A covert backscatter communication method based on multi-carrier randomized continuous wave

Abstract

The application provides a covert backscatter communication method based on a multicarrier randomized continuous wave, comprising: acquiring multicarrier randomized continuous wave signal characteristic parameters, backscatter signal characteristic parameters and channel parameters between a transceiver and a listener and each user; determining the relative entropy between the probability density function of the listener receiving signal when the user generates a backscatter signal and when the user does not generate a backscatter signal according to the multicarrier randomized continuous wave signal characteristic parameters and the channel parameters between the transceiver and the listener and each user; determining the total achievable rate between the transceiver and all users according to the multicarrier randomized continuous wave signal characteristic parameters, the backscatter signal characteristic parameters and the channel parameters; and maximizing the total achievable rate by a target optimization algorithm with the relative entropy satisfying the concealment condition as a constraint to obtain the statistical characteristic parameters of the optimized multicarrier randomized continuous wave. The application can realize covert backscatter communication.

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 application provides a covert backscatter communication method based on multi-carrier randomized continuous wave, comprising: obtaining a multi-carrier randomized continuous wave signal characteristic parameter sent by a transceiver, a backscatter signal characteristic parameter received by the transceiver, and channel parameters between the transceiver and a listener and each user, wherein the multi-carrier randomized continuous wave signal characteristic parameter comprises a statistical characteristic parameter of the multi-carrier randomized continuous wave, and the backscatter signal is obtained by modulation of each user according to the multi-carrier randomized continuous wave signal; determining a relative entropy between probability density functions of a listener received signal in a scenario where the user generates a backscatter signal and a scenario where the user does not generate the backscatter signal according to the multi-carrier randomized continuous wave signal characteristic parameter sent by the transceiver and the channel parameters between the transceiver and the listener and each user; determining a total achievable rate between the transceiver and all users according to the multi-carrier randomized continuous wave signal characteristic parameter sent by the transceiver, the backscatter signal characteristic parameter received by the transceiver, and the channel parameters between the transceiver and each user; and maximizing the total achievable rate by a target optimization algorithm with a constraint that the relative entropy meets a covert condition, to obtain an optimized statistical characteristic parameter of the multi-carrier randomized continuous wave.

[0007] According to a second aspect, an embodiment of the present application provides a covert backscatter communication device based on multi-carrier randomized continuous wave, comprising: an information obtaining module, configured to obtain a multi-carrier randomized continuous wave signal characteristic parameter sent by a transceiver, a backscatter signal characteristic parameter received by the transceiver, and channel parameters between the transceiver and a listener and each user, wherein the multi-carrier randomized continuous wave signal characteristic parameter comprises a statistical characteristic parameter of the multi-carrier randomized continuous wave, and the backscatter signal is obtained by modulation of each user according to the multi-carrier randomized continuous wave signal; a relative entropy determining module, configured to determine a relative entropy between probability density functions of a listener received signal in a scenario where the user generates a backscatter signal and a scenario where the user does not generate the backscatter signal according to the multi-carrier randomized continuous wave signal characteristic parameter sent by the transceiver and the channel parameters between the transceiver and the listener and each user; a total achievable rate determining module, configured to determine a total achievable rate between the transceiver and all users according to the multi-carrier randomized continuous wave signal characteristic parameter sent by the transceiver, the backscatter signal characteristic parameter received by the transceiver, and the channel parameters between the transceiver and each user; and an optimization module, configured to maximize the total achievable rate by a target optimization algorithm with a constraint that the relative entropy meets a covert condition, to obtain an optimized statistical characteristic parameter of the multi-carrier randomized continuous wave.

[0008] According to a third aspect, an electronic device is provided, the device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor performing the steps of the method for covert backscatter communication based on multi-carrier randomized continuous wave according to the first aspect or any of the embodiments of the first aspect.

[0009] According to a fourth aspect, a computer storage medium is provided, having stored thereon computer instructions, which when executed by a processor, implement the steps of the method for covert backscatter communication based on multi-carrier randomized continuous wave according to the first aspect or any of the embodiments of the first aspect.

[0010] The method for covert backscatter communication based on multi-carrier randomized continuous wave provided by the present application maximizes the multi-user achievable rate, effectively improves the concealment of multi-user BackCom by using the randomization characteristics of multi-carrier randomized continuous wave (RCW), and realizes covert backscatter communication.

