Hidden backscatter communication method based on multicarrier randomized continuous waves

Abstract

The invention provides a hidden backscatter communication method based on multicarrier randomized continuous waves. The method comprises the following steps: acquiring multicarrier randomized continuous wave signal characteristic parameters, backscatter signal characteristic parameters and channel parameters between a transceiver and a listener and between the transceiver and each user; according to the characteristic parameters of the multicarrier randomized continuous wave signal and channel parameters between the transceiver and the listener and between the transceiver and each user, determining relative entropy between probability density functions of the listener receiving signal when the user generates a backscattering signal and when the user does not generate the backscattering signal; determining the total reachable rate between the transceiver and all users according to the multicarrier randomized continuous wave signal characteristic parameters, the backscattering signal characteristic parameters and the channel parameters; and maximizing the total reachable rate through a target optimization algorithm by taking the condition that the relative entropy meets the concealment condition as the constraint, and obtaining the optimized statistical characteristic parameters of the multicarrier randomized continuous waves. According to the invention, hidden backscatter communication can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of backscatter communication, and particularly relates to a covert backscatter communication method based on multi-carrier randomization continuous wave. BACKGROUND

[0002] Due to the openness of a wireless channel, backscatter communication (BackCom) is vulnerable to eavesdropping attacks, and the low complexity characteristics of backscatter devices limit the application of complex encryption algorithms, so the security and privacy problems in the BackCom process have attracted widespread attention. Traditional physical layer security technology mainly aims to protect the content of information, and it is difficult to hide the existence of communication activities itself. In this context, covert communication as a low detection probability communication method has been widely studied.

[0003] The main technologies for realizing covert BackCom include deployment optimization, beamforming technology and artificial noise, etc. Deployment optimization can utilize the mobility of vehicles such as unmanned aerial vehicles (UAVs) to actively adjust the channel, differentiate the gains of backscatter links and eavesdropping links, and combine power optimization, so that the eavesdropper is difficult to discover the BackCom behavior. However, this method relies on the mobility of vehicles, and does not fully exploit the potential of physical layer related signal processing technology in covert communication. In contrast, beamforming technology can realize covert transmission by enhancing the signal in the direction of the legitimate receiver while reducing the signal strength of the monitoring link. However, the beamforming technology comes at the cost of the increase of radio frequency chains and the number of antennas, which puts higher requirements on the hardware design of backscatter devices. In addition, artificial noise assisted schemes are widely used in covert BackCom due to their characteristics of increasing the uncertainty of the received signal of the eavesdropper. By introducing the uncertainty of artificial noise, the detection of the eavesdropper is effectively disturbed. However, this method will increase the additional power consumption, and also cause interference to the legitimate receiving end. Therefore, it is urgent to propose a method to avoid the above problems and realize covert backscatter communication. SUMMARY

[0004] Therefore, the application aims to provide a covert backscatter communication method based on multi-carrier randomization continuous wave and a device, so as to meet the needs of realizing covert backscatter communication.

[0005] To achieve the above-mentioned purpose, the application provides the following technical scheme:

[0006] According to a first aspect, the present invention provides a covert backscatter communication method based on multi-carrier randomized continuous wave, comprising: obtaining characteristic parameters of a multi-carrier randomized continuous wave signal sent by a transceiver, characteristic parameters of a backscattered signal received by the transceiver, and channel parameters between the transceiver and a listener and each user, wherein the characteristic parameters of the multi-carrier randomized continuous wave signal include statistical characteristic parameters of the multi-carrier randomized continuous wave, and the backscattered signal is modulated by each user according to the multi-carrier randomized continuous wave signal; determining, based on the characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver and the channel parameters between the transceiver and the listener and each user, a relative entropy between probability density functions of a signal received by the listener in a scenario where the user generates a backscattered signal and a scenario where the user does not generate a backscattered signal; determining, based on the characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver, characteristic parameters of the backscattered signal received by the transceiver, and channel parameters between the transceiver and each user, a total achievable rate between the transceiver and all users; maximizing the total achievable rate through a target optimization algorithm with the relative entropy satisfying a concealment condition as a constraint, thereby obtaining the optimized statistical characteristic parameters of the multi-carrier randomized continuous wave.

