A Doppler estimation and compensation method for underwater acoustic direct-spread communication in time-varying Doppler channels

Abstract

A Doppler estimation and compensation method for underwater acoustic direct-spread communication in a time-varying Doppler channel belongs to the field of underwater acoustic communication. The present invention solves the problem of low Doppler estimation accuracy due to ambiguity in existing Doppler estimation methods in underwater acoustic direct-spread communication scenarios. The method of the present invention specifically comprises the following steps: using a copy-related frame synchronization technology to perform frame synchronization on the received direct-spread signal; then demodulating to baseband to obtain a coarse Doppler estimation value for each symbol in the baseband signal; then calculating the phase difference between adjacent symbols, and using the phase difference to calculate a fine estimation result with ambiguity; defuzzifying the fine estimation result with ambiguity to obtain a high-precision Doppler estimation result; finally, using the Doppler estimation result to compensate for the phase deviation caused by the time-varying Doppler, thereby improving the robustness of communication and the accuracy of signal reception. The method is simple, low in complexity, and suitable for practical applications. The method of the present invention can be applied to Doppler estimation compensation for underwater acoustic direct-spread communication.

Description

Technical Field

[0001] The invention belongs to the field of underwater acoustic communication, and in particular relates to a Doppler estimation and compensation method for underwater acoustic direct-spread communication under a time-varying Doppler channel. Background Art

[0002] Due to the low propagation speed of sound in underwater acoustic channels, the Doppler effect manifests not only as a frequency shift but also as compression and expansion of the signal in the time domain, severely impacting the performance of underwater acoustic communication equipment. Conventional Doppler processing methods assume that the Doppler factor within a signal frame is constant, and estimate and compensate for the Doppler factor of the entire frame. However, direct-sequence (DSS) communication rates are often low, with a single frame length sometimes exceeding 10 seconds. Therefore, the Doppler factor rarely remains constant within a frame and can vary significantly over time. This phenomenon is known as time-varying Doppler.

[0003] Estimating the Doppler variation within a DSSS signal frame and compensating for the impact of time-varying Doppler on DSSS communication have become pressing technical challenges. Among existing time-varying Doppler estimation methods, the mainstream approach is to use a phase-locked loop (PLL) to track the phase changes caused by Doppler. However, PLL-based methods suffer from divergence during tracking and struggle to converge when tracking DSSS signals with long durations. Performing an ambiguity function search on each symbol can estimate the Doppler within the entire signal frame, but this method is computationally complex and difficult to implement in practical systems.

[0004] To address these issues, researchers have proposed the phase method. This method calculates the phase difference between adjacent symbols to obtain accurate Doppler estimation results, and its computational complexity is low. However, when used for DSSS symbol velocity measurement, on the one hand, due to the limited phase measurement range, there is a 2π ambiguity. On the other hand, because adjacent symbols are modulated for communication, the symbol phase is used to transmit information, resulting in symbol ambiguity and impracticality. Therefore, in order to address the problem of ambiguity affecting the estimation accuracy of existing Doppler estimation methods in underwater acoustic DSSS communication scenarios, it is necessary to propose a new Doppler estimation method. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of low Doppler estimation accuracy due to ambiguity in existing Doppler estimation methods in underwater acoustic direct-spread communication scenarios, and to propose a Doppler estimation compensation method for underwater acoustic direct-spread communication under a time-varying Doppler channel.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel, the method specifically comprising the following steps:

[0007] Step 1: Frame synchronization of the received underwater acoustic direct-spread signal to obtain the signal start time and the initial Doppler estimation result

[0008] Step 2: According to the signal start time Intercept the direct spread communication signal y(t) from the received signal and demodulate the signal y(t) to baseband to obtain the baseband signal

[0009] Step 3: Based on the initial Doppler estimation results Generate a local baseband reference signal and then use the local baseband reference signal and baseband signal The kth symbol of Perform matching correlation to obtain the despread correlation signal r k (τ), k=1,2,…,K, K is the baseband signal The number of symbols in the

[0010] Then extract the relevant signal r k The position where the maximum correlation peak appears in (τ) is calculated based on the position where the maximum correlation peak appears.

