Low-altitude unmanned aerial vehicle timing synchronization method and system based on semantic communication assistance

Abstract

The application discloses a low-altitude unmanned aerial vehicle timing synchronization method and system based on semantic communication assistance, and the method comprises the following steps: S1, a semantic preamble library is constructed, and a transceiving end shared mapping relationship is determined; S2, timing metric vectors corresponding to each semantic preamble sequence are determined; S3, indexes of the semantic preamble sequence and coarse timing offset estimation values are determined; S4, a running speed range of a mobile node is determined, a running speed median value of the running speed range is determined, and a Doppler shift estimation median value is calculated; S5, the Doppler shift estimation median value is used for Doppler shift compensation of a received signal, so that a compensated received signal is obtained; and S6, timing metrics are updated, so that a refined timing offset estimation value is obtained. The application is helpful for breaking the common bottleneck of low-altitude communication synchronization which restricts the industrial scale, and has important strategic significance for the independent controllability of a low-altitude economic industry chain in China and the improvement of global competitiveness.

Description

Technical Field

[0001] This invention relates to the field of low-altitude communication support technology, specifically to a timing synchronization method for low-altitude unmanned aerial vehicles (UAVs) based on semantic communication assistance. Background Technology

[0002] With the low-altitude economy being included in the national strategic emerging industries, mobile nodes such as drones and electric vertical takeoff and landing (eVTOL) aircraft have been widely used in high-value commercial scenarios such as low-altitude inspection, logistics transportation, emergency communication, and air-to-ground coordination. These applications place rigid demands on the reliability and real-time performance of communication links. Therefore, synchronization deviations directly lead to data retransmission and communication delays, resulting in multiple chain reactions. On the one hand, scarce spectrum resources are wasted, and effective throughput drops sharply; on the other hand, the flight power consumption of mobile terminals increases significantly, and loiter time is shortened, thereby driving up the battery operating costs and charging frequency of a single mission. More seriously, in extreme cases, synchronization errors may lead to communication interruptions, directly endangering flight safety and mission execution. For critical scenarios such as logistics delivery and emergency search and rescue, link interruption often means mission failure or even major asset damage, which has become a core economic bottleneck restricting the large-scale implementation of the low-altitude economy.

[0003] Existing synchronization schemes mostly employ fixed preamble sequences for correlation peak detection. This fails to fully utilize the rich semantic information inherent in the mobile node's operational state. In low-altitude, high-dynamic scenarios, rapidly changing Doppler frequency shifts can cause nonlinear changes in the preamble sequence phase, severely weakening the concentration of correlation peaks and leading to inaccurate timing and position determination. To compensate for this deficiency, existing technologies typically involve significantly increasing pilot density or synchronization resource overhead, expanding the frequency offset search range, or introducing additional high-precision inertial navigation modules to acquire motion state for compensation. However, these methods all come at the cost of significantly increasing the computing power burden and hardware deployment costs of the receiver's baseband processing. They not only introduce additional synchronization delays to meet sudden service demands but also increase the design complexity and tape-out costs of terminal chips, facing significant cost-effectiveness bottlenecks in large-scale industrial deployments. Summary of the Invention

[0004] To address the problem that existing low-altitude communication does not fully utilize the rich semantic information contained in the operating state of mobile nodes, and that in low-altitude high-dynamic scenarios, rapidly changing Doppler frequency shifts can cause nonlinear changes in the phase of the preamble sequence, severely weakening the concentration of relevant peaks and leading to inaccurate timing and position determination, this invention proposes a timing synchronization method and system for low-altitude UAVs based on semantic communication assistance.

[0005] The technical solution of this invention is: a timing synchronization method for low-altitude unmanned aerial vehicles based on semantic communication assistance, comprising the following steps:

[0006] S1. Construct a semantic preamble library and determine the shared mapping relationship between the transceiver and receiver;

[0007] S2. Using each semantic preamble sequence in the semantic preamble code library, perform sliding correlation matching on the received signal to determine the timing metric vector corresponding to each semantic preamble sequence;

[0008] S3. Determine the index and coarse timing offset estimate of the semantic leader sequence based on the timing metric vector corresponding to each semantic leader sequence.

[0009] S4. Based on the index of the shared mapping relationship and the semantic preamble sequence, look up the table to determine the running speed range corresponding to the index, and determine the median running speed of the running speed range. Calculate the median Doppler frequency shift estimate based on the median running speed.