[0007] According to the second aspect, an embodiment of the present invention provides a covert backscatter communication device based on multi-carrier randomized continuous wave, comprising: an information acquisition module for acquiring characteristic parameters of a multi-carrier randomized continuous wave signal sent by a transceiver, characteristic parameters of a backscattered signal received by the transceiver, and channel parameters between the transceiver and the listener and each user, wherein the characteristic parameters of the multi-carrier randomized continuous wave signal include statistical characteristic parameters of the multi-carrier randomized continuous wave, and the backscattered signal is modulated by each user according to the multi-carrier randomized continuous wave signal; a relative entropy determination module for determining the backscattered signal according to the characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver and the channel parameters between the transceiver and the listener and each user, The channel parameters between the listener and each user are used to determine the relative entropy between the probability density functions of the signal received by the listener in the scenario where the user generates a backscatter signal and the scenario where the user does not generate a backscatter signal; the total achievable rate determination module is used to determine the total achievable rate between the transceiver and all users based on the characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver, the characteristic parameters of the backscatter signal received by the transceiver, and the channel parameters between the transceiver and each user; the optimization module is used to maximize the total achievable rate through the target optimization algorithm with the relative entropy satisfying the concealment condition as the constraint, and obtain the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave.

[0008] According to the third aspect, an embodiment of the present invention provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and runnable on the processor, wherein the processor executes the steps of the covert backscatter communication method based on multi-carrier randomized continuous wave described in the first aspect or any embodiment of the first aspect.

[0009] According to the fourth aspect, an embodiment of the present invention provides a computer storage medium having computer instructions stored thereon, which, when executed by a processor, implement the steps of the covert backscatter communication method based on multi-carrier randomized continuous wave as described in the first aspect or any embodiment of the first aspect.

[0010] The present invention provides a covert backscatter communication method based on multi-carrier randomized continuous wave, which aims to maximize the achievable rate of multiple users and effectively improves the concealment of multi-user BackCom by utilizing the randomization characteristics of multi-carrier randomized continuous wave (RCW), thereby realizing covert backscatter communication.

[0011] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to make the purpose, technical solutions and beneficial effects of the present invention more clear, the present invention provides the following drawings for illustration:

[0013] Figure 1 A model diagram of a multi-user covert backscatter communication system based on multi-carrier RCW in the present invention;

[0014] Figure 2 This is a specific example flow chart of a covert backscatter communication method based on multi-carrier randomized continuous waves of the present invention;

[0015] Figure 3 The relationship between the achievable rate of multiple users and the concealment requirement under different modulation modes is shown in the figure;

[0016] Figure 4 The relationship between the achievable rate and the maximum transmit power under different numbers of users is shown in the figure.

[0017] Figure 5 This is the relationship between multi-user transmission rate and maximum transmission power under different transmission schemes;

[0018] Figure 6This is a graph showing the relationship between multi-user transmission rate and the number of subcarriers in a multi-carrier RCW system;

[0019] Figure 7 is a graph showing the relationship between spectrum efficiency and multi-carrier RCW bandwidth;

[0020] Figure 8 This is a principle block diagram of a specific example of an electronic device in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components; wireless connections or wired connections. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0023] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0024] The use environment of the present invention is as follows: Figure 1 As shown in Figure 2, a multi-user covert BackCom scenario is considered. In this scenario, a full-duplex wireless transceiver (transceiver) communicates simultaneously with N users (users) equipped with backscattering tags under the monitoring of an eavesdropper (listener). The transceiver, listener, and tags are each equipped with a single antenna. Specifically, the transceiver transmits a multi-carrier randomized continuous wave signal with I discrete frequencies through a single antenna. The radio frequency (RF) signal is incident on the tags through different communication channels. These tags can use a portion of the energy from the received signal to modulate information or absorb all of the received signal energy and remain silent. During the information transmission phase, the tags simultaneously modulate the incident signal and backscatter it to the transceiver for information transmission. After receiving the backscattered signal from the tag, the transceiver can demodulate the modulated data embedded in the multi-carrier randomized continuous wave. Simultaneously, the listener uses a radiometer-based detector to detect whether the tag is backscattering.

[0025] In order to realize the covert scattering communication of multiple users, the embodiment of the present invention provides a covert backscattering communication method based on multi-carrier randomized continuous wave, such as Figure 2 Shown, including:

[0026] S101, obtaining characteristic parameters of a multi-carrier randomized continuous wave signal transmitted by a transceiver, characteristic parameters of a backscattered signal received by the transceiver, and channel parameters between the transceiver and a listener and each user, respectively. The characteristic parameters of the multi-carrier randomized continuous wave signal include statistical characteristic parameters of the multi-carrier randomized continuous wave. The backscattered signal is modulated by each user according to the multi-carrier randomized continuous wave signal.

[0027] S102, determining, based on characteristic parameters of a multi-carrier randomized continuous wave signal sent by the transceiver and channel parameters between the transceiver and the listener and each user, a relative entropy between probability density functions of a signal received by the listener in a scenario where the user generates a backscattered signal and a scenario where the user does not generate a backscattered signal;

[0028] S103, determining a total achievable rate between the transceiver and all users based on characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver, characteristic parameters of the backscattered signal received by the transceiver, and channel parameters between the transceiver and each user;

[0029] S104, with the relative entropy satisfying the concealment condition as a constraint, the total achievable rate is maximized through a target optimization algorithm to obtain the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave.

