Chirp modulation frequency offset and timing joint estimation signal synchronization method and system
By using a chirped signal synchronization reception algorithm, jointly estimating frequency offset and timing deviation, and employing coarse and fine compensation methods, the synchronization error and complexity issues of chirped modulated signals in low signal-to-noise ratio environments are resolved, thereby improving the performance of the communication system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-04-10
AI Technical Summary
Existing technologies, in low signal-to-noise ratio environments, suffer from large errors and high computational complexity in the frequency offset and timing synchronization algorithms of chirped modulation signals, and cannot effectively overcome the communication performance loss caused by Doppler frequency offset and time-varying characteristics.
A synchronous reception algorithm using chirped signals is adopted. By leveraging the characteristics of the pilot structure and chirped signals, and utilizing precise spectrum estimation, frequency offset and timing deviation are jointly estimated. Coarse compensation and fine compensation methods are employed to eliminate integer multiple frequency deviations and perform phase rotation compensation.
Under different chirp rates, computational complexity is reduced, signal synchronization accuracy and robustness are improved, and the performance of the communication system is enhanced.
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Figure CN121841392A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the fields of wireless communication and signal processing technology, and in particular to a signal synchronization method and system for joint estimation of frequency offset and timing of chirped modulation. Background Technology
[0002] Chirped modulation spreads signals, improving their anti-interference capability. It is a spread spectrum modulation technique that does not require pseudo-random coding sequences. Its most important characteristic is that the instantaneous frequency is a linear function of time, and the bandwidth occupied by the modulated signal is much larger than the information bandwidth. The characteristics of chirped modulation, including its time-domain waveform, frequency response, and autocorrelation function, exhibit constant mode and excellent autocorrelation in the frequency domain, thus ensuring good subsequent estimation and synchronization performance. Due to the high-speed movement of low-Earth orbit satellites, a large Doppler frequency offset is caused, and this offset exhibits significant time-varying characteristics with rapid changes in the satellite's position. Simultaneously, the rapid relative displacement between the transmitter and receiver causes the carrier frequency of the received signal to deviate from its original value due to the Doppler effect, resulting in a deviation between the received signal carrier frequency and the local oscillator frequency, leading to severe performance degradation. The higher the satellite's movement speed, the more severe the impact of the Doppler effect on communication performance, causing serious deterioration in multiple communication system performance indicators, including bit error rate, computational complexity, communication delay, data transmission rate, and transmission capacity. To ensure the requirements of high mobility and high data transmission rate, the carrier frequency offset must be overcome.
[0003] In chirped modulation-based transmission systems, most of the transmitted information is mapped to the start frequency of each chip, making linear spread spectrum modulation highly sensitive to frequency shifts. A simple solution is to discard the last two bits of each chip to ensure data accuracy, but this reduces system transmission efficiency. In practical communication systems, since signal sampling is random, frequency offset and delay are generally not integers; they are typically defined as an integer part plus a fractional part. Given the optimal receiver at the minimum sampling rate, traditional estimation schemes estimate the integer and fractional parts of frequency offset and timing independently. After fractional compensation for frequency offset, the signal still contains a fractional timing component and an integer frequency offset component. Because chirped signals possess time-frequency duality (i.e., time errors can be converted into frequency errors), after estimating the fractional frequency offset component, a frequency offset estimation algorithm is used to estimate the fractional timing component. A commonly used algorithm is the FFT-based frequency offset estimation algorithm, which is fast, low-complexity, suitable for real-time systems, and meets the requirements of chirped modulation. However, the FFT frequency offset estimation algorithm is limited by the picket fence effect of FFT, resulting in a large estimation error and low accuracy in low signal-to-noise ratio environments. In order to reduce the error of the FFT frequency offset estimation algorithm, scholars at home and abroad have proposed many FFT improvement algorithms based on interpolation, such as the parabolic interpolation algorithm, the Rife interpolation algorithm, and the Jacobsen algorithm. These algorithms are all based on the independent estimation of the integer and fractional parts of frequency offset and timing. Summary of the Invention
[0004] This application provides a signal synchronization method and system for joint estimation of frequency offset and timing of chirped modulation, which can estimate the error generated by the system with fewer symbols, is applicable under different chirp rate conditions, and can eliminate mutual interference.
