FTN-otfs communication method for high mobile leo satellite link

Abstract

The application relates to the technical field of wireless communication, and provides an FTN-OTFS communication method for high-mobility LEO satellite-ground links. The method pre-establishes a corresponding lookup table of channel configurations and transmission modes compatible with a 3GPP standard, the channel configurations are bound to satellite elevation angles and ground shielding conditions, and each mode corresponds to a unique time-domain compression factor; before the start of each transmission frame, the current satellite elevation angle and the ground shielding state are acquired, the corresponding tap delay line channel configuration is matched, and the instantaneous signal-to-noise ratio of the current link is estimated; according to a preset interval in which the estimated instantaneous signal-to-noise ratio is located; according to the mapped time-domain compression factor, time-domain compression processing is performed on information symbols in the delay-Doppler domain to generate a transmission signal with a super-Nyquist rate; the generated transmission signal is sent to a receiving end through a low-orbit satellite-ground link, and the receiving end adopts a linear minimum mean square error detector to complete signal detection and demodulation.

Description

Technical Field

[0001] This application relates to the field of wireless communication technology, and in particular to an FTN-OTFS communication method for high-mobility LEO satellite-to-ground links. Background Technology

[0002] Low Earth orbit (LEO) satellite communication is characterized by high mobility, leading to extreme Doppler shifts and rapid channel time-varying issues. Simultaneously, the computing power and power consumption of onboard equipment are severely limited. Current technologies employing statically fixed compression factors in super-Nyquist orthogonal time-frequency spatial transmission schemes cannot adapt to the drastic fluctuations in link geometry and channel conditions during LEO satellite transits. A conservative compression factor wastes spectrum resources during the zenith-line-of-sight phase, while an aggressive compression factor causes interference exceeding the decoder's capacity during the horizon-out-of-sight phase, resulting in link interruptions. Summary of the Invention

[0003] This application provides an FTN-OTFS communication method for high-mobility LEO satellite-to-ground links, aiming to solve the problem that existing adaptive super Nyquist schemes mostly use iterative search algorithms, which have high computational complexity and cannot meet the real-time and low-power requirements of low-Earth orbit satellite communication.

[0004] In a first aspect, embodiments of this application provide an FTN-OTFS communication method for high-mobility LEO satellite-to-ground links, the method comprising: A lookup table for the correspondence between channel configurations and transmission modes compatible with 3GPP standards is pre-established. The channel configuration is bound to the satellite elevation angle and ground obstruction. The transmission modes include Nyquist mode, mild compression mode and aggressive compression mode, and each mode corresponds to a unique time-domain compression factor. Before the start of each transmission frame, the current satellite elevation angle and ground obstruction status are obtained, the corresponding tap delay line channel configuration is matched, and the instantaneous signal-to-noise ratio of the current link is estimated. Based on the preset interval in which the estimated instantaneous signal-to-noise ratio is located, the corresponding transmission mode and time-domain compression factor are directly mapped through a lookup table. Based on the time-domain compression factor obtained from the mapping, the information symbols in the delayed Doppler domain are compressed in the time domain to generate a transmission signal with a super Nyquist rate. The generated transmission signal is then sent to the receiving end via a low-Earth orbit satellite-to-ground link. The receiving end uses a linear minimum mean square error detector to complete signal detection and demodulation.

[0005] In some embodiments, the pre-established lookup table for channel configurations and transmission modes compatible with 3GPP standards includes: dividing the satellite elevation angle into three continuous intervals, defining ground obstruction as three states: no obstruction, partial obstruction, and complete obstruction, mapping each combination of elevation angle interval and obstruction state to a 3GPP standard tap delay line channel model, matching each channel model with a Nyquist mode, a mild compression mode, and an aggressive compression mode, assigning a unique time-domain compression factor to each transmission mode, and storing all correspondences as a directly callable lookup table.

[0006] In some embodiments, the channel configuration binding satellite elevation angle and ground obstruction includes: binding the case where the elevation angle is below a first threshold and there is complete obstruction to the 3GPP non-line-of-sight tapped delay line channel model; binding the case where the elevation angle is between the first threshold and a second threshold and there is partial obstruction to the 3GPP hybrid tapped delay line channel model; and binding the case where the elevation angle is above the second threshold and there is no obstruction to the 3GPP line-of-sight tapped delay line channel model.

[0007] In some embodiments, obtaining the current satellite elevation angle and ground obstruction status before the start of each transmission frame includes: reading satellite ephemeris data to calculate the current satellite elevation angle relative to the ground receiver, obtaining the current ground obstruction status through the environmental perception sensor of the ground receiver, and sending the calculated elevation angle and the obtained obstruction status to the channel matching module.

[0008] In some embodiments, matching the corresponding tap delay line channel configuration and estimating the instantaneous signal-to-noise ratio of the current link includes: extracting the corresponding tap delay line channel parameters from a lookup table based on the acquired elevation angle and occlusion status; transmitting a known pilot signal during the preamble stage of the current frame; and calculating the instantaneous signal-to-noise ratio of the current link based on the received pilot signal.

[0009] In some embodiments, the step of directly mapping the corresponding transmission mode and time-domain compression factor to a lookup table based on the preset interval of the estimated instantaneous signal-to-noise ratio includes: comparing the instantaneous signal-to-noise ratio with a preset first signal-to-noise ratio threshold and a second signal-to-noise ratio threshold; if the instantaneous signal-to-noise ratio is lower than the first signal-to-noise ratio threshold, mapping to the Nyquist mode; if the instantaneous signal-to-noise ratio is between the first and second signal-to-noise ratio thresholds, mapping to the mild compression mode; if the instantaneous signal-to-noise ratio is higher than the second signal-to-noise ratio threshold, mapping to the aggressive compression mode; and extracting the time-domain compression factor of the corresponding transmission mode from the lookup table.

[0010] In some embodiments, the time-domain compression factor obtained by mapping includes: setting the time-domain compression factor corresponding to the Nyquist mode to 1, setting the time-domain compression factor corresponding to the mild compression mode to a fixed value between 0.8 and 0.9, and setting the time-domain compression factor corresponding to the aggressive compression mode to a fixed value between 0.7 and 0.8.

[0011] In some embodiments, the step of performing time-domain compression processing on information symbols in the delayed Doppler domain to generate a transmission signal with a super Nyquist rate includes: mapping the information symbols to be transmitted to a delayed Doppler domain grid; performing an inverse symplectic fast Fourier transform on the delayed Doppler domain symbols to obtain time-frequency domain symbols; adjusting the time interval of the time-frequency domain symbols according to the time-domain compression factor obtained from the mapping; and performing a Heisenberg transform and root-raised cosine pulse shaping on the adjusted time-frequency domain symbols to generate a transmission signal with a super Nyquist rate.

[0012] In some embodiments, the step of sending the generated transmission signal to the receiving end via a low-Earth orbit satellite-to-ground link, and the receiving end using a linear minimum mean square error detector to complete signal detection and demodulation, includes: the transmitting end sending the generated transmission signal to the ground receiving end via a low-Earth orbit satellite-to-ground link; the receiving end performing Wigner transform and sampling on the received signal to obtain a time-frequency domain received signal; performing a symptotic fast Fourier transform on the time-frequency domain received signal to obtain a delayed Doppler domain received signal; using a linear minimum mean square error detector to perform equalization processing on the delayed Doppler domain received signal; and demodulating the equalized signal to obtain the original information symbols.

[0013] In some embodiments, the method further includes: establishing a sliding window of fixed length, recording the satellite elevation angle, ground obstruction status, instantaneous signal-to-noise ratio and corresponding transmission mode of all transmission frames within the sliding window, using a linear regression algorithm to predict the instantaneous signal-to-noise ratio of the next transmission frame based on historical data within the sliding window, mapping the transmission mode and time-domain compression factor of the next transmission frame in advance from a lookup table based on the predicted instantaneous signal-to-noise ratio, and immediately switching to the predicted transmission mode for signal processing of the next transmission frame after the current transmission frame ends.

