A Multi-Mode Physical Layer Secure Transmission Method Based on Two-Component Combined GWFrFT

Abstract

The present invention belongs to the field of physical layer secure communication, and proposes a multi-mode physical layer secure transmission method based on a two-component combined GWFrFT. Aiming at the problem that the energy of the weighted fractional Fourier transform is not flexible in distribution among components, the present invention introduces the generalized weighted fractional Fourier transform into the field of physical layer security, fully utilizes the flexibility of energy distribution of the generalized weighted fractional Fourier transform, concentrates the signal energy in a two-component combination with the same characteristics, and reshapes the baseband signal characteristics by using its constellation fission and constellation ambiguity characteristics, and proposes two secure transmission modes, namely, a modulation mode camouflage mode and a low-intercept transmission mode. In a specific secure communication environment, without changing the system architecture, this secure communication method can flexibly switch between the two secure transmission modes by adjusting the parameter set construction scheme, significantly increasing the difficulty for non-cooperative receivers to intercept signals and decipher information, and enhancing the effectiveness and flexibility of secure communication.

Description

Technical Field

[0001] The present invention relates to a multi-mode physical layer secure transmission method based on two-component combined Generalized Weighted-type Fractional Fourier Transform (GWFrFT), and belongs to the field of physical layer secure communication. Background Art

[0002] In recent years, as a new transform domain signal processing means, Weighted-type Fractional Fourier Transform (WFrFT) has received extensive attention from domestic and foreign researchers due to its simple discrete algorithm and easy engineering implementation. In the field of physical layer security, many scholars have proposed schemes to change the physical characteristics of signals using WFrFT, that is, using WFrFT to preprocess signals, giving full play to its constellation fission and constellation ambiguity characteristics, realizing the Gaussian-like transformation of baseband signals, and improving the signal interception resistance performance; on the other hand, under the condition that the non-cooperating receiver does not know the transform order of WFrFT, even if the signal is intercepted, it is difficult to decipher the specific information.

[0003] However, the weighted coefficients of WFrFT satisfy relatively strict constraint relations, and the energy distribution method among the weighted terms is relatively single, making it difficult to give full play to the characteristics of the time domain term and the frequency domain term. Based on this consideration, Ma Cong et al. proposed GWFrFT. As a generalized form of WFrFT, GWFrFT does not change its weighted structure, but only relaxes the constraint conditions of the weighted parameters, realizing a more flexible distribution of the input signal energy among the weighted terms, providing an effective means for signal processing.

[0004] However, the current application of GWFrFT is still mainly concentrated in the field of robust communication. In the field of physical layer security, the current transform domain-based secure transmission schemes usually still adopt WFrFT and its parameter-expanded form, Multiple Parameters Weighted-type Fractional Fourier Transform (MP-WFrFT). The potential of GWFrFT in the field of physical layer security has not been fully exploited. Summary of the Invention

[0005] The object of the present invention is to improve the security of the system. By reasonably adjusting the transformation angle parameters, giving full play to the energy distribution flexibility of the GWFrFT, and using its constellation fission and constellation ambiguity characteristics to reshape the baseband signal characteristics, a multi-mode physical layer secure transmission method based on a two-component combined GWFrFT is proposed. This secure communication method uses the GWFrFT as a basic tool and has two secure communication modes, namely: modulation mode disguise mode and low-intercept transmission mode. In the modulation mode disguise mode, only the two time-domain components in the weighting term are combined, and the constellation fission characteristic of the GWFrFT is used to adjust the constellation distribution of the baseband modulation symbol sequence, disguising it as other modulation modes to achieve secure and confidential communication; in the low-intercept transmission mode, only the two frequency-domain components are combined, and the constellation ambiguity characteristic of the GWFrFT is used to realize the Gaussianization of the baseband modulation symbol sequence, reducing the probability of being intercepted by an illegal receiver and ensuring information security.