[0011] Calculate the phase information corresponding to the maximum correlation peak

[0012] Step 4: Calculate the baseband signal separately The rough Doppler estimation result of the kth symbol in according to Calculate the phase difference between the kth symbol and the adjacent symbol Reuse Obtain a detailed estimate with fuzziness And Defuzzification is performed to obtain the unambiguous Doppler estimation result

[0013] Step 5: Based on the unambiguous Doppler estimation results Calculate the phase deviation caused by time-varying Doppler Combined Benefit

[0014] With phase deviation Phase information Compensate and get the compensated phase

[0015] The beneficial effects of the present invention are:

[0016] 1) The Doppler estimation and compensation method for underwater acoustic direct-spread communication in a time-varying Doppler channel of the present invention removes the symbol ambiguity caused by phase modulation by jointly using the amplitude and phase information of the autocorrelation, thereby obtaining a high-precision and unambiguous Doppler estimation result;

[0017] 2) The Doppler estimation and compensation method for underwater acoustic direct-spread spectrum communication in a time-varying Doppler channel of the present invention can obtain the time-varying Doppler estimation result within a frame of signal by estimating the speed of each symbol in the direct-spread spectrum signal, and thus obtain the relative motion speed of the transmitting and receiving nodes;

[0018] 3) The Doppler estimation and compensation method for underwater acoustic direct-spread communication under a time-varying Doppler channel of the present invention estimates the time-varying Doppler within a frame of direct-spread signal, thereby obtaining and compensating for the phase change caused by the Doppler, thereby improving the robustness of direct-spread communication under the time-varying channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of a Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to the present invention;

[0020] Figure 2 This is a frame structure diagram of a signal transmitted in the present invention;

[0021] Figure 3 This is a diagram of the speed estimation result in the simulation scenario of the present invention;

[0022] Figure 4 This is a diagram of the bit error rate results in the simulation scenario of the present invention. DETAILED DESCRIPTION

[0023] Specific implementation method 1: Combination Figure 1 This embodiment describes a Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel, the method specifically comprising the following steps:

[0024] Step 1: Frame synchronization of the received underwater acoustic direct-spread signal to obtain the signal start time and the initial Doppler estimation result

[0025] Step 2: According to the signal start time Intercept the direct spread communication signal y(t) from the received signal and demodulate the signal y(t) to baseband to obtain the baseband signal

[0026] Step 3: Based on the initial Doppler estimation results Generate a local baseband reference signal and then use the local baseband reference signal and baseband signal The kth symbol of Perform matching correlation to obtain the despread correlation signal r k (τ), k=1,2,…,K, K is the baseband signal The number of symbols in the

[0027] Then extract the relevant signal rk The position where the maximum correlation peak appears in (τ) is calculated based on the position where the maximum correlation peak appears.

[0028] Calculate the phase information corresponding to the maximum correlation peak

[0029] Step 4: Calculate the baseband signal separately The rough Doppler estimation result of the kth symbol in according to Calculate the phase difference between the kth symbol and the adjacent symbol Reuse Obtain a detailed estimate with fuzziness And Defuzzification is performed to obtain the unambiguous Doppler estimation result

[0030] Step 5: Based on the unambiguous Doppler estimation results Calculate the phase deviation caused by time-varying Doppler Combined Benefit

[0031] With phase deviation Phase information Compensate and get the compensated phase

[0032] The present invention uses the combined use of autocorrelation amplitude and phase information to obtain a highly accurate and unambiguous Doppler estimate symbol by symbol, thereby determining the time-varying Doppler conditions within the entire frame. The phase deviation caused by Doppler is then calculated and compensated based on the Doppler estimate, eliminating the impact of time-varying Doppler on communications and improving the performance of direct-spread spectrum communications in time-varying Doppler channels.

[0033] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that, in step 1, the copy correlation method is used to perform frame synchronization on the received underwater acoustic direct-spread signal.

[0034] Other steps and parameters are the same as those in the first embodiment.

[0035] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that the specific process of step one is as follows:

[0036] Step 11: Obtain the synchronization header reference signal corresponding to each speed according to the speed search list;

[0037] Step 1 and 2: The frame structure of the transmitted signal is as follows: Figure 2As shown, the synchronization head reference signal corresponding to each speed is matched and correlated with the received underwater acoustic direct spread signal, and the matching correlation peak corresponding to each synchronization head reference signal is obtained (the height of the correlation peak represents the matching degree of the reference signal);

[0038] Step 13: determine the highest matching correlation peak and the synchronization header reference signal corresponding to the highest matching correlation peak;

[0039] The position where the highest matching correlation peak appears is taken as the signal start time The speed corresponding to the determined synchronization head reference signal is the initial Doppler estimation result.

[0040] Other steps and parameters are the same as those in the first or second embodiment.

