GDA0003240947550000057
after repeated iterations, until the expression is reached
Figure GDA0003240947550000058
The added value of (a) is smaller than a given arbitrary small positive number or the maximum number of iterations are completed, and finally the optimal solution of the beam forming coefficient and the reflection phase shift of the intelligent reflection surface is obtained.
Please refer to fig. 2 for a flow of implementing joint optimization of the transmit-end beamforming coefficient and the reflection phase shift of the intelligent reflective surface.
Further, the step S4 is as follows:
after the beam forming coefficient of the sending end and the orthogonal reflection phase shift of the intelligent reflection surface are optimized, the signals received by the receiving end are expressed as follows:
Figure GDA0003240947550000061
wherein phi represents the reflection phase shift of the intelligent reflection surface after orthogonal reflection modulation, and is recorded
Figure GDA0003240947550000062
Figure GDA0003240947550000063
The signal received by the receiving end is further represented as:
Figure GDA0003240947550000064
wherein phi is0To represent
Figure GDA0003240947550000065
The detection signal is expressed as:
Figure GDA0003240947550000066
further, the step S5 is as follows:
first note
Figure GDA0003240947550000067
Then
Figure GDA0003240947550000068
Is a constant that is known to be constant,
Figure GDA0003240947550000069
wherein r is an intermediate expression in the calculation process,
Figure GDA00032409475500000610
is noise in a wireless communication system, and obeys a mean of 0 and a variance of N0Normal distribution of (2);
the probability density function of r given the symbol information x and the channel state information vector v is expressed as:
Figure GDA00032409475500000611
solving the symbol information x sent by the sending end, wherein the expression of the estimated value is as follows:
Figure GDA00032409475500000612
for a signal with a constant envelope, the expression for the estimate of x is further simplified as:
Figure GDA00032409475500000613
the expression of the estimated value of the information s of the orthogonal reflection modulation of the intelligent reflection surface is as follows:
Figure GDA0003240947550000071
wherein,
Figure GDA0003240947550000072
Figure GDA0003240947550000073
and
Figure GDA0003240947550000074
and respectively representing the coefficient after the reflection phase shift simplification of the orthogonal reflection modulation of the intelligent reflection surface and the set of symbol information sent by the sending end.
Compared with the prior art, the invention has the following advantages and effects:
1) the element units of the intelligent reflecting surface are grouped, and different grouping schemes are adopted, so that certain bit of information can be additionally transmitted, and the overall gain of the intelligent reflecting surface can be obtained.
2) According to the invention, the sending end beam forming coefficient and the intelligent reflection surface reflection phase shift are optimized in a combined manner by combining the intelligent reflection surface orthogonal reflection modulation and the sending end beam forming technology, so that a lower error rate can be obtained compared with other beam forming schemes, and the accuracy of information transmission can be improved.
3) The demodulation scheme provided by the invention can demodulate symbol information and intelligent reflection surface modulation information sent by a sending end with lower complexity.
Drawings
Fig. 1 is a diagram of a downlink intelligent reflective surface assisted multiple-input single-output wireless communication system in an embodiment of the present invention;
FIG. 2 is a flowchart illustrating an implementation of jointly optimizing a transmit-end beamforming coefficient and an intelligent reflective surface reflection phase shift in an embodiment of the present invention;
fig. 3 is a bit error rate performance comparison simulation diagram of another beamforming method based on the beamforming method of the intelligent reflective surface orthogonal reflection modulation in the embodiment of the present invention; fig. 3(a) is a simulation diagram comparing bit error rate performance of symbol information sent by a sending end of the method according to the embodiment of the present invention and other beamforming methods, fig. 3(b) is a simulation diagram comparing bit error rate performance of intelligent reflective surface modulation information sent by a sending end of the method according to the embodiment of the present invention and other beamforming methods, and fig. 3(c) is a simulation diagram comparing bit error rate performance of symbol information sent by a sending end of the method according to the embodiment of the present invention and other beamforming methods combined with intelligent reflective surface modulation information;
fig. 4 is a flowchart of a beamforming method based on orthogonal reflection modulation of an intelligent reflective surface in an embodiment of the present invention.
