Binary CPFSK blind symbol synchronization method and system based on phase difference

Abstract

The invention relates to a binary CPFSK blind symbol synchronization method and system based on phase difference, belongs to the technical field of communication signal processing, and solves the technical problems of low precision and high complexity of the existing blind symbol synchronization method. Comprising the following steps: performing energy detection on a received binary CPFSK signal to determine a coarse synchronization initial position of the signal and obtain a coarse synchronization signal; performing phase difference operation on the coarse synchronization signal to obtain a first phase difference function including carrier frequency offset and symbol synchronization error; estimating the carrier frequency offset based on the first phase difference function to obtain a frequency offset estimation value, and performing frequency offset correction on the first phase difference function by using the frequency offset estimation value to obtain a second phase difference function after frequency offset correction; and estimating a symbol synchronization error based on the second phase difference function after frequency offset correction to obtain an estimated value of the symbol synchronization error, thereby realizing accurate blind symbol synchronization. And the complexity of blind symbol synchronization is reduced.

Description

Technical Field

[0001] This invention relates to the field of communication signal processing technology, and in particular to a blind symbol synchronization method and system based on phase difference binary CPFSK (Continuous Phase Frequency Shift Keying, a type of FSK signal with continuous phase). Background Technology

[0002] Due to its high anti-interference capability, FSK (Frequency Shift Keying) modulation technology has been widely used in communication systems. To further improve the performance of FSK modulation, CPFSK modulation technology was proposed. This modulation technique adjusts the symbol phase of FSK to make the symbol phase continuous, thereby reducing the signal's spectral spread and improving its spectral efficiency, leading to its widespread application. Meanwhile, considering secure communication, the more secure non-cooperative CPFSK communication mode is often chosen. Therefore, for third-party receivers, blind symbol synchronization is necessary to demodulate the signal. Currently, there are several methods for CPFSK blind symbol synchronization:

[0003] (1) Energy detection method: This method detects sudden changes in the power or amplitude of the received signal. Specifically, it calculates the current signal energy and compares it with a preset threshold. This method has low complexity, but it is easily affected by noise, has a large estimation error for symbol synchronization, and low detection accuracy. (2) Time-frequency analysis method: Symbol synchronization is achieved by analyzing how the frequency components of the signal evolve over time and identifying signal characteristics on the time-frequency graph. Compared with the energy detection method, the time-frequency analysis method has better noise resistance. Its final synchronization accuracy is affected by the time-frequency resolution. By selecting appropriate time-frequency analysis tools, the time-frequency analysis detection method can achieve high estimation accuracy, but it also requires high algorithm complexity. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a phase difference-based binary CPFSK blind symbol synchronization method to solve the technical problems of low accuracy and high complexity in existing blind symbol synchronization methods.

[0005] This invention provides a binary CPFSK blind symbol synchronization method based on phase difference, comprising the following steps: Step S1: Perform energy detection on the received binary CPFSK signal to determine the coarse synchronization start position of the signal and obtain the coarse synchronization signal; Step S2: Perform phase difference operation on the coarse synchronization signal to obtain a first phase difference function including carrier frequency offset and symbol synchronization error; Step S3: Based on the first phase difference function, estimate the carrier frequency offset to obtain a frequency offset estimate, and use the frequency offset estimate to correct the frequency offset of the first phase difference function to obtain a frequency offset corrected second phase difference function; Step S4: Based on the second phase difference function after frequency offset correction, estimate the symbol synchronization error to obtain the estimated value of the symbol synchronization error, thereby achieving accurate blind symbol synchronization.

[0006] Further, step S1 includes: A preset energy detection threshold and an energy accumulation window are defined; wherein the length of the energy accumulation window is less than or equal to half the length of a symbol. Slide the energy accumulation window and calculate the energy of the signal within the window to obtain the signal energy value within the window; When the signal energy value within the window exceeds the energy detection threshold, the sliding stops, and the current window position is determined as the coarse synchronization start position of the signal. Based on the coarse synchronization start position, the binary CPFSK signal Perform a time shift to obtain the coarse synchronization signal. ;in, is the sampling point index, and is the discrete-time index.