[0041] Specific embodiment 4: This embodiment differs from any one of the specific embodiments 1 to 3 in that the signal y(t) is demodulated to baseband to obtain a baseband signal Specifically:

[0042]

[0043] Where LPF(·) stands for low-pass filtering, e is the base of the natural logarithm, j is the imaginary unit, t is time, and f c is the carrier frequency.

[0044] The other steps and parameters are the same as those in the first to third embodiments.

[0045] Specific embodiment 5: This embodiment differs from any one of the specific embodiments 1 to 4 in that, in step 3, according to the initial Doppler estimation result, Generate a local baseband reference signal and then use the local baseband reference signal and baseband signal The kth symbol of Perform matching correlation to obtain the despread correlation signal r k (τ); specifically:

[0046] According to the initial Doppler estimation results and the spreading code c(t) to generate the local baseband reference signal

[0047]

[0048] Using local baseband reference signal and the kth symbol of the baseband signal Perform matching correlation to obtain the despread correlation signal r k (τ):

[0049]

[0050] where τ is the time delay.

[0051] The other steps and parameters are the same as those in the first to fourth embodiments.

[0052] Specific embodiment 6: This embodiment differs from any one of the specific embodiments 1 to 5 in that the extraction of the relevant signal r k The position where the maximum correlation peak appears in (τ) and the phase information corresponding to the maximum correlation peak is calculated based on the position where the maximum correlation peak appears Specifically:

[0053] Extract the relevant signal r k The position where the maximum correlation peak appears in (τ)

[0054]

[0055] Calculate position Corresponding phase information

[0056]

[0057] in, It's location In the correlation signal r k The corresponding value in (τ) is yes The imaginary part of yes The real part of .

[0058] The other steps and parameters are the same as those in the first to fifth embodiments.

[0059] Specific embodiment 7: This embodiment differs from any one of specific embodiments 1 to 6 in that the specific process of step 4 is as follows:

[0060] Step 4.1: Baseband signal Downsampling is performed to obtain

[0061]

[0062] Among them, T c is the baseband signal The chip length, λ is the oversampling rate, n is the nth point of downsampling, is the signal value corresponding to the nth point of downsampling;

[0063] Step 42: According to the speed search list, calculate the signal window length N corresponding to each search speed vl ;

[0064]

[0065] Where N is the spread spectrum code length, c is the speed of sound in water, Indicates rounding down;

[0066] Step 4.3: Calculate the autocorrelation result R corresponding to the kth symbol at different speeds based on the signal window length calculation result. k (v), k = 1, 2, ..., K;

[0067] Step 4. Calculate the rough Doppler estimation result of each symbol based on the autocorrelation result

[0068]

[0069] in, is the rough Doppler estimation result of the kth symbol;

[0070] Step 4.5: According to The corresponding autocorrelation results Calculate the phase difference between the kth symbol and the adjacent symbol

[0071]

[0072] in, yes The imaginary part of yes The real part of

[0073] Step 46: Pass Calculate the Doppler fine estimate with ambiguity for the kth symbol

[0074]

[0075] Among them, T s is the symbol pulse width;

[0076] Step 47: Calculate the fuzzy velocity v caused by M-order phase modulation and limited phase measurement range a :

[0077]

[0078] Step 48: According to v a To calculate The fuzziness

[0079]

[0080] Step 49: Utilize fuzziness right Defuzzification is performed to obtain the unambiguous Doppler estimation result

[0081]

[0082] The other steps and parameters are the same as those in the first to sixth embodiments.

[0083] Specific embodiment eight: This embodiment differs from specific embodiments one to seven in that the specific process of step four-three is as follows:

[0084]

[0085] Among them, |·| means taking the absolute value, Indicates taking The conjugate of is the signal value corresponding to the downsampled point i+λkN, i=0,1,…,N l -1, is the downsampled i+λkN+N l The signal value corresponding to each point.

[0086] The other steps and parameters are the same as those in the first to seventh embodiments.

[0087] Specific embodiment 9: This embodiment differs from any one of specific embodiments 1 to 8 in that the specific process of step 5 is as follows:

[0088] Step 5.1: Based on the unambiguous Doppler estimation result Calculate the phase deviation of the kth symbol caused by time-varying Doppler

[0089]

[0090] Where c represents the speed of sound in water, is the unambiguous Doppler estimation result of the mth symbol;

[0091] Step 52: Using the phase deviation of the kth symbol Phase information of the kth symbol To make compensation:

[0092]

[0093] in, is the phase of the kth symbol after compensation.

