Simulated radio frequency division multiplexing signal transmission method based on chirp parameter hopping

Abstract

The invention discloses an imitated radio frequency division multiplexing signal transmission method based on chirp parameter hopping. The simulation radio frequency division multiplexing system comprises a transmitter and a receiver, the transmitter transmits a modulation signal to the receiver, the receiver receives the modulation signal and demodulates the modulation signal to obtain a demodulation signal and a chirp parameter, and the chirp parameter is a hopping random parameter. The method has the characteristic of good secrecy effect.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and more particularly to a method for transmitting radio frequency division multiplexing (RFDM) signals based on chirp parameter hopping. Background Art

[0002] Affine frequency division multiplexing (AFDM) is a technology with the potential to mitigate the Doppler effect and enable reliable communications. Due to the open nature of the wireless channels used in AFDM, ensuring communication security is crucial. In the Integrated Sensing and Communication (ISAC) scenarios of 6G networks that utilize AFDM, communication security is a pressing issue.

[0003] In integrated communication and sensing applications, the open nature of wireless signal transmission exposes legitimate nodes to potential security risks and privacy issues. For example, eavesdroppers can analyze received signals to monitor channel state information or infer the target's movement and location. Existing technologies struggle to strike a balance between efficiency and confidentiality. While encryption algorithms offer good confidentiality, they are inefficient. Without confidentiality measures, message transmission is insecure.

[0004] The prior art discloses a signal transmission method, apparatus, device, system, and medium based on an optical network. The signal transmission method applied to a modulation device includes: receiving first control information generated by a management device; the first control information carries at least chirp phase information for phase modulating an optical signal; converting the chirp phase information to obtain first digital information corresponding to the chirp phase information; performing phase modulation on an initial optical signal to be transmitted based on the first digital information to obtain an encrypted optical signal; and transmitting the encrypted optical signal. Based on different first control information, the initial optical signal can be phase modulated differently, causing the waveform of the initial optical signal to be distorted in the time domain to obtain an encrypted optical signal, thereby achieving flexible adjustment of the optical signal encryption method. It is difficult for an eavesdropper to obtain a complete encrypted optical signal, and even more difficult to identify the initial optical signal based on the encrypted optical signal, thereby improving the security of optical signal transmission. This method is mainly aimed at optical fiber communications and has low efficiency. Summary of the Invention

[0005] The present invention addresses the drawback of the prior art in that it is difficult to balance efficiency and confidentiality, and provides a method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping. The method has the characteristic of good confidentiality.

[0006] The primary purpose of the present invention is to solve the above technical problems, and the technical solutions of the present invention are as follows: A method for transmitting radio frequency division multiplexing (RFDM) signals based on chirp parameter hopping, comprising: The RFDM system includes a transmitter and a receiver. The transmitter transmits a modulated signal to the receiver, and the receiver receives the modulated signal and demodulates it to obtain a demodulated signal. With chirp parameters 、 The chirp parameter 、 is a random jump parameter.

[0007] Furthermore, the expression of the modulation signal is as follows:

[0008] 、 represents the chirp parameter, N represents the number of subcarriers, m represents the DAFT domain index, n represents the discrete time index, j represents the imaginary unit, Represents the transmitted information symbol vector.

[0009] Furthermore, the expression of the demodulated signal is as follows:

[0010] 、 represents the chirp parameter, N represents the number of subcarriers, m represents the DAFT domain index, n represents the discrete time index, j represents the imaginary unit, and r represents the received modulated signal.

[0011] Furthermore, the chirp parameter The expression is as follows:

[0012] represents the first error interval, represents the first key, Indicates the basic value of the first parameter.

[0013] Furthermore, the chirp parameter The expression is as follows:

[0014] represents the second error interval, represents the second key, Indicates the basic value of the second parameter.

[0015] Furthermore, the first key With the second key same.

[0016] Furthermore, the conditions of the first error interval are as follows:

[0017] The basic value of the first parameter is as follows:

[0018] N represents the number of subcarriers; Indicates the maximum Doppler integer index.

[0019] Furthermore, the relationship between the Doppler integer index and the Doppler frequency shift is as follows:

[0020]

[0021] represents the integer index of the i-th Doppler, represents the ith Doppler fractional index, N represents the number of subcarriers, represents the i-th Doppler shift.

[0022] Furthermore, the formula for transmitting the signal in the channel is as follows:

[0023] n represents the sequence number of the signal to be modulated, l represents the signal delay, represents the i-th channel gain, represents the i-th Doppler shift, represents the delay of the i-th path, represents the impulse function, represents the complex field, and P represents the total number of paths.

