Fractional Doppler channel estimation method and system based on OTFS in low earth orbit satellite communication

Abstract

The invention belongs to but not limited to the technical field of satellite communication, and particularly relates to an OTFS-based fractional Doppler channel estimation method and system in low-orbit satellite communication, and the method comprises the steps: S1, employing a ZC sequence as a pilot frequency, and providing a low-PAPR DD domain pilot frequency structure; s2, analyzing the influence of IDI on a ZC pilot frequency period correlation result, and revealing a module value distribution rule; s3, initial estimation based on correlation peak value calculation is provided, and initial channel parameters can be obtained; and S4, constructing a non-convex constraint least square optimization problem, and performing solution by using an SQP algorithm so as to obtain more accurate channel parameters. According to the DD domain frame structure provided by the invention, the ZC sequence is adopted as the pilot frequency, and the guard interval is set, so that the PAPR can be reduced, and the interference between data and the pilot frequency can be effectively reduced. The module value distribution rule of the correlation result of the pilot frequency period of the ZC sequence under the influence of IDI is disclosed for the first time, and the rule is fully utilized to carry out initial channel estimation, so that the accuracy and reliability of estimation are improved.

Description

Technical Field

[0001] This invention belongs to, but is not limited to, the field of satellite communication technology, and particularly relates to a fractional Doppler channel estimation method and system based on OTFS in low-Earth orbit satellite communication. Background Technology

[0002] The upcoming 6G era aims to establish a globally seamless, integrated air-space-ground wireless communication network, in which Low Earth Orbit (LEO) satellites are an indispensable component due to their low transmission latency and flexible deployment. Against this backdrop, 3GPP has been actively engaged in research on non-terrestrial networks and has made substantial progress in standardization efforts. However, the high dynamic characteristics of LEO satellites inevitably introduce severe Doppler effects, posing significant challenges to traditional air interface communication mechanisms based on orthogonal frequency division multiplexing, especially in waveform design.

[0003] In recent years, a novel modulation technique called Orthogonal Time Frequency Space (OTFS) has been proposed and has become a key candidate technique for air interface waveforms. By utilizing full diversity in time and frequency, OTFS transforms fast time-varying channels into a quasi-static sparse representation in the Delay-Doppler (DD) domain, exhibiting strong robustness to Doppler shift and significantly reducing channel estimation overhead. However, the extremely short channel coherence time of satellite-to-ground links typically limits the duration of OTFS frames, and insufficient Doppler resolution directly leads to fractional Doppler shift, which causes the transmitted signal energy to be dispersed across all Doppler indices, i.e., inter-Doppler interference (IDI). Therefore, an effective fractional Doppler channel estimation scheme must be designed to ensure reliable data detection in LEO satellite communication systems.

[0004] For fractional Doppler channel estimation based on OTFS, existing methods utilize impulse pilots to estimate channel parameters. However, impulse pilots generate high time-domain peak values, resulting in a large peak-to-average power ratio (PAPR). Sequence-based pilots can diffuse the time-domain peak energy, thereby reducing PAPR, but existing methods often employ compressed sensing to estimate channel parameters. On the one hand, compressed sensing-based methods involve numerous iterations and high complexity, making them difficult to apply in practice. On the other hand, these methods do not fully utilize the characteristics of sequences, resulting in poor estimation performance. Therefore, it is necessary to consider improving existing methods to achieve effective and low-complexity channel estimation in LEO satellite communication scenarios.

[0005] Based on the above analysis, the urgent technical problems that need to be solved in the existing technology are: the compressed sensing-based methods have a large number of iterations and high complexity, making them difficult to apply in practice; and the existing methods do not make full use of sequence characteristics, resulting in poor estimation performance. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a fractional Doppler channel estimation method and system based on OTFS in low-Earth orbit satellite communication.

[0007] This invention is implemented as follows: a fractional Doppler channel estimation method based on OTFS in low-Earth orbit satellite communication, comprising:

[0008] S1 proposes a low PAPR DD domain pilot structure using the ZC (Zadoff-Chu) sequence as pilots.

