Time synchronization method for satellite communication system

Abstract

The application discloses a time synchronization method suitable for a satellite communication system, comprising the following steps: analyzing a forward broadcast signal to obtain a network clock reference time; constructing a geometric prediction handle based on satellite orbit data, and predicting a one-way propagation delay between a terminal and a satellite by using the geometric prediction handle; estimating a processing delay of the terminal according to a symbol rate of the terminal and an equipment working condition, and referring to delay calibration data; fusing the network clock reference time and the processing delay estimation to synthesize a terminal local time; and calculating a sending time of a return link based on the local time and the propagation delay prediction. The application can improve the synchronization accuracy to the microsecond level, accelerate the convergence speed in a dynamic scene, support adaptive compression of a guard interval, and effectively improve the stability and spectrum efficiency of the satellite communication system.

Description

Technical Field

[0001] This application relates to the field of satellite communications, specifically to a time synchronization method suitable for satellite communication systems. Background Technology

[0002] With the surge in global demand for broadband communication, high-throughput satellite communication systems have become a core direction for industrial development. The global market size is projected to reach $18-22 billion by 2030, with a compound annual growth rate exceeding 15%. High-throughput satellite systems have achieved a leap in single-satellite capacity from tens of Gbps to over 1 Tbps through the adoption of technologies such as multi-beamforming and frequency reuse. To match this trend, user terminals are also developing towards miniaturization and phased array architecture. In the complex network composed of hundreds of finely managed, rapidly switching point beams, establishing a high-precision terminal time synchronization mechanism is crucial to ensure accurate time slot alignment of the return link signal at the satellite receiver, avoid interference between users, and maximize system spectral efficiency. This mechanism aims to improve synchronization accuracy from the traditional millisecond level to the microsecond level, possessing significant research and application value.

[0003] Currently, time synchronization methods in satellite communication systems are typically based on a time synchronization-range measurement-compensation framework. Specifically, the master station obtains a unified network time reference (such as a Network Clock Reference, NCR) from a high-precision clock source like GPS and broadcasts it to all subordinate terminals via the forward link. Upon receiving this time reference, each terminal performs geometric calculations based on its own geographical location and satellite orbital ephemeris data to estimate the one-way propagation delay of the signal. Simultaneously, the terminal compensates for its inherent processing delay by referring to pre-stored calibration data and the symbol rate used by the current service. The terminal then integrates network time, propagation delay, and processing delay to calculate the precise transmission time of the return link burst. To address variations in propagation delay, the system typically reserves a fixed guard interval (GP) in the time slot design. The size of this interval is set based on the maximum delay difference within the beam coverage area; for example, a spot beam covering 200 kilometers has a maximum delay difference of approximately 667 microseconds.

[0004] However, existing technologies face several challenges when dealing with the highly dynamic and efficient modern high-throughput satellite systems, leading to slow system synchronization convergence, significant waste of guard interval resources, and limitations on overall performance improvement. In dynamic scenarios such as rapid beam switching, the group delay of the terminal processing link experiences a step-like nonlinear jump due to instantaneous changes in the symbol rate. Traditional static calibration tables cannot accurately model this transient effect, resulting in significant transient errors in the synchronization loop after switching, requiring a considerable amount of time to reconverge. For low-Earth orbit satellite scenarios with high-speed relative motion, existing methods fail to adequately account for real-time path changes caused by the Doppler effect within frames when estimating propagation delay. This forces the system to adopt overly conservative fixed guard intervals to absorb worst-case delay drift, resulting in a continuous waste of spectrum resources. Furthermore, even if the aforementioned delay estimation problems are improved, the overall synchronization accuracy is limited by the sampling clock resolution of the terminal digital system. Conventional time synthesis methods cannot perform fine-tuning at sub-sampling periods, setting an insurmountable quantization lower limit for synchronization errors and hindering breakthroughs in synchronization accuracy. Summary of the Invention

[0005] The purpose of this invention is to provide a time synchronization method suitable for satellite communication systems, so as to solve the above-mentioned problems existing in the prior art.

[0006] According to one aspect of this application, a time synchronization method suitable for satellite communication systems includes:

[0007] Analyze the forward broadcast signal to obtain the network clock reference time;

[0008] A geometric prediction handle is constructed based on satellite orbit data;

[0009] Using a geometric prediction handle, predict the one-way propagation delay between the terminal and the satellite;

[0010] Based on the terminal's symbol rate and equipment operating conditions, and referring to delay calibration data, the terminal's processing delay is estimated;

[0011] The network clock reference time and processing latency estimate are combined to synthesize the terminal's local time;

[0012] Based on the terminal's local time and one-way propagation delay prediction, and corrected according to the non-reciprocal bias, the transmission time of the return link is calculated.

[0013] According to one possible implementation of one aspect of this application, the network clock reference time and processing delay estimate are fused to synthesize the terminal's local time, including:

[0014] Integrate network clock reference time with processing latency estimation to generate a baseline local time;

[0015] Based on the one-way propagation delay prediction, a fractional delay control amount is determined for the baseline local time;

[0016] The fractional delay control quantity is processed by a variable fractional delay filter to generate a fractional delay adjustment quantity;

[0017] The baseline local time is corrected using a fractional delay adjustment, and a terminal local time with subsampling accuracy is synthesized.

[0018] According to one possible implementation of one aspect of this application, the synthesis of the terminal's local time also includes:

[0019] Determine whether the frequency correlation error introduced by the variable fractional delay filter is greater than the threshold.

[0020] If so, refer to the fractional delay control quantity and the spectral characteristics of the signal, and retrieve the group delay compensation quantity from the group delay calibration data;

[0021] The fractional delay adjustment and the group delay compensation are applied together to the baseline local time to synthesize the terminal local time.

[0022] According to one possible implementation of one aspect of this application, the variable fractional delay filtering process and the retrieval process of the group delay compensation amount are configured in a mutually bound processing module;

[0023] When the real-time performance or internal parameters of the processing module do not meet the preset conditions, the processing module is disabled as a whole, and the synthesized terminal local time is reverted to the baseline local time.

[0024] According to one possible implementation of one aspect of this application, the processing delay of the terminal is estimated based on the symbol rate of the terminal and the device operating conditions, and with reference to delay calibration data, including:

[0025] For the switching event of terminal symbol rate, construct a feedforward prediction value for processing delay;

[0026] Obtain the delay deviation measured from the probe signal;

[0027] Based on the measured delay deviation, feedback correction is applied to the feedforward prediction value to determine the processing delay estimate.

[0028] According to one possible implementation of one aspect of this application, obtaining the delay deviation measured from the probe signal includes:

[0029] The beam switching protection window is identified based on the beam switching schedule, and the terminal is instructed to transmit a dedicated detection burst during this window.

[0030] The network side performs correlation estimation on the received probe bursts to obtain the initial measured delay deviation and the corresponding measurement confidence level;

[0031] The initial measured delay deviation is timestamped using the frame sequence number to eliminate cross-frame measurement errors and generate an aligned measured delay deviation for feedback correction.

[0032] According to one possible implementation of one aspect of this application, based on the measured delay deviation, feedback correction is applied to the feedforward prediction value to determine the processing delay estimate, including:

[0033] The updated weights are dynamically determined based on whether the beam switching protection window is currently open and the measurement confidence level.

[0034] Among them, a higher first weight value is configured for updating the weight only when the measurement confidence is within the window and not lower than the preset threshold, and a lower second weight value is configured under other conditions.

[0035] Using determined update weights, the feedforward predicted values ​​and the aligned measured delay deviations are weighted and fused to determine the processing delay estimate.

[0036] According to one possible implementation of one aspect of this application, a geometric prediction handle is used to predict the one-way propagation delay between the terminal and the satellite, including:

[0037] Using the geometric prediction handle, the geometric propagation delay based on geometric distance is calculated;

[0038] Using the geometric prediction handle, the relative velocity between the terminal and the satellite is obtained, and the Doppler frequency shift is calculated accordingly, which is then mapped into a time delay correction term in the time domain.

[0039] The delay correction term is superimposed on the geometric propagation delay to generate a one-way propagation delay prediction that reflects real-time dynamics.

[0040] According to one possible implementation of one aspect of this application, the method further includes:

[0041] Continuously monitor the Doppler frequency shift or the slant range change rate derived from the relative velocity;

[0042] Evaluate the dynamic statistical characteristics of Doppler frequency shift or slant range change rate within a preset time window;

[0043] Based on dynamic statistical characteristics, the protection interval of the return link is adaptively configured. When the dynamic statistical characteristics do not exceed the threshold, the protection interval is reduced; otherwise, the protection interval is expanded to a conservative value.

[0044] According to one possible implementation of one aspect of this application, predicting the one-way propagation delay between the terminal and the satellite includes: superimposing a time-domain correction term mapped by Doppler frequency shift onto the geometric propagation delay for feedforward correction; estimating the terminal's processing delay includes: constructing a feedforward prediction value for symbol rate switching and performing feedback correction on the feedforward prediction value based on the delay deviation measured by the probe signal; and synthesizing the terminal's local time includes: applying a variable fractional delay filter to achieve fine adjustment at the subsampling level and synchronously compensating for the group delay introduced by the filter.