[0007] Furthermore, the first phase difference function, which includes carrier frequency offset and symbol synchronization error, is as follows:

[0008] in, Represents the phase difference function; This indicates a phase take operation; The symbol period; For symbol synchronization error, ; This is a signal representing unsigned synchronization error; For carrier frequency offset; The modulation index; , The first , Each code element symbol; This is the phase impulse response function.

[0009] Further, based on the first phase difference function, the carrier frequency offset of the coarse synchronization signal is estimated to obtain a frequency offset estimate, including: Set the first threshold With the second threshold ,and ; Based on the first threshold Second threshold The first set of extreme points and the second set of extreme points are selected from the phase difference function; The frequency offset estimate is calculated based on the values ​​of the samples in the first set of extreme points and the second set of extreme points.

[0010] Furthermore, based on the modulation index of the CPFSK signal Frequency deviation The first threshold is determined by the threshold selection coefficient. Second threshold ,as follows:

[0011] in, Select a coefficient for the threshold. .

[0012] Furthermore, the first set of extreme points and the second set of extreme points are obtained in the following manner: Based on the first phase difference function, values ​​greater than or equal to the first threshold are... The sample points are assigned to the first extreme point set; Values ​​less than or equal to the second threshold The sample points are assigned to the second extreme point set.

[0013] Furthermore, the frequency offset estimate is as follows:

[0014] in, This is the frequency offset estimate. express The sequence consisting of all sample values ​​in the first set of extreme points; express The sequence consisting of all sample values ​​in the set of the second extreme points; This indicates averaging the values ​​in the sequence; It is the mean of all sample values ​​in the first set of extreme points; It is the mean of all sample values ​​in the set of the second extreme points.

[0015] Furthermore, the second phase difference function after frequency offset correction is as follows:

[0016] in, This is the second phase difference function after frequency offset correction; The phase difference function of the shifted signal; This represents the signal offset.

[0017] Furthermore, the estimated symbol synchronization error includes: Within one symbol period, multiple signal offsets are traversed. ; For each signal offset The cumulative amount of the second phase difference function within a preset range after displacement is calculated. ;in, For the sampling point index, For symbol synchronization error, This is the signal offset; The candidate time offset that maximizes the cumulative amount The estimated value of the symbol synchronization error is determined as follows:

[0018] in, This is an estimate of the symbol synchronization error, i.e., the time offset that needs to be compensated.

[0019] The present invention also discloses a binary CPFSK blind symbol synchronization system based on phase difference, the system comprising a coarse synchronization module M1, a phase difference module M2, a frequency offset processing module M3, and a fine synchronization module M4; The coarse synchronization module M1 is used to perform energy detection on the received binary CPFSK signal to determine the coarse synchronization start position of the signal and obtain the coarse synchronization signal. The phase difference module M2 is used to perform phase difference operation on the coarse synchronization signal to obtain a first phase difference function including carrier frequency offset and symbol synchronization error. The frequency offset processing module M3 is used to estimate the carrier frequency offset based on the first phase difference function to obtain a frequency offset estimate, and use the frequency offset estimate to correct the frequency offset of the first phase difference function to obtain a frequency offset corrected second phase difference function. The precision synchronization module M4 is used to estimate the symbol synchronization error based on the second phase difference function after frequency offset correction, obtain the estimated value of the symbol synchronization error, and achieve precise blind symbol synchronization.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. This invention solves the problem of low accuracy caused by noise interference in the traditional energy detection method by constructing a phase difference function and utilizing the phase continuity characteristics of the CPFSK signal, and combining the phase difference information between multiple symbols to estimate the synchronization error, thereby improving the synchronization accuracy of blind symbols. 2. This invention employs low-complexity operations such as energy detection (coarse synchronization), phase difference operation, frequency offset estimation and correction, avoiding the high computational overhead of time-frequency analysis methods. While ensuring accuracy, it simplifies the implementation process and reduces algorithm complexity. 3. This invention is designed for non-cooperative CPFSK communication scenarios. It does not rely on prior synchronization information from the sending end and achieves blind synchronization through the phase characteristics of the signal itself, thus expanding its application scope in scenarios such as secure communication and enhancing the adaptability of non-cooperative communication.

