CN115314087A - Phase shift modulation and performance analysis method for intelligent reflector active information transmission - Google Patents
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- 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
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- H04B7/00—Radio transmission systems, i.e. using radiation field
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- H04L27/00—Modulated-carrier systems
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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
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 of an intelligent reflecting surface.
Background
The intelligent reflective surface (RIS) technology is an emerging technology with wide application prospect and facing to the future sixth generation mobile communication (6G). The phase of an incident signal is dynamically adjusted by utilizing a large number of integrated low-cost passive reflection units, so that the channel environment is remodeled, and the low-energy-consumption and high-speed data transmission of the conventional communication system is assisted. Because it has no energy for transmitting and receiving signals and further processing signals, much research is currently conducted to use the RIS as a passive device to enhance the signal-to-noise ratio of the receiving end, and neglects the ability of active information transmission using the RIS.
The RIS is used for carrying out active information transmission, so that data transmission with higher speed can be realized, and the requirement of a future network is supported. Some existing schemes provide methods of realizing additional information transmission through switches of RIS reflecting units or selecting mutually orthogonal reflecting unit phases and the like, but seriously affect received signal energy, and the number of transmitted information is limited, so that the potential of RIS deployment cannot be fully excited. Therefore, it is necessary to consider a more optimal RIS information modulation scheme to obtain a higher rate and channel capacity.
Disclosure of Invention
In view of this, the present invention aims to provide a method for phase shift modulation and performance analysis of active information transmission of an intelligent reflection surface, so as to implement reliable transmission of more information through an RIS and improve the communication rate of a system in practical application.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for phase shift modulation and performance analysis of intelligent reflective surface active information transmission, the method comprising:
step S1, aiming at a downlink communication system, establishing a phase shift modulation system model based on intelligent reflector active information transmission, wherein the downlink communication system comprises: the system comprises a base station side, a receiving side and an intelligent reflecting surface for auxiliary communication, wherein the intelligent reflecting surface is used for superposing phase shift on a signal sent by the base station side so as to improve the spectral efficiency of the system;
s2, aiming at the phase shift modulation system model constructed in the S1, constructing an optimal passive beam forming scheme under the condition of considering the signal-to-noise ratio of a maximized receiving side;
step S3, modulating additional information with phase shift at the intelligent reflective surface, which includes: keeping the precoding vector of the base station side unchanged, changing the phase shift configured at the RIS, and superposing the phase shift on the original phase to realize the transmission of additional information;
s4, the receiving side demodulates the symbols sent by the base station side and the extra information transmitted by the intelligent reflecting surface by utilizing the maximum likelihood criterion according to the acquired signals to obtain equivalent symbol vectors, wherein the expression of the equivalent symbol vectors comprises equivalent channels;
s5, approximating the equivalent channel by a Gaussian random variable by using a central limit theorem;
s6, calculating a moment mother function of the demodulation error;
and S7, calculating average pairwise error probability by using the approximation formula of the moment mother function and the Q function, and calculating to obtain an approximate expression of the bit error rate.
Further, in step S1, the phase shift modulation system model is obtained as follows:
for the downlink communication system, the following definitions and settings are performed, specifically including:
h r ＝[h r,1 ,…,h r,N ] T representing a channel between the intelligent reflecting surface and a user;
g represents a channel between the intelligent reflecting surface and the base station, and a direct link between a user and the base station is ignored due to the existing obstruction;
the channel between the intelligent reflecting surface 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 vector elements have a norm value of 1 · H Representing a vector conjugate transpose;
the channel between the intelligent reflecting surface and the user is formed byThe rich scattering present, modeled as Rayleigh channel, h r Are independent of each other, the nth element h r,n Obeying a circularly symmetric complex Gaussian distribution with a mean value of 0 and a variance of 1;
the symbol transmitted at the base station is s, M-order quadrature amplitude modulation is adopted, the average transmitting power is P, the noise of the system is z, the obedient mean value is 0, and the variance is sigma 2 A circularly symmetric complex gaussian distribution.