[0024] A computer-readable storage medium includes a program for a method for transmitting a simulated radio frequency division multiplexing signal based on chirp parameter hopping. When the method for transmitting a simulated radio frequency division multiplexing signal based on chirp parameter hopping is executed by a processor, the steps of the method for transmitting a simulated radio frequency division multiplexing signal based on chirp parameter hopping are implemented.

[0025] Compared with the prior art, the present invention has the following beneficial effects: The present invention transmits a modulated signal to a receiver through a transmitter, and the receiver receives the modulated signal and demodulates it to obtain a demodulated signal. With chirp parameters 、 The chirp parameter 、 It is a random jumping parameter; thus, an eavesdropper cannot interpret the transmitted signal without obtaining the chirp parameter, thereby achieving a good confidentiality effect of the present invention.

[0026] At the same time, since the present invention uses the method of adjusting the chirp parameters corresponding to the transmitting end and the receiving end to perform encryption at the physical layer, instead of using the encryption algorithm to perform bit operations for encryption as in the prior art, the present invention has a higher confidentiality efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a method for transmitting radio frequency division multiplexing (RFDM) signals based on chirp parameter hopping provided in Example 1.

[0028] Figure 2 This is a schematic diagram of chirp parameter jump values ​​provided in Example 1.

[0029] Figure 3 This is a schematic diagram of chirp parameter hopping provided in Example 1.

[0030] Figure 4 Chirp parameters provided in Example 1 Line chart with bit error rate.

[0031] Figure 5 Chirp parameters provided in Example 1 Line chart with bit error rate.

[0032] Figure 6 Chirp parameters provided in Example 1 constellation map.

[0033] Figure 7 Chirp parameters provided in Example 1 constellation map.

[0034] Figure 8 A bar chart of the constellation quantization entropy provided in Example 1.

[0035] Figure 9 A line graph of the estimated Cramer-Rao lower bound provided for Example 1. DETAILED DESCRIPTION

[0036] The accompanying drawings are for illustrative purposes only and are not to be construed as limiting this patent; In order to better illustrate this embodiment, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product size; It is understandable to those skilled in the art that some well-known structures and descriptions thereof may be omitted in the drawings.

[0037] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0038] Example 1 like Figure 1As shown, a method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping includes: The RFDM system includes a transmitter and a receiver. The transmitter transmits a modulated signal to the receiver, and the receiver receives the modulated signal and demodulates it to obtain a demodulated signal. With chirp parameters 、 The chirp parameter 、 is a random jump parameter.

[0039] It should be noted that the present invention does not rely on traditional high-level encryption protocols. Instead, it changes signal characteristics and introduces randomness at the lowest level of the communication link (i.e., the physical layer), thereby reducing the enemy's ability to intercept and identify it, and directly enhancing the confidentiality, integrity, and anti-interference capabilities of information transmission. When an eavesdropper cannot obtain the parameters used by the legitimate communicating party, the demodulated constellation diagram will be distorted and phase-shifted, making it impossible to correctly demodulate the data. To further enhance the security of AFDM systems, the present invention proposes a chirp parameter hopping (CPH) scheme. This scheme randomly changes the chirp parameters of each transmitted symbol, greatly increasing the difficulty for eavesdroppers to obtain the precise value of the parameters, thereby effectively protecting AFDM systems.

[0040] Furthermore, the expression of the modulation signal is as follows:

[0041] 、 represents the chirp parameter, N represents the number of subcarriers, m represents the DAFT domain index, n represents the discrete time index, j represents the imaginary unit, Represents the transmitted information symbol vector.

[0042] It should be noted that the above formula can be rewritten in matrix form:

[0043] F represents the Fourier transform (DFT) matrix, , n is 0, 1,…, N-1.

[0044] In order to overcome the multipath effect and make the channel lie in the periodic domain, it is necessary to A Chirp Periodic Prefix (CPP) of length L is added before transmission, as shown below:

[0045] Furthermore, the expression of the demodulated signal is as follows:

[0046] 、 represents the chirp parameter, N represents the number of subcarriers, m represents the DAFT domain index, n represents the discrete time index, j represents the imaginary unit, and r represents the received modulated signal.

[0047] The above expression can be rewritten into the following matrix form:

[0048]

[0049]

[0050] The received modulated signal is represented as follows:

[0051] represents additive Gaussian noise. It can be rewritten as the following matrix form:

[0052] , , n is 0, 1,…, N-1. represents the forward cyclic shift matrix.

