Time and frequency synchronization method and device in high dynamic communication environment of scattering channel

Abstract

The application relates to a time and frequency synchronization method and device in a high-dynamic communication environment of a scattering channel, which comprises the following steps: step 1: receiving an intermediate frequency analog signal generated by ionospheric scattered radio waves, wherein the intermediate frequency analog signal comprises a preamble sequence and communication data; step 2: pre-processing the intermediate frequency analog signal to obtain a plurality of signals; step 3: performing strongest path search on each signal by using an m pseudo-random sequence to determine a best sampling path and a strongest path of the best sampling path; step 4: obtaining a first-stage frequency offset estimation value according to the strongest path of the best sampling path, and performing first frequency offset correction on the intermediate frequency analog signal by using the first-stage frequency offset estimation value; and step 5: performing second frequency offset correction on the signal after the first frequency offset correction by using a repeated ZC sequence. The time and frequency synchronization method is suitable for an environment with dramatic change of signal-to-noise ratio, can accurately locate the strongest path, and improves positioning accuracy.

Description

Technical Field

[0001] This invention belongs to the field of ionospheric scattering communication technology, specifically relating to a time and frequency synchronization method and apparatus in a high dynamic communication environment of scattering channels. Background Technology

[0002] Due to its long single-hop distance, strong survivability, and the difficulty in intercepting electromagnetic waves emitted into the air, the ionospheric scattering channel has been widely used in military and civilian wireless communication networks. It can traverse bays and uninhabited areas, possessing full-airspace communication capabilities covering thousands of kilometers, thus providing reliable communication for offshore oil and gas platforms, remote islands, and border defense areas.

[0003] However, ionospheric scattering communication also has its drawbacks. Beyond-line-of-sight communication using ionospheric scattering channels suffers from significant transmission losses due to the extremely long propagation distances, as well as time-varying fading caused by multipath propagation. In actual tests, the time delay spread of signals transmitted in ionospheric scattering channels can reach hundreds of microseconds or more in severe cases. Signals arriving via different paths have inconsistent phases, and these multiple signals with inconsistent phases from different paths eventually superimpose at the receiver, leading to severe multipath fading. Furthermore, the high-speed movement of the aircraft causes the received signal to be affected by Doppler frequency shift, which can reach hundreds of hertz. Traditional time and frequency synchronization algorithms face challenges. Therefore, achieving time and frequency synchronization in time-varying multipath, low signal-to-noise ratio, and high dynamic environments is a critical issue.

[0004] Commonly used time synchronization algorithms mainly include autocorrelation and cross-correlation algorithms. The autocorrelation algorithm utilizes the repetitive structure in the training sequence to perform delayed autocorrelation on the received signal, thus obtaining a relatively obvious correlation peak when a data frame arrives. The cross-correlation algorithm, on the other hand, uses a local training sequence at the receiver to correlate with the received signal; cross-correlation can be performed in the time domain or the frequency domain.

[0005] Common time synchronization algorithms based on time-delay autocorrelation perform poorly at low signal-to-noise ratios (SNR) and exhibit peak plateaus, leading to inaccurate localization. PMF-FFT-based time synchronization algorithms suffer from secondary peaks, causing incorrect synchronization point determination. Local cross-correlation-based algorithms exhibit synchronization point offset issues in Doppler frequency offset environments; at large frequency offsets, the number of offset points exceeds the length of the cyclic prefix, and increasing the guard interval does not solve the problem. Among time-domain estimation-based frequency synchronization algorithms, autocorrelation algorithms are sensitive to noise power and are unsuitable for low SNR environments; maximum likelihood frequency synchronization algorithms have frequency offset estimation ranges affected by sequence length, making them unsuitable for both low SNR and Doppler frequency offset environments, and their high complexity prevents implementation on practical devices. Frequency-domain estimation-based frequency synchronization algorithms suffer from the picket-fence effect in FFT calculations; their frequency resolution is the ratio of sampling frequency to the number of FFT points, meaning the estimated frequency offset can only be an integer multiple of the frequency resolution. Increasing the resolution requires increasing the number of FFT points, which increases implementation difficulty. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a method and apparatus for time and frequency synchronization in a high-dynamic communication environment with scattering channels.