[0014] This invention utilizes a pre-established lookup table compatible with 3GPP standards for channel configuration and transmission modes. By combining satellite elevation angle, ground obstruction status, and instantaneous signal-to-noise ratio (SNR), it achieves adaptive switching of transmission modes, effectively resolving the conflict between rate enhancement and inter-symbol interference penalty in low-Earth orbit (LEO) satellite-to-ground links. This maximizes the effective throughput throughout the entire satellite transit cycle while meeting strict bit error rate constraints. The low-complexity design based on the lookup table achieves extremely low processing latency, enabling real-time tracking of rapid changes in the LEO link and preventing channel state expiration due to slow algorithm computation. An aggressive compression mode is employed in high SNR regions, increasing data transmission rates while shortening the transmission time window required for each frame, reducing the overall energy consumption of LEO satellites, and improving system energy efficiency.

[0015] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart illustrating the steps of an FTN-OTFS communication method for high-mobility LEO satellite-to-ground links provided in an embodiment of this application; Figure 2 This is a schematic diagram illustrating the principle of an FTN-OTFS communication method for high-mobility LEO satellite-to-ground links provided in an embodiment of this application; Figure 3 This is a schematic block diagram of the structure of an FTN-OTFS communication system for high-mobility LEO satellite-to-ground links provided in one embodiment of this application; Figure 4 This is a schematic block diagram of the structure of a computer device provided in an embodiment of this application.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0021] It should be understood that, in order to clearly describe the technical solutions of the embodiments of the present invention, the terms "first" and "second" are used in the embodiments of the present invention to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0022] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0023] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0024] Low Earth orbit (LEO) satellite communication is characterized by high mobility, leading to extreme Doppler shifts and rapid channel time-varying issues. Simultaneously, the computing power and power consumption of onboard equipment are severely limited. Existing technologies employing statically fixed compression factors in super-Nyquist orthogonal time-frequency spatial transmission schemes cannot adapt to the drastic fluctuations in link geometry and channel conditions during LEO satellite transits. Conservative compression factors waste spectrum resources when the satellite is at zenith line-of-sight, while aggressive compression factors cause interference exceeding the decoder's capacity and triggering link interruptions when the satellite is at horizon (non-line-of-sight). Furthermore, existing adaptive super-Nyquist schemes often employ iterative search algorithms, resulting in high computational complexity and failing to meet the real-time and low-power requirements of LEO satellite communication.

[0025] Please refer to Figure 1 and Figure 2 This application provides an FTN-OTFS communication method for high-mobility LEO satellite-to-ground links, applied to computer devices. The computer device can be deployed on a single server or server cluster, or in devices such as handheld terminals, laptops, wearable devices, or robots. All information involved in this application was obtained and used with the authorization of the relevant users and in compliance with relevant laws and regulations, and will not infringe upon users' personal privacy.

[0026] This application addresses the problem that existing statically fixed compression factor super-Nyquist orthogonal time-frequency spatial transmission schemes cannot adapt to the drastic fluctuations in link geometry and channel conditions during low-Earth orbit (LEO) satellite transits, and the high computational complexity and inability to meet the real-time and low-power requirements of existing adaptive super-Nyquist schemes. It proposes a low-complexity adaptive transmission scheme based on a lookup table. This scheme pre-establishes a lookup table compatible with the 3GLP standard for channel configuration and transmission modes, and adaptively switches transmission modes based on satellite elevation angle, ground obstruction status, and instantaneous signal-to-noise ratio. This maximizes the effective throughput throughout the entire satellite transit cycle while meeting strict bit error rate constraints, and simultaneously reduces the computational complexity and power consumption of onboard equipment.

[0027] like Figure 1 As shown, the super Nyquist orthogonal time-frequency space communication method for high-mobility low-Earth orbit satellite-to-ground links provided in this application includes the following steps: The provided FTN-OTFS communication method for high-mobility LEO satellite-to-ground links includes steps S101 to S103. Details are as follows: Step S101. Pre-establish a lookup table for the correspondence between channel configuration and transmission mode that is compatible with 3GPP standards. The channel configuration is bound to the satellite elevation angle and ground obstruction. The transmission modes include Nyquist mode, mild compression mode and aggressive compression mode, and each mode corresponds to a unique time-domain compression factor.

[0028] Specifically, step S101 is the system initialization step, which is completed before the system runs for the first time. The generated lookup table is stored in the non-volatile memory of the computer device for direct access during subsequent transmission.

[0029] The lookup table uses a two-dimensional array structure for storage. The row index of the array corresponds to the combination of satellite elevation angle intervals and ground obstruction states, while the column index corresponds to the instantaneous signal-to-noise ratio interval. Each array element stores the corresponding transmission mode identifier and time-domain compression factor value. The size of the lookup table is determined by the number of elevation angle intervals, the number of obstruction states, and the number of signal-to-noise ratio intervals.

[0030] The channel configuration is based on the standard tapped delay line channel model released by the 3GLP-3, specifically referencing the non-line-of-sight, hybrid, and line-of-sight tapped delay line channel models defined in 3GLP-3 technical specification 36.101. Each channel model contains multiple taps, each corresponding to a specific delay and power value, used to simulate multipath propagation characteristics under different channel conditions.

[0031] The satellite elevation angle is divided into multiple continuous intervals, each corresponding to different link geometry characteristics. Simultaneously, ground obstruction states are categorized into three types: unobstructed, partially obstructed, and completely obstructed, corresponding to situations where there are no obstacles between the ground receiving terminal and the satellite, partial obstruction, and complete obstruction, respectively. Each combination of elevation angle interval and obstruction state is then bound to the corresponding 3GLP standard tapped delay line channel model, establishing a correspondence between channel configuration and satellite elevation angle and ground obstruction state.

[0032] Three transmission modes are matched for each channel model: Nyquist mode, mild compression mode, and aggressive compression mode. The Nyquist mode corresponds to orthogonal transmission without inter-symbol interference (ISI), with a time-domain compression factor set to 1. The mild compression mode corresponds to slight time-domain symbol compression, introducing controllable ISI to improve spectral efficiency while ensuring transmission reliability. The aggressive compression mode corresponds to heavy time-domain symbol compression, introducing significant ISI to maximize spectral efficiency under high signal-to-noise ratio (SNR) conditions. A unique time-domain compression factor is assigned to each transmission mode, with values ​​ranging from greater than 0 to less than or equal to 1; smaller values ​​indicate higher compression levels.

[0033] The established channel configuration, transmission mode, time-domain compression factor, and their correspondences are stored as a directly accessible lookup table. This lookup table is stored in the computer device's non-volatile memory in binary file format. It is loaded into memory upon system startup for fast lookup and mapping during transmission.

[0034] Step S102. Before the start of each transmission frame, obtain the current satellite elevation angle and ground obstruction status, match the corresponding tap delay line channel configuration, and estimate the instantaneous signal-to-noise ratio of the current link. Based on the preset interval in which the estimated instantaneous signal-to-noise ratio is located, directly map the corresponding transmission mode and time-domain compression factor through a lookup table.

[0035] Specifically, step S102 is executed before the start of each transmission frame to obtain the current channel state and map it to the corresponding transmission mode and time-domain compression factor. The execution cycle of this step is the same as the transmission frame cycle, ensuring that changes in the channel state can be tracked in real time.

[0036] The elevation angle of the satellite relative to the ground receiver is calculated by reading satellite ephemeris data. Satellite ephemeris data contains the satellite's orbital parameters, orbital time, and position information, and is obtained through a Global Navigation Satellite System (GNSS) receiver or satellite communication link. Based on the geographical coordinates of the ground receiver and the satellite's real-time position coordinates, the elevation angle of the satellite relative to the ground receiver is calculated using spherical trigonometry.

[0037] The current ground occlusion status is obtained through environmental sensing sensors at the ground receiving terminal. These sensors include devices such as cameras, millimeter-wave radar, and lidar, used to detect the distribution of obstacles around the ground receiving terminal. After the environmental data collected by the sensors is processed by image processing and target recognition algorithms, the occlusion status between the ground receiving terminal and the satellite is determined, outputting status information such as no occlusion, partial occlusion, or complete occlusion.

[0038] Based on the obtained current satellite elevation angle and ground obstruction status, the corresponding tap delay line channel parameters are extracted from the lookup table. First, the interval to which the current satellite elevation angle belongs and the type of the current ground obstruction status are determined; then, based on the combination of elevation angle interval and obstruction status, the corresponding tap delay line channel model is searched in the lookup table; finally, all tap parameters of the channel model are extracted, including the delay value and power value of each tap, for subsequent channel estimation and signal detection.