[0009] S2, analyze the impact of IDI on the ZC pilot period correlation results, and reveal its magnitude distribution law;

[0010] S3 proposes an initial estimate based on correlation peak calculation, which can obtain the initial channel parameters;

[0011] S4. Construct a non-convex constrained least squares optimization problem and use the Sequential Quadratic Programming (SQP) algorithm to solve it, thereby obtaining more accurate channel parameters.

[0012] Furthermore, step S1 specifically includes: in the design of the DD domain frame structure, embedding a ZC pilot sequence of length M along the time delay axis. To effectively reduce interference from data symbols to the pilot and ensure clear identification of the pilot at the receiving end, a guard zone is set around the pilot. This guard zone consists of a certain number of zero-value units, isolating the pilot from the data symbols.

[0013] Furthermore, step S2 specifically includes performing a periodic correlation operation on the received pilot signal and the locally stored original ZC pilot signal at the receiving end. Due to the autocorrelation characteristics of the ZC sequence and the energy diffusion interference caused by the fractional Doppler effect, the symbol interference will not be randomly distributed in the correlation result. Instead, these interference energies will be distributed in a relatively deterministic manner in other correlation resource cells besides the main peak. Through theoretical analysis and simulation experiments, it is concluded that the magnitude of the interference value satisfies a specific distribution law.

[0014] Furthermore, step S3 specifically includes, based on the magnitude distribution pattern revealed in S2, first calculating the periodic correlation between the received signal and the local pilot, and obtaining a two-dimensional correlation matrix. Next, a threshold-based initial estimation method is proposed. The setting of this threshold directly depends on the magnitude distribution pattern obtained in the previous step. Only those positions where the correlation magnitude exceeds this preset threshold are determined as initial estimates of possible effective channel paths. Through this process, an initial set of channel parameters can be obtained, including initial estimates of the delay, Doppler, and channel gain for each path. Although this initial estimate has limited accuracy, it provides a high-quality starting point for the next step of precise optimization.

[0015] Furthermore, step S4 specifically includes constructing a least-squares optimization problem starting with the initially estimated channel parameters. The goal of this problem is to find a set of optimal channel parameters that minimizes the sum of squared errors between the reconstructed received signal and the actual received signal. Simultaneously, the magnitude distribution pattern analyzed in S2 is transformed into a constraint condition and introduced into the optimization problem. This constraint effectively limits the influence range of cross-symbol interference in the model, but due to its form, the entire optimization problem is mathematically non-convex, making the solution complex. Using the SQP algorithm, through iterative solving, high-precision channel parameter estimation results are finally output, including accurate fractional-fold Doppler frequency offset, delay, and channel gain for each path, thereby significantly improving the channel estimation performance of the OTFS system in the LEO scenario.

[0016] Another objective of this invention is to provide a fractional Doppler channel estimation system for low-Earth orbit satellite communication that implements the OTFS-based fractional Doppler channel estimation method, comprising:

[0017] The pilot module utilizes ZC sequences as pilots and proposes a low PAPR DD domain pilot structure.

[0018] The distribution pattern reveal module analyzes the impact of IDI on the ZC pilot period correlation results and reveals the distribution pattern of its magnitude.

[0019] The initial estimation module performs an initial estimation based on correlation peak calculation to obtain the initial channel parameters;

[0020] The channel parameter acquisition module constructs a non-convex constrained least squares optimization problem and uses the SQP algorithm to solve it, thereby obtaining more accurate channel parameters.

[0021] Another object of the present invention is to provide a computer device, the computer device including a memory and a processor, the memory storing a computer program, the computer program being executed by the processor causing the processor to perform the steps of the fractional Doppler channel estimation method based on OTFS in low-Earth orbit satellite communication.

[0022] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the fractional Doppler channel estimation method based on OTFS in low-Earth orbit satellite communication.