[0007] This invention provides a time and frequency synchronization method for high dynamic communication environments with scattering channels, comprising:

[0008] Step 1: Receive radio waves scattered by the ionosphere to generate an intermediate frequency analog signal. The intermediate frequency analog signal includes a preamble sequence and communication data. The preamble sequence includes a pseudo-random sequence of length L1 and two repeating ZC sequences of length L2.

[0009] Step 2: Preprocess the intermediate frequency analog signal to obtain multiple signals;

[0010] Step 3: Use the m pseudo-random sequence to perform a strongest path search for each signal to determine the optimal sampling path and the strongest path of the optimal sampling path;

[0011] Step 4: Based on the strongest path of the optimal sampling path, obtain the first-stage frequency offset estimate, and use the first-stage frequency offset estimate to perform the first frequency offset correction on the intermediate frequency analog signal;

[0012] Step 5: Use the repeated ZC sequence to perform a second frequency offset correction on the signal after the first frequency offset correction.

[0013] This invention provides a time and frequency synchronization device for high dynamic communication environments in scattering channels, comprising:

[0014] The receiving module is used to receive radio waves scattered by the ionosphere to generate an intermediate frequency analog signal. The intermediate frequency analog signal includes a preamble sequence and communication data. The preamble sequence includes a pseudo-random sequence of length L1 and two repeating ZC sequences of length L2.

[0015] The signal processing module is used to preprocess the intermediate frequency analog signal to obtain multiple signals;

[0016] The synchronization and coarse spectrum correction module is used to perform the strongest path search for each signal using the m pseudo-random sequence, determine the optimal sampling path and the strongest path of the optimal sampling path; obtain the first stage frequency offset estimate based on the strongest path of the optimal sampling path, and perform the first stage frequency offset correction on the intermediate frequency analog signal using the first stage frequency offset estimate.

[0017] The fine spectrum correction module is used to perform a second frequency offset correction on the signal after the first frequency offset correction using the repeated ZC sequence.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. The time and frequency synchronization method of the present invention for high-dynamic communication environments in scattering channels can solve the problems of synchronization point offset and synchronization peak loss in high-dynamic environments, and can also achieve adaptive synchronization, making it suitable for environments with drastic changes in signal-to-noise ratio. It can solve the problem of secondary peaks in synchronization points caused by multipath propagation under scattering channel conditions, accurately locate the strongest path, and is also applicable to low signal-to-noise ratio environments, which is beneficial for subsequent demodulation in communication systems.

[0020] 2. The time and frequency synchronization method of the present invention in a high dynamic communication environment of scattering channel solves the resolution loss problem of the traditional FFT picket fence effect and the limited estimation range of the frequency offset algorithm by using two-stage frequency offset correction. It can solve the secondary peak problem caused by the segmentation of PMF-FFT and improve positioning accuracy.

[0021] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a time and frequency synchronization method in a high dynamic communication environment of a scattering channel provided by an embodiment of the present invention;

[0023] Figure 2a This is a schematic diagram of a leader sequence provided in an embodiment of the present invention;

[0024] Figure 2b This is a flowchart of a timed synchronization method provided in an embodiment of the present invention;

[0025] Figure 3 This is a structural block diagram of a time and frequency synchronization device for a high dynamic communication environment in a scattering channel, provided by an embodiment of the present invention.