Further, the step S2 includes:
the phase theta of the n-th reflection unit of the intelligent reflection surface n And the precoding vector w at the base station is configured as the optimal phase
And optimal precoding w * As follows:
in the two formulas above, the phase shift matrix Θ * So as to make
Is a diagonal array of diagonal elements [ ·] n The nth element of the vector, | | · | non-woven phosphor 2 Representing the vector 2 norm.
Further, in the step S3, at the nth reflection unit of the intelligent reflection surface, the phase after the phase shift is superimposed is expressed as:
in the formula, K is RIS modulation information, and is selected from {0,1 \8230 } and K } according to the information needing modulation, wherein K is a modulation order, and delta theta is the minimum step length of fixed phase deviation;
the RIS is divided into L subblocks, each subblock has the same number of reflection units, and the reflection units have the same phase shift.
Further, in step S4, on the receiving side, the receiving signal of the user is represented as:
in this formula, x is the equivalent transmit symbol vector, defined as
k l Represents information modulated at the ith sub-block, h is an equivalent channel, defined as
Is the first subblock of the RIS;
equivalent symbol vector obtained by demodulation by maximum likelihood criterion
Comprises the following steps:
further, the step S5 includes:
because of the fact that
Can be approximately obeyed to normal distribution
Mean value μ h Sum variance
Respectively calculated as:
further, the step S6 specifically includes:
defining the demodulation error lambda as
Redefining the symbol error to
Respectively define the real parts delta thereof r And imaginary part delta i Comprises the following steps:
in the above two formulae, d l,r And d l,i Are respectively as
The real and imaginary parts of (c);
will real part delta r And imaginary part delta i Approximated by a normal distribution, obey:
defining a symbol error expansion vector
Characterizing λ as a quadratic form of the gaussian variable Δ, i.e. λ = Δ T Δ；
Calculating the mean vector m and covariance matrix C of the Gaussian variable Delta as follows:
wherein,
expressed as:
when det (C) ≠ 0, det (-) is the determinant of the matrix, and the moment quantity mother function is respectively calculated
Comprises the following steps:
wherein, I is a unit matrix, and t is an independent variable of a moment mother function.
When det (C) =0, δ r ,δ i One of the two is 0, or the two random variables are linearly related; setting delta r ,δ i Wherein optionally one of them is not 0 is δ x Not equal to 0, the other with δ x Is denoted as c, and the mean and variance are denoted as μ x And
calculating out
Comprises the following steps:
further, in the step S7, the average pair-wise error probability is calculated by:
the approximation of the Q function is:
then average the pairwise error probabilities
The calculation is as follows:
further, in step S7, the approximate bit error rate is calculated as:
in the formula, in the above-mentioned formula,
to estimate an equivalent symbol x as
The number of bits where the error occurred.
The beneficial effects of the invention are:
the invention realizes the transmission of extra information under the condition of ensuring the passive beamforming gain by superposing the specific phase offset on the optimal passive beamforming phase, realizes high-order modulation and can transmit more information. Aiming at the proposed modulation scheme, the invention provides an approximation method based on the central limit theorem, which can concisely obtain an approximate expression of the bit error rate, can accurately approximate the actual bit error rate, and has guiding significance for actual parameter selection and the like.
The invention provides an efficient information modulation scheme and an effective bit error rate analysis method, and higher spectral efficiency is obtained.
Drawings
Fig. 1 is a schematic view of an actual application scenario of a downlink communication system in embodiment 1;
fig. 2 is a schematic flowchart of a phase shift modulation and performance analysis method for active information transmission of 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 in embodiment 1 and the bit error rate approximation provided in embodiment 1.
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.
Example 1
Referring to fig. 1 to fig. 3, the present embodiment provides a phase offset modulation and performance analysis method for active information transmission of an intelligent reflector, in which a specific phase offset is superimposed on an optimal passive beamforming phase, so that transmission of additional information is achieved under the condition of ensuring passive beamforming gain; the bit error rate is approximated by means of the central limit theorem and an approximation of the Q-function. Before the method is explained in detail, the following explanations are made:
RIS: a smart reflective surface;
BER: bit error rate;
QAM: quadrature amplitude modulation.