[0011] Other advantages, objects, and features of the present application will be apparent to those skilled in the art from the following specification, which is to be taken in conjunction with the accompanying drawings, wherein like reference characters refer to like elements throughout. The objects and other advantages of the present application can be realized and attained by the structure particularly pointed out in the specification as follows. BRIEF DESCRIPTION OF DRAWINGS

[0012] In order to make the objects, technical solutions and beneficial effects of the present application clearer, the present application provides the following drawings for illustration:

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

[0014] Figure 2 A specific example flowchart of the method for covert backscatter communication based on multi-carrier randomized continuous wave in the present application;

[0015] Figure 3 A relationship diagram of multi-user achievable rate and concealment requirement under different modulation modes;

[0016] Figure 4 A relationship diagram of achievable rate and maximum transmission power under different user number access;

[0017] Figure 5 A relationship diagram of multi-user transmission rate and maximum transmission power under different transmission schemes;

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

[0019] Figure 7 A graph of the relationship between the spectral efficiency and the bandwidth of a multi-carrier RCW;

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

[0021] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0022] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection" and "linking" should be understood in a broad sense, for example, they can be fixed connection, detachable connection or integral connection; they can be mechanical connection or electrical connection; they can be direct connection or indirect connection through an intermediate medium; they can be internal connection of two elements; they can be wireless connection or wired connection. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0023] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0024] The use environment of the present application is as follows: as shown in Figure 1 A multi-user covert BackCom scenario is considered. In this scenario, a full-duplex wireless transceiver (transceiver) communicates with N users equipped with a backscatter tag under the monitoring of a listener (listener), where the transceiver, the listener and the tag are each equipped with an antenna. Specifically, the transceiver transmits a multi-carrier randomized continuous wave signal of I discrete frequencies through a single antenna, and the radio frequency (RF) signal is incident on the tag through different communication channels. These tags can modulate information using part of the energy from the received signal, or absorb all the received signal energy and remain silent. In the information transmission stage, the tags modulate and backscatter the incident signal 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. At the same time, the listener uses a radiometer-based detector to detect whether the tag has backscattering behavior.

[0025] To achieve covert backscatter communication for multiple users, embodiments of this invention provide a covert backscatter communication method based on multi-carrier randomized continuous waves, such as... Figure 2 As shown, it includes:

[0026] S101, acquire the characteristic parameters of the multi-carrier randomized continuous wave signal transmitted by the transceiver, the characteristic parameters of the backscatter signal received by the transceiver, and the channel parameters between the transceiver and the listener and each user respectively. The characteristic parameters of the multi-carrier randomized continuous wave signal include the statistical characteristic parameters of the multi-carrier randomized continuous wave. The backscatter signal is obtained by each user modulating the multi-carrier randomized continuous wave signal.

[0027] S102, 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 relative entropy between the probability density function of the signal received by the listener in the scenario where the user generates a backscatter signal and in the scenario where the user does not generate a backscatter signal.

[0028] S103, 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, determine the total reachable rate between the transceiver and all users;

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

[0030] For example, to illustrate the solution of this embodiment, firstly, a signal model of a multi-carrier randomized continuous wave, a receiver signal model, a receiver detection model, and the receiver detection performance are constructed, and the receiver detection performance is analyzed. Then, based on the multi-carrier randomized continuous wave signal model and the transceiver receiver signal model, the achievable rate expression is determined. Then, based on the receiver detection performance, the relative entropy between the probability density function of the receiver signal in the scenario where the user generates a backscattered signal and the scenario where the user does not generate a backscattered signal is determined. Finally, under the constraint of relative entropy, the statistical characteristic parameters of the multi-carrier randomized continuous wave are adjusted to maximize the achievable rate.

[0031] Specifically, the signal model for the multi-carrier randomized continuous wave in the k-th time slot is:

[0032]

[0033] Among them, s i,kLet represent the coefficients of the i-th subcarrier, which remain constant within a time slot and satisfy a cyclically symmetric complex Gaussian (CSCG) distribution across different time slots, and can be expressed as: in Let represent the mean vector, and Φ represent the covariance matrix corresponding to the multi-carrier randomized continuous wave. Additionally, ω... i =2πf i f represents the angular frequency of the i-th subcarrier. i The center frequency is I, the total number of subcarriers is e, the natural constant is e, and the imaginary unit is j.

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

[0035]

[0036] Among them, f1, f I Let represent the carrier frequency of the first subcarrier and the carrier frequency of the I-th subcarrier in a multi-carrier RCW, respectively.