[0045] Technical effects: Through the above technical solutions, this invention solves the problems of insufficient synchronization accuracy, slow convergence, and low resource utilization in high-speed dynamic scenarios. It can improve synchronization accuracy to the microsecond level, accelerate the convergence speed in dynamic scenarios, and support adaptive compression of guard intervals, effectively improving the stability and spectrum efficiency of satellite communication systems. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the overall process of a time synchronization method applicable to satellite communication systems.

[0047] Figure 2 A flowchart illustrating the process of synthesizing the terminal's local time by integrating the network clock reference time and processing latency estimation.

[0048] Figure 3 This is a flowchart illustrating the steps for estimating the processing delay of a terminal based on its symbol rate and operating conditions, and with reference to delay calibration data.

[0049] Figure 4 A schematic diagram of the process for obtaining the delay deviation measured from the probe signal. Detailed Implementation

[0050] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] The terms "first," "second," etc., used in the specification and accompanying drawings of this invention are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, or product comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or units.

[0052] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0053] This specification adopts a unified convention for symbols and data items. The main characters used in the embodiments of this invention are defined as follows:

[0054] t _NCR_rx This represents the network clock reference time parsed by the terminal from the forward broadcast signal, in seconds (s).

[0055] geo _handle This represents the geometric prediction handle, whose function is to take any time as input and output the geometric relationship parameters (such as distance, relative velocity, etc.) between the terminal and the satellite at that time.

[0056] τ _path_pred This represents the predicted one-way propagation delay between the terminal and the satellite, expressed in seconds (s).

[0057] device _conditions The device status of the terminal is represented by a vector containing multiple parameters, such as temperature, power supply voltage, and circuit operating mode.

[0058] delay _stat This represents the estimated terminal processing latency, expressed in seconds (s).

[0059] t _term_local This represents the final local time synthesized on the terminal, in seconds (s).

[0060] bias _nonrecip This represents the forward / backward non-reciprocal bias provided by the network or estimated by the terminal itself, in seconds (s).

[0061] t _txThis indicates the return link transmission time without non-reciprocal bias correction, in seconds (s).

[0062] t _tx_corrected This indicates the final return link transmission time after non-reciprocal bias correction, in seconds (s).

[0063] t _base The baseline local time is represented by t, which is directly synthesized from the network clock reference time and the processing delay estimate. _base =t _NCR_rx +delay _stat .

[0064] u _k This represents the fractional delay control value, which is a dimensionless normalized value, typically in the range of [-0.5, 0.5), and is used to control a variable fractional delay filter.

[0065] vfd(u _k This indicates that the variable fractional delay filter is based on the control quantity u. _k The generated fractional delay adjustment is expressed in seconds (s).

[0066] Δ _group_delay This represents the amount of compensation used to compensate for the group delay error introduced by the variable fractional delay filter, expressed in seconds (s).

[0067] delay _pred This represents the predicted feedforward processing delay, including the step term, in seconds (s).

[0068] e _meas_aligned It represents the end-to-end delay deviation measured and aligned by the network side using probe signals, in seconds (s).

[0069] α _k This represents the dynamically updated weights used for feedback correction. It is a dimensionless value and is typically in the range [0,1].

[0070] Example 1: This example describes the overall framework and basic process of a time synchronization method suitable for satellite communication systems, such as... Figure 1 As shown. Specifically, it includes the following steps:

[0071] Step S101: Analyze the forward broadcast signal and obtain the network clock reference time.

[0072] For example, the terminal continuously receives downlink forward broadcast channels from satellites. Specific physical channels or higher-layer signaling within this channel carry the network clock reference count (ncr). _count_rx With the corresponding frame number _index The terminal configures NCR according to the preset network clock reference. _config(This defines the counter's bit width, update frequency, and duration per count, etc.), and will use NCR. _count_rx Converted to absolute time t _NCR_rx This conversion process preferably considers the rule that the counter rewinds to zero after reaching its maximum value to ensure the continuity of time. For example, a 32-bit counter updated at a frequency of 10MHz has a rewind period of approximately 429.5 seconds, and the algorithm within the terminal needs to correctly handle the time calculations for crossing the rewind point.

[0073] Step S102: Construct a geometric prediction handle based on satellite orbit data.

[0074] Specifically, during the terminal initialization or network access phase, satellite orbital data (orbit) is retrieved from the network or local storage. _data For example, two lines of orbital elements or more precise ephemeris data. Based on this data, the orbit calculation module inside the terminal will construct a geometric prediction handle geo. _handle This handle can functionally be a function, an object, or a service. It receives an absolute timestamp as input and calculates and outputs the satellite's position and velocity vectors in a predetermined coordinate system (such as a geocentric inertial frame or a geocentric-Earth-fixed frame) at that moment. A preferred implementation is that the module pre-calculates the satellite's positions at a series of discrete time points and uses methods such as cubic spline interpolation or piecewise linear interpolation to provide high-precision position information for any input time. The module can also record a geometric accuracy index, geo. _accuracy For example, the maximum interpolation error is used for subsequent quality assessment.

[0075] Step S103: Use the geometric prediction handle to predict the one-way propagation delay between the terminal and the satellite.

[0076] During each period where the transmission time needs to be calculated, the terminal obtains its precise geographical location (e.g., via GNSS global navigation satellite system positioning), and then inputs the current time into geo _handle In the process, the real-time position of the satellite is obtained. Based on the position coordinates of the terminal and the satellite, the straight-line geometric distance between them is calculated. Dividing this distance by the speed of light c yields the propagation delay τ based on the geometric distance. _geometry In this basic embodiment, this τ can be... _geometry As a one-way propagation delay prediction τ _path_pred .

[0077] Step S104: Based on the terminal's symbol rate and device operating conditions, and referring to the delay calibration data, estimate the terminal's processing delay.

[0078] The processing delay of a terminal refers to the time it takes for a signal to travel from the input interface of the baseband processing module to the output (or vice versa) of the antenna port. This delay varies significantly with the symbol rate and device operating conditions (such as chip temperature and operating voltage). To accurately estimate this delay, this method employs a calibration data-based strategy. Specifically, the terminal pre-stores a processing delay calibration table. _calibration_table This table records the processing latency values ​​obtained from actual measurements or simulations under different symbol rates and typical operating conditions. When latency estimation is required, the terminal obtains the symbol rate of the current service configuration. _rate and current equipment operating conditions _conditions By delay _calibration_table The estimated processing delay under the current conditions is calculated by searching or using interpolation / extrapolation algorithms. _stat .

[0079] One exemplary implementation is that, if sufficient calibration data is available, a quadratic polynomial function of delay with respect to the reciprocal of the symbol rate can be fitted. _stat =a0+a1*(1 / symbol _rate )+a2*(1 / symbol _rate ) 2 , where a0, a1, a2 are fitting coefficients.

[0080] Step S105: Combine the network clock reference time and processing delay estimate to synthesize the terminal local time.

[0081] Obtain a unified time reference t from the network _NCR_rx and the processing delay that characterizes its internal properties _stat Then, the terminal merges the two. Specifically, this is done through a simple addition operation t. _term_local =t _NCR_rx +delay _stat This allows the local time t of the terminal to be synthesized. _term_local The t _term_local The physical meaning is that when the time on the network side is t _NCR_rx The time is the local time aligned with the network after processing and delay within the terminal. When performing this addition operation, attention must be paid to numerical precision. For example, time-related calculations can be uniformly represented using 64-bit floating-point numbers and follow preset rounding rules. _rule (e.g., rounding to the nearest nanosecond) to avoid the cumulative loss of precision.

[0082] Step S106: Based on the terminal local time and one-way propagation delay prediction, and optionally corrected according to non-reciprocal bias, calculate the transmission time of the return link.

[0083] To ensure that the return link signal sent by the terminal arrives at the satellite precisely at the predetermined time, the terminal needs to send it in advance. This advance time is the signal's propagation time in space. Therefore, the basic transmission time t... _tx The prediction is obtained by subtracting the propagation delay from the local time: t _tx =t _term_local -τ _path_pred In some systems, due to differences in uplink and downlink frequency bands, and variations in the filtering characteristics of onboard transponders, propagation paths exhibit non-reciprocity, meaning that uplink and downlink propagation delays are not entirely equal. To compensate for slowly varying systemic biases, a non-reciprocal bias can be introduced. _nonrecip Make corrections. At this point, the transmission time t... _tx_corrected Calculated as t _tx_corrected =t _tx -bias _nonrecip The terminal's transmission scheduling module will, based on t _tx_corrected To precisely control the sudden sending of returns.

[0084] In one exemplary embodiment, the steps of preparing and acquiring the network clock reference time may further include two parts:

[0085] The first part is data loading and network clock reference time acquisition, as detailed below:

[0086] Read satellite orbit data orbit _data Beam coverage and switching schedule _plan Network clock reference configuration (ncr) _config Processing delay calibration table delay _calibration_table Physical and system constants are used to complete file / message integrity verification and obtain the load status. _ok .