[0023] Another objective of this invention is to provide an information data processing terminal, which includes the fractional Doppler channel estimation system based on OTFS in low-Earth orbit satellite communication.

[0024] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0025] The OTFS fractional Doppler channel estimation algorithm based on relevant information assistance proposed in this invention has the following advantages over existing methods:

[0026] (1) The proposed DD domain frame structure uses ZC sequence as pilot and sets guard interval, which can reduce PAPR and effectively reduce interference between data and pilot.

[0027] (2) For the first time, the distribution law of the magnitude of the pilot period correlation results of ZC sequence under the influence of IDI was revealed, and this law was fully utilized for initial channel estimation, which improved the accuracy and reliability of the estimation.

[0028] (3) Based on the good correlation characteristics of the ZC sequence, the channel parameters are initially estimated, providing a better initial point for subsequent optimization, so that the SQP algorithm can quickly converge to the optimal solution, reducing complexity while further improving the estimation accuracy of the channel.

[0029] This invention proposes a groundbreaking channel estimation solution in the field of low-Earth orbit satellite high-speed communication. Addressing the core challenges faced by OTFS in the severe fractional Doppler environment, it designs a new channel estimation method with high accuracy and low complexity, effectively overcoming the limitations of traditional methods in terms of insufficient estimation accuracy under fractional Doppler conditions, and the excessively high computational complexity of existing compressed sensing and other schemes.

[0030] To address the three major technical bottlenecks of OTFS modulation in low-Earth orbit satellite communications—severe fractional Doppler effect, complex multipath interference, and limited onboard processing capabilities—this invention proposes a systematic solution. Through a fast coarse estimation mechanism based on ZC sequences, the system achieves efficient initial estimation of the DD domain channel; by establishing and solving a non-convex constraint optimization problem, the accuracy of channel parameter estimation under fractional Doppler conditions is significantly improved.

[0031] To address the conflict between the high dynamic characteristics of satellite-to-ground links and onboard processing resources, this invention designs a channel estimation method based on relevant information assistance. This method ensures estimation accuracy while reducing computational complexity to an engineering-feasible level. Furthermore, the algorithm design fully considers the characteristics of fractional Doppler, and by establishing an IDI interference model, it significantly improves the adaptability of the scheme under complex channel conditions, overcoming the shortcomings of existing channel estimation methods that suffer from drastic performance degradation in high-speed mobile scenarios.

[0032] This solution offers significant value in improving communication efficiency, enhancing transmission reliability, expanding applications in high-dynamic scenarios, and reducing system deployment costs. It provides satellite operators and communication equipment manufacturers with higher spectrum utilization efficiency and lower signal processing complexity, fully meeting the core requirements for highly reliable transmission in complex scenarios such as emergency rescue communications, high-speed mobile environment monitoring, and wide-area logistics tracking. It also demonstrates broad commercial application prospects in cutting-edge fields such as next-generation satellite IoT and integrated space-ground networks. Attached Figure Description

[0033] Figure 1 This is a flowchart of the fractional Doppler channel estimation method based on OTFS in low-Earth orbit satellite communication provided in this embodiment of the invention;

[0034] Figure 2 This is a DD domain frame structure diagram provided in an embodiment of the present invention;

[0035] Figure 3 This is a graph showing the variation of the expansion factor magnitude with the fractional Doppler coefficients provided in an embodiment of the present invention;

[0036] Figure 4 This is a comparison diagram of PAPR with different pilot structures provided in the embodiments of the present invention;

[0037] Figure 5 This is a comparison chart of the NMSE performance of different channel estimation methods provided in the embodiments of the present invention;

[0038] Figure 6 This is a comparison chart of the BER performance of different channel estimation methods provided in the embodiments of the present invention;

[0039] Figure 7This is a structural diagram of a fractional Doppler channel estimation system based on OTFS in low-Earth orbit satellite communication provided in an embodiment of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] like Figure 1 As shown in the embodiments of the present invention, the fractional Doppler channel estimation method based on OTFS in low-Earth orbit satellite communication includes:

[0042] Step 1: Using ZC sequences as pilots, a low PAPR DD domain pilot structure is proposed.