The specific flow of the method is shown in fig. 1, and specifically comprises the following steps:
step S1, aiming at a downlink communication system, establishing a phase shift modulation system model based on intelligent reflector active information transmission, wherein the downlink communication system comprises: the system comprises a base station side, a receiving side and an intelligent reflecting surface for auxiliary communication, wherein the intelligent reflecting surface superposes phase shift on signals transmitted 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 fig. 1, consider a downlink communication system comprising: one deployment has N t The base station of the root antenna, a user equipped with a single antenna, and an intelligent reflecting surface with N reflecting units for auxiliary communication.
Then, the following definitions and settings are performed for the downlink communication system, which specifically include:
h r ＝[h r,1 ,…,h r,N ] T representing a channel between the intelligent reflecting surface and a user;
g represents a channel between the intelligent reflecting surface and the base station, and a direct link between a user and the base station is ignored due to the existing obstruction;
the intelligent reflecting surface is deployed in a range with a strong line-of-sight link with a base station, and a channel between the intelligent reflecting surface and the base station can be represented as follows:
G＝ab H
in this formula, vectors a and b are known array steering vectors, respectively, and the vector elements have a norm value of 1 · H Representing the vector conjugate transpose.
The channel between the intelligent reflecting surface and the user is modeled as a Rayleigh channel h due to the rich scattering r Are independent of each other, the nth element h r,n A circularly symmetric complex gaussian distribution with mean 0 and variance 1 is obeyed.
The symbol sent by the base station is s, and M-order Quadrature Amplitude Modulation (QAM) is adopted, so that the average transmitting power is P. The noise of the system is z, the obedient mean is 0 and the variance is sigma 2 A circularly symmetric complex gaussian distribution.
The specific phase deviation is superposed on the basis of the original optimal phase at the RIS, so that the transmission of extra information is realized, and the frequency spectrum efficiency of the system is improved.
And S2, aiming at the phase shift modulation system model constructed in the step S1, under the condition of considering the signal-to-noise ratio of the maximum receiving side, selecting the optimal RIS reflection phase shift and the optimal precoding vector of the base station side, and constructing an optimal passive beam forming scheme.
Specifically, in this embodiment, the step S2 includes:
the phase theta at the nth reflection unit of RIS is measured n And the precoding vector w at the base station is configured as the optimal phase
And optimal precoding w * As follows:
in the above two equations, the phase shift matrix Θ * So as to make
Is a diagonal array of diagonal elements [ ·] n The nth element of the vector, | | · | non-woven phosphor 2 Represents a vector 2 norm;
step S3, modulating additional information with phase offset at RIS, comprising: and keeping the precoding vector of the base station side unchanged, changing the phase shift configured at the RIS, and superposing the phase shift on the original phase to realize the transmission of additional information.
Specifically, in the present embodiment, the phase after superimposing the phase shift at the nth reflection unit of the RIS is expressed as:
in this formula, K is RIS modulation information, selected from among {0,1 \8230;, K } depending on the information to be modulated, K is the modulation order, and Δ θ is the minimum step size of the fixed phase shift. Consider dividing the RIS into L sub-blocks with the same number of reflective elements in each sub-block and with the reflective elements assuming the same phase offset.
S4, the receiving side demodulates the symbols sent by the base station side and the extra information transmitted by the RIS by utilizing the maximum likelihood criterion according to the acquired signals to obtain equivalent symbol vectors, wherein the expression of the equivalent symbol vectors comprises equivalent channels;
specifically, in this embodiment, the user reception signal is represented as:
in this formula, x is the equivalent transmit symbol vector, defined as
k l Represents information modulated at the ith sub-block, h is an equivalent channel, defined as
Is the first subblock of the RIS;
equivalent symbol vector obtained by demodulation by maximum likelihood criterion
Comprises the following steps:
and S5, approximating the equivalent channel by a Gaussian random variable by using a central limit theorem.
Specifically, in this embodiment, the step S5 includes:
because of the fact that
Can be approximately obeyed to a normal distribution
Mean value of h Sum variance
Calculated as:
and S6, calculating a moment mother function of the demodulation error.