[0087] Loading status _ok When true, extract the network clock reference count (ncr) from the forward broadcast frame. _count_rx With frame number _index According to NCR _config The bit width and step size will determine the NCR. _count_rx Converted to network clock reference time t _NCR_rx (Consider the counting and rewinding rules).

[0088] Based on satellite orbit data orbit _data Constructing a geometric prediction handle geo _handle (Cubic spline or linear segment interpolation; step size derived from the time resolution in constants), and record geometric accuracy geo. _accuracy (For example, maximum position interpolation error).

[0089] The second part is the runtime environment self-check and calibration coverage check, specifically, reading the delay... _calibration_table Overlaid symbol rate set symbol _rate_set_calib , and the set of symbol rates that can be distributed by the network _rate_set_net Comparison to generate calibration coverage markers (calib). _ready_flag (Including a list of missing rates).

[0090] Example 2: This example provides a local time synthesis method with subsampling accuracy. This method breaks through the limitation of the sampling rate of the terminal digital system on the time synchronization accuracy and realizes subsampling fine-tuning.

[0091] In this embodiment, as Figure 2 As shown, the step of fusing network clock reference time and processing latency estimation to synthesize the terminal's local time further includes:

[0092] Step S201: Integrate the network clock reference time and processing delay estimate to generate the baseline local time; compare with the one-way propagation delay prediction to determine the fractional delay control quantity for the baseline local time; process the fractional delay control quantity through variable fractional delay filtering to generate the fractional delay adjustment quantity; use the fractional delay adjustment quantity to correct the baseline local time and synthesize the terminal local time with subsampling level accuracy.

[0093] Specifically, following the method of Example 1, t _NCR_rx With delay _stat Add them together to get the baseline local time t. _base The t _base The accuracy is limited by the system's sampling clock period Ts (Ts = 1 / Fs, where Fs is the sampling rate). To achieve finer adjustments, the fractional part of the difference between the target adjustment time and the currently achievable time needs to be calculated. An ideal transmission time should be t. _base -τ _path_pred However, due to t _base It is discrete; the fractional part of the ideal time cannot be directly realized. The fractional part that needs to be corrected is called the fractional delay, and the fractional delay control quantity u is calculated based on this. _k For example, u _k It can be calculated as the remainder of the ideal adjustment amount with respect to the sampling period, and then normalized to obtain the target fine-tuning amount Δ. _t_frac =(t _base -τ _path_pred )modTs, then u _k =Δ _t_frac / Ts. u _k It is a dimensionless value that typically ranges from (-0.5, 0.5).

[0094] will u _k The input is fed into a variable fractional delay (VFD) filter. For example, it can be implemented using a Farrow structure, characterized by filter coefficients that are about u. _k The polynomial can be modified by changing u. _k This allows for flexible adjustment of the introduced group delay. The VFD filter processes the internal timing signal stream and adjusts it according to u. _k Generate precise time adjustment, i.e., fractional delay adjustment vfd(u _k Applying this adjustment to the baseline local time achieves subsampling-level accuracy correction.

[0095] Furthermore, in order to eliminate the frequency-dependent error introduced by the variable fractional delay filter itself, the step of synthesizing the terminal local time also includes: determining whether the frequency-dependent error introduced by the variable fractional delay filter is greater than a threshold; if so, referring to the fractional delay control quantity and the spectral characteristics of the signal, retrieving the group delay compensation quantity from the group delay calibration data; and applying the fractional delay adjustment quantity and the group delay compensation quantity together to the baseline local time to synthesize the terminal local time.

[0096] While VFD filters achieve fractional delay, their group delay response is not flat across all frequencies, leading to signal waveform distortion. To address this issue, this embodiment introduces a secondary group delay compensation mechanism. The system pre-stores a group delay calibration table gd. _calibration_table This table records different u _k The equivalent group delay introduced by the VFD filter under different values ​​and signal spectral characteristics. During runtime, based on the current u... _k The group delay compensation Δ is obtained by looking up a table or interpolating from the signal spectrum. _group_delay The terminal local time, with subsampling accuracy and no frequency-dependent error, is synthesized as: t _term_local =t _base +vfd(u _k )+Δ _group_delay .

[0097] To ensure the stability and robustness of the system, the variable fractional delay filtering process and the retrieval process of the group delay compensation amount are preferably configured in a mutually bound processing module; when the real-time performance or internal parameters of the processing module execution state do not meet the preset conditions, the processing module is disabled as a whole, and the synthesized terminal local time is rolled back to the baseline local time.

[0098] In other words, VFD filtering and group delay compensation are considered as inseparable functional units. The system monitors the operating status of this module; for example, if vfd(u _k ) or search Δ _group_delayThe time consumed exceeded the preset real-time threshold, or u _k If the value exceeds the stable operating range, the entire functional unit will be disabled. In this case, the time synthesis process will automatically revert to the basic mode, i.e., t. _term_local =t _base This design sacrifices temporary accuracy degradation to ensure the stability and reliability of the entire synchronization loop.

[0099] As a strategy to balance performance and resource consumption, the step of processing fractional delay control variables through variable fractional delay filtering can further include an order adaptation mechanism. Specifically, the system continuously monitors the alignment error performance of the return link and the computational resource usage of the terminal processor. When the alignment error fails to meet the target threshold (e.g., less than 100 nanoseconds) for several consecutive cycles, and the computational resource usage is lower than the preset budget (e.g., lower than 80%), the system can temporarily increase the filter order of the variable fractional delay filter (e.g., increase the order of the Farrow structure Lagrange interpolator from 3rd to 4th) to enhance interpolation accuracy and converge the error faster. Once the alignment error performance recovers to the target level, the filter order is returned to the baseline level (e.g., 3rd order) to save computational resources and power consumption.

[0100] Example 3: This example provides an adaptive and accurate estimation method for processing delay, which solves the problem that static calibration methods cannot cope with the processing delay step caused by symbol rate switching, as well as the tracking difficulties caused by slow time-varying factors such as temperature drift and aging, and achieves dynamic, adaptive and high-precision estimation of processing delay.

[0101] In this embodiment, as Figure 3 As shown, the step of estimating the terminal's processing latency based on the terminal's symbol rate and device operating conditions, and referring to latency calibration data, further includes:

[0102] Step S301: For the symbol rate switching event at the terminal, construct a feedforward prediction value for the processing delay. The symbol rate switching causes an approximately step-like change in the group delay of the internal digital signal processing links (such as FIR filters, decimation / interpolation modules, etc.) of the terminal; this is a deterministic change that can be predicted in advance. Specifically, the system will not only acquire the current symbol rate... _rate It will also record the symbol rate before the switch. _rate_prev Based on both and the current operating conditions of the device. _conditions The system will construct a feedforward prediction value delay. _pred The predicted value is calculated as follows:

[0103] delay _pred =delay _stat (symbol_rate )+J _step (symbol _rate_prev ,symbol _rate device _conditions (where delay) _stat (symbol _rate ) is the static delay estimate obtained from the current symbol rate according to the method of Embodiment 1; while J _step This is the rate-switching step term obtained in advance through offline calibration or theoretical modeling. This step term J... _step Accurate quantization when processing links from symbol _rate_prev Switch to symbol _rate This refers to the additional delay variation introduced by changes in filter order, pipeline depth, etc. By introducing J... _step Perform feedforward compensation, delay _pred It can approximate the true delay value as closely as possible before the feedback correction loop intervenes, thus shortening the system's convergence time.

[0104] Step S302: Obtain the measured delay deviation from the detected signal. To correct for residual errors in feedforward prediction and unpredictable, slowly varying factors such as tracking temperature drift, this embodiment introduces a measurement-based feedback correction mechanism. For example... Figure 4 As shown, the specific process for obtaining this measured deviation includes:

[0105] According to the beam switching schedule beam _plan The beam switching protection window is identified, and during this window, the terminal is instructed to transmit a dedicated probe burst. This probe burst is a physical layer signal with a designed waveform structure, such as using a sequence with good autocorrelation characteristics (e.g., a ZC sequence), to facilitate high-precision time-of-arrival estimation on the network side. Probing is chosen during the beam switching protection window because this window period is a pause in service data transmission; inserting the probe signal will not affect normal communication, achieving zero overhead in the measurement process.

[0106] Furthermore, the network side performs correlation estimation on the received probe burst to obtain the initial measured delay bias and the corresponding measurement confidence level. After the network-side receiver captures the probe burst, it performs correlation operations with a locally stored copy of the ideal probe sequence. The position of the correlation peak corresponds to the actual arrival time of the signal. By comparing this with the ideal arrival time expected by the network side, the initial end-to-end delay bias e can be obtained. _meas Based on information such as the peak value, signal-to-noise ratio, and sidelobe suppression ratio of the relevant peaks, the measurement confidence level (meas) can be calculated. _conf This is used to characterize the reliability of this measurement.