Detailed Description
In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Examples
Referring to fig. 1, fig. 1 is a block diagram of a downlink intelligent reflective surface assisted mimo wireless communication system according to an embodiment of the present invention. As shown in fig. 1, the application scenario of the present invention includes a base station with N transmit antennas, an intelligent reflective surface using preset groupings, and a user.
In this embodiment, the smart reflectionThe surface can sense information such as ambient environment data through a self sensor and perform information interaction and phase control with a base station through a control link. The intelligent reflective surface has L0Element unit, in order to reduce the estimation complexity of the channel, the L of the intelligent reflecting surface is shown in the figure0The unit elements are divided into L groups, each group containing L1＝L0the/L element units, assuming that the unit elements in each group have the same reflection phase shift. The channel model is a quasi-static block fading channel, and the channel coefficients are constant and independently distributed in different fading blocks.
Figure GDA0003240947550000081
Indicating a channel from a transmitting end to a receiving end,
Figure GDA0003240947550000082
and
Figure GDA0003240947550000083
respectively, the channel from the intelligent reflective surface to the receiving end and the channel from the sending end to the intelligent reflective surface.
Figure GDA0003240947550000084
And
Figure GDA0003240947550000085
respectively representing the channel from the ith component element of the intelligent reflection surface to the receiving end and the channel from the ith antenna of the transmitting end to the ith component element of the intelligent reflection surface, wherein L is 1,2
Figure GDA0003240947550000091
Representing a set of complex numbers.
Figure GDA0003240947550000092
Representing the reflection coefficient of a constituent element of the L-component of the intelligent reflecting surface, wherein
Figure GDA0003240947550000093
e represents a natural constant, βl∈[0,1]And thetalE [0,2 π) represents the reflection amplitude and reflection phase shift, respectively, of the l-th component group element. In the present invention, in order to maximize the reflection energy of the intelligent reflection surface and simplify the hardware design, the reflection amplitude of each unit element of the intelligent reflection surface is set to a maximum value of 1, that is, βl1. The process steps for carrying out the process of the invention are described in detail below with reference to FIG. 1.
And S1, grouping the intelligent reflection surface element units and performing orthogonal reflection modulation. Information such as the ambient environment perceived by the intelligent reflective surface is embedded into the grouping elements of the intelligent reflective surface.
S101, for briefly explaining the principle of the quadrature reflection modulation, take a single-input single-output wireless communication system as an example and assume channel blocking from a transmitting end to a receiving end. Namely, N is equal to 1, and the total weight of the catalyst,
Figure GDA0003240947550000094
in this case, the signal of the receiving end is represented as:
y＝θH hx+n；
wherein,hthe method comprises the steps of representing a cascade channel from a sending end to a receiving end through an intelligent reflecting surface, wherein x represents symbol information sent by the sending end, and x is selected from a constellation diagram of an M-state signal, such as the constellation diagram of an M-ary phase shift keying or quadrature amplitude modulation signal.
Figure GDA0003240947550000095
Is additive white Gaussian noise, and obeys a mean value of 0 and a variance of N0Is normally distributed.
S102, in order to realize coherent signal combination at a receiving end, the optimal reflection phase shift of the intelligent reflection surface is expressed as follows:
θl＝∠h l,l＝1,2,...,L；
wherein,h lindicating a cascade channel from the transmitting end to the receiving end via the l group of packet elements of the intelligent reflecting surface.
S103, randomly dividing L groups of elements of the intelligent reflection surface into two parts, wherein the p groups of elements in the first part adjust the reflection phase shift to the optimal reflection phase shift, so that the phase shift of signals reflected by the elements in the first part is consistent; the second portion contains L-p sets of elements that adjust the reflection phase shift to an optimum reflection phase shift and adds pi/2 to make the phase shift of the signal reflected by the elements of the second portion orthogonal to the phase shift of the signal reflected by the elements of the first portion.
