A method and system for Doppler frequency offset estimation of a burst signal

Abstract

The application provides a burst signal Doppler frequency offset estimation method and system, and belongs to the field of Doppler frequency offset estimation; the method comprises the following steps: under the condition that a waveform in a received signal has a preamble, a middle pilot block and a postamble, when a period corresponding to the middle pilot block of the waveform in the received signal is less than or equal to a maximum cumulative symbol number, the middle pilot block, the preamble and the postamble in the waveform are subjected to integral multiple period accumulation; otherwise, non-integral multiple period accumulation is adopted; when the waveform in the received signal does not have the middle pilot block, the whole frame waveform is demodulated without using a pilot, and the demodulated waveform is subjected to block accumulation; the accumulated data sequence is extended by adding 0, subjected to N-point Fourier transform, and Fourier spectrum is output; the position of the maximum Fourier spectrum modulus value peak is found, and a Doppler frequency offset estimation value is obtained. The application can reduce the calculation complexity, and can obtain a frequency offset estimation result similar to or even better than the performance of a non-accumulation method.

Description

Technical Field

[0001] This invention belongs to the field of Doppler frequency offset estimation, and more specifically, relates to a Doppler frequency offset estimation method and system for burst signals. Background Technology

[0002] Existing frequency offset estimation methods mainly fall into two categories: frequency domain estimation methods and time domain estimation methods. Frequency domain methods employ two types of FFT-based synchronization algorithms—Data Aid (DA) and Non-Data Aid (NDA)—to address different waveform structures of DVB-RCS2 burst signals. When there are few intermediate pilot blocks, the DA method utilizes all pilot symbols in the received signal; when there are abundant intermediate pilot blocks, the DA method only utilizes the intermediate pilot block portion of the received signal, failing to fully leverage pilot information. When there are no intermediate pilot blocks, the NDA method treats all symbols of the received signal as non-pilot symbols. All of these methods achieve high frequency offset estimation accuracy; however, the high number of FFT points required to achieve the target performance also leads to high complexity. Time domain methods first perform a coarse frequency offset estimation, then utilize the phase deviation between the preceding and following preamps for a fine frequency estimation. This method achieves high accuracy when the preceding and following preamps are relatively long, the total waveform length is shorter than the preceding and following preamps (e.g., waveform 1 of DVB-RCS2), and the residual frequency offset to be estimated is small. However, this method has specific requirements for the frequency range after rough estimation. When the residual frequency offset range exceeds this range, it will lead to excessive frequency offset estimation error. In addition, it does not fully utilize all pilot symbols in the waveform, resulting in insufficient accuracy for most waveforms. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a Doppler frequency offset estimation method and system for burst signals. This addresses the problems of high computational complexity in existing frequency offset estimation methods due to the high number of FFT points required for estimation, and excessive frequency offset estimation errors caused by time-domain methods when the residual frequency offset range exceeds the coarsely estimated frequency range. Furthermore, time-domain methods do not fully utilize all pilot symbols in the waveform, resulting in insufficient accuracy for most waveforms.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a Doppler frequency offset estimation method for burst signals, comprising the following steps:

[0005] S1: Determine whether there is an intermediate pilot block in each waveform of the received signal. If the waveform has an intermediate pilot block, proceed to S2; if the waveform does not have an intermediate pilot block, proceed to S5.

[0006] S2: When the waveform in the received signal contains a preamble, intermediate pilot block and postamble, calculate the maximum number of accumulated symbols corresponding to different Doppler frequency offsets based on the maximum number of phase change cycles caused by Doppler frequency offset and the acceptable frequency offset range.

[0007] S3: Perform symbol synchronization on the waveform in the received signal, and use the known pilot reference waveform to demodulate the preamble, postamble and intermediate pilot block of the waveform in the received signal, and remove the symbol modulation phase used for frequency offset estimation;

[0008] S4: When the period corresponding to the middle pilot block of the waveform in the received signal is less than or equal to the maximum number of accumulated symbols, the middle pilot block, preamble, and postamble in the waveform are accumulated using an integer multiple of the period, and then proceed to S6; otherwise, non-integer multiple of the period is used for accumulation, and then proceed to S6.

[0009] S5: Demodulate the entire frame waveform without using pilot signals, accumulate the demodulated waveform in blocks, and then proceed to S6.

[0010] For example, if the waveforms 1-22 in the DVB-RCS2 system that do not contain intermediate pilot blocks are all MPSK modulated, then a method such as the doubling method can be used to demodulate the waveforms using MPSK.

[0011] S6: Pad the accumulated data sequence with zeros to expand it into an N-point data sequence, perform an N-point Fourier transform, and output the Fourier spectrum; where N is an integer power of 2;

[0012] S7: Locate the position with the largest peak value of the Fourier spectrum magnitude, obtain the estimated value of Doppler frequency offset, and use the normalized frequency offset representation.

[0013] More preferably, the method for determining the integer value in the integer multiple period accumulation is as follows: the integer multiplied by the period of the intermediate pilot block is less than or equal to the maximum number of accumulated symbols;

[0014] The method for accumulating integer multiples of the period corresponding to the intermediate pilot block is as follows:

[0015] The received data between adjacent intermediate pilot blocks is set to 0. When performing a single-period accumulation, the intermediate pilot block is ensured to be at the center of the accumulation. When performing an n-period accumulation, the n single-period accumulation results under the n periods are summed, where n is an integer greater than 1. The integer multiple-period accumulation method corresponding to the preamble is as follows:

[0016] The non-pilot portion of the waveform in the received signal is set to 0. The non-pilot portion between the preamble and the intermediate preamble block, as well as the preamble, are divided into intervals from high to low according to the period of the intermediate pilot block. Integer multiple period accumulation is performed in each interval. When the preamble in the lowest bit interval is less than one intermediate pilot block period, 0 is padded on the low bit side of the preamble. The integer multiple period accumulation method of the post-preamble is symmetrical to the integer multiple period accumulation method of the preamble.