[0107] Preferably, to improve measurement accuracy, before performing correlation estimation on the network side, the received probe burst signal can be preprocessed using a pre-calibrated transient response kernel to purify the signal and reduce distortion introduced by transient effects of the transmission link or channel. Correlation estimation is then performed on the purified signal obtained after deconvolution preprocessing. Specifically, devices such as the terminal's power amplifier may exhibit memory effects or filtering transients at the beginning of the burst signal. These effects can contaminate the waveform of the probe signal, causing correlation peak broadening or shift. By pre-calibrating the equivalent transient response kernel h of the transmission link... _txrx Performing fast deconvolution on the signal at the receiving end can eliminate distortion to a greater extent, obtain sharper and more accurate correlation peaks, and improve delay bias e. _meas Purity.

[0108] Based on this, the initial measured delay deviation is timestamped using the frame sequence number to eliminate cross-frame measurement errors and generate an aligned measured delay deviation e for feedback correction. _meas_aligned Because there may be a slight time deviation between the measurement time on the network side and the frame structure of the terminal, directly using e... _meas This may introduce cross-frame errors. Therefore, it is necessary to reduce e. _meas The timestamp and the frame number on the terminal side _index Strict alignment is performed to compensate for inter-frame deviations, resulting in e that can be used for local recursive updates. _meas_aligned .

[0109] Step S303: Based on the measured delay deviation, perform feedback correction on the feedforward prediction value to determine the processing delay estimate. Specifically, this is achieved by dynamically determining the update weight α based on whether the current state is within the beam switching protection window and the measurement confidence level. _k Among them, if and only if it is within the window and the measurement confidence is not lower than the preset threshold conf _th At that time, a higher first weight value α is configured for updating the weights. _k_hi Under other conditions, configure a lower second weight value α. _k_lo For example, α _k_hi It can be set to 0.5, while α _k_lo It can be set to 0.01. During the rate switching window, the system error is mainly caused by the step jump, at which time the measured value e _meas_aligned This is crucial and should be given high weight to achieve rapid tracking and convergence; however, during the stable period outside the window, the system error is mainly slow-changing temperature drift, etc., and should be given low weight to smooth out noise and avoid over-tracking of measurement jitter.

[0110] Using defined update weights, the deviations between the feedforward predicted values ​​and the aligned measured delays are weighted and fused to recursively determine the processing delay estimate, delay._stat The recursive formula is:

[0111] delay _stat_k =(1-α _k )*delay _pred_k +α _k *e _meas_aligned_k ; where the subscript k represents the current period.

[0112] As a more refined weight determination scheme, the step of dynamically determining and updating weights can be specifically implemented as a piecewise recursive update mechanism with multiple time constants. This mechanism includes: when within the beam switching protection window and the measurement confidence level meets the requirements, configuring the update weights to a fast update constant α. _fast (equivalent to α) _k_hi This allows for rapid correction of transient step errors; when outside the window, if the detected rate of change of device temperature dT / dt is greater than a preset threshold, the update weight is configured as the intermediate update constant α. _mid (e.g., 0.1) to accommodate faster temperature drift; when outside the window and the device temperature changes steadily, the update weight is configured to the slow update constant α. _slow (equivalent to α) _k_lo This allows for stable tracking of slow time-varying drift and aging.

[0113] To ensure the stability and reliability of the entire estimation process, after determining the processing delay estimate, the method also includes a step of performing boundary and saturation control. Specifically, this involves verifying the determined processing delay estimate. _stat Does the calibration exceed the preset allowable range? _bounds or its updated residual r _k =e _meas_aligned_k -delay _pred_k The system checks whether the absolute value of the delay is greater than a preset threshold. If any test result is true, a clamping operation is performed on the processing delay estimate to constrain it within the calibrated allowable range, and a delay flag indicating an abnormal current estimation state is generated. _bound_flag =1; otherwise, maintain the original processing delay estimate, and delay _bound_flag =0. The delay _bound_flag It is an important indicator of the system's health status and can be used by other control modules (such as adaptive gating of protection intervals).

[0114] This embodiment also includes a fallback strategy in the event of a probe burst loss. Specifically, when a dedicated probe burst loss is detected (e.g., via a probe loss identifier), _loss_flag=1 indicates that the feedback correction based on the measured delay deviation is paused; instead, a device condition compensation term g (device) is generated based on the terminal's device conditions, such as temperature. _conditions The equipment condition compensation term is then added to the feedforward prediction value to generate the processing delay estimate for the current cycle, i.e., delay. _stat =delay _pred +g(device _conditions Among them, g(device) _conditions The expression is a linear or nonlinear compensation function based on temperature changes. A backoff mechanism ensures that even when measurement information is temporarily unavailable, the system can still maintain basic tracking capability against slow drift using other auxiliary information (such as temperature sensor data), achieving progressive degradation.

[0115] For example, the steps for processing delay estimation can also be:

[0116] Read the symbol rate symbol from the business configuration. _rate With equipment operating conditions _conditions (Temperature, power supply, circuit mode), and with frame _index Alignment. Based on delay. _calibration_table symbol _rate device _conditions Calculate the static estimation of processing delay. _stat When the calibration covers the calib mark _ready_flag When insufficient coverage is detected, interpolate adjacent rates or use a fitted delay function. _stat (symbol _rate ) = a0 + a1 * symbol _rate -1 +a2*symbol _rate -2 Perform extrapolation and generate the upper limit of the residual. _bound .

[0117] Alternatively, the steps for processing delay estimation can also be:

[0118] In handling static estimation of delay _stat Based on this, the processing link step term caused by symbol rate switching is explicitly modeled to obtain the feedforward prediction delay. _pred :

[0119] delay _pred =delay _stat (symbol _rate )+J _step (symbol _rate_prev-symbol _rate device _conditions );

[0120] When the protection window for beam switching arrives, the network inserts an ultra-short probe burst during a very short interval without affecting services, and the network-side return end-to-end delay deviation e _meas ; Use a larger update weight within the window to reduce the delay _pred Recursion is delay _stat delay _stat =(1-α)*delay _pred +α*e _meas ;

[0121] Outside the window, α is set to a smaller value to slowly track temperature drift and aging. This embodiment outputs a delay. _stat .

[0122] Alternatively, the delay estimation step can also include steps involving rate jump feedforward and window short-test recursion, specifically:

[0123] Perform rate jump step term modeling and read the symbol. _rate_prev symbol _rate device _conditions and frame _index Alignment, forming a rate jump description _step Based on delay _calibration_table Obtain the static estimate of the processing delay. _stat_base Based on this, a step term J is introduced. _step (rate _step device _conditions ), to obtain the feedforward processing delay prediction delay _pred Record the feedforward confidence level (pred). _conf (Based on coverage and equipment operating condition weights).

[0124] Furthermore, a short-term needle-type test is performed within the beam switching window, based on beam... _plan Determine the beam switching protection window, insert an extremely short probe burst (1 beam symbol), and generate a short test plan. _probe_plan Net side press short _probe_plan The measured deviation e is obtained by estimating the end-to-end delay error. _meas With measurement confidence level (meas) _conf (Consider transmitter memory effect and filter transients). Let e _meas Timestamps and frames _index Alignment, eliminating cross-frame deviation, outputting the aligned e _meas_aligned .

[0125] Furthermore, a delay is applied to the recursive update process, and the input e is read. _meas_aligned delay _pred ,meas _conf , window _flag (Bundle switching window flag), update weight α based on measurement confidence and window state settings. _k If window _flag =1 and meas _conf Higher confidence levels require greater weighting; stable periods or low confidence levels require less weighting. Calculate the residual r. _k : Read input e _meas_aligned delay _pred Press r _k =e _meas_aligned -delay _pred Output r _k The static estimate of the processing delay is obtained recursively. _stat : Read input delay _pred α _k e _meas_aligned Press delay _stat =(1-α _k )*delay _pred +α _k *e _meas_aligned Output delay _stat Perform boundary and saturation control, and read the input r. _k delay _stat calibration _bounds (Specify allowable range), if delay _stat Crossing the boundary or |r _k If the threshold is exceeded, clamping is executed, and the estimated terminal processing delay after clamping is output. _stat_clamped With the status flag delay indicating an abnormal current estimated state _bound_flag Update rate to switch state, change symbol _rate Assigned to symbol _rate_prev .

[0126] Furthermore, exception handling and rollback (only when an exception is triggered), exception criteria: read the input meal. _conf r _k probe _loss_flag When meas _conf low, |r _k |Too large or probe _loss_flag An exception is triggered when the value is 1, and the output is delay. _est_status =degraded (rollback). Rollback strategy: Read input delay_pred delay _est_status If downgrading, set the estimated terminal processing delay to fall back. _stat_fallback =delay _pred At the same time, mark update _α_reduction (reducing α in the subsequent time period) _k Output delay _stat_fallback update _α_reduction .

[0127] For example, a local time synthesis method with subsampling precision (fractional delay execution) may also include the following steps:

[0128] Read input t _NCR_rx delay _stat (or delay) _stat_clamped / delay _stat_fallback ), to obtain the baseline local time t _base =t _NCR_rx +delay _stat .

[0129] Calculate the fractional delay control quantity; specifically, read the input t. _base τ _path_pred This forms the target fine-tuning amount Δ _t_frac =round _to_fraction (t _base -τ _path_pred The remaining fractional part of (1 / Fs) is used to calculate the VFD control quantity u. _k (Unit sampling).