On the premise of giving L and p, the total number of grouping schemes of the L groups of elements of the intelligent reflecting surface is calculated by a total probability formula, and the total number is
Figure GDA0003240947550000101
In a grouping manner, i.e. having at most
Figure GDA0003240947550000102
The bit information is additionally transmitted by grouping element units of the intelligent reflecting surface
Figure GDA0003240947550000103
An index representing p-group grouping elements of the first part,
Figure GDA0003240947550000104
an index representing the remaining L-p sets of elements, and the reflection phase shift of the L-th set of smart reflective surfaces is expressed as: :
Figure GDA0003240947550000105
wherein, thetalThe optimal reflection phase shift of the ith set of smart reflective surface grouping elements is represented, and l represents the index of the smart reflective surface grouping elements.
S104, expressing the reflection phase shift of the orthogonal reflection modulation of the intelligent reflection surface as
Figure GDA0003240947550000106
Wherein s represents a coefficient obtained by simplifying a reflection phase shift of the orthogonal reflection modulation of the intelligent reflection surface, theta represents an optimal reflection phase shift of each component element of the intelligent reflection surface, and the value of s of the component element of the ith group of the intelligent reflection surface is expressed as:
Figure GDA0003240947550000107
s105, to explain the inventive principle in detail, the intelligent reflective surface is divided into L-4 groups, where p-L-p-2 groups. According to the total probability calculation formula, the element units of the intelligent reflection surface are shared
Figure GDA0003240947550000108
In the grouping mode, 4 grouping modes are selected to represent transmission information, and the formula is as follows:
Figure GDA0003240947550000111
wherein,
Figure GDA0003240947550000112
b represents the total number of grouping ways, in this example B is 6.
S106, after the information is embedded into the grouping elements of the intelligent reflection surface, the signal from the sending end to the receiving end through the intelligent reflection surface is represented as follows:
y＝θH hx+n＝sHdiag(θH)hx+n；
let v ═ v1,v2,...,vL]H＝diag(θH)hWherein v isl＝|h lL represents a cascade channel from the transmitting end to the receiving end via the l-th group of packet elements of the intelligent reflection surface, and further represents the received signal as:
Figure GDA0003240947550000113
s107, assuming that the receiving end knows the channel of the cascade channel vState information, estimating symbol information transmitted from a transmitting end according to a maximum likelihood criterion
Figure GDA0003240947550000114
And information of orthogonal reflection modulation of intelligent reflection surface
Figure GDA0003240947550000115
The expression is as follows:
Figure GDA0003240947550000116
wherein,
Figure GDA0003240947550000117
and
Figure GDA0003240947550000118
and respectively representing the coefficient after the reflection phase shift simplification of the orthogonal reflection modulation of the intelligent reflection surface and the set of symbol information sent by the sending end.
And S2, introducing a beam forming technology at the transmitting end, and controlling the phase and the amplitude of a transmitting signal by using a beam former at the transmitting end to enable the energy of the signal received by the receiving end to be maximum. The signal received by the receiving end is represented as:
Figure GDA0003240947550000119
wherein,
Figure GDA00032409475500001110
and the energy of the active beamforming coefficient is P.
S201, further representing the signal received by the receiving end as:
Figure GDA0003240947550000121
wherein,
Figure GDA0003240947550000122
representing a cascade of channels from a transmitting end to a receiving end via an intelligent reflective surface.
S202, representing the signal-to-noise ratio of the wireless communication system as:
Figure GDA0003240947550000123
in the present invention, it is assumed that the base station is knownHAnd
Figure GDA0003240947550000124
the channel state information of (a).
S3, expanding the system design of the orthogonal reflection modulation of the intelligent reflection surface to a wireless communication system with multiple inputs and single output, and based onHAnd
Figure GDA0003240947550000125
the channel state information jointly optimizes a beam forming coefficient w of a sending end and a reflection phase shift theta of an intelligent reflection surface, and the energy of signals received by a receiving end is maximized through optimization.
