CN114205048A - Wireless single-input single-output vector synthesis safe transmission method based on RIS - Google Patents
Wireless single-input single-output vector synthesis safe transmission method based on RIS Download PDFInfo
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Abstract
The invention discloses a wireless single-input single-output vector synthesis safe transmission method based on RIS, which mainly solves the problem of guaranteeing the information safety of the existing RIS auxiliary wireless transmission technology in the physical layer of a single-input single-output system. The method comprises the following steps: the single antenna transmitting terminal transmits a signal to be synthesized, and the signal is designed according to the known channel state information; then, aiming at randomly selecting the RIS array element reflection coefficient, two different RIS reflection signal vector synthesis signal transmission schemes with different implementation complexity are respectively designed to implement the vector synthesis of a legal receiving end to a received signal to obtain a regular received constellation symbol, but the received signal at an eavesdropping end keeps random disturbance and ideal synthesis processing cannot be implemented; and finally, the legal receiving end and the eavesdropping end respectively detect and decode the received signals respectively obtained. The invention can ensure the safety of information transmission, effectively improve the reliability of information transmission and lower the realization cost of RIS control end hardware.
Description
Technical Field
The invention belongs to the technical field of communication, and further relates to a physical layer information security technology in wireless communication, in particular to a wireless single-input single-output vector synthesis secure transmission method based on a reconfigurable Intelligent surface RIS (reconfigurable Intelligent surface), which can be used for improving the transmission security of a RIS (RIS-enabled single-input single-output) wireless communication system.
Background
In recent years, the development of 5G mobile communication makes people's daily production and life more convenient and faster, but the characteristics of difficult arrangement, large energy consumption and openness of the propagation environment also bring a lot of problems to the update of mobile communication. The proposal of the reconfigurable intelligent surface RIS and the application thereof in the communication technology open up a new idea for the development of the future wireless network, and researchers can be dedicated to solving the problems of low wireless communication frequency spectrum efficiency, low resource utilization rate, incapability of guaranteeing safety and the like by combining the RIS with the prior art.
The RIS is composed of a large number of low-energy-consumption reflecting elements, and a controller connected with the RIS can independently adjust the amplitude and phase of each reflecting unit, so that the reflected beam forming is cooperatively realized. The RIS has the advantages of high controllability, flexible deployment, low cost and the like, and can provide an efficient solution for reliable communication in a future complex electromagnetic environment.
The physical layer security technology is based on the information theory, utilizes the physical characteristics of wireless channels, and seeks to improve the wireless information transmission security by means of the technologies such as multi-antenna signal processing, channel coding and decoding and the like. Similar to physical layer security technology based on multi-antenna signal processing, the RIS auxiliary passive beam management and control can enable the reflected signal waveform to realize energy convergence at a legal receiving end, and meanwhile, the receiving power of a confidential signal of an eavesdropping user is effectively weakened. By flexibly deploying the RIS, the safety of the communication system can be effectively improved. However, when the eavesdropping end is close to the single-antenna transmitting end and the transmission connection with the RIS is interrupted, the prior art cannot guarantee the communication safety of the single-antenna user.
The technical advantages of RIS in facilitating secure communications have gained wide acceptance in the industry. A great deal of research shows that the introduction of the RIS can effectively improve the security of the Communication link, as described in the document "Secrecy Performance Analysis of RIS-air Wireless Communication Systems" published in IEEE Transactions on Vehicular Technology in 10.2020, the phase shift of the RIS reflection signal is designed to maximize the signal-to-noise ratio of the signal received by the legal receiving end, the simulation proves that the security can be further improved along with the increase of the RIS reflection array element, and when an eavesdropper steals a direct path with the transmitting end, the security of the system is reduced, the security strategy aims at that the reflection phase of the single optimized RIS maximizes the signal-to-noise ratio of the legal user, but the signal Secrecy of the transmitting end can be directly stolen, and when the eavesdropper is closer to the transmitting end or can shield the RIS transmitting link, the security Performance can not be guaranteed.
Disclosure of Invention
The invention aims to provide a wireless single-input single-output vector synthesis safe transmission method based on RIS (RIS) aiming at the defects of the prior art, which is used for solving the defects of the prior RIS auxiliary wireless transmission technology in the problem of guaranteeing the information safety of the physical layer of a single-input single-output system. In the invention, the RIS array element reflection coefficient is randomly selected, and a vector synthesis signal transmission scheme is designed, so that the obvious difference exists between the legal received constellation and the intercepted constellation, and the transmission safety of a single-input single-output system is comprehensively and effectively ensured.
The basic idea for realizing the invention is as follows: the single antenna transmitting end transmits the signal to be synthesized, the signal is designed according to the known channel state information, the information transmission is completed through RIS reflection, the legal receiving end receives the signal to be synthesized and can realize vector synthesis to obtain regular receiving constellation symbols, then decoding of the secret information bits is completed, meanwhile, the eavesdropping end eavesdrops on the transmitted synthesized signal to keep random disturbance, synthesis processing cannot be realized, and therefore the information secret transmission is realized. And considering the hardware limit of RIS and the complexity of system implementation, RIS arrayThe element reflection phase shift selects discrete values, i.e. the reflection phase shift value is collected as
Where L is the number of quantization levels. When the number M of the RIS reflection array elements is more than or equal to 2, selecting L to 3 as the minimum RIS phase quantization stage number, and selecting the discrete phase shift quantization stage number to obtain the diversity gain to the maximum extent.