[0005] This application provides a signal synchronization method for joint estimation of frequency offset and timing in chirped modulation, including: Coarse synchronization is achieved using the demodulation result of the upper chirp in the preamble; Based on the positive and negative chirp signals in the synchronization header of the chirp signal pilot sequence, the frequency offset and time offset of the signal are accurately estimated by performing the following process: A segment of the forward sweep signal is captured by the sync header, and the peak position of the upper chirp spectrum of the forward sweep signal is estimated in a refined manner. A segment of the reverse sweep frequency signal is extracted from the synchronization header, and the peak position of the lower chirp spectrum of the reverse sweep frequency signal is estimated in a refined manner. Based on the refined spectrum estimation results of the forward and reverse frequency sweep signals, the frequency offset compensation result is obtained by solving the peak value generated by the signal spectrum. Signal synchronization is performed based on the frequency offset compensation results.
[0006] This application also provides a signal synchronization system for joint estimation of frequency offset and timing in chirped modulation, comprising: The offset estimation module is used to roughly estimate the frequency and time offset of the signal using the positive and negative chirp signals in the synchronization header of the chirp signal pilot sequence. It performs the following process: A segment of the forward sweep signal is captured by the sync header, and the peak position of the upper chirp spectrum of the forward sweep signal is estimated in a refined manner. A segment of the reverse sweep frequency signal is extracted from the synchronization header, and the peak position of the lower chirp spectrum of the reverse sweep frequency signal is estimated in a refined manner. Based on the refined spectrum estimation results of the forward and reverse frequency sweep signals, the frequency offset compensation result is obtained by solving the peak value generated by the signal spectrum. The signal compensation module is used to perform signal synchronization based on the frequency offset compensation result.
[0007] The embodiments of this application can estimate the system error with fewer symbols, are applicable under different chirp rate conditions, improve the performance of existing timing and frequency synchronization algorithms required for chirp modulation detection, and perform robust frame detection while focusing on the minimum complexity implementation of the proposed algorithm, thereby improving the synchronization performance of received linear frequency modulated signals.
[0008] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description
[0009] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of the overall architecture and process of the signal synchronization method for joint estimation of frequency offset and timing of chirped modulation, as described in an embodiment of this application. Figure 2 This is a schematic diagram of the frequency sweep signal extracted in the refined spectrum estimation of the signal synchronization method for joint estimation of frequency offset and timing of chirped modulation in the embodiments of this application. Figure 3 This is a schematic diagram of the N-point method for spectrum amplification of the signal synchronization method for joint estimation of frequency offset and timing of chirped modulation, as described in an embodiment of this application. Detailed Implementation
[0010] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
[0011] Traditional maximum likelihood estimation algorithms share common drawbacks: computational complexity, slow synchronization speed, and low estimation accuracy at low signal-to-noise ratios (SNR), making them unsuitable for such conditions. Directly using a synchronization reception scheme similar to chirped signals, employing forward and reverse frequency sweep signals in the synchronization module, allows for simultaneous estimation of the time and frequency offsets of the received signal. However, this method uses Direct Spectral Estimation (DFT) to estimate the peak value of the target signal. While spectral estimation methods based on Discrete Fourier Transform (DFT) are widely used due to their low computational cost (e.g., implementation via Fast Fourier Transform (FFT)), they suffer from picket fence effects and energy leakage, resulting in significant estimation errors with small sample lengths. Improving accuracy requires a large sample size N, limiting the application of DFT algorithms. Furthermore, these algorithms are insensitive to fractional multiples of frequency offset and have low accuracy, exhibiting both low accuracy with short data lengths N and excessive complexity with long data lengths N, making them impractical for real-world engineering applications. For accurate estimation of frequency offset and timing, there is generally no superior method compared to joint estimation because the calculation accuracy of decimal frequencies is poor, which in turn affects the accuracy of timing.
[0012] Due to factors such as channel transmission delay, Doppler frequency shift at both ends of the receiver, and timing offset, the receiver cannot find the optimal moment to sample and decide on the symbol. This results in errors between the data recovered by the receiver and the data transmitted. Therefore, the reliability of frequency offset synchronization technology in chirped spread spectrum communication becomes increasingly important in this communication environment.
[0013] The purpose of this application is to overcome the defects of the existing technology and improve the performance of the timing and frequency synchronization algorithms required for chirped modulation detection. It also describes how to perform robust frame detection while focusing on the minimum complexity of the proposed algorithm, and finally designs a method to improve the synchronization performance of received linear frequency modulated signals.
