A time offset estimation method based on hysteresis back difference processing
By setting a polarity threshold for time offset estimation using a hysteresis hysteresis processing method, the problem of time offset estimation being susceptible to noise in low-orbit satellite communication is solved, thereby achieving stability of terminal time offset compensation and reliability of the communication link.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAN INSTITUE OF SPACE RADIO TECH
- Filing Date
- 2023-10-26
- Publication Date
- 2026-07-07
Smart Images
Figure CN117527038B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of satellite communication technology, and in particular relates to a time offset estimation method based on hysteresis processing. Background Technology
[0002] This task originates from the "StarNet" low-Earth orbit mobile communication satellite constellation system project. The L-band user link processor in this project employs an FDMA / TDMA burst communication system to handle user voice and data communications. Because the communication signal between the satellite and ground has a varying time delay as the satellite moves in the low-Earth orbit link, ground tracking compensation for this dynamic delay is primarily used. Typically, the ground terminal uses ephemeris information to calculate the relative time delay based on orbital parameters and then performs compensation. However, limited by the accuracy of the ground terminal's compensation and the accuracy of the ephemeris information, the signal received by the satellite after time delay compensation still has a time offset. This offset is characterized by monotonically changing and slowly varying, but when affected by noise, the error in the time offset estimated by the satellite, especially the polarity jitter near the zero value, can cause errors in subsequent compensation by the terminal, leading to demodulation failure of the subsequent signal on the satellite.
[0003] Reference 1: H. Yizhou, et al., Timing advanced estimation algorithm of low complexity based on DFT spectrum analysis for satellite system. China Communications, vol. 12, 2015. This paper uses the DFT spectrum analysis method to improve the accuracy of timing advance estimation values affected by Doppler shift.
[0004] Reference 2: Wenjin Wang, et al, Location-based timing advance estimation for 5G integrated LEO satellite communication. IEEE Transactions on Vehicular Technology, 2021. This reference utilizes ephemeris information and UE geographic location information for timing advance estimation, transforming the estimation formula into a quadratic optimization problem, thereby improving the timing advance estimation results and ensuring uplink frame alignment for different users.
[0005] Reference 3: Zhen Li, Research on Key Technologies of Uplink Synchronization in Low-Earth Orbit LTE Satellite Mobile Communication System, Doctoral Dissertation, Xi'an University of Electronic Science and Technology, 2018. This paper proposes a TA update algorithm based on higher-order statistics by utilizing all autocorrelation products between two adjacent SRS received signals. Through the design of the autocorrelation function and differential normalization function in the timing metric function, the scalability range of the correlation length and the sharpness of the timing peak are effectively improved. The superiority of the proposed algorithm is theoretically evaluated based on criteria such as class separability, robustness to multipath effects and CFO, and computational complexity. Simulation results are consistent with the theoretical analysis, demonstrating that the proposed method can achieve lower false alarm probability, missed detection probability, and timing estimation error under the satellite multipath channel model, while its detection threshold has a larger dynamic range.
[0006] Reference 4: Xu Xiaoshun et al., An Uplink Synchronization Control Algorithm Based on LTE System, Information Technology, 2019. This paper proposes an uplink synchronization control algorithm based on the MAC layer of the LTE system, which provides the UE with reasonable timing advance instruction parameters and forces the terminal to adjust only once every 6 rounds of TA to avoid adjustment errors.
[0007] Reference 5: Chen Li, A method, apparatus, and system for acquiring and returning uplink timing advance, 2017. This patent first determines the target transmission point from which the terminal needs to transmit data; it then initiates a request to the network side to acquire the uplink timing advance, which is the uplink timing advance required by the terminal to transmit data to the target transmission point; and finally, it determines the uplink timing advance required by the terminal to transmit data to the target transmission point based on the message carrying the uplink timing advance returned by the network side.
[0008] Reference 6: Wang Wenjin et al., A Downlink Time-Frequency Synchronization Method for Low-Earth Orbit Satellite Mobile Communication System, 2018. This patent can solve the time-frequency asynchrony problem caused by large frequency offset and low signal-to-noise ratio when OFDM technology is applied to low-Earth orbit satellite mobile communication scenarios. It uses the master synchronization sequence specified by the LTE protocol to achieve downlink time-frequency synchronization of the low-Earth orbit satellite mobile communication system. First, a large-range time offset search is performed according to the time offset estimation formula, and then a small-range two-dimensional time-frequency search is performed near several time offset peaks. This reduces the complexity compared to directly performing a two-dimensional time-frequency search on the likelihood function. The time offset search is achieved by performing correlation operations between the local synchronization sequence multiplied by the weighting coefficient and the received sequence.