In order to achieve the above object, the technical solution of the present invention includes:
1) the method comprises the following steps that a single transmitting antenna is arranged at a transmitting end S in a system, single receiving antennas are respectively arranged at a legal receiving end D and an eavesdropping end Eve, a reconfigurable intelligent surface RIS is provided with M reflecting array elements, M is a non-negative integer power of 2, and the RIS is controlled through a connection controller;
2) the transmitting terminal S sends pilot frequency information to the legal receiving terminal D to obtain the channel vectors from the transmitting terminal S to RIS and from RIS to the legal receiving terminal D
And
and elements in both channel vectors obey Rayleigh fading; after the pilot information is intercepted by the interception end Eve, the intercepted channel vector from the transmitting end S to the interception end Eve and the reflected channel vector from the RIS to the interception end Eve are respectively obtained
And
wherein
Representing a complex field;
3) constructing a random vector synthesis RVS strategy:
3.1) acquiring a RIS reflection coefficient diagonal matrix:
(3.1.1) let the phase quantization step number L be 3, in which case the reflection coefficient of the mth reflection array element of RIS is discretePhase shift
In the collection
Wherein M is 1,2,.. M; obtaining discrete random phase shift of all single reflection array elements of the RIS;
(3.1.2) according to the discrete random phase shift of all single reflection array elements of the RIS, obtaining a first diagonal matrix phi consisting of the reflection coefficients of the RIS array elements:
wherein diag (g) denotes the diagonalization operator,
discrete phase shift vectors of reflection coefficients of each array element of the RIS are obtained;
3.2) the transmitting terminal designs and sends the first signal to be synthesized according to the RIS feedback
Wherein j represents an imaginary number, j2＝-1；
Represents a first Phase Shift Keying (PSK) signal, k represents the kth symbol of a PSK symbol set, and
is the secret signal power; q1Representing the phase, expressed, of the first signal to be synthesizedThe formula is as follows:
wherein, κmElements in the channel vector k representing the transmitting end S to the mth reflecting array element of RIS, gmRepresenting the element from the m-th reflection array element of the RIS to the D channel vector g of the legal receiving end;
3.3) the legal receiver D obtains the first legal receiving useful signal Z reflected by the RIS1And carrying out vector synthesis on the signals to obtain a regular first amplitude phase modulation signal
Wherein alpha is1Synthesizing signal amplitude gain for a first legal receiving end;
4) constructing a grouping vector synthesis GVS strategy:
4.1) acquiring a RIS reflection coefficient diagonal matrix:
(4.1.1) equally dividing all the reflecting array elements of the RIS into U subsets, each subset then containing a ═ M/U array elements; wherein U is a non-negative integer power of 2, s 1,2, U denoting the s-th subset thereof;
(4.1.2) taking the phase quantization order L as 3, when the discrete phase shift P of the reflection coefficient of the reflection array element in the s-th subsetsIn the collection
The medium value is specifically as follows: firstly, selecting the optimal discrete phase shift P of the reflection coefficient of the reflection array element in the subsets *：
Wherein,
is the t array element component in the channel from the s subset of RIS to the legal receiver D,
the t-th array element component in the channels from the transmitting terminal S to the S-th subset of the RIS is t 1, 2.