[0043] like Figure 2 The diagram shows the proposed DD domain frame structure. The ZC sequence is embedded as a pilot sequence along the time delay axis into the DD domain, and guard intervals are added around the pilot sequence along the Doppler axis to reduce interference between data and pilot signals. The transmitted signal can be specifically represented as follows:

[0044]

[0045] in, Let u ∈ {1,…,M-1} represent the pilot sequence, and let X represent the root index of the ZC sequence. d [k,l] represents the data symbol, k max k represents the maximum Doppler coefficient. p S represents the position index of the ZC sequence along the Doppler axis. k ={k p -k max ,…,k p +k max}, S l ={0,1,…,M-1}.

[0046] After passing through the satellite multipath fading channel, the DD domain pilot signal at the receiving end can be represented as:

[0047]

[0048] Where, k∈[k p -k max ,…,k p +k max ], l∈[0,M-1], w[k,l] represents the interference of data and noise. Q represents the total number of paths, h q l q k q and κq β(kk) represents the channel gain, delay coefficient, integer multiple of the Doppler coefficient, and fractional multiple of the Doppler coefficient for the q-th path, respectively. p -k q -κ q The diffusion factor caused by fractional Doppler frequency offset is represented as .

[0049]

[0050] Step 2: Analyze the impact of IDI on the ZC pilot period correlation results and reveal the distribution law of its magnitude.

[0051] Based on the excellent correlation characteristics of the ZC sequence, we sequentially performed periodic correlation operations on the received pilot signals at different Doppler indices to analyze the impact of IDI on the periodic correlation results. In this case, the periodic correlation result at Doppler index k can be expressed as...

[0052]

[0053] To analyze the impact of IDI on the ZC pilot period correlation results, we first focus on the magnitude of the diffusion factor |β(kk) p -k q -κ q When the Doppler tap is an integer, i.e., κ q When =0, |β(kk) p -k q -κ q )|Only at k=k p +k q The time term has a non-zero value. This non-zero value can be obtained through asymptotic expansion, which is equivalent to MN. In this case, the periodic correlation results are strictly limited to one row in the DD domain. On the other hand, when κ... q ≠0, for all k, |β(kk) p -k q -κ q )| are not zero, and the periodic correlation results have non-zero values ​​in each row of the DD field. Figure 3 This shows what happens when N=9, k p =5 and k q When =1, |β(kk) p -k q -κ q With the fractional Doppler coefficient κ q The changes are quite obvious. It's clear that |β(kk) p -k q -κ q )| Mainly concentrated in k=k p +k q and k = kp +k q -1 or k = k p +k q +1. Therefore, for a given Doppler coefficient k... q +κ q The modulus of the periodic correlation results is mainly concentrated in the two rows of the DD field, and can be specifically represented as follows:

[0054] k m =k p +k q

[0055]

[0056] Where, k m The Doppler index represents the maximum value of the periodic correlation result.

[0057] Oncek m Once determined, the range of Doppler coefficients for the corresponding path can be from [-k max ,k max ] becomes It can be represented as

[0058]

[0059] Therefore, based on the above analysis of the distribution law of the magnitude of the periodic correlation results, the Doppler coefficients are restricted to a significantly smaller interval, which is beneficial to reducing the computational complexity of subsequent channel estimation schemes.

[0060] Step 3: Based on the distribution law of the modulus, propose an initial estimation method.

[0061] Based on the above periodic correlation results, the time delay coefficient can be estimated by the cyclic shift value corresponding to the periodic correlation peak, and its expression is:

[0062]

[0063] in J represents the time delay coefficient of the q-th path in the initial estimate, and J is the periodic correlation result R for different cyclic shifts d. k The set of maximum values ​​of (d) can be represented as

[0064]

[0065] Among them, l max This represents the maximum delay coefficient.

