Cascade carrier frequency offset estimation method and device and storage medium

Abstract

The invention relates to a cascade carrier frequency offset estimation method and device and a storage medium. The method comprises the following steps: generating an initial local carrier signal, and performing coherent demodulation processing on a received quadrature amplitude modulation signal to obtain an initial receiving demodulation signal; performing discrete Fourier transform carrier coarse acquisition with adaptive precision adjustment, regenerating a coarse acquisition local carrier signal, performing coherent demodulation processing and clock synchronization on the quadrature amplitude modulation signal again, and outputting a first demodulation symbol; compensating the first demodulation symbol through a direct judgment phase-locked loop to obtain a second demodulation symbol, finding and outputting an ideal constellation symbol through a direct judgment method, and determining a second phase offset; tracking the phase error through phase integration and loop filtering according to the second phase offset, and determining a phase error tracking result; and determining the residual frequency offset of the first demodulation symbol according to the phase error tracking result. The method is high in anti-noise capability and high in execution efficiency.

Description

Technical Field

[0001] This application relates to the field of digital communication receiver technology, and in particular to a cascaded carrier frequency offset estimation method, apparatus and storage medium. Background Technology

[0002] Quadrature Amplitude Modulation (QAM) technology is widely used in various scenarios such as deep space communication and underwater communication due to its high spectral efficiency and high transmission rate. In particular, high-order QAM modulation systems have become a core choice for improving communication capacity. However, in harsh channel environments such as deep space and underwater, the received signal is often accompanied by a large carrier frequency offset and an extremely low signal-to-interference plus noise ratio (SNR). Carrier synchronization, as a key link in signal demodulation, directly determines the communication quality.

[0003] Traditional carrier synchronization methods have significant limitations: autocorrelation-based methods (such as delay multiplication) have a large frequency offset acquisition range, but poor frequency estimation accuracy and weak noise resistance, and their performance deteriorates sharply in low signal-to-noise ratio scenarios; while phase-locked loop (PLL)-based methods can achieve high-precision frequency offset tracking, their acquisition range is extremely narrow and cannot be adapted to large frequency offset scenarios. Furthermore, in high-order QAM systems, traditional PLLs need to rotate the entire reference constellation diagram to complete phase decision and phase detection, which causes the computational load to increase dramatically with the modulation order, making it difficult to meet real-time requirements. Summary of the Invention

[0004] Therefore, it is necessary to provide a cascaded carrier frequency offset estimation method, device, and storage medium that does not rely on prior knowledge, has strong noise resistance, and high execution efficiency to address the above-mentioned technical problems.

[0005] Firstly, this application provides a cascaded carrier frequency offset estimation method. The method includes:

[0006] An initial local carrier signal is generated, and coherent demodulation processing is performed on the received quadrature amplitude modulation signal to obtain the initial received demodulated signal.

[0007] The initial received demodulated signal is subjected to adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition, the coarse acquisition local carrier signal is regenerated, and the orthogonal amplitude modulation signal is subjected to coherent demodulation processing and clock synchronization again, and the first demodulated symbol with compensation and carrier frequency error and phase offset is output.

[0008] The first demodulated symbol is compensated and the first phase shift of the symbol is eliminated by a direct decision phase-locked loop to obtain the second demodulated symbol. The ideal constellation symbol is found and output by the direct decision method, and the second phase shift between the second demodulated symbol and the ideal constellation symbol is determined.

[0009] The phase error tracking result is determined by tracking the phase error through phase integration and loop filtering based on the second phase offset;

[0010] The residual frequency offset of the first demodulated symbol is determined based on the phase error tracking result.

[0011] In some embodiments of the method, the step of performing adaptive precision adjustment on the initial received demodulated signal using discrete Fourier transform carrier coarse acquisition, and regenerating the coarse acquisition local carrier signal, includes:

[0012] The initial received demodulated signal is continuously segmented according to the initial number of Fast Fourier Transform (FFT) points. Several segments of the signal are subjected to FFT to obtain the segmented signal spectrum. The segmented signal spectrum is then noncoherently accumulated and averaged to obtain the smoothed signal spectrum.

[0013] Perform spectral peak detection on the smoothed signal spectrum to determine the frequency offset estimate.

[0014] In some embodiments of the method, the step of performing adaptive precision adjustment on the initial received demodulated signal using discrete Fourier transform carrier coarse acquisition and regenerating the coarse acquisition local carrier signal further includes:

[0015] Increase the number of Fast Fourier Transform (FFT) points, segment the input signal according to the new FFT length, perform FFT and smoothing processing to obtain the new segmented signal spectrum, calculate the frequency offset estimate of the current segment, compare the frequency offset estimate of the current segment with the frequency offset estimate of the previous segment, and determine the reference frequency residual error.

[0016] Once the residual error of the reference frequency for a consecutive preset number of groups is reduced to a preset tracking range, spectrum acquisition is completed, and the coarse acquisition local carrier signal is regenerated based on the coarse frequency estimation result.

[0017] In some embodiments of the method, when increasing the number of Fast Fourier Transform (FFT) points, the ratio of the new number of segments to the new number of FFT points is consistent with the ratio of the number of segments to the number of FFT points of the previous segment, and the number of segments is a positive integer.

[0018] In some embodiments of the method, the spectral peak detection includes:

[0019] The maximum peak value of the search signal spectrum is traversed, and several spectral points before and after the maximum peak value are selected as the peak main lobe. The center frequency index value of the peak main lobe is calculated, and the frequency offset estimate is calculated based on the index value.

[0020] In some embodiments of the method, the step of compensating and eliminating the first phase shift of the first demodulated symbol using a direct decision phase-locked loop to obtain the second demodulated symbol includes:

[0021] The first demodulated symbol is processed one by one, and phase compensation is performed on the first demodulated symbol through a multiplier structure. The compensation signal is generated by a numerically controlled oscillator. Phase compensation is not performed on the first symbol in the first demodulated symbol.

[0022] In some embodiments of the method, the step of finding and outputting the ideal constellation symbol using a direct decision method, and determining the second phase offset between the second demodulated symbol and the ideal constellation symbol, includes:

[0023] By comparing the second demodulated symbol with the reference quadrature amplitude modulation constellation diagram using a direct decision unit, the ideal constellation symbol in the reference quadrature amplitude modulation constellation diagram that has the closest Euclidean distance to the second demodulated symbol is found and output.

[0024] The second phase offset between the second demodulated symbol and the ideal constellation symbol is determined by a phase detector.

[0025] In some embodiments of the method, the residual frequency offset is calculated based on the phase error tracking result, the number of symbols processed, and the sampling rate of the receiving system, and the frequency tracking range of the direct decision phase-locked loop matches the output residual error range of the adaptive precision-adjusted discrete Fourier transform carrier coarse acquisition.