Then, a set is selected
Middle distance Ps *Discrete phase shift P with nearest point as reflection coefficient of reflection array element in s-th subsetsIs what is needed
Then
Otherwise, the reverse is carried out
Wherein
Respectively represent collections
The ith or jth element in (e), i, j ∈ {1,2,3},
the method comprises the following steps of (1) indicating that unequal i and j are selected randomly;
(4.1.3) obtaining a second diagonal matrix Lambda composed of the reflection coefficients of the RIS array elements according to the discrete phase shift of the reflection coefficients of the reflection array elements in all the subsets of the RIS:
Λ＝diag(p)，
wherein
Discrete phase-shifted reflection coefficient vectors for respective subsets of the RIS;
4.2) the transmitting terminal designs and sends a second signal to be synthesized according to the RIS feedback
Wherein,
represents a second phase shift keying PSK signal, an
Is the secret signal power; q2Representing the phase of the second signal to be synthesized, the expression is as follows:
4.3) the legal receiver D obtains the second legal receiving useful signal Z reflected by the RIS2And carrying out vector synthesis on the signal to obtain a regular second amplitude phase modulation signal
Wherein alpha is2Synthesizing signal amplitude gain for a second legal receiving end;
5) the legal receiving end D and the eavesdropping end Eve respectively acquire respective receiving signals:
the legal receiving end D respectively carries out vector synthesis on the signals to be synthesized according to the random vector synthesis RVS strategy constructed in the step 3) and the grouping vector synthesis GVS strategy constructed in the step 4) to obtain an observation signal y of the first legal receiving endb1And a second legal receiving end observation signal yb2：
Wherein n isbRepresenting a complex Gaussian noise vector at a legal receiving end D;
the eavesdropping end is divided into the following two scenes to eavesdrop the signal to be synthesized, namely a secret signal:
the first method comprises the following steps: when the eavesdropping end has transmission connection with the transmitting end and is blocked from the RIS transmission connection, under the random vector synthesis RVS strategy constructed in the step 3) and the packet vector synthesis GVS strategy constructed in the step 4), the eavesdropping end receives signals which are respectively expressed as y1 idealAnd y2 ideal：
Wherein n isoRepresenting a complex Gaussian noise vector at an eavesdropping end Eve;
and the second method comprises the following steps: when the eavesdropping end is in transmission connection with the transmitting end and the RIS, under the random vector synthesis RVS strategy constructed in the step 3) and the packet vector synthesis GVS strategy constructed in the step 4), the eavesdropping end receives signals which are respectively expressed as y1 worstAnd y2 worst：
6) The legal receiving end and the eavesdropping end respectively detect and decode the received signals obtained by the legal receiving end and the eavesdropping end:
a legal receiving end performs optimal detection on the phase modulation symbol based on the maximum likelihood estimation criterion, completes secret information decoding and accurately obtains secret information;
the eavesdropping end decodes the secret information under the interference of the vector synthesis strategy constructed by the transmitting end, and the secret information cannot be accurately acquired.
Compared with the prior art, the invention has the following advantages:
firstly, the transmitting end of the invention transmits a signal to be synthesized, so that a legal receiving end can carry out vector synthesis on a received signal, and an eavesdropping end can not realize information stealing even under the condition of flat fading of a channel, thereby effectively ensuring the transmission safety and simultaneously reducing the complexity of realizing RIS beam control;
secondly, the vector synthesis scheme reasonably groups the RIS reflection array elements, and discretely selects the reflection phase shift coefficients of the set array elements, thereby effectively reducing the realization cost of RIS control end hardware and reducing the complexity of a signal to be synthesized design algorithm on the premise of ensuring information safety transmission;
thirdly, the invention can realize the RIS diversity order to the maximum extent by the minimum phase quantization level number while finishing the information transmission with high efficiency, and reasonably relieves the hardware limitation.
Drawings
FIG. 1 is a schematic diagram of a system model of the present invention;
FIG. 2 is a flow chart of an implementation of the method of the present invention;
FIG. 3 is a diagram showing comparison of simulation results of received signal constellations when a legal receiving end, a eavesdropping end and a RIS have transmission connection or not, respectively using RVS and GVS schemes under fast fading channel conditions; (a) medium SNR-10 dB, (b) medium SNR-0 dB;
wherein a, b and c are received signal constellation diagrams of a legal receiving end, a wiretapping end and RIS without transmission connection and with transmission connection under RVS scheme respectively; d. e and f are received signal constellation diagrams of a legal receiving end, an eavesdropping end and the RIS without transmission connection and the eavesdropping end and the RIS with transmission connection under the GVS scheme.
FIG. 4 is a comparison graph of simulation results of received signal constellations when there is transmission connection between the legal receiving end, the eavesdropping end and the RIS using RVS and GVS schemes respectively under flat fading channel conditions; (a) medium SNR is 0dB, and (b) medium SNR is 10 dB;
wherein a, b and c are received signal constellation diagrams of a legal receiving end, a wiretapping end and RIS without transmission connection and with transmission connection under RVS scheme respectively; d. e and f are received signal constellation diagrams of a legal receiving end, an eavesdropping end and the RIS without transmission connection and the eavesdropping end and the RIS with transmission connection under the GVS scheme.
FIG. 5 shows the BER comparison results of the legal receiving end and the eavesdropping end when the system uses RVS and GVS schemes under fast fading channel conditions and the GVS scheme is at different RIS packet numbers;
Detailed Description
The implementation process of the technical scheme of the invention is described in detail below with reference to the attached drawings:
referring to fig. 1, a schematic diagram of a system model in the present invention, the system model adopted by the method of the present invention specifically includes the following contents: the system comprises a transmitting terminal S, a legal receiving terminal D, an eavesdropping terminal and a reconfigurable intelligent surface RIS. The transmitting end, the legal receiving end and the eavesdropping end are respectively provided with a receiving antenna, and are respectively represented as N by a single receiving antennat、Nr、NeWhile the RIS has M reflecting units and is connected to the controller, M being a non-negative integer power of 2; in this example, N is usedt＝1，Nr＝1，NeFor example, the BPSK modulation signal is synthesized by 1, M64, S ∈ {2,4,8,16,32,64 }. Each sending time slot transmitting antenna sends a signal to be synthesized as a secret signal, then the RIS reflects and transmits the signal to be synthesized to a legal receiving end, and finally the legal receiving end carries out signal receiving synthesis and detection.