[0026] Figure 4 This is a three-dimensional time-frequency domain diagram of a scattering channel provided in an embodiment of the present invention;

[0027] Figure 5 This is an RMSE curve for frequency offset estimation when the frequency offset is -150Hz, provided by an embodiment of the present invention;

[0028] Figure 6 This is an RMSE curve for timing synchronization with a frequency offset of -150Hz provided in an embodiment of the present invention;

[0029] Figure 7 This is a synchronous detection probability curve provided by an embodiment of the present invention when the frequency offset is -150Hz;

[0030] Figure 8 This is an RMSE curve for frequency offset estimation when the frequency offset is 0Hz, provided by an embodiment of the present invention;

[0031] Figure 9 This is an RMSE curve for timing synchronization with a frequency offset of 0Hz provided in an embodiment of the present invention;

[0032] Figure 10 This is a synchronous detection probability curve provided by an embodiment of the present invention when the frequency offset is 0Hz;

[0033] Figure 11 This is a peak value diagram of the PMF-FFT synchronization method provided in the embodiments of the present invention;

[0034] Figure 12 This is a peak value diagram of the method of the present invention provided in the embodiments of the present invention;

[0035] Figure 13 This is a peak ratio diagram of the method of the present invention provided in the embodiments of the present invention. Detailed Implementation

[0036] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following describes in detail, with reference to the accompanying drawings and specific embodiments, a time and frequency synchronization method and apparatus for a high dynamic communication environment in a scattering channel proposed according to the present invention.

[0037] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0038] In a first aspect, embodiments of the present invention also provide a method for time and frequency synchronization in a high-dynamic communication environment with a scattering channel. Please refer to [link to relevant documentation]. Figure 1 , Figure 1 This is a schematic diagram of a time and frequency synchronization method in a high-dynamic communication environment with a scattering channel, provided by an embodiment of the present invention. Figure 1 As shown, the time and frequency synchronization method in a high-dynamic communication environment of a scattering channel in this embodiment includes:

[0039] Step 1: Receive radio waves scattered by the ionosphere to generate an intermediate frequency (IF) analog signal, which includes a preamble sequence and communication data;

[0040] In an optional embodiment, the preamble sequence comprises a pseudo-random sequence UW1 of length L1 and two repeating ZC sequences UW2 of length L2, as follows: Figure 2a The diagram shown is a schematic representation of a leader sequence provided by an embodiment of the present invention.

[0041] It should be noted that, in order to reduce the multipath effect, a narrowband communication system is chosen to address the high delay spread of the scattering channel.

[0042] Step 2: Preprocess the intermediate frequency analog signal to obtain multiple signals;

[0043] In an optional embodiment, step 2 includes:

[0044] Step 2.1: Perform analog-to-digital conversion, digital down-conversion, and half-band filtering on the intermediate frequency analog signal to generate the baseband signal;

[0045] Step 2.2: After performing matched filtering on the baseband signal, downsampling is performed to obtain multiple signals.

[0046] Step 3: Use m pseudo-random sequences to search for the strongest path for each signal to determine the optimal sampling path and the strongest path of the optimal sampling path;

[0047] In this embodiment, each signal is processed separately to achieve timing synchronization. The m pseudo-random sequence is a locally stored m pseudo-random sequence, which is consistent with the m pseudo-random sequence UW1 in the received preamble sequence.

[0048] In an optional embodiment, step 3 includes:

[0049] Step 3.1: Sample each signal using a buffer window of length L1 to obtain the sampled signal;

[0050] Step 3.2: Process the sampled signal using an m pseudo-random sequence to obtain the FFT operation result corresponding to the sampled signal, and determine the strongest path of each path based on the FFT operation result;

[0051] Please see Figure 2b As shown, optionally, step 3.2 includes:

[0052] Step 3.21: Perform dot product operation on the sampled signal using m pseudo-random sequences;

[0053] Step 3.22: After padding the data after dot product with zeros, perform FFT operation to obtain the FFT operation result corresponding to the sampled signal;

[0054] In this embodiment, the data after the dot product is padded with zeros to a length of N, and then an N-point FFT operation is performed, where N is 2m.

