A modulation parameter blind identification method, system, device and medium for a non-cooperative OTFS system

Abstract

A modulation parameter blind identification method, system, device and medium for a non-cooperative OTFS system, the method comprising: OTFS modulation of a sending end signal and transmission through a multipath fading and noise channel; OTFS system blind identification of a receiving end receiving an undemodulated OTFS signal in two steps: OTFS frame structure parameter blind identification based on a cyclic stationary autocorrelation function, obtaining a delay dimension grid point number, a cyclic prefix (CP) length and a Doppler dimension grid point number; time-frequency synchronization parameter estimation, estimating a symbol clock offset using a delay dimension and Doppler dimension joint autocorrelation method to obtain a symbol starting clock offset; and estimating a carrier frequency offset using a CP-tail phase difference method to obtain a carrier frequency offset factor; the present application realizes obtaining OTFS system modulation parameters in the case of being unable to predict pilots or prior frame information in non-cooperative communication, and has suppression capability for multipath and mobile Doppler, thereby providing key technical support for passive monitoring, classification and reconnaissance of non-cooperative OTFS signals.

Description

Technical Field

[0001] This invention belongs to the field of signal demodulation technology, and specifically relates to a method, system, device and medium for blind identification of modulation parameters for non-cooperative OTFS systems. Background Technology

[0002] As mobile communications evolve towards 6G and high-motion scenarios such as vehicle-to-everything (V2X) and high-speed rail, the demand for reliable, multipath-tolerant, and Doppler-resistant modulation techniques in communication systems is becoming increasingly urgent. Orthogonal Time-Frequency Space (OTFS) modulation technology, with its ability to equalize the channel in the delay-Doppler domain, has become an important candidate for next-generation wireless access. Researching OTFS signal demodulation technology can help effectively manage OTFS communication resources and assist in establishing a reliable OTFS communication environment.

[0003] Non-cooperative communication refers to a communication mode in wireless communication systems where a third party accesses the system without authorization to listen to, analyze, and demodulate signals. In non-cooperative communication, the receiver can only perform modulation identification based on the received signal and cannot rely on the sender's cooperation. Especially in applications such as military reconnaissance and civilian spectrum management, the effective decoding and identification of non-cooperative communication signals often determines the system's response speed and reliability.

[0004] Current OTFS demodulation methods convert the received time-domain signal to the time-frequency domain using a Wigner transform, and then convert it to the time-delay-Doppler (DD) domain using a Sin-Fourier transform. In this process, we need to obtain the delay vignetting points (subcarrier count) of the OTFS signal frame. , length of cyclic prefix Doppler-Vigg points (number of multicarrier symbols) Only after the signal frames are synchronized in the time and frequency domains can Wegener and Sin-Fourier transforms be performed; otherwise, demodulation cannot proceed. However, most OTFS demodulation research is based on cooperative communication scenarios, which cannot meet the needs of non-cooperative communication in third-party passive reconnaissance and cognitive radio. For example, the invention patent "A signal detection method and system for an OTFS system based on residual channel attention network" (CN 118432999 A) extracts deeper features from the demodulated OTFS signal to reduce the bit error rate, assuming that the parameters of the transmitting end are known during the demodulation process. In time-frequency synchronization, traditional symbol clock offset (STO) estimation methods can only handle a single dimension, but the delay dimension and Doppler dimension of OTFS signals have multi-dimensional coupling characteristics. Traditional symbol clock offset (STO) estimation methods are very prone to causing a decrease in estimation accuracy in high-speed scenarios.

[0005] In non-cooperative OTFS communication scenarios, once the transmitter parameters are unknown or dynamically changing, the receiver struggles to accurately synchronize and demodulate. Furthermore, due to the high mobility and high Doppler shift inherent in OTFS, the algorithm for estimating the transmitter modulation parameters needs to be sufficiently stable and accurate. For time-frequency synchronization, traditional STO estimation methods only consider a single dimension (such as CP autocorrelation). However, OTFS signals have a coupling of delay and Doppler dimensions, requiring a joint estimation combining the autocorrelation of these two dimensions to ensure accurate estimation of symbol clock offset. Therefore, there is an urgent need for a general method for OTFS systems that can quickly and blindly estimate the modulation parameters of the OTFS system based solely on the received signal, without requiring prior knowledge of the channel and frame structure, to meet the stable communication requirements in highly mobile and dynamic environments.

[0006] Patent application CN 116471158 A discloses a method, apparatus, and system for implementing OTFS modulation and demodulation. It achieves OTFS modulation based on OFDM modulation by preprocessing the encoded and high-order modulated data using ISFFT, and then demodulates the data based on OFDM using SFFT at the receiving end. However, if the receiving end cannot obtain the OTFS signal frame parameters from the transmitting end, it cannot perform OTFS demodulation based on OFDM. Furthermore, it does not take into account the demodulation error caused by time-frequency offset, which can easily lead to increased demodulation error and instability.