[0026] According to a second aspect of the present disclosure, a cascaded carrier frequency offset estimation apparatus is provided. The apparatus includes:

[0027] The initial signal matching module is used to generate an initial local carrier signal and perform coherent demodulation processing on the received quadrature amplitude modulation signal to obtain the initial received demodulated signal.

[0028] The coarse acquisition module is used to perform adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition on the initial received demodulated signal, regenerate the coarse acquisition local carrier signal, and re-perform coarse demodulation processing and clock synchronization on the orthogonal amplitude modulation signal, and output the compensated first demodulated symbol with carrier frequency error and phase offset.

[0029] The phase compensation and decision phase detection module is used to compensate and eliminate the first phase shift of the first demodulated symbol through a direct decision phase-locked loop to obtain the second demodulated symbol, find and output the ideal constellation symbol through the direct decision method, and determine the second phase shift between the second demodulated symbol and the ideal constellation symbol.

[0030] The phase error tracking module is used to track the phase error based on the second phase offset through phase integration and loop filtering, and determine the phase error tracking result.

[0031] The residual frequency offset calculation module is used to determine the residual frequency offset of the first demodulated symbol based on the phase error tracking result.

[0032] According to a third aspect of the present disclosure, a computer device is provided. The computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program performing the following steps:

[0033] An initial local carrier signal is generated, and coherent demodulation processing is performed on the received quadrature amplitude modulation signal to obtain the initial received demodulated signal.

[0034] The initial received demodulated signal is subjected to adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition, the coarse acquisition local carrier signal is regenerated, and the orthogonal amplitude modulation signal is subjected to coherent demodulation processing and clock synchronization again, and the first demodulated symbol with compensation and carrier frequency error and phase offset is output.

[0035] The first demodulated symbol is compensated and the first phase shift of the symbol is eliminated by a direct decision phase-locked loop to obtain the second demodulated symbol. The ideal constellation symbol is found and output by the direct decision method, and the second phase shift between the second demodulated symbol and the ideal constellation symbol is determined.

[0036] The phase error tracking result is determined by tracking the phase error through phase integration and loop filtering based on the second phase offset;

[0037] The residual frequency offset of the first demodulated symbol is determined based on the phase error tracking result.

[0038] According to a fourth aspect of the present disclosure, a computer-readable storage medium is provided. The computer-readable storage medium stores a computer program thereon, which, when executed by a processor, performs the following steps:

[0039] An initial local carrier signal is generated, and coherent demodulation processing is performed on the received quadrature amplitude modulation signal to obtain the initial received demodulated signal.

[0040] The initial received demodulated signal is subjected to adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition, the coarse acquisition local carrier signal is regenerated, and the orthogonal amplitude modulation signal is subjected to coherent demodulation processing and clock synchronization again, and the first demodulated symbol with compensation and carrier frequency error and phase offset is output.

[0041] The first demodulated symbol is compensated and the first phase shift of the symbol is eliminated by a direct decision phase-locked loop to obtain the second demodulated symbol. The ideal constellation symbol is found and output by the direct decision method, and the second phase shift between the second demodulated symbol and the ideal constellation symbol is determined.

[0042] The phase error tracking result is determined by tracking the phase error through phase integration and loop filtering based on the second phase offset;

[0043] The residual frequency offset of the first demodulated symbol is determined based on the phase error tracking result.

[0044] According to a fifth aspect of the present disclosure, a computer program product is provided. The computer program product includes a computer program that, when executed by a processor, performs the following steps:

[0045] An initial local carrier signal is generated, and coherent demodulation processing is performed on the received quadrature amplitude modulation signal to obtain the initial received demodulated signal.

[0046] The initial received demodulated signal is subjected to adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition, the coarse acquisition local carrier signal is regenerated, and the orthogonal amplitude modulation signal is subjected to coherent demodulation processing and clock synchronization again, and the first demodulated symbol with compensation and carrier frequency error and phase offset is output.

[0047] The first demodulated symbol is compensated and the first phase shift of the symbol is eliminated by a direct decision phase-locked loop to obtain the second demodulated symbol. The ideal constellation symbol is found and output by the direct decision method, and the second phase shift between the second demodulated symbol and the ideal constellation symbol is determined.

[0048] The phase error tracking result is determined by tracking the phase error through phase integration and loop filtering based on the second phase offset;

[0049] The residual frequency offset of the first demodulated symbol is determined based on the phase error tracking result.

[0050] The cascaded carrier frequency offset estimation scheme provided in this application can coarsely acquire the carrier frequency using an adaptively precision-adjusted discrete Fourier transform carrier coarse acquisition module. This requires only a small number of signal samples to complete the coarse acquisition, eliminating the need to calculate the complete received signal and significantly reducing the computational complexity of the coarse acquisition module. Then, a direct decision phase-locked loop (DLL) precise tracking module accurately tracks the residual frequency offset error. Compared to traditional methods, the improved DLL does not require rotation of the entire QAM reference constellation in phase compensation and symbol decision, significantly reducing the computational load of phase tracking. The reduction in complex multiplication computation is proportional to the QAM modulation order, making it particularly suitable for high-order QAM systems. By cascading the adaptively precision-adjusted discrete Fourier transform carrier coarse acquisition module and the DLL, it eliminates the need for prior knowledge and historical data training, enabling stable operation even in harsh channel environments with low signal-to-noise ratios and large frequency offsets. This demonstrates strong noise immunity and significantly improves the carrier synchronization efficiency of the QAM system.

[0051] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0052] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure, and are not intended to unduly limit this disclosure.

[0053] Figure 1 This is a flowchart illustrating a cascaded carrier frequency offset estimation method according to an exemplary embodiment;

[0054] Figure 2 The following is an execution flowchart of an adaptive precision-adjusted discrete Fourier transform coarse capture module according to an exemplary embodiment.

[0055] Figure 3 The following is an execution flowchart of an improved direct decision phase-locked loop frequency offset precise tracking module according to an exemplary embodiment;

[0056] Figure 4 This is a structural block diagram of a cascaded carrier frequency offset estimation device according to an exemplary embodiment;

[0057] Figure 5 This is a diagram illustrating the internal structure of a computer device according to an exemplary embodiment. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0059] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented in orders other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure. The terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, product, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, product, or apparatus. Without further limitations, the presence of other identical or equivalent elements in a process, method, product, or apparatus that includes said elements is not excluded. For example, the use of terms such as "first," "second," etc., to denote names does not indicate any specific order.