[0055] Step 3.23: Take the modulus of the complex numbers of the frequency points in the FFT operation result, calculate the average value of the complex modulus of all frequency points, record the maximum modulus value of all frequency points as the maximum peak value, and record the frequency point position corresponding to the maximum modulus value as the maximum peak value index;

[0056] In this embodiment, the maximum value of the modulus is denoted as A, and the position of the maximum value A at point N is denoted as u.

[0057] Step 3.24: Determine whether the sampling point corresponding to the sampling signal is a synchronization point based on the preset threshold coefficient;

[0058] Optionally, if Then the sampling point corresponding to the sampled signal is a synchronization point; otherwise, the sampling point corresponding to the sampled signal is not a synchronization point.

[0059] Where A is the maximum modulus value among all the complex moduli of the sampled signal at all frequencies, M is the average value of all the complex moduli of the sampled signal at all frequencies, and THR is the preset threshold coefficient.

[0060] Step 3.25: If it is not a synchronization point, the buffer window is delayed and slid to perform the next sampling, then return to step 3.21 until the first synchronization point of each path is determined, and the synchronization capture is completed;

[0061] In this embodiment, if Then, synchronization is considered complete, and the position of the sampling point at this time is recorded as SYNC_LOC, which is the synchronization point position. At the same time, the maximum peak value A is also recorded. max= A, record the maximum peak index U = u.

[0062] Step 3.26: After the first synchronization point, continue to slide the buffer window, search for a preset number of sampling points, repeat Steps 3.21 - 3.24 for each sampling point to determine the synchronization points, and record the positions, maximum peaks, and maximum peak indices of all synchronization points;

[0063] In this embodiment, after the synchronization capture is completed, enter the synchronization strongest path search stage to search for the strongest path of each signal. Optionally, the search time of the strongest path search stage is set to T f , which needs to satisfy T f > T d , that is, the search time T f is greater than the delay spread T of the scattering channel d .

[0064] In this embodiment, after the first synchronization point, continue to slide the buffer window and search for F s * T f sampling points, where F s is the sampling rate of the receiving end. It can be considered that starting from the capture of the first path, the search time covers all paths of the scattering channel.

[0065] Step 3.27: For each signal, compare the maximum peaks of all synchronization points, and select the synchronization point corresponding to the maximum value as the strongest path of this signal.

[0066] In this embodiment, compare the maximum peaks of all synchronization points, select the synchronization point corresponding to the maximum value as the strongest path of this signal. At the same time, synchronously select the synchronization point position SYNC_LOC and the maximum peak index U of the strongest path.

[0067] Step 3.3: Determine the best sampling path and the strongest path of the best sampling path according to the strongest paths of all signals.

[0068] In an optional embodiment, when the synchronization search of multiple signals is completed, compare the maximum peaks corresponding to the strongest paths of all signals, and select the signal path where the strongest path corresponding to the maximum value is located as the best sampling path.

[0069] Step 4: Obtain the first-stage frequency offset estimation value according to the strongest path of the best sampling path, and use the first-stage frequency offset estimation value to perform the first frequency offset correction on the intermediate-frequency analog signal;

[0070] In an optional embodiment, Step 4 includes:

[0071] Step 4.1: According to the strongest path of the best sampling path, determine whether U < N / 2 + 1 holds. If it holds, the first-stage frequency offset estimation value is:

[0072] fd _est_rough=(U-1) / N*F s ;

[0073] If this is not the case, then the first-stage frequency offset estimate is:

[0074] f d _est_rough=(U-1+N) / N*F s ;

[0075] Where U is the maximum peak index of the strongest path of the optimal sampling path, N is the length of the FFT operation, and F... s The sampling rate at the receiving end;

[0076] Step 4.2: Perform the first frequency offset correction on the intermediate frequency analog signal based on the frequency offset estimate from the first stage.