[0066] At this time, when The expression for the periodic correlation result can be further expressed as:

[0067]

[0068] Analyzing the above formula, we can obtain the Doppler coefficient of the q-th path through the correlation results of two periods. and The ratio is obtained and can be expressed as

[0069]

[0070] in, Let represent the Doppler coefficient of the q-th path in the initial estimate. The time delay and Doppler coefficients can be obtained by fully utilizing the periodic correlation results. Furthermore, the channel gain is determined by constructing a system of linear equations using the received pilot signal, expressed as follows:

[0071]

[0072] in,(·) -1 Represents the inverse operator. It is the vector for the initial estimated channel gain.

[0073] It is a vector consisting of Q selected received symbols. The main energy of the selected received symbols comes from the pilot symbols, which helps to reduce interference from data symbols, thus ensuring more accurate channel gain estimation. The coefficient matrix is ​​given by the following formula:

[0074]

[0075] Where, k i and l i This represents the Doppler index and time delay index of the i-th received pilot symbol.

[0076] Step 4: Construct a non-convex constrained least squares optimization problem and use the SQP algorithm to obtain a refined estimate.

[0077] The initial channel parameters can be obtained through the above derivation. However, in practice, interference between paths can significantly exacerbate the channel estimation error, so a joint optimization of the channel estimation parameters is proposed. Specifically, a non-convex constrained least squares optimization problem is constructed, the goal of which is to minimize the error between the reconstructed received pilot signal and the actual received pilot signal. To solve this non-convex optimization problem, the SQP algorithm is used. Furthermore, during the optimization process... The real and imaginary parts are considered as independent variables.

[0078]

[0079] in, and Let represent the Doppler coefficient, time delay coefficient, and channel gain of the precise estimate for the q-th path, respectively. ||·||2 represents... Norm, This indicates the reconstructed pilot received signal.

[0080] Simulation results

[0081] The performance of this invention is analyzed below using simulation. The time delay dimension M and Doppler dimension N are 31 and 16, respectively, and the carrier frequency and subcarrier spacing are 4 GHz and 15 kHz, respectively. The NTN-TDL-A channel model is used in the simulation to simulate the channel in a low-Earth orbit satellite scenario. It is assumed that the time delay coefficients are integers, the Doppler coefficients are generated by the Jake model, and a linear minimum mean square error detector is used for data recovery. The accuracy of the channel estimation is evaluated using the normalized mean square error (NMSE), which is calculated as the mean square error between the estimated channel value and its true value, divided by a normalization factor of the true channel energy.

[0082] Figure 4 The PAPR performance of the proposed DD-domain pilot structure is compared with that of other pilot structures. It can be seen that the PAPR performance of the proposed DD-domain pilot structure is significantly better than other methods. This is mainly because the energy of the ZC pilot sequence is diffused throughout the time domain, reducing the time-domain peak value.

[0083] Figure 5 This paper presents a comparison of the NMSE performance of the proposed channel estimation method based on relevant information assistance with other schemes. It can be observed that the proposed scheme exhibits a significant improvement in NMSE performance across the entire signal-to-noise ratio range. This improvement stems from fully utilizing the correlation characteristics of the ZC sequence to analyze the magnitude distribution of the periodic correlation results, thereby achieving higher channel estimation accuracy.

[0084] Figure 6 The performance comparison of different schemes in terms of bit error rate is shown. It can be seen that the bit error rate of the present invention is very close to the performance under perfect channel state information, proving its superiority in data decoding.

[0085] like Figure 7 As shown in the embodiment of the present invention, a fractional Doppler channel estimation system based on OTFS for low-Earth orbit satellite communication includes:

[0086] The pilot module utilizes ZC sequences as pilots and proposes a low PAPR DD domain pilot structure.

[0087] The distribution pattern reveal module analyzes the impact of IDI on the ZC pilot period correlation results and reveals the distribution pattern of its magnitude.

[0088] The initial estimation module performs an initial estimation based on correlation peak calculation to obtain the initial channel parameters;

[0089] The channel parameter acquisition module constructs a non-convex constrained least squares optimization problem and uses the SQP algorithm to solve it, thereby obtaining more accurate channel parameters.