[0017] More preferably, the non-integer multiple period accumulation is performed sequentially from the beginning to the end of the received signal waveform; the calculation method for the number of accumulated symbols corresponding to the non-integer multiple accumulation is as follows:

[0018]

[0019] Among them, f d1 The Doppler frequency offset is calculated as an integer multiple of the period; L coh1 f d1 The corresponding number of accumulated signs; L coh2 When the Doppler frequency offset f is a non-integer multiple of the sum, d2 The corresponding number of accumulated symbols.

[0020] Furthermore, the Doppler frequency offset estimate is:

[0021]

[0022] Where, k max L represents the position where the peak value of the Fourier spectrum is the largest; N is the number of points in the expanded data sequence; L coh This is the number of accumulated signs.

[0023] More preferably, after S7, the method further includes: correcting the position of the peak value of the Fourier spectrum magnitude to obtain the corrected Doppler frequency offset estimate;

[0024] The index of the position with the largest peak value of the corrected Fourier spectrum modulus is:

[0025]

[0026]

[0027] Where, k l and k r The index k represents the position of the maximum peak value of the Fourier spectrum before correction. max The left and right neighboring points; Z(.) represents the index of the position with the largest peak value of the corrected Fourier spectrum modulus; Z(.) represents the spectrum sequence.

[0028] Secondly, the present invention provides a Doppler frequency offset estimation system for burst signals, comprising:

[0029] The intermediate pilot block identification module is used to determine whether there are intermediate pilot blocks in each waveform of the received signal;

[0030] The maximum accumulated symbol count calculation module is used to calculate the maximum accumulated symbol count under different Doppler frequency offsets when the waveform in the received signal contains a preamble, intermediate pilot block, and postamble, based on the maximum number of phase change cycles caused by the Doppler frequency offset and the acceptable frequency offset range.

[0031] The symbol modulation phase removal module is used to perform symbol synchronization on the waveform in the received signal. It uses a known pilot reference waveform to demodulate the preamble, postamble, and intermediate pilot block of the waveform in the received signal, and removes the symbol modulation phase used for frequency offset estimation.

[0032] The integer multiple period accumulation module is used to accumulate the intermediate pilot block, preamble, and postamble in the waveform when the period corresponding to the intermediate pilot block in the received signal is less than or equal to the maximum number of accumulated symbols.

[0033] The non-integer multiple period accumulation module is used to accumulate the intermediate pilot block, preamble, and postamble in the waveform in a non-integer multiple period when the period corresponding to the intermediate pilot block in the waveform of the received signal is greater than the maximum number of accumulated symbols.

[0034] The non-data auxiliary module is used to demodulate the entire frame waveform without using pilots when the waveform in the received signal does not have an intermediate pilot block, and then accumulate the demodulated waveform in blocks. For example, if the waveforms 1-22 in the DVB-RCS2 system that do not have an intermediate pilot block are all MPSK modulated, then a method such as the doubling method can be used to demodulate the waveform with MPSK, and then the demodulated waveform can be accumulated in blocks.

[0035] The Fourier transform module is used to pad the accumulated data sequence with zeros to expand it into an N-point data sequence, perform an N-point Fourier transform, and output the Fourier spectrum; where N is an integer power of 2.

[0036] The Doppler frequency offset estimation module is used to find the position with the largest peak value of the Fourier spectrum and obtain the Doppler frequency offset estimate.

[0037] More preferably, the integer value method in the integer multiple period accumulation module is: the integer multiplied by the period of the intermediate pilot block is less than or equal to the maximum number of accumulated symbols;

[0038] The integer multiple period accumulation module includes: an intermediate pilot block integer multiple period accumulation unit, a preamble integer multiple period accumulation unit, and a postamble integer multiple period accumulation unit;

[0039] The intermediate pilot block integer multiple period accumulation unit is used to set the received data between adjacent intermediate pilot blocks to 0, and when performing 1-period accumulation, it ensures that the intermediate pilot block is in the accumulation center; when performing n-period accumulation, it sums the n 1-period accumulation results under n periods; where n is an integer greater than 1.

[0040] The preamble integer multiple period accumulation unit is used to set the non-pilot portion of the waveform in the received signal to 0, divide the non-pilot portion between the preamble and the intermediate pilot block, as well as the preamble itself, into intervals from high to low according to the period of the intermediate pilot block, and accumulate the preamble in integer multiple periods within each interval; when the preamble in the lowest bit interval is less than one intermediate pilot block period, 0 is padded on the low bit side of the preamble.

[0041] The method for accumulating multiple periods of the postcode in the multiple period accumulation unit is symmetrical to the method for accumulating multiple periods of the precode in the multiple period accumulation unit.

[0042] More preferably, in the non-integer multiple period accumulation module, the non-integer multiple period accumulation adopts sequential accumulation from the beginning of the waveform of the received signal to the end of the waveform;

[0043] The method for calculating the accumulated sign number corresponding to non-integer multiple accumulations is as follows:

[0044]

[0045] Among them, f d1 The Doppler frequency offset is calculated as an integer multiple of the period; L coh1 f d1 The corresponding number of accumulated signs; L coh2 When the Doppler frequency offset f is a non-integer multiple of the sum, d2 The corresponding number of accumulated symbols.