[0010] S5. Use the median of the Doppler frequency shift estimation to perform Doppler frequency shift compensation on the received signal to obtain the compensated received signal;

[0011] S6. Based on the compensated received signal and the semantic preamble sequence corresponding to the index, update the timing metric, and refine the coarse timing offset estimate according to the updated timing metric to obtain the refined timing offset estimate.

[0012] Furthermore, the semantic preamble code library includes several semantic preamble sequences;

[0013] Each semantic preamble sequence corresponds to a different semantic primitive representing the running state of a mobile node;

[0014] Shared mapping relationships are used to construct the correspondence between semantic preamble sequences, runtime state semantic primitives, and runtime speed ranges.

[0015] Furthermore, the semantic primitives of the mobile node's operating state include several operating speed states of the mobile node;

[0016] Mobile nodes include drones, ground vehicles, or low-altitude electric vertical takeoff and landing (EVTOL) aircraft.

[0017] Furthermore, when the mobile node is an unmanned aerial vehicle (UAV), the operational state semantic primitives include at least two of the UAV's hovering state, constant speed navigation state, acceleration maneuvering state, and landing state.

[0018] Furthermore, S2 includes the following sub-steps:

[0019] S21. Perform sliding correlation operation on the received signal and each semantic preamble sequence to obtain the sliding correlation output;

[0020] S22. Perform energy normalization on the sliding correlation output to obtain the timing metric corresponding to each semantic leader sequence;

[0021] S23. Based on the timing metrics corresponding to each semantic preamble sequence, form timing metric vectors corresponding to each semantic preamble sequence.

[0022] Furthermore, sliding correlation output for:

[0023] ;

[0024] in, In order to receive signals, For the first A semantic leading sequence, The length of the semantic leader sequence. This is the starting position of the sliding window. Indicates conjugate operation;

[0025] Energy normalization is performed as follows:

[0026] ;

[0027] in, For the first A semantic preamble sequence at the beginning of the sliding window Timed measurement at the location.

[0028] Furthermore, in S3, the maximum value of the timing metric vector corresponding to the semantic preamble sequence is taken as the maximum matching value of the semantic preamble sequence. All semantic preamble sequences in the semantic preamble code library are traversed to obtain a set of matching values ​​composed of each maximum matching value.

[0029] The index of the semantic preamble sequence actually transmitted by the transmitter is determined based on the set of matching values, and a coarse timing offset estimate is obtained based on the position of the maximum value of the timing metric vector corresponding to the matched semantic preamble sequence.

[0030] Index of semantic leader sequence for:

[0031] ;

[0032] in, For the first A semantic preamble sequence at the beginning of the sliding window Timed measurement at the location, To obtain the maximum value.

[0033] Furthermore, the median of the Doppler frequency shift estimate for:

[0034] ;

[0035] in, The median running speed of the mobile node is obtained by looking up a table based on the estimated semantic preamble sequence index and shared mapping relationship. The subcarrier spacing.

[0036] Furthermore, updated timing metrics for:

[0037] ;

[0038] in, This is the starting position of the sliding window. The length of the semantic leader sequence. The received signal after Doppler frequency shift compensation. To match the estimated index The corresponding semantic leader sequence;

[0039] Refined timing offset estimate for:

[0040] .

[0041] Based on the above methods, this invention also proposes a timing synchronization system for low-altitude unmanned aerial vehicles (UAVs) based on semantic communication assistance, comprising:

[0042] The semantic preamble library construction and sharing module is used to construct the semantic preamble library and determine the shared mapping relationship between the transceiver end;

[0043] The timing metric calculation module is used to perform sliding correlation matching on the received signal using each semantic preamble sequence in the semantic preamble code library to determine the timing metric vector corresponding to each semantic preamble sequence.

[0044] The semantic preamble index and coarse timing estimation module determines the index and coarse timing offset estimate of the semantic preamble sequence based on the timing metric vector corresponding to each semantic preamble sequence.

[0045] The Doppler estimation and compensation module is used to look up the table based on the shared mapping relationship and the index of the semantic preamble sequence to determine the running speed range corresponding to the index, and to determine the median running speed of the running speed range. The median running speed is then used to calculate the median Doppler frequency shift estimate. The median Doppler frequency shift estimate is used to compensate the received signal for Doppler frequency shift to obtain the compensated received signal.