[0030] By way of example, in order to illustrate the solution of this embodiment, we first construct a signal model of a multi-carrier randomized continuous wave, a listener receiving signal model, and a listener detection model, and analyze the detection performance of the listener. Then, we determine the achievable rate expression based on the signal model of the multi-carrier randomized continuous wave and the transceiver receiving signal model. Then, based on the detection performance of the listener, we determine the relative entropy between the probability density functions of the listener receiving signal in the scenario where the user generates a backscattered signal and in the scenario where the user does not generate a backscattered signal. Finally, under the relative entropy constraint, we adjust the statistical characteristic parameters of the multi-carrier randomized continuous wave to maximize the achievable rate.

[0031] Specifically, the signal model of the multi-carrier randomized continuous wave in the kth time slot is:

[0032]

[0033] Among them, s i,krepresents the coefficient of the i-th subcarrier and remains constant within a time slot. It satisfies the Circularly Symmetric Complex Gaussian (CSCG) distribution in different time slots and can be expressed as in represents the mean vector, Φ represents the covariance matrix corresponding to the multi-carrier randomized continuous wave. In addition, ω i =2πf i represents the angular frequency of the i-th subcarrier, f i is the center frequency, I represents the total number of subcarriers, e is a natural constant, and j is an imaginary unit.

[0034] Therefore, the carrier frequency f of the transmitted signal C for:

[0035]

[0036] Among them, f1, f I They respectively represent the carrier frequency of the first subcarrier and the carrier frequency of the I-th subcarrier of the multicarrier RCW.

[0037] The complex channel gain experienced by the i-th subcarrier of the RF signal when transmitted to the n-th user is:

[0038]

[0039] Where χ is the Rice factor, the Line of Sight (LoS) component and the None Line of Sight (NLoS) Rayleigh fading component are and d RU,n is the distance between the transceiver and the nth user, α LoS and α NLoS is the fading coefficient of LoS and NloS channels, G0 = (λ / 4π) 2 is the channel power gain, where λ = ν / f C and θ i =ω i / ν, ν represents the wave velocity. Assume that due to the reciprocity of the channel, h RU,n,i With h UR,n,i equal.

[0040] Based on the multi-carrier randomized continuous wave signal model constructed above, the received signal model of the nth user in the kth time slot is:

[0041] y U,n,k =S k h RU,n ; (4)

[0042] Among them, the RF signal The complex channel coefficient matrix between the transceiver and the user can be expressed as The tag absorbs a portion of the energy of the received RF signal for information modulation and then backscatters the modulated carrier signal.

[0043] Based on the above formula, the backscattered signal received by the transceiver is:

[0044]

[0045] Among them, c n,k It represents the equally probable data symbol transmitted by the nth tag in the kth time slot. Taking Binary Phase Shift Keying (BPSK) as an example, ⊙ represents the Hadamard product between two vectors. The power reflection coefficient of the tag is Γ, and the self-interference coefficient is defined as φ∈[0,1]. Considering that the transceiver knows the randomization information of the multi-carrier randomized continuous wave completely, φ=0. The additive white Gaussian noise on the subcarrier in the received signal is n R,k =[n R,1,k ,n R,2,k ,...,n R,I,k ] T , obeys the zero-mean CSCG distribution, that is, Among them I I is an I×I identity matrix.

[0046] The equivalent channel matrix is ​​defined as:

[0047]

[0048] in, Therefore, (5) can be simplified as:

[0049] y R,k =S k H RUR c k +n R,k ; (7)

[0050] Among them, c k =[c 1,k ,c 2,k ,...,c N,k ] T ∈B N Represents data symbols modulated by N tags, satisfying

[0051] Next, we construct a detection model for the listener. The listener's received signal model is a binary hypothesis problem. Specifically, hypothesis H0 represents the case where the user's backscatter tag absorbs all RF signal energy (that is, when the user does not generate a backscatter signal), while hypothesis H1 corresponds to the tag's backscatter transmission behavior (that is, when the user generates a backscatter signal). Therefore, the listener's received signal is:

[0052]

[0053] Among them, n W,k =[n W,1,k ,n W,2,k ,...,n W,I,k ] T The noise on the subcarrier of the received signal satisfies the zero-mean CSCG distribution, that is, the expectation is h RW is the complex channel coefficient matrix between the transceiver and the listener, h UW,n is the complex channel coefficient matrix between the nth user and the listener, H RUW The equivalent channel matrix experienced by the listener when the RF signal sent by the transceiver is received via user backscatter can be expressed as:

[0054]

[0055] After receiving the signal in each time slot, the listener needs to determine whether the tag has backscattering behavior. Due to the randomization characteristics of the multi-carrier randomized continuous wave, the listener may make an incorrect judgment on the occurrence of backscattering behavior. For the sake of clarity, let D0 and D1 represent the listener's judgment on the tag being unmodulated and modulated respectively, and the false alarm probability P FA = P(D1|H0) means that the listener mistakenly detects the modulation, and the probability of missed detection is P MD = P(D0|H1) corresponds to the listener failing to detect the modulation. Consider a scenario where the prior probabilities are equal, such that P(H0) / P(H1) = 1. This indicates that the listener cannot use past detection results to improve its judgment. In this case, the listener's detection performance can be expressed in terms of the probability of detection error, specifically:

[0056] ξ=P FA +P MD ; (10)

[0057] The goal of the listener is to minimize ξ by adjusting the optimal threshold for power detection. For the transceiver, ensuring covert communication requires achieving ξ ≥ 1-∈ in the worst case to satisfy the covert constraint, where ∈∈(0, 1) represents the covertness requirement. To ensure sufficient covertness, the value of ∈ is usually kept relatively low.

[0058] Then, the detection performance of the listener is analyzed. The detection error probability of the listener can be expressed by the relative entropy (Kullback-Leibler divergence) as:

[0059]

[0060] where D(P0||P1)) represents the relative entropy between the probability distribution of the listener receiving the signal P0 (the listener does not receive the backscattered signal) and P1 (the listener receives the backscattered signal). In order to meet the required concealment constraint ξ≥1-∈, the lower bound of ξ is used instead, that is, Therefore, the hiddenness constraint can be further expressed as:

[0061]

[0062] Considering the independence between multi-carrier randomized continuous wave and noise, y W Satisfied with CSCG distribution:

[0063]

[0064] Among them, c m It's B N The mth vector, I I represents the I-dimensional identity matrix, and the channel coefficient matrix is ​​defined as:

[0065]

[0066] Considering the given c m situation, It can be expressed as:

[0067]

[0068] Among them, h W0,i and h W0 and The i-th element of . Column vector h W0 and It is by H W0 and In addition, the mean and covariance associated with the ith carrier are given by and Φ i Therefore, the relative entropy between the probability density functions of the listener receiving the signal under H0 and H1 can be expressed as:

[0069]

[0070] Wherein, L represents that there are L possibilities for N users to transmit data symbol vectors.

[0071] The achievable rate between the transceiver and the user tag is used to evaluate the BackCom performance. Since the user tag uses a limited alphabet for information transmission, the achievable rate can be derived from the mutual information. The transmission performance of the covert BackCom is measured by the number of bits per channel used (BPCU). The received signal y R The mutual information between the transmitted signal s is:

[0072]

[0073] Among them, h(y R |c,s) means y given s and c R The entropy, h(y R |s) means that given s, y R Since the transceiver has complete knowledge of the transmitted signal s, the achievable rate can be expressed as:

[0074] C U =I(y R ;c|s) (18)

[0075] Because n R Satisfies the zero mean CSCG, so the differential entropy h(n R ) can be expressed as:

[0076]

[0077] In addition, since s is known, the received signal y R The conditional probability distribution of is:

[0078]

[0079] in, Indicates the received signal y R When s and c=c are known m Conditional probability distribution under the condition, ||*|| 2 Therefore, the conditional differential entropy h(y R |s) is:

[0080]

[0081] Among them, E s represents all possible expectations for s, Indicates the received signal y R Conditional probability distribution under the condition that s is known;

[0082] definition in You can get:

[0083] y-SH RUR c l =n′ R +SH RUR (c m -c l ) (twenty two)

[0084] Among them, c l It's B N The lth vector of .

[0085] Therefore, the achievable rate can be expressed as:

[0086]

[0087] in, Represents the random variables s and n′ R The mathematical expectation of the joint distribution of .

[0088] Because C U The expression contains the expected expression, so C U It can be approximately expressed as:

[0089]

[0090] in, Therefore, through (24), a low-complexity algorithm can be designed to optimize the rate.

[0091] Based on the above-mentioned construction content, the covert backscatter communication method based on multi-carrier randomized continuous wave provided in this embodiment first obtains the following parameters: characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver, characteristic parameters of the backscattered signal received by the transceiver, and channel parameters between the transceiver and the listener and each user, wherein the characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver include statistical characteristic parameters of the multi-carrier randomized continuous wave signal, such as the mean vector and covariance matrix of the multi-carrier randomized continuous wave, as well as the total number of subcarriers of the multi-carrier signal, the total bandwidth of the multi-carrier signal, etc.; the characteristic parameters of the backscattered signal received by the transceiver include modulation symbols and power reflection coefficients; the channel parameters between the transceiver and the listener and each user include channel noise of each channel and the variance of the noise, complex channel coefficient matrix, etc.