[0014] In this application, a chirped frequency sweep synchronization receiving algorithm is proposed based on the structure of the pilot and the characteristics of the chirped signal. First, the upper chirped signal is dechirped at the receiving end. During the dechirping process, precise spectrum estimation is used to obtain the precise position of the upper chirped pilot. Similarly, a similar operation is performed on the lower chirped signal to obtain the precise position of the lower chirped pilot. Finally, the specific value of the frequency offset is estimated based on the positions of the upper and lower chirped pilots, and the offset value is compensated using the estimated value. Specifically, this application provides a signal synchronization method for joint estimation of frequency offset and timing in chirped modulation, such as... Figure 1 As shown, it includes the following steps: First, a preamble detection is performed on the received frame. In step S100, a preamble detection is performed on the received frame. When multiple consecutive identical symbol values are detected, it is determined that the preamble code has arrived.
[0015] In step S101, coarse synchronization is achieved using the demodulation result of the upper chirp in the preamble. The purpose of the coarse synchronization process in this application is mainly to capture the preamble, preparing for the subsequent joint estimation and compensation of frequency offset and timing. Further, the demodulation result of the lower chirp is combined, and fine compensation is performed based on the magnitude of the jointly estimated frequency offset and timing deviation.
[0016] In step S102, based on the positive and negative chirp signals in the chirp signal pilot sequence synchronization header, the frequency offset and time offset of the signal are accurately estimated, and the following process is performed: A segment of the forward sweep signal is captured by the sync header, and the peak position of the upper chirp spectrum of the forward sweep signal is estimated in a refined manner.
[0017] A segment of the reverse frequency sweep signal is intercepted in the synchronization header, and the peak position of the lower chirp spectrum of the reverse frequency sweep signal is finely estimated. In this embodiment, the demodulation result of the upper chirp in the preamble is used to perform fine-grained spectrum estimation on the upper chirp demodulation result to obtain the precise value of the upper chirp pilot position. Then, combined with the demodulation result of the lower chirp, the precise value of the lower chirp pilot position is obtained in the same way. Specifically, this application proposes a chirp signal compensation method. In some embodiments of this application, when multiple consecutive identical symbol values are detected, coarse synchronization is first completed using the demodulation result of the upper chirp in the preamble. Then, combined with the demodulation result of the lower chirp, the magnitude of frequency offset and time shift is derived through joint estimation. Fine synchronization is then performed to compensate for the frequency offset and time shift respectively. The estimated fractional frequency offset is compensated using a phase rotation method. The received signal is multiplied by a compensation factor. ,in This is an estimate of the frequency shift, which is a fractional multiple. The sampling frequency is used. The compensation value depends on the signal estimation result. Importantly, the compensation process employs a coarse-compensation followed by fine-compensation. Coarse compensation is used to quickly correct large-scale frequency shifts by directly shifting the demodulation result based on the estimated frequency shift to achieve initial frequency alignment. This step primarily eliminates integer multiples of frequency deviation, ensuring the demodulated signal falls within the correct frequency band. Fine-compensation, as described above, is then performed.
[0018] In step S103, based on the refined spectrum estimation results of the forward and reverse frequency sweep signals, the peak values generated by the signal spectrum are calculated to obtain the frequency offset compensation results.
[0019] In step S104, signal synchronization is performed based on the frequency offset compensation result.
[0020] The embodiments of this application can estimate the system error with fewer symbols, are applicable under different chirp rate conditions, improve the performance of existing timing and frequency synchronization algorithms required for chirp modulation detection, and perform robust frame detection while focusing on the minimum complexity implementation of the proposed algorithm, thereby improving the synchronization performance of received linear frequency modulated signals.
[0021] In some embodiments, such as Figure 2 As shown, the process of extracting a segment of the forward sweep signal from the synchronization header and performing refined spectral estimation on the upper chirp peak position of the forward sweep signal includes: A segment of the forward frequency sweep signal is captured by the sync head. The interval between the initial time of the intercept and the initial time of the symbol Symbol periods that are multiples of each other The positive chirped signal is multiplied by the conjugate chirped signal at the receiver, and the real part is taken and denoted as . .
[0022] Spectral granularity amplification using the N-point method, such as Figure 3 As shown, the N-point method is: in, The frequency shift factor calculated by the N-point method. The index corresponding to the peak output. , as well as This represents the peak energy and the energies at its left and right edges.
[0023] In some embodiments, spectral granularity amplification using the N-point method specifically includes: For the intercepted forward sweep frequency signal Perform a DFT transform to obtain the position corresponding to the maximum spectrum. ; Record the maximum spectral value and its adjacent positions Spectrum values , … , ; Determine the direction of correction; according to , … , Calculate the fractional frequency shift factor .