[0130] Perform fractional delay filtering, specifically using a Farrow structure or equivalent implementation, and convert u... _k Applying this to the local timing link, we obtain the fractional delay vfd(u _k ), output vfd(u _k ) and execution status vfd _status .

[0131] Furthermore, secondary compensation for group delay is performed, specifically: reading input u _k ,spectrum,vfd _status gd _calibration_table (Group delay calibration table), find the group delay compensation Δ according to the spectrum and control quantity. _group_delay (u _k (spectrum). Synthesize the local time of the terminal and read the input t. _base vfd(u _k ), Δ _group_delay Calculate t _term_local =t _base+vfd(u _k )+Δ _group_delay .

[0132] Furthermore, the transmission time and non-reciprocity correction are performed, specifically by reading the input t. _term_local τ _path_pred Calculate t _tx =t _term_local -τ _path_pred Non-reciprocal correction, read input t _tx bias _nonrecip (If applicable), calculate t _tx_corrected =t _tx -bias _nonrecip .

[0133] Furthermore, alignment verification and adaptive protection interval are performed, specifically: scheduling transmission and measurement: with input t _tx_corrected The scheduling returned a burst, and the network side obtained the alignment error ε. _align Align with measurement labels _conf Adaptive protection interval: Read input GP _static ε _align align _conf delay _bound_flag update _α_reduction τ _path_pred_conf (Single-way propagation delay prediction confidence) (if applicable), calculate the guard interval configuration GP _config When ε _align When the threshold is met, the annotation is good, and there are no degradation flags, GP _config Converges towards the upper limit given by the adaptive protection interval; otherwise, it reverts to GP. _static Output GP _config .

[0134] Perform synchronization status and statistics: summarize ε _align align _conf delay _est_status sync state _state Output sync _state As an endpoint, it is used for operation and maintenance and performance statistics.

[0135] Example 4: This example provides a propagation delay prediction and adaptive guard interval method based on Doppler correction. Specifically, in high-speed relative motion scenarios such as low Earth orbit (LEO) satellites, calculating propagation delay solely based on static geometric distance introduces significant errors because the satellite-to-ground distance itself changes within the duration of a frame. This example improves the dynamic accuracy of delay prediction by introducing first-order Doppler feedforward correction, and based on this, achieves adaptive configuration of the return link guard interval.

[0136] In this embodiment, the step of predicting the one-way propagation delay between the terminal and the satellite using a geometric prediction handle specifically includes:

[0137] Step S401: Using the geometric prediction handle, calculate the geometric propagation delay based on the geometric distance. This step is the same as the basic part of S103 in Embodiment 1, that is, calculate the geometric distance d between the terminal and the satellite based on their instantaneous position coordinates. _geometry And obtain the geometric propagation delay τ _geometry =d _geometry / c. Where c is the speed of light. This τ _geometry This constitutes the main part of the propagation delay.

[0138] Step S402: Using the geometric prediction handle, the relative velocity between the terminal and the satellite is obtained, and the Doppler frequency shift is calculated accordingly. (Geometric prediction handle geo) _handle It can provide not only location information but also velocity vector information. This is achieved by acquiring the terminal's velocity vector v. _term (For a stationary terminal, this velocity is the linear velocity of the Earth's rotation at that location) and the satellite's velocity vector v. _sat The relative velocity vector v between the two can be calculated. _rel =v _sat -v _term Projecting this relative velocity vector onto the line of sight between the star and the ground yields the radial relative velocity, which is also known as the slant range rate of change. _rate Doppler frequency shift _hz with range _rate The relationship is doppler _hz =-range _rate *f _c / c, where f _c This is the center frequency of the signal's carrier wave. (doppler) _hz A positive value indicates that the distance between the satellite and the Earth is decreasing.

[0139] Step S403 maps the Doppler frequency shift to a time delay correction term in the time domain. The physical essence of the Doppler frequency shift is a continuous change in path length. A non-zero Doppler... _hz This means that within a basic time unit (such as the period T of a radio frame) _frame Within this range, the length of the propagation path will change slightly by Δ. _d =range _rate *T _frame Changes in path length directly lead to changes in propagation delay. Therefore, the Doppler frequency shift can be mapped to a delay correction term Δ. _τ_doppThis correction term aims to compensate for the time delay drift caused by distance changes from the current moment to the next frame. Δ _τ_dopp It can be approximated as Δ _τ_dopp =-doppler _hz *T _frame / f _c This correction term is a first-order linear prediction of the time delay change within a short future time window, and belongs to feedforward correction.

[0140] Step S404: The delay correction term is superimposed on the geometric propagation delay to generate a one-way propagation delay prediction that better reflects real-time dynamics. The one-way propagation delay prediction τ after Doppler first-order correction... _path_pred Calculated as: τ _path_pred =τ _geometry +Δ_τ _dopp Therefore, τ _path_pred It is no longer a static geometric snapshot, but a predicted value that includes first-order dynamic trends, which can more accurately reflect the actual propagation time experienced after the signal is emitted, especially during the satellite overpass or low elevation phase when the slant range change rate is large.

[0141] Based on this, the method further includes: step S405, continuously monitoring the Doppler frequency shift or the slant range change rate derived from the relative velocity; evaluating the dynamic statistical characteristics of the Doppler frequency shift or slant range change rate within a preset time window; and adaptively configuring the guard interval of the return link based on these characteristics. Traditional guard intervals (GP) are usually configured fixedly according to the worst case (i.e., the maximum possible range of delay variation), which results in a waste of spectrum resources for most of the time.

[0142] This embodiment utilizes real-time acquired doppler data. _hz or range _rate Information, enabling control of the protection interval GP _config The terminal will adaptively adjust. Specifically, it will maintain a sliding window (e.g., a range containing the past 100 frames). _rate (Measured values), and continuously calculate statistical properties within the window, such as range. _rate The maximum, minimum, mean, and standard deviation of the values. Based on these statistical characteristics, the system executes the following adaptive rule: when the dynamic statistical characteristics are characterized as stationary (e.g., range), _rate The standard deviation is less than a certain stationarity threshold th _stable (This usually occurs during the high-elevation-angle satellite transit phase), so the protection interval is shortened to improve link efficiency. GP _config It can be set to a value based on a measured statistical upper bound with a small margin. This is useful when it characterizes a highly dynamic environment (e.g., range). _rate The standard deviation is greater than a certain dynamic threshold th_dynamic (This usually occurs during the low-elevation, high-speed movement phase of a satellite), in which case the protection interval is extended to a conservative value GP. _static To ensure alignment robustness, the guard interval size is matched to the actual channel dynamic risks, maximizing spectral efficiency and system throughput while ensuring communication reliability.

[0143] For example, the steps of geometric and propagation delay prediction and guard interval configuration can also be as follows:

[0144] According to geo _handle beam _plan constants, frame _index Calculate the geometric distance from the current service area to the satellite to obtain the predicted one-way propagation delay τ. _path_pred and accompanying timestamp ts _pred Output τ _path_pred ts _pred For calculating the transmission time. (Based on beam) _plan The coverage radius and the speed of light in constants are used to calculate the conservative protection interval GP. _static (e.g., GP) _static =Coverage radius / one-way upper limit of the speed of light, or a multiple thereof according to system rules). Output GP _static Provides protection interval configuration. For τ _path_pred With GP _static Generate quality label _tag (e.g., too low elevation angle, interpolation extrapolation exceeding limits).

[0145] Optionally, the geometry and propagation delay prediction and guard interval configuration can also be: utilizing the geometry prediction handle geo _handle The output relative velocity introduces a first-order Doppler correction at the single-frame scale, which is used in calculating the one-way propagation delay prediction τ. _path_pred Add doppler _hz The mapped advance correction term is used to reduce alignment drift caused by beam switching or relative motion; in the guard interval, GP _static Adaptive upper bound convergence is performed based on the statistical upper bound of Doppler and slope range change rate, and the value is regressed to a conservative value when the environment is stable.

[0146] Alternatively, the steps for geometric and Doppler first-order correction can also be:

[0147] Doppler first-order correction time delay prediction, by geo _handle ,frame _index Obtain the relative velocity between the satellite's position and velocity and the center of the service area, and calculate the Doppler frequency shift. _hz With the rate of change of slope distance range _rateDoppler _hz Mapped to propagation delay advance Δ _τ_dopp (Based on a linear approximation of frame period and carrier wavelength), the one-way propagation delay prediction τ is formed by superimposing it with the geometric term. _path_pred τ _path_pred =Geometric delay + Δ _τ_dopp Record the predicted timestamp ts _pred Doppler confidence _conf (From elevation angle and range) _rate (Estimated and provided for risk weighting).

[0148] Adaptive protection interval upper limit calculation, statistical analysis of doppler over a period of time. _hz range _rate Upper bound: Calculate the upper limit of the adaptive protection interval GP _static (In a stable environment, it reverts to a conservative value) and outputs the upper limit confidence level.

[0149] Example 5: This example provides a chain-coupled system-level time synchronization method.