[0007] Patent application CN 117614777 A discloses a joint synchronization and channel estimation method for OTFS systems. This method simultaneously implements receiver synchronization and channel estimation modules by inserting a specified pilot sequence at the OTFS transmitter, utilizing pilot sequence correlation characteristics for symbol synchronization, and extracting cyclic prefix correlation characteristics for precise time-frequency synchronization. However, in non-cooperative communication, pilot sequence information cannot be obtained in advance, making it difficult to perform symbol and frequency synchronization with a predetermined received pilot sequence. Furthermore, since only a single cyclic prefix autocorrelation is used for precise time-frequency synchronization, the delay-Doppler multidimensional characteristics of the OTFS system are not considered, which can easily lead to increased synchronization errors in complex environments. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the present invention aims to provide a method, system, device, and medium for blind identification of modulation parameters in non-cooperative OTFS systems. This method involves blindly identifying the OTFS frame structure parameters based on the cyclic stationary autocorrelation function (CAF) from the undemodulated OTFS signal received in the receiver buffer at the receiving end, thereby obtaining the delay vignetting points (number of subcarriers). , length of cyclic prefix Doppler-Vigg points (number of multicarrier symbols) The symbol clock offset (STO) is estimated using a joint autocorrelation method combining the signal delay dimension and the Doppler dimension, thus obtaining the symbol initial clock offset. Receive stream from After alignment, the carrier frequency offset (CFO) is estimated using the cyclic prefix and corresponding tail phase difference method to obtain the carrier frequency offset factor ε. Blind estimation of OTFS modulation parameters is achieved in non-cooperative scenarios. The proposed distributed blind estimation algorithm fully considers the characteristics of the delay Doppler domain of the OTFS system, improving not only the estimation accuracy of frame structure and synchronization parameters but also maintaining stability in high-mobility and high-dynamic scenarios.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for blind identification of modulation parameters in non-cooperative OTFS systems includes the following steps: Step 1: The OTFS system transmitter generates a delayed-Doppler two-dimensional baseband signal. The OTFS modulated signal is generated and transmitted through OTFS modulation. ; Step 2: Modulate the OTFS signal generated in Step 1. By simulating signal transmission in a wireless channel under real-world scenarios through multipath fading and noisy channels, the undemodulated OTFS received signal after wireless channel transmission is obtained. ; Step 3: The OTFS system blind identification receiver receives the OTFS received signal obtained in Step 2. The OTFS received sequence is obtained through discrete sampling. For discrete OTFS received sequences Blind identification of specific frame structure parameters in OTFS based on the Cyclic Stationary Autocorrelation Function (CAF) to obtain the delay vignetting points. , length of cyclic prefix , Dopplervig points ; Step 4: Based on the delayed vig points obtained in Step 3 , length of cyclic prefix And Dopplervig points Joint estimation of time-frequency synchronization parameters is performed, including symbol clock offset (STO) and carrier frequency offset (CFO) parameters. A flat-top timing metric is used to measure the cyclic prefix correlation of the received stream at different alignment points in both the signal delay and Doppler dimensions. The index corresponding to the maximum cyclic prefix correlation is the symbol start clock offset. The received stream is offset from the symbol start clock. After alignment, the carrier frequency offset (CFO) is estimated using the cyclic prefix and corresponding tail phase difference method to obtain the carrier frequency offset factor. Ultimately, the clock offset is initiated by the symbol. and carrier frequency offset factor Correcting symbol clock offset (STO) and carrier frequency offset (CFO) enables precise time and frequency synchronization of the OTFS system.

[0010] The specific method of step 1 includes: The OTFS system transmitter generates a random bitstream signal. Random bitstream signal The baseband signal is obtained after LDPC encoding and QAM modulation. For baseband signals By parallelizing the signal and filling empty carriers, a delayed-Doppler two-dimensional baseband signal is constructed. , ; Delayed-Doppler two-dimensional baseband signal The transmitted OTFS modulated signal is obtained through OTFS modulation. ; The modulation process of the OTFS system is as follows: First, the delayed-Doppler two-dimensional baseband signal is modulated using the inverse symplectic finite Fourier transform (ISFFT). Mapping from the delay-Doppler domain to the time-frequency domain yields the first... The time domain and the first Time-frequency domain modulation symbols at each frequency domain index grid point The specific formula is as follows:

[0011] in, For delayed dimension indexes, For Doppler index, To achieve phase rotation from the delay dimension to the frequency dimension, Achieve phase rotation from the Doppler dimension to the time dimension; Time-frequency domain modulation symbols Then, through OFDM modulation, time-domain subcarrier symbols with cyclic prefixes are generated sequentially for each point of the time-frequency grid to obtain the transmitted OTFS modulated signal. :

[0012] in, Baseband transmit pulse: rectangular window + cyclic prefix; Subcarrier spacing ensures that the subcarriers are mutually orthogonal.

[0013] In step 2, the OTFS received signal that has not been demodulated after being transmitted through the wireless channel. The expression is:

[0014] in, , represents the channel impulse response caused by the time-varying multipath channel, and represents the response at time . After passing through the channel, it will have different delays Upon reaching the receiving end, different gains and phase rotations are generated. This indicates that the signal is delayed as it travels along different paths. This represents additive white Gaussian noise.