[0077] In this embodiment, the first frequency offset correction is performed on all signals in the intermediate frequency analog signal excluding the m pseudo-random sequence based on the first-stage frequency offset estimate.

[0078] Step 5: Use a repeated ZC sequence to perform a second frequency offset correction on the signal after the first frequency offset correction.

[0079] In an optional embodiment, step 5 includes:

[0080] Step 5.1: For the signal of the optimal sampling path, take the first sequence and the second sequence, both of length L2, sequentially from the synchronization point position corresponding to its strongest path.

[0081] Step 5.2: Perform a cross-correlation operation between the first sequence and a repeating ZC sequence to obtain the first cross-correlation result; perform a cross-correlation operation between the second sequence and another repeating ZC sequence to obtain the second cross-correlation result.

[0082] In this embodiment, the two repeated ZC sequences are locally stored repeated ZC sequences, which are consistent with the two repeated ZC sequences UW2 in the received preamble sequence.

[0083] Step 5.3: Select the first P values ​​from the first cross-correlation result and the second cross-correlation result, and calculate the phase deviation angle based on the selection result:

[0084]

[0085] In the formula, phase is the offset phase angle, P is the number of separable multipaths in the scattering channel, RP1 is the result of the first cross-correlation operation, RP2 is the result of the second cross-correlation operation, and conj(·) represents the conjugate operation;

[0086] Step 5.4: Based on the phase deviation angle, the estimated value of the second-stage frequency offset is calculated as follows:

[0087]

[0088] In the formula, angle(·) is the radian operation, L2 is the length of the repeated ZC sequence, and RB is the symbol rate;

[0089] Step 5.5: Perform a second frequency offset correction on the signal after the first frequency offset correction based on the second-stage frequency offset estimation value.

[0090] In this embodiment, the communication data after the first frequency offset correction is corrected a second time based on the second-stage frequency offset estimation value to achieve frequency synchronization.

[0091] The time and frequency synchronization method for high-dynamic communication environments in scattering channels, as described in this invention, can solve the problems of synchronization point offset and synchronization peak loss in high-dynamic environments. It also enables adaptive synchronization and is suitable for environments with drastic changes in signal-to-noise ratio. Furthermore, it can address the secondary peak problem of synchronization points caused by multipath propagation in scattering channels, accurately locating the strongest path. It is also applicable to low signal-to-noise ratio environments, which is beneficial for subsequent demodulation in the communication system. Moreover, by utilizing two-stage frequency offset correction, it solves the resolution loss problem of the traditional FFT picket fence effect and the limited estimation range of the frequency offset algorithm. It can also resolve the secondary peak problem caused by the segmentation of PMF-FFT, improving positioning accuracy.

[0092] Secondly, embodiments of the present invention also provide a time and frequency synchronization device for a high dynamic communication environment in a scattering channel. Please refer to [link to relevant documentation]. Figure 3 , Figure 3 This is a structural block diagram of a time and frequency synchronization device for a high dynamic communication environment in a scattering channel, provided by an embodiment of the present invention. Figure 3 As shown, the time and frequency synchronization device for a high-dynamic communication environment in a scattering channel according to this embodiment includes:

[0093] The receiving module is used to receive radio waves scattered by the ionosphere to generate intermediate frequency analog signals. The intermediate frequency analog signals include a preamble sequence and communication data. The preamble sequence includes a pseudo-random sequence of length L1 and two repeating ZC sequences of length L2.

[0094] The signal processing module is used to preprocess the intermediate frequency analog signal to obtain multiple signals;

[0095] The synchronization and coarse spectrum correction module is used to search for the strongest path of each signal using m pseudo-random sequences to determine the optimal sampling path and the strongest path of the optimal sampling path; based on the strongest path of the optimal sampling path, the first stage frequency offset estimate is obtained, and the first stage frequency offset estimate is used to perform the first frequency offset correction on the intermediate frequency analog signal.