[0021] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0022] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0023] Figure 1 This is a flowchart of a binary CPFSK blind symbol synchronization method based on phase difference in an embodiment of the present invention; Figure 2 This is a schematic diagram of the phase difference function in an embodiment of the present invention; Figure 3 This is a schematic diagram of the blind symbol synchronization process in an embodiment of the present invention; Figure 4 This is a schematic diagram of a binary CPFSK blind symbol synchronization system module based on phase difference in an embodiment of the present invention. Detailed Implementation

[0024] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0025] Example 1: This invention improves the accuracy of blind symbol synchronization and reduces algorithm complexity by utilizing the phase change characteristics of CPFSK modulation to achieve symbol blind synchronization. It fully leverages the feature information between multiple symbols for blind symbol localization, thereby improving the accuracy of blind symbol synchronization. Simultaneously, during algorithm implementation, low-complexity phase differential operations are performed on the symbol phases, further reducing the overall algorithm complexity.

[0026] A specific embodiment of the present invention discloses a binary CPFSK blind symbol synchronization method based on phase difference, such as... Figure 1 As shown, it includes the following steps: Step S1: Perform energy detection on the received binary CPFSK signal to determine the coarse synchronization start position of the signal and obtain the coarse synchronization signal; Step S2: Perform phase difference operation on the coarse synchronization signal to obtain a first phase difference function including carrier frequency offset and symbol synchronization error; Step S3: Based on the first phase difference function, estimate the carrier frequency offset to obtain a frequency offset estimate, and use the frequency offset estimate to correct the frequency offset of the first phase difference function to obtain a frequency offset corrected second phase difference function; Step S4: Based on the second phase difference function after frequency offset correction, estimate the symbol synchronization error to obtain the estimated value of the symbol synchronization error, thereby achieving accurate blind symbol synchronization.

[0027] Before step S1, the signal model is first modeled, considering the binary single-exponential CPFSK modulation method, as shown below: Formula (1) in, To transmit signals; For time; It is a binary symbol sequence. , The symbol index represents the position of the symbol in the sequence, starting from 0; Indicates the imaginary part; Indicates the instantaneous phase information of the transmitted signal; The modulation index is a positive real number. This determines the magnitude of the frequency offset (or frequency deviation). The symbol period represents the duration of each symbol. It is a phase impulse response; The time delay signal representing the impulse response is delayed by Time, used to indicate the first The contribution of each symbol to the phase; This represents the summation of all symbols from 0 to infinity.

[0028] Among them, phase impulse response As shown below: Formula (2) in, Let be the frequency impulse response function, and be the phase impulse response function. The derivative of the pulse determines the trajectory of the instantaneous frequency change, and there are three common forms: raised cosine pulse (RC), rectangular pulse (REC), and Gaussian pulse (GMSK).

[0029] The variable being integrated is in the function. The value in the middle represents time and has no independent physical meaning. A software-defined radio receiver is used to receive the transmitted signal. The received signal is a continuous-time signal that includes all distortions and noise of the transmitted signal after propagation through the channel. .

[0030] Received signal Modeling, as shown below: Formula (3) in, Path loss represents the amplitude attenuation and fixed phase shift of the signal during transmission; It is natural number An exponential function with base 0; Carrier frequency offset represents the difference between the receiver's local oscillator frequency and the transmitter's carrier frequency, which causes the phase of the received signal to rotate continuously. Path delay represents the time delay in the propagation of a signal from the transmitter to the receiver, causing a time shift in the received signal. The noise, typically Gaussian white noise, is an unwanted random interference in the received signal. For ease of analysis and representation, the noise component is not considered in the following formulas.

[0031] Continuous time received signal By time interval Sampling is performed to obtain discrete-time sampled signals. The sampling process is as follows: , The sampling time interval, is the sampling point index, is the discrete-time index, and is an integer representing the . One sampling point.

[0032] Step S1, specifically.

[0033] Step S1 includes: A preset energy detection threshold and an energy accumulation window are defined; wherein the length of the energy accumulation window is less than or equal to half the length of a symbol. Slide the energy accumulation window and calculate the energy of the signal within the window to obtain the signal energy value within the window; When the signal energy value within the window exceeds the energy detection threshold, the sliding stops, and the current window position is determined as the coarse synchronization start position of the signal. Based on the coarse synchronization start position, the binary CPFSK signal Perform a time shift to obtain the coarse synchronization signal. ;in, is the sampling point index, and is the discrete-time index.