[0006] In a specific secure communication environment, this secure communication method can flexibly switch between the two secure transmission modes by adjusting the parameter set construction scheme without changing the system architecture, significantly increasing the difficulty for a non-cooperative receiver to intercept the signal and decipher the information, and enhancing the effectiveness and flexibility of secure communication.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A multi-mode physical layer secure transmission method based on a two-component combined GWFrFT, comprising the following steps:

[0009] The steps at the sending end include:

[0010] Step 1, before signal transmission, according to the specific secure communication environment and requirements, select a secure transmission mode and set the initial transformation angle parameters, and design a scheme based on the i.i.d. parameter set of the selected secure transmission mode to construct a variety of transformation angle parameter sets {θ} in the corresponding mode;

[0011] Step 2, perform a serial-to-parallel conversion process on the input baseband symbol sequence X, and randomly select a transformation angle parameter set θ = [θ0, θ1, θ2, θ3] from the transformation angle parameter sets, and perform a GWFrFT with the transformation angle parameter θ on the serially-parallel converted baseband symbol sequence X to obtain the symbol sequence X θ ;

[0012] Step 3, if the modulation mode disguise mode is adopted for secure transmission, then correct the angle of the constellation distribution of the symbol sequence X θ , and the constellation adjustment process is X Rev = X θ exp(-jθ Rev ); if the low-intercept transmission mode is adopted, then X Rev = Xθ , directly proceed to the next step; where θ Rev is the correction angle for constellation adjustment;

[0013] Step 4, perform parallel-to-serial conversion and digital-to-analog conversion on the symbol sequence X after constellation adjustment, and finally send it to the channel for transmission; Rev

[0014] The steps at the receiving end include:

[0015] Step 5, receive the symbol sequence Y Rev , and perform analog-to-digital conversion, equalization, and serial-to-parallel conversion. If the modulation mode camouflage mode is adopted, perform the inverse processing of the angle correction at the sending end on the converted symbol sequence Y. The constellation adjustment process is Y Rev = Y θ = Y Rev exp(jθ Rev ); If the low-intercept transmission mode is adopted, then Y θ = Y Rev , directly proceed to the next step;

[0016] Step 6, perform GWFrFT on the symbol sequence Y after constellation adjustment at the parameter -θ. The expression of the transformation result is Y = G θ Y -θ ; θ ;

[0017] Step 7, perform parallel-to-serial conversion on the symbol sequence Y after GWFrFT, and perform baseband demodulation processing to restore the confidential information.

[0018] Furthermore, the specific construction of the set of multiple transformation angle parameters {θ} in Step 1 is as follows:

[0019] The construction process of the parameter set based on the modulation mode camouflage mode is:

[0020] Initialization: k = 1;

[0021] Step 101: Input the parameter θ0;

[0022] Step 102: Calculate θ2 and θ3 according to the following formula constraint conditions, construct the transformation angle parameters, and store them in the same constellation distribution parameter set {θ};

[0023]

[0024] or

[0025]

[0026] Step 103: Let θ0 = θ0 + π / 2. If k ≥ 3, directly proceed to the next step; otherwise, k = k + 1, and return to Step 102; ​

[0027] Step 104: The construction of the angle parameter set for the same constellation distribution transformation is completed, and multiple transformation angle parameter sets {θ} are obtained.

[0028] The process of constructing the parameter set based on the low-intercept transmission mode is as follows:

[0029] Initialization: Set the transformation angle search step size θ c , θ1 = 0;

[0030] Step 201: Input the parameter θ0;

[0031] Step 202: If θ1 < 2π, directly proceed to the next step; otherwise, execute Step 205;

[0032] Step 203: According to the following formula constraint conditions, calculate θ2 and θ3, construct the transformation angle parameters, and store them in the same Gaussian distribution parameter set {θ};

[0033]

[0034] Step 204: Let θ1 = θ1 + θ c , and return to Step 202;

[0035] Step 205: The construction of the angle parameter set for the same Gaussian distribution transformation is completed, and multiple transformation angle parameter sets {θ} are obtained.

[0036] Furthermore, the correction angle θ for constellation adjustment in Steps 3 and 5 Rev satisfies the following relationship:

[0037]

[0038] The present invention has the following advantages:

[0039] 1. The core of the system of the present invention is to utilize the energy flexible distribution characteristic of GWFrFT, concentrate its signal energy fully on two components with the same characteristics, give full play to the constellation fission and constellation ambiguity characteristics, and propose two secure transmission modes, which improve the secrecy and security performance of the communication system from two aspects: the disguise processing of the baseband modulation method and the reduction of the interception probability of the transmitted signal, making it significantly more difficult for non-cooperative receivers to intercept signals and decipher information;

[0040] 2. The present invention proposes a method for constructing the transformation angle parameter set of the same distribution and different mapping methods corresponding to the two secure modes. During the secure transmission process, by randomly selecting the elements of the parameter set, it can effectively induce non-cooperative receivers to make misjudgments, ensuring communication security;

[0041] 3. Both of the two secure transmission modes proposed by the present invention adopt the same system architecture, without the need to adjust each module. Only by adjusting the parameter set construction scheme can the mode switching be realized. While improving the flexibility, the hardware implementation complexity of the system is not increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is the system block diagram of the present invention.