[0150] Specifically, in this embodiment: the step of predicting the one-way propagation delay between the terminal and the satellite includes superimposing a time-domain correction term mapped by the Doppler frequency shift onto the geometric propagation delay for feedforward correction; the step of estimating the processing delay of the terminal includes constructing a feedforward prediction value for symbol rate switching and performing feedback correction on the feedforward prediction value based on the delay deviation measured by the probe signal; and the step of synthesizing the local time of the terminal includes applying a variable fractional delay filter to achieve fine adjustment at the subsampling level and synchronously compensating for the group delay introduced by the filter.

[0151] The design points in this scheme are as follows: the gain of geometric feedforward correction on processing delay estimation, specifically, the Doppler-corrected τ provided in Example 4. _path_pred This provides more accurate data for the entire synchronization system. When the network side measures the arrival time of the probe burst within the framework of Example 3, and uses this to calculate the delay deviation e... _meas At that time, because the ideal arrival time on which it is based is itself closer to the true value due to Doppler correction, the calculated e _meas It can reflect the processing delay error of the terminal, while being less affected by geometric prediction error. In other words, the feedforward correction on the geometric side reduces the observation noise of the processing delay estimation loop, allowing the feedback correction loop in Example 3 to operate under conditions with a higher signal-to-noise ratio, converge faster, and produce more stable estimation results.

[0152] To support subsampling synthesis, the processing of delay fast loop tracking is addressed in Example 3. Specifically, through a step feedforward + window probe fast loop mechanism, the processing of delay estimation is improved._stat It can track real-time and rapid changes in latency caused by symbol rate switching and temperature drift. Therefore, the baseline local time t provided in Example 2 is... _base =t _NCR_rx +delay _stat This is already a very close estimate of the ideal value at the integer sampling period level, which is the optimal estimate. This reduces the burden on the fractional delay actuator in Example 2. It no longer needs to compensate for large, integer sampling period level errors, but only needs to focus on processing the small residuals at the sub-sampling period level. This allows the VFD filter to operate within its fine-tuning range with the highest linearity and accuracy, ensuring the final synthesized t... _term_local It can achieve high precision.

[0153] The subsampling accuracy enables the closed-loop adaptive guard interval; specifically, the result of the entire chain of improvements is reflected in the extremely low alignment error ε achieved by Example 2. _align Up. Only when the system can continuously and reliably deliver ε _align The adaptive shrinking guard interval strategy in Example 4 can only be implemented when the system alignment error is stable within a very small threshold. If the system alignment error itself is large and unstable, any attempt to compress the guard interval will lead to a risk of disconnection. Therefore, the subsampling-level execution accuracy provided in Example 2 provides a closed-loop decision-making basis and feasibility guarantee for the spectral efficiency improvement strategy in Example 4.

[0154] Example 6 describes the steps in Example 1: Optionally, correction is performed based on non-reciprocal bias. In practical satellite communication systems, since uplink and downlink typically use different frequency bands, the delay experienced by the signal when passing through the ionosphere and troposphere is not exactly the same; this difference is the non-reciprocal bias. This bias is not a fixed constant but changes slowly with factors such as satellite elevation angle and atmospheric conditions. This example provides a lightweight, proxy-data-based slow-loop tracking compensation method, particularly suitable for terminals without dual-frequency measurement hardware.

[0155] In this embodiment, optionally, the step of correcting based on non-reciprocal bias specifically includes:

[0156] Step S601: Obtain the terminal's current elevation angle and meteorological proxy data representing the propagation path. The terminal obtains this data through its positioning module and geo... _handle Calculate the current satellite's apparent elevation relative to the local area. _est At the same time, the terminal will also acquire a set of meteorological proxy data. _proxy Meteorological proxy data can be implemented at multiple levels:

[0157] Basic implementation: This can be parameters output by a standard atmospheric model (such as the ITU-RP.835-6 model) based on geographic location, season, and time of day, such as total water vapor content.

[0158] Enhanced implementation: If the terminal is equipped with basic sensors (such as temperature, humidity, and barometric pressure sensors), metao _proxy It can include these measured ground meteorological parameters.

[0159] Optimal Implementation: If the terminal has network connectivity, it can obtain more accurate and real-time local meteorological data, such as tropospheric zenith delay (ZTD), through internet APIs. These data collectively form the basis for assessing atmospheric impacts.

[0160] Step S602: Based on elevation angle and meteorological proxy data, model and estimate the current non-reciprocal bias update. Based on the above input, the system uses a preset non-reciprocal bias model f(elevation) to... _est ,meteo _proxy This allows for the estimation of the non-reciprocal bias at the current moment. Ionospheric delay is inversely proportional to the square of the signal frequency, while tropospheric delay is related to a mapping function of the elevation angle. Therefore, simplified mathematical models or empirical lookup tables for these physical effects can be pre-established. For example, model f can be specified as: f = f _iono (elevation _est )+f _tropo (elevation _est ,meteo _proxy ), where f _iono It is an ionospheric non-reciprocal delay model that is only related to elevation angle (because the delay difference between uplink and downlink frequencies can be modeled), f _tropo It is simultaneously related to the elevation angle and surface water vapor pressure (from Meteor). _proxy The relevant tropospheric non-reciprocal delay model. Outputs the instantaneous estimate of the bias under the current environment.

[0161] Step S603: A recursive update algorithm is used to integrate the estimated bias update into the existing non-reciprocal bias estimate to continuously track the slow changes in the bias. Since atmospheric parameters change slowly and the model itself contains errors, directly using instantaneous estimates may introduce noise. Therefore, this embodiment uses low-pass filtering for recursive updates to achieve smooth and stable tracking. The update formula is:

[0162] bias _nonrecip_k =(1-β)*bias _nonrecip_(k-1) +β*f(elevation _est_k ,meteo _proxy_k Among them, bias_nonrecip_k It is the updated non-reciprocal bias; bias _nonrecip_(k-1) β is the bias value of the previous cycle; β is a filter coefficient with a value much less than 1 (e.g., 0.001), which determines the bandwidth of the tracking loop. The smaller the value of β, the slower the tracking speed, but the better the smoothing effect on model noise.

[0163] Step S604: Correct the transmission time using the updated non-reciprocal bias. This step is the same as S106 in Embodiment 1, that is, when calculating the final transmission time, subtract the bias updated by the slow loop tracking. _nonrecip_k Value: t _tx_corrected =t _tx -bias _nonrecip_k Through the above steps, this embodiment can effectively model and track the error sources of key slowly varying systems without additional hardware costs, using readily available auxiliary data, thereby further improving the accuracy of time synchronization.

[0164] Example 7: This embodiment provides a gating method for adaptive shrinking of the protection interval, as a preferred implementation of step S405 in Example 4, which adaptively configures the protection interval of the return link. Example 4 proposed dynamically shrinking or expanding the protection interval based on the channel. This embodiment establishes a strict set of multi-index consistency gating rules for its shrinking operation. Only when all internal state indicators of the system show health and stability can the operation of compressing the protection interval, which may bring risks, be performed, to avoid communication quality degradation due to incorrect decisions.

[0165] In this embodiment, the step of adaptively configuring the protection interval of the return link specifically includes:

[0166] Step S701: Perform multi-index consistency gating judgment. In each decision cycle, the system attempts to shrink the protection interval GP. _config Previously, a gating system was required. The pass condition for this judgment was that several of the following sub-conditions must be met simultaneously:

[0167] (i) The alignment error of the return link meets the preset threshold: i.e., ε _align <=ε _th ε _align It is the system's performance output, and its value must have converged to a sufficiently small range (e.g., ε). _th =50 nanoseconds), indicating that the main synchronization loop is working normally.

[0168] (ii) The measurement confidence level associated with the alignment error meets a preset threshold: that is, align _conf >=conf _th Network side against ε _alignThe measurement itself also has a confidence level. _conf This value must be high enough (e.g., conf). _th =95%), to ensure that ε is used for decision-making. _align The data is reliable, and is not an outlier due to noise or interference.

[0169] (iii) The internal state flag for processing delay estimation is normal: that is, the delay from Example 3. _bound_flag A value of 0 indicates that the processing delay estimation loop is operating stably without any out-of-bounds errors or saturation clamping. If the loop itself is in a degraded state, its output should not be relied upon, and aggressive contraction operations should not be performed.

[0170] (iv) The confidence level of the one-way propagation delay prediction meets the preset condition: that is, the quality from Example 4 _tag It does not include critical alarms, and / or τ _path_pred_conf >=conf _geo_th Ensure that the geometric predictions used to calculate the transmission time are of high quality. For example, if the current satellite elevation angle is too low or the orbit data is obtained through extrapolation, even if the alignment error temporarily meets the requirements, the guard interval cannot be reduced due to potential risks.

[0171] Step S702: The protection interval contraction operation is performed only if the gating judgment passes. If all conditions (i) to (iv) above are satisfied, the gating judgment passes, and the system performs the protection interval contraction operation. A preferred contraction method is step-by-step contraction: GP _config_k =max(GP _min ,GP _config_(k-1) -Δ _GP ), among which, GP _min It is the minimum allowable protection interval of the system, Δ _GP This is the preset shrinkage step size. Gradual shrinkage can avoid oscillations caused by excessively large single adjustments.