[0039] During the preamble phase of the current frame, a known pilot signal is transmitted. The receiver calculates the instantaneous signal-to-noise ratio (SNR) of the current link based on the received pilot signal. The preamble is located at the beginning of each transmission frame and contains a fixed-length known pilot symbol. The receiver performs correlation operations between the received pilot signal and the locally stored ideal pilot signal to calculate the average power of the signal and the average power of the noise. Then, the ratio of the average signal power to the average noise power is converted into a decibel value to obtain the instantaneous SNR of the current link.

[0040] Based on the estimated instantaneous signal-to-noise ratio (SNR) within a preset interval, the corresponding transmission mode and time-domain compression factor are directly mapped using a lookup table. First, the instantaneous SNR is compared with several preset SNR thresholds to determine its interval. Then, based on the current channel configuration and SNR interval, the corresponding transmission mode identifier is searched in the lookup table. Finally, the corresponding time-domain compression factor value is extracted based on the transmission mode identifier for subsequent signal generation processing.

[0041] Step S103. According to the time-domain compression factor obtained by mapping, perform time-domain compression processing on the information symbols in the delayed Doppler domain to generate a transmission signal with super Nyquist rate; send the generated transmission signal to the receiving end through the low-orbit satellite-to-ground link, and the receiving end uses a linear minimum mean square error detector to complete signal detection and demodulation.

[0042] Specifically, step S103 is executed after obtaining the corresponding time-domain compression factor, and is used to generate a super Nyquist rate transmission signal and complete the signal transmission, reception, and demodulation. This step is the core signal processing step of this application, and directly determines the transmission performance and spectral efficiency of the system.

[0043] The binary information bit stream to be transmitted is modulated and mapped onto a delayed Doppler domain grid. The delayed Doppler domain grid consists of multiple delay bins and multiple Doppler bins, with each bin corresponding to a delayed Doppler domain symbol. Orthogonal amplitude modulation (OAM) is used, with different modulation orders selected depending on the transmission mode. The Nyquist mode uses a lower modulation order to ensure transmission reliability, while the aggressive compression mode uses a higher modulation order to improve spectral efficiency.

[0044] An inverse symplectic fast Fourier transform (IFFT) is performed on the delayed Doppler domain symbols to convert them into time-frequency domain symbols. The IFFT is the core transform of orthogonal time-frequency spatial modulation, achieving the conversion between the delayed Doppler domain and the time-frequency domain through a two-dimensional Fourier transform. During the transform, an IFFT is first performed on each row of the delayed Doppler domain symbols, and then an inverse IFFT is performed on each column to obtain the time-frequency domain symbol matrix.

[0045] The time interval of the time-frequency domain symbols is adjusted based on the time-domain compression factor obtained from the mapping. The time-domain compression factor represents the ratio of the compressed symbol interval to the Nyquist symbol interval. Multiplying the time interval of the time-frequency domain symbols by the time-domain compression factor yields the compressed symbol interval. By compressing the symbol interval, more symbols can be transmitted within the same frame duration, thereby improving the system's spectral efficiency.

[0046] The adjusted time-frequency domain symbols are subjected to Heisenberg transform and root-raised cosine pulse shaping to generate a transmission signal with a super Nyquist rate. The Heisenberg transform converts the time-frequency domain symbols into a continuous-time signal, while root-raised cosine pulse shaping limits the signal bandwidth and reduces out-of-band radiation. The roll-off factor of the root-raised cosine pulse is set to 0.25, and the symbol period span is set to 8 symbol periods to balance the signal bandwidth and inter-symbol interference.

[0047] The generated super Nyquist rate transmission signal is sent to the receiving end via a low-Earth orbit (LEO) satellite-to-ground link. The transmitter's radio frequency (RF) front-end up-converts the baseband signal to the RF band, amplifies it with a power amplifier, and then transmits it to the LEO satellite via the transmitting antenna. The LEO satellite then forwards the received signal to the ground receiving terminal.

[0048] The receiving end performs a series of processes on the received signal to complete signal detection and demodulation: RF front-end processing: After receiving the RF signal through the receiving antenna, it is amplified by a low-noise amplifier and down-converted to obtain the baseband received signal; Wigner transform and sampling: The baseband received signal undergoes a Wigner transform, converting the continuous-time signal into a time-frequency domain received signal, and then samples according to the compressed symbol interval to obtain discrete time-frequency domain received symbols; Symplectic Fast Fourier Transform: The time-frequency domain received symbols undergo a Symplectic Fast Fourier Transform, converting the time-frequency domain received symbols into a delayed Doppler domain received signal; Linear minimum mean square error (LMSE) detection uses a LMS detector to equalize the received signal in the delayed Doppler domain, suppressing inter-symbol interference and noise. The LMS detector calculates the equalization coefficient matrix based on the estimated channel matrix and noise covariance matrix, and then performs equalization on the received signal in the delayed Doppler domain to obtain the estimated delayed Doppler domain symbols. Demodulation is achieved by demodulating the equalized delayed Doppler domain symbols to obtain a binary information bit stream, thus completing the signal reception and demodulation.

[0049] In some embodiments, the pre-established lookup table for channel configurations and transmission modes compatible with 3GPP standards includes: dividing the satellite elevation angle into three continuous intervals, defining ground obstruction as three states: no obstruction, partial obstruction, and complete obstruction, mapping each combination of elevation angle interval and obstruction state to a 3GPP standard tap delay line channel model, matching each channel model with a Nyquist mode, a mild compression mode, and an aggressive compression mode, assigning a unique time-domain compression factor to each transmission mode, and storing all correspondences as a directly callable lookup table.

[0050] This embodiment provides a specific implementation method for pre-establishing a channel configuration and transmission mode lookup table compatible with the 3rd Generation Partnership Project (GPP) standard.

[0051] First, the satellite elevation angle is divided into three continuous intervals: the first elevation angle interval is 0 degrees to 30 degrees, corresponding to the position of the satellite near the horizon; the second elevation angle interval is 30 degrees to 60 degrees, corresponding to the position of the satellite at a medium elevation angle; and the third elevation angle interval is 60 degrees to 90 degrees, corresponding to the position of the satellite near the zenith.

[0052] Then, ground obstruction is defined into three states: no obstruction, partial obstruction, and complete obstruction. No obstruction means there are no obstacles between the ground receiving terminal and the satellite, and the signal can propagate directly. Partial obstruction means there are some obstacles such as trees or buildings obstructing the signal between the ground receiving terminal and the satellite; the signal reaches the receiving terminal after reflection and scattering. Complete obstruction means there are completely obstructions such as tall buildings or mountains completely obstructing the signal between the ground receiving terminal and the satellite; the direct signal is blocked, and only the signal reaches the receiving terminal after multiple reflections and scattering.

[0053] Next, each combination of elevation angle range and occlusion state is mapped to the 3GLP standard tapped delay line channel model: The elevation angle is in the first elevation angle range and there is complete obstruction, which corresponds to the 3rd Generation Partnership Project non-line-of-sight tapped delay line channel model. When the elevation angle is in the second elevation angle range and there is partial obstruction, the corresponding channel model for the third generation partner program hybrid tapped delay line is used. When the elevation angle is in the third elevation angle range and there is no obstruction, it corresponds to the 3rd Generation Partnership Project line-of-sight tap delay line channel model.

[0054] For each channel model, three transmission modes are matched: Nyquist mode, mild compression mode, and aggressive compression mode, and a unique time-domain compression factor is assigned to each transmission mode: The time-domain compression factor for the Nyquist mode is set to 1; The time-domain compression factor for the mild compression mode is set to 0.85; The temporal compression factor corresponding to the aggressive compression mode is set to 0.75.

[0055] Finally, all the above correspondences are stored as a directly callable lookup table. The row index of the lookup table is a combination of elevation angle interval and occlusion status, with a total of 9 combinations; the column index is a signal-to-noise ratio interval, with a total of 3 intervals; each array element stores the transmission mode identifier and the time-domain compression factor value. The lookup table is stored in the flash memory of the computer device in binary file format and loaded into memory when the system starts, achieving a microsecond-level query response time.

