A method for detecting synchronization and demodulation based on high-speed burst communication system

Abstract

The application discloses a detection synchronization and demodulation design method based on a high-speed burst communication system, comprising the following steps: S1, performing fast acquisition on a burst synchronization sequence in a high-speed QPSK and OQPSK satellite communication system; S2, after the matching flag of the synchronization sequence in S1 is valid, performing M&M frequency offset estimation on current on-the-fly complex signal data and a preset synchronization sequence, generating a corresponding carrier compensation value by using the calculated frequency difference value, and outputting the frequency-compensated on-the-fly complex signal; S3, performing phase estimation on the frequency-compensated on-the-fly signal and the preset synchronization sequence, generating a corresponding phase compensation value by using the calculated phase difference value, and outputting the frequency-phase-compensated on-the-fly signal; and S4, after the frequency-phase compensation is completed, the on-the-fly complex signal is sent into a small-bandwidth synchronization tracking loop to generate a compensation value, a constellation diagram is output, and a symbol hard decision is performed on the loop output to output a synchronization code stream. The application meets the requirements of low bit error rate and missed detection and false detection rate, and provides good demodulation performance.

Description

Technical Field

[0001] This application belongs to the field of wireless communication technology, and in particular relates to a detection synchronization and demodulation design method based on a high-speed burst communication system. Background Technology

[0002] High-speed burst communication systems, due to their intermittent transmission characteristics, can achieve multi-user communication across different burst time slots, i.e., time division multiple access (TDMA) systems. On one hand, for a single user, communication occurs only during the allocated time slot, with the radio remaining silent outside of it, effectively avoiding unnecessary interference and providing a degree of anti-interception capability. On the other hand, for the entire communication system, each user transmits signals in the form of data frames, achieving time division multiplexing of the channel and improving the utilization efficiency of system channel resources. Compared to continuous communication systems, the starting position and duration of the signal are not critical. However, high-speed burst communication systems, especially satellite communication systems under the TDMA framework, are characterized by high transmission rates, short durations, and multi-user access. Therefore, synchronization detection and demodulation must be completed within a very short time, and the requirements for bit error rate and frame drop rate are much higher than in continuous systems. Furthermore, in a multi-user environment, the statistical characteristics (noise and level) between each burst are independent, and synchronization information between any two bursts is not inherited.

[0003] Satellite communication systems and terrestrial mobile cellular radio systems often use high-speed burst signals for data transmission. These systems insert synchronization sequences before or in a distributed manner before burst frames for burst frame synchronization and alignment, guiding subsequent demodulation, decoding, and interpretation signal processing. Therefore, using synchronization sequences to detect burst signals is the foundation and prerequisite for subsequent demodulation. If burst signal frames cannot be detected correctly, frame drops or false detections will occur, leading to errors in subsequent demodulation, decoding, and interpretation, or failure to pass verification. Generally, burst signal detection can be divided into time-domain detection and frequency-domain detection. Traditional time-domain direct correlation has low computational cost and high speed, but is easily affected by frequency offset and signal-to-noise ratio. Traditional frequency-domain detection has strong resistance to frequency offset and noise suppression capabilities, but has a large computational cost and cannot accurately estimate the burst start position.

[0004] Conventional closed-loop synchronization circuits typically obtain an error between the signal and the standard constellation through an algorithm, and then use this error to compensate for the phase in the original signal—a slow approximation process. These feedback loops often suffer from hang-up (incorrect steady-state equilibrium point) and clamp slip (phase jump) problems, and their demodulation synchronization performance depends on preset loop parameters. Therefore, this algorithm, which requires a long acquisition time, is not suitable for high-speed, short-burst signals. When the feedback loop has not reached a steady state, the current burst has ended, and its locked state is invalid for the next burst. In contrast, feedforward schemes are very suitable for high-speed, short-burst communication systems. Carrier offset and phase compensation are obtained through maximum probability estimation, which is approximately close to the Cramé-Rao boundary (CRB).