[0172] Step S703: If the gating judgment fails, the protection interval is reverted to a conservative value. In any decision cycle, if any sub-condition of the above gating judgment is not met, the gating is closed. At this time, the system will immediately adopt a conservative strategy and configure the protection interval with GP. _config Reset to conservative value GP _static GP _static It is the maximum protection interval calculated based on the beam coverage area to ensure no collisions occur. Through a rigorous gating mechanism, this embodiment achieves both spectral efficiency and robustness and reliability throughout the adaptive process.

[0173] Example 8 describes an optional or parallel refinement scheme for propagation delay prediction. While Example 4 uses first-order (linear) Doppler compensation to predict intra-frame delay variations, this example employs a higher-order interpolation method to more accurately fit the nonlinear motion trajectory of the satellite within a single frame period, further reducing quantization and model errors in geometric prediction.

[0174] In this embodiment, the step of predicting the one-way propagation delay between the terminal and the satellite using a geometric prediction handle specifically includes:

[0175] Step S801: Within the period corresponding to the current network frame, multi-point sampling is performed using a geometric prediction handle according to a preset intra-frame sub-timetable to obtain the geometric distance at a series of sub-times. Assume the start time of the current frame is T. _start The frame period is T _frame The system will execute the sequence according to a preset sub-timetable within the time interval [T] of this frame. _start ,T _start +T _frame Within, geo is called multiple times. _handle For example, a simple three-point sampling table could be used in T _start T _start +0.5*T _frame T _start +T _frame Sampling was performed at three time points to obtain three corresponding satellite-to-ground geometric distances d. _0 ,d _1 ,d _2 .

[0176] Step S802, wherein, within the sub-time interval of the adjacent beam switching event, the multi-point sampling density is increased. As a preferred adaptive implementation, the sampling density is not constant. When the system adjusts the sampling density according to the beam... _plan When a beam switching is anticipated to occur in the next frame or several frames, the accuracy of the geometric position becomes crucial. In this case, the system automatically increases the number of sampling points. For example, only 3 points might be sampled in a regular frame, but in a key frame before the switch, this might be increased to 5 or 7 sampling points to capture the trajectory details of the switch edge at a higher temporal resolution.

[0177] Step S803: For the acquired geometric distance series of sampling points, a spline interpolation algorithm is applied to fit the data, generating a refined one-way propagation delay prediction with higher temporal resolution. After obtaining the (time, distance) sampling point pairs, the system applies a spline interpolation algorithm (such as cubic spline interpolation) to fit a smooth curve function d(t) that continuously describes the distance change over time within the frame. The effective domain of this function d(t) is [T...]. _start ,T _start +T_frame Within the interval. Used to calculate the one-way propagation delay prediction τ at the transmission time. _path_pred It is no longer a single numerical value, but a time function τ(t) = d(t) / c obtained by dividing the function d(t) by the speed of light c. When calculating t _tx At that time, it is necessary to solve the equation t _tx =t _term_local -τ(t _tx +τ(t _tx The fixed point of the propagation delay can be determined, or an approximate solution can be obtained using iterative numerical methods. This embodiment can improve the accuracy of propagation delay prediction from the frame level to the intra-frame continuous level with a smaller computational cost, effectively suppressing the prediction error introduced by the nonlinear motion of the satellite, and providing a more accurate input for the entire synchronization system.

[0178] In some embodiments, the steps of local time synthesis, transmission time calculation, and alignment verification may also be:

[0179] Synthetic terminal local time t _term_local Specifically, using t _NCR_rx With delay _stat Execute t _term_local =t _NCR_rx +delay _stat and with frame _index To ensure timing consistency.

[0180] Calculate the transmission time t _tx Specifically, with t _term_local With τ _path_pred Execute t _tx =t _term_local -τ _path_pred Record numerical precision rounding _rule (e.g., nanosecond-level rounding).

[0181] Non-reciprocal modification, specifically, in bias _nonrecip If it exists, calculate the transmission time correction t. _tx_corrected =t _tx -bias _nonrecip Otherwise t _tx_corrected =t _tx .

[0182] Alignment verification and protection interval configuration, specifically, according to t _tx_corrected The scheduling returned a burst, and the alignment error ε was measured on the network side. _align If ε _align If the value is less than the target threshold, a conservative protection interval (GP) is used. _static GP is configured as a protection interval. _config Otherwise, record the deviation and quality label. _tagUpper limit of residual _bound Association, GP _config Maintain a conservative approach. Output ε _align GP _config This is the end point of the process; proceed to statistics.

[0183] Statistics and reports, specifically, summarizing ε _align With quality _tag geo _accuracy ,residual _bound Generate a synchronization state sync _state Used for operations and maintenance visualization. Output sync. _state Provided for external system calls.

[0184] Optionally, the steps of local time synthesis, transmission time calculation, and alignment verification can also be as follows:

[0185] At the terminal's local time t _term_local During synthesis, a variable fractional delay filter and its group delay quadratic compensation term are introduced to overcome the time resolution limitation of 1 / sampling rate:

[0186] t _term_local =t _NCR_rx +delay _stat +vfd(u _k )+Δ _group_delay (u _k (spectrum);

[0187] Where vfd(u _k ) is a fractional delay actuator, Δ _group_delay (u _k ,spectrum) is its frequency-dependent group delay compensation (provided by calibration tables or small-scale online updates).

[0188] Sending time t _tx Still press t _tx =t _term_local -τ _path_pred Calculate; if a non-reciprocal bias exists. _nonrecip t is still calculated _tx_corrected =t _tx -bias _nonrecip With t _tx_corrected The scheduler returns a burst, and ε is obtained. _align When ε _align If the threshold is met, the protection interval can be configured with GP. _config The adaptive approximation is based on the upper limit given in the protection interval configuration, and automatically reverts to a conservative value when environmental disturbances increase.

[0189] Output: t _term_local t_tx_corrected ε _align GP _config .

[0190] Example 9: The calculation process is described through an example in a real-world scenario.

[0191] Assume a device operating in the Ka band (carrier frequency f) _c The LEO satellite communication terminal (GHz = 30 GHz) has a digital baseband system sampling rate Fs = 40 Msps (sampling period Ts = 25 ns). At a certain moment, the terminal switches beams according to the beam switching plan. _plan A service switch needs to be performed, and its symbol rate is [not specified]. _rate From 5.12 Msps (symbol _rate_prev Switch to 9.1 Msps.

[0192] At the beginning of this cycle, the terminal parses the network clock reference time t from the forward broadcast signal. _NCR_rx =12345.678910000s.

[0193] via geo _handle The calculated pure geometric propagation delay τ at the current moment is... _geometry =0.012500100s (12.5001ms). Simultaneously, the range of change in slant distance between the satellite and the ground was calculated. _rate =-1500m / s (a negative value indicates that the distance is decreasing).

[0194] The processing latency corresponding to 5.12 Msps is 23.966620 μs; the processing latency corresponding to 9.1 Msps is 22.252590 μs. Assume that the latency step term J for switching from 5.12 Msps to 9.1 Msps is known through offline calibration. _step =-1.500000μs.

[0195] Within the beam switching protection window, the terminal transmits a probe burst, and the network side measures and returns the aligned delay deviation e. _meas_aligned =-0.000000050s(-50ns).

[0196] Set the wireless frame period T _frame =1ms. Fast update weight α for feedback correction. _fast =0.5. Non-reciprocal bias _nonrecip The current value, obtained by tracking using the method in Example 6, is +0.000000020s (+20ns).

[0197] Calculate the Doppler frequency shift:

[0198] doppler _hz =-range _rate *f _c / c=-(-1500)*(30e9) / (3e8)=150,000Hz=150kHz.

[0199] Calculate the delay correction term Δ _τ_dopp =-doppler _hz *T _frame / f _c =-(150e3)*(1e-3) / (30e9)=-5e-9s=-5ns.

[0200] Calculate the final propagation delay prediction:

[0201] τ _path_pred =τ _geometry +Δ _τ_dopp =0.012500100s-0.000000005s=0.012500095s.

[0202] It can be seen that Doppler correction brings nanosecond-level correction to the prediction of propagation delay.

[0203] Obtain the static delay estimate at the new symbol rate (9.1 Msps). _stat (9.1) = 0.000022253s (22.253μs, an approximate value is taken for ease of calculation).

[0204] Constructing feedforward predictions:

[0205] delay _pred =delay _stat (9.1)+J _step =22.253μs+(-1.500μs)=20.753μs=0.000020753s.

[0206] Perform feedback correction, and use fast update weight α because it is in a switching window and the measurement is reliable. _fast =0.5.

[0207] Updated processing delay _stat_k =(1-α _fast )*delay _pred +α _fast *(delay _stat (5.12)+e _meas_aligned Note: e here _meas_aligned It is the deviation relative to the delay of the previous state, therefore the correction target should be the delay of the previous state. _stat(5.12). A more accurate recursion should be delay. _stat_k =delay _pred_k +α _fast *(e _meas_aligned_k For simplicity, delay is used. _stat_k =(1-α _k )*delay _pred_k +α _k *(delay _pred_k +e _meas_aligned_k In the form of )

[0208] delay _stat_k =delay _pred_k +α _k *e _meas_aligned_k .