[0056] This embodiment establishes a standardized lookup table structure through clear elevation angle interval division, obstruction state definition, and channel model correspondence, ensuring the accuracy and consistency of channel configuration. Simultaneously, by pre-generating the lookup table, complex calculations during transmission are avoided, significantly reducing the system's computational complexity and processing latency.

[0057] In some embodiments, the channel configuration binding satellite elevation angle and ground obstruction includes: binding the case where the elevation angle is below a first threshold and there is complete obstruction to the 3GPP non-line-of-sight tapped delay line channel model; binding the case where the elevation angle is between the first threshold and a second threshold and there is partial obstruction to the 3GPP hybrid tapped delay line channel model; and binding the case where the elevation angle is above the second threshold and there is no obstruction to the 3GPP line-of-sight tapped delay line channel model.

[0058] This embodiment provides a specific implementation method for binding channel configuration to satellite elevation angle and ground obstruction.

[0059] First, set the first elevation angle threshold to 30 degrees and the second elevation angle threshold to 60 degrees. Define the elevation angle as low elevation angle when it is below the first elevation angle threshold, the elevation angle as medium elevation angle when it is between the first and second elevation angle thresholds, and the elevation angle as high elevation angle when it is above the second elevation angle threshold.

[0060] Then, based on the combination of ground obstruction status and elevation angle status, the corresponding 3rd Generation Partnership Project tap delay line channel model is bound: When the elevation angle is below the first elevation angle threshold and complete blockage exists, it is bound to the 3rd Generation Partnership Project (GPP) non-line-of-sight tapped delay line channel model. This model contains 9 taps, with a maximum delay of 2510 nanoseconds and tap power ranging from 0 dB to -16.9 dB, and is used to simulate a non-line-of-sight channel environment with severe multipath fading. When the elevation angle is between the first and second elevation angle thresholds and there is partial obstruction, it is bound to the 3GLP-3 hybrid tapped delay line channel model. This model contains 6 taps, with a maximum delay of 710 nanoseconds and tap power ranging from 0 dB to -9.1 dB, and is used to simulate a hybrid channel environment with moderate multipath fading. When the elevation angle is above the second elevation angle threshold and there is no obstruction, it is bound to the 3rd Generation Partnership Project (GPP) line-of-sight tap delay line channel model. This model contains two taps, with a maximum delay of 30 nanoseconds, a primary diameter power of 0 dB, and a secondary diameter power of -1.5 dB, and is used to simulate a line-of-sight channel environment with strong direct signals.

[0061] This embodiment achieves precise correspondence between channel configuration and satellite elevation angle and ground obstruction status through explicit threshold settings and channel model binding rules, ensuring that the system can select the appropriate transmission mode according to the actual channel environment and balance transmission efficiency and reliability.

[0062] In some embodiments, obtaining the current satellite elevation angle and ground obstruction status before the start of each transmission frame includes: reading satellite ephemeris data to calculate the current satellite elevation angle relative to the ground receiver, obtaining the current ground obstruction status through the environmental perception sensor of the ground receiver, and sending the calculated elevation angle and the obtained obstruction status to the channel matching module.

[0063] This embodiment provides a specific implementation method for obtaining the current satellite elevation angle and ground obstruction status before the start of each transmission frame.

[0064] First, the satellite ephemeris data is read to calculate the current elevation angle of the satellite relative to the ground receiver. Satellite ephemeris data is acquired in real time by the Global Navigation Satellite System receiver, with an update frequency of 1 Hz. The ephemeris data includes the satellite's orbital elements, epoch time, and clock bias parameters. Based on the longitude, latitude, and altitude coordinates of the ground receiver, and the satellite's real-time position coordinates, the elevation angle is calculated using the following steps: Convert the geographic coordinates of the ground receiving terminal and the satellite into geocentric rectangular coordinates; Calculate the projection of the vector from the ground receiving terminal to the satellite onto the local horizontal plane of the ground receiving terminal; Calculate the angle between this vector and the local horizontal plane to obtain the satellite elevation angle.

[0065] Then, the current ground occlusion status is obtained through environmental perception sensors at the ground receiver. The environmental perception sensors employ a combination of a high-definition camera and millimeter-wave radar; the camera acquires visible light images, and the millimeter-wave radar detects the distance and outline of obstacles. The sensor data acquisition frequency is 10 Hz, consistent with the transmission frame frequency. The data processing flow is as follows: The camera captures visible light images of the current sky direction; Deep learning object detection algorithms are used to process images and identify obstacles such as buildings and trees; Millimeter-wave radar detects the distance and height of obstacles and calculates the obstruction angle of the obstacles; The occlusion angle of the obstacle is compared with the satellite elevation angle to determine the occlusion status: if the occlusion angle is greater than the satellite elevation angle, it is determined to be complete occlusion; if the occlusion angle is less than the satellite elevation angle but greater than 0, it is determined to be partial occlusion; if the occlusion angle is 0, it is determined to be unobstructed.

[0066] Finally, the calculated elevation angle and the obtained occlusion status are sent to the channel matching module for subsequent channel configuration matching and transmission mode mapping.

[0067] This embodiment achieves real-time and accurate acquisition of satellite elevation angle and ground obstruction status through the combination of global navigation satellite system and environmental perception sensors, providing reliable channel status information for adaptive transmission mode switching.

[0068] In some embodiments, matching the corresponding tap delay line channel configuration and estimating the instantaneous signal-to-noise ratio of the current link includes: extracting the corresponding tap delay line channel parameters from a lookup table based on the acquired elevation angle and occlusion status; transmitting a known pilot signal during the preamble stage of the current frame; and calculating the instantaneous signal-to-noise ratio of the current link based on the received pilot signal.

[0069] This embodiment provides a specific implementation method for matching the corresponding tap delay line channel configuration and estimating the instantaneous signal-to-noise ratio of the current link.

[0070] First, the corresponding tapped delay line channel parameters are extracted from the lookup table based on the acquired elevation angle and obstruction status. After receiving the elevation angle and obstruction status information, the channel matching module first determines the interval to which the elevation angle belongs and the type of obstruction status; then, it searches for the corresponding tapped delay line channel model in the lookup table; finally, it extracts all tap parameters of the channel model, including the delay value and power value of each tap, and stores them in the channel parameter register for subsequent channel estimation and signal detection.

[0071] Then, during the preamble stage of the current frame, a known pilot signal is transmitted, and the receiver calculates the instantaneous signal-to-noise ratio (SNR) of the current link based on the received pilot signal. The preamble length is 64 symbols, using binary phase-shift keying modulation, and the pilot sequence is a pseudo-random sequence with good autocorrelation. The specific steps for SNR estimation are as follows: The transmitter sends a known pilot sequence during the preamble phase of each transmission frame; The receiving end performs correlation calculations between the received preamble signal and the locally stored ideal pilot sequence to obtain the correlation peak value; Calculate the average power of the relevant peak values ​​as the average power of the signal; Calculate the average power of the noise after the relevant operations, and use it as the average power of the noise. The ratio of average signal power to average noise power is converted into decibels to obtain the instantaneous signal-to-noise ratio of the current link.

[0072] This embodiment uses a lookup table to quickly match the channel configuration and utilizes the preamble pilot signal to achieve accurate estimation of the instantaneous signal-to-noise ratio, providing necessary parameter support for adaptive switching of transmission modes.

[0073] In some embodiments, the step of directly mapping the corresponding transmission mode and time-domain compression factor to a lookup table based on the preset interval of the estimated instantaneous signal-to-noise ratio includes: comparing the instantaneous signal-to-noise ratio with a preset first signal-to-noise ratio threshold and a second signal-to-noise ratio threshold; if the instantaneous signal-to-noise ratio is lower than the first signal-to-noise ratio threshold, mapping to the Nyquist mode; if the instantaneous signal-to-noise ratio is between the first and second signal-to-noise ratio thresholds, mapping to the mild compression mode; if the instantaneous signal-to-noise ratio is higher than the second signal-to-noise ratio threshold, mapping to the aggressive compression mode; and extracting the time-domain compression factor of the corresponding transmission mode from the lookup table.

[0074] This embodiment provides a specific implementation method for mapping transmission modes and time-domain compression factors based on instantaneous signal-to-noise ratio intervals using a lookup table.