S301, the problem of jointly optimizing the beam forming coefficient of the transmitting end and the reflection phase shift of the intelligent reflection surface is expressed as follows:
Figure GDA0003240947550000126
s302, according to the property of the triangle inequality, the following conclusion is obtained:
Figure GDA0003240947550000127
the above expression is only given in
Figure GDA0003240947550000128
The time-waiting sign is true.
S303, receiving signal energy of receiving end and sending end sendingThe energy of the signal is in linear relation, so the energy of the system is limited | | w | | non-woven cells2The optimal solution w is obtained only by the beamforming coefficient of the transmitting end which is less than or equal to 1*When satisfying the limiting condition, i.e. | w*||21. Therefore, firstly, the beamforming coefficient w of the transmitting end is fixed, and then the optimization problem of the system is expressed as:
Figure GDA0003240947550000131
according to the expression, the optimal solution of the reflection phase shift of the intelligent reflection surface is obtained, namely
Figure GDA0003240947550000132
The optimal reflection phase shift of the l-th group of intelligent reflection surfaces is expressed as:
Figure GDA0003240947550000133
s304, given the reflection phase shift theta of the grouping elements of the intelligent reflection surface, obtaining the optimal solution of the beam forming coefficient according to the maximum ratio transmission principle, wherein the expression is as follows:
Figure GDA0003240947550000134
s305, repeating iteration until the expression is obtained
Figure GDA0003240947550000135
Is less than a given arbitrarily small positive number or has completed a maximum number of iterations. And finally obtaining the optimal solution of the beam forming coefficient and the reflection phase shift of the intelligent reflection surface.
Please refer to fig. 2 for a flow of implementing joint optimization of the transmit-end beamforming coefficient and the reflection phase shift of the intelligent reflective surface.
S4, the wireless communication system is analyzed integrally, and the random rotation phase introduced from the channel from the sending end to the receiving end is eliminated before the received signal is detected, so that the detection performance of the system is improved.
S401, after the beam forming coefficient of the sending end and the orthogonal reflection phase shift of the intelligent reflection surface are optimized, the signals received by the receiving end are expressed as follows:
Figure GDA0003240947550000136
s402, recording
Figure GDA0003240947550000137
The signal received by the receiving end is further represented as:
Figure GDA0003240947550000138
wherein phi is0To represent
Figure GDA0003240947550000141
S403, it can be observed that a random rotation phase phi is introduced into the channel from the transmitting end to the receiving end0To improve the performance of the system, it is considered to eliminate the influence of the random phase before the signal detection at the receiving end. The detection signal after the random phase is eliminated is expressed as:
Figure GDA0003240947550000142
and S5, demodulating the symbol information and the intelligent reflection surface modulation information sent by the sending end at the receiving end.