[0024] In practical applications, estimation is performed using the amplitude of the maximum spectral line and the amplitudes of the two second-largest spectral lines on either side of the maximum spectral line. Taking the three-point method as an example, the current fractional frequency shift is estimated using the peak energy of the current symbol's FFT output and the energies of its two adjacent points. The three-point method formula is as follows: in, The timing error calculated using the N-point method, with the index corresponding to the peak output being... , , as well as Peak energy and the energies at its left and right edges. In some embodiments, refined spectral estimation of the peak position of the upper chirped spectrum of the forward sweep signal further includes estimation using the amplitude of the maximum spectral line and the amplitudes of the second largest spectral lines on both sides of the maximum spectral line. The larger the number of amplitude spectral lines obtained on both sides, the more accurate the estimated value of the fractional frequency offset.
[0025] In some embodiments, fine-grained spectral estimation of the upper-chirped peak position of the forward frequency sweep signal further includes: Based on the correction direction used in the N-point method, the index corresponding to the peak output, and the calculated frequency shift factor, the precise peak index position is calculated. , The formula for the DFT direct spectral estimation method is: .
[0026] Based on the calculated peak index position Using the DFT direct spectrum estimation method, the corresponding frequency estimate is: , Sampling frequency, The number of sampling points. For precise indexing of spectral peak locations; For signal The peak values generated by precise spectral analysis are denoted as .
[0027] In some embodiments, extracting a segment of the reverse sweep signal from the synchronization header and performing refined spectral estimation on the lower chirp peak position of the reverse sweep signal includes: Extract a segment of the forward frequency sweep signal Equal-length reverse chirping signal The reverse frequency sweep signal is spaced at the same interval as the initial time of the symbol. The reverse chirped signal is multiplied by the conjugate swept frequency signal at the receiver, and the real part is taken and denoted as . Using the forward sweep frequency signal The same method is used for refined spectrum estimation.
[0028] Calculate the signal and After determining the precise location, the peak values generated based on the signal spectrum can be solved. , .
[0029] The joint estimation proposed in this application can estimate the system-generated error with fewer symbols. The calculation process relies on spectral data, which in turn relies on chirp deskewing. It is applicable under different chirp rates and can eliminate mutual interference, reducing computational processing costs while ensuring the accuracy of the calculation.
[0030] This application also proposes a signal synchronization system for joint estimation of frequency offset and timing in chirped modulation, comprising: The offset estimation module uses the demodulation results of the upper chirp in the preamble to complete coarse synchronization.
[0031] Based on the positive and negative chirp signals in the chirp pilot sequence synchronization header, the frequency and time offsets of the signal are accurately estimated, and the following steps are performed: A segment of the forward sweep signal is captured by the sync header, and the peak position of the upper chirp spectrum of the forward sweep signal is estimated in a refined manner. A segment of the reverse sweep frequency signal is extracted from the synchronization header, and the peak position of the lower chirp spectrum of the reverse sweep frequency signal is estimated in a refined manner. Based on the refined spectrum estimation results of the forward and reverse frequency sweep signals, the peak values generated by the signal spectrum are calculated to obtain the frequency offset compensation results. The signal compensation module is used to perform signal synchronization based on the frequency offset compensation result.
[0032] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, 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, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.
[0033] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.
[0034] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of this application.
[0035] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.
Claims
1. A signal synchronization method for joint estimation of frequency offset and timing in chirped modulation, characterized in that, include: Coarse synchronization is achieved using the demodulation result of the upper chirp in the preamble; Based on the positive and negative chirp signals in the synchronization header of the chirp signal pilot sequence, the frequency offset and time offset of the signal are accurately estimated by performing the following process: A segment of the forward sweep signal is captured by the sync header, and the peak position of the upper chirp spectrum of the forward sweep signal is estimated in a refined manner. A segment of the reverse sweep frequency signal is extracted from the synchronization header, and the peak position of the lower chirp spectrum of the reverse sweep frequency signal is estimated in a refined manner. Based on the refined spectrum estimation results of the forward and reverse frequency sweep signals, the frequency offset compensation result is obtained by solving the peak value generated by the signal spectrum. Signal synchronization is performed based on the frequency offset compensation results.