[0005] Therefore, achieving rapid synchronization detection and accurate frequency and phase estimation is crucial for ensuring carrier synchronization performance in high-speed burst mode signal demodulation. In conventional methods, point-by-point waveform correlation is affected by frequency and phase offsets. In FPGAs, long vector multiplication consumes significant resources, and traditional feedback loops have a certain locking time. This application, based on a high-speed burst communication system, employs parallel symbol-level synchronization and feedforward M&M frequency and phase correction to complete demodulation preprocessing. Only simple loop tracking is required to achieve loop locking from the starting bit, resulting in faster synchronization demodulation speed and a larger frequency offset acquisition range. Summary of the Invention

[0006] The purpose of this application is to overcome the problems of the prior art and disclose a detection synchronization and demodulation design method based on a high-speed burst communication system. This application is for fast signal detection and synchronization of synchronization sequence, and uses a feedforward loop demodulation method based on frequency correction and phase correction. It is applied to burst high-speed communication system scenarios such as satellite communication system and terrestrial mobile cellular radio, and meets the requirements of low bit error rate and false detection rate, and provides good demodulation performance.

[0007] The objective of this application is achieved through the following technical solution: A detection synchronization and demodulation design method based on a high-speed burst communication system, the detection synchronization and demodulation design method comprising: S1: Rapidly acquire burst synchronization sequences in high-speed QPSK and OQPSK satellite communication systems; S2: After the matching flag of the synchronization sequence in S1 is valid, perform M&M frequency offset estimation on the current accompanying complex signal data and the preset synchronization sequence, generate the corresponding carrier compensation value using the calculated frequency difference, and output the frequency-compensated accompanying complex signal. S3: Perform phase estimation on the frequency-compensated accompanying signal and the preset synchronization sequence, generate the corresponding phase compensation value using the calculated phase difference, and output the frequency-phase-compensated accompanying signal. S4: After the frequency and phase compensation is completed, the accompanying complex signal is sent into the synchronous tracking loop with a smaller bandwidth to generate the compensation value, output the constellation diagram, and perform hard sign decision on the loop output to output the synchronous code stream.

[0008] According to a preferred embodiment, step S1 includes: under a 250MHz operating clock, performing down-conversion, CIC decimation, and matched filtering on the complex signal data of the TDMA data. The data is extracted into parallel data to be inspected and sent to the fast burst detection module, which outputs the relevant matching values ​​of each channel and outputs the current data along with each channel.

[0009] According to a preferred embodiment, the fast burst detection module performs the fast burst detection steps as follows: first, the DDC and the matched filtered complex signal are extracted, serial-to-parallel conversion is completed, symbol-by-symbol correlation is performed with the synchronization sequence through the delayed conjugate phase difference, the parallel-to-serial correlation coefficient is recovered, and the matching position of the synchronization sequence is obtained through threshold detection, which also completes the traversal of the optimal sampling point.

[0010] According to a preferred embodiment, the frequency offset estimation process in step S2 includes: performing conjugate correlation on QPSK or OQPSK complex baseband signals with a certain frequency offset and phase offset to obtain a correlation value sequence, and using the phase difference of the autocorrelation function, i.e., M&M estimation, to obtain the estimated frequency offset.

[0011] According to a preferred embodiment, the phase estimation process in step S3 includes: multiplying the complex signal output by the path after frequency offset correction with the synchronization codeword by conjugate to obtain the estimated phase, so as to complete the phase correction of the signal.

[0012] According to a preferred embodiment, steps S2 and S3 are implemented based on the frequency offset and phase offset estimation module.

[0013] According to a preferred embodiment, the detection synchronization and demodulation design method further includes: S5: After the current TDMA frame complex signal data ends, the fast burst detection module, frequency offset and phase offset estimation module and loop tracking module in the high-speed burst communication system are reset and transferred to S1 until the next synchronization sequence matching is valid.

[0014] According to a preferred embodiment, the loop tracking module is configured to perform: digital frequency discrimination, digitally controlled oscillation, loop filtering, and code stream decision.