S501, first, remember
Figure GDA0003240947550000143
Then
Figure GDA0003240947550000144
Is a known constant. Derived from the detection signal expression of S403:
Figure GDA0003240947550000145
wherein r is an intermediate quantity in the calculation process, and r is given to symbol information x and a channel state information vector
Figure GDA0003240947550000146
The probability density function under the condition of (1) is expressed as:
Figure GDA0003240947550000147
s502, solving symbol information x sent by a sending end, wherein the expression of an estimated value is as follows:
Figure GDA0003240947550000148
for a signal with a constant envelope, the expression for the estimate of x is further simplified as:
Figure GDA0003240947550000149
s503, the expression of the estimated value of the information S of the orthogonal reflection modulation of the intelligent reflection surface is as follows:
Figure GDA00032409475500001410
wherein,
Figure GDA00032409475500001411
in order to illustrate the technical progress of the method, the scheme of carrying out beam forming on the basis of the intelligent reflection surface provided by the invention on an MATLAB platform is compared with other beam forming schemes in terms of error rate performance under the condition that the signal to noise ratio is different. Other beamforming schemes include: performing beamforming operation at a transmitting end to maximize the gain in the channel direction from the transmitting end to the receiving end, wherein a simulation diagram is represented as a scheme 1; selecting a channel with the maximum channel power as a beamforming direction from a cascade channel from a sending end to a receiving end through an intelligent reflecting surface and a channel from the sending end to the receiving end, wherein a simulation diagram is indicated as a scheme 2; selecting a channel with the minimum channel power as a beamforming direction from a cascade channel from a transmitting end to a receiving end through an intelligent reflecting surface and a channel from the transmitting end to the receiving end, wherein a simulation diagram is indicated as a scheme 3; in the specific parameter setting, the number N of the transmitting antennas is 4, the elements of the intelligent reflective surface unit are divided into 4 groups, the first part includes the number p of the element groups is 3, and the transmitting signal x is selected from an octal quadrature amplitude modulation constellation. Fig. 3 is a bit error rate performance comparison simulation diagram of other beamforming schemes of the beamforming method based on the intelligent reflective surface orthogonal reflection modulation in the embodiment of the present invention. Specifically, as shown in fig. 3(a), compared with the beamforming methods in the above schemes 1,2, and 3, the bit error rate of the symbol information sent by the sending end is the lowest, and is close to the lower bound of the theoretical bit error rate. As shown in fig. 3(b), the method according to the embodiment of the present invention has the lowest bit error rate compared with the beamforming methods of the scheme 1, the scheme 2, and the scheme 3. As shown in fig. 3(c), compared with the beamforming methods of scheme 1, scheme 2, and scheme 3, the method according to the embodiment of the present invention has the lowest bit error rate performance when the symbol information sent by the sending end and the smart reflective surface modulation information are transmitted simultaneously.
Compared with the prior art, the invention has the following technical progress.
1) The spectrum efficiency or the bit error rate performance is improved. As shown in fig. 3(a), the bit error rate of the symbol information sent by the sending end, which is obtained by jointly optimizing the beamforming coefficient and the intelligent reflection surface reflection phase shift by the algorithm of the present invention, is close to the lower bound of the theoretical bit error rate, as shown in fig. 3(b), the intelligent reflection surface modulation information also has a lower bit error rate, and as shown in fig. 3(c), when the symbol information sent by the sending end and the intelligent reflection surface modulation information are transmitted simultaneously, the communication system has the lowest bit error rate, which can improve the accuracy of information transmission, compared to other beamforming schemes;
2) the detection algorithm proposed at the receiving end can demodulate the sent symbol information and the information embedded by the intelligent reflection surface with lower complexity, and has lower bit error rate.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (7)

1. An information transmission method based on intelligent reflection surface for beam forming is applied to a wireless communication system with the assistance of orthogonal reflection modulation of the intelligent reflection surface, the wireless communication system comprises at least one base station with N transmitting antennas, at least one intelligent reflection surface adopting preset grouping and a user, the intelligent reflection surface is provided with L0An element unit of L0The element units are divided into L groups, wherein each group of unit reflection channels has strong correlation, and the information transmission method is characterized by comprising the following steps:
s1, randomly dividing the L-component elements of the intelligent reflection surface into two parts, wherein the p-component elements contained in the first part adjust the reflection phase shift to the optimal reflection phase shift, so that the phase shifts of signals reflected by the elements of the first part are consistent; the L-p group elements contained in the second part adjust the reflection phase shift to the optimal reflection phase shift and add pi/2 to ensure that the phase shift of the signals reflected by the elements of the second part is orthogonal to the phase shift of the signals reflected by the elements of the first part, and the information sensed by the intelligent reflecting surface is embedded into the group elements of the intelligent reflecting surface through orthogonal reflection modulation;
s2, introducing a beam forming technology at the transmitting end, and controlling the phase and amplitude of the transmitted signal by using a beam former at the transmitting end to enable the signal energy received by the receiving end to be maximum;
s3, jointly optimizing a beam forming coefficient of a transmitting end and reflection phase shift of an intelligent reflection surface;
s4, analyzing the whole wireless communication system, and eliminating the random rotation phase introduced by the channel from the sending end to the receiving end before detecting the received signal;
and S5, demodulating the information sent by the sending terminal and the intelligent reflection surface modulation information at the receiving terminal.