[0060] In some embodiments provided in this disclosure, the execution of the cascaded carrier frequency offset estimation method can be controlled by a unified controller or by multiple controllers. These controllers may include the controller of a local terminal or the controller of a remote server. In some embodiments, the controller of the local terminal and the controller of the server may jointly assist in completing the cascaded carrier frequency offset estimation. The local terminal mentioned in this disclosure may include, but is not limited to, various robotic devices, vehicle-mounted devices, personal computers, laptops, smartphones, tablets, wearable devices, medical devices, VR (Virtual Reality) devices, etc. The server may also be a server, server cluster, distributed subsystem, cloud processing platform, server containing blockchain nodes, and combinations thereof. The controllers described in this disclosure may include various control units capable of implementing logic processing functions, including but not limited to CPU (Central Processing Unit), PLC (Programmable Logic Controller), ECU (Electronic Control Unit), MCU (Microcontroller Unit), FPGA (Field Programmable Gate Array), and CPLD (Complex Programmable Logic Device), as well as controllers composed of one or more logic function units, chips, etc.

[0061] In some embodiments of this disclosure, a cascaded carrier frequency offset estimation method is provided, such as... Figure 1 As shown, it includes the following steps:

[0062] S20. Generate an initial local carrier signal and perform coherent demodulation processing on the received quadrature amplitude modulation signal to obtain the initial received demodulated signal.

[0063] The initial local carrier signal usually refers to the local reference signal generated according to the carrier frequency specified by the quadrature amplitude modulation transmission system. Its frequency is theoretically consistent with the carrier frequency of the transmitting end. It is used to coherently demodulate the received quadrature amplitude modulation signal and provide a basic reference for subsequent signal processing.

[0064] Quadrature amplitude modulation (QAM) signals typically refer to digital signals modulated using quadrature amplitude modulation technology. They possess both amplitude and phase modulation characteristics, have high spectral efficiency and fast transmission rates, and are widely used in deep space communication, underwater communication, and other scenarios. The QAM signals acquired by the receiving end are usually accompanied by carrier frequency errors and phase shifts.

[0065] The initial received demodulated signal usually refers to the signal obtained after the receiver generates an initial local carrier signal based on the carrier frequency agreed upon by the quadrature amplitude modulation transmission system, performs coherent demodulation processing on the received quadrature amplitude modulation signal, and performs operations such as matched filtering and digital sampling.

[0066] S22. Perform adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition on the initial received demodulated signal, regenerate the coarse acquisition local carrier signal, and re-perform coarse demodulation processing and clock synchronization on the orthogonal amplitude modulation signal, and output the compensated first demodulated symbol with carrier frequency error and phase offset.

[0067] Adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition is a process of segmenting the received demodulated signal, smoothing the spectrum, detecting peaks, and dynamically adjusting the relevant parameters of fast Fourier transform to achieve preliminary acquisition and compensation of large carrier frequency offset. The acquisition efficiency and accuracy can be improved through adaptive adjustment.

[0068] The coarse acquisition of the local carrier signal typically refers to the coarse acquisition process of the discrete Fourier transform carrier signal after adaptive precision adjustment. After obtaining a coarse frequency estimate, the local reference carrier signal is regenerated. Its frequency, corrected in the coarse acquisition stage, can initially compensate for most of the carrier frequency deviation in the received signal, and is used to perform coherent demodulation and clock synchronization operations on the received quadrature amplitude modulation signal.

[0069] The first demodulation symbol typically refers to the demodulation symbol output after coarsely demodulating the received quadrature amplitude modulation signal by coarsely capturing the local carrier signal and completing clock synchronization.

[0070] S24. The first demodulated symbol is compensated and the first phase offset of the symbol is eliminated by direct decision phase-locked loop to obtain the second demodulated symbol. The ideal constellation symbol is found and output by direct decision method, and the second phase offset between the second demodulated symbol and the ideal constellation symbol is determined.

[0071] Direct decision phase-locked loops (PDLs) are modules that do not require rotating the entire reference constellation diagram. They compensate for residual frequency offset and phase shift by directly determining the ideal constellation symbol and tracking phase error in real time, thus reducing computational complexity while ensuring accuracy.

[0072] Ideal constellation symbols typically refer to the standard symbols preset in the quadrature amplitude modulation constellation diagram. Each symbol corresponds to fixed amplitude and phase information and serves as the benchmark for judging the deviation of the received demodulation symbols.

[0073] The first phase offset is the phase offset carried by the first demodulated symbol itself. This offset is caused by factors such as the transmission channel and residual carrier frequency offset, and is a phase deviation that was not eliminated after coarse acquisition processing. The second phase offset is the phase difference between the second demodulated symbol and the ideal constellation symbol determined by the direct decision method.

[0074] S26. Based on the second phase offset, track the phase error through phase integration and loop filtering to determine the phase error tracking result.

[0075] The phase error tracking result is a stable phase error information obtained by integrating multiple phase deviation information through phase integration based on the detected second phase offset, and then filtering out high-frequency noise and sudden interference through loop filtering.

[0076] S28. Determine the residual frequency offset of the first demodulated symbol based on the phase error tracking result.

[0077] After all the received demodulated symbols have been processed, the residual frequency offset of the system after processing by the coarse acquisition module can be calculated based on the phase error obtained from the last loop operation.

[0078] In some embodiments of this disclosure, a coarse carrier acquisition module with adaptive precision adjustment of discrete Fourier transform can be used to coarsely acquire the carrier frequency. Only a small number of signal samples are needed to complete the coarse carrier acquisition, and there is no need to calculate the complete received signal, which significantly reduces the computational complexity of the coarse acquisition module. Then, a direct decision phase-locked loop (PDL) precise tracking module is used to accurately track the residual frequency offset error. Compared with the traditional method, the improved PLL does not require rotation of the entire QAM reference constellation in phase compensation and symbol decision, which significantly reduces the computational load of phase tracking. The reduction in the computational load of complex multiplication is proportional to the QAM modulation order, which is especially suitable for high-order QAM systems. By cascading the coarse carrier acquisition module with adaptive precision adjustment of discrete Fourier transform and the PLL, there is no need to rely on prior knowledge and historical data training. It can still work stably in harsh channel environments with low signal-to-noise ratio and large frequency offset, with strong noise resistance, and significantly improves the carrier synchronization efficiency of the QAM system.

[0079] In some embodiments of this disclosure, S22 includes:

[0080] The initial received demodulated signal is continuously segmented according to the initial number of Fast Fourier Transform (FFT) points. Several segments of the signal are subjected to FFT to obtain the segmented signal spectrum. The segmented signal spectrum is then noncoherently accumulated and averaged to obtain the smoothed signal spectrum.

[0081] Perform spectral peak detection on the smoothed signal spectrum to determine the frequency offset estimate.