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

[0038]

[0039] Where χ is the Rice factor, and the Rayleigh fading components of the line of sight (LoS) and the non-line of sight (NLoS) are respectively... and d RU,n Let α be the distance between the transceiver and the nth user. LoS and α NLoS Let G0 be the fading coefficient for the LoS and NloS channels, and G0 = (λ / 4π). 2 Let λ be the channel power gain, where λ = ν / f C and θ i =ω i / ν, where ν represents the wave speed. 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 for the nth user in the kth time slot is as follows:

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

[0042] Among them, RF signal The complex channel coefficient matrix between the transceiver and the user can be represented as follows: 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 This represents the equally probable data symbols 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 is fully aware of the randomization information of the multi-carrier randomized continuous wave, φ=0. The additive white Gaussian noise on the subcarriers in the received signal is n. R,k =[n R,1,k ,n R,2,k ,...,n R,I,k ] T It follows a zero-mean CSCG distribution, i.e. Where I I It is an I×I identity matrix.

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

[0047]

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

[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, a detection model for the eavesdropper is constructed. The model for the eavesdropper's received signal is a binary assumption problem. Specifically, H0 represents the case where the user's backscattering tag absorbs all RF signal energy (i.e., when the user does not generate a backscattering signal), while H1 corresponds to the tag exhibiting backscattering transmission behavior (i.e., when the user generates a backscattering signal). Therefore, the eavesdropper's received signal is:

[0052]

[0053] Where, n W,k =[n W,1,k ,n W,2,k ,...,n W,I,k ] T The noise on the subcarrier of the signal received by the eavesdropper follows a zero-mean CSCG distribution, i.e., the expected noise is... h RW Let h be the complex channel coefficient matrix between the transceiver and the eavesdropper. UW,n Let H be the complex channel coefficient matrix between the nth user and the eavesdropper. RUW The equivalent channel matrix experienced by the radio frequency signal transmitted by the transceiver and received by the eavesdropper after being backscattered by the user can be expressed as:

[0054]

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

[0056] ξ=P FA +P MD (10)

[0057] The eavesdropper's goal 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 typically kept at a relatively low level.

[0058] Then, the detection performance of the eavesdropper is analyzed. The probability of the eavesdropper's detection error can be represented by the relative entropy (Kullback-Leibler divergence):

[0059]

[0060] Where D(P0||P1)) represents the relative entropy between the probability distributions of the received signals by the eavesdropper, P0 (the eavesdropper did not receive the backscattered signal) and P1 (the eavesdropper received the backscattered signal). To satisfy the required concealment constraint ξ≥1-∈, a lower bound of ξ is used instead, i.e. Therefore, the concealment constraint can be further expressed as:

[0061]

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

[0063]

[0064] Among them, c m It is B N The m-th vector, I I The channel coefficient matrix is ​​defined as an I-dimensional identity matrix.

[0065]

[0066] Considering a given c m In this situation, It can be represented as:

[0067]

[0068] Among them, h W0,i and for h W0 and The i-th element. Column vector h W0 and It is H W0 and It is composed of the diagonal elements. Furthermore, the mean and covariance associated with the i-th carrier are formed by... and Φ i Therefore, the relative entropy between the probability density functions of the signals received by the eavesdropper under H0 and H1 can be expressed as:

[0069]

[0070] Where L represents that there are L possibilities for the data symbol vectors transmitted by N users.

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

[0072]

[0073] Where h(y) R |c,s) represents y given s and c. R The entropy, h(y) R |s) represents y given s. R The entropy, since the transceiver fully understands the transmitted signal s, can be expressed as:

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

[0075] Because n R Satisfying the zero-mean CSCG, therefore the differential entropy h(n) R This can be represented as:

[0076]

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

[0078]

[0079] in, Indicates the received signal y R Given s and c = c m Conditional probability distribution under given conditions, ||*|| 2 This is represented as the L2 norm. Therefore, the conditional differential entropy h(y) R |s) is:

[0080]

[0081] Among them, E s This represents the expectation of taking all possible values ​​of s. Indicates the received signal y R Conditional probability distribution given that s is known;

[0082] definition in We can obtain:

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

[0084] Among them, c l It is B N The l-th vector.

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

[0086]

[0087] in, Represents the relationship between random variables s and n′ R The joint distribution takes the expected value.