[0009] Current literature on timing advance and timing skew estimation shows that timing skew estimation mainly uses other methods to process timing skew, and does not use methods based on hysteresis processing. Summary of the Invention
[0010] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a time offset estimation method based on hysteresis processing. This method utilizes the monotonic and slow change characteristics of the terminal delay compensation value to prevent noise from causing abnormal polarity jitter in the estimated time offset of the satellite and thus leading to incorrect terminal compensation.
[0011] The present invention further provides a time offset compensation system that can be adapted to low-Earth orbit satellite-to-ground systems.
[0012] The objective of this invention is achieved through the following technical solution: a time-bias estimation method based on hysteresis processing, comprising:
[0013] Based on the symbol rate of the communication signal, set the hysteresis processing threshold T. th ;
[0014] The satellite completes the initial time offset estimation based on the received uplink access signal; then, based on the polarity of the previously estimated time offset, it processes the polarity of the current estimated time offset in a hysteresis manner.
[0015] Preferably, a processing threshold T for hysteresis is set. th Symbol rate R s The reciprocal of.
[0016] Preferably, if the previous estimated time bias was positive, then the current estimated time bias is not greater than -T. th Only when the time bias is considered to have truly reached a negative value is a negative time bias reported; if the previous estimated time bias was negative, a negative time bias is reported only if the current estimated time bias is not less than T. th Only when the time deviation is considered to have truly reached a positive value will a positive time deviation be reported.
[0017] Preferably, the currently estimated time bias is expressed as:
[0018] In the formula, T' A (i) represents the time offset estimated by the current satellite, T' A (i-1) represents the time offset estimated by the previous satellite.
[0019] A satellite-to-ground time offset compensation system for a low-Earth orbit satellite includes a ground terminal and a low-Earth orbit satellite; the ground terminal and the low-Earth orbit satellite use an FDMA / TDMA communication system.
[0020] During initial access, the ground terminal calculates the satellite-to-ground time delay based on ephemeris information and sends uplink access data to the low-Earth orbit satellite based on the satellite-to-ground time delay; the low-Earth orbit satellite receives the uplink access data sent by the ground terminal, estimates the time offset at this time, and attaches the time offset estimate to the next satellite downlink signal and sends it to the ground terminal.
[0021] After obtaining the time offset estimate from the satellite downlink signal, the ground terminal corrects the time delay and retransmits the uplink access data to the low-Earth orbit satellite based on the corrected time delay. The low-Earth orbit satellite receives the uplink access data sent by the ground terminal, estimates the time offset at this time, processes it according to the method described above to obtain a new time offset estimate, and attaches the new time offset estimate to the satellite downlink signal before sending it to the ground terminal. This process is repeated throughout the entire communication process to ensure the normal operation of the satellite-to-ground communication link.
[0022] Preferably, the physical layer of the low-orbit satellite receives the uplink access data sent by the ground terminal, estimates the time offset at this time, processes it to obtain a new time offset, sends the new time offset to the MAC layer, and the MAC layer attaches the new time offset estimate to the satellite downlink data of the user number to be forwarded, sends it to the physical layer, and the physical layer sends it to the ground terminal.
[0023] Preferably, the processing to obtain the new time offset includes:
[0024] If the previous time bias was positive, then the current estimated time bias is only positive if it is not greater than -T. th Only when the time bias is considered to have truly reached a negative value will a negative time bias be reported.
[0025] If the previous time bias was negative, then the current estimated time bias is not less than T only if the previous time bias was negative. th Only when the time deviation is considered to have truly reached a positive value will a positive time deviation be reported.
[0026] Preferably, the time bias of the current estimate obtained after processing is expressed as:
[0027]
[0028] In the formula, T' A (i) represents the time offset estimated by the current satellite, T' A (i-1) represents the time offset estimated by the previous satellite.
[0029] Preferably, the uplink access data needs to be filled with a certain number of fixed patterns and unique codes at fixed positions. The distribution of the unique codes can be discrete or continuous, and they are used for time-bias estimation.
[0030] The present invention eliminates the need for pre-synchronization between the low-orbit satellite and the ground terminal.
[0031] Compared with the prior art, the present invention has the following advantages:
[0032] This invention employs a hysteresis-based approach. First, a time offset estimation polarity threshold is set. Then, considering the relationship between the previously obtained time offset, the current time offset, and the estimated polarity threshold, the delay compensation value that the ground terminal needs to process is determined and sent to the corresponding ground terminal. This invention primarily utilizes the monotonic and slow-changing characteristics of the terminal delay compensation value to correct the abnormal polarity jitter in the estimated on-board time offset caused by noise, and the resulting terminal erroneous compensation, thereby improving the accuracy of the satellite-to-ground closed-loop time offset adjustment.