[0015] The specific method for step 3 includes: The OTFS received signal obtained in step 2 Discrete sampling is performed to obtain the OTFS received sequence.

[0016]

[0017] in, Indicates the sampling interval; Constructing delayed Vig point and cyclic prefix length Corresponding cycle frequency estimate Cyclic stationary autocorrelation function The function formula is defined as follows:

[0018] in, For OTFS receive sequence, It is the delay size. It is the cumulative window length. It is the cycle frequency, defined as:

[0019] in, It is the sampling rate at the receiving end; For delayed Vig points When performing a normalized peak search, set the cyclic frequency estimate. According to the peak search function Determine the highest scorer That is, the delayed Vig point. Delayed Vig point peak search function The definition is as follows:

[0020] Cyclic frequency estimates When performing normalized peak search, set the delayed Vig point number to 1. According to the peak search function Determine the highest scorer This is the estimated value of the cycle frequency. Cyclic frequency search function The definition is as follows:

[0021] Then based on the loop frequency and loop prefix The equation relationship is used to obtain the estimated cyclic prefix length. It can also be done through formulas Convert to sample cyclic prefix sample index length ; Constructing short-window CAF sequences To estimate the Dopplervig points At each time location Measuring a length Cyclic prefix related energy, The expression is as follows:

[0022] The specific method for step 4 includes: First, a flat-top timing metric function is constructed for the delay dimension and Doppler dimension of the OTFS received sequence. , The expression is:

[0023] in, and These correspond to the cyclic indices of the OTFS received sequence delay dimension and Doppler dimension, respectively; y(n) is the time-domain sample at the receiving end, with internal double summation: inner summation Take samples from the middle of CP and sum them outside the sample. Consider all multicarrier symbol numbers together; For flat-top time series metric functions Introducing a flat-top window, which selects the center of the CP. and These represent the start and end positions of the flat-top window, defined as follows:

[0024] Secondly, the maximum index of the first search cycle is the estimated symbol clock offset (STO), and the position of the maximum value is the symbol starting clock offset. :

[0025] Receive stream offset from symbol start clock After alignment, carrier frequency offset (CFO) estimation is performed. The phase correlation of each symbol of the received signal in the middle region of the cyclic prefix and the corresponding tail portion is calculated, and the carrier frequency offset factor is obtained after normalization. Carrier frequency offset factor The calculation formula is as follows:

[0026] in, This refers to the CP portion of the received signal. This indicates the corresponding tail portion, with the two portions separated by Dopplervigne points. ,in These are time-domain samples of the transmitted signal. This indicates the carrier frequency offset, measured in Hertz (Hz). Indicates the sampling frequency at the receiving end. Indicates a time index. This indicates taking the phase angle, that is, calculating the phase difference between signals.

[0027] The signal parallelization process involves converting the serially modulated QAM baseband signal... Transformed into a two-dimensional grid with one frame per column Each row corresponds to a time delay resolution unit, and each column corresponds to a Doppler resolution unit; The process of filling empty carriers occurs within a two-dimensional grid after signal parallelization. By inserting all zeros at the beginning, middle, and end, a delayed-Doppler two-dimensional baseband signal is constructed. , .

[0028] This invention also provides a blind modulation parameter identification system for non-cooperative OTFS systems, comprising: OTFS modulated signal The modulation module is used to generate a delayed-Doppler two-dimensional baseband signal at the transmitter of the OTFS system. The OTFS modulated signal is generated and transmitted through OTFS modulation. ; OTFS received signal The transmission module is used to transmit the generated OTFS modulated signal. By simulating signal transmission in a wireless channel under real-world scenarios through multipath fading and noisy channels, the undemodulated OTFS received signal after wireless channel transmission is obtained. ; The OTFS specific frame structure parameter blind identification module is used to enable the receiver to receive OTFS received signals. The OTFS received sequence is obtained through discrete sampling. For discrete OTFS received sequences Blind identification of specific frame structure parameters in OTFS based on the Cyclic Stationary Autocorrelation Function (CAF) to obtain the delay vignetting points. , length of cyclic prefix , Dopplervig points ; The OTFS system's precise time-frequency synchronization module is used to synchronize latency based on the number of Vig points. , length of cyclic prefix And Dopplervig points Joint estimation of time-frequency synchronization parameters is performed, including symbol clock offset (STO) and carrier frequency offset (CFO) parameters. A flat-top timing metric is used to measure the cyclic prefix correlation of the received stream at different alignment points in both the signal delay and Doppler dimensions. The index corresponding to the maximum cyclic prefix correlation is the symbol start clock offset. The received stream is offset from the symbol start clock. After alignment, the carrier frequency offset (CFO) is estimated using the cyclic prefix and corresponding tail phase difference method to obtain the carrier frequency offset factor. Ultimately, the clock offset is initiated by the symbol. and carrier frequency offset factor Correcting symbol clock offset (STO) and carrier frequency offset (CFO) enables precise time and frequency synchronization of the OTFS system.