[0046] More preferably, the Doppler frequency offset estimate value in the Doppler frequency offset estimation module is:

[0047]

[0048] Where, k max L represents the position where the peak value of the Fourier spectrum is the largest; N is the number of points in the expanded data sequence; L coh This is the number of accumulated signs.

[0049] More preferably, the Doppler frequency offset estimation system further includes a correction module for the position of the maximum peak value of the Fourier spectrum magnitude, which is used to correct the position of the maximum peak value of the Fourier spectrum magnitude to obtain the corrected Doppler frequency offset estimate.

[0050] The index of the position with the largest peak value of the corrected Fourier spectrum modulus is:

[0051]

[0052]

[0053] Where, k l and k r The index k represents the position of the maximum peak value of the Fourier spectrum before correction. max The left and right neighboring points; Z(.) represents the index of the position with the largest peak value of the corrected Fourier spectrum modulus; Z(.) represents the spectrum sequence.

[0054] Thirdly, the present invention provides an electronic device comprising: at least one memory for storing a program; and at least one processor for executing the program stored in the memory, wherein when the program stored in the memory is executed, the processor is configured to execute the method described in the first aspect or any further preferably of the first aspect.

[0055] Fourthly, the present invention provides a computer-readable storage medium storing a computer program that, when run on a processor, causes the processor to perform the method described in the first aspect or any further preferably of the first aspect.

[0056] Fifthly, the present invention provides a computer program product that, when run on a processor, causes the processor to perform the method described in the first aspect or any further preferably of the first aspect.

[0057] It is understood that the beneficial effects of the second to fifth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0058] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0059] This invention provides a Doppler frequency offset estimation method and system for burst signals. To address the need for high-precision Doppler frequency offset estimation, an accumulation method is introduced to improve the signal-to-noise ratio (the maximum number of accumulated symbols is calculated based on the maximum number of phase change cycles caused by the Doppler frequency offset and the acceptable frequency offset range). For different Doppler frequency offset scenarios (first scenario: the waveform in the received signal contains a preamble, intermediate pilot block, and postamble, and the period corresponding to the intermediate pilot block is less than or equal to the maximum number of accumulated symbols; second scenario: the waveform in the received signal contains a preamble, intermediate pilot block, and postamble, and the period corresponding to the intermediate pilot block is greater than the maximum number of accumulated symbols; third scenario: the waveform in the received signal does not contain an intermediate pilot block), the number of accumulation points and the accumulation center position of the received signal are set according to the pilot period of the burst waveform. Simultaneously, fewer Fourier transform points can be used for frequency offset estimation, reducing computational complexity and obtaining frequency offset estimation results with performance similar to or even better than non-accumulation methods. Attached Figure Description

[0060] Figure 1 This is a flowchart of the Doppler frequency offset estimation method for burst signals provided in an embodiment of the present invention;

[0061] Figure 2 This is a schematic diagram of the frame structure of DVB-RCS2 provided in an embodiment of the present invention;

[0062] Figure 3 This is a schematic diagram of the intermediate pilot block accumulation method under integer multiple accumulation provided in an embodiment of the present invention;

[0063] Figure 4 This is a schematic diagram of the preamble accumulation method under integer multiple accumulation provided in an embodiment of the present invention;

[0064] Figure 5 This is a flowchart of the coarse capture process provided in an embodiment of the present invention;

[0065] Figure 6 This is a performance comparison chart of various methods for waveform 1 provided in the embodiments of the present invention under a symbol rate frequency offset of 0.5% / 1%;

[0066] Figure 7 This is a performance comparison chart of various methods for waveform 1 provided in the embodiments of the present invention under a symbol rate frequency offset of 2% / 3%;

[0067] Figure 8 This is a performance comparison chart of various methods for waveform 5 provided in the embodiments of the present invention under a symbol rate frequency offset of 0.5% / 1%;

[0068] Figure 9 This is a performance comparison chart of various methods for waveform 5 provided in the embodiments of the present invention under a symbol rate frequency offset of 2% / 3%;

[0069] Figure 10 This is a schematic diagram of a Doppler frequency offset estimation system for burst signals provided in an embodiment of the present invention. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0071] The terms "first" and "second," etc., used in the specification and claims herein are used to distinguish different objects, not to describe a specific order of objects.

[0072] In embodiments of the present invention, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" or "for example" in embodiments of the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0073] like Figure 1 As shown, this invention provides a Doppler frequency offset estimation method for burst signals, comprising the following steps:

[0074] S1: Determine whether there is an intermediate pilot block in each waveform of the received signal. If the waveform has an intermediate pilot block, proceed to S2; if the waveform does not have an intermediate pilot block, proceed to S5.

[0075] S2: When the waveform in the received signal contains a preamble, intermediate pilot block and postamble, calculate the maximum number of accumulated symbols corresponding to different Doppler frequency offsets based on the maximum number of phase change cycles caused by Doppler frequency offset and the acceptable frequency offset range.

[0076] S3: Perform symbol synchronization on the waveform in the received signal, and use the known pilot reference waveform to demodulate the preamble, postamble and intermediate pilot block of the waveform in the received signal, and remove the symbol modulation phase used for frequency offset estimation;

[0077] S4: When the period corresponding to the middle pilot block of the waveform in the received signal is less than or equal to the maximum number of accumulated symbols, the middle pilot block, preamble, and postamble in the waveform are accumulated using an integer multiple of the period, and then proceed to S6; otherwise, non-integer multiple of the period is used for accumulation, and then proceed to S6.