[0082] In some implementations, the adaptive precision-adjusted Discrete Fourier Transform coarse acquisition module can be implemented based on piecewise smoothing windows and Discrete Fourier Transform (DFT) spectrum analysis. This module is used to perform piecewise cumulative averaging of the spectrum of the QAM received signal under low signal-to-noise ratio conditions, reducing peak jitter caused by noise and spectral leakage. Coherent demodulation of the QAM signal is achieved through a local carrier signal and a matched filter. The smoothed signal spectrum is obtained through piecewise smoothing windows and Fast Fourier Transform. The segmented signal frequency offset is calculated using a peak detector. The coarse frequency offset estimation accuracy is obtained through an error controller. The number of Fast Fourier Transform points in the subsequent piecewise smoothing window is adjusted to control the residual frequency offset within the tracking range of the secondary precision tracking module (i.e., the aforementioned preset tracking range). The frequency estimate is output, and a corresponding local carrier signal is generated for preliminary signal compensation. The preliminarily compensated signal is then input into the secondary precision tracking module.

[0083] In some implementations, adaptive precision-adjusted discrete Fourier transform coarse acquisition may include a spectrum segmentation smoothing step, a spectrum peak detection step, a frequency offset error control step, and a carrier acquisition output step.

[0084] The spectrum segmentation and smoothing steps include: continuously segmenting the initial received demodulated signal according to the initial number of Fast Fourier Transform (FFT) points; performing FFT on several segments to obtain the segmented signal spectrum; and averaging the segmented signal spectra after incoherent accumulation to obtain the smoothed signal spectrum.

[0085] The peak detection step includes: performing peak detection on the smoothed signal spectrum to determine the frequency offset estimate.

[0086] In some embodiments of this disclosure, S22 further includes:

[0087] Increase the number of Fast Fourier Transform (FFT) points, segment the input signal according to the new FFT length, perform FFT and smoothing processing to obtain the new segmented signal spectrum, calculate the frequency offset estimate of the current segment, compare the frequency offset estimate of the current segment with the frequency offset estimate of the previous segment, and determine the reference frequency residual error.

[0088] Once the residual error of the reference frequency for a consecutive preset number of groups is reduced to a preset tracking range, spectrum acquisition is completed, and the coarse acquisition local carrier signal is regenerated based on the coarse frequency estimation result.

[0089] In some implementations, the frequency offset error control steps include: increasing the number of Fast Fourier Transform (FFT) points, segmenting the input signal according to the new FFT length, performing FFT, and smoothing to obtain a new segmented signal spectrum; calculating the frequency offset estimate of the current segment; comparing the current segment's frequency offset estimate with the previous segment's frequency offset estimate to determine the reference frequency residual error. If the reference frequency residual error of a consecutive preset number of groups decreases to a preset tracking range, spectrum acquisition is completed, and a coarse acquisition local carrier signal is regenerated based on the coarse frequency estimation result. Otherwise, the error control process continues.

[0090] The carrier acquisition output step includes: regenerating the local carrier signal based on the coarse frequency estimation result output by the error control step, performing matched filtering and clock synchronization on the received QAM digital signal, and obtaining the first demodulated symbol with compensated carrier frequency error and phase offset.

[0091] After the adaptive precision-adjusted discrete Fourier transform coarse acquisition module captures the carrier frequency of the received QAM signal, it obtains a first demodulated signal with residual frequency offset and phase error. The first demodulated signal can be input into the improved direct decision phase-locked loop precision tracking module.

[0092] In some embodiments of this disclosure, adaptive accuracy adjustment can be achieved by dynamically adjusting the number of Fast Fourier Transform points and combining it with the comparison of frequency offset errors in continuous segments. This ensures the accuracy of coarse acquisition while avoiding the high computational complexity caused by always using a large number of Fast Fourier Transform points. It can converge quickly in the processing of limited signal samples and control the residual frequency offset within the range that the subsequent precise tracking module can handle, thereby improving the flexibility and efficiency of the coarse acquisition process.

[0093] In some embodiments of this disclosure, when increasing the number of Fast Fourier Transform (FFT) points, the ratio of the new number of segments to the new number of FFT points is consistent with the ratio of the number of segments to the number of FFT points of the previous segment, and the number of segments is a positive integer.

[0094] In some implementations, the segment length and the number of FFT points can be adjusted: adjust the segment length and the number of FFT points during the (K+1)th segment grouping and FFT processing to N. FFT (K+1) and the number of segments L(K+1); where N is taken as N. FFT (K+1)=2N FFT(K), L(K+1)=L(K)+l, where l is an integer greater than 0. After parameter adjustment, proceed to the signal continuous segmentation and FFT processing step, and repeat the (K+1)th continuous segmentation and FFT processing until the conditions are met to complete coarse frequency acquisition. By keeping the ratio of the number of segments to the number of FFT points constant, the number of signal segments accumulated per unit spectral resolution can be kept consistent, avoiding fluctuations in noise suppression effect caused by adjusting the number of FFT points individually (e.g., reduced smoothing effect when the number of segments is insufficient, or redundant computation when the number of segments is excessive), thus significantly improving the stability and adaptability of coarse acquisition.

[0095] In some embodiments of this disclosure, the spectral peak detection includes:

[0096] The maximum peak value of the search signal spectrum is traversed, and several spectral points before and after the maximum peak value are selected as the peak main lobe. The center frequency index value of the peak main lobe is calculated, and the frequency offset estimate is calculated based on the index value.

[0097] In some implementations, the smoothed signal spectrum can be scanned point-by-point, comparing the amplitude of each spectral point to select the spectral point with the largest amplitude as the core peak point. During the traversal, spectral points with amplitudes below a preset noise threshold can be ignored to avoid misjudging noise interference as signal peaks and ensure the authenticity of the maximum peak. The core peak point initially reflects the location of the carrier frequency of the received signal, but due to spectral leakage and residual noise, the location of a single peak point cannot be directly used as an accurate basis for frequency offset estimation. Therefore, several spectral points before and after the maximum peak can be selected as the peak main lobe, and the center frequency index value of the peak main lobe can be calculated. This index value can be dynamically adjusted according to the modulation order of the QAM signal, the number of Fast Fourier Transform points, and the channel noise to ensure coverage of the region where the peak energy is most concentrated. By integrating the positional information of multiple spectral points within the main lobe, the stability and accuracy of the center frequency calculation are improved, avoiding the influence of random jitter of a single peak point.

[0098] In some embodiments of this disclosure, the frequency offset estimate is determined by selecting the peak main lobe and calculating the center frequency index value. Compared with simply selecting the maximum peak point, this effectively avoids the influence of peak jitter caused by noise and improves the accuracy of frequency offset estimation.

[0099] In some embodiments of this disclosure, S24 includes:

[0100] The first demodulated symbol is processed one by one, and phase compensation is performed on the first demodulated symbol through a multiplier structure. The compensation signal is generated by a numerically controlled oscillator. Phase compensation is not performed on the first symbol in the first demodulated symbol.