Referring to fig. 2, the invention provides a wireless single-input single-output vector synthesis secure transmission method based on RIS, which comprises the following specific steps:
step 1: a transmitting end S in the system is provided with a single transmitting antenna, a legal receiving end D and an eavesdropping end Eve, and is also respectively provided with a single receiving antenna, a reconfigurable intelligent surface RIS is provided with M reflecting array elements, M is a non-negative integer power of 2, and the RIS is controlled by a connecting controller;
step 2: the transmitting terminal S sends pilot frequency information to the legal receiving terminal D, the pilot frequency information is reflected to the legal receiving terminal D through the RIS, the legal receiving terminal processes the received pilot frequency information and feeds back the scheme of power distribution to the transmitting terminal, when the received power is less than a certain value, the accurate estimation of the channel can be completed according to the information by only inserting a single pilot frequency in the transmission time, and the channel vector from the transmitting terminal S to the RIS and from the RIS to the legal receiving terminal is obtained
And
and elements in both channel vectors obey Rayleigh fading; after the pilot information is intercepted by the eavesdropping end Eve, the eavesdropping channel vector from the transmitting end to the eavesdropping end and the reflected channel vector from the RIS to the eavesdropping end are respectively obtained
And
wherein
Representing a complex field;
in this embodiment, the channel vectors from the transmitting end S to the RIS and from the RIS to the legal receiving end
And
obtained as follows: the transmitting terminal S sends pilot frequency information to a legal receiving terminal D, the pilot frequency information is reflected to the legal receiving terminal D through the RIS, the RIS and the legal receiving terminal D estimate a first hopping channel matrix according to the pilot frequency information respectively, then the first hopping channel matrix is used as the input of a deep residual error network, the second hopping channel matrix is used as the output of the deep residual error network, and the channel state is obtained after the network is trainedAnd the transmitting end completes accurate estimation of the channel according to the state information, and the channel vectors from the transmitting end to the RIS and from the RIS to the legal receiving end are obtained. Certainly, the method can also adopt other methods to obtain, the transmitting terminal S is used for sending pilot frequency information to the legal receiving terminal D, the pilot frequency information is reflected to the legal receiving terminal D through the RIS, the legal receiving terminal processes the received pilot frequency information and feeds back the scheme of power distribution to the transmitting terminal, when the received power is less than a certain value, only a single pilot frequency needs to be inserted in the transmission time, the accurate estimation of the channel can be completed according to the information, and the channel vector from the transmitting terminal to the RIS and the channel vector from the RIS to the legal receiving terminal can also be obtained.
And setting the known ideal channel state information of both communication parties of the legal communication, and designing and transmitting the signal to be synthesized by the transmitting terminal S according to the known channel vectors kappa and g and the random reflection coefficient of the RIS array element. Specifically, according to the channel characteristics, the security of the system under the channel conditions, and the complexity of the RIS control link, two different Vector synthesis strategies, namely Random Vector Synthesis (RVS) and Group Vector Synthesis (GVS), are constructed, and the two Vector synthesis schemes can respectively obtain the phases of the signals to be synthesized transmitted by the respective schemes. The channels comprise flat fading channels and fast fading channels; the transmitting terminal transmits the signal to be synthesized according to a random vector synthesis strategy, and the phase shift of a single reflection array element is discretely and randomly valued.
And step 3: constructing a random vector synthesis RVS strategy:
3.1) acquiring a RIS reflection coefficient diagonal matrix:
(3.1.1) let the phase quantization level number L be 3, when the reflection coefficient of the mth reflection array element of RIS is discretely phase-shifted
In the collection
Wherein M is 1,2,.. M; obtaining discrete random phase shift of all single reflection array elements of the RIS;
(3.1.2) according to the discrete random phase shift of all single reflection array elements of the RIS, obtaining a first diagonal matrix phi consisting of the reflection coefficients of the RIS array elements:
wherein diag (g) denotes the diagonalization operator,
discrete phase shift vectors of reflection coefficients of each array element of the RIS are obtained;
3.2) the transmitting terminal designs and sends the first signal to be synthesized according to the RIS feedback
Wherein j represents an imaginary number, j2＝-1；
Represents a first Phase Shift Keying (PSK) signal, k represents the kth symbol of a PSK symbol set, and
is the secret signal power; q1Representing the phase of the first signal to be synthesized, the expression is as follows:
wherein, κmElements in the channel vector k representing the transmitting end S to the mth reflecting array element of RIS, gmRepresenting the element from the m-th reflection array element of the RIS to the D channel vector g of the legal receiving end;
3.3) acquisition of the RIS-reflected by the legal receiver DFirst legally received useful signal Z1And carrying out vector synthesis on the signals to obtain a regular first amplitude phase modulation signal
Wherein alpha is1Synthesizing signal amplitude gain for a first legal receiving end;
in this embodiment, the first legally received useful signal Z1And the first legal receiving end synthesizes the signal amplitude gain alpha1Obtained according to the following formula:
and 4, step 4: constructing a grouping vector synthesis GVS strategy:
4.1) acquiring a RIS reflection coefficient diagonal matrix:
(4.1.1) equally dividing all the reflecting array elements of the RIS into U subsets, each subset then containing a ═ M/U array elements; wherein U is a non-negative integer power of 2, s 1,2, U denoting the s-th subset thereof;
(4.1.2) taking the phase quantization order L as 3, when the discrete phase shift P of the reflection coefficient of the reflection array element in the s-th subsetsIn the collection
The medium value is specifically as follows: firstly, selecting the optimal discrete phase shift P of the reflection coefficient of the reflection array element in the subsets *：
Wherein,
as the s-th subset of the RISThe t-th element component in the channel to the legitimate receiver D,
the t-th array element component in the channels from the transmitting terminal S to the S-th subset of the RIS is t 1, 2.