[0046] The timing refinement module is used to update the timing metric based on the compensated received signal and the semantic preamble sequence corresponding to the index, and refine the coarse timing offset estimate based on the updated timing metric to obtain the refined timing offset estimate.

[0047] The beneficial effects of this invention are:

[0048] (1) This invention establishes a shared mapping relationship between the semantic preamble sequence and the semantic primitives of the mobile node's operating state, enabling the semantic preamble sequence to have both timing synchronization and operating state representation functions. Furthermore, by comparing timing metrics, the semantic preamble sequence index and coarse timing offset estimate are obtained simultaneously, thereby improving the utilization efficiency of preamble resources and simplifying the synchronization processing flow at the receiving end. Based on this, the corresponding operating speed range is determined according to the semantic preamble sequence index. The midpoint value within this range is used for Doppler frequency shift estimation and compensation, and the coarse timing offset is refined, effectively reducing the interference of high-dynamic motion on timing synchronization and significantly improving the synchronization reliability and anti-Doppler capability of the communication link. The above technical means solve the technical problem of easy loss of communication synchronization for low-altitude aircraft under high-maneuver conditions, realizing a technological leap from "single synchronization function" to "synchronization + state awareness fusion," demonstrating outstanding technological advancement and irreplaceability.

[0049] (2) This invention helps reduce data retransmission, communication delay, terminal power consumption, and receiver processing overhead caused by synchronization mismatch, directly reducing the battery operating cost and charging turnover frequency of a single mission for low-altitude aircraft, extending loiter time, and improving the mission execution efficiency of a single sortie. For commercial scenarios such as logistics transportation, emergency communication, low-altitude inspection, and air-ground coordination, this invention can effectively avoid mission failure and asset damage caused by link interruption, ensuring the continuity and safety of high-value operations, and has clear market application prospects and considerable economic benefits.

[0050] (3) This invention promotes the development of traditional fixed leader from a single synchronization function to a combination of timing synchronization and operational status representation, providing key core technology support for the large-scale, high-frequency, and high-reliability communication needs in the low-altitude economy. As a core invention patent of a strategic emerging industry, this invention helps to break through the common bottleneck of low-altitude communication synchronization that restricts the industry's scale, and has important strategic significance for the independent control of my country's low-altitude economic industrial chain and the enhancement of its global competitiveness. Attached Figure Description

[0051] Figure 1 A flowchart of a timing synchronization method for low-altitude unmanned aerial vehicles based on semantic communication;

[0052] Figure 2 Flowchart for semantic leader sequence loop matching processing;

[0053] Figure 3 A schematic diagram of a timing synchronization system for low-altitude unmanned aerial vehicles (UAVs) based on semantic communication assistance;

[0054] Figure 4 This is a comparison chart of the timing synchronization error rates of the method of the present invention and the comparative method under different signal-to-noise ratio conditions;

[0055] Figure 5 This is a comparison chart of the timing synchronization error rates of the method of the present invention and the comparative method under different operating speed ranges. Detailed Implementation

[0056] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0057] like Figure 1 As shown, this invention provides a timing synchronization method for low-altitude unmanned aerial vehicles (UAVs) based on semantic communication assistance, comprising the following steps:

[0058] S1. Construct a semantic preamble library and determine the shared mapping relationship between the transceiver and receiver;

[0059] S2. Using each semantic preamble sequence in the semantic preamble code library, perform sliding correlation matching on the received signal to determine the timing metric vector corresponding to each semantic preamble sequence;

[0060] S3. Determine the index and coarse timing offset estimate of the semantic leader sequence based on the timing metric vector corresponding to each semantic leader sequence.

[0061] S4. Based on the index of the shared mapping relationship and the semantic preamble sequence, look up the table to determine the running speed range corresponding to the index, and determine the median running speed of the running speed range. Calculate the median Doppler frequency shift estimate based on the median running speed.

[0062] S5. Use the median of the Doppler frequency shift estimation to perform Doppler frequency shift compensation on the received signal to obtain the compensated received signal;

[0063] S6. Based on the compensated received signal and the semantic preamble sequence corresponding to the index, update the timing metric, and refine the coarse timing offset estimate according to the updated timing metric to obtain the refined timing offset estimate.