[0088] Because of C U The expression contains the expected expression, therefore C U It can be approximated as:

[0089]

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

[0091] Based on the above-described construction, 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 transmitted 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 respectively. The characteristic parameters of the multi-carrier randomized continuous wave signal transmitted 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 the modulation symbol and power reflection coefficient. The channel parameters between the transceiver and the listener and each user respectively include the channel noise of each channel, the variance of the noise, the complex channel coefficient matrix, etc.

[0092] Then, 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 the scenario where the user does not generate a backscatter signal (H0) and the scenario where the user generates a backscatter signal (H1) are determined. Based on 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. For the specific process, please refer to formulas (13)-(16), which will not be repeated here.

[0093] Next, given that the transmitted multi-carrier randomized continuous wave signal is known, the total uncertainty of the received backscattered signal is determined based on 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. (Uncertainty is measured by entropy; see h(y) corresponding to formula (17)). R |s)); Under the condition that the transmitted multi-carrier randomized continuous wave signal and the modulation symbol are known, the uncertainty of the received backscattered signal caused by the channel noise is determined according to the channel noise between the transceiver and each user (the uncertainty is measured by entropy, see h(n) corresponding to formula (17)). R Based on the total uncertainty of the received backscattered signal and the uncertainty caused by channel noise, the total reachability rate between the transceiver and all users is determined, which is the received signal y of the transceiver. R The mutual information between the transceiver and the data symbol vector c under the known transmitted signal s, and the total reachability between the transceiver and all users based on the total uncertainty of the received backscattered signal and the uncertainty caused by the channel noise, are explained in formulas (18)-(24), and will not be repeated here.

[0094] After determining the relative entropy and achievable rate, and constrained by the relative entropy satisfying the concealment condition and the transceiver's maximum transmission power, a target optimization algorithm is used to maximize the total achievable rate, yielding the optimized statistical characteristic parameters of the multi-carrier randomized continuous wave. This includes: constructing a first optimization objective by maximizing the total achievable rate under the constraints of relative entropy satisfying the concealment condition and the transceiver's maximum transmission power; transforming the first optimization objective using the Lagrange dual ascending algorithm to obtain a second optimization objective; calculating locally optimal target parameters within the second optimization objective, where the target parameters are related to the statistical characteristic parameters of the multi-carrier randomized continuous wave; updating the Lagrange multipliers and iteratively recalculating the locally optimal target parameters until convergence, yielding the optimal target parameters; and determining the optimized statistical characteristic parameters of the multi-carrier randomized continuous wave based on the optimal target parameters.

[0095] For example, the first optimization objective is:

[0096]

[0097] stD(P0||P1)≤2∈ 2 ,

[0098]

[0099] η±0,

[0100]

[0101] in, P is a column vector consisting of the diagonal elements of Φ. max 1 is the maximum transmit power of the transceiver. N Let be a unit vector of length N. This optimization problem is a non-convex problem; to obtain η and , we need to find η and η. The analytical solution is extremely difficult. To solve this nonconvex problem, the Lagrange dual ascent algorithm is used to search for η and η that satisfy the constraints. By introducing Lagrange multipliers, the original problem is transformed into a dual problem, thus enabling distributed solution. The Lagrange function can be expressed as:

[0102]

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

[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 optima η and η. Based on this, the Lagrange multipliers are updated accordingly. Through iterative steps, the process gradually converges to the optimal η and Thus maximize Thus, the achievable rate C can be obtained further through (23). U .

[0110] This invention aims to maximize the reachability of multi-user networks by effectively improving the stealth of multi-user BackComs using the randomization characteristics of multi-carrier RCW. The simulation employs a uniform carrier frequency and node location coordinates, with BPSK modulation.

[0111] To analyze the achievable rate under different concealment requirements, Figure 3 This demonstrates that multi-carrier continuous wave (CW) schemes cannot achieve efficient transmission at relatively low values. This is because the determinism of CW signals makes backscatter transmission easily detectable by eavesdroppers. Therefore, the transceiver must significantly reduce the tag's backscatter power to ensure stealth, which significantly reduces the reachability rate. Furthermore, while multi-carrier CW schemes can achieve high reachability rates at sufficiently high values, eavesdroppers can easily detect transmission activity in this situation. In contrast, multi-carrier RCW schemes show a rapid increase in reachability rate with increasing ω, approaching the unstealthy 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 stealth with only a small amount of randomization components. Moreover, employing higher-order modulation schemes (M-order phase shift keying), such as Quadrature Phase Shift Keying (QPSK), can further improve the reachability rate.