[0015] The aforementioned main solution and its various further alternative solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed in this application. Those skilled in the art, after understanding the solution of this application, will realize that there are many combinations based on the prior art and common general knowledge, all of which are technical solutions to be protected in this application, and will not be exhaustively listed here.

[0016] The beneficial effects of this application are: With the increasing use of high-speed burst mode for transmission in various shortwave and satellite communication methods, multi-path parallel symbol-level correlation can reduce FPGA synchronization delay, ignore the effects of frequency and phase offset, and lock the burst synchronization sequence faster. Furthermore, performing M&M frequency and phase estimation on the signal can provide a larger carrier synchronization acquisition range. At the same time, smaller frequency and phase offsets that occur in subsequent demodulation can be tracked in the loop using a smaller bandwidth, ensuring a certain level of noise immunity and good adaptability and versatility. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the detection, synchronization, and demodulation principles of a high-speed burst communication system.

[0018] Figure 2 These are illustrations of FPGA detection synchronization results and QPSK demodulation results for high-speed burst communication systems. Detailed Implementation

[0019] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] refer to Figure 1 As shown, this application discloses a detection synchronization and demodulation design method based on a high-speed burst communication system. It aims to provide a feedforward loop demodulation method based on frequency correction and phase correction to achieve fast signal detection and synchronization for synchronization sequences. This method is applicable to burst high-speed communication system scenarios such as satellite communication systems and terrestrial mobile cellular radio, meeting the requirements of low bit error rate and false detection rate, and providing good demodulation performance.

[0022] The present invention is achieved through the following technical solution: by using multi-path parallel symbol-level correlation, the FPGA synchronization delay can be reduced, the influence of frequency offset and phase offset can be ignored, and the burst synchronization sequence can be locked faster; while performing M&M frequency estimation and phase estimation on the signal can have a larger carrier synchronization acquisition range, and the small frequency offset and phase offset that occur in subsequent demodulation can be tracked in the loop using a small bandwidth, ensuring a certain degree of noise immunity.

[0023] The detection synchronization and demodulation design method of this application specifically includes the following steps.

[0024] Step S1: Quickly acquire burst synchronization sequences in high-speed QPSK and OQPSK satellite communication systems.

[0025] Preferably, step S1 includes: performing down-conversion, CIC decimation, and matched filtering on the complex signal data after TDMA data is processed under a 250MHz operating clock. The data is extracted into parallel data to be inspected and sent to the fast burst detection module, which outputs the relevant matching values ​​of each channel and outputs the current data along with each channel.

[0026] Furthermore, the fast burst detection module performs the following steps for fast burst detection: first, it extracts the complex signal after DDC and matched filtering, completes serial-to-parallel conversion, performs symbol-by-symbol correlation with the synchronization sequence through the delayed conjugate phase difference, recovers the parallel-to-serial correlation coefficient, obtains the matching position of the synchronization sequence through threshold detection, and also completes the traversal of the optimal sampling point.

[0027] Step S2: After the matching flag of the synchronization sequence in S1 is valid, perform M&M frequency offset estimation on the current accompanying complex signal data and the preset synchronization sequence, generate the corresponding carrier compensation value using the calculated frequency difference, and output the frequency-compensated accompanying complex signal.

[0028] Preferably, the frequency offset estimation process in step S2 includes: performing conjugate correlation on QPSK or OQPSK complex baseband signals with a certain frequency offset and phase offset to obtain a correlation value sequence, and using the phase difference of the autocorrelation function, i.e., M&M estimation, to obtain the estimated frequency offset.

[0029] Step S3: Perform phase estimation on the frequency-compensated accompanying signal and the preset synchronization sequence, generate the corresponding phase compensation value using the calculated phase difference, and output the frequency-phase-compensated accompanying signal.

[0030] Preferably, the phase estimation process in step S3 includes: multiplying the complex signal output by the path after frequency offset correction with the synchronization codeword by conjugate to obtain the estimated phase, so as to complete the phase correction of the signal.

[0031] Preferably, steps S2 and S3 are implemented based on the frequency offset and phase offset estimation module.