Then, a set is selected
Middle distance Ps *Discrete phase shift P with nearest point as reflection coefficient of reflection array element in s-th subsetsIs what is needed
Then
Otherwise, the reverse is carried out
Wherein
Respectively represent collections
The ith or jth element in (e), i, j ∈ {1,2,3},
the method comprises the following steps of (1) indicating that unequal i and j are selected randomly;
(4.1.3) obtaining a second diagonal matrix Lambda composed of the reflection coefficients of the RIS array elements according to the discrete phase shift of the reflection coefficients of the reflection array elements in all the subsets of the RIS:
Λ＝diag(p)，
wherein
Discrete phase-shifted reflection coefficient vectors for respective subsets of the RIS;
4.2) the transmitting terminal designs and sends a second signal to be synthesized according to the RIS feedback
Wherein,
represents a second phase shift keying PSK signal, an
Is the secret signal power; q2Representing the phase of the second signal to be synthesized, the expression is as follows:
4.3) the legal receiver D obtains the second legal receiving useful signal Z reflected by the RIS2And carrying out vector synthesis on the signal to obtain a regular second amplitude phase modulation signal
Wherein alpha is2Synthesizing signal amplitude gain for a second legal receiving end;
in this embodiment, the second legally received useful signal Z2And the amplitude gain alpha of the combined signal of the second legal receiving end2Obtained according to the following formula:
and 5: the legal receiving end D and the eavesdropping end Eve respectively acquire respective receiving signals:
the legal receiving end D respectively carries out vector synthesis on the signals to be synthesized according to the random vector synthesis RVS strategy constructed in the step 3) and the grouping vector synthesis GVS strategy constructed in the step 4) to obtain an observation signal y of the first legal receiving endb1And a second legal receiving end observation signal yb2：
Wherein n isbRepresenting a complex Gaussian noise vector at a legal receiving end D;
the eavesdropping end is divided into the following two scenes to eavesdrop the signal to be synthesized, namely a secret signal:
the first method comprises the following steps: when the eavesdropping end has transmission connection with the transmitting end and is blocked from the RIS transmission connection, under the random vector synthesis RVS strategy constructed in the step 3) and the packet vector synthesis GVS strategy constructed in the step 4), the eavesdropping end receives signals which are respectively expressed as y1 idealAnd y2 ideal：
Wherein n isoRepresenting a complex Gaussian noise vector at an eavesdropping end Eve;
and the second method comprises the following steps: when the eavesdropping end is connected with the transmitting end and the RIS in a transmission way, under the random vector synthesis RVS strategy constructed in the step 3) and the packet vector synthesis GVS strategy constructed in the step 4), the eavesdropping end receives the signal componentsIs denoted by y1 worstAnd y2 worst：
Step 6: the legal receiving end and the eavesdropping end respectively detect and decode the received signals obtained by the legal receiving end and the eavesdropping end:
a legal receiving end performs optimal detection on the phase modulation symbol based on the maximum likelihood estimation criterion, completes secret information decoding and accurately obtains secret information;
the eavesdropping end decodes the secret information under the interference of the vector synthesis strategy constructed by the transmitting end, the detection performance is limited, and the secret information cannot be accurately known.
In this embodiment, it is assumed that a legal receiving end can obtain the state information of the ideal fading channel, and the legal receiving end performs maximum likelihood detection expressions based on the maximum likelihood estimation criterion under two vector synthesis schemes, respectively, where c belongs to {1,2}, and represents the c-th policy:
the vector synthesis signal of the eavesdropping end is a random disturbance signal, the signal detection performance of the eavesdropping end is limited, and an accurate phase modulation symbol cannot be synthesized like a legal receiving end. Specifically, under two vector synthesis schemes, the maximum likelihood detection of the eavesdropping-end received signal can be implemented as follows corresponding to two scenes respectively:
A. the eavesdropping end is connected with the transmitting end in a transmission way, and when the eavesdropping end is blocked from the RIS transmission connection: the eavesdropping end receives the estimated signal and expresses the estimated signal as the ideal fading channel state information
The corresponding maximum likelihood detection expression is as follows:
B. when the eavesdropping end is connected with the transmitting end and the RIS in a transmission way: the eavesdropping end receives the estimated signal and expresses the estimated signal as the ideal fading channel state information
The RIS reflection interference signal and the receiving noise are taken as color noise to be processed, and the maximum likelihood detection is carried out on the eavesdropping signal after the noise whitening as follows:
referring to fig. 3, N is depicted under fast fading channel conditionst＝1、NrWhen the SNR is-10 dB, two schemes receive signal constellations under different eavesdropping scenes, a, b, c are respectively a received signal constellation of a sink server system (RVS) scheme lower legal receiving end, an eavesdropping end and an RIS non-transmission connection and a received signal constellation of a eavesdropping end and an RIS transmission connection, d, e, f are respectively a received signal constellation of a GVS scheme lower legal receiving end, an eavesdropping end and an RIS non-transmission connection and a received signal constellation of an eavesdropping end and an RIS transmission connection; fig. 3 (b) shows the above case where the SNR is 0 dB.