[0033] Low-Earth orbit satellites and ground terminals do not need to complete satellite-to-ground time synchronization in advance; this system and method can automatically achieve convergence of satellite-to-ground time synchronization. Attached Figure Description
[0034] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:
[0035] Figure 1 This is a schematic diagram of the satellite-to-ground time offset compensation process for a low-orbit satellite according to an embodiment of the present invention;
[0036] Figure 2 This is a diagram of the satellite-to-ground communication frame format according to an embodiment of the present invention;
[0037] Figure 3 The above is a simulation diagram of the algorithm processing in an embodiment of the present invention. Detailed Implementation
[0038] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0039] In the time offset estimation process, this invention utilizes the monotonic and slow-changing characteristics of the terminal delay compensation value to prevent noise from causing abnormal polarity jitter in the estimated on-board time offset, thus leading to incorrect terminal compensation. This invention employs hysteresis to set the time offset estimation polarity threshold, achieving the effect of eliminating time offset jitter near 0, ensuring effective processing after terminal compensation. The method steps are as follows:
[0040] (1) Set the hysteresis processing threshold T according to the symbol rate of the communication signal. th
[0041] Since the noise in low-Earth orbit satellite communication links is generally additive white Gaussian noise, its time bias estimation error usually does not exceed one symbol. Therefore, the processing threshold T for hysteresis can be set according to the symbol rate of the communication signal. th Symbol rate R s The reciprocal of, that is:
[0042]
[0043] (2) The satellite completes the first time offset estimation based on the received uplink access signal; then, based on the polarity of the previously estimated time offset, it processes the polarity of the current estimated time offset in a hysteresis manner.
[0044] This invention primarily utilizes hysteresis processing to study an uplink time offset estimation method for communication signals when noise causes abnormal polarity jitter in the estimated on-board time offset, leading to terminal error compensation. If the previously estimated time offset was positive, the method is applied only if the current estimated time offset is not greater than -T. th Only when the time bias is considered to have truly reached a negative value is a negative time bias reported; if the previous estimated time bias was negative, a negative time bias is reported only if the current estimated time bias is not less than T. th Only when the time offset reaches a positive value is the time offset considered to have truly reached a positive value, and a positive time offset is reported. In subsequent processing, the polarity of the current time offset is recorded each time, and the processing is the same as above.
[0045] The current estimated time bias is expressed as:
[0046] In the formula, T' A (i) represents the time offset estimated by the current satellite, T' A (i-1) represents the time offset estimated by the previous satellite.
[0047] The system used in this invention is a low-Earth orbit (LEO) satellite communication system. A schematic diagram of the LEO satellite's time offset compensation system is shown below. Figure 1 As shown, this system uses a regenerative forwarding processing mode and employs an FDMA / TDMA communication architecture.
[0048] During initial access, the ground terminal calculates the latency based on ephemeris information and sends uplink access data to the low-Earth orbit satellite according to the latency.
[0049] The physical layer of a low-Earth orbit satellite receives uplink access data sent by a ground terminal, estimates the time offset at that time, and sends the time offset to the MAC layer. The MAC layer then attaches the estimated time offset to the satellite downlink signal according to the user number to be forwarded, sends it to the physical layer, and finally sends it to the ground terminal.
[0050] Among them, the time-biased estimation algorithm can utilize Figure 2 The embodiment of the satellite-to-ground communication frame format has an effective information length of N, including a guard time and effective information. The effective information is filled with a fixed pattern of a certain number of symbols and a unique code at a fixed position. The distribution of the unique code can be discrete or continuous, and its length is K (generally greater than or equal to 16 symbols). Using the autocorrelation function formula 3 of the unique code, an autocorrelation spectrum can be obtained. The peak value of this spectrum is taken using formula 4, and the position corresponding to the peak value is the estimated value of the current time offset.
[0051]
[0052] T' A (i)=n max{R(n)} (Formula 4)
[0053] x() represents the valid information, and m and n represent the unique code and the position of the symbol in the valid information, respectively.
[0054] After obtaining the time offset from the satellite downlink signal, the ground terminal corrects the time delay and sends uplink access data to the low-Earth orbit satellite according to the corrected time delay.
[0055] The physical layer of the low-orbit satellite receives uplink access data sent by the ground terminal, estimates the time offset at this time, and processes it according to the time offset estimation method based on hysteresis processing to obtain a new time offset. The new time offset is sent to the MAC layer, which attaches the new time offset estimate to the satellite downlink signal according to the user number to be forwarded, sends it to the physical layer, and then sends it to the ground terminal.