[0032] Step S4: After the frequency and phase compensation is completed, the accompanying complex signal is sent into the synchronous tracking loop with a smaller bandwidth to generate the compensation value, output the constellation diagram, and perform symbol hard decision on the loop output to output the synchronous code stream.

[0033] Step S5: After the current TDMA frame complex signal data ends, reset the fast burst detection module, frequency offset and phase offset estimation module and loop tracking module in the high-speed burst communication system and return to S1 until the next synchronization sequence matching is valid.

[0034] Preferably, the loop tracking module is configured to perform: digital frequency discrimination, numerically controlled oscillation, loop filtering, and code stream decision.

[0035] In a specific implementation case: After the receiver receives the raw data with a certain frequency offset and phase offset, it performs symbol-level delay-conjugate multiplication on the data to be detected to obtain a set of self-conjugate sequences. A Simultaneously, the modulated complex signal of the locally known synchronization sequence is also subjected to symbol-level delay conjugate multiplication B.

[0036]

[0037] B =

[0038] in, Given the symbol length of the synchronization sequence, , This indicates the complex signal received by the receiver. Indicates conjugate. Indicates the number of dots on the symbol. This represents a modulated complex signal with a locally known synchronization sequence.

[0039] Each time, two correlation operations of length L are performed to obtain a correlation value, and the process is continued until the correlation coefficient sequence of length LN is completed. Finally, the correlation coefficient of the entire data segment is obtained, and the known synchronization sequence matching position is output after threshold detection.

[0040]

[0041] in, A r This represents the amplitude of the self-conjugate sequence of the complex signal received by the receiver. A u This represents the amplitude of the locally known synchronous complex signal's self-conjugate sequence, where w0 is the natural frequency of the signal to be detected. T=1 / Fs , Fs Δy represents the signal sampling rate, and Δy represents the phase difference value. .like Right now If the correlation value is maximized, it means the symbol at the current position perfectly matches the synchronization sequence. At other positions, due to the randomness of the codeword, the correlation values ​​for each unit vector are... The values ​​cancel each other out. The difference is relatively small. Before correlation, the detection data undergoes symbol-level delayed conjugate multiplication, at which point the inherent frequency offset becomes the inherent phase offset, which will not affect the correlation results.

[0042] When the synchronization flag is high, the current synchronization output path is the optimal sampling point. At this time, a QPSK or OQPSK complex baseband signal with a certain frequency offset and phase offset is sent to the frequency and phase estimation module, which can be represented as follows:

[0043] in, For signal amplitude, To estimate the small frequency offset, To estimate the phase bias, The symbol period is 1 (after being extracted at the symbol level based on the optimal sampling point). For the first l The values ​​that a symbol can take. The variance is The additive white Gaussian noise sequence, whether it is a rectangular square wave or a shaped filtered signal, does not affect the estimation of frequency offset and phase offset.

[0044] Since the sampling points of a digital receiver are independent of each other when sampling a signal, the probability density function for N sampling points can be derived as follows:

[0045] Taking its logarithm and omitting irrelevant terms yields the likelihood function:

[0046] The modulation signal is QPSK. The maximum probability estimate of this fourth-power frequency offset can be expressed as:

[0047] in, Indicates that the function When taking the maximum value The value of . QPSK Frequency offset estimation of a signal is equivalent to finding the frequency point corresponding to the peak value of its fourth power spectral value. The unbiased range of this estimation is then... , This represents the code rate of the QPSK signal. For frequency estimation... Cramer-Rao Bound (The Craméro boundary can be represented as:

[0048] in, This represents the signal-to-noise ratio.

[0049] To obtain the frequency offset estimate of the signal, taking the modulus of the maximum likelihood estimation function yields:

[0050] According to the common method of maxima estimation, the maximum value can be obtained by taking the derivative of the above equation and setting the derivative value to 0.

[0051] make for Given the autocorrelation function, we can obtain the derivative of the magnitude of the maximum likelihood estimate by taking the derivative of the maximum likelihood estimate as follows:

[0052] Will The proposal .