[0096] The fine spectrum correction module is used to perform a second frequency offset correction on the signal after the first frequency offset correction using a repeating ZC sequence.

[0097] In an optional embodiment, the signal processing module includes:

[0098] The A / D conversion unit is used to perform analog-to-digital conversion on intermediate frequency analog signals to obtain digital signals.

[0099] The DDC downsampling unit is used to perform digital signal downconversion and half-band filtering on digital signals to generate baseband signals.

[0100] The matched filtering unit is used to perform matched filtering on the baseband signal and then downsample it to obtain multiple signals.

[0101] For details regarding the time and frequency synchronization device in a high-dynamic communication environment with a scattering channel and its corresponding beneficial effects, please refer to the relevant content on the time and frequency synchronization method in a high-dynamic communication environment with a scattering channel provided in the first aspect; it will not be elaborated upon here.

[0102] Furthermore, the effectiveness of the time and frequency synchronization method in the high dynamic communication environment of the scattering channel in this embodiment is illustrated through simulation experiments.

[0103] (1) Simulation conditions:

[0104] Using MATLAB as the simulation platform and the Monte Carlo method as the simulation statistical method, a performance comparison analysis was conducted between the method of this invention and the method proposed in patent publication number CN102857251A. The bandwidth was set to 25kHz, i.e., the sampling rate was 25kHz. Figure 2a As shown, the preamble sequence is designed as a UW1 structure with two repeated UW2 segments. The UW1 sequence is an m-sequence of length 1640, and the UW2 sequence is a ZC sequence of length 400. The channel conditions are an additive Gaussian channel and the actual acquired scattering channel. The three-dimensional time-frequency domain plot of the scattering channel is shown below. Figure 4 As shown. The traditional method for comparison is local cross-correlation synchronization and delayed autocorrelation frequency offset estimation. The ideal synchronization position is located at the strongest path, and RMSE is the deviation from the strongest path. If synchronization is not captured, both the synchronization position and frequency offset estimation are set to 0. The simulation signal-to-noise ratio is -20dB to 0dB, and the number of simulations is 10,000.

[0105] (2) Simulation results

[0106] Figure 5 The curve shows the RMSE of frequency offset estimation when the frequency offset is -150Hz. It can be seen that the RMSE of frequency offset estimation by the method of this invention drops to less than 10 at -18dB and is about 3 at -15dB. The traditional method has an RMSE of around 150 due to the synchronization point offset caused by the large frequency offset and the limitation of the frequency offset range.

[0107] Figure 6 The curve shows the RMSE of the synchronization performance when the frequency offset is -150Hz. It can be seen that the RMSE of the method of this invention is 0 from -17dB, and the positioning is very accurate. The traditional method has a large deviation at -17dB, and the RMSE is 10 from -16dB. This is due to the synchronization point offset caused by the frequency offset.

[0108] Figure 7 The detection curve shows the synchronization performance at a frequency offset of -150Hz. It can be seen that the correct detection probability of the method of this invention is close to 1 at -15dB, while the detection probability of the traditional method is always 0. The deviation point at this time is 10, which has exceeded the time delay extension range.

[0109] Figure 8 This is the RMSE curve for frequency offset estimation when the frequency offset is 0Hz. Figure 9 This is the RMSE curve of synchronization performance when the frequency offset is 0Hz. Figure 10 This is the detection curve of synchronization performance when the frequency offset is 0Hz. It can be seen that, without frequency offset, the synchronization performance of the method of this invention is slightly weaker than the method in the patent literature. Overall, the method of this invention performs excellently in high-dynamic environments of the scattering channel.

[0110] Figure 11 and Figure 12 The figures show the peak values ​​of the PMF-FFT synchronization method and the method of this invention, respectively. It can be seen that the PMF-FFT synchronization method, due to segmented correlation and the accumulation of multiple peak values, results in a secondary peak near the accurate synchronization point, which is close to the main peak value. Under low signal-to-noise ratio conditions, this can easily cause false alarms, leading to incorrect synchronization positions. In contrast, the peak value of the method of this invention does not exhibit any secondary peaks.