[0034] For the received signal Energy detection is performed, symbol coarse synchronization is conducted, and the signal after coarse synchronization is obtained. .

[0035] This step is based on the sampled signal. Energy accumulation window and energy detection threshold Obtain the sampled signal Signal after coarse synchronization Its main function is to roughly determine the starting position of the signal symbol, preparing for precise symbol synchronization. The specific processing flow is as follows: Set energy detection threshold and energy accumulation window Energy detection threshold Adjust according to the actual situation, and set to the background noise power. times.

[0036] For example, It is 128. It is 128 times the background noise power; energy accumulation window The length is half the length of a symbol. In practical applications, this can be modified according to specific requirements. Sliding window For the received sampled signal In the window Energy calculations are performed on a portion of the data to obtain the cumulative energy value within the window. At each sliding window position, a signal energy value within that window will be calculated.

[0037] like Then continue sliding the window, if If a valid signal is found in the current window, the sliding window is stopped, and the starting position of the current window is recorded as the coarse synchronization position. .

[0038] Based on coarse synchronization position For the original sampled signal Time-shift alignment is performed to obtain a coarse synchronization signal. .

[0039] Step S1 is to perform energy detection on the received binary CPFSK signal to determine the coarse synchronization start position of the signal and obtain the coarse synchronization signal.

[0040] Step S2, specifically.

[0041] This step involves processing the signal after coarse synchronization. By performing phase difference calculation, the first phase difference function is obtained. and the first threshold Second threshold .

[0042] Its main function is to calculate the signal phase difference function and extract information containing carrier frequency offset and symbol synchronization error from it, so as to prepare for frequency offset correction and accurate symbol synchronization.

[0043] Based on the coarse synchronization signal, the first phase difference function is obtained. .

[0044] The first phase difference function, which includes carrier frequency offset and symbol synchronization error, is as follows: Formula (4) in, Represents the phase difference function; This indicates a phase take operation; The symbol period; For symbol synchronization error, ; This is a signal representing unsigned synchronization error; For carrier frequency offset; The modulation index; , The first , Each code element symbol; This is the phase impulse response function.

[0045] This indicates a phase operation on a function, returning the phase angle, with a range of values ​​of 1 to 2. ; Here, is the sample point index (discrete-time index), and is an integer representing the _th __. Each sampling time; The signal is considered to be an unsigned synchronization error, that is, it is assumed that... and Therefore, substituting formula (1) into... It can be obtained The result. According to... as well as The difference in phase difference function The range of values ​​varies.

[0046] This is a direct calculation method for phase difference, under ideal sign boundaries. and Calculate the front and rear phases of the received signal and determine the phase difference; Substituting the actual error, due to the signal after coarse synchronization It inherently contains time offset Therefore, when in time During sampling, what is actually sampled is The signal at a given moment, this step will synchronize the error. The model is explicitly introduced; middle, Due to frequency offset Fixed phase rotation caused within one symbol period; Including synchronization error The term reflects the situation where the current symbol is not on the true integral sign boundary, resulting in the sampling point not being on the true integral sign boundary. and the next symbol Phase contribution at sampling point The effects of mutual superposition / cancellation; From the current code element The inherent phase increment is determined by the CPFSK modulation principle.

[0047] This invention utilizes phase difference characteristics to achieve frequency offset Symbol synchronization error Joint estimation.

[0048] like Figure 2 As shown, specifically, the phase difference function is based on two consecutive symbols. and Combinations of values ​​for the phase difference function The cases are divided into the following four categories: ( (b) In the case of the same sign, there is no jump. The phase difference value does not include symbol synchronization error. , solely due to frequency offset and Decide; (c) and (d) cases with different signs, involving sign transitions. The phase difference value is affected by the symbol synchronization error. The effect, including the phase impulse response function in the expression. Its value fluctuates within a certain range.

[0049] Formula (5) Among them, the ( ) in formula (5) Cases (a) and (b) involve symbol synchronization errors. Irrelevant. Therefore, consider the function... Extract and The value of the time is used to estimate the frequency offset. Due to the function The value of is positive and less than 0.5, that is Furthermore, the modulation index h is a positive number; this is a basic requirement of CPFSK modulation. .

