A metasurface coding method and wireless transmission system

Abstract

The present invention discloses a metasurface coding method and a wireless transmission system. In the implementation of the present invention, firstly, by calculating the continuous phase to be compensated and quantizing it, a 1-bit programmable metasurface can perform spatial beam control, so that most of the energy of the signal is concentrated in the direction of the legitimate user; an optimization algorithm is used to obtain the weak unit with the largest contribution under the premise of ensuring the communication quality in the legitimate direction; the rotation interference generated by phase noise on the constellation diagram used for demodulation data is used; then, by changing the 1-bit phase compensation of the metasurface for the weak unit, a metasurface code that can introduce effective phase noise to a single eavesdropping direction is selected, and the fuzzy entropy judgment standard is used for evaluation, and the code carrying effective phase noise is added again for the direction whose result is lower than the threshold to enhance protection. Further, by controlling the rapid change of the code set of the metasurface entropy, wireless communication security protection in the eavesdropping direction is completed.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication security, and in particular to a metasurface coding method and a wireless transmission system. Technical Background

[0002] As a new revolutionary wave in the digital world, the Internet of Things (IoT) is changing every aspect of human life through smart homes, smart healthcare, etc. Wireless communication technology has always been the basis for communication among IoT devices.

[0003] However, as wireless technology penetrates into daily life, it is causing strong concerns about privacy. Due to the broadcast nature of wireless media, eavesdroppers can eavesdrop on a legitimate link to steal personal information or even control personal IoT devices such as voice assistants and self-driving cars. To avoid the risk of eavesdropping, a simple solution is to use a complex encryption protocol. However, current IoT devices generally use weak encryption algorithms due to their low cost and low power consumption, making them vulnerable to security attacks. Currently, there are several main types of communication security protection:

[0004] The first one is to add artificial noise, the generation of which relies on multiple antennas or cooperative relays. Although artificial noise-assisted security can ensure the confidentiality of wireless transmission, it is achieved at the cost of wasting precious transmission power resources, which is not available in low-cost and lightweight IoT devices.

[0005] The second method is to perform directional beamforming, which focuses energy in the direction of legitimate users and reduces the signal energy in the sidelobe direction. However, they can only weaken the eavesdropped signal and still pose a risk of being eavesdropped by eavesdroppers with highly sensitive receivers. In addition, this protection measure requires knowing the location information of the eavesdropper.

[0006] In summary, an omnidirectional, low-cost, low-power wireless communication anti-eavesdropping protection method suitable for IoT devices is needed. Summary of the invention

[0007] In view of the defects or shortcomings of the prior art, the present invention first provides a hypersurface encoding method. To this end, the hypersurface encoding method provided by the present invention includes:

[0008] Step 1, perform spatial beam control on the 1-bit programmable metasurface so that the 1-bit programmable metasurface beam points to the legal direction, and obtain the continuous compensation phase of each unit of the 1-bit programmable metasurface and the theoretical phase of the beam in the legal direction of each unit, and at the same time obtain the phase error between the continuous compensation phase of each unit and the 1-bit quantized actual compensation phase;

[0009] Step 2: Use the particle swarm optimization algorithm to maximize the objective function (1) under the two constraints (2) and (3) to obtain the optimized upper boundary UB′ and lower boundary LB′.

[0010]

[0011]

[0012]

[0013] In formula (1)-(3):

[0014] Q * For quantitative rules;

[0015] (m,n) is the position coordinate of any unit on the metasurface, m is the coordinate value in the x direction, m=1,2,3,…,M, M is an integer greater than or equal to 2; n is the coordinate value in the y direction, n=1,2,3,…,N, M is an integer greater than or equal to 2;

[0016] is the continuous compensation phase of unit (m,n);

[0017] is the gain in the main lobe direction of the metasurface;

[0018] is the gain in the direction of the strongest sidelobe of the metasurface energy;

[0019] ξ is the constraint parameter, 8-10;

[0020] is the theoretical phase of the legal directional beam of unit (m, n);

[0021] is the phase error between the continuous compensation phase of unit (m, n) and the 1-bit quantized actual compensation phase;

[0022] is the phase error between the continuous compensation phase of unit (m, n) and the actual compensation phase under the quantization rule updated during the optimization process;

[0023] j is the imaginary unit, j 2 = -1;

[0024] θ l and φ l are the elevation and azimuth angles of the legal directions of the metasurface, respectively;

[0025] γ is the offset component, 0≤γ≤5°;