[0101] In some implementations, the processing steps of the direct decision phase-locked loop frequency offset precise tracking module may include symbol phase compensation, direct decision and phase detection, phase integration step and frequency offset estimation.

[0102] In symbol phase compensation, the first demodulated symbol can be extracted sequentially according to the receiving order and fed into the multiplier structure one by one for phase compensation. The first phase offset is affected by factors such as real-time channel changes and residual frequency offset fluctuations, resulting in individual differences. Batch processing is difficult to accurately match the offset characteristics of each symbol, while processing one symbol at a time can achieve precise compensation based on the specific situation of each symbol, ensuring the consistency and accuracy of the compensation effect. If phase compensation is not performed on the first symbol, the phase error tracking module has not yet accumulated effective phase error data in the initial stage, and the compensation signal generated by the numerically controlled oscillator lacks a reliable reference. If phase compensation is forcibly performed on the first symbol, random deviations are easily introduced, and these deviations will accumulate and amplify in subsequent symbol processing, affecting the overall compensation effect.

[0103] In some embodiments of this disclosure, phase compensation is performed on each of the first demodulated symbols, but no compensation is performed on the first symbol. This ensures the accurate elimination of the phase offset of each symbol and avoids the cumulative propagation of the initial compensation deviation, thus ensuring the continuity and stability of the phase compensation process.

[0104] In some embodiments of this disclosure, S24 further includes:

[0105] By comparing the second demodulated symbol with the reference quadrature amplitude modulation constellation diagram using a direct decision unit, the ideal constellation symbol in the reference quadrature amplitude modulation constellation diagram that has the closest Euclidean distance to the second demodulated symbol is found and output.

[0106] The second phase offset between the second demodulated symbol and the ideal constellation symbol is determined by a phase detector.

[0107] In some implementations, the direct decision and phase detection steps may include: comparing the compensated symbol with a reference QAM constellation diagram using a direct decision unit, finding and outputting the ideal constellation symbol in the constellation diagram that has the closest Euclidean distance to the compensated symbol; and calculating the second phase offset between the ideal constellation symbol output by the decision unit and the compensated symbol. The phase integration step may include: accumulating the second phase offset output by the phase detector with the phase error used for symbol phase compensation in the current loop operation to obtain the integrated phase error, filtering it through a loop filter, and inputting it into a numerically controlled oscillator to generate the phase error used for symbol phase compensation in the next loop operation, thus completing phase tracking.

[0108] In some embodiments of this disclosure, the ideal constellation symbol is determined by Euclidean distance comparison. The decision logic is simple and direct with low computational load. At the same time, combined with the phase detector, the second phase offset is accurately obtained without complex signal preprocessing. This improves decision efficiency while ensuring the accuracy of phase offset detection, providing accurate input for phase error tracking.

[0109] In some embodiments of this disclosure, the residual frequency offset is calculated based on the phase error tracking result, the number of symbols processed, and the sampling rate of the receiving system, and the frequency tracking range of the direct decision phase-locked loop matches the output residual error range of the adaptive precision-adjusted discrete Fourier transform carrier coarse acquisition.

[0110] In some implementations, the frequency offset estimation step may include: after processing all received demodulated symbols, calculating the residual frequency offset of the system after coarse acquisition module processing based on the phase error obtained from the last loop run (i.e., the phase error tracking result mentioned above). Specifically, the residual frequency offset of the system after coarse acquisition module processing can be calculated by combining the phase error tracking result, the number of symbols processed, and the sampling rate of the receiving system.

[0111] In some embodiments of this disclosure, by matching the frequency tracking range of the direct decision phase-locked loop with the output residual error range of the coarse acquisition module, efficient collaboration between the two modules is achieved, avoiding frequency offset omissions or resource waste caused by range mismatch, and further improving the stability and reliability of the entire carrier frequency offset estimation system.

[0112] In some examples, embodiments of this application will be described exemplarily below. For example... Figure 2 As shown, an exemplary illustration is provided for the discrete Fourier transform carrier coarse acquisition module with adaptive precision adjustment: it can be based on the carrier frequency f specified by the QAM transmission system. c Generate an initial local carrier signal, perform matched filtering and digital sampling on the received quadrature amplitude modulation signal, and obtain the initial received demodulated signal after coherent demodulation, as shown in the following formula (1):

[0113] (1)

[0114] In equation (1), s(k) is the QAM baseband transmitted signal, A is the amplitude attenuation of the transmission channel, n(k) is additive white Gaussian noise (AWGN), Δf is the total carrier frequency offset of the system, θ is the cumulative phase offset, and r(k) is the initial received demodulated signal. Based on the baseband model of the received signal after coherent demodulation, the frequency domain model of the QAM baseband transmitted signal s(k) can be expressed as S(f). Then, the frequency domain model of the received signal r(k) is actually a translation of S(f) by a length of Δf to obtain S(f+Δf). At this time, the problem of estimating Δf is transformed into the problem of estimating the spectral offset of the received signal.

[0115] In some examples, the specific steps for spectral segment smoothing may include initializing the segment length and the number of FFT points. Specifically, the initial parameters of the coarse acquisition module can be configured: setting the Kth segment grouping, the segment length during FFT processing, and the number of FFT points to N. FFT (K), the number of segments is L(K). Initially, the initial segment length and the number of FFT points are N. FFT (1), the value is usually an integer power of 2; the initial segmentation takes L(1) segments of signal to form the first signal group; the decision threshold of the group relative to the normalized frequency offset estimate is set to Δf. d .

[0116] Then, the signal is continuously segmented and grouped, and processed by FFT: The received signal is segmented and grouped into K-th segments and processed by FFT, and the received signal is divided from the N-th segment... FFT Starting from position (K-1)·L(K-1)+1, cut off segment L(K) of length N. FFT (K) signal. For each segment, perform N... FFT (K)-point FFT yields the frequency domain form R(K,I,f) of the i-th segment signal in the K-th group.

[0117] Then, perform spectrum superposition and averaging: window and cumulative smoothing are applied to all R(K,I,f) in group K to obtain: the smoothed spectrum of the Kth group, as shown in the following formula (2):

[0118] (2)

[0119] In equation (2), W K (nf) is the window function in the frequency domain of the Kth group.

[0120] The specific steps for spectral peak detection may include: searching for the maximum peak and main lobe, and calculating the main lobe offset and frequency offset.

[0121] Specifically, searching for the maximum peak value and the main lobe can include: searching W K The location of the maximum peak value of (f) is determined by the following formula (3):

[0122] (3)

[0123] With P max Find W centered at (K,f). K The position of the peak main lobe in (f) is given by the following formula (4):

[0124] (4)

[0125] In equation (4), P max(K)-M, P max (K)+N represent the start and end positions of the main lobe, respectively.