[0056] The ground terminal uses the new time offset to correct the previously adjusted delay again, and then proceeds to transmit the uplink signal at the next moment. This process is repeated throughout the communication process to ensure the normal operation of the satellite-to-ground communication link even when the low-Earth orbit satellite is moving rapidly.
[0057] Simulation as Figure 3 As shown. By Figure 3 As can be seen, by using the hysteresis method to set the polarity threshold for time skew estimation, the polarity jitter of the estimation result of on-board time skew caused by noise is greatly reduced.
[0058] Another drawback of this method is that it increases the amount of satellite-to-ground signaling interaction. Generally, it should be combined with higher-level protocol processing to reduce this interaction. For example, in higher-level protocol processing, the modification interval for time offset changes should be determined based on parameters such as orbit and uplink / downlink communication intervals. Instead of sending the delay compensation value to the terminal every time, the delay compensation value can be sent to the terminal only after several satellite-to-ground communication intervals. This ensures that the number of satellite-to-ground signaling interactions is reduced without affecting terminal communication, thereby improving communication efficiency.
[0059] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.
[0060] The parts of this invention not described in detail are common knowledge to those skilled in the art.
Claims
1. A time-biased estimation method based on hysteresis processing, characterized in that... include: Set the hysteresis processing threshold based on the symbol rate of the communication signal. ; The satellite completes the initial time offset estimation based on the received uplink access signal; then, based on the polarity of the previously estimated time offset, it processes the polarity of the current estimated time offset in a hysteresis manner. Set the processing threshold for hysteresis Symbol rate The reciprocal of; If the previous estimated time bias was positive, then the current estimated time bias is not greater than 1. Only when the estimated time bias is negative is it considered to have truly reached a negative value, and a negative time bias is reported; if the previous estimated time bias was negative, only if the current estimated time bias is not less than Only when the time deviation is considered to have truly reached a positive value will a positive time deviation be reported.
2. The time-bias estimation method based on hysteresis processing according to claim 1, characterized in that: The current estimated time bias is expressed as: ; In the formula, The time offset estimated by the current satellite. This is the time offset estimated by the previous satellite.
3. A satellite-to-ground time offset compensation system for a low-Earth orbit satellite, comprising a ground terminal and a low-Earth orbit satellite; characterized in that: The ground terminal and the low-orbit satellite use an FDMA / TDMA communication system. During initial access, the ground terminal calculates the satellite-to-ground time delay based on ephemeris information and sends uplink access data to the low-Earth orbit satellite based on the satellite-to-ground time delay; The low-orbit satellite receives uplink access data sent by the ground terminal, estimates the time offset at this time, and attaches the estimated time offset value to the next satellite downlink signal and sends it to the ground terminal. After obtaining the time offset estimate from the satellite downlink signal, the ground terminal corrects the time delay and then sends uplink access data to the low-Earth orbit satellite again based on the corrected time delay. The low-orbit satellite receives uplink access data sent by the ground terminal, estimates the time offset at this time, processes it according to the method described in claim 1 to obtain a new time offset estimate, and attaches the new time offset estimate to the satellite downlink signal and sends it to the ground terminal. This process is repeated throughout the entire communication process to ensure the normal operation of the satellite-to-ground communication link. The new time offset obtained from the processing includes: If the previous time bias was positive, then the current estimated time bias is not greater than 1. Only when the time bias is considered to have truly reached a negative value will a negative time bias be reported. If the previous time bias was negative, then only if the current estimated time bias is not less than 1 / 3. Only when the time deviation is considered to have truly reached a positive value will a positive time deviation be reported.
4. The system according to claim 3, characterized in that: The physical layer of the low-Earth orbit satellite receives uplink access data sent by the ground terminal, estimates the time offset at this time, processes it to obtain a new time offset, and sends the new time offset to the MAC layer. The MAC layer, based on the user number to be forwarded, appends the new time offset estimate to the satellite downlink data of that user number and sends it to the physical layer, which then sends it to the ground terminal.
5. The system according to claim 3, characterized in that: The current estimated time bias is expressed as: ； In the formula, The time offset estimated by the current satellite. This is the time offset estimated by the previous satellite.
6. The system according to claim 3, characterized in that: The uplink access data needs to be filled with a certain number of fixed patterns and unique codes at fixed positions. The distribution of the unique codes can be discrete or continuous, and they are used for time-bias estimation.
7. The system according to claim 3, characterized in that: Low-Earth orbit satellites and ground terminals do not need to complete satellite-to-ground time synchronization in advance.