Timing deviation compensation method and device for orthogonal frequency division multiplexing signals

Abstract

The invention provides a timing deviation compensation method and device for an orthogonal frequency division multiplexing signal, which can be applied to the technical field of signal processing. Comprising the following steps: performing up-sampling on a to-be-synchronized orthogonal frequency division multiplexing signal to obtain an up-sampling signal; according to a first matching degree between the time domain synchronization symbol sequence template and a target time domain synchronization symbol sequence, determining respective first-level timing of N to-be-synchronized orthogonal frequency division multiplexing symbols; for any to-be-synchronized orthogonal frequency division multiplexing symbol, obtaining a second-level timing error of the to-be-synchronized orthogonal frequency division multiplexing symbol according to a second matching degree between cyclic prefixes and tail sections, which are respectively corresponding to a plurality of candidate starting moments, in the up-sampling signal; performing timing compensation on the up-sampling signal according to respective first-level timing and second-level timing errors of the N to-be-synchronized orthogonal frequency division multiplexing symbols to obtain a compensated up-sampling signal; and obtaining an orthogonal frequency division multiplexing signal according to the compensation up-sampling signal.

Description

Technical Field

[0001] This invention relates to the field of signal processing technology, and more specifically to a method and apparatus for timing deviation compensation of orthogonal frequency division multiplexed signals. Background Technology

[0002] With the development of mobile communication technology, terrestrial mobile communication networks can now achieve network speeds of up to gigabits per second and millisecond-level latency. However, due to the limited coverage of terrestrial cellular networks, communication and network service capabilities in areas not covered by terrestrial cellular networks, such as suburbs, mountainous areas, or sea areas, remain insufficient. To meet the demand for ubiquitous global connectivity, there has been a surge in the construction of space-segment information networks, such as low-Earth orbit satellite internet.

[0003] Due to the time-varying, high-speed relative motion between the low-Earth orbit (LEO) satellite and the ground terminal, the actual transmitted OFDM symbol period dynamically compresses or expands with this relative motion. Consequently, the number of sampling points and the sampling rate for each OFDM signal at the receiver exhibit dynamic changes. While the transmitter and receiver of a LEO satellite system can calculate the sampling rate correction factor and perform resampling compensation based on satellite ephemeris and terminal location information, timing errors can occur due to non-ideal factors in the satellite ephemeris or terminal location. This leads to inaccurate calculation of the sampling rate correction factor, and time-varying sampling rate errors remain even after resampling compensation. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method and apparatus for timing deviation compensation of orthogonal frequency division multiplexed signals.

[0005] According to a first aspect of the present invention, a method for timing deviation compensation of an orthogonal frequency division multiplexing (OFDM) signal is provided, comprising: upsampling an OFDM signal to be synchronized to obtain an upsampled signal, wherein the upsampled signal includes N sequentially arranged OFDM symbols to be synchronized, each OFDM symbol to be synchronized including a cyclic prefix and a valid portion including a tail segment, and N being an integer greater than 1; obtaining a first-level timing for each of the N OFDM symbols to be synchronized based on a first matching degree between a time-domain synchronization symbol sequence template and a target time-domain synchronization symbol sequence, wherein the sampling rate of the time-domain synchronization symbol sequence template is the same as the sampling rate of the upsampled signal, the target time-domain synchronization symbol sequence is extracted from the upsampled signal, and the first-level timing characterizes the OFDM symbol to be synchronized. The expected start time of the multiplexed symbol; for any one of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized, the second-level timing error of the OFDM symbol to be synchronized is obtained based on the second matching degree between the cyclic prefix and tail segments corresponding to the multiple candidate start times in the upsampled signal. The candidate start times are determined based on the first-level timing of the OFDM symbol to be synchronized, and the second-level timing error characterizes the offset of the actual start time of the OFDM symbol to be synchronized relative to the first-level timing. Based on the first-level timing and second-level timing errors of each of the N OFDM symbols to be synchronized, timing compensation is performed on the upsampled signal to obtain the compensated upsampled signal. Based on the compensated upsampled signal, the OFDM signal is obtained. According to an embodiment of the present invention, obtaining the first-level timing of each of N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized based on a first matching degree between a time-domain synchronization symbol sequence template and a target time-domain synchronization symbol sequence includes: determining a target relative delay from multiple candidate relative delays based on a first matching degree between multiple target time-domain synchronization symbol subsequences and the time-domain synchronization symbol sequence template, wherein the candidate relative delays are generated by sliding the time-domain synchronization symbol sequence template on the target time-domain synchronization symbol sequence, and the target time-domain synchronization symbol subsequences are subsequences extracted from the target time-domain synchronization symbol sequence with the same preset duration as the time-domain synchronization symbol sequence template, starting from the candidate relative delays; obtaining the expected start time of the target time-domain synchronization symbol sequence based on the target relative delays; and obtaining the first-level timing of each of the N OFDM symbols to be synchronized based on the expected start time of the target time-domain synchronization symbol sequence and the preset duration of the OFDM symbols to be synchronized.

[0006] According to an embodiment of the present invention, the target time-domain synchronization symbol sequence is a subsequence of the target time period extracted from the upsampled signal. The target time period is determined based on the preset protection duration, the estimated start time of the preset time-domain synchronization symbol sequence, and the preset duration of the preset time-domain synchronization symbol sequence; and / or the first matching degree is characterized by the cross-correlation function value.

[0007] According to an embodiment of the present invention, the second-level timing error of the orthogonal frequency division multiplexing (OFDM) symbol to be synchronized is obtained based on the second matching degree between the cyclic prefix and tail segment corresponding to each of the multiple candidate start times in the upsampled signal, including: for any candidate start time among the multiple candidate start times, extracting the cyclic prefix and tail segment corresponding to the candidate start time from the upsampled signal; determining the target start time from the multiple candidate start times based on the second matching degree between the cyclic prefix and tail segment corresponding to each of the multiple candidate start times; and obtaining the second-level timing error of the OFDM symbol to be synchronized based on the target start time.

[0008] According to an embodiment of the present invention, extracting a cyclic prefix and a tail segment corresponding to a candidate start time from an upsampled signal includes: extracting data corresponding to a first preset time period from the upsampled signal to obtain a cyclic prefix corresponding to a candidate start time, wherein the first preset time period is determined based on a preset duration of the candidate start time and the cyclic prefix; and extracting data corresponding to a second preset time period from the upsampled signal to obtain a tail segment corresponding to a candidate start time, wherein the second preset time period is determined based on the candidate start time, the preset duration of the cyclic prefix, and the preset duration of the orthogonal frequency division multiplexing symbol to be synchronized.

[0009] According to an embodiment of the present invention, obtaining an orthogonal frequency division multiplexing (OFDM) signal based on a compensated upsampled signal includes: performing OFDM demultiplexing demodulation on the compensated upsampled signal to obtain pilot symbols for each of N OFDM symbols to be synchronized; obtaining a third-level timing error for each of the N OFDM symbols to be synchronized based on the phase error between each of the N pilot symbols and the expected pilot symbol set, wherein the third-level timing error characterizes the residual timing deviation of the OFDM symbols to be synchronized after the first two levels of timing compensation; performing timing compensation on the upsampled signal based on the first-level timing error, the second-level timing error, and the third-level timing error of each of the N OFDM symbols to obtain a target compensated upsampled signal; and obtaining the OFDM signal based on the target compensated upsampled signal.

[0010] According to an embodiment of the present invention, the third-level timing error of each of the N pilot symbols to be synchronized is obtained based on the phase error between each of the N pilot symbols and the expected pilot symbol set, including: correcting the phase error between each of the N pilot symbols and the expected pilot symbol set to obtain the target phase error for each of the N pilot symbols; determining the demodulation bit error rate threshold and the number of groups of pilot symbols based on the demodulation bit error rate of the M previous orthogonal frequency division multiplexing signals to be synchronized; grouping the N pilot symbols according to the bit error rate threshold, the number of groups, and the index of the pilot symbols to obtain multiple groups of pilot symbols; and averaging the target phase errors of the multiple groups of pilot symbols to obtain the third-level timing error of the orthogonal frequency division multiplexing signal to be synchronized.

[0011] According to an embodiment of the present invention, the phase error between each of the N pilot symbols and the expected pilot symbol set is corrected to obtain the target phase error of each of the N pilot symbols. This includes: obtaining the average phase error of each of the N orthogonal frequency division multiplexing symbols to be synchronized based on the phase error between each of the N pilot symbols and the expected pilot symbol set; obtaining the intermediate phase error of each of the N pilot symbols based on the difference between each of the N phase errors and the average phase error; and smoothing the intermediate phase error of each of the N pilot symbols to obtain the target phase error of each of the N pilot symbols.