[0078] S5: Demodulate the entire frame waveform without using pilot signals, accumulate the demodulated waveform in blocks, and then proceed to S6.

[0079] For example, if the waveforms of waveforms 1-22 in the DVB-RCS2 system that do not contain intermediate pilot blocks are all MPSK modulated, then the waveforms can be demodulated by MPSK using a method such as the doubling method, and then the demodulated waveforms can be accumulated in blocks.

[0080] S6: Pad the accumulated data sequence with zeros to expand it into an N-point data sequence, perform an N-point Fourier transform, and output the Fourier spectrum; where N is an integer power of 2;

[0081] S7: Doppler frequency offset estimation module, which finds the position with the largest peak value of the Fourier spectrum magnitude, and thus obtains the estimated value of Doppler frequency offset.

[0082] More preferably, the method for determining the integer value in the integer multiple period accumulation is as follows: the integer multiplied by the period of the intermediate pilot block is less than or equal to the maximum number of accumulated symbols;

[0083] The method for accumulating integer multiples of the period corresponding to the intermediate pilot block is as follows:

[0084] The received data between adjacent intermediate pilot blocks is set to 0. When performing a single-period accumulation, the intermediate pilot block is ensured to be at the center of the accumulation. When performing an n-period accumulation, the sum of the n single-period accumulation results under the n periods needs to be calculated. Here, n is an integer greater than 1. The integer multiple-period accumulation method corresponding to the preamble is as follows:

[0085] The non-pilot portion of the waveform in the received signal is set to 0. The non-pilot portion between the preamble and the intermediate pilot block, as well as the preamble, are divided into intervals from high to low according to the period of the intermediate pilot block. In each interval, an integer multiple of the period is accumulated. When the preamble in the lowest interval is less than one intermediate pilot block period, 0 is padded on the low-bit side of the preamble.

[0086] The method of accumulating multiple periods of the postcode is symmetrical to the method of accumulating multiple periods of the precode.

[0087] Further explanation is needed here. The method for accumulating integer multiples of the period of the back preamble is as follows: set the non-pilot portion of the waveform in the received signal to 0, divide the non-pilot portion between the back preamble and the intermediate pilot block, as well as the back preamble, into intervals from low to high according to the period of the intermediate pilot block, and accumulate integer multiples of the period in each interval; when the back preamble in the highest interval is less than one intermediate pilot block period, add 0 to the high-order side of the back preamble.

[0088] More preferably, the non-integer multiple period accumulation adopts sequential accumulation from the beginning to the end of the waveform of the received signal;

[0089] The method for calculating the accumulated sign number corresponding to non-integer multiple accumulations is as follows:

[0090]

[0091] Among them, f d1 The Doppler frequency offset is calculated as an integer multiple of the period; L coh1 f d1 The corresponding number of accumulated signs; L coh2 When the Doppler frequency offset f is a non-integer multiple of the sum, d2 The corresponding number of accumulated symbols.

[0092] More preferably, the Doppler frequency offset estimate is:

[0093]

[0094] Where, k max L represents the position where the peak value of the Fourier spectrum is the largest; N is the number of points in the expanded data sequence; L coh This is the number of accumulated signs.

[0095] More preferably, after S7, the method further includes: correcting the position of the peak value of the Fourier spectrum magnitude to obtain the corrected Doppler frequency offset estimate;

[0096] The index of the position with the largest peak value of the corrected Fourier spectrum modulus is:

[0097]

[0098]

[0099] Where, k l and k r The index k represents the position of the maximum peak value of the Fourier spectrum before correction. max The left and right neighboring points; Z(.) represents the index of the position with the largest peak value of the corrected Fourier spectrum modulus; Z(.) represents the spectrum sequence.

[0100] Example 1

[0101] This invention provides a Doppler frequency offset estimation method and system for burst signals. This invention can obtain accurate frequency offset estimates with low complexity. The method is mainly aimed at... Figure 2 The frame structure shown is similar to DVB-RCS2, with the low-order bits of the waveform shown from left to right;

[0102] The DVB-RCS2 protocol states that the tolerable burst frequency offset within the gateway modem depends on the implementation of the gateway receiver modem. Based on opinions from DVB-RCS2 system and gateway manufacturing practices, the protocol provides a set of representative values ​​for acceptable burst frequency offsets, ranging from 0.5% to 3% of the symbol rate. The protocol also includes tables showing the corresponding frequency offsets for various mobile device types at 0.5%, 1%, 2%, and 3% of the symbol rate. Therefore, the following estimations will use four scenarios with frequency offsets of 0.5%, 1%, 2%, and 3% of the symbol rate.

[0103] As shown in Table 1, taking burst waveforms 1-22 of DVB-RCS2 as an example, the following Doppler precision estimation method is designed according to the characteristics of different waveforms, and the idea of ​​coherent accumulation is introduced to improve the signal-to-noise ratio. At the same time, fewer FFT points can be used for frequency offset estimation, reducing computational complexity, and obtaining frequency offset estimation results with similar or even better performance than non-accumulation methods.

[0104] As the Doppler frequency offset increases, a larger number of accumulation points will greatly reduce the frequency offset estimation performance. Therefore, it is necessary to select an appropriate number of accumulation points based on the basic waveform parameters.