[0050] Assumption ; ; ; ; Will Substitute the value ; middle; Will Substitute the value In the middle, as follows: hour; ; hour;

[0051] Due to the shape of the curve, near the sign transition point, Typically less than 0.5, making The maximum value is actually not reached. ;so , The maximum value is 0.

[0052] ,so .

[0053] Therefore, we obtain formula (6) as follows: Formula (6) Based on the first phase difference function, the carrier frequency offset of the coarse synchronization signal is estimated to obtain the frequency offset estimate, including: Set the first threshold With the second threshold ,and ; Based on the first threshold Second threshold The first set of extreme points and the second set of extreme points are selected from the phase difference function; The frequency offset estimate is calculated based on the values ​​of the samples in the first set of extreme points and the second set of extreme points.

[0054] Comparing the maximum and minimum values ​​of the phase difference function in cases (a)-(d) of formula (5), we obtain: Formula (7) Due to the influence of noise, the extreme values ​​in formula (7) will fluctuate within the theoretical values.

[0055] Modulation index based on CPFSK signal Frequency deviation The first threshold is determined by the threshold selection coefficient. Second threshold ,as follows: Formula (8) in, Select a coefficient for the threshold. .

[0056] when Greater than the first threshold or less than the second threshold When the value is 7, it is considered that the extreme value in formula (7) has been obtained.

[0057] The first set of extreme points and the second set of extreme points are obtained in the following way: Based on the first phase difference function, values ​​greater than or equal to the first threshold are... The sample points are assigned to the first extreme point set; Values ​​less than or equal to the second threshold The sample points are assigned to the second extreme point set.

[0058] Step S2 performs phase difference operation on the coarse synchronization signal to obtain the first phase difference function, which includes carrier frequency offset and symbol synchronization error, in preparation for frequency offset correction and precise symbol synchronization.

[0059] Step S3 includes steps S31-S32.

[0060] This step is based on the first phase difference function. First and second thresholds and The output is the second phase difference function after frequency offset correction. Its main function is to analyze the phase difference function. Frequency offset correction is performed to prepare for precise symbol blind synchronization.

[0061] Step S31: Calculate the frequency offset estimate based on the values ​​of the samples in the first extreme point set and the second extreme point set.

[0062] The frequency offset estimate is as follows: Formula (9) in, This is the frequency offset estimate. express The sequence consisting of all sample values ​​in the first set of extreme points; express The sequence consisting of all sample values ​​in the set of the second extreme points; This indicates averaging the values ​​in the sequence; It is the mean of all sample values ​​in the first set of extreme points; It is the mean of all sample values ​​in the set of the second extreme points.

[0063] Based on frequency offset estimate Frequency offset correction is performed on the first phase difference function.

[0064] The second phase difference function after frequency offset correction is as follows:

[0065] Formula (10) in, This is the second phase difference function after frequency offset correction; The phase difference function of the shifted signal; This represents the signal offset.

[0066] Observing formula (5), we can find the symbol synchronization error. It will affect the first phase difference function Therefore, the value of can be considered using the second phase difference function. To perform blind symbol synchronization.

[0067] Step S3 estimates and corrects the carrier frequency offset based on the first phase difference function, resulting in the corrected second phase difference function.

[0068] Step S4: Signal blind symbol synchronization.

[0069] This step is based on the second phase difference function after frequency offset correction. Precise blind symbol synchronization of binary CPFSK signals.

[0070] The output is the symbol synchronization error. Estimate Its main function is to estimate and compensate for the symbol synchronization error t1, thereby achieving accurate blind symbol synchronization.

[0071] Combining formulas (5) and (10), the second phase difference function is further analyzed. :

[0072] Formula (11) When there is no synchronization deviation, i.e. and At this point, the second phase difference function of formula (11) The modulus of cases (c)-(d) will reach the maximum value.

[0073] like Figure 3 As shown, it is possible to traverse within a symbol period. , and calculate the function The cumulative amount of the sampling point index n is used to estimate the synchronization error.