[0090] At the transmitting end, the pilot module generates a pilot signal with low PAPR using a ZC sequence. This pilot signal is mapped into a DD domain resource grid modulated by OTFS, converted into a time-frequency domain signal through a two-dimensional inverse Singer's transform (ISFFT) and windowing operations, and then transmitted to the low-Earth orbit satellite link via upconversion at the RF front end. This step ensures that the pilot maintains good autocorrelation characteristics under strong Doppler spread and multipath conditions.

[0091] At the receiving end, the signal is down-converted and sampled to recover the time-frequency domain signal, and then subjected to a two-dimensional Singer-Fold Transform (SFFT) to obtain the DD domain received signal. The distribution pattern revealing module performs correlation analysis on the received ZC pilot signal to reveal the influence of IDI on the ZC pilot periodic correlation results, thereby determining the magnitude distribution characteristics caused by fractional Doppler frequency shift, which is used to guide subsequent peak extraction and matching.

[0092] The initial estimation module performs a two-dimensional cyclic correlation operation in the DD domain, obtaining initial values ​​of delay and fractional Doppler by detecting the peak positions in the correlation matrix. Due to peak leakage caused by the fractional Doppler effect, this module utilizes the correlation peaks to calculate and obtain initial channel parameter estimates.

[0093] The channel parameter acquisition module uses the initial estimation results as the initial values ​​of the optimization variables to construct a non-convex constrained least squares optimization problem to minimize the error function between the received signal and the reconstructed signal. This optimization problem combines channel sparsity and power constraints, and introduces the SQP algorithm for iterative solution, gradually correcting the time delay, Doppler, and gain parameters to obtain high-precision channel estimation results.

[0094] The final module inputs the optimized channel parameters into the demodulation and equalization unit to achieve channel compensation and symbol detection in the OTFS system. The entire signal data processing chain realizes a closed-loop process from pilot generation, signal transmission, correlation detection, parameter optimization to demodulation recovery, significantly improving the channel estimation accuracy and system robustness in high-speed motion scenarios of low-Earth orbit satellites.

[0095] Example 1: Design of a low PAPR pilot structure based on ZC sequence

[0096] In this embodiment, the transmitting end constructs a pilot signal by generating a ZC sequence of length 31 and maps it onto the time delay axis of the DD domain frame structure. To prevent data symbol energy leakage into the pilot region, three rows of zero-value resource units are inserted before and after the pilot as protection zones, ensuring complete isolation between the pilot and the data. The pilot signal is transformed into a time-frequency domain signal after a two-dimensional inverse Singer transform and then transmitted via radio frequency up-conversion. Because the ZC sequence has continuous phase and constant amplitude, the peak-to-average power ratio of the pilot signal is low, avoiding power amplifier nonlinear distortion and improving transmission stability in high-speed moving environments of low-Earth orbit satellites.

[0097] At the receiving end, after down-conversion and demodulation, the signal is mapped back to the DD domain. By performing two-dimensional correlation detection on the received signal in the DD domain, the pilot peak position and noise interference can be clearly distinguished, and the channel delay and preliminary Doppler distribution can be obtained. This structure can maintain stable pilot identification performance under different satellite velocities and signal-to-noise ratios, providing high signal-to-noise guidance for subsequent channel parameter estimation.

[0098] Example 2: Analysis of Interference Mode Distribution Caused by Fractional Doppler

[0099] In this embodiment, the propagation characteristics of the ZC pilot in a fractional Doppler channel are modeled, and the receiver performs a periodic correlation operation to obtain a two-dimensional correlation matrix. Simulation observations reveal that when there is a fractional Doppler offset, the interference energy is no longer randomly distributed, but rather exhibits a symmetrical attenuation distribution around the main peak according to the index distance. This pattern indicates that the impact of Doppler diffusion is predictable and deterministic, conforming to a monotonically decreasing trend.