As can be seen from the constellation diagrams a and d in fig. 3 (a) and (b), compared with the RVS scheme, the GVS scheme can synthesize a constellation symbol with better aggregation effect at a legal receiving end; further comparing a, b, and c in (a) and (b) in fig. 3, it can be seen that a legal receiving end has a better aggregation function under the RVS scheme than the receiving situation of the constellation symbol at the eavesdropping end under the same condition, which indicates that the RVS scheme also ensures the security of signal transmission while reducing the complexity of the RIS control link. Further comparing (a) and (b) in fig. 3, after the signal-to-noise ratio is improved, the effect of synthesizing and separating the received signal of the legal receiving end is obviously enhanced, and the eavesdropping end still cannot separate the signal.
Referring to fig. 4, N is depicted under flat fading channel conditionst＝1、NrWhen the SNR is 0dB, the two schemes receive signal constellations in different eavesdropping scenes, a, b, c are respectively a received signal constellation diagram of a legal receiving end under the RVS scheme, a connection between the eavesdropping end and the RIS without transmission, and a connection between the eavesdropping end and the RIS with transmission, d, e, f are respectively a received signal constellation diagram of a legal receiving end under the GVS scheme, a connection between the eavesdropping end and the RIS without transmission, and a connection between the eavesdropping end and the RIS with transmission; fig. 4 (b) shows the above case where the SNR is 10 dB.
As can be seen from the constellations a and d (a) and (b) in fig. 4, the GVS scheme can obtain a reception constellation with better separation effect than the RVS scheme under the flat fading channel condition; comparing d, e, and f in (a) and (b) in fig. 4, it can be known that, under the condition of flat fading channel, the eavesdropping end can synthesize a rotated constellation diagram under the condition of high signal-to-noise ratio of the GVS scheme, and the legal receiving end can synthesize regular constellation symbols. In addition, comparing the receiving constellation of the RVS and GVS schemes in fig. 4, the RVS scheme still synthesizes a randomly scrambled constellation at the eavesdropping end under high signal-to-noise ratio, further illustrating that the scheme of the present invention can achieve better security performance even under flat fading channel.
Referring to fig. 5, the bit error rate performance of the legal receiving end and the eavesdropping end compared to the RVS scheme synthesized by random vectors in the case of the GVS scheme synthesized by packet vectors with the number of packets S E {2,4,8,16,32,64} is depicted under fast fading channel conditions; it can be seen from the figure that with the increasing of SNR, the BER performance of the legal receiving end under the two schemes is continuously improved, while the bit error rate performance of the eavesdropping end is maintained at about 0.5, and simultaneously the performance of the legal receiving end is gradually improved with the increasing of the number of packets under the GVS scheme, which indicates that the scheme selects the discrete phase coefficient after the RIS packet reduces the hardware limit of the RIS system, and simultaneously reasonably selects the packets to obtain the lower bit error rate performance; and further comparing the two vector synthesis schemes, the RIS array element phase coefficient in the RVS scheme randomly takes values in a discrete set, the GVS scheme randomly takes values in the discrete set after the optimal phase of the packet is calculated, and the complexity of a signal algorithm to be synthesized based on the RVS scheme is lower.
The effect of the present invention is further explained by combining simulation experiments as follows:
A. simulation conditions
Using matlab simulation tool to simulate, assuming that the information is under rayleigh fading channel, the transmitter obtains all channel state information, and the specific simulation parameters are set as follows:
simulation 1: setting Nt＝1，Nr＝1，Ne＝1，M＝64，SNR∈{-10,0}；
Simulation 2: setting Nt＝1，Nr＝1，Ne＝1，M＝64，SNR∈{0,10}；
Simulation 3: setting Nt＝1，Nr＝1，Ne＝1，M＝64，S∈{2,4,8,16,32,64}
B. Emulated content
Simulation 1: in order to use the method of the invention under the fast fading channel condition with different signal to noise ratios, RVS scheme and GVS scheme, the two-dimensional constellation simulation result comparison chart of legal receiving end and eavesdropping end, the simulation result is shown in figure 3;
simulation 2: in order to use the method of the invention under the condition of different signal-to-noise ratios of flat fading channels, RVS scheme and GVS scheme are used, the comparison graph of the two-dimensional constellation simulation results of legal receiving end and interception end is shown in figure 4;
simulation 3: comparing the BER of the system under the condition of fast fading channel and the use of the GVS scheme and the RVS scheme under the condition of different RIS packet numbers, a legal receiving end and a wiretapping end, and the simulation result is shown in figure 5;
C. simulation result
As can be seen from fig. 3, a legal receiving end can better separate the transmitted signals under different vector synthesis schemes, the surface scheme has better confidential transmission performance, the larger the signal-to-noise ratio is, the higher the constellation separation degree is, and under the same condition, the GVS scheme has a better synthetic signal constellation convergence effect than the RVS scheme.