[0074] The estimated symbol synchronization error includes: Within one symbol period, multiple signal offsets are traversed. ; For each signal offset The cumulative amount of the second phase difference function within a preset range after displacement is calculated. ;in, For the sampling point index, For symbol synchronization error, This is the signal offset; The candidate time offset that maximizes the cumulative amount The estimated value of the symbol synchronization error is determined as follows:

[0075] in, This is an estimate of the symbol synchronization error, i.e., the time offset that needs to be compensated.

[0076] The purpose of step S4 is to estimate the symbol synchronization error based on the second phase difference function after frequency offset correction, obtain the estimated value of the symbol synchronization error, and achieve accurate blind symbol synchronization.

[0077] Example 2: A specific embodiment of the present invention discloses a phase-difference-based binary CPFSK blind symbol synchronization system, thereby implementing the phase-difference-based binary CPFSK blind symbol synchronization method in Embodiment 1. The specific implementation methods of each module are described in the corresponding descriptions in Embodiment 1.

[0078] like Figure 4 As shown, a binary CPFSK blind symbol synchronization system based on phase difference is disclosed. The system includes a coarse synchronization module M1, a phase difference module M2, a frequency offset processing module M3, and a fine synchronization module M4. The coarse synchronization module M1 is used to perform energy detection on the received binary CPFSK signal to determine the coarse synchronization start position of the signal and obtain the coarse synchronization signal. The phase difference module M2 is used to perform phase difference operation on the coarse synchronization signal to obtain a first phase difference function including carrier frequency offset and symbol synchronization error. The frequency offset processing module M3 is used to estimate the carrier frequency offset based on the first phase difference function to obtain a frequency offset estimate, and use the frequency offset estimate to correct the frequency offset of the first phase difference function to obtain a frequency offset corrected second phase difference function. The precision synchronization module M4 is used to estimate the symbol synchronization error based on the second phase difference function after frequency offset correction, obtain the estimated value of the symbol synchronization error, and achieve precise blind symbol synchronization.

[0079] Since the system in this embodiment and the method in Embodiment 1 are related and can be referenced from each other, this description is redundant and will not be repeated here. Because this system embodiment shares the same principle as the above method embodiment, it also possesses the corresponding technical effects of the above method embodiment.

[0080] In summary, the binary CPFSK blind symbol synchronization method and system based on phase difference according to embodiments of the present invention have the following beneficial effects: 1. This invention solves the problem of low accuracy caused by noise interference in the traditional energy detection method by constructing a phase difference function and utilizing the phase continuity characteristics of the CPFSK signal, and combining the phase difference information between multiple symbols to estimate the synchronization error, thereby improving the synchronization accuracy of blind symbols. 2. This invention employs low-complexity operations such as energy detection (coarse synchronization), phase difference operation, frequency offset estimation and correction, avoiding the high computational overhead of time-frequency analysis methods. While ensuring accuracy, it simplifies the implementation process and reduces algorithm complexity. 3. This invention is designed for non-cooperative CPFSK communication scenarios. It does not rely on prior synchronization information from the sending end and achieves blind synchronization through the phase characteristics of the signal itself, thus expanding its application scope in scenarios such as secure communication and enhancing the adaptability of non-cooperative communication.

[0081] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0082] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A binary CPFSK blind symbol synchronization method based on phase difference, characterized in that, include: Step S1: Perform energy detection on the received binary CPFSK signal to determine the coarse synchronization start position of the signal and obtain the coarse synchronization signal; Step S2: Perform phase difference operation on the coarse synchronization signal to obtain a first phase difference function including carrier frequency offset and symbol synchronization error; Step S3: Based on the first phase difference function, estimate the carrier frequency offset to obtain a frequency offset estimate, and use the frequency offset estimate to correct the frequency offset of the first phase difference function to obtain a frequency offset corrected second phase difference function; Step S4: Based on the second phase difference function after frequency offset correction, estimate the symbol synchronization error to obtain the estimated value of the symbol synchronization error, thereby achieving accurate blind symbol synchronization.