[0064] This method is applied to an orthogonal frequency division multiplexing (OFDM) communication system between a low-altitude unmanned aerial vehicle (UAV) and a ground receiver. The UAV acts as the transmitter, and the ground base station or ground receiving equipment acts as the receiver. The communication frames transmitted by the transmitter include a semantic preamble sequence and data information. The receiver uses the semantic preamble sequence to perform semantic preamble recognition, coarse timing offset estimation, Doppler frequency shift compensation, and timing offset refinement.

[0065] In this embodiment of the invention, the semantic preamble library includes several semantic preamble sequences;

[0066] Each semantic preamble sequence corresponds to a different semantic primitive representing the running state of a mobile node;

[0067] Shared mapping relationships are used to construct the correspondence between semantic preamble sequences, runtime state semantic primitives, and runtime speed ranges.

[0068] In this embodiment of the invention, the semantic primitive of the mobile node running state includes several running speed states of the mobile node;

[0069] Mobile nodes include drones, ground vehicles, or low-altitude electric vertical takeoff and landing (EVTOL) aircraft.

[0070] In this embodiment of the invention, when the mobile node is a drone, the operational state semantic primitive includes at least two of the drone's hovering state, constant speed navigation state, acceleration maneuvering state, and landing state.

[0071] A semantic preamble sequence is generated for each runtime state semantic primitive. The semantic preamble sequence is an orthogonal sequence generated based on the runtime state semantic primitive, and different runtime state semantic primitives correspond to different semantic preamble sequences.

[0072] In practice, multiple distinct root indices can be selected to generate Zadoff-Chu sequences, and the lengths of each root index and the semantic preamble sequence can be made coprime, thus obtaining semantic preamble sequences with different sequence structures and good correlation properties. After energy normalization, each generated semantic preamble sequence is stored in the semantic preamble code library according to a preset index.

[0073] The transmitter and receiver are pre-configured with the same semantic preamble library and a shared mapping relationship is established between the running state semantic primitives, running speed range, semantic preamble sequence index, and semantic preamble sequence.

[0074] In practice, the shared mapping relationship can be stored in the form of a mapping table at both the transmitter and receiver. Each entry in the mapping table includes at least one runtime semantic primitive, the runtime speed range corresponding to that runtime semantic primitive, the semantic preamble sequence index, and the corresponding semantic preamble sequence.

[0075] When a UAV sends a communication signal, it determines the corresponding semantic primitive of the current operating state, selects the corresponding semantic preamble sequence according to the shared mapping relationship, sets the selected semantic preamble sequence in the preamble position of the communication frame, and then sends it.

[0076] In this embodiment, the operational state semantic primitive is used to represent the operational state of the low-altitude UAV and its corresponding speed information, so that the semantic preamble sequence can characterize the operational state of the low-altitude UAV while being used for timing synchronization.

[0077] In this embodiment of the invention, S2 includes the following sub-steps:

[0078] S21. Perform sliding correlation operation on the received signal and each semantic preamble sequence to obtain the sliding correlation output;

[0079] S22. Perform energy normalization on the sliding correlation output to obtain the timing metric corresponding to each semantic leader sequence;

[0080] S23. Based on the timing metrics corresponding to each semantic preamble sequence, form timing metric vectors corresponding to each semantic preamble sequence.

[0081] In this embodiment of the invention, sliding correlation output for:

[0082] ;

[0083] in, In order to receive signals, For the first A semantic leading sequence, The length of the semantic leader sequence. This is the starting position of the sliding window. Indicates conjugate operation;

[0084] To reduce the impact of changes in received signal energy on the correlation matching results, the sliding correlation output is... Energy normalization is performed.

[0085] Energy normalization is performed as follows:

[0086] ;

[0087] in, For the first A semantic preamble sequence at the beginning of the sliding window Timed measurement at the location.

[0088] The following describes in detail the cyclic matching process of semantic leader sequences, such as... Figure 2 As shown.

[0089] The semantic preamble library includes There are semantic leader sequences, among which... This represents the total number of semantic leader sequences.

[0090] A1. Initialize the semantic leader sequence index , i =0,1,…, K -1.

[0091] A2. Select the first from the semantic preamble library. semantic leading sequence .

[0092] A3. Receive the signal With the The sliding correlation operation is performed on the semantic leader sequence to obtain the th semantic leader sequence. A semantic preamble sequence at the starting position Sliding correlation output at the location .

[0093] A4. Obtain the sliding correlation output. After energy normalization, we obtain the first... A leading index in Timed measurement at the location ,

[0094] A5. Update and save the first... Timing metric vector corresponding to each semantic preamble sequence .