[0209] delay _stat_k =0.000020753s+0.5*(-0.000000050s)=0.000020753s-0.000000025s=0.000020728s.

[0210] After two steps of feedforward and feedback, the processing delay was accurately estimated to be 20.728 μs.

[0211] Calculate the baseline local time:

[0212] t _base =t _NCR_rx +delay _stat_k =12345.678910000s+0.000020728s=12345.678930728s.

[0213] Calculate the fractional delay control quantity u _k Calculate the relationship between the ideal adjustment amount and the sampling period:

[0214] The fractional part of the ideal transmission time reference = (t) _base -τ _path_pred modTs

[0215] =(12345.678930728-0.012500095)mod25e-9=12345.666430633mod25e-9.

[0216] 12345.666430633 / 25e-9=493826657225.32, with a decimal part of 0.32.

[0217] Therefore, the ideal timing is 0.32 times ahead of the clock cycle of the most recent sampling point. A delay of +0.32Ts is required. The fractional delay control variable u... _k =0.32.

[0218] According to u _k =0.32, querying the VFD filter and group delay compensation module, assuming the following result:

[0219] Fractional delay adjustment amount vfd(u _k )=u _k *Ts=0.32*25ns=+8ns=+0.000000008s.

[0220] Group delay compensation Δ _group_delay =-1.5ns=-0.0000000015s.

[0221] Synthesized final local time:

[0222] t _term_local =t _base +vfd(u _k )+Δ _group_delay =12345.678930728s+0.000000008s-0.0000000015s=12345.6789307345s.

[0223] Calculate the transmission time:

[0224] t _tx =t _term_local -τ _path_pred =12345.6789307345s-0.012500095s=12345.6664306395s.

[0225] Correction is performed using a non-reciprocal bias.

[0226] t _tx_corrected =t _tx -bias _nonrecip =12345.6664306395s-0.000000020s=12345.6664306195s.

[0227] The terminal will be in t _tx_corrected =12345.6664306195s initiates the transmission of the return link burst. The calculation at this moment comprehensively considers millisecond-level propagation delay, microsecond-level processing delay step and tracking, and nanosecond-level Doppler effect, subsampling fine-tuning and non-reciprocal bias.

[0228] This invention employs an adaptive estimation method that combines feedforward prediction and feedback correction, specifically by pre-constructing an estimation method containing a step term J. _step feedforward prediction delay _pred And during the beam switching window, the measured deviation e obtained by detecting bursts is used. _meas_aligned High-weighted, rapid feedback correction is implemented. This proactively compensates for most step errors and rapidly converges residuals using measured data, reducing the post-switching synchronization loss time from hundreds of milliseconds in traditional solutions to within several frame periods, thus improving system stability and service continuity in dynamic switching scenarios. It also solves the transient delay step problem caused by symbol rate switching.

[0229] This invention refines propagation delay prediction by introducing feedforward correction based on Doppler frequency shift. Precise quantification of real-time changes in the intra-frame path provides higher temporal resolution and accuracy for delay prediction. Based on this, and combined with a multi-index consistency gating mechanism, the system can safely and adaptively shrink the guard interval (GP) while ensuring synchronization robustness. _config This allows it to closely match the actual channel dynamics, transforming the spectrum resources wasted by traditional fixed intervals into effective user data throughput, thereby improving link efficiency and the utilization rate of guard interval resources.

[0230] By employing a variable fractional delay (VFD) filter and synchronously compensating for group delay, the system is endowed with the ability to perform fine-tuning of time between integer sampling clock grids. This scheme overcomes the bottleneck of quantization accuracy determined by the sampling period Ts, thereby improving the alignment error ε. _align It can be stably controlled at the microsecond or even sub-microsecond level. This not only directly reflects the synchronization performance, but also forms the basis for the reliable implementation of advanced functions such as the aforementioned adaptive protection interval, thus improving the time synchronization accuracy of the entire system.

[0231] In propagation delay prediction, a time-domain correction term mapped by Doppler frequency shift is superimposed for feedforward correction; in processing delay estimation, a feedforward prediction value for symbol rate switching is constructed, and feedback correction is performed based on the measured delay deviation of the probe signal; in local time synthesis, a variable fractional delay filter is applied and its introduced group delay is compensated synchronously, achieving fine adjustment at the subsampling level.

[0232] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A method of time synchronization suitable for use in a satellite communication system, characterized by, The method comprises the following steps: Resolving a forward broadcast signal to obtain a network clock reference time; Based on satellite orbit data, a geometric prediction handle is constructed; Using the geometric prediction handle, the one-way propagation time delay between the terminal and the satellite is predicted; According to the symbol rate of the terminal and the equipment working condition, and referring to the delay calibration data, the processing delay of the terminal is estimated; Fusing the network clock reference time and the processing delay estimation to synthesize the terminal local time; Based on the terminal local time and the one-way propagation time delay prediction, and according to the non-reciprocal bias, the sending time of the return link is calculated; The fusing of the network clock reference time and the processing delay estimation to synthesize the terminal local time comprises: Integrating the network clock reference time and the processing delay estimation to generate a baseline local time; Determining a fractional delay control amount for the baseline local time according to the one-way propagation time delay prediction; Generating a fractional delay adjustment amount by variable fractional delay filtering processing the fractional delay control amount; Using the fractional delay adjustment amount to correct the baseline local time to synthesize the terminal local time with sub-sampling level precision; The estimating of the processing delay of the terminal according to the symbol rate of the terminal and the equipment working condition, and referring to the delay calibration data comprises: For the switching event of the terminal symbol rate, a feedforward prediction value of the processing delay is constructed; Obtaining the delay deviation measured by the probe signal; According to the measured delay deviation, the feedforward prediction value is corrected by feedback to determine the processing delay estimation; The using of the geometric prediction handle to predict the one-way propagation time delay between the terminal and the satellite comprises: Using the geometric prediction handle to calculate the geometric propagation time delay based on the geometric distance; Using the geometric prediction handle to obtain the relative velocity between the terminal and the satellite, to calculate the Doppler frequency shift therefrom, and to map it to a time delay correction item in the time domain; Superimposing the time delay correction item on the geometric propagation time delay to generate a one-way propagation time delay prediction reflecting real-time dynamics; Continuously monitoring the Doppler frequency shift or the slant range change rate derived from the relative velocity; Evaluating the dynamic statistical characteristics of the Doppler frequency shift or the slant range change rate within a preset time window; Based on the dynamic statistical characteristics, the guard interval of the return link is adaptively configured, wherein when the dynamic statistical characteristics do not exceed a threshold, the guard interval is contracted, otherwise the guard interval is expanded to a conservative value.

2. The method of claim 1, wherein, The synthesizing of the terminal local time further comprises: Judging whether the frequency-related error introduced by the variable fractional delay filtering is greater than a threshold; If yes, referring to the fractional delay control amount and the spectral characteristics of the signal, a group delay compensation amount is retrieved from the group delay calibration data; The fractional delay adjustment amount and the group delay compensation amount are jointly applied to the baseline local time to synthesize the terminal local time.

3. The method of claim 2, wherein, The retrieval process of the variable fractional delay filtering processing and the group delay compensation amount is configured in a mutually bound processing module; When the real-time performance of the processing module execution state or the internal parameters do not meet the preset conditions, the processing module is disabled as a whole, and the synthesized terminal local time is rolled back to the baseline local time.

4. The method of claim 1, wherein, The obtaining of the delay deviation measured by the probe signal comprises: According to the beam switching time table, a beam switching guard window is identified, and during this window, the terminal is instructed to transmit a dedicated probe burst; The network side performs correlation estimation on the received probe burst to obtain an initial measured delay bias and a corresponding measurement confidence; The initial measured delay bias is time-stamped aligned using a frame sequence number to eliminate cross-frame measurement errors and generate an aligned measured delay bias for feedback correction.

5. The method of claim 1, wherein, The feedback prediction value is corrected according to the measured delay bias to determine a processing delay estimation, including: The update weight is dynamically determined based on whether the terminal is in a beam switching protection window and the measurement confidence; The update weight is configured with a higher first weight value only when the terminal is in the window and the measurement confidence is not lower than a preset threshold, and is configured with a lower second weight value in other conditions; The determined update weight is used to weight and fuse the feedback prediction value and the aligned measured delay bias to determine the processing delay estimation.

6. The method of claim 1, wherein: The one-way propagation delay between the terminal and the satellite is predicted by superimposing a time-domain correction term mapped from a Doppler frequency shift on a geometric propagation delay for feedforward correction; The processing delay of the terminal is estimated by constructing a feedforward prediction value for symbol rate switching and performing feedback correction on the feedforward prediction value according to a delay bias measured from the probe signal; The terminal local time is synthesized by applying a variable fractional delay filter to achieve fine adjustment at a sub-sampling level and synchronously compensating for a group delay introduced by the filter.

Images