[0126] Calculating the main lobe offset and frequency shift can specifically include: calculating the offset of the peak main lobe center relative to zero frequency, as shown in the following formula (5):

[0127] (5)

[0128] Calculate the first based on the offset. The estimated value of the frequency offset of each group is given by the following formula (6):

[0129] (6)

[0130] In equation (6), F S It is the sampling rate of the QAM system receiver.

[0131] In some implementations, the specific steps of frequency offset error control may include: calculating the relative frequency offset error of the group, adjusting the segment length and the number of FFT points, and carrier acquisition output.

[0132] Specifically, the calculation of the relative frequency offset error of the group can include: calculating the normalized relative residual error based on the frequency offset error results between the current group and the previous group, referring to the following formula (7):

[0133] (7)

[0134] In equation (7), the relative residual error Δf can be expressed. normal (K) and △f d Compare, if △f normal (K) less than or equal to Δf d This completes the coarse frequency acquisition and outputs the acquired frequency offset Δf. coarse =△f est (K). Otherwise, it means the relative residual error has not yet reached the preset threshold requirement, and the following process continues: Adjust the segment length and FFT points: Adjust the segment length and FFT points during the (K+1)th segment grouping and FFT processing to N. FFT (K+1) and the number of segments L(K+1); where N is taken as N. FFT (K+1)=2N FFT (K), L(K+1)=L(K)+l, where l is an integer greater than 0. After completing the parameter adjustment, proceed to the signal continuous segmentation and FFT processing step, and repeat the (K+1)th continuous segmentation and FFT processing until the conditions are met to complete the coarse frequency acquisition.

[0135] The specific steps for carrier acquisition output may include:

[0136] The carrier frequency is corrected based on the captured frequency offset. The local carrier is regenerated, and the received QAM digital signal is matched, filtered, and clocked to obtain the first demodulated symbol y(k) with carrier frequency error and phase offset after compensation, which is then input into the secondary precision tracking module.

[0137] In this embodiment, by adaptively comparing the relative carrier frequency offset error of continuous group signals, the segment length and the number of Fast Fourier Transform (FFT) points are dynamically adjusted until the residual relative carrier frequency offset error can quickly converge to the effective tracking range of the secondary precise tracking module. Under low signal-to-noise ratio (SNR) conditions, by adaptively adjusting the segment length and the number of FFT points, the residual frequency offset of the system can be reduced to within [-0.15%, 0.15%] in a finite number of groups. Under high SNR conditions, by setting a smaller segment length and the number of FFT points, the residual frequency offset of the system can be reduced to within [-0.125%, 0.125%] in a very small number of groups. This method only requires a small number of signal samples to complete carrier coarse acquisition, without calculating the complete received signal or using a large number of FFT points to calculate the Fourier transform for all groups, significantly reducing the computational complexity of the coarse acquisition module.

[0138] In other examples, such as Figure 3 As shown, the improved direct decision phase-locked loop frequency offset precise tracking module is illustrated by example: symbol phase compensation may specifically include: processing the first demodulated symbol input one by one, compensating the input symbol through a multiplier structure, eliminating the symbol phase offset caused by residual frequency offset and phase error, and obtaining the compensated symbol, as shown in the following formula (8):

[0139] (8)

[0140] In equation (8), y(k) is the first demodulated symbol with carrier frequency error and phase offset, where phase error is... The compensation signal is obtained from the phase integrator during one run of the loop. The compensation signal is generated by the numerically controlled oscillator. The first symbol in the received demodulated symbol is not compensated. At this time, the final demodulated symbol z(k) is output after the improved direct decision phase-locked loop precise tracking module eliminates the residual error. This is the second demodulated symbol.

[0141] The direct decision step may include: comparing the compensated symbol z(k) with the ideal QAM symbol in the reference QAM constellation diagram point by point, directly calculating the Euclidean distance between z(k) and the ideal symbol, and finding the nearest ideal decision symbol. .

[0142] The phase detection step includes: calculating the compensated symbol z(k) and the ideal decision symbol. Phase error between .

[0143] The phase integration step may specifically include: performing an integration and accumulation operation on the phase error used for compensation, and updating the phase error used for compensation next time, as shown in the following equation (9):

[0144] (9)

[0145] The loop filter can correct the updated phase error. Obtained after loop filter The numerically controlled oscillator can perform a symbol phase compensation step on the filtered phase error through the output of the numerically controlled oscillator, and then process the next symbol y(k+1).

[0146] Frequency offset estimation can specifically include:

[0147] After processing all L symbols of y(k) in the above steps, z(k) is output as the final demodulated symbol output by the improved direct decision phase-locked loop precise tracking.

[0148] The residual frequency offset estimate is calculated using the following formula (10):

[0149] (10)

[0150] In equation (10), That is, the phase tracking error result, where L is the number of symbols processed, and T is the number of symbols processed. S It is the sampling rate of the receiving system.

[0151] In this embodiment, by optimizing the phase integrator structure of the secondary module loop, compared with the traditional method, the improved loop does not require rotation of the entire QAM reference constellation diagram in phase compensation and symbol decision, significantly reducing the computational load of phase tracking. The reduction in complex multiplication computation is proportional to the QAM modulation order. For an M-order QAM system, each phase error tracking step reduces the number of complex multiplication operations by M-1, and carrier synchronization of N symbols reduces the number of complex multiplication operations by N(M-1), significantly lowering computational complexity, especially suitable for high-order QAM systems. Frequency tracking accuracy is maintained while reducing computational load, and the final frequency offset estimation error can be reduced to 10. -6 The effective frequency offset tracking range of this method is approximately [-0.7%, 0.7%], which is much larger than the residual error range after DFT acquisition. By efficiently cascading the adaptive precision-adjusted discrete Fourier transform carrier coarse acquisition module with the improved direct decision phase-locked loop frequency offset precise tracking module, the overall carrier synchronization efficiency of the QAM system is significantly improved.

[0152] The cascaded carrier frequency offset estimation methods disclosed herein can coarsely acquire the carrier frequency using an adaptively precision-adjusted Discrete Fourier Transform carrier coarse acquisition module. This requires only a small number of signal samples to complete the carrier coarse acquisition, eliminating the need to calculate the complete received signal and significantly reducing the computational complexity of the coarse acquisition module. Then, a direct decision phase-locked loop (DLL) precise tracking module is used to accurately track the residual frequency offset error. Compared with traditional methods, the improved DLL does not require rotation of the entire QAM reference constellation in phase compensation and symbol decision, significantly reducing the computational load of phase tracking. The reduction in complex multiplication computation is proportional to the QAM modulation order, making it particularly suitable for high-order QAM systems. By cascading the adaptively precision-adjusted Discrete Fourier Transform carrier coarse acquisition module and the DLL, no prior knowledge or historical data training is required. This allows for stable operation in harsh channel environments with low signal-to-noise ratios and large frequency offsets, demonstrating strong noise immunity and significantly improving the carrier synchronization efficiency of the QAM system.