[0111] Figure 13 The peak ratio diagram of the method of the present invention shows that the peak ratio increases with the increase of the signal-to-noise ratio. As shown in the figure, the adaptive decision threshold can be set to 4. When the signal-to-noise ratio changes, no matter how the peak value changes, as long as the peak ratio exceeds the decision threshold, the synchronous acquisition is considered to be successful.

[0112] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0113] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A time and frequency synchronization method for a high-dynamic communication environment with a scattering channel, characterized in that, include: Step 1: Receive radio waves scattered by the ionosphere to generate an intermediate frequency (IF) analog signal. The IF analog signal includes a preamble sequence and communication data, wherein the preamble sequence includes a segment of length [missing information]. m pseudo-random sequences and two segments of length m Repeating ZC sequences; Step 2: Preprocess the intermediate frequency analog signal to obtain multiple signals; Step 3: Use the m pseudo-random sequence to perform a strongest path search for each signal to determine the optimal sampling path and the strongest path of the optimal sampling path; Step 4: Based on the strongest path of the optimal sampling path, obtain the first stage frequency offset estimate, and use the first stage frequency offset estimate to perform the first frequency offset correction on the multi-channel signal; Step 4 includes: Step 4.1: Based on the strongest path of the optimal sampling path, determine... If it holds true, then the estimated value of the first-stage frequency offset is: ； If this is not the case, then the first-stage frequency offset estimate is: ； in, The maximum peak index of the strongest path in the optimal sampling path. The length of the FFT operation. The sampling rate at the receiving end; Step 4.2: Perform the first frequency offset correction on the multi-channel signals based on the frequency offset estimation value of the first stage; Step 5: Use the repeated ZC sequence to perform a second frequency offset correction on the signal after the first frequency offset correction.

2. The time and frequency synchronization method in a high-dynamic communication environment with a scattering channel according to claim 1, characterized in that, Step 2 includes: Step 2.1: Perform analog-to-digital conversion, digital down-conversion, and half-band filtering on the intermediate frequency analog signal to generate a baseband signal; Step 2.2: After performing matched filtering on the baseband signal, downsampling is performed to obtain the multi-channel signal.

3. The time and frequency synchronization method under high dynamic communication environment of scattering channel according to claim 1, characterized in that, Step 3 includes: Step 3.1: Use a length of [length missing] for each signal channel. The sampled signal is obtained by sampling within the buffer window; Step 3.2: Process the sampled signal using the m pseudo-random sequence to obtain the FFT operation result corresponding to the sampled signal, and determine the strongest path of each path based on the FFT operation result; Step 3.3: Determine the optimal sampling path and the strongest path of the optimal sampling path based on the strongest path of all paths.

4. The time and frequency synchronization method under high dynamic communication environment of scattering channel according to claim 3, characterized in that, Step 3.2 includes: Step 3.21: Perform a dot product operation on the sampled signal using the m pseudo-random sequence; Step 3.22: After padding the data after the dot product with zeros, perform an FFT operation to obtain the FFT result corresponding to the sampled signal; Step 3.23: Take the modulus of the complex numbers of the frequency points in the FFT operation result, calculate the average value of the complex modulus of all frequency points, record the maximum modulus value of all frequency points as the maximum peak value, and record the frequency point position corresponding to the maximum modulus value as the maximum peak value index; Step 3.24: Determine whether the sampling point corresponding to the sampling signal is a synchronization point based on the preset threshold coefficient; Step 3.25: If it is not a synchronization point, the buffer window is delayed and slid to perform the next sampling, then return to step 3.21 until the first synchronization point of each path is determined, and the synchronization capture is completed; Step 3.26: After the first synchronization point, continue to slide the cache window to search for a preset number of sampling points. Repeat steps 3.21-3.24 to determine the synchronization point for each sampling point, and record the position, maximum peak value, and maximum peak value index of all synchronization points. Step 3.27: For each signal, compare the maximum peak value of all synchronization points and select the synchronization point corresponding to the maximum value as the strongest path of that signal.