[0100] Further statistical analysis of the superimposed responses of multiple channel paths revealed a fixed proportional relationship between the average magnitude intensity of each interference peak and the energy of the main peak. By extracting this pattern, this invention introduces a constraint template at the algorithm layer, enabling subsequent least-squares optimization to be solved based on the actual energy distribution, thus improving the stability and convergence speed of channel estimation. This embodiment verifies the existence and repeatability of the interference magnitude distribution pattern, supporting the technical ideas of claims 1 and 3.

[0101] Example 3: Initial Channel Parameter Estimation Based on Threshold Decision

[0102] The initial estimation method proposed in this embodiment employs a threshold determination strategy in the two-dimensional correlation matrix. First, the average energy value E_avg of the correlation matrix is ​​calculated, and a threshold T = k × E_avg is set, where k is an empirical coefficient taken as 1.8. Only when the correlation magnitude exceeds the threshold is the corresponding delay-Doppler index determined as a valid path. This method effectively suppresses interference from noise and spurious peaks, thereby obtaining the initial estimation result of the true channel path.

[0103] The resulting initial channel parameter set includes the delay, fractional Doppler, and complex gain for each path. Although this initial estimate is slightly biased due to the influence of the signal-to-noise ratio, the results accurately reflect the sparse distribution characteristics of the channel, providing good initial values ​​for non-convex optimization. Through simulation comparisons of multiple sets of low-Earth orbit satellite channels, the threshold initial estimate based on this embodiment can control the average parameter deviation within 1%, providing experimental support for the technical solution described in claim 4.

[0104] Example 4: Channel parameter optimization solution based on non-convex constraint least squares

[0105] In this embodiment, the initially estimated parameters are used as optimization variables to construct a non-convex constrained least squares problem. The objective function is the mean square error between the received signal and the signal reconstructed from the parameters. The constraints include the range of values ​​for the delay parameter and the Doppler parameter, as well as the distribution law of the energy magnitude. The problem is solved using the SQP algorithm, updating the quadratic approximation form of the objective function and correcting the parameter vector in each iteration until the error converges.

[0106] After multiple iterations, the algorithm can obtain high-precision channel estimation results within a finite number of iterations. Under typical low-Earth orbit satellite relative speeds of 500 km / h and signal-to-noise ratios of 10 dB, the optimized channel parameter estimation error is reduced by approximately 85% compared to the initial estimate, significantly improving the system's robustness to fractional Doppler disturbances. This embodiment fully supports the technical effects of claims 1 and 5.

[0107] Example 5: System and computer equipment working together

[0108] This embodiment provides a systematic implementation scheme, including a pilot module, a distribution pattern revealing module, an initial estimation module, and a channel parameter acquisition module. The pilot module completes ZC sequence generation and frame embedding at the baseband end; the distribution pattern revealing module constructs a modulus distribution template through a two-dimensional periodic correlation unit and a feature extraction unit; the initial estimation module performs threshold detection and outputs initial channel parameters; and the channel parameter acquisition module runs a sequential quadratic programming algorithm for optimization.

[0109] In the computer device implementation, the aforementioned algorithm program is pre-installed in the memory, and the processor automatically completes the entire process from pilot signal generation, correlation calculation, threshold determination to parameter optimization during execution. This system can run on ground terminals, onboard processors, or edge computing nodes, and is suitable for multi-satellite link channel estimation tasks. Through modular design and hardware-software collaboration, this embodiment simultaneously supports the system and media protection themes of claims 6 to 10, achieving the integrated implementation of the algorithm, device, and program.

[0110] It should be noted that embodiments of the present invention can be implemented in hardware, software, or a combination of both. The hardware portion can be implemented using dedicated logic; the software portion can be stored in memory and executed by a suitable instruction execution system, such as a microprocessor or dedicated-design hardware. Those skilled in the art will understand that the above-described devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuitry such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field-programmable gate arrays, programmable logic devices, etc., or by software executed by various types of processors, or by a combination of the above-described hardware circuitry and software, such as firmware.