[0153] It is understood that the various embodiments of the methods described in this specification are presented in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. Related details can be found in the descriptions of other method embodiments.

[0154] It should be understood that although the steps in the flowcharts shown in the accompanying drawings are displayed sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the accompanying drawings may include multiple steps or stages, which are not necessarily completed at the same time, but may be executed at different times, and the execution order of these steps or stages is not necessarily sequential, but may be performed alternately or in turn with other steps or at least a portion of the steps or stages of other steps.

[0155] Based on the description of the cascaded carrier frequency offset estimation method embodiments described above, this disclosure also provides a cascaded carrier frequency offset estimation apparatus for implementing the cascaded carrier frequency offset estimation method involved above. The apparatus may include a system (including a distributed system), software (application), module, component, controller, server, terminal, etc., using the method described in the embodiments of this specification, combined with necessary implementation hardware. Based on the same innovative concept, the apparatuses in one or more embodiments provided by the embodiments of this disclosure are as described in the following embodiments. Since the implementation schemes and methods for solving the problem by the apparatus are similar, the implementation of the specific apparatus in the embodiments of this specification can refer to the implementation of the foregoing method, and repeated details will not be repeated. As used below, the terms "unit" or "module" can refer to a combination of software and / or hardware that implements a predetermined function. Although the apparatus described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0156] Figure 4 This is a schematic block diagram illustrating a cascaded carrier frequency offset estimation device according to an exemplary embodiment. The device can be the aforementioned terminal, a server, or a module, component, device, control unit, etc., integrated into the terminal. For details, please refer to... Figure 4 The device 100 may include: an initial signal matching module 120, a coarse acquisition module 140, a phase compensation and decision phase detection module 160, a phase error tracking module 180, and a residual frequency offset calculation module 190. The initial signal matching module 120 is used to generate an initial local carrier signal, perform coherent demodulation processing on the received quadrature amplitude modulation signal, and obtain an initial received demodulated signal. The coarse acquisition module 140 is used to perform adaptive precision adjustment discrete Fourier transform carrier coarse acquisition on the initial received demodulated signal, regenerate the coarse acquisition local carrier signal, and re-perform coherent demodulation processing and clock synchronization on the quadrature amplitude modulation signal, and output a compensated first demodulated symbol with carrier frequency error and phase offset. The phase compensation and decision phase detection module 160 is used to compensate and eliminate the first phase offset of the first demodulated symbol through a direct decision phase-locked loop to obtain a second demodulated symbol, find and output the ideal constellation symbol through the direct decision method, and determine the second phase offset between the second demodulated symbol and the ideal constellation symbol. The phase error tracking module 180 is used to track the phase error through phase integration and loop filtering based on the second phase offset and determine the phase error tracking result. The residual frequency offset calculation module 190 is used to determine the residual frequency offset of the first demodulated symbol based on the phase error tracking result.

[0157] In some embodiments of the device, the coarse acquisition module 140 is further configured to continuously segment the initial received demodulated signal according to the initial number of fast Fourier transform points, perform fast Fourier transform on several segments of the signal to obtain the segmented signal spectrum, perform incoherent accumulation of the segmented signal spectrum and then average it to obtain the smoothed signal spectrum; and perform spectral peak detection on the smoothed signal spectrum to determine the frequency offset estimate.

[0158] In some embodiments of the device, the coarse acquisition module 140 is further configured to increase the number of Fast Fourier Transform (FFT) points, segment the input signal according to the new FFT length, perform FFT and smoothing processing to obtain a new segmented signal spectrum, calculate the frequency offset estimate of the current segment, compare the frequency offset estimate of the current segment with the frequency offset estimate of the previous segment, and determine the reference frequency residual error; it is also configured to complete spectrum acquisition when the reference frequency residual error of a consecutive preset number of groups is reduced to a preset tracking range, and regenerate the coarse acquisition local carrier signal based on the frequency coarse estimation result.

[0159] In some embodiments of the device, the coarse capture module 140 is further configured to ensure that, when the number of fast Fourier transform points is increased, the ratio of the new number of segments to the new number of fast Fourier transform points is consistent with the ratio of the number of segments to the number of fast Fourier transform points of the previous segment, and the number of segments is a positive integer.

[0160] In some embodiments of the device, the coarse acquisition module 140 is also used to traverse the maximum peak value of the search signal spectrum, select several spectral points before and after the maximum peak value as the peak main lobe, calculate the center frequency index value of the peak main lobe, and calculate the frequency offset estimate value based on the index value.

[0161] In some embodiments of the device, the phase compensation and decision phase detection module 160 is further used to process the first demodulated symbol one by one, perform phase compensation on the first demodulated symbol through a multiplier structure, and generate the compensation signal by a numerically controlled oscillator. The first symbol in the first demodulated symbol does not undergo phase compensation.

[0162] In some embodiments of the device, the phase compensation and decision phase detection module 160 is further configured to compare the second demodulated symbol with the reference quadrature amplitude modulation constellation diagram using a direct decision device, find and output the ideal constellation symbol in the reference quadrature amplitude modulation constellation diagram that is closest to the second demodulated symbol in Euclidean distance; and to determine the second phase offset between the second demodulated symbol and the ideal constellation symbol using a phase detector.

[0163] In some embodiments of the device, the residual frequency offset is calculated based on the phase error tracking result, the number of symbols processed, and the sampling rate of the receiving system, and the frequency tracking range of the direct decision phase-locked loop matches the output residual error range of the adaptive precision-adjusted discrete Fourier transform carrier coarse acquisition.

[0164] Each module in the aforementioned cascaded carrier frequency offset estimation device can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can call and execute the corresponding operations of each module.

[0165] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 5 As shown, the computer device includes a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, mobile cellular networks, NFC (Near Field Communication), or other technologies. When executed by the processor, the computer program implements a cascaded carrier frequency offset estimation method.

[0166] Those skilled in the art will understand that Figure 5 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0167] Based on the foregoing description of the relevant methods and apparatus embodiments, this disclosure also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, it implements the cascaded carrier frequency offset estimation method described in any embodiment of this specification.

[0168] Based on the foregoing description of the relevant methods and apparatus embodiments, this disclosure also provides a computer-readable storage medium that, when the instructions in the computer-readable storage medium are executed by the processor of a computer device, enables the computer device to implement the cascaded carrier frequency offset estimation method as described in any embodiment of this disclosure.