[0053]

[0054] Furthermore, the chirp parameter The expression is as follows:

[0055] represents the first error interval, represents the first key, Indicates the basic value of the first parameter.

[0056] Furthermore, the chirp parameter The expression is as follows:

[0057] represents the second error interval, represents the second key, Indicates the basic value of the second parameter.

[0058] It should be noted that the chirp parameter variation formula above ensures that the method of the present invention can generate parameters efficiently, thereby achieving physical layer confidentiality. With chirp parameters All can be changed according to the above formula.

[0059] In one embodiment, the key 、 Master key Obtained, or it can be agreed to be generated by a unified seed.

[0060] Binary key By step length Divided into The group binary key, i.e. ,in is the i-th group of binary key bits, with a length of . In addition, for the binary key of the group , convert it to its decimal equivalent ,in is the i-th positive integer key.

[0061] Furthermore, the first key With the second key same.

[0062] Furthermore, the conditions of the first error interval are as follows:

[0063] The basic value of the first parameter is as follows:

[0064] N represents the number of subcarriers; Indicates the maximum Doppler integer index.

[0065] Should be an irrational number or much smaller than rational number.

[0066] In a specific embodiment, Desirable , The value is 2. Chirp parameter Changes such as Figure 2 、 Figure 3 shown. Figure 3 middle Indicates the chirp parameter in the first transmission In this embodiment, the error interval 、 As long as it is large enough, the encryption parameters of each signal (symbol) are different from the parameters used for other signals (symbols) in the same frame.

[0067] Furthermore, the relationship between the Doppler integer index and the Doppler frequency shift is as follows:

[0068]

[0069] represents the integer index of the i-th Doppler, represents the ith Doppler fractional index, N represents the number of subcarriers, represents the i-th Doppler shift.

[0070] Furthermore, the formula for transmitting the signal in the channel is as follows:

[0071] n represents the sequence number of the signal to be modulated, l represents the signal delay, represents the i-th channel gain, represents the i-th Doppler shift, represents the delay of the i-th path, represents the impulse function, represents the complex domain, and P represents the total number of paths.

[0072] Assuming that the eavesdropper does not know the parameters used by the transmitter, the analysis of the demodulation performance change of the demodulated signal through exhaustive search is as follows: Assume that the signal received by the legal receiver is:

[0073]

[0074] Assume that the signal demodulated by the legal receiver is:

[0075] Through Channel equalization is performed to obtain a demodulated signal (symbol).

[0076] It can be seen that in the AFDM system, the receiver needs to know the parameters and The precise value of is needed to correctly demodulate the transmitted information. For an eavesdropper, the parameter is unknown and therefore the transmitted information cannot be deciphered.

[0077] If the eavesdropper knows the legitimate parameter i-th channel gain , the i-th Doppler shift , the delay of the i-th path , a training sequence for channel estimation , try to estimate the parameters and .

[0078] In order to quantify the eavesdropper's and The accuracy of the estimate is characterized using the Cramer-Rao lower bound (CRLB). The Cramer-Rao lower bound (CRLB) provides a lower bound on the variance of any unbiased estimator. By evaluating the Cramer-Rao lower bound (CRLB), we can evaluate the accuracy of the eavesdropper in trying to estimate and The minimum estimation error achievable when averaging is used to evaluate the anti-eavesdropping performance of the AFDM system.

[0079] The parameters that need to be estimated are as follows:

[0080] CRLB is given by the inverse Fisher information matrix, i.e.

[0081] in,

[0082] is the log-likelihood function. and , we can get , .

[0083] So, the probability density function as follows:

[0084] in, , by taking the logarithm of the above formula, we can get:

[0085] Taking the derivative we get:

[0086] because ,function satisfy . Therefore, the expectation of the second derivative of f can be simplified to:

[0087] in express

[0088]

[0089] in, .when When is an integer and N is an even number, since

[0090] because

[0091] We can get:

[0092] Finally, the CRLB is:

[0093] The modulation scheme based on AFDM is BPSK, and the number of subcarriers per frame is N =128. Chirp parameters are and , the maximum Doppler index is , the maximum delay index is , the number of paths is P =4, the algorithm of the present invention is evaluated.

[0094] Depend on Figure 4 、 Figure 5 It can be seen that when the chirp parameter and chirp parameters There is an error, and the error interval and When , the eavesdropper's bit error rate (BER) remains at 0.5. The number of searches required by the eavesdropper is as follows:

[0095] It can be seen that if the eavesdropper does not know the chirp parameters and chirp parameters When , the search space using the exhaustive method is very large.