Specifically, in this embodiment, the step S6 includes:
defining the demodulation error lambda as
Redefining the symbol error to
Respectively define the real part delta r And imaginary part delta i Comprises the following steps:
in the above two formulae, d l,r And d l,i Are respectively as
Real and imaginary parts of (c); will real part delta r And imaginary part delta i Approximated by a normal distribution, dividedCompliance is as follows:
defining a symbol error expansion vector
Characterizing λ as a quadratic form of the gaussian variable Δ, i.e. λ = Δ T And delta. Calculating the mean vector m and covariance matrix C of the Gaussian variable Delta as follows:
wherein,
expressed as:
when det (C) ≠ 0, det (-) is the determinant of the matrix, the moment quantity mother function that can be calculated separately
Comprises the following steps:
in this formula, I is the unit matrix and t is the argument of the moment mother function.
When det (C) =0, δ r ,δ i One of the two is 0 or one is the linear product of the other. Setting delta r ,δ i Optionally one of which is different from 0 is δ x Not equal to 0, the other with δ x Is denoted c, and its mean and variance are denoted μ x And
computing
Comprises the following steps:
s7, calculating average pairwise error probability by using the approximation formula of the moment quantity mother function and the Q function
And calculating to obtain the bit error rate P b An approximate expression of (c).
Specifically, in this embodiment, the step S7 includes:
the approximation of the Q function is:
the average pair-wise error probability can be calculated as:
further, the bit error rate of the approximation is calculated as:
in the formula, in the above-mentioned formula,
to estimate an equivalent symbol x as
The number of bits where the error occurred.
As shown in fig. 2, the main process of this embodiment is to establish a model, obtain an optimal passive beamforming scheme, superimpose a specific phase offset on the basis of the optimal phase shift to realize additional information transmission, and then demodulate at a receiving end by using a maximum likelihood criterion. Further, the equivalent channel is approximated by using the central limit theorem, then the moment mother function of the demodulation error lambda is calculated, and finally the average pairwise error probability and the approximated bit error rate are calculated by combining the approximate expression of the Q function.
To verify the effect of the present embodiment, a simulation experiment was performed, in which the number of transmitting antennas was set to 8, the number of ris transmitting units was set to 128, and the antenna was divided into two sub-blocks. As shown in fig. 3, the modulation method proposed in this embodiment can achieve effective transmission of information, and the proposed theoretical approximation of bit error rate can effectively approximate the real bit error rate.
In summary, the invention can realize error-free transmission of more bits of information and realize higher spectral efficiency by using the proposed phase shift modulation and performance analysis method based on the intelligent reflecting surface.
The invention is not described in detail, but is well known to those skilled in the art.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations can be devised by those skilled in the art in light of the above teachings. Therefore, the technical solutions that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the prior art according to the concepts of the present invention should be within the scope of protection determined by the claims.
Claims (9)
1. A phase shift modulation and performance analysis method for intelligent reflector active information transmission is characterized by comprising the following steps:
step S1, aiming at a downlink communication system, establishing a phase shift modulation system model based on intelligent reflector active information transmission, wherein the downlink communication system comprises: the system comprises a base station side, a receiving side and an intelligent reflecting surface for auxiliary communication, wherein the intelligent reflecting surface superposes phase shift on signals transmitted by the base station side so as to improve the spectral efficiency of the system;
s2, aiming at the phase shift modulation system model constructed in the S1, constructing an optimal passive beam forming scheme under the condition of considering the signal-to-noise ratio of a maximized receiving side;
step S3, modulating additional information with phase shift at the intelligent reflective surface, which includes: keeping the precoding vector of the base station side unchanged, changing the phase shift configured at the RIS, and superposing the phase shift on the original phase to realize the transmission of additional information;
s4, demodulating symbols sent by a base station side and extra information transmitted by an intelligent reflecting surface by using a maximum likelihood criterion according to the acquired signals by a receiving side to obtain equivalent symbol vectors, wherein the expression of the equivalent symbol vectors comprises an equivalent channel;
s5, approximating the equivalent channel by a Gaussian random variable by using a central limit theorem;
s6, calculating a moment mother function of the demodulation error;
and S7, calculating average pairwise error probability by using the approximation formula of the moment mother function and the Q function, and calculating to obtain an approximation expression of the bit error rate.