[0012] According to an embodiment of the present invention, the orthogonal frequency division multiplexing signal is demultiplexed and demodulated to obtain the target pilot symbols of each of the N orthogonal frequency division multiplexing symbols.

[0013] A second aspect of the present invention provides a timing deviation compensation device for an orthogonal frequency division multiplexing (OFDM) signal, comprising: a first obtaining module, configured to upsample the OFDM signal to be synchronized to obtain an upsampled signal, wherein the upsampled signal includes N sequentially arranged OFDM symbols to be synchronized, each OFDM symbol including a cyclic prefix and a valid portion including a tail segment, and N being an integer greater than 1; and a second obtaining module, configured to obtain a first-level timing for each of the N OFDM symbols to be synchronized based on a first matching degree between a time-domain synchronization symbol sequence template and a target time-domain synchronization symbol sequence, wherein the sampling rate of the time-domain synchronization symbol sequence template is the same as the sampling rate of the upsampled signal, the target time-domain synchronization symbol sequence is extracted from the upsampled signal, and the first-level timing characterizes the pre-synchronization of the OFDM symbols to be synchronized. The first module obtains the timing error of the orthogonal frequency division multiplexing (OFDM) symbol from the N OFDM symbols to be synchronized. The second module determines the timing error based on the second matching degree between the cyclic prefix and tail segments corresponding to the multiple candidate start times in the upsampled signal. The candidate start times are determined based on the first-level timing of the OFDM symbol, and the second-level timing error represents the offset of the actual start time of the OFDM symbol relative to the first-level timing. The third module compensates the upsampled signal based on the timing errors of the first and second levels of the N OFDM symbols to be synchronized, obtaining a compensated upsampled signal. The fifth module obtains the OFDM signal based on the compensated upsampled signal.

[0014] A third aspect of the present invention provides an electronic device comprising: one or more processors; and a memory for storing one or more computer programs, wherein the one or more processors execute the one or more computer programs to implement the steps of the method described above.

[0015] A fourth aspect of the present invention also provides a computer-readable storage medium having a computer program or instructions stored thereon, wherein the computer program or instructions, when executed by a processor, implement the steps of the above-described method.

[0016] A fifth aspect of the present invention also provides a computer program product, including a computer program or instructions that, when executed by a processor, implement the steps of the above-described method.

[0017] According to the timing deviation compensation method for orthogonal frequency division multiplexing (OFDM) signals provided by this invention, the sampling resolution of the OFDM signal to be synchronized can be improved by upsampling the signal to be synchronized, resulting in an upsampled signal. Then, based on the first matching degree between the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence, a more accurate first-level timing can be obtained, achieving high-precision timing synchronization of the initial N OFDM symbols to be synchronized. Based on the first-level timing, the timing accuracy is further refined to obtain the second-level timing error, solving the problem that a single OFDM symbol to be synchronized is easily affected by noise, leading to unstable timing error estimation. Based on the first-level timing and the second-level timing error, timing compensation is performed on the upsampled signal to obtain a compensated upsampled signal. Then, the compensated upsampled signal is downsampled to obtain the OFDM signal, enabling high-precision compensation of the timing error of the OFDM signal to be synchronized. Thus, at the receiving end, the correct reception and demodulation processing of the low-orbit internet satellite OFDM signal can be achieved without relying on satellite ephemeris or terminal location for sampling rate correction factor calculation and resampling correction. Attached Figure Description

[0018] The above-described features, other objects, and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0019] Figure 1 The diagram illustrates an application scenario of a timing deviation compensation method for orthogonal frequency division multiplexed signals according to an embodiment of the present invention.

[0020] Figure 2 A flowchart of a timing deviation compensation method for orthogonal frequency division multiplexed signals according to an embodiment of the present invention is shown;

[0021] Figure 3 A schematic diagram of the timing position corresponding to the relative time delay of the target according to an embodiment of the present invention is shown;

[0022] Figure 4 A schematic diagram of a target index according to an embodiment of the present invention is shown;

[0023] Figure 5 A schematic diagram of intermediate phase error and target phase error according to an embodiment of the present invention is shown;

[0024] Figure 6A The target pilot symbol of the 11th orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown.

[0025] Figure 6B The target pilot symbol of the 101st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown.

[0026] Figure 6C The target pilot symbol of the 201st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown.

[0027] Figure 6D The target pilot symbol of the 241st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexed signal according to an embodiment of the present invention is shown.

[0028] Figure 7A The target pilot symbol of the 11th orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown.

[0029] Figure 7B The target pilot symbol of the 101st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown.

[0030] Figure 7C The target pilot symbol of the 201st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown.

[0031] Figure 7D The target pilot symbol of the 241st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexed signal according to an embodiment of the present invention is shown.

[0032] Figure 8 A structural block diagram of a timing deviation compensation device for orthogonal frequency division multiplexed signals according to an embodiment of the present invention is shown; and

[0033] Figure 9 A block diagram of an electronic device suitable for implementing a timing deviation compensation method for orthogonal frequency division multiplexed signals according to an embodiment of the present invention is shown. Detailed Implementation

[0034] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0036] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0037] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0038] With the development of mobile communication technology, terrestrial mobile communication networks can now achieve network speeds of up to gigabits per second (Gbps) and millisecond-level latency. However, due to the limited coverage of terrestrial cellular networks, communication and network service capabilities in areas not covered by terrestrial cellular networks, such as suburbs, mountainous areas, or sea areas, remain insufficient. To meet the demand for ubiquitous global connectivity, there has been a surge in the construction of space-segment information networks, such as low-Earth orbit satellite internet.

[0039] To support high data rates, low-Earth orbit satellite internet systems employ air interface technologies including large-scale phased arrays, dynamic beamforming, and orthogonal frequency division multiplexing (OFDK). Among these, OFDM technology, through orthogonal subcarrier design, can effectively improve subchannel multiplexing efficiency, significantly increase transmission rates, and also has advantages such as resistance to inter-symbol crosstalk. It has already been widely used in terrestrial mobile communication systems and broadcasting systems.

[0040] Low-Earth orbit (LEO) satellite communication presents greater challenges to the application of OFDM technology. Due to the time-varying, high-speed relative motion between LEO satellites and ground terminals, the period of the actually transmitted OFDM symbols dynamically compresses or expands with this relative motion. Consequently, the number of sampling points and the sampling rate for each OFDM symbol at the receiver exhibit dynamic changes. Furthermore, imperfect synchronization of local clocks can also lead to discrepancies in the sampling rates between the transmitter and receiver. When the LEO satellite ephemeris and ground terminal position are accurate, the transmitter can estimate potential sampling rate distortion to obtain a sampling rate correction factor and perform pre-transmission compensation. The receiver can also infer the sampling rate correction factor and perform resampling correction after reception.

[0041] However, if the ephemeris of the low-orbit satellite or the location of the ground terminal is inaccurate, or if the sampling rate correction factor is not calculated accurately due to other non-ideal external factors, the received signal will have a large residual sampling rate deviation, causing timing errors in each OFDM symbol. This will lead to a decrease in the demodulation performance of the digital modulation signal after OFDM demultiplexing or even failure.

[0042] To address the sampling rate error problem, related technologies estimate the true sampling rate using known data or structural features and then resample. However, in low-Earth orbit satellite broadband communication scenarios, the time-varying nature of the sampling rate makes it difficult to estimate the accurate sampling rate in real time, resulting in insufficient precision in sampling rate error compensation. When the sampling rate error is small, sampling rate error correction can be further transformed into a timing synchronization problem for each OFDM symbol. Achieving precise timing synchronization for each OFDM symbol can simultaneously solve the performance degradation in receiver processing caused by sampling rate errors.

[0043] In related technologies, OFDM timing synchronization can be based on time-domain and frequency-domain synchronization sequences. However, when there are differences between the timing of subsequent OFDM symbols and the synchronization sequence, it is difficult to achieve accurate timing synchronization of subsequent OFDM symbols. Other single timing synchronization methods also struggle to effectively address the problem of time-varying sampling rate correction for low-Earth orbit satellite OFDM signals. Considering the non-ideal factors in practical application scenarios, it is necessary to comprehensively utilize synchronization sequences, cyclic prefix structure characteristics, pilot symbol data, and structural characteristics to achieve a step-by-step approximation of accurate timing synchronization. Furthermore, the timing synchronization method must also possess a certain degree of robustness to time-varying residual frequency offset errors, environmental noise, and interference.