[0095] A6. Determine all semantic preamble sequences in the semantic preamble code library. Has all processing been completed? If not, proceed to S27; if completed, proceed to S28.

[0096] A7, Order Then return to step S22 and select the next semantic leader sequence for processing.

[0097] A8. Obtain the set of timing metric vectors corresponding to each semantic preamble sequence.

[0098] It should be noted that each timing metric vector reflects the degree of matching between the corresponding semantic preamble sequence and the received signal at different candidate timing positions. The larger the timing metric, the higher the degree of matching between the semantic preamble sequence and the received signal at the corresponding position.

[0099] In this embodiment of the invention, in S3, the maximum value of the timing metric vector corresponding to the semantic preamble sequence is taken as the maximum matching value of the semantic preamble sequence. All semantic preamble sequences in the semantic preamble code library are traversed to obtain a set of matching values ​​composed of each maximum matching value.

[0100] The index of the semantic preamble sequence actually transmitted by the transmitter is determined based on the set of matching values, and a coarse timing offset estimate is obtained based on the position of the maximum value of the timing metric vector corresponding to the matched semantic preamble sequence.

[0101] Index of semantic leader sequence for:

[0102] ;

[0103] in, For the first A semantic preamble sequence at the beginning of the sliding window Timed measurement at the location, To obtain the maximum value.

[0104] In practice, the receiver sets up a maximum value search unit to search for the maximum value in each timing metric vector, and then compares the maximum matching value corresponding to each semantic preamble sequence. The semantic preamble sequence with the largest maximum matching value is determined as the semantic preamble sequence actually sent by the transmitter.

[0105] After determining the semantic preamble sequence index, the receiver at the first... The position of the maximum timing metric is determined from the timing metric vector corresponding to each semantic leader sequence, and this position is determined as the coarse timing offset estimate.

[0106] Thus, the receiver obtains both the index of the semantic preamble sequence actually transmitted by the transmitter and the coarse timing offset estimate of the received signal through a single semantic preamble library matching.

[0107] It should be noted that the semantic preamble sequence index is not only used to determine the actual semantic preamble sequence sent, but also to determine the operating status and operating speed range of the low-altitude UAV based on the shared mapping relationship between the transmitting and receiving ends.

[0108] In this embodiment of the invention, the median of the Doppler frequency shift estimation... for:

[0109] ;

[0110] in, The median running speed of the mobile node is obtained by looking up a table based on the estimated semantic preamble sequence index and shared mapping relationship. The subcarrier spacing.

[0111] In practical implementation, the receiving end uses the estimated semantic preamble sequence index as the lookup address of the shared mapping table to read the corresponding runtime semantic primitives and runtime speed range. Let the runtime speed range be... Then the median operating speed within this operating speed range for:

[0112] ;

[0113] in, Indicates the left endpoint of the operating speed range. Indicates the right endpoint of the operating speed range.

[0114] The receiver uses the median operating speed as a representative value of the current operating speed state, and calculates the median Doppler frequency shift estimate based on the median operating speed.

[0115] It should be noted that the operating speed estimation result obtained by this invention is the median of the operating speed range corresponding to the semantic preamble sequence index, rather than a direct estimation of the continuous operating speed values ​​of the mobile node. The operating speed range corresponds to the actual operating state of the low-altitude UAV and is pre-configured by the transmitter and receiver according to the same rules, thereby ensuring that the receiver obtains speed information consistent with the current operating state of the transmitter based on the semantic preamble sequence index.

[0116] In S5, in specific implementation, a compensation signal can be generated by controlling the numerically controlled oscillator based on the median of the Doppler frequency shift estimation, and the compensation signal can be multiplied with the received signal sample by sample by a complex multiplier to offset or reduce the Doppler phase change caused by the movement of the low-altitude UAV.

[0117] In the software implementation, the processor can also generate the corresponding compensation sequence based on the median of the Doppler frequency shift estimation and perform sample-by-sample compensation on the received signal stored in the receive buffer.

[0118] It should be noted that the purpose of Doppler frequency shift compensation is to reduce the phase rotation of the semantic preamble sequence caused by the movement of the UAV and enhance the correlation peak of the semantic preamble sequence after compensation, thereby providing a basis for the received signal for timing offset refinement.