[0029] The present invention also provides a modulation parameter blind identification device for non-cooperative OTFS systems, comprising: Memory: A computer program for blind identification of modulation parameters for a non-cooperative OTFS system, which is stored in the above-mentioned computer program and is a computer-readable device; Processor: Used to implement the aforementioned method for blind identification of modulation parameters for non-cooperative OTFS systems when executing the computer program.

[0030] The present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, enables the implementation of the aforementioned method for blind identification of modulation parameters for non-cooperative OTFS systems.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention proposes a blind identification method for signal frame parameters based on the cyclic stationary autocorrelation function, specifically addressing the unique delay-Doppler frame structure of OTFS, i.e., constructing the delay vignetting points. and cyclic prefix length Corresponding cycle frequency The cyclic stationary autocorrelation function, then based on the delayed vignetting points. and cyclic prefix length A short-window CAF sequence was constructed, successfully obtaining the delay vig points (number of subcarriers) M and the cyclic prefix length in non-cooperative scenarios. The Doppler Vignette number (multi-carrier symbol number) N eliminates the dependence on cooperative information and still ensures estimation accuracy in high-mobility scenarios.

[0032] 2. This invention estimates symbol clock offset using a joint autocorrelation method based on signal delay and Doppler dimensions. Specifically, it uses a flat-top timing metric to measure the cyclic prefix correlation of the received stream at different alignment points in both the signal delay and Doppler dimensions. The index corresponding to the maximum cyclic prefix correlation is the symbol start clock offset. Compared to traditional STO estimation methods that can only handle a single dimension, this invention considers the coupling relationship under multiple dimensions, including delay and Doppler, thus improving synchronization accuracy in complex channels and high-dynamic environments. After eliminating STO, the carrier frequency offset is estimated using the cyclic prefix and corresponding tail phase difference method. The two methods work together to successfully achieve accurate time-frequency synchronization of the OTFS system.

[0033] In summary, this invention provides a blind identification method for modulation parameters in non-cooperative OTFS systems, utilizing a cyclic stationary autocorrelation function to determine the number of delay vignetting points in OTFS signal frames. , length of cyclic prefix , Dopplervig points The method identifies the symbol clock offset by using a joint autocorrelation method based on the signal delay dimension and the Doppler dimension, and estimates the carrier frequency offset using the cyclic prefix and corresponding tail phase difference method. This method eliminates the dependence on cooperative information and has the ability to suppress multipath and moving Doppler, making it suitable for high-mobility scenarios. Attached Figure Description

[0034] Figure 1 This is a flowchart of the method of the present invention.

[0035] Figure 2 This is a flowchart of the OTFS modulation signal generation process of the present invention.

[0036] Figure 3 is a schematic diagram of the OTFS signal frame structure of the present invention, wherein Figure 3(a) is the delayed-Doppler two-dimensional baseband signal. Figure 3(b) is a schematic diagram of the grid structure of the OTFS modulated signal frame.

[0037] Figure 4 This is a flowchart of the OTFS signal frame parameter estimation based on the cyclic stationary autocorrelation function of the present invention.

[0038] Figure 5 This is a flowchart of the estimation process for the combined autocorrelation STO and CFO of the delayed dimension and Doppler dimension of the present invention.

[0039] Figure 6(a) shows the results of the joint autocorrelation q value of the present invention being 5 to 8, and Figure 6(b) shows the results of the joint autocorrelation q value of the present invention being CP length.

[0040] Figure 7 This is a schematic diagram of the simulation results for estimating the structural parameters of the OTFS signal frame.

[0041] Figure 8 This is a schematic diagram of the simulation results for OTFS signal symbol clock offset (STO) estimation.

[0042] Figure 9 This is a schematic diagram of the simulation results for estimating the carrier frequency offset (CFO) of the OTFS signal. Detailed Implementation

[0043] The technical solution adopted by the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0044] like Figure 1 The diagram shows a flowchart of a blind modulation parameter identification method for non-cooperative OTFS systems provided by the present invention. In this embodiment, the method utilizes the cyclic stationary autocorrelation function (CAF) to determine the number of delay vignettes in the OTFS signal frame. , length of cyclic prefix , Dopplervig points The method involves identifying modulation parameters of an OTFS system in a non-cooperative communication scenario. It estimates the symbol clock offset (STO) using a joint autocorrelation method combining signal delay and Doppler dimensions, and estimates the carrier frequency offset (CFO) using the cyclic prefix and corresponding tail phase difference method. This method also suppresses multipath and moving Doppler effects. The method includes at least the following steps: Step 1: The process of generating the OTFS modulated signal at the OTFS system transmitter is as follows: Figure 2 As shown, firstly, a random bitstream signal with a bitstream length of K and random bit data in the range [0,1] is generated. : ,right LDPC encoding is performed. LDPC encoding is widely used in multi-carrier modulation signal generation modules due to its excellent channel transmission and error correction capabilities. Specifically, it involves converting the random bit data generated at the transmitting end into LDPC encoding. The data is packaged into a 64,800-bit sparse parity codeword conforming to the DVB-S2 specification. Every 32,400 information bits (½ bit rate) are mapped to a 64,800-bit LDPC codeword. Zeros are padded to the end of any bits shorter than the specified block length. The padded bitstream is then subjected to pseudo-random permutations to shuffle adjacent bits. Finally, the length is output. LDPC encoded bit sequence QAM modulation: per Bit mapping to an M-QAM complex symbol yields the output baseband complex symbol sequence: , It is the modulation order, and its value is... , It is a positive integer. Parallelization and empty carrier padding: ... (The sentence is incomplete and requires more context to translate accurately.) Valid data symbol sequence { Arrange the rows (or columns) into a K×L matrix, and set all remaining positions to 0 to form the transmission grid of the delayed Doppler domain. : The "non-zero" regions in the grid carry the actual data, while the "zero" regions serve as protection and buffer space. These zero elements do not affect reception but ensure data security and more stable transmission. Delay-Doppler two-dimensional baseband signal. The mesh structure is shown in Figure 3(a), and the Doppler N corresponds to Delay dimension M corresponds to Using two-dimensional grid symbols OTFS transmission frames are generated by inverse symplectic finite fourier transform (ISFFT) of formula (1) and OFDM modulation (Heisenberg transform) of formula (2). The baseband signal is transformed from the DD domain to the TF domain, and then from the TF domain to a continuous time-domain OTFS transmission waveform. Its signal frame structure is shown in Figure 3(b). Each frame of the OTFS signal consists of... Multicarrier symbols and It consists of a number of subcarriers.