2. The method for phase shift modulation and performance analysis of intelligent reflector active information transmission as claimed in claim 1, wherein in step S1, the phase shift modulation system model is obtained by:
for the downlink communication system, the following definitions and settings are performed, specifically including:
h r ＝[h r,1 ,…,h r,N ] T representing a channel between the intelligent reflecting surface and a user;
g represents a channel between the intelligent reflecting surface and the base station, and a direct link between a user and the base station is ignored due to the existing obstruction;
the channel between the intelligent reflecting surface 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 vector elements have a norm value of 1 · H Representing a vector conjugate transpose;
the channel between the intelligent reflecting surface and the user is modeled as a Rayleigh channel h due to the rich scattering r Are independent of each other, the nth element h r,n Obeying a circularly symmetric complex Gaussian distribution with a mean value of 0 and a variance of 1;
the symbol sent by the base station is s, M-order quadrature amplitude modulation is adopted, the average transmitting power is P, the noise of the system is z, the obeying mean value is 0, and the variance is sigma 2 A circularly symmetric complex gaussian distribution.
3. The method of claim 2, wherein the step S2 comprises:
the phase theta of the n-th reflection unit of the intelligent reflection surface n And the precoding vector w at the base station is configured as the optimal phase
And optimal precoding w * As follows:
in the above two equations, the phase shift matrix Θ * So as to make
Is a diagonal array of diagonal elements [ ·] n The nth element of the vector is expressed, | | · | non-calculation 2 Representing the vector 2 norm.
4. The method as claimed in claim 3, wherein in step S3, the phase after the phase shift is superimposed at the nth reflection unit of the intelligent reflection surface is expressed as:
in the formula, K is RIS modulation information, and is selected from {0,1 \8230;, K } according to the information to be modulated, K is the modulation order, and Delta theta is the minimum step length of the fixed phase offset;
the RIS is divided into L sub-blocks, each sub-block has the same number of reflection units, and the reflection units adopt the same phase shift.
5. The method as claimed in claim 4, wherein in step S4, the receiving signal of the user is represented as:
in this formula, x is the equivalent transmitted symbol vector, defined as
k l Represents information modulated at the ith sub-block, h is an equivalent channel, defined as
Is the first subblock of the RIS;
equivalent symbol vector obtained by demodulation by utilizing maximum likelihood criterion
Comprises the following steps:
6. the method of claim 5, wherein the step S5 comprises:
because of
Can be approximately obeyed to normal distribution
Mean value μ h Sum variance
Respectively calculated as:
7. the method of claim 6, wherein the step S6 specifically comprises:
defining the demodulation error lambda as
Redefining the symbol error to
Respectively define the real part delta r And imaginary part delta i Comprises the following steps:
in the above two formulae, d l,r And d l,i Are respectively as
Real and imaginary parts of (c);
will real part delta r And imaginary part delta i Approximated by a normal distribution, obey:
defining a symbol error expansion vector
Characterizing λ as a quadratic form of the Gaussian variable Δ, i.e., λ = Δ T Δ；
Calculating a mean vector m and a covariance matrix X of the Gaussian variable Delta as follows:
wherein,
expressed as:
when det (C) ≠ 0, det (-) is the determinant of the matrix, and the moment quantity mother function is respectively calculated
Comprises the following steps:
wherein, I is a unit matrix, and t is an independent variable of a moment mother function.
When det (C) =0, δ r ,δ i One of the two is 0, or the two random variables are linearly related; setting delta r ,δ i Optionally one of which is different from 0 is δ x Not equal to 0, the other with δ x Is denoted as c, and the mean and variance are denoted as μ x And
computing
Comprises the following steps:
8. the method of claim 7, wherein in step S7, the average pair-wise error probability is calculated as follows:
the approximation of the Q function is:
then the pairwise error probabilities are averaged
The calculation is as follows:
9. the method of claim 8, wherein in step S7, the bit error rate is calculated as:
in the formula, in the above-mentioned formula,
to estimate the equivalent symbol x as
The number of bits in error.
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| CN116015452A (en) * | 2023-03-24 | 2023-04-25 | 南昌大学 | Transmission-reflection combined multi-RIS visible light communication method and system |
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