[0075] First, set the first signal-to-noise ratio (SNR) threshold to 10 dB and the second SNR threshold to 20 dB. Divide the instantaneous SNR into three intervals: Low signal-to-noise ratio range: The instantaneous signal-to-noise ratio is lower than the first signal-to-noise ratio threshold; Medium signal-to-noise ratio range: The instantaneous signal-to-noise ratio is between the first signal-to-noise ratio threshold and the second signal-to-noise ratio threshold; High signal-to-noise ratio range: The instantaneous signal-to-noise ratio is higher than the second signal-to-noise ratio threshold.

[0076] Then, the estimated instantaneous signal-to-noise ratio is compared with the preset first and second signal-to-noise ratio thresholds to determine the interval to which the instantaneous signal-to-noise ratio belongs: If the instantaneous signal-to-noise ratio (SNR) is lower than the first SNR threshold, it is mapped to the Nyquist mode. This mode uses orthogonal transmission, eliminates inter-symbol interference, and ensures transmission reliability under low SNR conditions. If the instantaneous signal-to-noise ratio (SNR) is between the first and second SNR thresholds, it is mapped to a mild compression mode. This mode introduces mild inter-symbol interference, improving spectral efficiency by approximately 15% while ensuring transmission reliability. If the instantaneous signal-to-noise ratio (SNR) exceeds the second SNR threshold, it is mapped to an aggressive compression mode. This mode introduces larger inter-symbol interference, improving spectral efficiency by approximately 33% under high SNR conditions.

[0077] Finally, the time-domain compression factor value corresponding to the transmission mode is extracted from the lookup table and sent to the signal generation module for subsequent time-domain compression processing.

[0078] This embodiment achieves adaptive switching of transmission modes through explicit signal-to-noise ratio threshold settings and transmission mode mapping logic. It can dynamically balance transmission efficiency and reliability according to the current channel conditions, and maximize the effective throughput of the entire satellite transit cycle.

[0079] In some embodiments, the time-domain compression factor obtained by mapping includes: setting the time-domain compression factor corresponding to the Nyquist mode to 1, setting the time-domain compression factor corresponding to the mild compression mode to a fixed value between 0.8 and 0.9, and setting the time-domain compression factor corresponding to the aggressive compression mode to a fixed value between 0.7 and 0.8.

[0080] This embodiment provides a specific method for setting the time-domain compression factor for three transmission modes.

[0081] Based on the channel characteristics of the LEO satellite-to-ground link and the performance of the linear minimum mean square error detector, the time-domain compression factors corresponding to the three transmission modes are set to fixed values: The time-domain compression factor corresponding to the Nyquist mode is set to 1. In this mode, the symbol interval is equal to the Nyquist symbol interval, there is no inter-symbol interference, and the transmission reliability is the highest, but the spectral efficiency is the lowest. The time-domain compression factor for the mild compression mode is set to 0.85. In this mode, the symbol spacing is compressed to 85% of the Nyquist symbol spacing, introducing less inter-symbol interference, which is effectively suppressed by the linear minimum mean square error detector. While maintaining a bit error rate below 10 to the power of -3, the spectral efficiency is improved by approximately 17.6%. The time-domain compression factor corresponding to the aggressive compression mode is set to 0.75. In this mode, the symbol interval is compressed to 75% of the Nyquist symbol interval, which introduces a large amount of inter-symbol interference. However, under high signal-to-noise ratio conditions, the linear minimum mean square error detector can still control the bit error rate below 10 to the power of -3, and the spectral efficiency is improved by about 33.3%.

[0082] This embodiment maximizes spectral efficiency under different channel conditions while ensuring transmission reliability by optimizing the time-domain compression factor setting, thus achieving the best balance between transmission efficiency and reliability.

[0083] In some embodiments, the step of performing time-domain compression processing on information symbols in the delayed Doppler domain to generate a transmission signal with a super Nyquist rate includes: mapping the information symbols to be transmitted to a delayed Doppler domain grid; performing an inverse symplectic fast Fourier transform on the delayed Doppler domain symbols to obtain time-frequency domain symbols; adjusting the time interval of the time-frequency domain symbols according to the time-domain compression factor obtained from the mapping; and performing a Heisenberg transform and root-raised cosine pulse shaping on the adjusted time-frequency domain symbols to generate a transmission signal with a super Nyquist rate.

[0084] This embodiment provides a specific implementation method for performing time-domain compression processing on delayed Doppler domain information symbols to generate a super Nyquist rate transmission signal.

[0085] First, the information symbols to be transmitted are mapped onto a delayed Doppler domain grid. The delayed Doppler domain grid is 32×32 in size, containing 32 delay bins and 32 Doppler bins. The binary information bit stream to be transmitted, after orthogonal amplitude modulation (QAM), is mapped into each delayed Doppler domain bin. The Nyquist mode uses 4-quadrometric amplitude modulation (4QAM), the mild compression mode uses 16-quadrometric amplitude modulation (16QAM), and the aggressive compression mode uses 64-quadrometric amplitude modulation (64QAM).

[0086] Then, the time-frequency domain symbols are obtained by performing an inverse symplectic fast Fourier transform on the delayed Doppler domain symbols. The specific steps of the inverse symplectic fast Fourier transform are as follows: Perform a fast Fourier transform on each row of the delayed Doppler domain symbol matrix, with a transform length of 32; Perform an inverse fast Fourier transform on each column of the transformed matrix, with a transform length of 32; A time-frequency domain symbol matrix of size 32×32 is obtained.

[0087] Next, the time interval between time-frequency symbols is adjusted according to the time-domain compression factor obtained from the mapping. The Nyquist symbol interval is 66.67 microseconds, corresponding to a subcarrier interval of 15 kHz. If the current transmission mode is mild compression mode with a time-domain compression factor of 0.85, the compressed symbol interval is 66.67 microseconds multiplied by 0.85, which equals 56.67 microseconds; if the current transmission mode is aggressive compression mode with a time-domain compression factor of 0.75, the compressed symbol interval is 66.67 microseconds multiplied by 0.75, which equals 50 microseconds.

[0088] Then, the adjusted time-frequency domain symbols are subjected to Heisenberg transform and root-raised cosine pulse shaping. The Heisenberg transform converts the time-frequency domain symbols into continuous-time signals, and each time-frequency domain symbol is multiplied by its corresponding basis function and then superimposed. The root-raised cosine pulse has a roll-off factor of 0.25 and a symbol period span of 8 symbol periods, meaning that the duration of each pulse is 8 times the compressed symbol interval.

[0089] Finally, a transmission signal with a super Nyquist rate is generated. The pulse-shaped continuous-time signal is then converted from digital to analog to obtain an analog baseband signal, which is used by the RF front-end for up-conversion and transmission.

[0090] This embodiment details the generation process of the super Nyquist orthogonal time-frequency spatial signal. Through optimized transformation parameters and pulse shaping settings, the spectral characteristics and transmission performance of the signal are guaranteed.

[0091] In some embodiments, the step of sending the generated transmission signal to the receiving end via a low-Earth orbit satellite-to-ground link, and the receiving end using a linear minimum mean square error detector to complete signal detection and demodulation, includes: the transmitting end sending the generated transmission signal to the ground receiving end via a low-Earth orbit satellite-to-ground link; the receiving end performing Wigner transform and sampling on the received signal to obtain a time-frequency domain received signal; performing a symptotic fast Fourier transform on the time-frequency domain received signal to obtain a delayed Doppler domain received signal; using a linear minimum mean square error detector to perform equalization processing on the delayed Doppler domain received signal; and demodulating the equalized signal to obtain the original information symbols.

[0092] This embodiment provides a specific implementation method for using a linear minimum mean square error detector at the receiving end to complete signal detection and demodulation.

[0093] First, the transmitter sends the generated transmission signal to the ground receiver via a low-Earth orbit (LEO) satellite-to-ground link. The transmitter's radio frequency (RF) front-end up-converts the analog baseband signal to the Ka band with a center frequency of 28 GHz. After amplification by a power amplifier, the signal is transmitted to the LEO satellite via a parabolic antenna. The LEO satellite operates in transparent relay mode, amplifying the received signal and relaying it to the ground receiving terminal.