[0045] Step 2: The OTFS modulated time-domain signal is passed through a multipath fading and noise channel. Multipath delay and fixed attenuation are introduced, and Doppler frequency shift is added. The analog signal is passed through the AWGN channel, completing the modeling of a typical wireless channel. The expression of the OTFS signal through the wireless channel is shown in formula (3).

[0046] Step 3: The OTFS signal obtained in Step 2 is received in the buffer, and blind identification of specific frame structure parameters of OTFS is performed. The overall process is as follows: Figure 4 As shown, a cyclic stationary autocorrelation function is constructed for the delay vignetting points and the cyclic frequency. See formula (5). The commonly used CP ratio and subcarrier symbol FFT points are determined according to the 3GPP wireless access standard and the IEEE 802.11 wireless LAN standard. They can also be adjusted according to specific scenarios to construct a candidate delay vignetting point set. and candidate cycle frequency set Candidate cycle frequency set Transform according to formula (6). Set the loop frequency to 0 and convert the candidate delay vig point set. Substituting the value into formula (7), we search for the number of delay dimension points corresponding to the maximum autocorrelation energy index. That is, the delayed Vig point. The value is set to the delay vig point value. Set of candidate cycle frequencies Substitute the value into formula (8) to search for the largest estimated value of the autocorrelation energy index cycle frequency. Corresponding estimated cyclic prefix length Through formula Convert to cyclic prefix sample index length Constructing short-window CAF sequences To estimate the Dopplervig points See formula (9) for Take each time The relevant calculations are performed using a short window of length, and the index length of the cyclic prefix sample is used. Perform average smoothing noise reduction, reduce noise, highlight correlation peaks, and adaptively set thresholds. Peak detection was then performed to maximize the detection of true peaks and suppress false peaks and repetitive fluctuations. The Doppler-Vigg points were obtained by taking the higher of direct counting and peak-average interval estimates. The double counting method improves robustness to peak loss / multiple peak cases.

[0047] Step 4: Time-frequency synchronization parameter estimation is based on the signal frame parameters from Step 3: delay vig points. , length of cyclic prefix And Dopplervig points The symbol clock offset (STO) and carrier frequency offset (CFO) are estimated and compensated. The symbol clock offset (STO) represents the time deviation between the start time of the received symbol and the ideal alignment time of the transmitted symbol, manifested as a misalignment of time-domain sampling points. The carrier frequency offset (CFO) represents the absolute difference between the carrier frequencies of the transmitting and receiving ends, manifested as a continuous phase rotation of the received signal. The specific estimation process is as follows: Figure 5 As shown. In Symbol Clock Offset (STO) estimation, this invention fully considers the high coupling between the delay and Doppler domains of OTFS, and constructs a joint autocorrelation function of the delay and Doppler dimensions. The flat-top timing metric function is described in the figure. As shown in formula (10), a flat-top window is constructed to avoid the problem of multipath tail mutations at both ends of the CP part. Generally speaking, The value is 5~8, but the appearance of the flat top causes a certain error in the symbol timing. This invention The value is taken as the length of the cyclic prefix obtained in step three. Window start and end positions , Referring to formula (11), the originally unstable "flat top" was eliminated, making the timing position more prominent and accurate. The results are compared in Figure 6(a) and Figure 6(b). Figure 6(a) shows the joint autocorrelation. The results for values ​​of 5 to 8 are shown in Figure 6(b), which shows the joint autocorrelation. The result image showing the CP length value clearly indicates... The value has a significant impact on the result. The value is taken as the CP length ratio Using a value of 5-8 reduces the flat top, making the positioning more prominent and accurate. The calculation of the symbol clock offset (STO) and joint autocorrelation function includes a triple-loop calculation: outer candidate position... Mid-level symbol index Inner window position Index calculation: Cumulative addition of numerators: Add up the denominators: Normalized metric: Finally, according to formula (12), the maximum index of the first search cycle is found, which is the symbol starting clock offset. Clock offset from the symbol Begin capturing and aligning the signal. For the received signal... Each symbol i=0… Take the CP segment Take the tail section: Calculate the phase cross-correlation according to formula (13), accumulate the phases and average them. The average value is the number of symbols. The carrier frequency offset factor is obtained by normalizing the carrier frequency offset (CFO). Multiply the signal by , Implement carrier frequency offset (CFO) compensation.