As can be seen from fig. 4, the RVS scheme performs better than the GVS scheme in terms of eavesdropping resistance under flat fading channel conditions. Under the high signal-to-noise ratio, the GVS scheme is used, and when the eavesdropping end is in transmission connection with the RIS, signal separation can be realized, but only the rotating constellation symbol can be solved, and the constellation diagram of the eavesdropping end under the RVS scheme is still dispersed, thereby verifying the technical advantages of the invention in the aspect of comprehensively guaranteeing single-input single-output safe transmission.
As can be seen from fig. 5, with the increasing of the signal-to-noise ratio, the transmission reliability of the legal receiving end under the two schemes is obviously improved, and the eavesdropping end is interfered by the vector synthesis signal and cannot correctly decode the signal regardless of the existence of the transmission connection with the RIS, which indicates the high security of the scheme of the present invention.
The simulation analysis proves the correctness and the effectiveness of the method provided by the invention.
The invention has not been described in detail in part of the common general knowledge of those skilled in the art.
While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.
Claims (6)
1. A wireless single-input single-output vector synthesis safe transmission method based on a reconfigurable intelligent surface RIS is characterized by comprising the following steps:
1) the method comprises the following steps that a single transmitting antenna is arranged at a transmitting end S in a system, single receiving antennas are respectively arranged at a legal receiving end D and an eavesdropping end Eve, a reconfigurable intelligent surface RIS is provided with M reflecting array elements, M is a non-negative integer power of 2, and the RIS is controlled through a connection controller;
2) the transmitting terminal S sends pilot frequency information to the legal receiving terminal D to obtain the channel vectors from the transmitting terminal S to RIS and from RIS to the legal receiving terminal D
And
and elements in both channel vectors obey Rayleigh fading; after the pilot information is intercepted by the interception end Eve, the intercepted channel vector from the transmitting end S to the interception end Eve and the reflected channel vector from the RIS to the interception end Eve are respectively obtained
And
wherein
Representing a complex field;
3) constructing a random vector synthesis RVS strategy:
3.1) acquiring a RIS reflection coefficient diagonal matrix:
(3.1.1) let the phase quantization level number L be 3, when the reflection coefficient of the mth reflection array element of RIS is discretely phase-shifted
In the collection
Wherein M is 1,2,.. M; obtaining discrete random phase shift of all single reflection array elements of the RIS;
(3.1.2) according to the discrete random phase shift of all single reflection array elements of the RIS, obtaining a first diagonal matrix phi consisting of the reflection coefficients of the RIS array elements:
wherein diag (·) represents the diagonalization operator,
discrete phase shift vectors of reflection coefficients of each array element of the RIS are obtained;
3.2) the transmitting terminal designs and sends the first signal to be synthesized according to the RIS feedback
Wherein j represents an imaginary number, j2＝-1；
Represents a first Phase Shift Keying (PSK) signal, k represents the kth symbol of a PSK symbol set, and
is the secret signal power; q1Representing the phase of the first signal to be synthesized, the expression is as follows:
wherein, κmElements in the channel vector k representing the transmitting end S to the mth reflecting array element of RIS, gmRepresenting the element from the m-th reflection array element of the RIS to the D channel vector g of the legal receiving end;
3.3) the legal receiver D obtains the first legal receiving useful signal Z reflected by the RIS1And carrying out vector synthesis on the signals to obtain a regular first amplitude phase modulation signal
Wherein alpha is1Synthesizing signal amplitude gain for a first legal receiving end;
4) constructing a grouping vector synthesis GVS strategy:
4.1) acquiring a RIS reflection coefficient diagonal matrix:
(4.1.1) equally dividing all the reflecting array elements of the RIS into U subsets, each subset then containing a ═ M/U array elements; wherein U is a non-negative integer power of 2, s 1,2, U denoting the s-th subset thereof;
(4.1.2) taking the phase quantization order L as 3, when the discrete phase shift P of the reflection coefficient of the reflection array element in the s-th subsetsIn the collection
The medium value is specifically as follows: firstly, selecting the optimal discrete phase shift of the reflection coefficient of the reflection array element in the subset
Wherein,
is the t array element component in the channel from the s subset of RIS to the legal receiver D,
the t-th array element component in the channels from the transmitting terminal S to the S-th subset of the RIS is t 1, 2.