[0044] In view of this, embodiments of the present invention provide a timing deviation compensation method for orthogonal frequency division multiplexing (OFDM) signals, comprising: upsampling the OFDM signal to be synchronized to obtain an upsampled signal, wherein the upsampled signal includes N sequentially arranged OFDM symbols to be synchronized, each OFDM symbol to be synchronized including a cyclic prefix and a valid portion including a tail segment, and N being an integer greater than 1; obtaining a first-level timing for each of the N OFDM symbols to be synchronized based on a first matching degree between a time-domain synchronization symbol sequence template and a target time-domain synchronization symbol sequence, wherein the sampling rate of the time-domain synchronization symbol sequence template is the same as the sampling rate of the upsampled signal, the target time-domain synchronization symbol sequence is extracted from the upsampled signal, and the first-level timing characterizes the OFDM signal to be synchronized. The expected start time of the multiplexed symbol; for any one of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized, the second-level timing error of the OFDM symbol to be synchronized is obtained based on the second matching degree between the cyclic prefix and tail segments corresponding to the multiple candidate start times in the upsampled signal. The candidate start times are determined based on the first-level timing of the OFDM symbol to be synchronized, and the second-level timing error characterizes the offset of the actual start time of the OFDM symbol to be synchronized relative to the first-level timing. Based on the first-level timing and second-level timing errors of each of the N OFDM symbols to be synchronized, timing compensation is performed on the upsampled signal to obtain the compensated upsampled signal. Based on the compensated upsampled signal, the OFDM signal is obtained.

[0045] Figure 1 The diagram illustrates an application scenario of the timing deviation compensation method for orthogonal frequency division multiplexed signals according to an embodiment of the present invention.

[0046] like Figure 1 As shown, application scenario 100 according to this embodiment may include a first terminal device 101, a second terminal device 102, a third terminal device 103, a network 104, and a server 105. The network 104 serves as a medium for providing a communication link between the first terminal device 101, the second terminal device 102, the third terminal device 103, and the server 105. The network 104 may include various connection types, such as wired or wireless communication links, or fiber optic cables, etc.

[0047] Users can use the first terminal device 101, the second terminal device 102, and the third terminal device 103 to interact with the server 105 via the network 104 to receive or send messages, etc. Various communication client applications can be installed on the first terminal device 101, the second terminal device 102, and the third terminal device 103, such as shopping applications, web browser applications, search applications, instant messaging tools, email clients, social media platform software, etc. (for example only).

[0048] The first terminal device 101, the second terminal device 102, and the third terminal device 103 can be various electronic devices with displays and support web browsing, including but not limited to smartphones, tablets, laptops, and desktop computers.

[0049] Server 105 can be a server that provides various services, such as a backend management server that supports websites browsed by users using the first terminal device 101, the second terminal device 102, and the third terminal device 103 (this is just an example). The backend management server can analyze and process data such as received user requests, and feed back the processing results (such as web pages, information, or data obtained or generated according to user requests) to the terminal devices.

[0050] It should be noted that the timing deviation compensation method for orthogonal frequency division multiplexing (OFDM) signals provided in this embodiment of the invention can generally be executed by server 105. Correspondingly, the timing deviation compensation device for OFDM signals provided in this embodiment of the invention can generally be located in server 105. The timing deviation compensation method for OFDM signals provided in this embodiment of the invention can also be executed by a server or server cluster that is different from server 105 and capable of communicating with the first terminal device 101, the second terminal device 102, the third terminal device 103, and / or server 105. Correspondingly, the timing deviation compensation device for OFDM signals provided in this embodiment of the invention can also be located in a server or server cluster that is different from server 105 and capable of communicating with the first terminal device 101, the second terminal device 102, the third terminal device 103, and / or server 105.

[0051] It should be understood that Figure 1 The number of first terminal devices, second terminal devices, third terminal devices, networks, and servers shown in the diagram is merely illustrative. Depending on implementation needs, any number of first terminal devices, second terminal devices, third terminal devices, networks, and servers can be included.

[0052] Figure 2 A flowchart of a timing deviation compensation method for orthogonal frequency division multiplexed signals according to an embodiment of the present invention is shown.

[0053] like Figure 2 As shown, the timing deviation compensation method 200 for orthogonal frequency division multiplexing signals in this embodiment includes operations S210 to S250.

[0054] In operation S210, the orthogonal frequency division multiplexing signal to be synchronized is upsampled to obtain an upsampled signal, which includes N orthogonal frequency division multiplexing symbols to be synchronized.

[0055] In operation S220, the first-level timing of each of the N orthogonal frequency division multiplexing symbols is obtained based on the matching degree between the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence.

[0056] In operation S230, for any one of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized, the second-level timing error of the OFDM symbol to be synchronized is obtained based on the second matching degree between the cyclic prefix and tail segment corresponding to the multiple candidate start times in the upsampled signal.

[0057] In operation S240, timing compensation is performed on the upsampled signal based on the first-stage and second-stage timing errors of each of the N orthogonal frequency division multiplexing symbols to be synchronized, resulting in a compensated upsampled signal.

[0058] During operation of S250, an orthogonal frequency division multiplexed signal is obtained based on the compensated upsampled signal.

[0059] Orthogonal Frequency Division Kultiplexing (OFDK) signals can characterize signals modulated using orthogonal frequency division multiplexing techniques. In one implementation, the OFDK signal to be synchronized can characterize an OFDK signal with a sampling rate deviation.

[0060] In one implementation, based on a preset upsampling factor Upsampling the received orthogonal frequency division multiplexing (OFDM) signal to be synchronized yields an upsampled signal, allowing the determination of its sampling rate. The OFDM signal can include N sequentially arranged OFDM symbols to be synchronized. Each symbol can include a cyclic prefix and a valid portion including a tail segment, where N is an integer greater than 1. In one implementation, the cyclic prefix is ​​obtained by copying the tail segment; that is, the cyclic prefix is ​​a copy of the tail segment.

[0061] The target time-domain synchronization symbol sequence can be extracted from the upsampled signal based on the sampling rate of the upsampled signal. The first-level timing of the orthogonal frequency division multiplexing symbol to be synchronized can characterize the expected start time of the orthogonal frequency division multiplexing symbol to be synchronized.

[0062] Correlation operations, such as cross-correlation, can be performed on the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence to determine the first matching degree between them. This determines the timing position of each of the N orthogonal frequency division multiplexing symbols to be synchronized, and further determines the first-level timing of each of the N orthogonal frequency division multiplexing symbols to be synchronized.

[0063] The second-level timing error characterizes the offset of the actual start time of the orthogonal frequency division multiplexing (OFDM) symbol to be synchronized relative to the first-level timing. The candidate start time can be determined based on the first-level timing of the OFDM symbol to be synchronized. The process of determining the second-level timing error of each of the N OFDM symbols to be synchronized is similar. For any of the N OFDM symbols to be synchronized, the second-level timing error of the OFDM symbol to be synchronized can be obtained based on the second matching degree between the cyclic prefix and tail segments corresponding to the multiple candidate start times in the upsampled signal.

[0064] Timing compensation can be performed on the upsampled signal based on the first-level and second-level timing errors of each of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized. That is, based on the first-level and second-level timing errors, timing compensation is performed on each of the N OFDM symbols to be synchronized in the upsampled signal to obtain the compensated upsampled signal. Then, the compensated upsampled signal is downsampled based on a preset downsampling factor to obtain the OFDM signal.

[0065] In one implementation, the bandwidth of the orthogonal frequency division multiplexed signal to be synchronized can be Preset upsampling factor and preset downsampling factor The following formula (1) applies between them.

[0066] (1);

[0067] in, This indicates the sampling rate of the upsampled signal. In some implementations, and It can be a positive integer.

[0068] By upsampling the orthogonal frequency division multiplexing (OFDM) signal to be synchronized, the sampling resolution of the signal can be improved, resulting in an upsampled signal. Then, based on the first matching degree between the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence, a relatively accurate first-level timing can be obtained, achieving high-precision timing synchronization of the initial N OFDM symbols to be synchronized. Based on the first-level timing, the timing accuracy is further refined to obtain the second-level timing error, solving the problem that a single OFDM symbol to be synchronized is easily affected by noise, leading to unstable timing error estimation. Based on the first-level timing and the second-level timing error, timing compensation is performed on the upsampled signal to obtain a compensated upsampled signal. Then, the compensated upsampled signal is downsampled to obtain the OFDM signal, enabling high-precision compensation of the timing error of the OFDM signal to be synchronized. Thus, at the receiving end, the correct reception and demodulation processing of the low-orbit internet satellite OFDM signal can be achieved without relying on satellite ephemeris or terminal location for sampling rate correction factor calculation and resampling correction.