[0048] The above steps one through four complete a method for blind identification of modulation parameters for non-cooperative OTFS systems in this embodiment. The present invention will now undergo actual simulation analysis to verify its effectiveness.

[0049] Using Matlab as the simulation platform, OTFS simulation signals with different signal-to-noise ratios were generated. The specific parameter settings are shown below:

[0050] The signal frame parameter identification and time-frequency synchronization identification methods mentioned in this invention are applied to OTFS modulated signals with different SNR 16QAM baseband modulation. Figure 7 Based on the simulation results of the invention proposed in step three, commonly used delay candidates are set. for CP ratio candidate is The results show that the estimation accuracy of the three structural parameters of the OTFS signal frame increases with the increase of the signal-to-noise ratio (SNR). This is because the reduction of noise peaks in the signal makes the periodic peaks of the real frame more prominent and easier to detect. The estimation performance of the subcarrier number M is the best, reaching almost 100% when SNR ≥ 10dB. The estimation performance of CP length and multicarrier symbol number N is slightly weaker in the low to medium SNR region (0-5 dB), but tends to saturate above 10dB. The Doppler Vig point count is most affected by dynamic frequency changes and needs to search for the real value after estimating the subcarrier number and CP length, making its estimation the most unstable at low SNR. Utilizing the cyclostationary characteristics of the signal in the DD domain, it shows good adaptability to multipath and high-speed mobile environments.

[0051] Figure 8 This is the result of estimating the symbol clock offset (STO) using the joint autocorrelation method of signal delay and Doppler dimensions proposed in step four. Compared with the traditional STO method, the proposed scheme for OTFS has advantages in recognition accuracy across various signal-to-noise ratios. Figure 8 As can be seen, in the high SNR region (≥10 dB), the present invention achieves an accuracy of nearly 100%, which is much higher than the traditional method. Especially at SNR=10 dB, the traditional method has large fluctuations and a significant drop in the middle region, indicating that the traditional method is easily affected by multipath interference, noise interference or parameter mismatch, and is not as good as the method proposed in the present invention in high-speed scenarios.

[0052] Figure 9 The result diagram of the carrier frequency offset (CFO) estimation proposed in step four using the phase difference between the cyclic prefix and the corresponding tail is shown. Under the frequency offset settings of 10kHz, 15kHz and 20kHz, the present invention tends to be stable when the SNR is greater than 12dB, achieving 100% estimation accuracy. Because this method requires OTFS signal frame parameters as prior information, the CFO estimation result is consistent with the overall trend of the signal frame parameter estimation result, and it can still maintain high accuracy under various frequency offset conditions. It is an effective strategy to deal with the Doppler effect of high-speed motion.

[0053] This invention also provides a blind modulation parameter identification system for non-cooperative OTFS systems, comprising: OTFS modulated signal The modulation module is used to generate the delayed-Doppler two-dimensional baseband signal at the OTFS system transmitter in step 1. The OTFS modulated signal is generated and transmitted through OTFS modulation. ; OTFS received signal The transmission module is used to transmit the OTFS modulated signal generated in step 1 in step 2. By simulating signal transmission in a wireless channel under real-world scenarios through multipath fading and noisy channels, the undemodulated OTFS received signal after wireless channel transmission is obtained. ; The OTFS specific frame structure parameter blind identification module is used to enable the receiver to receive the OTFS received signal obtained in step 2 in step 3. The OTFS received sequence is obtained through discrete sampling. For discrete OTFS received sequences Blind identification of specific frame structure parameters in OTFS based on the Cyclic Stationary Autocorrelation Function (CAF) to obtain the delay vignetting points. , length of cyclic prefix , Dopplervig points ; The OTFS system's precise time-frequency synchronization module is used to implement the delay vig point count obtained in step 3 in step 4. , length of cyclic prefix And Dopplervig points Joint estimation of time-frequency synchronization parameters is performed, including symbol clock offset (STO) and carrier frequency offset (CFO) parameters. A flat-top timing metric is used to measure the cyclic prefix correlation of the received stream at different alignment points in both the signal delay and Doppler dimensions. The index corresponding to the maximum cyclic prefix correlation is the symbol start clock offset. The received stream is offset from the symbol start clock. After alignment, the carrier frequency offset (CFO) is estimated using the cyclic prefix and corresponding tail phase difference method to obtain the carrier frequency offset factor. Ultimately, the clock offset is initiated by the symbol. and carrier frequency offset factor Correcting symbol clock offset (STO) and carrier frequency offset (CFO) enables precise time and frequency synchronization of the OTFS system.