2. The binary CPFSK blind symbol synchronization method based on phase difference according to claim 1, characterized in that, Step S1 includes: A preset energy detection threshold and an energy accumulation window are defined; wherein the length of the energy accumulation window is less than or equal to half the length of a symbol. Slide the energy accumulation window and calculate the energy of the signal within the window to obtain the signal energy value within the window; When the signal energy value within the window exceeds the energy detection threshold, the sliding stops, and the current window position is determined as the coarse synchronization start position of the signal. Based on the coarse synchronization start position, the binary CPFSK signal Perform a time shift to obtain the coarse synchronization signal. ;in, is the sampling point index, and is the discrete-time index.

3. The binary CPFSK blind symbol synchronization method based on phase difference according to claim 1, characterized in that, The first phase difference function, which includes carrier frequency offset and symbol synchronization error, is as follows: in, Represents the phase difference function; This indicates a phase take operation; The symbol period; For symbol synchronization error, ; This is a signal representing unsigned synchronization error; For carrier frequency offset; The modulation index; , The first , Each code element symbol; This is the phase impulse response function.

4. The binary CPFSK blind symbol synchronization method based on phase difference according to claim 3, characterized in that, Based on the first phase difference function, the carrier frequency offset of the coarse synchronization signal is estimated to obtain the frequency offset estimate, including: Set the first threshold With the second threshold ,and ; Based on the first threshold Second threshold The first set of extreme points and the second set of extreme points are selected from the phase difference function; The frequency offset estimate is calculated based on the values ​​of the samples in the first set of extreme points and the second set of extreme points.

5. The binary CPFSK blind symbol synchronization method based on phase difference according to claim 3, characterized in that, Modulation index based on CPFSK signal Frequency deviation The first threshold is determined by the threshold selection coefficient. Second threshold ,as follows: in, Select a coefficient for the threshold. .

6. The binary CPFSK blind symbol synchronization method based on phase difference according to claim 4 or 5, characterized in that, The first set of extreme points and the second set of extreme points are obtained in the following way: Based on the first phase difference function, values ​​greater than or equal to the first threshold are... The sample points are assigned to the first extreme point set; Values ​​less than or equal to the second threshold The sample points are assigned to the second extreme point set.

7. The binary CPFSK blind symbol synchronization method based on phase difference according to claim 6, characterized in that, The frequency offset estimate is as follows: in, This is the frequency offset estimate. express The sequence consisting of all sample values ​​in the first set of extreme points; express The sequence consisting of all sample values ​​in the set of the second extreme points; This indicates averaging the values ​​in the sequence; It is the mean of all sample values ​​in the first set of extreme points; It is the mean of all sample values ​​in the set of the second extreme points.

8. The binary CPFSK blind symbol synchronization method based on phase difference according to claim 7, characterized in that, The second phase difference function after frequency offset correction is as follows: in, This is the second phase difference function after frequency offset correction; This is the phase difference function of the shifted signal; This represents the signal offset.

9. The binary CPFSK blind symbol synchronization method based on phase difference according to claim 1, characterized in that, The estimated symbol synchronization error includes: Within one symbol period, multiple signal offsets are traversed. ; For each signal offset The cumulative amount of the second phase difference function within a preset range after displacement is calculated. ;in, For the sampling point index, For symbol synchronization error, This is the signal offset; The candidate time offset that maximizes the cumulative amount The estimated value of the symbol synchronization error is determined as follows: in, This is an estimate of the symbol synchronization error, i.e., the time offset that needs to be compensated.

10. A binary CPFSK blind symbol synchronization system based on phase difference, characterized in that, The system includes a coarse synchronization module M1, a phase difference module M2, a frequency offset processing module M3, and a fine synchronization module M4. The coarse synchronization module M1 is used to perform energy detection on the received binary CPFSK signal to determine the coarse synchronization start position of the signal and obtain the coarse synchronization signal. The phase difference module M2 is used to perform phase difference operation on the coarse synchronization signal to obtain a first phase difference function including carrier frequency offset and symbol synchronization error. The frequency offset processing module M3 is used to estimate the carrier frequency offset based on the first phase difference function to obtain a frequency offset estimate, and use the frequency offset estimate to correct the frequency offset of the first phase difference function to obtain a frequency offset corrected second phase difference function. The precision synchronization module M4 is used to estimate the symbol synchronization error based on the second phase difference function after frequency offset correction, obtain the estimated value of the symbol synchronization error, and achieve precise blind symbol synchronization.

Images