[0069] Based on the first matching degree between the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence, the first-level timing of each of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized is obtained, including: determining the target relative delay from multiple candidate relative delays based on the first matching degree between each of the multiple target time-domain synchronization symbol subsequences and the time-domain synchronization symbol sequence template; obtaining the expected start time of the target time-domain synchronization symbol sequence based on the target relative delay; and obtaining the first-level timing of each of the N OFDM symbols to be synchronized based on the expected start time of the target time-domain synchronization symbol sequence and the preset duration of the OFDM symbols to be synchronized.

[0070] In one implementation, the target time-domain synchronization symbol sequence may include multiple target time-domain synchronization symbol subsequences. The candidate relative delay may be generated by sliding the time-domain synchronization symbol sequence template on the target time-domain synchronization symbol sequence, and the target time-domain synchronization symbol subsequence may be a subsequence extracted from the target time-domain synchronization symbol sequence with the same preset duration as the time-domain synchronization symbol sequence template, starting from the candidate relative delay.

[0071] In one implementation, the target time-domain synchronization symbol sequence can be a subsequence of the target time period extracted from the upsampled signal. The target time period can be determined based on the preset protection duration, the estimated start time of the preset time-domain synchronization symbol sequence, and the preset duration of the preset time-domain synchronization symbol sequence.

[0072] In one implementation, the estimated start time of the preset time-domain synchronization symbol sequence can be a rough estimate obtained through preamble signal detection. The start time can be determined based on the preset time-domain synchronization symbol sequence. Duration of the preset time-domain synchronization symbol sequence and preset protection duration Determine the target time period The target time-domain synchronization symbol sequence can be extracted from the upsampled signal based on the target time period.

[0073] In one implementation, the first matching degree can be characterized by the cross-correlation function value. Based on the first matching degree between each of the multiple target time-domain synchronization symbol subsequences and the time-domain synchronization symbol sequence template, the target relative delay can be determined from multiple candidate relative delays. In another implementation, the candidate relative delay corresponding to the maximum value among the multiple first matching degrees can be determined as the target relative delay.

[0074] Based on the target relative time delay, the expected start time of the target time-domain synchronization symbol sequence can be obtained. Based on the expected start time of the target time-domain synchronization symbol sequence and the preset duration of the orthogonal frequency division multiplexing (OFDM) symbols to be synchronized, the first-level timing of each of the N OFDM symbols to be synchronized can be obtained. In one implementation, the first-level timing of the first OFDM symbol to be synchronized can be the expected start time of the target time-domain synchronization symbol sequence plus the preset duration of the OFDM symbol to be synchronized. The first-level timing of the second OFDM symbol to be synchronized can be the expected start time of the target time-domain synchronization symbol sequence plus twice the preset duration of the OFDM symbol to be synchronized.

[0075] Figure 3 A schematic diagram of the timing position corresponding to the relative time delay of the target according to an embodiment of the present invention is shown.

[0076] like Figure 3 As shown, the peak position is the timing position corresponding to the relative time delay of the target.

[0077] In one implementation, the relative time delay of the target can be obtained by calculating the similarity between the target time-domain synchronization symbol sequence and the time-domain synchronization symbol sequence template. In another implementation, the relative time delay of the target can be obtained by performing correlation operations on the target time-domain synchronization symbol sequence and the time-domain synchronization symbol sequence template.

[0078] The timing position corresponding to the relative delay of the target is the starting reference symbol of the upsampled signal, that is, the time base of the upsampled signal. Based on the relative delay of the target and the preset duration of the orthogonal frequency division multiplexing symbol to be synchronized, the first-level timing of each of the N orthogonal frequency division multiplexing symbols can be determined.

[0079] In one implementation, when the target relative delay is 1000 and the preset duration of the orthogonal frequency division multiplexing (OFDM) symbol to be synchronized is 100, the first-level timing of the first OFDM symbol to be synchronized is 1100, the first-level timing of the second OFDM symbol to be synchronized is 1200, and the first-level timing of the third OFDM symbol to be synchronized is 1300.

[0080] By calculating the first matching degree between the target time-domain synchronization symbol sequence and the time-domain synchronization symbol sequence template, the target relative delay can be determined from multiple candidate relative delays. This allows for the determination of the expected start time of the target time-domain synchronization sequence from a rough range. Based on this, and according to the preset duration of the orthogonal frequency division multiplexing symbols to be synchronized, the first-level timing of each of the N orthogonal frequency division multiplexing symbols to be synchronized is determined one by one, thus improving the accuracy of the determined first-level timing.

[0081] Based on the second matching degree between the cyclic prefix and tail segment corresponding to each of the multiple candidate start times in the upsampled signal, the second-level timing error of the orthogonal frequency division multiplexing symbol to be synchronized is obtained, including: for any candidate start time among the multiple candidate start times, extracting the cyclic prefix and tail segment corresponding to the candidate start time from the upsampled signal; determining the target start time from the multiple candidate start times based on the second matching degree between the cyclic prefix and tail segment corresponding to each of the multiple candidate start times; and obtaining the second-level timing error of the orthogonal frequency division multiplexing symbol to be synchronized based on the target start time.

[0082] For any candidate start time among multiple candidate start times, a cyclic prefix and a tail segment corresponding to the candidate start time can be extracted from the upsampled signal. Specifically, data corresponding to a first preset time period is extracted from the upsampled signal to obtain the cyclic prefix corresponding to the candidate start time; data corresponding to a second preset time period is extracted from the upsampled signal to obtain the tail segment corresponding to the candidate start time.

[0083] In one implementation, for any one of the multiple candidate start times, the candidate start time can be determined based on the first-level timing of the orthogonal frequency division multiplexing symbol to be synchronized, the sampling rate of the upsampled signal, and the candidate index, as shown in the following formula (2).

[0084] (2);

[0085] in, Indicates the range of candidate indexes. It is a positive integer. Indicates a candidate index. This represents the first-stage timing of the nth orthogonal frequency division multiplexing symbol to be synchronized. This indicates the sampling rate.

[0086] In one implementation, a first preset time period can be determined based on the candidate start time and the preset duration of the cyclic prefix, as shown in formula (3). A second preset time period can be determined based on the candidate start time, the preset duration of the cyclic prefix, and the preset duration of the orthogonal frequency division multiplexing symbol to be synchronized, as shown in formula (4).

[0087] (3);

[0088] (4);

[0089] in, Indicates the preset duration of the loop prefix. Indicates the preset duration of the orthogonal frequency division multiplexing symbol to be synchronized.

[0090] By extracting data corresponding to the first preset time period from the upsampled signal, a cyclic prefix corresponding to the candidate start time is obtained; by extracting data corresponding to the second preset time period from the upsampled signal, a tail segment corresponding to the candidate start time is obtained.

[0091] In one implementation, multiple first sampling points associated with each first preset time period are extracted from the upsampled signal. Multiple first sampling points constitute a cyclic prefix corresponding to the candidate start time, where L1 represents the number of first sampling points. Multiple second sampling points associated with each second preset time period are extracted from the upsampled signal. Multiple second sampling points constitute the tail segment corresponding to the candidate start time, and L2 represents the number of second sampling points.

[0092] The target start time can be determined from multiple candidate start times based on a second matching degree between the cyclic prefix and tail segments corresponding to each candidate start time. In one implementation, the second matching degree can be determined by calculating the sum of the squared absolute differences between the first and second sampling points. As shown in formula (5). In another implementation, the second matching degree can be determined by calculating the sum of the absolute differences between the first and second sampling points. As shown in formula (6). In another implementation, the second matching degree can be determined by calculating the sum of the conjugate cross-correlation of the first and second sampling points. As shown in formula (7).

[0093] (5);

[0094] (6);

[0095] (7);

[0096] in, To perform absolute value operations, This is a conjugate operation.

[0097] The target start time is determined from multiple candidate start times based on multiple second matching degrees. In one implementation, the value of m corresponding to the smallest second matching degree can be used as the target index corresponding to the target start time, based on the multiple second matching degrees determined by formula (5) above. In another implementation, the value of m corresponding to the smallest second matching degree can be used as the target index corresponding to the target start time, based on the multiple second matching degrees determined by formula (6) above. In yet another implementation, the value of m corresponding to the largest second matching degree can be used as the target index corresponding to the target start time, based on the multiple second matching degrees determined by formula (7) above.

[0098] In one implementation, data normalization can be performed on the target index corresponding to the target start time to obtain a target index line segment composed of the target indices corresponding to the target start time. Based on the slope and intercept of the target index line segment, the second-level timing error of the orthogonal frequency division multiplexing symbol to be synchronized is obtained. In one implementation, data normalization may include at least one of fitting, smoothing, or outlier removal. In some implementations, fitting may include, but is not limited to, linear fitting, multinomial fitting, etc., and smoothing may include, but is not limited to, median filtering, mean filtering, Gaussian filtering, etc.