[0054] The present invention also provides a modulation parameter blind identification device for non-cooperative OTFS systems, comprising: Memory: A computer program for blind identification of modulation parameters for a non-cooperative OTFS system, which is stored in the above-mentioned computer program and is a computer-readable device; Processor: Used to implement the aforementioned method for blind identification of modulation parameters for non-cooperative OTFS systems when executing the computer program.

[0055] The present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, enables the implementation of the aforementioned method for blind identification of modulation parameters for non-cooperative OTFS systems.

[0056] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for blind identification of modulation parameters in a non-cooperative OTFS system, characterized in that, Includes the following steps: Step 1: The OTFS system transmitter generates a delayed-Doppler two-dimensional baseband signal. The OTFS modulated signal is generated and transmitted through OTFS modulation. ; Step 2: Modulate the OTFS signal generated in Step 1. By simulating signal transmission in a wireless channel under real-world scenarios through multipath fading and noisy channels, the undemodulated OTFS received signal after wireless channel transmission is obtained. ; Step 3: The OTFS system blind identification receiver receives the OTFS received signal obtained in Step 2. The OTFS received sequence is obtained through discrete sampling. For discrete OTFS received sequences Blind identification of specific frame structure parameters in OTFS based on the Cyclic Stationary Autocorrelation Function (CAF) yields an estimate of the number of delay vignettes. Estimated value of cyclic prefix length Estimated Doppler-Vigg points ; Step 4: Based on the estimated value of the delayed vig points obtained in Step 3 Estimated value of cyclic prefix length And the estimated value of the Dopplervig points Joint estimation of time-frequency synchronization parameters is performed, including symbol clock offset (STO) and carrier frequency offset (CFO) parameters. A flat-top timing metric is used to measure the cyclic prefix correlation of the received stream at different alignment points in both the signal delay and Doppler dimensions. The index corresponding to the maximum cyclic prefix correlation is the symbol start clock offset. The received stream is offset from the symbol start clock. After alignment, the carrier frequency offset (CFO) is estimated using the cyclic prefix and corresponding tail phase difference method to obtain the carrier frequency offset factor. Ultimately, the clock offset is initiated by the symbol. and carrier frequency offset factor Correcting symbol clock offset (STO) and carrier frequency offset (CFO) enables precise time and frequency synchronization of the OTFS system.

2. The method for blind identification of modulation parameters in a non-cooperative OTFS system according to claim 1, characterized in that, The specific method of step 1 includes: The OTFS system transmitter generates a random bitstream signal. Random bitstream signal The baseband signal is obtained after LDPC encoding and QAM modulation. For baseband signals By parallelizing the signal and filling empty carriers, a delayed-Doppler two-dimensional baseband signal is constructed. , ; Delayed-Doppler two-dimensional baseband signal The transmitted OTFS modulated signal is obtained through OTFS modulation. ; The modulation process of the OTFS system is as follows: First, the delayed-Doppler two-dimensional baseband signal is modulated using the inverse symplectic finite Fourier transform (ISFFT). Mapping from the delay-Doppler domain to the time-frequency domain yields the first... The time domain and the first Time-frequency domain modulation symbols at each frequency domain index grid point The specific formula is as follows: in, For Doppler index, For delayed dimension indexes, To achieve phase rotation from the Doppler dimension to the frequency dimension, Achieve phase rotation from the delay dimension to the time dimension; Time-frequency domain modulation symbols Then, through OFDM modulation, time-domain subcarrier symbols with cyclic prefixes are generated sequentially for each point of the time-frequency grid to obtain the transmitted OTFS modulated signal. : in, Baseband transmit pulse: rectangular window + cyclic prefix; Subcarrier spacing ensures that the subcarriers are mutually orthogonal.

3. The method for blind identification of modulation parameters in a non-cooperative OTFS system according to claim 1, characterized in that, In step 2, the OTFS received signal that has not been demodulated after being transmitted through the wireless channel. The expression is: in, , represents the channel impulse response caused by the time-varying multipath channel, and represents the response at time . After passing through the channel, it will have different delays Upon reaching the receiving end, different gains and phase rotations are generated. This indicates that the signal is delayed as it travels along different paths. This represents additive white Gaussian noise.

4. The method for blind identification of modulation parameters in a non-cooperative OTFS system according to claim 1, characterized in that, The specific method for step 3 includes: The OTFS received signal obtained in step 2 Discrete sampling is performed to obtain the OTFS received sequence. in, Indicates the sampling interval; Constructing delayed Vig point and cyclic prefix length Corresponding cycle frequency Cyclic stationary autocorrelation function The function formula is defined as follows: in, For OTFS receive sequence, It is the delay size. It is the cumulative window length. It is the cycle frequency, defined as: in, It is the sampling rate at the receiving end. It is a set of candidate cycle frequencies. It is the set of candidate delayed vig points; For delayed Vig points When performing normalized peak search, set the loop frequency. According to the peak search function Determine the highest scorer This is the estimated value of the delayed Vig point. Delayed Vig point peak search function The definition is as follows: For cycle frequency When performing normalized peak search, set the delayed Vig point number to 1. According to the peak search function Determine the highest scorer This is the estimated value of the cycle frequency. Cyclic frequency search function The definition is as follows: Then based on the loop frequency and loop prefix By applying the equation, we can obtain an estimate of the cyclic prefix length. , or through formula Convert to an estimate of the sample index length of the sample cyclic prefix. ; Constructing short-window CAF sequences To estimate the Dopplervig points At each time location Measuring a length Cyclic prefix related energy, The expression is as follows:

5. The method for blind identification of modulation parameters in a non-cooperative OTFS system according to claim 1, characterized in that, The specific method for step 4 includes: First, a flat-top timing metric function is constructed for the delay dimension and Doppler dimension of the OTFS received sequence. , The expression is: in, and These correspond to the cyclic indices of the OTFS received sequence delay dimension and Doppler dimension, respectively; y(n) is the time-domain sample at the receiving end, with internal double summation: inner summation Take samples from the middle of CP and sum them from the outside. Consider all multicarrier symbol numbers together; For flat-top time series metric functions Introducing a flat-top window, which selects the center of the CP. and These represent the start and end positions of the flat-top window, defined as follows: Secondly, the maximum index of the first search cycle is the estimated symbol clock offset (STO), and the position of the maximum value is the symbol starting clock offset. : Receive stream offset from symbol start clock After alignment, carrier frequency offset (CFO) estimation is performed. The phase correlation of each symbol of the received signal in the middle region of the cyclic prefix and the corresponding tail portion is calculated, and the carrier frequency offset factor is obtained after normalization. Carrier frequency offset factor The calculation formula is as follows: in, This refers to the CP portion of the received signal. This represents the estimated number of Doppler-Vigg points between the two portions corresponding to the tail portion. ,in It is a time-domain sample of the transmitted signal. This indicates the carrier frequency offset, measured in Hertz (Hz). Indicates the sampling frequency at the receiving end. Indicates a time index. This indicates taking the phase angle, that is, calculating the phase difference between signals.

6. A method for blind identification of modulation parameters in a non-cooperative OTFS system according to claim 2, characterized in that, The signal parallelization process involves converting the serially modulated QAM baseband signal... Transformed into a two-dimensional grid with one frame per column Each row corresponds to a time delay resolution unit, and each column corresponds to a Doppler resolution unit; The process of filling empty carriers occurs within a two-dimensional grid after signal parallelization. By inserting all zeros at the beginning, middle, and end, a delayed-Doppler two-dimensional baseband signal is constructed. , .

7. A blind modulation parameter identification system for non-cooperative OTFS systems based on the method of claim 1, characterized in that, include: O TFS modulated signal The modulation module is used to generate a delayed-Doppler two-dimensional baseband signal at the transmitter of the OTFS system. The OTFS modulated signal is generated and transmitted through OTFS modulation. ; OTFS received signal The transmission module is used to transmit the generated OTFS modulated signal. By simulating signal transmission in a wireless channel under real-world scenarios through multipath fading and noisy channels, the undemodulated OTFS received signal after wireless channel transmission is obtained. ; The OTFS specific frame structure parameter blind identification module is used to enable the receiver to receive OTFS received signals. The OTFS received sequence is obtained through discrete sampling. For discrete OTFS received sequences Blind identification of specific frame structure parameters in OTFS based on the Cyclic Stationary Autocorrelation Function (CAF) yields an estimate of the number of delay vignettes. Estimated value of cyclic prefix length Estimated Doppler-Vigg points ; The OTFS system's precise time-frequency synchronization module is used to synchronize the time and frequency based on the estimated delay vig points. Estimated value of cyclic prefix length And the estimated value of the Dopplervig points Joint estimation of time-frequency synchronization parameters is performed, including symbol clock offset (STO) and carrier frequency offset (CFO) parameters. A flat-top timing metric is used to measure the cyclic prefix correlation of the received stream at different alignment points in both the signal delay and Doppler dimensions. The index corresponding to the maximum cyclic prefix correlation is the symbol start clock offset. The received stream is offset from the symbol start clock. After alignment, the carrier frequency offset (CFO) is estimated using the cyclic prefix and corresponding tail phase difference method to obtain the carrier frequency offset factor. Ultimately, the clock offset is initiated by the symbol. and carrier frequency offset factor Correcting symbol clock offset (STO) and carrier frequency offset (CFO) enables precise time and frequency synchronization of the OTFS system.

8. A blind modulation parameter identification device for non-cooperative OTFS systems, characterized in that, include: Memory: A computer program for a blind identification method of modulation parameters for a non-cooperative OTFS system as described in any one of claims 1-5, and is a computer-readable device; Processor: Used to implement the method for blind identification of modulation parameters for non-cooperative OTFS systems as described in any one of claims 1-5 when executing the computer program.

9. A computer-readable storage medium, characterized in that, A computer-readable storage medium stores a computer program that, when executed by a processor, enables the implementation of a method for blind identification of modulation parameters for a non-cooperative OTFS system as described in any one of claims 1-5.

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