5. The time and frequency synchronization method under high dynamic communication environment of scattering channel according to claim 4, characterized in that, Step 3.24 includes: if If the sampling point is a synchronization point, then the sampling point corresponding to the sampling signal is a synchronization point; otherwise, the sampling point corresponding to the sampling signal is not a synchronization point. in, It is the maximum modulus among all the complex moduli of the sampled signal at all frequencies. It is the average of the complex modulus of the sampled signal at all frequency points. This is the preset threshold coefficient.

6. The time and frequency synchronization method in a high-dynamic communication environment with a scattering channel according to claim 4, characterized in that, Step 3.3 includes: Compare the maximum peak value corresponding to the strongest path of all paths, and select the path containing the strongest path corresponding to the maximum value as the best sampling path.

7. The time and frequency synchronization method in a high-dynamic communication environment with a scattering channel according to claim 4, characterized in that, Step 5 includes: Step 5.1: For the signal of the optimal sampling path, take sequentially samples of length 1 from the synchronization point corresponding to its strongest path. The first and second sequences; Step 5.2: Perform a cross-correlation operation between the first sequence and a segment of the repeating ZC sequence to obtain a first cross-correlation result; perform a cross-correlation operation between the second sequence and another segment of the repeating ZC sequence to obtain a second cross-correlation result. Step 5.3: Select the first cross-correlation result and the second cross-correlation result from the first cross-correlation result. Based on the selected values, the deviation phase angle is calculated as follows: ； In the formula, To deviate from the phase angle, The number of separable multipaths in the scattering channel. This is the result of the first cross-correlation operation. This is the result of the second cross-correlation operation. This indicates the conjugate operation; Step 5.4: Based on the deviation phase angle, the estimated value of the second-stage frequency offset is calculated as follows: ； In the formula, To perform the operation of taking radians, For the length of the repeating ZC sequence, Symbol rate; Step 5.5: Perform a second frequency offset correction on the signal after the first frequency offset correction based on the frequency offset estimation value of the second stage.

8. A time and frequency synchronization device for a high-dynamic communication environment in a scattering channel, characterized in that, The time and frequency synchronization method for a high-dynamic communication environment with a scattering channel as described in any one of claims 1 to 7 includes: The receiving module is used to receive radio waves scattered by the ionosphere to generate an intermediate frequency (IF) analog signal. The IF analog signal includes a preamble sequence and communication data, wherein the preamble sequence includes a segment of length [missing information]. The two segments of the m pseudo-random sequence have lengths of Repeating ZC sequences; The signal processing module is used to preprocess the intermediate frequency analog signal to obtain multiple signals; The synchronization and coarse spectrum correction module is used to perform the strongest path search for each signal using the m pseudo-random sequence, determine the optimal sampling path and the strongest path of the optimal sampling path; obtain the first stage frequency offset estimate based on the strongest path of the optimal sampling path, and perform the first stage frequency offset correction on the multi-channel signal using the first stage frequency offset estimate. The fine spectrum correction module is used to perform a second frequency offset correction on the signal after the first frequency offset correction using the repeated ZC sequence.

9. The time and frequency synchronization device for high dynamic communication environments in scattering channels according to claim 8, characterized in that, The signal processing module includes: The A / D conversion unit is used to perform analog-to-digital conversion on the intermediate frequency analog signal to obtain a digital signal; The DDC downsampling unit is used to perform digital signal downconversion and half-band filtering on the digital signal to generate a baseband signal. The matched filtering unit is used to perform matched filtering on the baseband signal and then downsample it to obtain the multi-channel signal.

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