[0099] Figure 4 A schematic diagram of a target index according to an embodiment of the present invention is shown.

[0100] like Figure 4 As shown, the circle and cross symbol The point is the target index used, and the cross flag is... The dots represent outliers that were removed, and the dashed lines represent the second-level timing error.

[0101] For any candidate start time, the cyclic prefix and tail segment corresponding to the candidate start time are extracted from the upsampled signal. Then, the second matching degree between the cyclic prefix and tail segment corresponding to each candidate start time is compared to determine the target start time. Thus, the second-level timing error of the orthogonal frequency division multiplexing symbol to be synchronized can be obtained. That is, within a small neighborhood of the first-level timing, the second matching degree between the cyclic prefix and tail segment of each candidate start time is verified one by one, the target start time is determined from multiple candidate start times, and the second-level timing error is determined based on the target index of the target start time, thereby improving the accuracy of the determined second-level timing error.

[0102] The process of obtaining the orthogonal frequency division multiplexing (OFDM) signal based on the compensated upsampled signal includes: performing OFDM demultiplexing demodulation on the compensated upsampled signal to obtain pilot symbols for each of the N OFDM symbols to be synchronized; obtaining the third-level timing error for each of the N OFDM symbols to be synchronized based on the phase error between each of the N pilot symbols and the expected pilot symbol set; performing timing compensation on the upsampled signal based on the first-level timing error, second-level timing error, and third-level timing error of each of the N OFDM symbols to obtain the target compensated upsampled signal; and obtaining the OFDM signal based on the target compensated upsampled signal.

[0103] Specifically, based on the phase errors between each of the N pilot symbols and the expected set of pilot symbols, the third-level timing error of each of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized is obtained. This can include: correcting the phase errors between each of the N pilot symbols and the expected set of pilot symbols to obtain the target phase error of each of the N pilot symbols; determining the demodulation bit error rate threshold and the number of groups of pilot symbols based on the demodulation bit error rate of the M preceding OFDM signals to be synchronized; grouping the N pilot symbols according to the bit error rate threshold, the number of groups, and the index of the pilot symbols to obtain multiple groups of pilot symbols; and averaging the target phase errors of the multiple groups of pilot symbols to obtain the third-level timing error of the OFDM signal to be synchronized.

[0104] The third-level timing error can characterize the residual timing deviation of the orthogonal frequency division multiplexed symbol to be synchronized after the first two-level timing compensation.

[0105] The upsampled signal can be demultiplexed and demodulated using orthogonal frequency division multiplexing (OFDM) to obtain pilot symbols for each of the N OFDM symbols to be synchronized. Each pilot symbol of the N OFDM symbols to be synchronized has its own phase, and the phase error between the phase of each pilot symbol of the N OFDM symbols to be synchronized and the phase of the expected pilot symbol set can be calculated.

[0106] In one implementation, the pilot symbols of an orthogonal frequency division multiplexing (OFDM) symbol to be synchronized may include multiple pilot symbols, and the expected pilot symbol set may include multiple expected pilot symbols. The expected pilot symbols in the expected pilot symbol set corresponding to the pilot symbols of the OFDM symbol to be synchronized are compared with the pilot symbols of the OFDM symbol to be synchronized to obtain the phase error.

[0107] Specifically, the phase errors between each of the N pilot symbols and the expected set of pilot symbols are corrected to obtain the target phase errors of each of the N pilot symbols. This can include: obtaining the average phase error of each of the N orthogonal frequency division multiplexing symbols to be synchronized based on the phase errors between each of the N pilot symbols and the expected set of pilot symbols; obtaining the intermediate phase error of each of the N pilot symbols based on the difference between each of the N phase errors and the average phase error; and smoothing the intermediate phase errors of the N pilot symbols to obtain the target phase error of each of the N pilot symbols.

[0108] The average phase error of each of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized can be obtained by averaging the phase errors of the pilot symbols of each symbol. For example, if the first OFDM symbol to be synchronized has multiple pilot symbols, the average phase error of the first OFDM symbol to be synchronized can be obtained by averaging the phase errors of these multiple pilot symbols.

[0109] For each orthogonal frequency division multiplexing symbol to be synchronized, the intermediate phase error of each pilot symbol can be obtained by subtracting the mean phase error from the phase error of each pilot symbol. As shown in formula (9).

[0110] (9);

[0111] in, This represents the phase error of the pilot symbol. This represents the average phase error of N pilot symbols.

[0112] By smoothing the intermediate phase error of each pilot symbol, the target phase error of each pilot symbol can be obtained. .

[0113] Figure 5 A schematic diagram of intermediate phase error and target phase error according to an embodiment of the present invention is shown.

[0114] like Figure 5 As shown, the points marked with a triangle and a cross represent the intermediate phase errors of two specific pilot symbols, respectively. The solid line with triangles and the dashed line with crosses represent the target phase errors obtained after smoothing the intermediate phase errors of two specific pilot symbols, respectively. .

[0115] The demodulation error rate threshold and the number of pilot symbols can be determined based on the demodulation error rate of the pilot symbols of the M orthogonal frequency division multiplexing signals preceding the orthogonal frequency division multiplexing signal to be synchronized.

[0116] Multiple pilot symbols can be grouped according to the bit error rate threshold, the number of groups, and the index of the pilot symbols to obtain multiple groups of pilot symbols.

[0117] In one implementation, among the unselected pilot symbols, two pilot symbols with a demodulation bit error rate less than the bit error rate threshold and the largest index difference are selected and grouped into one group of pilot symbols. This process is repeated until no pilot symbols meet the requirements, or the number of combinations of selected pilot symbols reaches the number of groups of pilot symbols required.

[0118] In one implementation, where there is only one group of pilot symbols, for a group of pilot symbols... The average of the target phase error of the intermediate pilot symbol can be used to obtain the third-order timing error of the orthogonal frequency division multiplexing symbol to be synchronized. As shown in formula (10).

[0119] (10);

[0120] in, Indicates pilot symbol The target phase error, Indicates pilot symbol The target phase error, Indicates pilot symbol index, Indicates pilot symbol The index.

[0121] In one implementation, when there are multiple groups of pilot symbols, the average target phase error of each group of pilot symbols is calculated to obtain the average target phase error. Then, the average target phase error of multiple groups of pilot symbols is calculated to obtain the third-level timing error.

[0122] Grouping multiple pilot symbols based on the bit error rate threshold, number of groups, and pilot symbol index can improve the anti-interference and high sensitivity of pilot symbol timing. Since timing errors cause the phase difference of pilot symbols at different frequencies to change linearly, that is, the larger the index difference of pilot symbols, the higher the sensitivity of the phase difference to timing. By averaging the target phase error of the pilot symbols, the accuracy of the third-level timing error can be improved.

[0123] Based on the first-level timing, second-level timing error, and third-level timing error of each of the N orthogonal frequency division multiplexing symbols, timing compensation is performed on the upsampled signal to obtain the target upsampled signal. This can include: determining the third timing based on the first-level timing, second-level timing error, and third-level timing error; and performing timing compensation on the upsampled signal based on the third timing to obtain the target upsampled signal.

[0124] Based on the first-stage timing error, second-stage timing error, and third-stage timing error of each of the N orthogonal frequency division multiplexing symbols, the third timing error can be determined. The following formula (11) performs timing compensation on the upsampled signal based on the third timing to obtain the target compensated upsampled signal.

[0125] (11);

[0126] in, Indicates the first-level timing. This indicates the second-order timing error. This indicates the third-level timing error.

[0127] By downsampling the target compensation upsampled signal, an orthogonal frequency division multiplexed signal can be obtained. The timing deviation compensation method for the above-mentioned orthogonal frequency division multiplexed signal also includes: by performing orthogonal frequency demultiplexing demodulation on the orthogonal frequency division multiplexed signal to achieve the conversion from the time domain to the frequency domain, the target pilot symbols of each of the N orthogonal frequency division multiplexed symbols can be obtained.

[0128] By performing orthogonal frequency division multiplexing demodulation on the compensated upsampled signal, pilot symbols for each of the N orthogonal frequency division multiplexing symbols to be synchronized can be obtained. Based on the phase error between each of the N pilot symbols and the expected pilot symbol set, the third-level timing error of each of the N orthogonal frequency division multiplexing symbols to be synchronized can be determined. Combining the first-level timing error and the second-level timing error, timing compensation can be performed on the upsampled signal to obtain the target compensated upsampled signal. Then, the target compensated upsampled signal is downsampled to obtain the orthogonal frequency division multiplexing signal, which can further improve the timing accuracy of the obtained orthogonal frequency division multiplexing signal to achieve high-precision sampling rate compensation.