[0105] Table 1

[0106]

[0107] a. When using all pilot symbols, after demodulating the pilot symbols of the received signal, the phase change of the accumulated symbols caused by the Doppler frequency offset should preferably not exceed one-quarter of a cycle. Therefore, the maximum number of accumulated symbols under each Doppler frequency offset can be obtained, as shown in Table 2.

[0108] The accumulated number of symbols is the number of symbols required for each accumulation; the maximum accumulated number of symbols is calculated as follows:

[0109]

[0110] Where MaxSymNum is the maximum number of accumulated symbols; MaxPhase is the maximum number of phase change cycles; f d This is the normalized frequency offset value;

[0111] Table 2

[0112] 0.5％ 50 1％ 25 2％ 12 3％ 8

[0113] b. When pilot symbols are not used, a series of experiments and comparisons are required to set the cumulative symbol count;

[0114] The Doppler frequency bias estimation method specifically includes the following steps:

[0115] (1) Use all pilot symbols

[0116] For waveforms that simultaneously possess preamble, intermediate pilot block, and postamble, such as waveforms 1-4, 8-14, and 18-22, it is necessary to make full use of all known information data to perform frequency offset estimation.

[0117] Before frequency offset estimation, the received signal is first symbol synchronized to locate the positions of the preamble, postamble, and intermediate pilot blocks. Since the specific content of the pilot symbols is known in advance, the known pilot reference waveform c is first used. PSam (n) Demodulating the preamble, postamble, and intermediate pilot block in the received signal s(n) can remove the symbol modulation phase used for frequency offset estimation, thereby improving the accuracy of frequency offset estimation:

[0118]

[0119] Among them, z P (n) represents the demodulated signal;

[0120] The periods of the intermediate pilot blocks of waveforms 1-22 are all less than or equal to 25. Therefore, the symbol accumulation can be divided into two accumulation methods: integer multiple period accumulation and non-integer multiple period accumulation.

[0121] A. Integer multiple periodic accumulation:

[0122] This accumulation method can ensure that the phase before and after accumulation does not deviate as much as possible. For example, when the Doppler frequency deviation is 1%, waveforms 1-4 and 13-14 can be accumulated using a single period; when the Doppler frequency deviation is 2%, waveforms 8-12 and 18-22 can be accumulated using a single period. In the integer multiple period accumulation, the integer value is determined by multiplying the integer by the period of the intermediate pilot block by less than or equal to the maximum number of accumulated symbols.

[0123] The intermediate pilot block accumulation method is as follows: Figure 3 As shown; set the data received between intermediate pilot blocks to 0, while ensuring that the intermediate pilot block is at the center of the accumulation; double-cycle accumulation is a second accumulation based on the result of single-cycle accumulation. For example, in the figure, the result of single-cycle accumulation is P, and the result of double-cycle accumulation is 2P, where T is the intermediate pilot period; Figure 3 In this context, floor means rounding down;

[0124] The preamble part is accumulated as follows: Figure 4 As shown, the non-pilot portion of the received signal is set to 0. The non-pilot portion between the preamble and the intermediate pilot block, as well as the preamble, are divided into intervals from right to left according to the period of the intermediate pilot block and accumulated. If the preamble is less than one period, 0 is added to the low-order side of the preamble. The accumulation method of the post-preamble is symmetrical to that of the preamble.

[0125] B. Non-integer multiple period accumulation

[0126] If the maximum number of accumulated symbols corresponding to the Doppler frequency offset is less than the period of the intermediate pilot block, and since the pilot interval is the periodic interval of the intermediate pilot block, using an integer multiple period accumulation method would result in a large phase deviation. Therefore, a sequential accumulation method from the start to the end of the received signal is adopted. To ensure the uniformity of dimensions, the selection of the number of accumulated symbols is still related to the pilot period, and its calculation formula is as follows:

[0127]

[0128] Among them, f d1 The Doppler frequency offset is calculated as an integer multiple of the period; L coh1 f d1 The corresponding number of accumulated signs, L coh2 When the Doppler frequency offset f is a non-integer multiple of the sum, d2 The corresponding number of accumulated signs;

[0129] For z p In (n), the data of each accumulated sign number is accumulated, and the result of the nth accumulation is:

[0130]

[0131] The accumulated sequence z(m) of length L is padded with zeros and expanded into an N-point sequence (N points are the FFT points in Tables 3 and 4). The expanded sequence z(n) is then subjected to an N-point FFT, and the Fourier spectrum is output.

[0132]

[0133] Table 3

[0134]

[0135] Table 4

[0136]

[0137] Find the position k where the peak value of the spectral magnitude is the largest after FFT. max :

[0138]

[0139] Then the normalized frequency offset estimate f d The estimated value is:

[0140]

[0141] (2) Non-data-aided methods

[0142] For received signals that do not contain intermediate pilot block data, such as waveforms 5-7 and 15-17, MPSK modulation is used. A non-data-aided method can be used to analyze and process a frame as a whole without using a known pilot reference waveform. Demodulation of the received signal can be achieved by performing an M-th power nonlinear transformation, i.e.:

[0143]

[0144] Where s(n) is the received signal;

[0145] Based on formula (2), z(n) is accumulated in blocks, and the position k of the maximum value output after FFT is obtained according to formulas (3) and (4). max n = 1, 2, 3, ... are the symbol indices of the received signals;

[0146] Then the normalized frequency offset estimate f d The estimated value is:

[0147]

[0148] This method does not use information from known pilot symbols. After a series of experimental comparisons, the number of accumulated symbols and the number of FFT points are set for different Doppler frequency offsets of each waveform, as shown in Table 5 below.