[0112] Furthermore, the impact of different numbers of access tags on the reachable rate was further analyzed. Figure 4 This indicates that as P max With increasing transmit power, the achievable rate of the multi-carrier RCW scheme gradually increases, eventually converging to Nlog2M, reflecting the inherent multi-user concurrent transmission capability of the multi-carrier system. This paper uses 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 transmit power increases, the achievable rate of the CSCG single-carrier scheme converges to log2M. Meanwhile, due to 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 may even reduce the overall rate. In contrast, the multi-carrier RCW scheme significantly improves the overall achievable rate of multi-tag communication.

[0113] Next, we will analyze the multi-user access performance of multi-carrier RCW. Figure 5The transmission rates under different transmission schemes are shown. For comparison, this paper uses a single-carrier transmission scheme with TDMA technology to realize multi-tag communication as the benchmark. The following three points can be seen: (1) Compared with multi-carrier CW, the multi-carrier RCW system effectively interferes with the detection of eavesdroppers by utilizing its inherent randomization characteristics, thereby achieving a higher transmission rate. A similar effect is also achieved 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 near-optimal performance comparable to the multi-carrier CW scheme in the non-concealed transmission scenario. The same conclusion is also reached in the single-carrier scenario; (3) Multi-carrier RCW can realize simultaneous communication of multiple tags in a single time slot, thereby improving the transmission rate.

[0114] Figure 6 This demonstrates that as the bandwidth of multi-carrier RCW increases (while maintaining a constant 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, thus effectively improving transmission reliability. In contrast, the TDMA-based CSCG single-carrier scheme achieves a higher transmission rate by shortening the symbol duration with increasing bandwidth. However, its transmission rate is still lower than that of the multi-carrier RCW scheme.

[0115] Figure 7 This indicates that, with a constant number of subcarriers, the overall spectral efficiency decreases as the bandwidth increases. This trend is primarily due to the wider noise bandwidth introduced by bandwidth expansion, which increases the total noise power of the communication system, reduces the signal-to-noise ratio of each subcarrier, and consequently lowers the spectral efficiency. Furthermore, the multi-carrier RCW scheme proposed in this application consistently outperforms the CSCG-based single-carrier TDMA scheme across the entire bandwidth. Even at relatively low transmit power, the multi-carrier RCW system achieves higher spectral efficiency, surpassing the single-carrier scheme at higher transmit power levels. This result highlights the performance advantages of the multi-carrier RCW structure in spectrum reuse.

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

[0117] The information acquisition module is used to acquire 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 the listener and each user. The characteristic parameters of the multi-carrier randomized continuous wave signal include the statistical characteristic parameters of the multi-carrier randomized continuous wave. The backscatter signal is obtained by each user modulating the multi-carrier randomized continuous wave signal.

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

[0119] The total reachability determination module is used to determine the total reachability between the transceiver and all users 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.

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

[0121] This application also provides an electronic device, such as... Figure 8 As shown, processor 501 and memory 502 are connected via a bus or other means.

[0122] Processor 501 can be a central processing unit (CPU). Processor 501 can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or combinations of the above types of chips.

[0123] The 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 covert backscatter communication method based on multi-carrier randomized continuous waves in this embodiment of the invention. The processor executes various functional applications and data processing by running the non-transitory software programs, instructions, and modules stored in the memory.

[0124] Memory 502 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created by the processor, etc. Furthermore, the memory may include high-speed random access memory and non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory 502 may optionally include memory remotely located relative to the processor, which can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

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

[0126] For specific details regarding the aforementioned electronic devices, please refer to the relevant documentation. Figure 2 The relevant descriptions and effects in the illustrated embodiments are for understanding purposes only and will not be repeated here.

[0127] This embodiment also provides a computer storage medium storing computer-executable instructions that can execute the covert backscatter communication method based on multi-carrier randomized continuous wave in any of the above method embodiments. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk drive (HDD), or solid-state drive (SSD), etc.; the storage medium may also include combinations of the above 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 intended to limit it. 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 to it in form and detail 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: The system acquires the characteristic parameters of the multi-carrier randomized continuous wave signal transmitted by the transceiver, the characteristic parameters of the backscatter signal received by the transceiver, and the channel parameters between the transceiver and the listener and each user. The characteristic parameters of the multi-carrier randomized continuous wave signal include the statistical characteristic parameters of the multi-carrier randomized continuous wave. The backscatter signal is obtained by each user modulating the multi-carrier randomized continuous wave signal. Based on the characteristic parameters of the multi-carrier randomized continuous wave signal transmitted by the transceiver and the channel parameters between the transceiver and the listener and each user, the relative entropy between the probability density function of the signal received by the listener in the scenario where the user generates a backscatter signal and in the scenario where the user does not generate a backscatter signal is determined. 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 reachable rate between the transceiver and all users is determined. By using the constraint that relative entropy satisfies the concealment condition, the total reachability rate is maximized through a target optimization algorithm, and the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave are obtained.