[0111] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A fractional Doppler channel estimation method based on OTFS in low-Earth orbit satellite communication, characterized in that, Includes the following steps: S1, use the ZC sequence to generate pilot signals, and embed a pilot sequence of length M along the time delay axis in the delay-Doppler domain frame structure. Set up a guard area composed of several zero-value units around the pilot to isolate data symbols. S2, at the receiving end, perform periodic correlation calculation between the received pilot signal and the locally stored original ZC pilot, analyze the interference diffusion law based on the fractional Doppler effect and obtain the correlation modulus distribution characteristics; S3, calculate the correlation peak based on the correlation results and perform an initial estimation based on the threshold to obtain the initial delay, Doppler and complex gain parameters of the channel path; S4 uses the initial estimation results as input to construct a non-convex constrained least squares optimization problem, takes the relevant magnitude distribution characteristics as constraints, and uses the SQP algorithm to solve iteratively, thereby outputting high-precision channel parameter estimation results.

2. The method according to claim 1, characterized in that, The amplitude of the pilot signal in step S1 is constant, and the phase difference between adjacent symbols increases linearly according to the ZC sequence to ensure that the pilot signal has the characteristics of low peak-to-average power ratio and excellent autocorrelation performance.

3. The method according to claim 1, characterized in that, In step S2, the interference energy caused by the fractional Doppler exhibits a symmetrical distribution around the main peak in the correlation matrix, and its magnitude gradually decreases as the resource cell index of the distance from the main peak increases, with the interference intensity distribution conforming to a monotonically decreasing trend.

4. The method according to claim 1, characterized in that, The threshold mentioned in step S3 is determined by the product of the average energy of the correlation matrix and a set coefficient. Only when the correlation magnitude is greater than the threshold is it determined to be a valid path point. The set of path points is used to form the initial channel parameter set.

5. The method according to claim 1, characterized in that, The non-convex constrained least squares optimization problem described in step S4 takes the mean square error between the received signal and the signal reconstructed from the channel parameters as the objective function. It iteratively minimizes this error by updating the delay parameter, Doppler frequency offset parameter, and complex gain parameter until convergence.

6. A fractional Doppler channel estimation system based on orthogonal time-frequency spatial modulation for implementing the method of any one of claims 1 to 5 in low-Earth orbit satellite communication, characterized in that, include: Pilot module, used to generate pilots with low peak-to-average power ratio using ZC sequence and embed pilot structure in DD domain; The distribution pattern revealing module is used to analyze the impact of fractional Doppler interference on pilot period correlation results and reveal its magnitude distribution pattern. The initial estimation module is used to obtain initial channel parameters based on the correlation peak and threshold determination; The channel parameter acquisition module is used to construct a non-convex constrained least squares optimization problem and solve it using the SQP algorithm to output high-precision channel parameters.

7. The system according to claim 6, characterized in that, The set of output channel parameters of the initial estimation module is used as the initial input value of the channel parameter acquisition module. After iteratively updating the parameters, the channel parameter acquisition module returns the result to the initial estimation module to complete the adaptive correction.

8. The system according to claim 6, characterized in that, The distribution pattern revealing module includes a correlation calculation unit and a feature extraction unit. The correlation calculation unit performs two-dimensional periodic correlation operations, and the feature extraction unit extracts the modulus decay pattern based on the correlation matrix to generate a constraint template.

9. A computer-readable storage medium having a computer program stored thereon, the computer program, when executed by a processor, implementing the steps of the fractional Doppler channel estimation method based on orthogonal time-frequency spatial modulation in low-Earth orbit satellite communication as described in any one of claims 1 to 5.

10. A computer device, comprising a memory and a processor, characterized in that, The memory stores a computer program, which, when executed by a processor, causes the processor to perform the fractional Doppler channel estimation method based on orthogonal time-frequency spatial modulation in low-Earth orbit satellite communication as described in any one of claims 1 to 5.

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