[0043] Figure 2 is the constellation diagram of the transmission symbol sequences corresponding to four transformation angle parameters in the same constellation distribution set with the input parameter θ0 = π / 2 in the QPSK baseband modulation symbol sequence, 16QAM baseband modulation symbol sequence, and modulation mode camouflage mode.

[0044] Figure 3 is the constellation distribution and probability density function diagram of the transmission symbol sequences corresponding to two transformation angle parameters randomly selected from the same Gaussian distribution parameter set in the low-intercept transmission mode.

[0045] Figure 4 is the schematic diagram of the principle for setting the constellation adjustment correction angle.

[0046] Figure 5 is the constellation diagram of the transmission symbol sequence corresponding to the input parameter θ0 = π / 2 in the modulation mode camouflage mode after constellation adjustment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The present invention will be further described below in conjunction with the embodiments and the drawings.

[0048] A multi-mode physical layer secure transmission method based on two-component combined GWFrFT, referring to the attached Figure 1 , includes the following steps:

[0049] Step 1, before signal transmission, according to the specific secure communication environment and requirements, select a suitable secure transmission mode and input initial parameters, and then construct the same-distribution transformation angle parameter set {θ} corresponding to the mode. The construction schemes of the same-distribution transformation angle parameter sets in the two secure transmission modes will be described in detail below.

[0050] For any input sequence X, the four-term GWFrFT with its transformation angle parameter θ is defined as

[0051] X θ =G θ X = g0(θ)X0 + g1(θ)X1 + g2(θ)X2 + g3(θ)X3 (6)

[0052] where X kis the k-th discrete Fourier transform (DFT) of X, satisfying X k = F k X, where k = 0, 1, 2, 3. Among the four weighted terms of the GWFrFT, g0(θ)X0 and g2(θ)X2 are time-domain components, which determine the constellation fission characteristics of the transformation result; g1(θ)X1 and g3(θ)X3 are frequency-domain components, which determine the constellation ambiguity characteristics of the transformation result.

[0053] If the modulation method camouflage mode is adopted for transmission, taking the camouflage of QPSK modulated baseband signal to 16QAM signal as an example, the construction method of the parameter set is described. In the modulation method camouflage mode, in order to make full use of the constellation fission characteristics, it is necessary to concentrate all the signal energy on the time-domain term, so the transformation angle parameter and the time-domain term weighting coefficient need to satisfy

[0054]

[0055] In order to realize the effective simulation of QPSK to 16QAM, each element of the transformation angle parameter needs to satisfy the following relationship

[0056]

[0057] or

[0058]

[0059] In view of the above analysis, any input θ0 can be expanded into the transformation angle parameter θ. In order to further expand the parameter selection space, considering the input parameters with similar constellation distributions and different mapping relationships, the following relationship is satisfied

[0060]

[0061] When two input parameters θ0' and θ0 satisfy the parameter relationship of Equation (11), the transformation results have the same characteristics.

[0062] Appendix Figure 2 shows the constellation distributions of 4 transformation angle parameter corresponding transmission symbol sequences in the same constellation distribution set corresponding to the QPSK baseband modulation symbol sequence, the 16QAM baseband modulation symbol sequence, and the input parameter θ0 = π / 2 under the modulation method camouflage mode. The parameter set design scheme based on the modulation method camouflage mode is summarized as follows

[0063] Initialization: k = 1;

[0064] Step 101: Input parameter θ0;

[0065] Step 102: Construct the transformation angle parameter according to the constraint conditions of Equation (7), Equation (9) and Equation (10), and store it in the same constellation distribution parameter set {θ};

[0066] Step 103: Let θ0 = θ0 + π / 2. If k ≥ 3, directly go to the next step; otherwise, k = k + 1, and return to Step 102;

[0067] Step 104: The construction of the same constellation distribution transformation angle parameter set is completed, and {θ} is output.