[0149] Table 5

[0150]

[0151] (3) Amplitude interpolation

[0152] To correct for frequency shift, the maximum value position index k can be considered. max left neighbor k l and right neighbor k r It can be used to derive the approximate value Δk of a parabola:

[0153]

[0154] Corrected position index have:

[0155]

[0156] Will Replace k max Substituting these values ​​into the final frequency offset estimation formula yields the corrected frequency offset estimate.

[0157] Figure 5 The coarse acquisition method used before frequency offset estimation mainly consists of the following parts:

[0158] (1) Dual-window energy detection: used to detect the approximate starting position of the signal and simultaneously obtain the estimated positions of the preamble and postamble;

[0159] (2) Using the reference waveforms of the preceding and following precodes, a two-dimensional search is performed by pre-compensated Doppler and cyclic correlation to obtain the precise starting position of the entire frame signal and the coarsely estimated Doppler frequency offset; the performance comparison of each frequency offset estimation method is then carried out under this coarse capture result.

[0160] Figure 6 and Figure 7 The frequency offset estimation performance of each method is presented for waveform 1 under Doppler frequency offsets ranging from 0.5% to 3% symbol rate; Figure 6 and Figure 7 It can be seen that the frequency offset estimation accuracy obtained by this invention is better than that of existing frequency domain methods, and the number of FFT points used in this invention is much lower than that of existing frequency domain methods, resulting in lower complexity. The high proportion of preamble and postamble symbols in waveform 1 is a special case. Therefore, for frequency offset estimation of waveform 1, the performance of the method used in this invention has both advantages and disadvantages compared to existing time domain methods.

[0161] like Figure 8 and Figure 9 As shown in waveform 5, the frequency offset estimation accuracy obtained by the present invention is far superior to that of existing time-domain methods. The number of FFT points in the present invention is lower than that of existing frequency-domain methods, and the complexity is relatively low. The present invention has similar performance to existing frequency-domain methods under lower complexity, and is superior to existing frequency-domain methods under lower signal-to-noise ratio conditions.

[0162] Example 2

[0163] like Figure 10 As shown, the present invention provides a Doppler frequency offset estimation system for burst signals, comprising:

[0164] The intermediate pilot block identification module 101 is used to determine whether there are intermediate pilot blocks in each waveform of the received signal;

[0165] The maximum accumulated symbol count calculation module 201 is used to calculate the maximum accumulated symbol count under different Doppler frequency offsets when the waveform in the received signal contains a preamble, an intermediate pilot block, and a postamble, based on the maximum number of phase change cycles caused by the Doppler frequency offset and the acceptable frequency offset range.

[0166] The symbol modulation phase removal module 301 is used to perform symbol synchronization on the waveform in the received signal, and to demodulate the preamble, postamble and intermediate pilot block of the waveform in the received signal using a known pilot reference waveform, thereby removing the symbol modulation phase used for frequency offset estimation.

[0167] The integer multiple period accumulation module 401 is used to accumulate the intermediate pilot block, preamble and postamble in the waveform when the period corresponding to the intermediate pilot block in the waveform is less than or equal to the maximum number of accumulated symbols.

[0168] The non-integer multiple period accumulation module 501 is used to perform non-integer multiple period accumulation on the middle pilot block, preamble, and postamble in the waveform when the period corresponding to the middle pilot block of the waveform in the received signal is greater than the maximum number of accumulated symbols.

[0169] The non-data auxiliary module 601 is used to demodulate the entire frame waveform without using pilots when the waveform in the received signal does not have an intermediate pilot block, and to accumulate the demodulated waveform in blocks.

[0170] If all waveforms in waveforms 1-22 that do not contain intermediate pilot blocks are MPSK modulated, then methods such as the doubling method can be used to demodulate the waveforms using MPSK, and then the demodulated waveforms can be accumulated in blocks.

[0171] The Fourier transform module 701 is used to pad the accumulated data sequence with zeros to expand it into an N-point data sequence, perform an N-point Fourier transform, and output the Fourier spectrum; where N is an integer power of 2.

[0172] The Doppler frequency offset estimation module 801 is used to find the position where the peak value of the Fourier spectrum is the largest and obtain the Doppler frequency offset estimate.

[0173] More preferably, the integer value method in the integer multiple period accumulation module is: the integer multiplied by the period of the intermediate pilot block is less than or equal to the maximum number of accumulated symbols;

[0174] The integer multiple period accumulation module includes: an intermediate pilot block integer multiple period accumulation unit, a preamble integer multiple period accumulation unit, and a postamble integer multiple period accumulation unit;

[0175] The intermediate pilot block integer multiple period accumulation unit is used to set the received data between adjacent intermediate pilot blocks to 0, and when performing 1-period accumulation, it ensures that the intermediate pilot block is in the accumulation center; when performing n-period accumulation, it sums the n 1-period accumulation results under n periods; where n is an integer greater than 1.

[0176] The preamble integer multiple period accumulation unit is used to set the non-pilot portion of the waveform in the received signal to 0, divide the non-pilot portion between the preamble and the intermediate pilot block and the preamble into intervals from high to low according to the period of the intermediate pilot block, and accumulate the preamble in integer multiple periods within each interval; when the preamble in the lowest bit interval is less than one intermediate pilot block period, 0 is padded on the low bit side of the preamble.

[0177] The method for accumulating multiple periods of the postcode in the multiple period accumulation unit is symmetrical to the method for accumulating multiple periods of the precode in the multiple period accumulation unit.