[0092] Then, according to the characteristic parameters of the multicarrier randomized continuous wave signal and the channel parameters between the transceiver and the listener and each user, the probability distribution parameters of the listener's received signal in the scenario where the user does not generate a backscattering signal (H0) and the scenario where the user generates a backscattering signal (H1) are determined; according to the probability distribution parameters of the listener's received signal in the two scenarios, the relative entropy of the probability density function of the listener's received signal in the two scenarios is determined, and details are described in formulas (13)-(16) and will not be described herein.

[0093] Then, under the condition that the transmitted multicarrier randomized continuous wave signal is known, according to the channel parameters between the transceiver and each user and the characteristic parameters of the multicarrier randomized continuous wave signal transmitted by the transceiver, the total uncertainty of the received backscattering signal is determined (the uncertainty is measured by entropy, see formula (17) corresponding to h(y R )) ; under the condition that the transmitted multicarrier randomized continuous wave signal and the modulation symbol are known, according to the channel noise between the transceiver and each user, the uncertainty caused by the channel noise of the received backscattering signal is determined (the uncertainty is measured by entropy, see formula (17) corresponding to h(n R )) ; according to the total uncertainty of the received backscattering signal and the uncertainty caused by the channel noise, the total achievable rate between the transceiver and all users is determined, that is, the mutual information between the received signal y R and the data symbol vector c under the condition that the transmitted signal s is known, and the specific process is described in formulas (18)-(24) and will not be described herein.

[0094] After the relative entropy and the achievable rate are determined, the relative entropy satisfies the concealment condition and the maximum transmission power of the transceiver is constrained, the total achievable rate is maximized by a target optimization algorithm, and the statistical characteristic parameters of the optimized multicarrier randomized continuous wave are obtained, including: the first optimization target is constructed by maximizing the total achievable rate as the target and constraining the relative entropy to satisfy the concealment condition and the maximum transmission power of the transceiver; the Lagrange dual ascent algorithm is used to transform the first optimization target to obtain the second optimization target; in the second optimization target, the local optimal target parameter is calculated, the target parameter is related to the statistical characteristic parameters of the multicarrier randomized continuous wave; the Lagrange multiplier is updated, and the local optimal target parameter is iteratively calculated again until convergence, and the optimal target parameter is obtained; according to the optimal target parameter, the statistical characteristic parameters of the optimized multicarrier randomized continuous wave are determined.

[0095] Exemplarily, the first optimization target is:

[0096]

[0097] stD(P0||P1)≤2∈ 2 ,

[0098]

[0099] η±0,

[0100]

[0101] in, is a column vector consisting of the diagonal elements in Φ, P max is the maximum transmit power of the transceiver, 1 N is a unit vector of length N. This optimization problem is a non-convex optimization problem. To obtain η and The analytical solution of is very difficult. In order to solve this non-convex problem, the Lagrangian dual ascent algorithm is used to search for η and By introducing the Lagrange multiplier, the original problem is transformed into a dual problem, thus achieving distributed solution. The Lagrange function can be expressed as

[0102]

[0103] Where α1, α2, β, and γ represent Lagrange multipliers. After the optimization objective in (25) is expressed as a Lagrangian function, the second optimization objective related to its Lagrangian dual function can be given by the following formula:

[0104]

[0105] stα1>0,

[0106] α2>0,

[0107] β±0,

[0108] γ±0, (27)

[0109] Given the initial values ​​of the Lagrange multipliers, the optimization problem (27) first calculates the local optimal η and On this basis, the Lagrange multiplier is updated accordingly. By iterating these two steps, the process gradually converges to the optimal η and Thus maximizing Then, we can further obtain the achievable rate C through (23): U .

[0110] The present invention aims to maximize the achievable rate of multiple users and effectively improves the concealment of multi-user BackCom by utilizing the randomization characteristics of multi-carrier RCW. During the simulation process, a unified carrier frequency and node position coordinates are used, and the modulation mode is BPSK, where

[0111] In order to analyze the achievable rate under different concealment requirements, Figure 3 This paper demonstrates that multi-carrier continuous wave (CW) schemes cannot achieve efficient transmission when ω is relatively low. This is because the deterministic nature of CW signals allows eavesdroppers to easily detect backscattered transmissions. Therefore, transceivers must significantly reduce the tag's backscatter power to ensure concealment, which significantly reduces the achievable rate. Furthermore, while multi-carrier CW schemes can achieve a high achievable rate when ω is sufficiently large, eavesdroppers can easily detect transmission activity in this case. In contrast, multi-carrier RCW schemes rapidly increase their achievable rate as ω increases, approaching the non-covert transmission rate of multi-carrier CW schemes. This is because multi-carrier RCW allocates most of the transmission power to the mean vector, while maintaining concealment through only a small randomized component. Furthermore, employing higher-order modulation schemes (M-order phase shift keying), such as quadrature phase shift keying (QPSK), can further improve the achievable rate.