[0026] Step 3: Use the upper boundary UB′ and the lower boundary LB′ obtained in step 2 to construct the quantization rule (4):

[0027]

[0028] In formula (4), m = 1, 2, 3, ..., M; n = 1, 2, 3, ..., N;

[0029] Step 4, obtain the phase noise of different metasurface codes on each side lobe under the quantization rule (4), and select the one that can introduce π, or Metasurface coding of phase noise, constructing a metasurface coding set using the selected metasurface coding;

[0030] Step 5, evaluate the anti-eavesdropping protection quality of each sidelobe direction under the current metasurface coding set, and for the sidelobe direction that does not meet the protection requirements, select the one that can introduce π, or The phase noise metasurface is coded and added to the current metasurface coding set until all sidelobe methods meet the protection requirements.

[0031] Furthermore, in step 5, a constellation diagram is obtained when demodulating all side lobe directions under the current metasurface coding set, and the entropy value of the constellation diagram is used as an evaluation index of the anti-eavesdropping protection quality of each side lobe direction. The side lobe with an entropy value greater than a threshold meets the protection requirement. The threshold can be determined according to the strictness of confidentiality, such as 0.5 to 1. The larger the threshold, the better the anti-eavesdropping protection effect.

[0032] The present invention also provides a wireless communication system. The wireless communication system provided includes a transmitter, a metasurface and a user end, and the coding set of the metasurface is obtained by the above method; the metasurface is used for anti-eavesdropping protection of the wireless communication system. Furthermore, the metasurface is controlled by FPGA.

[0033] The present invention can not only improve the signal strength in the direction of legitimate users, i.e., the main lobe direction, and enhance the throughput of legitimate communication links by quickly switching the code set on the selected programmable metasurface, but also prevent eavesdropping and improve communication security performance. In particular, communication security protection is performed when the channel state information of the eavesdropping user is unknown. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the compensation phase quantization during 1-bit metasurface beamforming control. The left figure shows the phase of metasurface compensation under theoretical conditions; the right figure shows the phase of actual metasurface compensation under 1-bit quantization.

[0035] Figure 2 The diagrams are the effects of constellation diagram rotation caused by different phase noises; the first row of diagrams are, from left to right, the metasurface coding, the amplitude pattern corresponding to the coding, and the phase pattern corresponding to the coding; the second row of diagrams are, from left to right, the results after changing the variable unit coding, the amplitude pattern corresponding to the changed coding, and the phase pattern.

[0036] Figure 3 The signal strength evaluation results of a legitimate user of an embodiment of the present invention when using the invention in different directions and when not using the invention.

[0037] Figure 4 The diagram is an evaluation result of the bit error rate when the legitimate user of the embodiment of the present invention uses the present invention and does not use the present invention in different directions.

[0038] Figure 5 It is the signal strength result of the embodiment of the present invention in the reverse link.

[0039] Figure 6 This is the bit error rate result of the embodiment of the present invention in the reverse link communication.

[0040] Figure 7 Graphs 1 and 2 are the bit error rate results of the communication of the present invention when using different modulation and demodulation methods.

[0041] Figure 8 The communication performance results of the present invention are shown when wireless signals are modulated and demodulated using common modulation methods: QPSK, 8PSK, QAM, 16QAM, and OFDM.

[0042] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0043] Unless otherwise specified, the scientific and technical terms and methods in this document are based on the understanding of ordinary technicians in the relevant fields or are implemented using relevant methods known to ordinary technicians in the relevant fields.

[0044] The present invention firstly calculates the continuous compensation phase and quantizes it, so that the 1-bit programmable metasurface can perform spatial beam control, so that most of the signal energy is concentrated in the direction of the legitimate user, and then calculates the continuous compensation phase of each unit and the theoretical phase of the beam in the legitimate direction of each unit, and simultaneously obtains the phase error between the continuous compensation phase of each unit and the 1-bit quantized actual compensation phase; uses the optimization algorithm to obtain the weak units with the largest contribution under the premise of ensuring the communication quality in the legitimate direction; uses Phase noise produces rotational interference on the constellation diagram used for demodulating data; then, by changing the 1-bit phase compensation of the metasurface for weak units, the metasurface code that can introduce effective phase noise to a single eavesdropping direction is selected, and the fuzzy entropy judgment standard is used for evaluation. For directions with results below the threshold, codes carrying effective phase noise are added again to enhance protection. Furthermore, by controlling the rapid change of the code set of the metasurface entropy, wireless communication security protection in the eavesdropping direction is completed.