[0119] In this embodiment of the invention, the updated timing metric for:

[0120] ;

[0121] in, The length of the semantic leader sequence. The received signal after Doppler frequency shift compensation. To match the estimated index The corresponding semantic leader sequence;

[0122] Refined timing offset estimate for:

[0123] .

[0124] In practice, the receiving end can update the timing metric within the original candidate timing position range, or it can set a refined search interval near the coarse timing offset estimate and update the timing metric only within the refined search interval to reduce the amount of computation.

[0125] Unlike the semantic preamble library traversal in step S2, in step S6, the receiver only utilizes the already identified first... Each semantic preamble sequence is used to match the compensated received signal, eliminating the need to traverse all semantic preamble sequences in the semantic preamble code library again.

[0126] After obtaining the refined timing offset estimate, the receiving end determines the starting position of the orthogonal frequency division multiplexing symbol based on the refined timing offset estimate, and performs cyclic prefix removal, discrete Fourier transform and subsequent data demodulation processing on the received signal.

[0127] Based on the above methods, such as Figure 3 As shown, the present invention also proposes a timing synchronization system for low-altitude unmanned aerial vehicles (UAVs) based on semantic communication assistance. The system includes a UAV as the transmitter, a ground base station as the receiver, a memory, and a processor.

[0128] (1) The UAV selects the corresponding semantic preamble sequence according to the current operating status, combines the semantic preamble sequence and data information to form a communication frame, and sends the communication frame to the ground base station. Among them, the semantic preamble sequence is used to provide timing synchronization reference and characterize the semantics of the UAV's operating status, and the data information is used to carry the service data to be transmitted.

[0129] (2) The ground base station is used to receive communication frames sent by the UAV, form a received signal to be processed, and input the received signal into the processor. The communication frame includes a semantic preamble sequence and data information.

[0130] (3) The memory and processor are interconnected and work together to complete the timing synchronization processing of the received signal. The memory stores the semantic preamble library and the shared mapping relationship between the transceiver and receiver. The processor calls the semantic preamble library and queries the shared mapping relationship between the transceiver and receiver based on the index of the semantic preamble sequence. It then performs timing measurement calculations, semantic preamble index recognition, coarse timing estimation, Doppler compensation, and timing refinement processing on the received signal. The memory and processor are equipped with the following functional modules:

[0131] 1) The semantic preamble library and shared module are located in memory 1 and are used to store the semantic preamble library and the shared mapping relationship between the transceiver and receiver. The shared mapping relationship is stored in the form of a mapping table, which includes an index, semantic state, speed range, and preamble sequence;

[0132] Among them, the operating speed of the drone is divided into Each speed range corresponds to semantic states and A semantic leading sequence. The index values ​​are 0, 1, ... K -1. Index 0 corresponds to state 1 and speed range. and semantic leader sequence Index 1 corresponds to state 2 and speed range. and semantic leader sequence Index 2 corresponds to state 3 and speed range. and semantic leader sequence And so on, index Corresponding state Speed ​​range and semantic leader sequence .in, Let be the boundary of the velocity intervals arranged sequentially by velocity magnitude, and satisfy . .

[0133] 2) Timing metric calculation module 2, located in the processor, is used to perform sliding correlation matching on the received signal using each semantic preamble sequence in the semantic preamble code library to determine the timing metric vector corresponding to each semantic preamble sequence;

[0134] 3) Semantic Preamble Index and Timing Estimation Module 3, located in the processor, is used to determine the index and coarse timing offset estimate of the semantic preamble sequence based on the timing metric vector corresponding to each semantic preamble sequence.

[0135] 4) Doppler estimation and compensation module 4, located in the processor, is used to query the shared mapping relationship between the transceiver end according to the index of the semantic preamble sequence, determine the running speed range corresponding to the index, determine the median running speed of the running speed range, calculate the median Doppler frequency shift estimate based on the median running speed, and use the median Doppler frequency shift estimate to perform Doppler frequency shift compensation on the received signal to obtain the compensated received signal;

[0136] 5) Timing refinement module 5, located in the processor, is used to update the timing metric based on the compensated received signal and the semantic preamble sequence corresponding to the index, and refine the coarse timing offset estimate based on the updated timing metric to obtain the refined timing offset estimate.