[0096] Generally speaking, in the modulation and demodulation scheme of the radio frequency division multiplexing system, QPSK constellation mapping is often used. Figure 6 As shown, when and When, if Deviation , then the constellation points of the receiver form a circle, this is because The corresponding modulation matrix The phase offset encryption effect is introduced to the constellation point x in the DAFT domain. Therefore, if the parameter , then the phase offset cannot be determined. Similarly, if Figure 7 As shown, The corresponding modulation matrix A phase shift is introduced to the time domain signal. When using the guessed parameters When demodulated, this results in a complete obfuscation of the constellation points in the DAFT domain. This obfuscation creates an encryption effect, making the signal incomprehensible to unauthorized receivers.

[0097] like Figure 8 As shown in FIG, the constellation quantization entropy of the AFDM using the CPH solution of the present invention is much greater than that of the AFDM not using the CPH solution, indicating that the AFDM using the CPH solution of the present invention has significantly better security performance than the AFDM not using the CPH solution of the present invention.

[0098] The calculation formula of constellation quantization entropy is as follows:

[0099]

[0100] is the joint probability density. The larger the constellation quantization entropy, the greater the uncertainty in the constellation diagram, which means less information leakage and greater difficulty for eavesdroppers to demodulate by receiving large amounts of data.

[0101] like Figure 9 As shown in Figure 2, as N increases, and It can be observed that when SNR = 25dB and N = 128, and The estimation accuracy can reach about At this point, the eavesdropper can obtain most of the correct information. However, in this analysis, it is assumed that the eavesdropper knows the legitimate parameter i-th channel gain , the i-th Doppler shift , the delay of the i-th path , a training sequence for channel estimation In reality, this type of data is difficult to obtain.

[0102] A computer-readable storage medium includes a program for a method for transmitting a simulated radio frequency division multiplexing signal based on chirp parameter hopping. When the method for transmitting a simulated radio frequency division multiplexing signal based on chirp parameter hopping is executed by a processor, the steps of the method for transmitting a simulated radio frequency division multiplexing signal based on chirp parameter hopping are implemented.

[0103] The same or similar reference numerals correspond to the same or similar components; The terms used in the drawings to describe positional relationships are for illustrative purposes only and should not be construed as limiting this patent; Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping, characterized in that: include: The RFDM system includes a transmitter and a receiver. The transmitter transmits a modulated signal to the receiver, and the receiver receives the modulated signal and demodulates it to obtain a demodulated signal. With chirp parameters 、 The chirp parameter 、 is a random jump parameter.

2. The method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping according to claim 1, wherein: The expression of the modulation signal is as follows: 、 represents the chirp parameter, N represents the number of subcarriers, m represents the DAFT domain index, n represents the discrete time index, j represents the imaginary unit, Represents the transmitted information symbol vector.

3. The method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping according to claim 1, wherein: The expression of the demodulated signal is as follows: 、 represents the chirp parameter, N represents the number of subcarriers, m represents the DAFT domain index, n represents the discrete time index, j represents the imaginary unit, and r represents the received modulated signal.

4. The method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping according to claim 2 or 3, wherein: The chirp parameter The expression is as follows: represents the first error interval, represents the first key, Indicates the basic value of the first parameter.

5. The method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping according to claim 4, wherein: The chirp parameter The expression is as follows: represents the second error interval, represents the second key, Indicates the basic value of the second parameter.

6. The method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping according to claim 5, wherein: The first key With the second key same.

7. The method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping according to claim 4, wherein: The conditions of the first error interval are as follows: The basic value of the first parameter is as follows: N represents the number of subcarriers; Indicates the maximum Doppler integer index.

8. The method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping according to claim 7, wherein: The relationship between the Doppler integer index and the Doppler frequency shift is as follows: represents the integer index of the i-th Doppler, represents the ith Doppler fractional index, N represents the number of subcarriers, represents the i-th Doppler shift.

9. The method for transmitting radio frequency division multiplexing signals based on chirp parameter hopping according to claim 8, wherein: The formula for transmitting the signal in the channel is as follows: n represents the sequence number of the signal to be modulated, l represents the signal delay, represents the i-th channel gain, represents the i-th Doppler shift, represents the delay of the i-th path, represents the impulse function, represents the complex domain, and P represents the total number of paths.

10. A computer-readable storage medium, comprising a program for a method for transmitting RF division multiplexing-like signals based on chirp parameter hopping. When the method for transmitting RF division multiplexing-like signals based on chirp parameter hopping is executed by a processor, the steps of the method for transmitting RF division multiplexing-like signals based on chirp parameter hopping as described in claims 1 to 9 are implemented.

Images