[0045] Step 1 of the present invention can be implemented by using the existing technical method, wherein the continuous compensation phase of each unit can be modeled by using Matlab mathematical simulation modeling software on the path of feed source-metasurface-user, and the continuous compensation phase of unit (m, n) in:

[0046]

[0047]

[0048]

[0049] in, is the continuous phase value of the beam in the legal direction (i.e., main lobe) of the unit (m, n), (m, n) is the position of the metasurface unit, k = 2π / λ, x m and n are the x-component and y-component of the distance of the (m,n)th hypersurface unit from the origin (the structural center of the hypersurface) in the Cartesian coordinate system, respectively, λ is the wavelength; θ l and φ l are the elevation angle and azimuth angle of the legitimate user, i.e. the main lobe of the beam; is the actual phase value of the electromagnetic wave arriving at the metasurface from the feed source (transmitter), d (m，n) is the distance from the feed source to the (m, n)th super-surface unit. Since the programmable metasurface used in the present invention is a 1-bit metasurface, it can only be regulated by 0 or π. The quantization rule is used so that most of the signal energy is concentrated in the direction of the legitimate user, and the direction of the legitimate user is used as the main lobe direction of the desired beam for beam forming.

[0050] Due to the quantization rule of 1-bit programmable metasurface beamforming, the compensation phase close to 0 may become 0 after 1-bit quantization. It is also possible that the compensation phase is actually close to π but is also quantized to 0 according to the quantization rule, such as Figure 1 As shown in (a, b), this makes the contribution of each unit to the main lobe inconsistent, such as Figure 2As shown, different quantized phase values ​​of units with weaker contribution have little effect on the main lobe, but have a great impact on the phase of the side lobe. Units with weaker contribution can be defined as "weak units". In order to obtain more "weak units", the present invention uses the particle swarm optimization algorithm to optimize the upper and lower phase value boundaries of quantization under the two constraints (2) and (3), and then constructs a new quantization rule (4).

[0051] After the signal sent by the transmitter is modulated by the metasurface, the signal received by the receiver will be affected by phase noise. Specifically, for the signal S sent by the feed end r , Where E0 is the signal energy, φ(r) is the signal phase; the received signal S′ after metasurface modulation r for:

[0052]

[0053] in, is the phase noise caused by the metasurface, is the phase change generated in the transmission path from the metasurface to the receiving end. Based on this, the present invention further studies the rotation effect of phase noise on the sidelobe constellation diagram during demodulation under the quantization rule (4), selects the effective phase noise, and finds that phase noise will cause the rotation effect of the constellation diagram during demodulation. Figure 3 As shown in (a, b, c, d), The three phase noises of π can respectively cause the rotation of the constellation diagram across the first quadrant, the second quadrant, and the third quadrant. The effective phase noise selected for the present invention.

[0054] Example:

[0055] The metasurface of this embodiment is a 1-bit programmable metasurface. A DC regulator (MESTEK DP3005B) is used to provide a bias voltage for the metasurface. By giving different DC voltage levels (0V or 5V), a pair of PIN diodes in each unit is switched to opposite states, thereby acting as a 1-bit phase shifter to introduce a phase value of 0 or π.

[0056] In order to control each cell independently, a Kintex-7 FPGA and 32 SN74HC595 shift registers are used to provide bias voltage. Specifically, 256 cells are divided into 8 groups in parallel, and each group consists of 4 shift registers to control 32 elements continuously.

[0057] The method of the present invention is used to construct coding sets for 11 legal directions (-50, -40, -30, -20, -10, 0, 10, 20, 30, 40, 50°) of the super surface, and finally the coding sets in the 11 legal directions are summarized to obtain a total coding set, which contains 300 sets of codes; ξ=9, γ=3° in the process, and this embodiment evaluates the effectiveness of communication protection in all directions, specifically including:

[0058] Use MATLAB to obtain the entropy data of the aliasing effect in each direction. The entropy calculation is shown as follows:

[0059]

[0060]

[0061] Where L cluster represents the number of categories, R c Indicates the total amount of data transferred. Indicates the number of data belonging to class p in all transmitted data; P pq is the probability that the data of cluster p belongs to class q;

[0062] When e p <0.5, it is determined that the aliasing effect in this direction is poor; for the sidelobe direction where e is less than 0.5, more coding modes with gain phase noise are added to this direction to enhance the degree of confusion.