[0137] Reference Figure 4 and Figure 5 This embodiment further verifies the timing synchronization effect of the method of the present invention through simulation. The simulation scenario is an orthogonal frequency division multiplexing communication scenario between a low-altitude UAV and a ground receiver, and the receiver uses the timing synchronization error rate as a performance evaluation index. The comparison methods include the traditional fixed preamble timing synchronization method, the semantic preamble timing synchronization method without Doppler shift compensation, and the method of the present invention. Among them, the traditional fixed preamble timing synchronization method uses a fixed preamble sequence for sliding correlation matching; the semantic preamble timing synchronization method without Doppler shift compensation can use the semantic preamble sequence for index recognition and coarse timing estimation, but does not use the operating speed range for Doppler shift compensation; the method of the present invention, after obtaining the semantic preamble sequence index and coarse timing offset estimate, further determines the operating speed range according to the shared mapping relationship, and uses the operating speed range to assist in Doppler shift compensation and timing offset refinement.

[0138] like Figure 4As shown, under different signal-to-noise ratio (SNR) conditions, the timing synchronization error rates of both the proposed method and the comparative method decrease overall with increasing SNR. Compared with traditional fixed preamble timing synchronization methods and semantic preamble timing synchronization methods without Doppler shift compensation, the proposed method achieves a lower timing synchronization error rate. This result demonstrates that the proposed method, by obtaining the mobile node's operating speed range through semantic preamble sequence recognition and utilizing this operating speed range to assist in Doppler shift compensation and timing offset refinement, can improve the accuracy of the receiver in determining the start position of communication frames or orthogonal frequency division multiplexing (OFDM) symbols.

[0139] like Figure 5 As shown, under different operating speed ranges, the impact of Doppler frequency shift on timing synchronization performance increases with the increase of the mobile node's operating speed range, and the timing synchronization error rate of the comparative methods increases to varying degrees. The method of this invention queries the shared mapping relationship based on the estimated semantic preamble sequence index to obtain the corresponding operating speed range, and calculates the estimated Doppler frequency shift value based on the operating speed range to compensate for the Doppler frequency shift of the received signal. Therefore, it can maintain a low timing synchronization error rate even under a large operating speed range. This result demonstrates that the method of this invention can adapt to the Doppler frequency shift changes caused by the high-speed movement of low-altitude UAVs, improving the timing synchronization reliability in low-altitude, high-dynamic communication scenarios.

[0140] The simulation results above show that by combining semantic preamble sequence recognition, operating speed range determination, Doppler frequency shift compensation and timing offset refinement, the present invention can reduce the impact of noise and high dynamic motion on timing synchronization and improve the synchronization reliability of the orthogonal frequency division multiplexing communication link of low-altitude UAVs.

[0141] In this embodiment, the receiving end can directly use the coarse timing offset estimate as the timing synchronization result. This embodiment does not require Doppler frequency shift compensation and timing offset refinement, and is suitable for scenarios where the Doppler frequency shift caused by the movement of mobile nodes has a small impact, or where the receiving end needs to reduce the computational load of synchronization processing.

[0142] The above modules can be implemented by a processor executing a computer program stored in memory, or by a digital signal processor, a field-programmable gate array, or an application-specific integrated circuit, or by a combination of software and hardware.

[0143] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A timing synchronization method for low-altitude unmanned aerial vehicles (UAVs) based on semantic communication assistance, characterized in that, Includes the following steps: S1. Construct a semantic preamble library and determine the shared mapping relationship between the transceiver and receiver; S2. Using each semantic preamble sequence in the semantic preamble code library, perform sliding correlation matching on the received signal to determine the timing metric vector corresponding to each semantic preamble sequence; S3. Determine the index and coarse timing offset estimate of the semantic leader sequence based on the timing metric vector corresponding to each semantic leader sequence. S4. Based on the index of the shared mapping relationship and the semantic preamble sequence, look up the table to determine the running speed range corresponding to the index, and determine the median running speed of the running speed range. Calculate the median Doppler frequency shift estimate based on the median running speed. S5. Use the median of the Doppler frequency shift estimation to perform Doppler frequency shift compensation on the received signal to obtain the compensated received signal; S6. Based on the compensated received signal and the semantic preamble sequence corresponding to the index, update the timing metric, and refine the coarse timing offset estimate according to the updated timing metric to obtain the refined timing offset estimate.