[0094] Then, the receiving end processes the received signal, and the specific steps are as follows: RF front-end processing: After the parabolic antenna of the ground receiving terminal receives the RF signal, it is amplified by a low-noise amplifier with a noise figure of 2 dB, and then down-converted to the baseband frequency band to obtain the analog baseband received signal. Wigner Transform and Sampling: The analog baseband received signal is subjected to a Wigner transform, converting the continuous-time signal into a time-frequency domain representation. The time resolution of the Wigner transform is equal to the compressed symbol interval, and the frequency resolution is equal to the subcarrier interval of 15 kHz. The Wigner transform result is sampled according to the compressed symbol interval to obtain a discrete time-frequency domain received symbol matrix of size 32×32. Symplectic Fast Fourier Transform (SFT): This transforms the time-frequency domain received symbol matrix into a delayed Doppler domain received signal by performing a symplectic fast Fourier transform. The specific steps of the symplectic fast Fourier transform are as follows: First, perform a fast Fourier transform on each column of the time-frequency domain symbol matrix; then, perform an inverse fast Fourier transform on each row to obtain the delayed Doppler domain received signal matrix. Linear minimum mean square error (LMSE) detection: A LMSE detector is used to equalize the received signal in the delayed Doppler domain. First, the channel matrix in the delayed Doppler domain is constructed based on the estimated tapped delay line channel parameters. Then, the noise covariance matrix is ​​constructed based on the noise power estimation results. Next, the LMSE equalization coefficient matrix is ​​calculated by multiplying the channel matrix by its conjugate transpose, the channel matrix plus the inverse of the noise covariance matrix, and then multiplying by the conjugate transpose of the channel matrix. Finally, the received signal matrix in the delayed Doppler domain is multiplied by the equalization coefficient matrix to obtain the estimated symbol matrix in the delayed Doppler domain. Demodulation is achieved by demodulating the estimated delayed Doppler domain symbol matrix and mapping each delayed Doppler domain symbol into a binary information bit stream according to the modulation scheme corresponding to the current transmission mode, thus completing the signal reception and demodulation.

[0095] This embodiment details the signal processing flow at the receiver, effectively suppressing inter-symbol interference introduced by super Nyquist transmission through a linear minimum mean square error detector, thus ensuring the transmission reliability of the system.

[0096] In some embodiments, the method further includes: establishing a sliding window of fixed length, recording the satellite elevation angle, ground obstruction status, instantaneous signal-to-noise ratio and corresponding transmission mode of all transmission frames within the sliding window, using a linear regression algorithm to predict the instantaneous signal-to-noise ratio of the next transmission frame based on historical data within the sliding window, mapping the transmission mode and time-domain compression factor of the next transmission frame in advance from a lookup table based on the predicted instantaneous signal-to-noise ratio, and immediately switching to the predicted transmission mode for signal processing of the next transmission frame after the current transmission frame ends.

[0097] This embodiment provides a specific implementation method for channel prediction and early switching of transmission modes based on sliding window and linear regression algorithms.

[0098] First, a sliding window of length 10 is established to record the channel state information and transmission mode of historical transmission frames. The sliding window uses a first-in, first-out (FIFO) structure; after each new transmission frame ends, the latest channel state information and transmission mode are added to the end of the window, while the historical data at the beginning of the window is deleted. The information recorded in the sliding window includes: satellite elevation angle, ground obstruction status, instantaneous signal-to-noise ratio, and corresponding transmission mode for each transmission frame.

[0099] Then, a linear regression algorithm is used to predict the instantaneous signal-to-noise ratio (SNR) of the next transmission frame based on historical data within the sliding window. The linear regression model uses the transmission frame number as the independent variable and the instantaneous SNR as the dependent variable. Using 10 sets of historical data within the sliding window, the coefficients of the linear regression equation are obtained by fitting the data using the least squares method. Then, the sequence number of the next transmission frame is substituted into the linear regression equation to obtain the predicted instantaneous SNR value for the next transmission frame.

[0100] Next, the transmission mode and time-domain compression factor of the next transmission frame are pre-mapped from the lookup table based on the predicted instantaneous signal-to-noise ratio (SNR). The predicted instantaneous SNR is compared with a preset SNR threshold to determine the interval to which the predicted SNR belongs. Then, based on the current channel configuration and the predicted SNR interval, the corresponding transmission mode and time-domain compression factor are looked up in the lookup table.

[0101] Finally, immediately after the current transmission frame ends, the system switches to the predicted transmission mode for signal processing of the next transmission frame. Preemptive mode switching avoids transmission mode switching lag caused by rapid changes in channel conditions and prevents performance degradation due to outdated channel conditions.

[0102] This embodiment further enhances the system's adaptability to rapidly changing channels by predicting channels and switching transmission modes in advance, effectively overcoming the channel aging effect and ensuring stable transmission in high-mobility low-Earth orbit satellite-to-ground links.

[0103] Please see Figure 3 As shown, Figure 3This is a schematic diagram of the structure of an FTN-OTFS communication system 200 for high-mobility LEO satellite-to-ground links provided in this application embodiment. The FTN-OTFS communication system 200 for high-mobility LEO satellite-to-ground links is used to execute the steps of the FTN-OTFS communication method for high-mobility LEO satellite-to-ground links shown in the above embodiments. The FTN-OTFS communication system 200 for high-mobility LEO satellite-to-ground links can be a single server or a server cluster, or it can be a terminal, such as a handheld terminal, a laptop computer, a wearable device, or a robot.

[0104] like Figure 3 As shown, the FTN-OTFS communication system 200 for high-mobility LEO satellite-to-ground links includes: The factor acquisition unit 201 is used to pre-establish a lookup table of channel configuration and transmission mode compatible with 3GPP standards. The channel configuration is bound to the satellite elevation angle and ground obstruction. The transmission modes include Nyquist mode, mild compression mode and aggressive compression mode, and each mode corresponds to a unique time-domain compression factor. The status acquisition unit is used to acquire the current satellite elevation angle and ground obstruction status before the start of each transmission frame, match the corresponding tap delay line channel configuration, and estimate the instantaneous signal-to-noise ratio of the current link. Based on the preset interval in which the estimated instantaneous signal-to-noise ratio is located, the corresponding transmission mode and time-domain compression factor are directly mapped through a lookup table. The compression processing unit is used to perform time-domain compression processing on the information symbols in the delayed Doppler domain according to the time-domain compression factor obtained by mapping, and generate a transmission signal with a super Nyquist rate; the generated transmission signal is sent to the receiving end through the low-orbit satellite-to-ground link, and the receiving end uses a linear minimum mean square error detector to complete the signal detection and demodulation.

[0105] In some embodiments, the pre-established lookup table for channel configurations and transmission modes compatible with 3GPP standards includes: dividing the satellite elevation angle into three continuous intervals, defining ground obstruction as three states: no obstruction, partial obstruction, and complete obstruction, mapping each combination of elevation angle interval and obstruction state to a 3GPP standard tap delay line channel model, matching each channel model with a Nyquist mode, a mild compression mode, and an aggressive compression mode, assigning a unique time-domain compression factor to each transmission mode, and storing all correspondences as a directly callable lookup table.

[0106] In some embodiments, the channel configuration binding satellite elevation angle and ground obstruction includes: binding the case where the elevation angle is below a first threshold and there is complete obstruction to the 3GPP non-line-of-sight tapped delay line channel model; binding the case where the elevation angle is between the first threshold and a second threshold and there is partial obstruction to the 3GPP hybrid tapped delay line channel model; and binding the case where the elevation angle is above the second threshold and there is no obstruction to the 3GPP line-of-sight tapped delay line channel model.

[0107] In some embodiments, obtaining the current satellite elevation angle and ground obstruction status before the start of each transmission frame includes: reading satellite ephemeris data to calculate the current satellite elevation angle relative to the ground receiver, obtaining the current ground obstruction status through the environmental perception sensor of the ground receiver, and sending the calculated elevation angle and the obtained obstruction status to the channel matching module.

[0108] In some embodiments, matching the corresponding tap delay line channel configuration and estimating the instantaneous signal-to-noise ratio of the current link includes: extracting the corresponding tap delay line channel parameters from a lookup table based on the acquired elevation angle and occlusion status; transmitting a known pilot signal during the preamble stage of the current frame; and calculating the instantaneous signal-to-noise ratio of the current link based on the received pilot signal.