[0112] In addition, the impact of different access tag numbers on the achievable rate is further analyzed. Figure 4 It shows that as P max With the increase of , the achievable rate under the multi-carrier RCW scheme gradually increases and eventually converges to Nlog2M, which reflects the inherent multi-user concurrent transmission capability of the multi-carrier system. This paper adopts the CSCG single-carrier scheme as a benchmark and implements multi-tag access through the Time Division Multiple Access (TDMA) method. It can be seen that as the transmission power increases, the achievable rate of the CSCG single-carrier scheme converges to log2M. At the same time, due to the differences in channel conditions between tags, increasing the number of tags in a single-carrier system does not significantly improve the achievable rate. In some cases, adding tags with poor channel quality can even reduce the overall rate. In contrast, the multi-carrier RCW scheme significantly improves the overall achievable rate of multi-tag communications.

[0113] Next, the multi-user access performance of multi-carrier RCW is analyzed. Figure 5The transmission rates under different transmission schemes are shown. For comparison, this paper uses a single-carrier transmission scheme that uses TDMA technology to achieve multi-tag communication as a benchmark. The following three points can be seen: (1) Compared with multi-carrier CW, the multi-carrier RCW system uses its inherent randomization characteristics to effectively interfere with the detection of the eavesdropper, thereby achieving a higher transmission rate. A similar effect is also seen in the single-carrier transmission scheme; (2) Multi-carrier RCW only requires a small amount of randomization components to maintain the concealment of multi-user BackCom. Therefore, the multi-carrier RCW scheme achieves nearly optimal performance comparable to the multi-carrier CW scheme in the non-covert transmission scenario. The same conclusion is also reached in the single-carrier scenario; (3) Multi-carrier RCW can achieve simultaneous communication of multiple tags in a single time slot, thereby improving the transmission rate.

[0114] Figure 6 The results show that as the bandwidth of multicarrier RCW increases (while maintaining the subcarrier spacing, i.e., increasing the number of subcarriers), the transmission rate increases and gradually converges. This is because the increased number of subcarriers enhances the communication system's robustness against interference in frequency-selective fading channels, effectively improving transmission reliability. In contrast, the TDMA-based CSCG single-carrier scheme achieves higher transmission rates by shortening the symbol duration as the bandwidth increases. However, its transmission rate is still lower than that of the multicarrier RCW scheme.

[0115] Figure 7 It shows that when the number of subcarriers remains unchanged, the total spectral efficiency decreases with the increase of bandwidth. This trend is mainly due to the fact that bandwidth expansion introduces a wider noise bandwidth, which increases the total noise power of the communication system and reduces the signal-to-noise ratio of each subcarrier, resulting in a decrease in spectral efficiency. In addition, the multi-carrier RCW scheme proposed in this application is always better than the CSCG single-carrier TDMA-based scheme across the entire bandwidth range. Even at relatively low transmit power, the multi-carrier RCW system can achieve higher spectral efficiency, exceeding the single-carrier scheme at higher transmit power levels. This result highlights the performance advantage of the multi-carrier RCW structure in spectrum reuse.

[0116] This embodiment provides a covert backscatter communication device based on multi-carrier randomized continuous waves, including:

[0117] An information acquisition module is used to obtain characteristic parameters of a multi-carrier randomized continuous wave signal transmitted by the transceiver, characteristic parameters of a backscattered signal received by the transceiver, and channel parameters between the transceiver and the listener and each user, wherein the characteristic parameters of the multi-carrier randomized continuous wave signal include statistical characteristic parameters of the multi-carrier randomized continuous wave, and the backscattered signal is modulated by each user according to the multi-carrier randomized continuous wave signal;

[0118] A relative entropy determination module is used to determine the relative entropy between the probability density functions of the signal received by the listener in a scenario where the user generates a backscatter signal and a scenario where the user does not generate a backscatter signal based on the characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver and the channel parameters between the transceiver and the listener and each user respectively;

[0119] a total achievable rate determination module, configured to determine the total achievable rate between the transceiver and all users based on characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver, characteristic parameters of the backscattered signal received by the transceiver, and channel parameters between the transceiver and each user;

[0120] The optimization module is used to maximize the total achievable rate by using a target optimization algorithm with the relative entropy satisfying the concealment condition as a constraint, and obtain the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave.