[0129] Figure 6A The target pilot symbol of the 11th orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown. Figure 6B The target pilot symbol of the 101st target orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown. Figure 6C The target pilot symbol of the 201st target orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown. Figure 6D The target pilot symbol of the 241st target orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown.

[0130] Figure 7A The target pilot symbol of the 11th orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown. Figure 7B The target pilot symbol of the 101st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown. Figure 7C The target pilot symbol of the 201st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown. Figure 7D The target pilot symbol of the 241st orthogonal frequency division multiplexing symbol obtained after demultiplexing an orthogonal frequency division multiplexing signal according to an embodiment of the present invention is shown.

[0131] exist Figures 6A-6D The orthogonal frequency division multiplexed signal involved is obtained by downsampling the compensated upsampled signal. Figures 7A-7D The orthogonal frequency division multiplexing signal involved is obtained by downsampling the target compensation upsampled signal.

[0132] from Figure 6A As can be seen, the distribution of the target pilot symbols after the second-stage timing error correction of the 11th orthogonal frequency division multiplexing symbol is already relatively clustered, indicating that the timing of the 11th orthogonal frequency division multiplexing symbol after the second-stage timing error correction is quite accurate. After a third-stage timing error correction, an even more clustered distribution can be obtained. Figure 7A .contrast Figures 6B-6D As you can see, Figure 6D The distribution of the target pilot symbol after the second-level timing error correction of the 241st orthogonal frequency division multiplexing symbol still shows divergence, indicating that the 241st orthogonal frequency division multiplexing symbol still has a large timing error after the second-level timing error correction. Further third-level timing error correction is then performed to obtain... Figure 7D .contrast Figure 6D and Figure 7D It can be seen that, Figure 7D The target pilot symbol distribution clustering has been significantly improved, indicating that the timing accuracy of each orthogonal frequency division multiplexing symbol has been further improved through the third-level timing error correction. Figures 7B-7C Yes Figures 6B-6C The distribution of the target pilot symbols is obtained by performing a third-level timing error correction.

[0133] By employing a three-stage timing error estimation and timing compensation approach, timing correction for each orthogonal frequency division multiplexing (OFDM) symbol can be achieved, effectively solving the problem of time-varying sampling rate error correction. This enables correct reception and demodulation of OFDM signals from low-Earth orbit internet satellites at the receiving end, eliminating the need to rely on satellite ephemeris or terminal location for sampling rate correction factor calculation and resampling correction. Specifically, the first-stage timing estimation involves correlation processing of the target time-domain synchronization symbol sequence and the time-domain synchronization symbol sequence template. The accuracy of the first-stage timing is superior to the original sampling rate accuracy limitation of the OFDM signal to be synchronized, thus obtaining relatively accurate first-stage timing for each of the N OFDM symbols to be synchronized. The second-stage timing error estimation utilizes the cyclic prefix of each OFDM symbol for matching processing and performs multi-symbol joint estimation of timing errors. This addresses the problem that single OFDM symbols are susceptible to noise, leading to unstable estimation results, and effectively achieves second-stage timing correction for subsequent OFDM symbols. The third-level timing error estimation further utilizes the phase rotation characteristics of pilot symbols to estimate the subtle timing errors of each orthogonal frequency division multiplexing (OFDM) symbol, achieving precise timing synchronization and demultiplexing of each OFDM symbol. By designing a method to remove the mean phase error of pilot symbols symbol by symbol-by-symbol, the influence of residual subtle frequency offset errors on timing error estimation is eliminated. Smoothing of the intermediate phase errors of pilot symbols across multiple OFDM symbols eliminates the random effects of noise. Timing error calculation using multiple sets of pilot symbols eliminates the impact of interference or other non-ideal factors on timing estimation for some pilot symbols. Finally, through the step-by-step estimation and compensation of the first-level timing error, the second-level timing error, and the third-level timing error, precise timing synchronization of each OFDM symbol to be synchronized is achieved, realizing the correction of the time-varying sampling rate of the low-Earth orbit satellite OFDM signal.

[0134] Based on the above-mentioned timing deviation compensation method for orthogonal frequency division multiplexed signals, this invention also provides a timing deviation compensation device for orthogonal frequency division multiplexed signals. The following will be combined with... Figure 8 The device is described in detail.

[0135] Figure 8 A structural block diagram of a timing deviation compensation device for orthogonal frequency division multiplexed signals according to an embodiment of the present invention is shown.

[0136] like Figure 8 As shown, the timing deviation compensation device 800 for orthogonal frequency division multiplexing signals in this embodiment includes a first obtaining module 810, a second obtaining module 820, a third obtaining module 830, a fourth obtaining module 840, and a fifth obtaining module 850.

[0137] The first obtaining module 810 is used to upsample the orthogonal frequency division multiplexing (OFDM) signal to be synchronized to obtain an upsampled signal. The upsampled signal includes N sequentially arranged OFDM symbols to be synchronized. Each OFDM symbol includes a cyclic prefix and a valid portion including a tail segment, where N is an integer greater than 1. In one embodiment, the first obtaining module 810 can be used to perform the operation S210 described above, which will not be repeated here.

[0138] The second obtaining module 820 is used to obtain the first-level timing of each of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized based on the first matching degree between the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence. The sampling rate of the time-domain synchronization symbol sequence template is the same as the sampling rate of the upsampled signal, the target time-domain synchronization symbol sequence is extracted from the upsampled signal, and the first-level timing characterizes the expected start time of the OFDM symbols to be synchronized. In one embodiment, the second obtaining module 820 can be used to execute the operation S220 described above, which will not be repeated here.

[0139] The third obtaining module 830 is used to, for any one of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized, obtain the second-level timing error of the OFDM symbol to be synchronized based on the second matching degree between the cyclic prefix and tail segments corresponding to the multiple candidate start times in the upsampled signal. The candidate start times are determined based on the first-level timing of the OFDM symbol to be synchronized, and the second-level timing error characterizes the offset of the actual start time of the OFDM symbol to be synchronized relative to the first-level timing. In one embodiment, the third obtaining module 830 can be used to perform the operation S230 described above, which will not be repeated here.

[0140] The fourth obtaining module 840 is used to perform timing compensation on the upsampled signal based on the first-level timing and second-level timing errors of each of the N orthogonal frequency division multiplexing symbols to be synchronized, to obtain a compensated upsampled signal. In one embodiment, the fourth obtaining module 830 can be used to perform the operation S240 described above, which will not be repeated here.

[0141] The fifth obtaining module 850 is used to downsample the target upsampled orthogonal frequency division multiplexed signal to obtain the target orthogonal frequency division multiplexed signal. In one embodiment, the fifth obtaining module 840 can be used to perform the operation S250 described above, which will not be repeated here.

[0142] According to an embodiment of the present invention, the second obtaining module 820 includes: a first obtaining submodule, configured to determine a target relative delay from multiple candidate relative delays based on a first matching degree between each of the multiple target time-domain synchronization symbol subsequences and the time-domain synchronization symbol sequence template, wherein the candidate relative delays are generated by sliding the time-domain synchronization symbol sequence template on the target time-domain synchronization symbol sequence, and the target time-domain synchronization symbol subsequence is a subsequence extracted from the target time-domain synchronization symbol sequence with the same preset duration as the time-domain synchronization symbol sequence template, starting from the candidate relative delay; a second obtaining submodule, configured to obtain the expected start time of the target time-domain synchronization symbol sequence based on the target relative delay; and a third obtaining submodule, configured to obtain the first-level timing of each of the N orthogonal frequency division multiplexing symbols to be synchronized based on the expected start time of the target time-domain synchronization symbol sequence and the preset duration of the orthogonal frequency division multiplexing symbols to be synchronized.

[0143] According to an embodiment of the present invention, the third obtaining module 830 includes: a fourth obtaining submodule, configured to extract a cyclic prefix and a tail segment corresponding to any candidate start time from the upsampled signal for any candidate start time among a plurality of candidate start times; a fifth obtaining submodule, configured to determine a target start time from the plurality of candidate start times based on a second matching degree between the cyclic prefix and tail segments corresponding to each of the plurality of candidate start times; and a sixth obtaining submodule, configured to obtain a second-level timing error of the orthogonal frequency division multiplexing symbol to be synchronized based on the target start time.