2. The timing synchronization method for low-altitude unmanned aerial vehicles based on semantic communication assistance according to claim 1, characterized in that, The semantic preamble code library includes several semantic preamble sequences; each semantic preamble sequence corresponds to a different semantic primitive of the running state of a mobile node. The shared mapping relationship is used to construct the correspondence between the semantic preamble sequence, the semantic primitive of the running state, and the running speed range.

3. The timing synchronization method for low-altitude UAVs based on semantic communication assistance according to claim 2, characterized in that, The semantic primitives of the mobile node's running state include several running speed states of the mobile node; The mobile nodes include drones, ground vehicles, or low-altitude electric vertical takeoff and landing aircraft.

4. The timing synchronization method for low-altitude UAVs based on semantic communication assistance according to claim 3, characterized in that, When the mobile node is an unmanned aerial vehicle (UAV), the operational state semantic primitives include at least two of the following: hovering state, constant speed navigation state, acceleration maneuvering state, and landing state.

5. The timing synchronization method for low-altitude unmanned aerial vehicles based on semantic communication assistance according to claim 1, characterized in that, S2 includes the following sub-steps: S21. Perform sliding correlation operation on the received signal and each semantic preamble sequence to obtain the sliding correlation output; S22. Perform energy normalization on the sliding correlation output to obtain the timing metric corresponding to each semantic leader sequence; S23. Based on the timing metrics corresponding to each semantic preamble sequence, form timing metric vectors corresponding to each semantic preamble sequence.

6. The timing synchronization method for low-altitude unmanned aerial vehicles based on semantic communication assistance according to claim 5, characterized in that, The sliding correlation output for: ； in, In order to receive signals, For the first A semantic leading sequence, The length of the semantic leader sequence. This is the starting position of the sliding window. Indicates conjugate operation; The energy normalization process is as follows: ； in, For the first A semantic preamble sequence at the beginning of the sliding window Timed measurement at the location.

7. The timing synchronization method for low-altitude unmanned aerial vehicles based on semantic communication assistance according to claim 1, characterized in that, In S3, the maximum value of the timing metric vector corresponding to the semantic preamble sequence is taken as the maximum matching value of the semantic preamble sequence. All semantic preamble sequences in the semantic preamble code library are traversed to obtain a set of matching values ​​composed of each maximum matching value. The index of the semantic preamble sequence actually transmitted by the transmitter is determined based on the set of matching values, and a coarse timing offset estimate is obtained based on the position of the maximum value of the timing metric vector corresponding to the matched semantic preamble sequence. The index of the semantic preamble sequence for: ； in, For the first A semantic preamble sequence at the beginning of the sliding window Timed measurement at the location, To obtain the maximum value.

8. The timing synchronization method for low-altitude unmanned aerial vehicles based on semantic communication assistance according to claim 1, characterized in that, The median of the Doppler frequency shift estimate for: ； in, The median running speed of the mobile node is obtained by looking up a table based on the estimated semantic preamble sequence index and shared mapping relationship. The subcarrier spacing.

9. The timing synchronization method for low-altitude unmanned aerial vehicles based on semantic communication assistance according to claim 1, characterized in that, The updated timing metric for: ； in, This is the starting position of the sliding window. The length of the semantic leader sequence. The received signal after Doppler frequency shift compensation. To match the estimated index The corresponding semantic leader sequence; The refined timing offset estimate for: 。 10. A timing synchronization system for low-altitude unmanned aerial vehicles (UAVs) based on semantic communication assistance, characterized in that, include: The semantic preamble library construction and sharing module is used to construct the semantic preamble library and determine the shared mapping relationship between the transceiver end; The timing metric calculation module is used to perform sliding correlation matching on the received signal using each semantic preamble sequence in the semantic preamble code library to determine the timing metric vector corresponding to each semantic preamble sequence. The semantic preamble index and coarse timing estimation module determines the index and coarse timing offset estimate of the semantic preamble sequence based on the timing metric vector corresponding to each semantic preamble sequence. The Doppler estimation and compensation module is used to look up a table based on the shared mapping relationship and the index of the semantic preamble sequence to determine the running speed range corresponding to the index, and to determine the median running speed of the running speed range. Based on the median running speed, the median Doppler frequency shift estimate is calculated. The Doppler frequency shift is compensated by using the median of the Doppler frequency shift estimation to obtain the compensated received signal; The timing refinement module is used to update the timing metric based on the compensated received signal and the semantic preamble sequence corresponding to the index, and refine the coarse timing offset estimate based on the updated timing metric to obtain the refined timing offset estimate.

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