2. The signal synchronization method for joint estimation of frequency offset and timing of chirped modulation as described in claim 1, characterized in that, Extracting a segment of the forward sweep signal from the synchronization header and performing refined spectral estimation on the upper chirp peak position of the forward sweep signal includes: A segment of the forward frequency sweep signal is captured by the sync head. The interval between the initial time of the intercept and the initial time of the symbol Symbol periods that are multiples of each other The positive chirped signal is multiplied by the conjugate chirped signal at the receiver, and the real part is taken and denoted as . ; Spectral granularity amplification is performed using the N-point method, where the N-point method is as follows: in, The frequency shift factor calculated by the N-point method. The index corresponding to the peak output. , as well as This represents the peak energy and the energies at its left and right edges.
3. The signal synchronization method for joint estimation of frequency offset and timing of chirped modulation as described in claim 2, characterized in that, The specific methods for spectral granularity amplification using the N-point method include: For the intercepted forward sweep frequency signal Perform a DFT transform to obtain the position corresponding to the maximum spectrum. ; Record the maximum spectral value and its adjacent positions Spectrum values , … , ; The correction direction is determined based on the relationship between the magnitudes of the spectra on both sides of the peak. calculate , Correct to the right; conversely, Correct to the left.
4. The signal synchronization method for joint estimation of frequency offset and timing of chirped modulation as described in claim 3, characterized in that, The refined spectrum estimation of the peak position of the upper chirped spectrum of the forward sweep signal also includes: estimating using the amplitude of the maximum spectral line and the amplitude of the second largest spectral line on both sides of the maximum spectral line.
5. The signal synchronization method for joint estimation of frequency offset and timing of chirped modulation as described in claim 3, characterized in that, Refined spectral estimation of the upper-chirped peak position of the forward sweep signal further includes: Based on the correction direction used in the N-point method, the index corresponding to the peak output, and the calculated frequency shift factor, the precise peak index position is calculated. , ; Based on the calculated peak index position Using the DFT direct spectrum estimation method, the corresponding frequency estimate is: , Sampling frequency, The number of sampling points. For precise indexing of spectral peak locations; For signal The peak values generated by precise spectral analysis are denoted as .
6. The signal synchronization method for joint estimation of frequency offset and timing of chirped modulation as described in claim 5, characterized in that, Extracting a segment of the reverse sweep signal from the synchronization header and performing refined spectral estimation on the lower chirp peak position of the reverse sweep signal includes: Extract a segment of the forward frequency sweep signal Equal-length reverse chirping signal The reverse frequency sweep signal is spaced at the same interval as the initial time of the symbol. The reverse chirped signal is multiplied by the conjugate swept frequency signal at the receiver, and the real part is taken and denoted as . Using the forward sweep frequency signal The same method is used for refined spectrum estimation.
7. The signal synchronization method for joint estimation of frequency offset and timing of chirped modulation as described in claim 1, characterized in that, The synchronization header using the chirped pilot sequence includes the following steps before the positive and negative chirped signals: Preamble detection is performed on the received frame. If multiple consecutive identical symbol values are detected, it is determined that the preamble has arrived.
8. The signal synchronization method for joint estimation of frequency offset and timing of chirped modulation as described in claim 7, characterized in that, Also includes: When multiple consecutive identical symbol values are detected, coarse synchronization is achieved using the demodulation result of the upper chirp in the preamble; Based on the coarse synchronization results and the demodulation results of joint chirping, the magnitudes of frequency offset and time shift are estimated and derived, and fine synchronization is performed to compensate for frequency offset and time shift respectively. The estimated fractional frequency offset is compensated using a phase rotation method, and the received signal is multiplied by a compensation factor. ,in This is an estimate of the frequency shift, which is a fractional multiple. The sampling frequency.
9. A signal synchronization system for joint estimation of frequency offset and timing using chirped modulation, characterized in that, include: The offset estimation module is used to perform coarse synchronization using the demodulation results of the upper chirp in the preamble; Based on the positive and negative chirp signals in the synchronization header of the chirp signal pilot sequence, the frequency offset and time offset of the signal are accurately estimated by performing the following process: A segment of the forward sweep signal is captured by the sync header, and the peak position of the upper chirp spectrum of the forward sweep signal is estimated in a refined manner. A segment of the reverse sweep frequency signal is extracted from the synchronization header, and the peak position of the lower chirp spectrum of the reverse sweep frequency signal is estimated in a refined manner. Based on the refined spectrum estimation results of the forward and reverse frequency sweep signals, the frequency offset compensation result is obtained by solving the peak value generated by the signal spectrum. The signal compensation module is used to perform signal synchronization based on the frequency offset compensation result.