[0121] The present application also provides an electronic device, such as Figure 8 As shown, a processor 501 and a memory 502 , wherein the processor 501 and the memory 502 may be connected via a bus or other means.

[0122] The processor 501 may be a central processing unit (CPU). The processor 501 may also be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or a combination of the above chips.

[0123] Memory 502, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs, non-transitory computer-executable programs, and modules, such as the program instructions / modules corresponding to the multi-carrier randomized continuous wave covert backscatter communication method in the embodiments of the present invention. The processor executes the non-transitory software programs, instructions, and modules stored in the memory to perform various processor functions and data processing.

[0124] The memory 502 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created by the processor, etc. In addition, the memory may include a high-speed random access memory, and may also include a non-transitory memory, such as at least one disk storage device, a flash memory device, or other non-transitory solid-state storage device. In some embodiments, the memory 502 may optionally include a memory remotely located relative to the processor, and these remote memories may be connected to the processor via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0125] The one or more modules are stored in the memory 502 and when executed by the processor 501, perform the following steps: Figure 2 The covert backscatter communication method based on multi-carrier randomized continuous waves in the illustrated embodiment.

[0126] For details of the above electronic equipment, please refer to Figure 2 The corresponding descriptions and effects in the embodiments shown can be understood and will not be repeated here.

[0127] This embodiment further provides a computer storage medium storing computer-executable instructions capable of executing the multi-carrier randomized continuous wave covert backscatter communication method in any of the above-described method embodiments. The storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM), a random access memory (RAM), a flash memory, a hard disk drive (HDD), or a solid-state drive (SSD); the storage medium may also include a combination of the above-described types of memory.

[0128] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A covert backscatter communication method based on multi-carrier randomized continuous wave, characterized in that: include: Acquire characteristic parameters of a multi-carrier randomized continuous wave signal transmitted by the transceiver, characteristic parameters of a backscattered signal received by the transceiver, and channel parameters between the transceiver and the listener and each user, respectively. The characteristic parameters of the multi-carrier randomized continuous wave signal include statistical characteristic parameters of the multi-carrier randomized continuous wave. The backscattered signal is modulated by each user according to the multi-carrier randomized continuous wave signal. Determine the relative entropy between the probability density functions of the listener's received signal in a scenario where the user generates a backscattered signal and in a scenario where the user does not generate a backscattered signal, based on the characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver and the channel parameters between the transceiver and the listener and each user; Determine the total achievable rate between the transceiver and all users based on characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver, characteristic parameters of the backscattered signal received by the transceiver, and channel parameters between the transceiver and each user; With the relative entropy satisfying the concealment condition as the constraint, the total achievable rate is maximized through the target optimization algorithm, and the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave are obtained.

2. A covert backscatter communication method based on multi-carrier randomized continuous wave according to claim 1, characterized in that: Determining, based on characteristic parameters of a multi-carrier randomized continuous wave signal sent by a transceiver and channel parameters between the transceiver and a listener, a relative entropy between probability density functions of a signal received by the listener in a scenario where a user generates a backscattered signal and a scenario where the user does not generate a backscattered signal, including: Determine, based on the characteristic parameters of the multi-carrier randomized continuous wave signal and the channel parameters between the transceiver and the listener and each user, the probability distribution parameters of the listener's received signal in a scenario where the user generates a backscattered signal and a scenario where the user does not generate a backscattered signal; According to the probability distribution parameters of the listener receiving the signal in the two scenarios, the relative entropy of the probability density function of the listener receiving the signal in the two scenarios is determined.

3. The covert backscatter communication method based on multi-carrier randomized continuous wave according to claim 1, characterized in that: The channel parameters between the transceiver and each user include channel noise. Based on the characteristic parameters of the multi-carrier randomized continuous wave signal transmitted by the transceiver, the characteristic parameters of the backscattered signal received by the transceiver, and the channel parameters between the transceiver and each user, the total achievable rate between the transceiver and all users is determined, including: Under the condition that the transmitted multi-carrier randomized continuous wave signal is known, determining the total uncertainty of the received backscattered signal according to the channel parameters between the transceiver and each user and the characteristic parameters of the multi-carrier randomized continuous wave signal transmitted by the transceiver; Under the condition that the transmitted multi-carrier randomized continuous wave signal and the modulation symbols are known, the uncertainty of the received backscattered signal caused by the channel noise between the transceiver and each user is determined; The total achievable rate between the transceiver and all users is determined based on the total uncertainty of the received backscattered signal and the uncertainty caused by channel noise.