[0178] More preferably, in the non-integer multiple period accumulation module, the non-integer multiple period accumulation adopts sequential accumulation from the beginning of the waveform of the received signal to the end of the waveform;

[0179] The method for calculating the accumulated sign number corresponding to non-integer multiple accumulations is as follows:

[0180]

[0181] Among them, f d1 The Doppler frequency offset is calculated as an integer multiple of the period; L coh1 f d1 The corresponding number of accumulated signs; L coh2 When the Doppler frequency offset f is a non-integer multiple of the sum, d2 The corresponding number of accumulated symbols.

[0182] More preferably, the Doppler frequency offset estimate value in the Doppler frequency offset estimation module is:

[0183]

[0184] Where, k max L represents the position where the peak value of the Fourier spectrum is the largest; N is the number of points in the expanded data sequence; L coh This is the number of accumulated signs.

[0185] More preferably, the Doppler frequency offset estimation system further includes a correction module for the position of the maximum peak value of the Fourier spectrum magnitude, which is used to correct the position of the maximum peak value of the Fourier spectrum magnitude to obtain the corrected Doppler frequency offset estimate.

[0186] The index of the position with the largest peak value of the corrected Fourier spectrum modulus is:

[0187]

[0188]

[0189] Where, k l and k r The index k represents the position of the maximum peak value of the Fourier spectrum before correction. max The left and right neighboring points; Z(.) represents the index of the position with the largest peak value of the corrected Fourier spectrum modulus; Z(.) represents the spectrum sequence.

[0190] It should be understood that the above system is used to execute the methods in the above embodiments. The corresponding program modules in the system are similar in implementation principle and technical effect to those described in the above methods. The working process of the system can be referred to the corresponding process in the above methods, and will not be repeated here.

[0191] Based on the methods described in the above embodiments, this invention provides an electronic device. The device may include at least one memory for storing a program and at least one processor for executing the program stored in the memory. When the program stored in the memory is executed, the processor performs the methods described in the above embodiments.

[0192] Based on the methods in the above embodiments, this embodiment of the invention provides a computer-readable storage medium storing a computer program that, when run on a processor, causes the processor to execute the methods in the above embodiments.

[0193] Based on the methods in the above embodiments, this embodiment of the invention provides a computer program product that, when run on a processor, causes the processor to execute the methods in the above embodiments.

[0194] It is understood that the processor in the embodiments of the present invention can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The general-purpose processor can be a microprocessor or any conventional processor.

[0195] The method steps in the embodiments of the present invention can be implemented in hardware or by a processor executing software instructions. The software instructions can consist of corresponding software modules, which can be stored in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can reside in an ASIC.

[0196] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable system. The computer instructions can be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state disk (SSD)).

[0197] It is understood that the various numerical designations used in the embodiments of the present invention are merely for descriptive convenience and are not intended to limit the scope of the embodiments of the present invention.

[0198] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for estimating the Doppler frequency offset of burst signals, characterized in that, Includes the following steps: S1: Determine whether there is an intermediate pilot block in each waveform of the received signal. If the waveform has an intermediate pilot block, proceed to S2; if the waveform does not have an intermediate pilot block, proceed to S5. S2: When the waveform in the received signal contains a preamble, intermediate pilot block and postamble, calculate the maximum number of accumulated symbols corresponding to different Doppler frequency offsets based on the maximum number of phase change cycles caused by Doppler frequency offset and the acceptable frequency offset range. S3: Perform symbol synchronization on the waveform in the received signal, and use the known pilot reference waveform to demodulate the preamble, postamble and intermediate pilot block of the waveform in the received signal, and remove the symbol modulation phase used for frequency offset estimation; S4: When the period corresponding to the middle pilot block of the waveform in the received signal is less than or equal to the maximum number of accumulated symbols, the middle pilot block, preamble, and postamble in the waveform are accumulated using an integer multiple of the period, and then proceed to S6; otherwise, non-integer multiple of the period is used for accumulation, and then proceed to S6. S5: Demodulate the entire frame waveform without using pilot signals, accumulate the demodulated waveform in blocks, and then proceed to S6. S6: Pad the accumulated data sequence with zeros to expand it into an N-point data sequence, perform an N-point Fourier transform, and output the Fourier spectrum; where N is an integer power of 2; S7: Find the position with the largest peak value of the Fourier spectrum magnitude and obtain the Doppler frequency offset estimate; The method for determining the integer value in the integer multiple period accumulation is as follows: the integer multiplied by the period of the intermediate pilot block is less than or equal to the maximum number of accumulated symbols; The method for accumulating integer multiples of the period corresponding to the intermediate pilot block is as follows: The data received between adjacent intermediate pilot blocks is set to 0. When performing a single-cycle accumulation, the intermediate pilot block is ensured to be at the center of the accumulation. When performing an n-cycle accumulation, the n single-cycle accumulation results under n cycles are summed. Here, n is an integer greater than 1. The method for accumulating integer multiples of the preamble period is as follows: The non-pilot portion of the waveform in the received signal is set to 0. The non-pilot portion between the preamble and the intermediate preamble block, as well as the preamble, are divided into intervals from high to low according to the period of the intermediate pilot block. In each interval, an integer multiple of the period is accumulated. When the preamble in the lowest bit interval is less than one intermediate pilot block period, 0 is padded on the low bit side of the preamble. The method of accumulating multiple periods of the postcode is symmetrical to the method of accumulating multiple periods of the precode.