Then, a set is selected
Middle distance
Nearest point as the s-th subset reflectionDiscrete phase shift P of array element reflection coefficientsIs what is needed
Then
Otherwise, the reverse is carried out
Wherein
Respectively represent collections
The ith or jth element in (e), i, j ∈ {1,2,3},
the method comprises the following steps of (1) indicating that unequal i and j are selected randomly;
(4.1.3) obtaining a second diagonal matrix Lambda composed of the reflection coefficients of the RIS array elements according to the discrete phase shift of the reflection coefficients of the reflection array elements in all the subsets of the RIS:
Λ＝diag(p)，
wherein
Discrete phase-shifted reflection coefficient vectors for respective subsets of the RIS;
4.2) the transmitting terminal designs and sends a second signal to be synthesized according to the RIS feedback
Wherein,
represents a second phase shift keying PSK signal, an
Is the secret signal power; q2Representing the phase of the second signal to be synthesized, the expression is as follows:
4.3) the legal receiver D obtains the second legal receiving useful signal Z reflected by the RIS2And carrying out vector synthesis on the signal to obtain a regular second amplitude phase modulation signal
Wherein alpha is2Synthesizing signal amplitude gain for a second legal receiving end;
5) the legal receiving end D and the eavesdropping end Eve respectively acquire respective receiving signals:
the legal receiving end D respectively carries out vector synthesis on the signals to be synthesized according to the random vector synthesis RVS strategy constructed in the step 3) and the grouping vector synthesis GVS strategy constructed in the step 4) to obtain an observation signal y of the first legal receiving endb1And a second legal receiving end observation signal yb2：
Wherein n isbRepresenting complex Gaussian noise vectors at the legitimate receiver DAn amount;
the eavesdropping end is divided into the following two scenes to eavesdrop the signal to be synthesized, namely a secret signal:
the first method comprises the following steps: when the eavesdropping end has transmission connection with the transmitting end and is blocked from the RIS transmission connection, under the random vector synthesis RVS strategy constructed in the step 3) and the packet vector synthesis GVS strategy constructed in the step 4), the eavesdropping end receives signals which are respectively expressed as
And
wherein n isoRepresenting a complex Gaussian noise vector at an eavesdropping end Eve;
and the second method comprises the following steps: when the eavesdropping end is in transmission connection with the transmitting end and the RIS, under the random vector synthesis RVS strategy constructed in the step 3) and the packet vector synthesis GVS strategy constructed in the step 4), the eavesdropping end receiving signals are respectively expressed as
And
6) the legal receiving end and the eavesdropping end respectively detect and decode the received signals obtained by the legal receiving end and the eavesdropping end:
a legal receiving end performs optimal detection on the phase modulation symbol based on the maximum likelihood estimation criterion, completes secret information decoding and accurately obtains secret information;
the eavesdropping end decodes the secret information under the interference of the vector synthesis strategy constructed by the transmitting end, and the secret information cannot be accurately acquired.
2. The method of claim 1, wherein: channel vectors from transmitting terminal S to RIS and from RIS to legal receiving terminal in step 2)
And
obtained as follows: the transmitting terminal S sends pilot frequency information to the legal receiving terminal D, the pilot frequency information is reflected to the legal receiving terminal D through the RIS, the RIS and the legal receiving terminal D estimate a first channel hopping matrix according to the pilot frequency information, then the first channel hopping matrix is used as the input of the deep residual error network, the second channel hopping matrix is used as the output of the deep residual error network, the network is trained to obtain channel state information, the transmitting terminal completes the accurate estimation of the channel according to the information, and the channel vector from the transmitting terminal to the RIS and the channel vector from the RIS to the legal receiving terminal are obtained.
3. The method of claim 1, wherein: the random vector synthesis RVS strategy in the step 3) and the packet vector synthesis GVS strategy in the step 4) are both constructed according to the channel characteristics, the security of the system under the channel condition and the complexity of the RIS control link, wherein the channel comprises a flat fading channel and a fast fading channel.
4. The method of claim 1The method of (2), characterized by: first legal reception of useful signal Z in step 3.3)1And the first legal receiving end synthesizes the signal amplitude gain alpha1Obtained according to the following formula:
5. the method of claim 1, wherein: second legal reception of useful signal Z in step 4.3)2And the amplitude gain alpha of the combined signal of the second legal receiving end2Obtained according to the following formula:
6. the method of claim 1, wherein: in step 6), the eavesdropping end limits the detection of the signal under the interference of the vector synthesis strategy constructed by the transmitting end, and the detection is specifically divided into the following two conditions:
A. the eavesdropping end has transmission connection with the user end, and when the transmission connection with the RIS is blocked: the eavesdropping end has limited signal detection performance according to the obtained ideal fading channel state information, and cannot synthesize an accurate phase modulation symbol like a legal receiving end;
B. when the eavesdropping end is in transmission connection with the user side and the RIS: and the interception end processes the RIS reflection interference signal and the received noise as color noise according to the obtained ideal fading channel state information, and performs maximum likelihood detection on the intercepted signal after the noise whitening to obtain a decoded signal.
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