2. The covert backscatter communication method based on multi-carrier randomized continuous wave according to claim 1, characterized in that, Based on the characteristic parameters of the multi-carrier randomized continuous wave signal transmitted by the transceiver and the channel parameters of the transceiver and the eavesdropper, determine the relative entropy between the probability density functions of the eavesdropper's received signal in scenarios where the user generates a backscattered signal and scenarios where the user does not generate a backscattered signal, including: 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 signal received by the listener in the scenario where the user generates a backscatter signal and in the scenario where the user does not generate a backscatter signal are determined. Based on the probability distribution parameters of the signal received by the eavesdropper in the two scenarios, the relative entropy of the probability density function of the signal received by the eavesdropper 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 reachable rate between the transceiver and all users is determined, including: Given that the transmitted multi-carrier randomized continuous wave signal is known, the total uncertainty of the received backscattered signal is determined based on 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. Given 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 is determined based on the channel noise between the transceiver and each user. The total reachability 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, Before obtaining the statistical characteristic parameters of the optimized multi-carrier randomized continuous wave by maximizing the total reachable rate through a target optimization algorithm, constrained by the condition that the relative entropy satisfies the concealment condition, the following steps are included: Get the transceiver's maximum transmit power; With the constraint that relative entropy satisfies the concealment condition, a target optimization algorithm is used to maximize the total reachability rate, yielding the optimized statistical characteristic parameters of the multi-carrier randomized continuous wave, including: By taking the relative entropy satisfying the concealment condition and the maximum transmission power of the transceiver as constraints, the total reachable rate is maximized through the objective 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 objective optimization algorithm is a Lagrange dual ascending algorithm. It takes the relative entropy satisfying the concealment condition and the transceiver's maximum transmit power as constraints. Through this algorithm, the total reachable rate is maximized, yielding the optimized statistical characteristic parameters of the multi-carrier randomized continuous wave, including: With the constraints of relative entropy satisfying the concealment condition and the maximum transmission power of the transceiver, and with the goal of maximizing the total achievable rate, a first optimization objective is constructed. The first optimization objective is transformed using the Lagrange dual ascent algorithm to obtain the second optimization objective; In the second optimization objective, the local optimal objective parameters are calculated, and the objective parameters are related to the statistical characteristic parameters of the multi-carrier randomized continuous wave; Update the Lagrange multipliers and recalculate the local optimal objective parameters until convergence, thus obtaining the optimal objective parameters; Based on 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 1-5, characterized in that, The relative entropy between the probability density functions of the signal received by the eavesdropper in scenarios where the user generates a backscattered signal and scenarios where the user does not generate a backscattered 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 in a multi-carrier signal, and h W0,i and for h W0 and The i-th element, I represents h W0 and The number of dimensions, h W0 and It is H W0 and Composed of diagonal elements, h RW H represents the complex channel coefficient matrix between the transceiver and the listener. RUW c represents the equivalent channel matrix between the radio frequency signal transmitted by the transceiver, the user, and the listener after backscattering. m This represents the m-th case of equally probable transmitted data symbols. and Φ i Let represent the mean and variance associated with the i-th carrier, respectively. This represents the variance of the additive white Gaussian noise 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 1-5, characterized in that, The total reachable rate between the transceiver and all users is: Where L represents the total number of subcarriers in a multi-carrier signal, Let Φ denote the mean vector, Φ denote the covariance matrix corresponding to the multi-carrier randomized continuous wave, and I denote the identity matrix. Γ represents the user's power reflection coefficient, h RU,N This represents the complex channel coefficient matrix between the transceiver and user N. This represents the variance of additive white Gaussian noise on a single subcarrier for the transceiver. c m and c l The m-th and l-th cases of equally probable transmitted data symbols are indicated by the superscript H, which indicates the conjugate transpose.

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

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

10. A computer storage medium storing computer instructions thereon, characterized in that, When executed by the processor, this instruction implements the steps of the covert backscatter communication method based on multi-carrier randomized continuous waves as described in any one of claims 1-7.

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