[0169] Based on the foregoing description of the relevant methods and apparatus embodiments, this disclosure also provides a computer program product, including a computer program that, when executed by a processor, implements the cascaded carrier frequency offset estimation method described in any embodiment of this specification.

[0170] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. In particular, hardware + program embodiments are relatively simple in description because they are fundamentally similar to method embodiments; relevant parts can be referred to the descriptions in the method embodiments.

[0171] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties.

[0172] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0173] It should be noted that the apparatus, computer equipment, storage medium, and computer program products described above may also include other implementation methods according to the description of the method embodiments. Specific implementation methods can be found in the description of the relevant method embodiments. Furthermore, new embodiments formed by combinations of features from various methods, apparatuses, devices, and server embodiments still fall within the scope of this disclosure and will not be elaborated upon here.

[0174] For ease of description, the above devices are described in terms of function, divided into various modules. Of course, when implementing one or more of these specifications, the functions of each module can be implemented in the same or different software and / or hardware, or a module that performs the same function can be implemented by a combination of multiple sub-modules or sub-units. The device embodiments described above are merely illustrative. For example, the division of modules or units is only a logical functional division; in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling and communication connections between the devices or units shown or described can be implemented through direct and / or indirect coupling / connection, through standard or custom interfaces or protocols, and can be implemented electrically, mechanically, or in other forms.

[0175] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the following claims.

[0176] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A method for estimating the frequency offset of a cascaded carrier, characterized in that, The method includes: An initial local carrier signal is generated, and coherent demodulation processing is performed on the received quadrature amplitude modulation signal to obtain the initial received demodulated signal. The initial received demodulated signal is subjected to adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition, the coarse acquisition local carrier signal is regenerated, and the orthogonal amplitude modulation signal is subjected to coherent demodulation processing and clock synchronization again, and the first demodulated symbol with compensation and carrier frequency error and phase offset is output. The first demodulated symbol is compensated and the first phase shift of the symbol is eliminated by a direct decision phase-locked loop to obtain the second demodulated symbol. The ideal constellation symbol is found and output by the direct decision method, and the second phase shift between the second demodulated symbol and the ideal constellation symbol is determined. The phase error tracking result is determined by tracking the phase error through phase integration and loop filtering based on the second phase offset; The residual frequency offset of the first demodulated symbol is determined based on the phase error tracking result.

2. The method according to claim 1, characterized in that, The step of performing adaptive precision adjustment on the initial received demodulated signal using discrete Fourier transform carrier coarse acquisition, and regenerating the coarse acquisition local carrier signal, includes: The initial received demodulated signal is continuously segmented according to the initial number of Fast Fourier Transform (FFT) points. Several segments of the signal are subjected to FFT to obtain the segmented signal spectrum. The segmented signal spectrum is then noncoherently accumulated and averaged to obtain the smoothed signal spectrum. Perform spectral peak detection on the smoothed signal spectrum to determine the frequency offset estimate.

3. The method according to claim 1 or 2, characterized in that, The step of performing adaptive precision adjustment on the initial received demodulated signal using discrete Fourier transform carrier coarse acquisition and regenerating the coarse acquisition local carrier signal further includes: increasing the number of fast Fourier transform points, segmenting the input signal according to the new fast Fourier transform length, performing fast Fourier transform and smoothing processing to obtain a new segmented signal spectrum, calculating the frequency offset estimate of the current segment, comparing the frequency offset estimate of the current segment with the frequency offset estimate of the previous segment, and determining the reference frequency residual error. Once the residual error of the reference frequency for a consecutive preset number of groups is reduced to a preset tracking range, spectrum acquisition is completed, and the coarse acquisition local carrier signal is regenerated based on the coarse frequency estimation result.

4. The method according to claim 3, characterized in that, When increasing the number of Fast Fourier Transform (FFT) points, the ratio of the new number of segments to the new number of FFT points is consistent with the ratio of the number of segments to the number of FFT points of the previous segment, and the number of segments is a positive integer.

5. The method according to claim 2, characterized in that, The spectral peak detection includes: The maximum peak value of the search signal spectrum is traversed, and several spectral points before and after the maximum peak value are selected as the main lobe of the peak. The center frequency index value of the main lobe of the peak value is calculated, and the frequency offset estimate is calculated based on the index value.

6. The method according to claim 1, characterized in that, The step of compensating and eliminating the first phase shift of the first demodulated symbol through a direct decision phase-locked loop to obtain the second demodulated symbol includes: The first demodulated symbol is processed one by one, and phase compensation is performed on the first demodulated symbol through a multiplier structure. The compensation signal is generated by a numerically controlled oscillator. Phase compensation is not performed on the first symbol in the first demodulated symbol.

7. The method according to claim 1, characterized in that, The step of finding and outputting the ideal constellation symbol through the direct decision method, and determining the second phase shift between the second demodulated symbol and the ideal constellation symbol, includes: By comparing the second demodulated symbol with the reference quadrature amplitude modulation constellation diagram using a direct decision unit, the ideal constellation symbol in the reference quadrature amplitude modulation constellation diagram that has the closest Euclidean distance to the second demodulated symbol is found and output. The second phase offset between the second demodulated symbol and the ideal constellation symbol is determined by a phase detector.

8. The method according to claim 1, characterized in that, The residual frequency offset is calculated based on the phase error tracking result, the number of symbols processed, and the sampling rate of the receiving system. The frequency tracking range of the direct decision phase-locked loop matches the output residual error range of the adaptive precision-adjusted discrete Fourier transform carrier coarse acquisition.

9. A cascaded carrier frequency offset estimation device, characterized in that, The device includes: The initial signal matching module is used to generate an initial local carrier signal and perform coherent demodulation processing on the received quadrature amplitude modulation signal to obtain the initial received demodulated signal. The coarse acquisition module is used to perform adaptive precision adjustment of discrete Fourier transform carrier coarse acquisition on the initial received demodulated signal, regenerate the coarse acquisition local carrier signal, and re-perform coarse demodulation processing and clock synchronization on the orthogonal amplitude modulation signal, and output the compensated first demodulated symbol with carrier frequency error and phase offset. The phase compensation and decision phase detection module is used to compensate and eliminate the first phase shift of the first demodulated symbol through a direct decision phase-locked loop to obtain the second demodulated symbol, find and output the ideal constellation symbol through the direct decision method, and determine the second phase shift between the second demodulated symbol and the ideal constellation symbol. The phase error tracking module is used to track the phase error based on the second phase offset through phase integration and loop filtering, and determine the phase error tracking result. The residual frequency offset calculation module is used to determine the residual frequency offset of the first demodulated symbol based on the phase error tracking result.

10. A computer-readable storage medium, characterized in that, It stores a computer program thereon, which, when executed by a processor, implements the steps of the method according to any one of claims 1 to 8.

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