4. The covert backscatter communication method based on multi-carrier randomized continuous wave according to claim 1, characterized in that: With the relative entropy satisfying the concealment condition as a constraint, the total achievable rate is maximized through the target optimization algorithm to obtain the optimized statistical characteristic parameters of the multi-carrier randomized continuous wave, including: Get the maximum transmit power of the transceiver; With the relative entropy satisfying the concealment condition as the constraint, the total achievable rate is maximized through the target optimization algorithm, and the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave are obtained, including: With the relative entropy satisfying the concealment condition and the maximum transmit power of the transceiver as constraints, the total achievable rate is maximized through the target optimization algorithm, and the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave are obtained.

5. A covert backscatter communication method based on multi-carrier randomized continuous wave according to claim 4, characterized in that: The target optimization algorithm is the Lagrangian dual ascent algorithm. With the relative entropy satisfying the concealment condition and the maximum transmit power of the transceiver as constraints, the total achievable rate is maximized through the target optimization algorithm, and the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave are obtained, including: The first optimization objective is constructed with the constraints of relative entropy satisfying the concealment condition and the maximum transmit power of the transceiver, and the goal of maximizing the total achievable rate; The Lagrange dual ascent algorithm is used to transform the first optimization objective to obtain the second optimization objective; In the second optimization objective, local optimal target parameters are calculated, and the target parameters are related to statistical characteristic parameters of the multi-carrier randomized continuous wave; Update the Lagrange multiplier and iteratively calculate the local optimal target parameters until convergence to obtain the optimal target parameters; According to the optimal target parameters, the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave are determined.

6. A covert backscatter communication method based on multi-carrier randomized continuous wave according to any one of claims 1 to 5, characterized in that: The relative entropy between the probability density functions of the listener's received signal in the scenario where the user generates a backscatter signal and the scenario where the user does not generate a backscatter signal is: in, P0 represents the probability density function of the received signal in the scenario where the user does not generate a backscatter signal, P1 represents the probability density function of the received signal in the scenario where the user generates a backscatter signal, D(P0||P1) represents the relative entropy, I represents the total number of subcarriers of the multicarrier signal, and h W0,i and h W0 and The i-th element of W0 and The number of dimensions, h W0 and It is by H W0 and The diagonal elements of h RW represents the complex channel coefficient matrix between the transceiver and the listener, H RUW represents the equivalent channel matrix between the RF signal sent by the transceiver and the user and then backscattered to the listener, c m Indicates the mth case of the transmitted data symbol with equal probability, and Φ i denote the mean and variance associated with the ith carrier, respectively, It represents the additive white Gaussian noise variance of the signal received by the listener on a single subcarrier.

7. A covert backscatter communication method based on multi-carrier randomized continuous wave according to any one of claims 1 to 5, characterized in that: The total achievable rate between the transceiver and all users is: Where L represents the total number of subcarriers in the multicarrier signal. represents the mean vector, Φ represents the covariance matrix corresponding to the multi-carrier randomized continuous wave, I represents the identity matrix, Γ is the power reflection coefficient of the user, h RU,N represents the complex channel coefficient matrix between the transceiver and user N, represents the additive white Gaussian noise variance of the transceiver on a single subcarrier, c m and c l Indicates the mth and lth cases of transmitted equally probable data symbols, and the superscript H represents conjugate transpose.

8. A covert backscatter communication device based on multi-carrier randomized continuous wave, characterized in that: include: An information acquisition module is used to obtain characteristic parameters of a multi-carrier randomized continuous wave signal transmitted by the transceiver, characteristic parameters of a backscattered signal received by the transceiver, and channel parameters between the transceiver and the listener and each user, wherein the characteristic parameters of the multi-carrier randomized continuous wave signal include statistical characteristic parameters of the multi-carrier randomized continuous wave, and the backscattered signal is modulated by each user according to the multi-carrier randomized continuous wave signal; A relative entropy determination module is used to determine the relative entropy between the probability density functions of the signal received by the listener in a scenario where the user generates a backscatter signal and a scenario where the user does not generate a backscatter signal based on the characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver and the channel parameters between the transceiver and the listener and each user respectively; a total achievable rate determination module, configured to determine the total achievable rate between the transceiver and all users based on characteristic parameters of the multi-carrier randomized continuous wave signal sent by the transceiver, characteristic parameters of the backscattered signal received by the transceiver, and channel parameters between the transceiver and each user; The optimization module is used to maximize the total achievable rate by using a target optimization algorithm with the relative entropy satisfying the concealment condition as a constraint, and obtain the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave.

9. An electronic device, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the steps of the covert backscatter communication method based on multi-carrier randomized continuous wave according to any one of claims 1 to 7.

10. A computer storage medium having computer instructions stored thereon, characterized in that: When the instruction is executed by the processor, the steps of the covert backscatter communication method based on multi-carrier randomized continuous wave according to any one of claims 1 to 7 are implemented.

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