2. The Doppler frequency offset estimation method according to claim 1, characterized in that, Non-integer multiple period accumulation uses sequential accumulation from the beginning to the end of the received signal waveform; The method for calculating the accumulated sign number corresponding to non-integer multiple accumulations is as follows: in, Doppler frequency offset when accumulated as an integer multiple of the period; for The corresponding number of accumulated signs; Doppler frequency offset when accumulated as a non-integer multiple The corresponding number of accumulated symbols.

3. The Doppler frequency offset estimation method according to claim 1 or 2, characterized in that, The Doppler frequency offset estimate is: in, The position where the peak value of the Fourier spectrum magnitude is the largest; N is the number of points in the expanded data sequence; This is the number of accumulated signs.

4. The Doppler frequency offset estimation method according to claim 1, characterized in that, S7 also includes: correcting the position of the maximum peak value of the Fourier spectrum magnitude to obtain the corrected Doppler frequency offset estimate; The index of the position with the largest peak value of the corrected Fourier spectrum modulus is: in, and These are the indices of the maximum peak position of the Fourier spectrum magnitude before correction. The left and right neighboring points; Z(.) represents the index of the position with the largest peak value of the corrected Fourier spectrum modulus; Z(.) represents the spectrum sequence.

5. A Doppler frequency offset estimation system for burst signals, characterized in that, include: The intermediate pilot block identification module is used to determine whether there are intermediate pilot blocks in each waveform of the received signal; The maximum accumulated symbol count calculation module is used to calculate the maximum accumulated symbol count under different Doppler frequency offsets when the waveform in the received signal contains a preamble, intermediate pilot block, and postamble, based on the maximum number of phase change cycles caused by the Doppler frequency offset and the acceptable frequency offset range. The symbol modulation phase removal module is used to perform symbol synchronization on the waveform in the received signal. It uses a known pilot reference waveform to demodulate the preamble, postamble, and intermediate pilot block of the waveform in the received signal, and removes the symbol modulation phase used for frequency offset estimation. The integer multiple period accumulation module is used to accumulate the intermediate pilot block, preamble, and postamble in the waveform when the period corresponding to the intermediate pilot block in the received signal is less than or equal to the maximum number of accumulated symbols. The non-integer multiple period accumulation module is used to accumulate the intermediate pilot block, preamble, and postamble in the waveform in a non-integer multiple period when the period corresponding to the intermediate pilot block of the waveform in the received signal is greater than the maximum number of accumulated symbols. The non-data auxiliary module, when the waveform in the received signal does not have an intermediate pilot block, uses a method that does not utilize pilots to demodulate the entire frame waveform, and then performs block accumulation on the demodulated waveform; The Fourier transform module is used to pad the accumulated data sequence with zeros to expand it into an N-point data sequence, perform an N-point Fourier transform, and output the Fourier spectrum; where N is an integer power of 2. The Doppler frequency offset estimation module is used to find the position with the largest peak value of the Fourier spectrum magnitude and obtain the Doppler frequency offset estimate. The integer value method in the integer multiple period accumulation module is as follows: the integer multiplied by the period of the intermediate pilot block is less than or equal to the maximum number of accumulated symbols; The integer multiple period accumulation module includes: an intermediate pilot block integer multiple period accumulation unit, a preamble integer multiple period accumulation unit, and a postamble integer multiple period accumulation unit; The intermediate pilot block integer multiple period accumulation unit is used to set the received data between adjacent intermediate pilot blocks to 0, and when performing 1-period accumulation, it ensures that the intermediate pilot block is in the accumulation center; when performing n-period accumulation, it sums the n 1-period accumulation results under n periods; where n is an integer greater than 1. The preamble integer multiple period accumulation unit is used to set the non-pilot portion of the waveform in the received signal to 0, divide the non-pilot portion between the preamble and the intermediate pilot block, as well as the preamble itself, into intervals from high to low according to the period of the intermediate pilot block, and accumulate the preamble in integer multiple periods within each interval; when the preamble in the lowest bit interval is less than one intermediate pilot block period, 0 is padded on the low bit side of the preamble. The method for accumulating multiple periods of the postcode in the multiple period accumulation unit is symmetrical to the method for accumulating multiple periods of the precode in the multiple period accumulation unit.

6. The Doppler frequency offset estimation system according to claim 5, characterized in that, In the non-integer multiple period accumulation module, the non-integer multiple period accumulation adopts sequential accumulation from the beginning of the received signal waveform to the end of the waveform; The method for calculating the accumulated sign number corresponding to non-integer multiple accumulations is as follows: in, Doppler frequency offset when accumulated as an integer multiple of the period; for The corresponding number of accumulated signs; Doppler frequency offset when accumulated as a non-integer multiple The corresponding number of accumulated symbols.

7. The Doppler frequency offset estimation system according to claim 5 or 6, characterized in that, The Doppler frequency offset estimate in the Doppler frequency offset estimation module is: in, The position where the peak value of the Fourier spectrum magnitude is the largest; N is the number of points in the expanded data sequence; This is the number of accumulated signs.

8. The Doppler frequency offset estimation system according to claim 5, characterized in that, It also includes a correction module for the position of the maximum peak of the Fourier spectrum magnitude, which is used to correct the position of the maximum peak of the Fourier spectrum magnitude and obtain the corrected Doppler frequency offset estimate. The index of the position with the largest peak value of the corrected Fourier spectrum modulus is: in, and These are the indices of the maximum peak position of the Fourier spectrum magnitude before correction. The left and right neighboring points; Z(.) represents the index of the position with the largest peak value of the corrected Fourier spectrum modulus; Z(.) represents the spectrum sequence.

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