[0053] in The noise is Gaussian white noise with a mean of 0. Consider the frequency to be estimated... Using autocorrelation function Difference representation:

[0054] Therefore, the frequency estimation expression for the algorithm can be obtained as follows:

[0055] in, This is the preset window function.

[0056] frequency estimate After compensating for the synchronized complex signal, the accompanying complex signal is output. There is still a certain phase bias, and the phase bias value can be obtained by directly accumulating the correlations:

[0057] When the synchronization sequence is known, phase ambiguity issues can be resolved synchronously. Continuously tracking the frequency-offset phase-compensated follower path through a low-bandwidth loop filter can enhance synchronization accuracy and improve noise immunity.

[0058] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A detection synchronization and demodulation design method based on a high-speed burst communication system, characterized in that, The detection synchronization and demodulation design method includes: S1: Rapidly acquire burst synchronization sequences in high-speed QPSK and OQPSK satellite communication systems; S2: After the matching flag of the synchronization sequence in S1 is valid, perform M&M frequency offset estimation on the current accompanying complex signal data and the preset synchronization sequence, generate the corresponding carrier compensation value using the calculated frequency difference, and output the frequency-compensated accompanying complex signal. S3: Perform phase estimation on the frequency-compensated accompanying signal and the preset synchronization sequence, generate the corresponding phase compensation value using the calculated phase difference, and output the frequency-phase-compensated accompanying signal. S4: After the frequency and phase compensation is completed, the accompanying complex signal is sent into the synchronous tracking loop with a smaller bandwidth to generate the compensation value, output the constellation diagram, and perform hard sign decision on the loop output to output the synchronous code stream.

2. The detection synchronization and demodulation design method based on a high-speed burst communication system as described in claim 1, characterized in that, Step S1 includes: At a working clock speed of 250MHz, the complex signal data after down-conversion, CIC decimation, and matched filtering of TDMA data is processed. The data is extracted into parallel data to be inspected and sent to the fast burst detection module, which outputs the relevant matching values ​​of each channel and outputs the current data along with each channel.

3. The detection synchronization and demodulation design method based on a high-speed burst communication system as described in claim 2, characterized in that, The rapid burst detection module performs the following rapid burst detection steps: First, the complex signal after DDC and matched filtering is decimated to complete serial-to-parallel conversion. Then, the correlation coefficient between the delayed conjugate phase difference and the synchronization sequence is performed symbol by symbol. Finally, the parallel-to-serial correlation coefficient is recovered. The matching position of the synchronization sequence is obtained through threshold detection, and the traversal of the optimal sampling point is also completed.

4. The detection synchronization and demodulation design method based on a high-speed burst communication system as described in claim 3, characterized in that, Step S2, the frequency offset estimation process, includes: The conjugate correlation of QPSK or OQPSK complex baseband signals with a certain frequency and phase offset is performed to obtain the correlation value sequence. The estimated frequency offset is obtained by using the phase difference of the autocorrelation function, i.e., M&M estimation.

5. The detection synchronization and demodulation design method based on a high-speed burst communication system as described in claim 4, characterized in that, The phase estimation process in step S3 includes: After correcting the frequency offset, the complex signal output by the accompanying path is multiplied by the synchronization codeword using a conjugate multiplication to obtain the estimated phase, thereby completing the phase correction of the signal.

6. The detection synchronization and demodulation design method based on a high-speed burst communication system as described in claim 5, characterized in that, Steps S2 and S3 are implemented based on the frequency offset and phase offset estimation module.

7. The detection synchronization and demodulation design method based on a high-speed burst communication system as described in claim 6, characterized in that, The detection synchronization and demodulation design method also includes: S5: After the current TDMA frame complex signal data ends, the fast burst detection module, frequency offset and phase offset estimation module and loop tracking module in the high-speed burst communication system are reset and transferred to S1 until the next synchronization sequence matching is valid.

8. The detection synchronization and demodulation design method based on a high-speed burst communication system as described in claim 7, characterized in that, The loop tracking module is configured to perform: digital frequency discrimination, digitally controlled oscillation, loop filtering, and code stream decision.

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