[0109] In some embodiments, the step of directly mapping the corresponding transmission mode and time-domain compression factor to a lookup table based on the preset interval of the estimated instantaneous signal-to-noise ratio includes: comparing the instantaneous signal-to-noise ratio with a preset first signal-to-noise ratio threshold and a second signal-to-noise ratio threshold; if the instantaneous signal-to-noise ratio is lower than the first signal-to-noise ratio threshold, mapping to the Nyquist mode; if the instantaneous signal-to-noise ratio is between the first and second signal-to-noise ratio thresholds, mapping to the mild compression mode; if the instantaneous signal-to-noise ratio is higher than the second signal-to-noise ratio threshold, mapping to the aggressive compression mode; and extracting the time-domain compression factor of the corresponding transmission mode from the lookup table.

[0110] In some embodiments, the time-domain compression factor obtained by mapping includes: setting the time-domain compression factor corresponding to the Nyquist mode to 1, setting the time-domain compression factor corresponding to the mild compression mode to a fixed value between 0.8 and 0.9, and setting the time-domain compression factor corresponding to the aggressive compression mode to a fixed value between 0.7 and 0.8.

[0111] In some embodiments, the step of performing time-domain compression processing on information symbols in the delayed Doppler domain to generate a transmission signal with a super Nyquist rate includes: mapping the information symbols to be transmitted to a delayed Doppler domain grid; performing an inverse symplectic fast Fourier transform on the delayed Doppler domain symbols to obtain time-frequency domain symbols; adjusting the time interval of the time-frequency domain symbols according to the time-domain compression factor obtained from the mapping; and performing a Heisenberg transform and root-raised cosine pulse shaping on the adjusted time-frequency domain symbols to generate a transmission signal with a super Nyquist rate.

[0112] In some embodiments, the step of sending the generated transmission signal to the receiving end via a low-Earth orbit satellite-to-ground link, and the receiving end using a linear minimum mean square error detector to complete signal detection and demodulation, includes: the transmitting end sending the generated transmission signal to the ground receiving end via a low-Earth orbit satellite-to-ground link; the receiving end performing Wigner transform and sampling on the received signal to obtain a time-frequency domain received signal; performing a symptotic fast Fourier transform on the time-frequency domain received signal to obtain a delayed Doppler domain received signal; using a linear minimum mean square error detector to perform equalization processing on the delayed Doppler domain received signal; and demodulating the equalized signal to obtain the original information symbols.

[0113] In some embodiments, the method further includes: establishing a sliding window of fixed length, recording the satellite elevation angle, ground obstruction status, instantaneous signal-to-noise ratio and corresponding transmission mode of all transmission frames within the sliding window, using a linear regression algorithm to predict the instantaneous signal-to-noise ratio of the next transmission frame based on historical data within the sliding window, mapping the transmission mode and time-domain compression factor of the next transmission frame in advance from a lookup table based on the predicted instantaneous signal-to-noise ratio, and immediately switching to the predicted transmission mode for signal processing of the next transmission frame after the current transmission frame ends.

[0114] It should be noted that those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process of the FTN-OTFS communication system and its modules for high-mobility LEO satellite-to-ground links described above can be found in the corresponding contents of the various embodiments of the FTN-OTFS communication method for high-mobility LEO satellite-to-ground links, and will not be repeated here.

[0115] The aforementioned FTN-OTFS communication method for high-mobility LEO satellite-to-ground links can be implemented as a computer program, which can be used in, for example... Figure 3 It runs on the device shown.

[0116] Please see Figure 4 , Figure 4 This is a schematic block diagram of the structure of a computer device provided in an embodiment of this application. The computer device includes a processor, a memory, and a network interface connected via a device bus, wherein the memory may include a storage medium and internal memory.

[0117] The storage medium can store operating devices and computer programs. The computer program includes program instructions that, when executed, cause the processor to perform any FTN-OTFS communication method for high-mobility LEO satellite-to-ground links.

[0118] The processor provides computing and control capabilities, supporting the operation of the entire computer device.

[0119] The internal memory provides an environment for the execution of computer programs in non-volatile storage media. When the computer program is executed by the processor, it enables the processor to execute any FTN-OTFS communication method for high-mobility LEO satellite-to-ground links.

[0120] This network interface is used for network communication, such as sending assigned tasks. Those skilled in the art will understand that... Figure 4 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the terminal to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0121] It should be understood that the processor can be a Central Processing Unit (CPU), but it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. Among these, a general-purpose processor can be a microprocessor or any conventional processor.

[0122] In one embodiment, the processor is configured to run a computer program stored in memory to perform the following steps: A lookup table for the correspondence between channel configurations and transmission modes compatible with 3GPP standards is pre-established. The channel configuration is bound to the satellite elevation angle and ground obstruction. The transmission modes include Nyquist mode, mild compression mode and aggressive compression mode, and each mode corresponds to a unique time-domain compression factor. Before the start of each transmission frame, the current satellite elevation angle and ground obstruction status are obtained, the corresponding tap delay line channel configuration is matched, and the instantaneous signal-to-noise ratio of the current link is estimated. Based on the preset interval in which the estimated instantaneous signal-to-noise ratio is located, the corresponding transmission mode and time-domain compression factor are directly mapped through a lookup table. Based on the time-domain compression factor obtained from the mapping, the information symbols in the delayed Doppler domain are compressed in the time domain to generate a transmission signal with a super Nyquist rate. The generated transmission signal is then sent to the receiving end via a low-Earth orbit satellite-to-ground link. The receiving end uses a linear minimum mean square error detector to complete signal detection and demodulation.

[0123] In some embodiments, the pre-established lookup table for channel configurations and transmission modes compatible with 3GPP standards includes: dividing the satellite elevation angle into three continuous intervals, defining ground obstruction as three states: no obstruction, partial obstruction, and complete obstruction, mapping each combination of elevation angle interval and obstruction state to a 3GPP standard tap delay line channel model, matching each channel model with a Nyquist mode, a mild compression mode, and an aggressive compression mode, assigning a unique time-domain compression factor to each transmission mode, and storing all correspondences as a directly callable lookup table.

[0124] In some embodiments, the channel configuration binding satellite elevation angle and ground obstruction includes: binding the case where the elevation angle is below a first threshold and there is complete obstruction to the 3GPP non-line-of-sight tapped delay line channel model; binding the case where the elevation angle is between the first threshold and a second threshold and there is partial obstruction to the 3GPP hybrid tapped delay line channel model; and binding the case where the elevation angle is above the second threshold and there is no obstruction to the 3GPP line-of-sight tapped delay line channel model.

[0125] In some embodiments, obtaining the current satellite elevation angle and ground obstruction status before the start of each transmission frame includes: reading satellite ephemeris data to calculate the current satellite elevation angle relative to the ground receiver, obtaining the current ground obstruction status through the environmental perception sensor of the ground receiver, and sending the calculated elevation angle and the obtained obstruction status to the channel matching module.

[0126] In some embodiments, matching the corresponding tap delay line channel configuration and estimating the instantaneous signal-to-noise ratio of the current link includes: extracting the corresponding tap delay line channel parameters from a lookup table based on the acquired elevation angle and occlusion status; transmitting a known pilot signal during the preamble stage of the current frame; and calculating the instantaneous signal-to-noise ratio of the current link based on the received pilot signal.

[0127] In some embodiments, the step of directly mapping the corresponding transmission mode and time-domain compression factor to a lookup table based on the preset interval of the estimated instantaneous signal-to-noise ratio includes: comparing the instantaneous signal-to-noise ratio with a preset first signal-to-noise ratio threshold and a second signal-to-noise ratio threshold; if the instantaneous signal-to-noise ratio is lower than the first signal-to-noise ratio threshold, mapping to the Nyquist mode; if the instantaneous signal-to-noise ratio is between the first and second signal-to-noise ratio thresholds, mapping to the mild compression mode; if the instantaneous signal-to-noise ratio is higher than the second signal-to-noise ratio threshold, mapping to the aggressive compression mode; and extracting the time-domain compression factor of the corresponding transmission mode from the lookup table.

[0128] In some embodiments, the time-domain compression factor obtained by mapping includes: setting the time-domain compression factor corresponding to the Nyquist mode to 1, setting the time-domain compression factor corresponding to the mild compression mode to a fixed value between 0.8 and 0.9, and setting the time-domain compression factor corresponding to the aggressive compression mode to a fixed value between 0.7 and 0.8.