[0144] According to an embodiment of the present invention, the fourth obtaining submodule includes: a first obtaining unit, configured to extract data corresponding to a first preset time period from the upsampled signal to obtain a cyclic prefix corresponding to a candidate start time, wherein the first preset time period is determined based on the candidate start time and a preset duration of the cyclic prefix; and a second obtaining unit, configured to extract data corresponding to a second preset time period from the upsampled signal to obtain a tail segment corresponding to a candidate start time, wherein the second preset time period is determined based on the candidate start time, the preset duration of the cyclic prefix, and the preset duration of the orthogonal frequency division multiplexing symbol to be synchronized.

[0145] According to an embodiment of the present invention, the fifth obtaining module 850 includes: a seventh obtaining submodule, used to perform orthogonal frequency division multiplexing demodulation on the compensated upsampled signal to obtain pilot symbols for each of the N orthogonal frequency division multiplexing symbols to be synchronized; an eighth obtaining submodule, used to obtain the third-level timing error of each of the N orthogonal frequency division multiplexing symbols to be synchronized based on the phase error between each of the N pilot symbols and the expected pilot symbol set, wherein the third-level timing error characterizes the residual timing deviation of the orthogonal frequency division multiplexing symbols to be synchronized after the first two levels of timing compensation; a ninth obtaining submodule, used to perform timing compensation on the upsampled signal based on the first-level timing error, the second-level timing error and the third-level timing error of each of the N orthogonal frequency division multiplexing symbols to obtain the target compensated upsampled signal; and a tenth obtaining submodule, used to obtain the orthogonal frequency division multiplexing signal based on the target compensated upsampled signal.

[0146] According to an embodiment of the present invention, the ninth obtaining submodule includes: a third obtaining unit, used to correct the phase error between each of the N pilot symbols and the expected pilot symbol set to obtain the target phase error of each of the N pilot symbols; a fourth obtaining unit, used to determine the demodulation bit error rate threshold and the number of groups of multiple pilot symbols based on the demodulation bit error rate of the M orthogonal frequency division multiplexing signals to be synchronized before the orthogonal frequency division multiplexing signal to be synchronized; a fifth obtaining unit, used to group multiple pilot subcarrier modulation symbols according to the bit error rate threshold, the number of groups and the pilot subcarrier number to obtain multiple groups of pilot subcarrier modulation symbols; and a sixth obtaining unit, used to average the target phase errors of the multiple groups of pilot subcarrier modulation symbols to obtain the third-level timing error of the orthogonal frequency division multiplexing symbol to be synchronized.

[0147] According to an embodiment of the present invention, the third obtaining unit includes: a first obtaining subunit, configured to obtain the average phase error of each of the N pilot symbols to be synchronized based on the phase error between each of the N pilot symbols and the expected pilot symbol set; a second obtaining subunit, configured to obtain the intermediate phase error of each of the N pilot symbols based on the difference between each of the N phase errors and the average phase error; and a third obtaining subunit, configured to smooth the intermediate phase error of each of the N pilot symbols to obtain the target phase error of each of the N pilot symbols.

[0148] According to embodiments of the present invention, any plurality of modules among the first obtaining module 810, the second obtaining module 820, the third obtaining module 830, the fourth obtaining module 840, and the fifth obtaining module 850 may be combined into one module, or any one of these modules may be split into multiple modules. Alternatively, at least part of the functionality of one or more of these modules may be combined with at least part of the functionality of other modules and implemented in one module. According to embodiments of the present invention, at least one of the obtaining module 810, the first obtaining module 820, the second obtaining module 830, the third obtaining module 840, and the fourth obtaining module 850 may be at least partially implemented as hardware circuitry, such as a field-programmable gate array (FPGA), a programmable logic array (PLA), a system-on-a-chip, a system-on-a-substrate, a system-on-package, an application-specific integrated circuit (ASIC), or any other reasonable means of integrating or packaging the circuitry, or implemented in any one of the three implementation methods of software, hardware, and firmware, or in a suitable combination of any of these. Alternatively, at least one of the acquisition module 810, the first acquisition module 820, the second acquisition module 830, the third acquisition module 840, and the fourth acquisition module 850 may be at least partially implemented as a computer program module, which can perform corresponding functions when the computer program module is run.

[0149] Figure 9 A block diagram of an electronic device suitable for implementing a timing deviation compensation method for orthogonal frequency division multiplexed signals according to an embodiment of the present invention is shown.

[0150] like Figure 9 As shown, an electronic device 900 according to an embodiment of the present invention includes a processor 901, which can perform various appropriate actions and processes according to a program stored in ROM 902 or a program loaded from storage portion 908 into RAM 903. The processor 901 may include, for example, a general-purpose microprocessor (e.g., a CPU), an instruction set processor and / or an associated chipset and / or a special-purpose microprocessor (e.g., an application-specific integrated circuit (ASIC)), etc. The processor 901 may also include onboard memory for caching purposes. The processor 901 may include a single processing unit or multiple processing units for performing different actions of the method flow according to an embodiment of the present invention.

[0151] RAM 903 stores various programs and data required for the operation of electronic device 900. Processor 901, ROM 902, and RAM 903 are interconnected via bus 904. Processor 901 executes various operations of the method flow according to embodiments of the present invention by executing programs in ROM 902 and / or RAM 903. It should be noted that the programs may also be stored in one or more memories other than ROM 902 and RAM 903. Processor 901 may also execute various operations of the method flow according to embodiments of the present invention by executing programs stored in said one or more memories.

[0152] According to an embodiment of the present invention, the electronic device 900 may further include an input / output (I / O) interface 905, which is also connected to a bus 904. The electronic device 900 may also include one or more of the following components connected to the input / output (I / O) interface 905: an input section 906 including a keyboard, mouse, etc.; an output section 907 including a cathode ray tube (CRT), liquid crystal display (LCD), etc., and a speaker, etc.; a storage section 908 including a hard disk, etc.; and a communication section 909 including a network interface card such as a LAN card, modem, etc. The communication section 909 performs communication processing via a network such as the Internet. A drive 910 is also connected to the input / output (I / O) interface 905 as needed. A removable medium 911, such as a disk, optical disk, magneto-optical disk, semiconductor memory, etc., is installed on the drive 910 as needed so that computer programs read from it can be installed into the storage section 908 as needed.

[0153] The present invention also provides a computer-readable storage medium, which may be included in the device / apparatus / system described in the above embodiments; or it may exist independently and not assembled into the device / apparatus / system. The computer-readable storage medium carries one or more programs, which, when executed, implement the method according to the embodiments of the present invention.

[0154] According to embodiments of the present invention, a computer-readable storage medium may be a non-volatile computer-readable storage medium, such as including but not limited to: portable computer disks, hard disks, RAM (Random Access Memory), ROM (Read Only Memory), erasable programmable read-only memory (EPROM or flash memory), portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In the present invention, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. For example, according to embodiments of the present invention, a computer-readable storage medium may include ROM 902 and / or RAM 903 and / or one or more memories other than ROM 902 and RAM 903 described above.

[0155] Embodiments of the present invention also include a computer program product comprising a computer program containing program code for performing the methods shown in the flowchart. When the computer program product is run on a computer system, the program code is used to enable the computer system to implement the timing deviation compensation method for orthogonal frequency division multiplexing signals provided in the embodiments of the present invention.

[0156] When the computer program is executed by the processor 901, it performs the functions defined in the system / apparatus of this invention. According to embodiments of the invention, the systems, apparatuses, modules, units, etc., described above can be implemented by computer program modules.

[0157] In one embodiment, the computer program may rely on a tangible storage medium such as an optical storage device or a magnetic storage device. In another embodiment, the computer program may also be transmitted and distributed in the form of signals over a network medium, and downloaded and installed via the communication section 909, and / or installed from a removable medium 911. The program code contained in the computer program can be transmitted using any suitable network medium, including but not limited to: wireless, wired, etc., or any suitable combination thereof.

[0158] In such an embodiment, the computer program can be downloaded and installed from a network via the communication section 909, and / or installed from the removable medium 911. When the computer program is executed by the processor 901, it performs the functions defined in the system of this embodiment of the invention. According to embodiments of the invention, the systems, devices, apparatuses, modules, units, etc., described above can be implemented by computer program modules.