[0068] If the low-intercept transmission mode is adopted for transmission and it is desired to make full use of the constellation ambiguity characteristic, and all the signal energy needs to be concentrated in the frequency domain term, then the transformation angle parameter and the frequency domain weighting coefficient need to satisfy

[0069]

[0070] When the number of subcarriers is large, if the baseband symbol sequence X satisfies a uniform distribution and the real part and the imaginary part are independently and identically distributed, it can be deduced based on the central limit theorem and the properties of unitary transformation that the combination of the two components in the frequency domain follows a Gaussian distribution with a mean of 0 and a variance of 1. As long as it is ensured that each element in its transformation angle parameter θ satisfies the constraint relationship of Equation (12), the GWFrFT result presents a Gaussian distribution with the same statistical characteristics. Attached Figure 3 are the constellation distributions and probability density functions of the transmission symbol sequences corresponding to two transformation angle parameters randomly selected from the same Gaussian distribution parameter set in the low-intercept transmission mode. From this, the parameter design method for the low-intercept transmission mode can be summarized as follows

[0071] Initialization: Set the transformation angle search step size θ c , θ1 = 0;

[0072] Step 201: Input the parameter θ0;

[0073] Step 202: If θ1 < 2π, directly go to the next step; otherwise, execute Step 205;

[0074] Step 203: Calculate θ2 and θ3 according to the constraint conditions of Equation (12), construct the transformation angle parameter, and store it in the same Gaussian distribution parameter set {θ};

[0075] Step 204: Let θ1 = θ1 + θ c , and return to Step 202;

[0076] Step 205: The construction of the same Gaussian distribution transformation angle parameter set is completed, and {θ} is output.

[0077] Step 2: The source input symbol sequence S is modulated by the baseband to generate a baseband symbol sequence X of length N. The baseband symbol sequence X is subjected to serial / parallel conversion processing, and a parameter θ = [θ0, θ1, θ2, θ3] is randomly selected from the constructed set of angle parameter sets with the same distribution. The GWFrFT with the transformation angle parameter θ is performed on the baseband symbol sequence X, and the transformation result expression is defined as X θ = G θ X;

[0078] Step 3: The symbol sequence X θ after GWFrFT is passed into the constellation adjustment module. If the modulation mode disguise mode is adopted for secure transmission, the constellation distribution of the symbol sequence after GWFrFT needs to be corrected in terms of angle. The constellation adjustment process is defined as X Rev = X θ exp(-jθ Rev ), where θ Rev is the correction angle for constellation adjustment. The design of the constellation adjustment correction angle will be described in detail below.

[0079] If QPSK modulation is adopted for the baseband signal, the constellation set can be expressed as {1 + j, 1 - j, -1 - j, -1 + j}, and the vector form is Given that all terms of X0 and X2 are taken from the same constellation set, the nth term of the output sequence X θ in the disguise mode can be defined as

[0080]

[0081] If the weighting coefficients g0(θ) and g2(θ) are defined as the constellation reference vectors, and k1π / 4 and k2π / 4 are regarded as the rotation angles, X θ,n (k1, k2) is the weighted result vector, and its endpoints can be regarded as the fission constellation points.

[0082] To simplify the theoretical analysis process, define

[0083]

[0084] Appendix Figure 4 shows the relationship between the angles of X θ,n (1, 1), v0(θ, 1) and v2(θ, 1) with the horizontal coordinate axis. Since the three vectors satisfy equations (14) and (15), the relationship between the angles of the three should satisfy the following

[0085]

[0086] In the formula, α0 is the angle between v0(θ, 1) and the horizontal axis; α2 is the angle between v2(θ, 1) and the horizontal axis. Then the constellation adjustment process can be defined as X Rev = Xθ exp(-jθ Rev ), attached Figure 5 shows the constellation distribution after constellation adjustment of the transmitted symbol sequence corresponding to the input parameter θ0 = π / 2 in the modulation mode camouflage mode. If the low-intercept transmission mode is adopted for secure transmission, in this mode, only the statistical distribution law of the signal is analyzed, and the specific constellation distribution form does not need to be considered. Therefore, there is no need to correct and adjust its constellation distribution, then X Rev = X θ , and directly enter the next step.

[0087] Step 4, after the symbol sequence X Rev after constellation adjustment is input into the serial / parallel conversion module, the converted symbol sequence is then subjected to digital-to-analog conversion, and finally sent to the channel for transmission.