2. The method of claim 1, wherein the total number of grouping schemes for the L groups of elements of the intelligent reflective surface is calculated by a total probability formula given L and p, and there is a total
Figure FDA0003240947540000011
In a grouping manner, i.e. having at most
Figure FDA0003240947540000021
The bit information is additionally transmitted by grouping element units of the intelligent reflecting surface
Figure FDA0003240947540000022
An index representing p-group grouping elements of the first part,
Figure FDA0003240947540000023
an index representing the remaining L-p sets of elements, and the reflection phase shift of the L-th set of smart reflective surfaces is expressed as:
Figure FDA0003240947540000024
wherein, thetalThe optimal reflection phase shift of the I group of elements of the intelligent reflection surface is shown.
3. The method as claimed in claim 2, wherein the process of embedding the perception information of the intelligent reflection surface into the grouping elements of the intelligent reflection surface through orthogonal reflection modulation in the single-input single-output wireless communication system is as follows:
the reflection phase shift of the smart reflective surface quadrature reflection modulation is expressed as:
Figure FDA0003240947540000025
wherein e is a natural constant, and the natural constant is,
Figure FDA0003240947540000026
s represents a coefficient obtained by simplifying the reflection phase shift of the orthogonal reflection modulation of the intelligent reflection surface, theta represents the optimal reflection phase shift of each group element of the intelligent reflection surface, and the value of s of the group element of the ith group of the intelligent reflection surface is expressed as:
Figure FDA0003240947540000027
after embedding information into the grouping elements of the intelligent reflection surface, the receiving signal of the receiving end is expressed as:
y＝θH hx+n＝sHdiag(θH)hx+n；
wherein,hthe method comprises the steps of representing a cascade channel from a sending end to a receiving end through an intelligent reflection surface, x representing symbol information sent by the sending end, and n representing noise of a wireless communication system.
4. The method for transmitting information based on intelligent reflective surface beamforming according to claim 1, wherein the step S2 comprises the following steps:
the signal received by the user at the receiving end is represented as:
Figure FDA0003240947540000031
where L denotes the index of the smart reflective surface L component element and L is 1, 2.
Figure FDA0003240947540000032
Representing the channel from the r-th antenna of the transmitting end to the l-th component group element of the intelligent reflecting surface, r is 1,2lRepresents the optimal reflection phase shift of the l group of elements of the intelligent reflecting surface,G lrepresenting the channel of the l-th group of packet elements of the intelligent reflecting surface to the receiving end,
Figure FDA0003240947540000033
indicating a channel from a transmitting end to a receiving end,
Figure FDA0003240947540000034
representing active beamforming coefficients of a transmitting end, wherein symbols
Figure FDA0003240947540000035
Represents a complex set with energy P, x represents symbol information transmitted by a transmitting end, n represents noise of a system, and
Figure FDA0003240947540000036
is additive white Gaussian noise, obeys a mean value of 0 and a variance of N0Normal distribution of (2);
the signal received by the user at the receiving end is further represented as:
Figure FDA0003240947540000037
wherein,
Figure FDA0003240947540000038
represents a cascade channel from the transmitting end to the receiving end through the I group of the group elements of the intelligent reflecting surface, theta represents the optimal reflection phase shift of each group of the group elements of the intelligent reflecting surface,
Figure FDA0003240947540000039
representing a cascade channel from a sending end to a receiving end through an intelligent reflecting surface;
the signal-to-noise ratio of a wireless communication system is expressed as:
Figure FDA00032409475400000310
wherein it is assumed that the base station is knownHAnd
Figure FDA00032409475400000311
the channel state information of (a).