[0159] According to embodiments of the present invention, program code for executing the computer programs provided in the embodiments of the present invention can be written in any combination of one or more programming languages. Specifically, these computational programs can be implemented using high-level procedural and / or object-oriented programming languages, and / or assembly / machine languages. Programming languages ​​include, but are not limited to, languages ​​such as Java, C++, Python, "C", or similar programming languages. The program code can be executed entirely on the user's computing device, partially on the user's device, partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0160] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram or flowchart, and combinations of blocks in a block diagram or flowchart, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0161] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

[0162] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A method for compensating timing deviation of orthogonal frequency division multiplexed signals, characterized in that... include: The orthogonal frequency division multiplexing (OFDM) signal to be synchronized is upsampled to obtain an upsampled signal, wherein the upsampled signal includes N sequentially arranged OFDM symbols to be synchronized, the OFDM symbols to be synchronized include a cyclic prefix and an effective part including a tail segment, and N is an integer greater than 1. Based on the first matching degree between the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence, the first-level timing of each of the N orthogonal frequency division multiplexing symbols to be synchronized is obtained, wherein the sampling rate of the time-domain synchronization symbol sequence template is the same as the sampling rate of the upsampled signal, the target time-domain synchronization symbol sequence is extracted from the upsampled signal, and the first-level timing characterizes the expected start time of the orthogonal frequency division multiplexing symbol to be synchronized; For any one of the N orthogonal frequency division multiplexing (OFDM) symbols to be synchronized, the second-level timing error of the OFDM symbol to be synchronized is obtained based on the second matching degree between the cyclic prefix and tail segment corresponding to each of the multiple candidate start times in the upsampled signal. The candidate start times are determined based on the first-level timing of the OFDM symbol to be synchronized, and the second-level timing error characterizes the offset of the actual start time of the OFDM symbol to be synchronized relative to the first-level timing. Based on the first-level and second-level timing errors of each of the N orthogonal frequency division multiplexing symbols to be synchronized, timing compensation is performed on the upsampled signal to obtain a compensated upsampled signal; Based on the compensated upsampled signal, an orthogonal frequency division multiplexing signal is obtained.

2. The method according to claim 1, characterized in that, The step of obtaining the first-level timing of each of the N orthogonal frequency division multiplexing symbols to be synchronized based on the first matching degree between the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence includes: Based on the first matching degree between each of the multiple target time-domain synchronization symbol subsequences and the time-domain synchronization symbol sequence template, a target relative delay is determined from multiple candidate relative delays. The candidate relative delays are generated by sliding the time-domain synchronization symbol sequence template on the target time-domain synchronization symbol sequence. The target time-domain synchronization symbol subsequences are subsequences extracted from the target time-domain synchronization symbol sequence with the candidate relative delay as the starting point and having the same preset duration as the time-domain synchronization symbol sequence template. Based on the target relative time delay, the expected start time of the target time-domain synchronization symbol sequence is obtained; Based on the expected start time of the target time-domain synchronization symbol sequence and the preset duration of the orthogonal frequency division multiplexing (OFDM) symbols to be synchronized, the first-level timing of each of the N OFDM symbols to be synchronized is obtained.

3. The method according to claim 1 or 2, characterized in that, The target time-domain synchronization symbol sequence is a sub-sequence of a target time period extracted from the upsampled signal. The target time period is determined based on a preset protection duration, an estimated start time of the preset time-domain synchronization symbol sequence, and a preset duration of the preset time-domain synchronization symbol sequence; and / or The first matching degree is characterized by the cross-correlation function value.

4. The method according to claim 1 or 2, characterized in that, The second-level timing error of the orthogonal frequency division multiplexing symbol to be synchronized is obtained based on the second matching degree between the cyclic prefix and tail segment corresponding to each of the multiple candidate start times in the upsampled signal, including: For any candidate start time among the multiple candidate start times, extract the cyclic prefix and tail segment corresponding to the candidate start time from the upsampled signal; The target start time is determined from the plurality of candidate start times based on the second matching degree between the cyclic prefix and tail segment corresponding to each of the plurality of candidate start times; Based on the target start time, the second-level timing error of the orthogonal frequency division multiplexing symbol to be synchronized is obtained.

5. The method according to claim 4, characterized in that, Extracting the cyclic prefix and tail segment corresponding to the candidate start time from the upsampled signal includes: Data corresponding to the first preset time period is extracted from the upsampled signal to obtain a cyclic prefix corresponding to the candidate start time, wherein the first preset time period is determined based on the candidate start time and the preset duration of the cyclic prefix; Data corresponding to the second preset time period is extracted from the upsampled signal to obtain the tail segment corresponding to the candidate start time. The second preset time period is determined based on the candidate start time, the preset duration of the cyclic prefix, and the preset duration of the orthogonal frequency division multiplexing symbol to be synchronized.

6. The method according to claim 1 or 2, characterized in that, The step of obtaining the orthogonal frequency division multiplexed signal based on the compensated upsampled signal includes: The compensated upsampled signal is subjected to orthogonal frequency division multiplexing demodulation to obtain the pilot symbols of each of the N orthogonal frequency division multiplexing symbols to be synchronized; Based on the phase error between each of the N pilot symbols and the expected pilot symbol set, the third-level timing error of each of the N orthogonal frequency division multiplexing symbols to be synchronized is obtained, wherein the third-level timing error characterizes the residual timing deviation of the orthogonal frequency division multiplexing symbol to be synchronized after the first two levels of timing compensation. Based on the first-level timing error, second-level timing error, and third-level timing error of each of the N orthogonal frequency division multiplexing symbols, timing compensation is performed on the upsampled signal to obtain the target compensated upsampled signal. The orthogonal frequency division multiplexing signal is obtained based on the target compensation upsampled signal.

7. The method according to claim 6, characterized in that, The step of obtaining the third-level timing error of each of the N orthogonal frequency division multiplexing symbols to be synchronized based on the phase error between each of the N pilot symbols and the expected pilot symbol set includes: The phase error between each of the N pilot symbols and the expected pilot symbol set is corrected to obtain the target phase error of each of the N pilot symbols; Based on the demodulation bit error rate of the M orthogonal frequency division multiplexed signals preceding the orthogonal frequency division multiplexed signal to be synchronized, determine the demodulation bit error rate threshold and the number of groups of the pilot symbols. Based on the bit error rate threshold, the number of groups, and the index of the pilot symbol, the N pilot symbols are grouped to obtain multiple groups of pilot symbols; The average of the target phase errors of multiple sets of pilot symbols is used to obtain the third-level timing error of the orthogonal frequency division multiplexed signal to be synchronized.

8. The method according to claim 7, characterized in that, The step of correcting the phase error between each of the N pilot symbols and the expected pilot symbol set to obtain the target phase error of each of the N pilot symbols includes: Based on the phase error between each of the N pilot symbols and the expected pilot symbol set, the average phase error of each of the N orthogonal frequency division multiplexing symbols to be synchronized is obtained; The intermediate phase error of each of the N pilot symbols is obtained by the difference between each of the N phase errors and the mean of the phase errors; The intermediate phase errors of each of the N pilot symbols are smoothed to obtain the target phase errors of each of the N pilot symbols.

9. The method according to claim 7, characterized in that, The method further includes: The orthogonal frequency division multiplexed signal is demultiplexed and demodulated to obtain the target pilot symbols of each of the N orthogonal frequency division multiplexed symbols.

10. A timing deviation compensation device for orthogonal frequency division multiplexing signals, characterized in that, The device includes: The first obtaining module is used to upsample the orthogonal frequency division multiplexing signal to be synchronized to obtain an upsampled signal, wherein the upsampled signal includes N orthogonal frequency division multiplexing symbols to be synchronized in sequence, the orthogonal frequency division multiplexing symbols to be synchronized include a cyclic prefix and an effective part including a tail segment, and N is an integer greater than 1. The second obtaining module is used to obtain the first-level timing of each of the N orthogonal frequency division multiplexing symbols to be synchronized based on the first matching degree between the time-domain synchronization symbol sequence template and the target time-domain synchronization symbol sequence. The sampling rate of the time-domain synchronization symbol sequence template is the same as the sampling rate of the upsampled signal. The target time-domain synchronization symbol sequence is extracted from the upsampled signal. The first-level timing represents the expected start time of the orthogonal frequency division multiplexing symbol to be synchronized. The third obtaining module is used to obtain the second-level timing error of any one of the N orthogonal frequency division multiplexing symbols to be synchronized, based on the second matching degree between the cyclic prefix and tail segments corresponding to the multiple candidate start times in the upsampled signal. The candidate start times are determined based on the first-level timing of the orthogonal frequency division multiplexing symbol to be synchronized, and the second-level timing error characterizes the offset of the actual start time of the orthogonal frequency division multiplexing symbol to be synchronized relative to the first-level timing. The fourth module is used to perform timing compensation on the upsampled signal based on the first-level timing and second-level timing errors of each of the N orthogonal frequency division multiplexing symbols to be synchronized, so as to obtain a compensated upsampled signal. The fifth module is used to obtain an orthogonal frequency division multiplexed signal based on the compensated upsampled signal.

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