[0063] The chaotic coding pattern set for each legal direction is pre-stored in the FPGA. When a legal direction is determined, a coding pattern is randomly selected from the corresponding total coding set to reconfigure the metasurface. In order to perform parallel control, the data in the coding set is divided into 8 groups, and then the 8 groups of codes are input into 8 data memories to control 32 shift registers to quickly output the entire coding set.

[0064] Furthermore, the inventors attempted to evaluate the method for improving the security performance of wireless communications based on programmable metasurfaces provided by the present invention from the following aspects:

[0065] Signal strength and communication quality performance in different legitimate user directions:

[0066] Figure 4 The evaluation results of the signal strength when the method for improving wireless communication security performance based on programmable metasurface is used by a legitimate user in different directions and when it is not used, Figure 5The communication quality evaluation results of the method for improving wireless communication security performance based on programmable metasurface when the legitimate users are located at different locations. It can be seen that when the legitimate users are located at different locations, the method can significantly improve the signal strength in the legitimate direction and maintain a high communication quality.

[0067] Reverse link performance:

[0068] Figure 6 is the signal strength result in the reverse link, Figure 7 The communication bit error rate result in the reverse link. From the figure, we can see that our method can also improve the signal strength and communication security performance of the directional link.

[0069] Comparative evaluation of performance of different modulation modes:

[0070] Figure 8 The communication performance results of wireless signal modulation and demodulation using common modulation methods: QPSK, 8PSK, QAM, 16QAM, and OFDM. From the figure, we can see that this method can maintain good performance under different modulation schemes.

Claims

1. A super surface encoding method, characterized in that the method include: Step 1, perform spatial beam control on the 1-bit programmable metasurface so that the 1-bit programmable metasurface beam points to the legal direction, and obtain the continuous compensation phase of each unit of the 1-bit programmable metasurface and the theoretical phase of the beam in the legal direction of each unit, and at the same time obtain the phase error between the continuous compensation phase of each unit and the 1-bit quantized actual compensation phase; Step 2: Use the particle swarm optimization algorithm to maximize the objective function (1) under the two constraints (2) and (3) to obtain the optimized upper boundary UB′ and lower boundary LB′. In formula (1)-(3): Q * For quantitative rules; (m,n) is the position coordinate of any unit on the metasurface, m is the coordinate value in the x direction, m=1,2,3,…,M, M is an integer greater than or equal to 2; n is the coordinate value in the y direction, n=1,2,3,…,N, M is an integer greater than or equal to 2; is the continuous compensation phase of unit (m,n); is the gain in the main lobe direction of the metasurface; is the gain in the direction of the strongest sidelobe of the metasurface energy; ξ is a constraint parameter, with a value range of 8-10; is the theoretical phase of the legal directional beam of unit (m,n); is the phase error between the continuous compensation phase of unit (m,n) and the 1-bit quantized actual compensation phase; is the phase error between the continuous compensation phase of unit (m, n) and the actual compensation phase under the quantization rule updated during the optimization process; j is the imaginary unit, j 2 = -1; θ l and φ l are the elevation and azimuth angles of the legal directions of the metasurface, respectively; γ is the offset component, 0≤γ≤5°; Step 3: Use the upper boundary UB′ and the lower boundary LB′ obtained in step 2 to construct the quantization rule (4): In formula (4), m = 1, 2, 3, ..., M; n = 1, 2, 3, ..., N; Step 4, obtain the phase noise of different metasurface codes on each side lobe under the quantization rule (4), and select the one that can introduce π, or Metasurface coding of phase noise, constructing a metasurface coding set using the selected metasurface coding; Step 5, evaluate the anti-eavesdropping protection quality of each sidelobe direction under the current metasurface coding set, and for the sidelobe direction that does not meet the protection requirements, select the one that can introduce π, or The phase noise metasurface is coded and added to the current metasurface coding set until all sidelobe methods meet the protection requirements.

2. The supersurface encoding method according to claim 1, characterized in that: In step 5, the constellation diagram of all sidelobe directions demodulated under the current metasurface coding set is obtained, and the entropy value of the constellation diagram is used as an evaluation index of the anti-eavesdropping protection quality of each sidelobe direction. The sidelobe with an entropy value greater than the threshold meets the protection requirements.

3. A wireless communication system, comprising a transmitting end, a metasurface and a user end, characterized in that: The coding set of the metasurface is obtained by the method described in claim 1; the metasurface is used for anti-eavesdropping protection of wireless communication systems.

4. The wireless communication system according to claim 3, wherein: The metasurface is controlled by FPGA.

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