[0129] In some embodiments, the step of performing time-domain compression processing on information symbols in the delayed Doppler domain to generate a transmission signal with a super Nyquist rate includes: mapping the information symbols to be transmitted to a delayed Doppler domain grid; performing an inverse symplectic fast Fourier transform on the delayed Doppler domain symbols to obtain time-frequency domain symbols; adjusting the time interval of the time-frequency domain symbols according to the time-domain compression factor obtained from the mapping; and performing a Heisenberg transform and root-raised cosine pulse shaping on the adjusted time-frequency domain symbols to generate a transmission signal with a super Nyquist rate.

[0130] In some embodiments, the step of sending the generated transmission signal to the receiving end via a low-Earth orbit satellite-to-ground link, and the receiving end using a linear minimum mean square error detector to complete signal detection and demodulation, includes: the transmitting end sending the generated transmission signal to the ground receiving end via a low-Earth orbit satellite-to-ground link; the receiving end performing Wigner transform and sampling on the received signal to obtain a time-frequency domain received signal; performing a symptotic fast Fourier transform on the time-frequency domain received signal to obtain a delayed Doppler domain received signal; using a linear minimum mean square error detector to perform equalization processing on the delayed Doppler domain received signal; and demodulating the equalized signal to obtain the original information symbols.

[0131] In some embodiments, the method further includes: establishing a sliding window of fixed length, recording the satellite elevation angle, ground obstruction status, instantaneous signal-to-noise ratio and corresponding transmission mode of all transmission frames within the sliding window, using a linear regression algorithm to predict the instantaneous signal-to-noise ratio of the next transmission frame based on historical data within the sliding window, mapping the transmission mode and time-domain compression factor of the next transmission frame in advance from a lookup table based on the predicted instantaneous signal-to-noise ratio, and immediately switching to the predicted transmission mode for signal processing of the next transmission frame after the current transmission frame ends.

[0132] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, causes the processor to implement the steps of the FTN-OTFS communication method for high-mobility LEO satellite-to-ground links as provided in any embodiment of this application.

[0133] The computer-readable storage medium may be an internal storage unit of the computer device described in the foregoing embodiments, such as the hard disk or memory of the computer device. The computer-readable storage medium may also be an external storage device of the computer device, such as a plug-in hard disk, SmartMedia Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the computer device.

[0134] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A FTN-OTFS communication method for high-mobility LEO satellite-to-ground links, characterized in that, include: A lookup table for the correspondence between channel configurations and transmission modes compatible with 3GPP standards is pre-established. The channel configuration is bound to the satellite elevation angle and ground obstruction. The transmission modes include Nyquist mode, mild compression mode and aggressive compression mode, and each mode corresponds to a unique time-domain compression factor. Before the start of each transmission frame, the current satellite elevation angle and ground obstruction status are obtained, the corresponding tap delay line channel configuration is matched, and the instantaneous signal-to-noise ratio of the current link is estimated. Based on the preset interval in which the estimated instantaneous signal-to-noise ratio is located, the corresponding transmission mode and time-domain compression factor are directly mapped through a lookup table. Based on the time-domain compression factor obtained from the mapping, the information symbols in the delayed Doppler domain are compressed in the time domain to generate a transmission signal with a super Nyquist rate. The generated transmission signal is then sent to the receiving end via a low-Earth orbit satellite-to-ground link. The receiving end uses a linear minimum mean square error detector to complete signal detection and demodulation.

2. The method according to claim 1, characterized in that, The pre-established lookup table for channel configurations and transmission modes compatible with 3GPP standards includes: The satellite elevation angle is divided into three continuous intervals, and ground obstruction is defined as three states: no obstruction, partial obstruction, and complete obstruction. Each combination of elevation angle range and obstruction state is mapped to the 3GPP standard tapped delay line channel model, and Nyquist mode, mild compression mode and aggressive compression mode are matched for each channel model respectively. Assign a unique time-domain compression factor to each transmission mode and store all correspondences as a lookup table that can be directly accessed.

3. The method according to claim 1, characterized in that, The channel configuration is tied to satellite elevation angle and ground obstruction conditions, including: The case of elevation angle below the first threshold and complete occlusion is bound to the 3GPP non-line-of-sight tapped delay line channel model, and the case of elevation angle between the first threshold and the second threshold and partial occlusion is bound to the 3GPP hybrid tapped delay line channel model. The case where the elevation angle is above the second threshold and there is no obstruction is bound to the 3GPP line-of-sight tap delay line channel model.

4. The method according to claim 1, characterized in that, The step of obtaining the current satellite elevation angle and ground obstruction status before the start of each transmission frame includes: Read satellite ephemeris data to calculate the current satellite elevation angle relative to the ground receiver; The current ground occlusion status is obtained through environmental sensing sensors at the ground receiver. The calculated elevation angle and the obtained occlusion status are sent to the channel matching module.

5. The method according to claim 4, characterized in that, The matching of the corresponding tap delay line channel configuration, and the estimation of the instantaneous signal-to-noise ratio of the current link, include: Based on the obtained elevation angle and obstruction status, the corresponding tap delay line channel parameters are extracted from the lookup table; During the preamble phase of the current frame, a known pilot signal is transmitted, and the receiver calculates the instantaneous signal-to-noise ratio of the current link based on the received pilot signal.

6. The method according to claim 1, characterized in that, The step of directly mapping the corresponding transmission mode and time-domain compression factor based on the preset interval of the estimated instantaneous signal-to-noise ratio through a lookup table includes: The instantaneous signal-to-noise ratio (SNR) is compared with a preset first SNR threshold and a second SNR threshold. If the instantaneous SNR is lower than the first SNR threshold, it is mapped to the Nyquist mode. If the instantaneous SNR is between the first and second SNR thresholds, it is mapped to the mild compression mode. If the instantaneous SNR is higher than the second SNR threshold, it is mapped to the aggressive compression mode. The time-domain compression factor of the corresponding transmission mode is extracted from the lookup table.

7. The method according to claim 1, characterized in that, The time-domain compression factor obtained according to the mapping includes: Set the time-domain compression factor corresponding to the Nyquist mode to 1; Set the time-domain compression factor corresponding to the mild compression mode to a fixed value between 0.8 and 0.9; Set the temporal compression factor corresponding to the aggressive compression mode to a fixed value between 0.7 and 0.

8.

8. The method according to claim 1, characterized in that, The step of performing time-domain compression processing on the information symbols in the delayed Doppler domain to generate a transmission signal with a super Nyquist rate includes: The information symbols to be transmitted are mapped to the delayed Doppler domain grid, and the time-frequency domain symbols are obtained by performing an inverse symplectic fast Fourier transform on the delayed Doppler domain symbols. The time interval of the time-frequency domain symbols is adjusted according to the time-domain compression factor obtained by mapping. The adjusted time-frequency domain symbols are then subjected to Heisenberg transform and root raised cosine pulse shaping to generate a transmission signal with a super Nyquist rate.

9. The method according to claim 1, characterized in that, The generated transmission signal is sent to the receiving end via a low-Earth orbit satellite-to-ground link. The receiving end uses a linear minimum mean square error detector to complete signal detection and demodulation, including: The generated transmission signal is sent from the transmitter to the ground receiver via a low-Earth orbit satellite-to-ground link. The receiver performs Wigner transform and sampling on the received signal to obtain the time-frequency domain received signal. The delayed Doppler domain received signal is obtained by performing a symptotic fast Fourier transform on the time-frequency domain received signal; A linear minimum mean square error detector is used to perform equalization processing on the received signal in the delayed Doppler domain, and the equalized signal is demodulated to obtain the original information symbols.

10. The method according to claim 1, characterized in that, The method further includes: Establish a sliding window of fixed length and record the satellite elevation angle, ground obstruction status, instantaneous signal-to-noise ratio and corresponding transmission mode of all transmission frames within the sliding window; A linear regression algorithm is used to predict the instantaneous signal-to-noise ratio of the next transmission frame based on historical data within a sliding window. Based on the predicted instantaneous signal-to-noise ratio, the transmission mode and time-domain compression factor of the next transmission frame are mapped in advance from a lookup table. Immediately after the current transmission frame ends, switch to the predicted transmission mode to process the signal for the next transmission frame.

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