5. The method of claim 4, wherein the method is based on a smart reflective surface for beamforming information transmissionHAnd
Figure FDA00032409475400000312
the optimization process of jointly optimizing the beam forming coefficient w of the transmitting end and the reflection phase shift theta of the intelligent reflection surface to enable the energy of the receiving signal of the receiving end to be maximum by the channel state information is as follows:
the problem of jointly optimizing the beam forming coefficient of the transmitting end and the reflection phase shift of the intelligent reflection surface is expressed as follows:
Figure FDA0003240947540000041
wherein, thetalRepresenting the optimal reflection phase shift of the I group of intelligent reflection surface grouping elements;
from the nature of the triangle inequality, the following conclusions are drawn:
Figure FDA0003240947540000042
the above expression is only given in
Figure FDA0003240947540000043
The time equal sign is established;
fixing the beamforming coefficient w of the transmitting end, the optimization problem of the wireless communication system is expressed as:
Figure FDA0003240947540000044
s.t.0≤θl＜2π,l＝1,2,...,L；
Figure FDA0003240947540000045
obtaining an optimal solution of the reflection phase shift of the intelligent reflection surface according to the expression, namely
Figure FDA0003240947540000046
The optimal reflection phase shift of the l-th group of intelligent reflection surfaces is expressed as:
Figure FDA0003240947540000047
giving an intelligent reflection surface grouping element reflection phase shift theta, and obtaining an optimal solution of a beam forming coefficient according to a maximum ratio transmission principle, wherein the expression is as follows:
Figure FDA0003240947540000048
after repeated iterations, until the expression is reached
Figure FDA0003240947540000049
The added value of (a) is smaller than a given arbitrary small positive number or the maximum number of iterations are completed, and finally the optimal solution of the beam forming coefficient and the reflection phase shift of the intelligent reflection surface is obtained.
6. The method for transmitting information based on intelligent reflective surface beamforming according to claim 5, wherein the step S4 comprises the following steps:
after the beam forming coefficient of the sending end and the orthogonal reflection phase shift of the intelligent reflection surface are optimized, the signals received by the receiving end are expressed as follows:
Figure FDA0003240947540000051
wherein phi represents the reflection phase shift of the intelligent reflection surface after orthogonal reflection modulation, and s represents the coefficient of the intelligent reflection surface after the reflection phase shift of the orthogonal reflection modulation is simplified;
note the book
Figure FDA0003240947540000052
The signal received at the receiving end is further represented as:
Figure FDA0003240947540000053
wherein phi is0To represent
Figure FDA0003240947540000054
The detection signal is expressed as:
Figure FDA0003240947540000055
7. the method for transmitting information based on intelligent reflective surface beamforming according to claim 6, wherein the procedure of step S5 is as follows:
first note
Figure FDA0003240947540000056
Then
Figure FDA0003240947540000057
Is a constant that is known to be constant,
Figure FDA0003240947540000058
wherein r is an intermediate expression in the calculation process,
Figure FDA0003240947540000059
is systematic noise and obeys a mean of 0 and a variance of N0Normal distribution of (2);
r is given symbol information x and channel state information vector
Figure FDA00032409475400000510
The probability density function under the condition of (1) is expressed as:
Figure FDA00032409475400000511
solving the symbol information x sent by the sending end, wherein the expression of the estimated value is as follows:
Figure FDA0003240947540000061
for a signal with a constant envelope, the expression for the estimate of x is further simplified as:
Figure FDA0003240947540000062
the expression of the estimated value of the information s of the orthogonal reflection modulation of the intelligent reflection surface is as follows:
Figure FDA0003240947540000063
wherein,
Figure FDA0003240947540000064
Figure FDA0003240947540000065
and
Figure FDA0003240947540000066
and respectively representing the coefficient after the reflection phase shift simplification of the orthogonal reflection modulation of the intelligent reflection surface and the set of symbol information sent by the sending end.
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