[0088] The steps at the receiving end include:

[0089] Step 5, the receiving end receives the signal from the channel, inputs it into the analog-to-digital conversion module to convert it into a digital signal, and performs serial / parallel conversion processing to obtain the received symbol sequence Y Rev ;

[0090] Step 6, the symbol sequence Y Rev after serial / parallel conversion is input into the constellation adjustment module. If the modulation mode camouflage mode is adopted, the inverse processing of the angle correction at the sending end needs to be performed on the symbol sequence. The constellation adjustment process is defined as Y θ = Y Rev exp(jθ Rev ); If the low-intercept transmission mode is adopted, there is no need to perform the inverse processing Y θ = Y Rev , and directly enter the next step;

[0091] Step 7, in order to accurately restore the characteristics of the baseband symbol sequence, the inverse transform of the GWFrFT at the sending end needs to be performed on the symbol sequence. According to the inverse transform property of GWFrFT, when the corresponding elements of the transform angle parameters of the forward and inverse transforms are opposite to each other, the original signal can be accurately restored. Therefore, the symbol sequence Y θ after constellation adjustment is subjected to GWFrFT with the parameter -θ, and the expression of the transformation result is defined as Y = G -θ Y θ ;

[0092] Step 8, the symbol sequence Y after GWFrFT is input into the serial / parallel conversion module and subjected to baseband demodulation processing to restore the confidential information.

Claims

1. A multi-mode physical layer security transmission method based on two-component combined GWFrFT, characterized in that It includes the following steps: The steps at the sending end include: Step 1: Before signal transmission, according to the specific secure communication environment and requirements, select a secure transmission mode and set the initial parameters of the transformation angle. Design a scheme based on the i.i.d. parameter set of the selected secure transmission mode, and construct a set of multiple transformation angle parameters {θ} under the corresponding mode; Step 2: Perform a serial-to-parallel conversion on the input baseband symbol sequence X, and randomly select a set of transformation angle parameters θ = [θ0, θ1, θ2, θ3] from the set of transformation angle parameters, and perform a GWFrFT with the transformation angle parameter θ on the baseband symbol sequence X after the serial-to-parallel conversion to obtain the symbol sequence X after the GWFrFT transformation θ ; Step 3, if the modulation mode camouflage mode is adopted for secure transmission, the constellation distribution of the symbol sequence X θ is corrected in terms of angle. The constellation adjustment process is X Rev = X θ exp(-jθ Rev ); if the low-intercept transmission mode is adopted, then X Rev = X θ , and directly proceed to the next step; where θ Rev is the correction angle for constellation adjustment; Step 4, perform parallel-to-serial conversion and digital-to-analog conversion on the symbol sequence X after constellation adjustment, and finally send it to the channel for transmission; Rev ​ The steps at the receiving end include: Step 5, receive the symbol sequence Y Rev , and perform analog-to-digital conversion, equalization, and serial-to-parallel conversion. If the modulation method is used for the camouflage mode, then perform the inverse process of the angle correction at the transmitting end on the converted symbol sequence Y Rev . The constellation adjustment process is Y θ = Y Rev exp(jθ Rev ); If the low-intercept transmission mode is adopted, then Y θ = Y Rev , and directly enter the next step; Step 6, perform GWFrFT on the symbol sequence Y after constellation adjustment θ at parameter -θ, and the expression of the transformation result is Y = G -θ Y θ ; Step 7: Perform parallel-to-serial conversion on the symbol sequence Y after GWFrFT, and perform baseband demodulation processing to recover the secure information.

2. The multi-mode physical layer security transmission method based on two-component combined GWFrFT according to claim 1, characterized in that, The specific construction of the set of multiple transformation angle parameters {θ} in Step 1 is as follows: The construction process of the parameter set based on the modulation mode disguise mode is: Initialization: k = 1; Step 101: Input the parameter θ0; Step 102: Calculate θ2 and θ3 according to the following formula constraints, construct the transformation angle parameters, and store them in the same constellation distribution parameter set {θ}; Or Step 103: Let θ0 = θ0 + π / 2. If k ≥ 3, directly go to the next step; otherwise, k = k + 1, and return to Step 102; Step 104: The construction of the same constellation distribution transformation angle parameter set is completed, and a set of multiple transformation angle parameters {θ} is obtained; The construction process of the parameter set based on the low intercept transmission mode is: Initialization: Set the search step θ for the transformation angle c , θ1 = 0; Step 201: Input the parameter θ0; Step 202: If θ1 < 2π, directly go to the next step; Otherwise, execute Step 205; Step 203: Calculate θ2 and θ3 according to the following formula constraints, construct the transformation angle parameters, and store them in the same Gaussian distribution parameter set {θ}; Step 204: Let θ1 = θ1 + θ c , and return to Step 202; Step 205: The construction of the same Gaussian distribution transformation angle parameter set is completed, and a set of multiple transformation angle parameters {θ} is obtained.

3. A multi-mode physical layer security transmission method based on a two-component combined GWFrFT according to claim 1, characterized in that The correction angle θ for constellation adjustment in Step 3 and Step 5 Rev Satisfies the following relationship:

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