[0094] The other steps and parameters are the same as those in Specific Embodiments 1 to 8.

[0095] Specific embodiment 10: This embodiment differs from any one of specific embodiments 1 to 9 in that the method further includes step 6, which is specifically:

[0096] The phase of the kth symbol after compensation Demodulate and get the kth original bit

[0097] The other steps and parameters are the same as those in Specific Embodiments 1 to 9.

[0098] Example

[0099] This embodiment proposes a Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel. The method is specifically as follows:

[0100] Step 1: Use the copy correlation method to synchronize the received underwater acoustic direct spread signal and obtain the signal start time and the initial Doppler estimation result Specifically:

[0101] Step 11: Obtain the synchronization header reference signal corresponding to each speed according to the speed search list;

[0102] Step 1 and 2: The frame structure of the transmitted signal is as follows: Figure 2 As shown, the synchronization head reference signal corresponding to each speed is matched and correlated with the received underwater acoustic direct spread signal, and the matching correlation peak corresponding to each synchronization head reference signal is obtained (the height of the correlation peak represents the matching degree of the reference signal);

[0103] Step 13: determine the highest matching correlation peak and the synchronization header reference signal corresponding to the highest matching correlation peak;

[0104] The position where the highest matching correlation peak appears is taken as the signal start time The speed corresponding to the determined synchronization head reference signal is the initial Doppler estimation result.

[0105] Step 2: According to the signal start time Intercept the direct spread communication signal y(t) from the received signal and demodulate the signal y(t) to baseband to obtain the baseband signal

[0106]

[0107] Where LPF(·) stands for low-pass filtering, e is the base of the natural logarithm, j is the imaginary unit, t is time, and f c is the carrier frequency.

[0108] Step 3: Based on the initial Doppler estimation results Generate a local baseband reference signal and then use the local baseband reference signal and baseband signal The kth symbol of Perform matching correlation to obtain the despread correlation signal r k (τ), k=1,2,…,K, K is the baseband signal The number of symbols in ; specifically:

[0109] According to the initial Doppler estimation results and the spreading code c(t) to generate the local baseband reference signal

[0110]

[0111] Using local baseband reference signal and the kth symbol of the baseband signal Perform matching correlation to obtain the despread correlation signal r k (τ):

[0112]

[0113] where τ is the time delay.

[0114] Then extract the relevant signal r k The position where the maximum correlation peak appears in (τ) is calculated based on the position where the maximum correlation peak appears.

[0115] Calculate the phase information corresponding to the maximum correlation peak Specifically:

[0116] Extract the relevant signal r k The position where the maximum correlation peak appears in (τ)

[0117]

[0118] Calculate position Corresponding phase information

[0119]

[0120] in, It's location In the correlation signal r k The corresponding value in (τ) is yes The imaginary part of yes The real part of .

[0121] Step 4: Calculate the baseband signal separately The rough Doppler estimation result of the kth symbol in according to Calculate the phase difference between the kth symbol and the adjacent symbol Reuse Obtain a detailed estimate with fuzziness And Defuzzification is performed to obtain the unambiguous Doppler estimation result

[0122] The specific process of step 4 is as follows:

[0123] Step 4.1: Baseband signal Downsampling is performed to obtain

[0124]

[0125] Among them, T c is the baseband signal The chip length, λ is the oversampling rate, n is the nth point of downsampling, is the signal value corresponding to the nth point of downsampling;

[0126] Step 42: According to the speed search list, calculate the signal window length N corresponding to each search speed v l ;

[0127]

[0128] Where N is the spread spectrum code length, c is the speed of sound in water, Indicates rounding down;

[0129] Step 4.3: Calculate the autocorrelation result R corresponding to the kth symbol at different speeds based on the signal window length calculation result. k (v), k = 1, 2, ..., K;

[0130]

[0131] Among them, |·| means taking the absolute value, Indicates taking The conjugate of is the signal value corresponding to the downsampled point i+λkN, i=0,1,…,N l -1, is the downsampled i+λkN+N l The signal value corresponding to each point;

[0132] Step 4. Calculate the rough Doppler estimation result of each symbol based on the autocorrelation result

[0133]

[0134] in, is the rough Doppler estimation result of the kth symbol;

[0135] Step 4.5: According to The corresponding autocorrelation results Calculate the phase difference between the kth symbol and the adjacent symbol

[0136]

[0137] in, yes The imaginary part of yes The real part of

[0138] Step 46: Pass Calculate the Doppler fine estimate with ambiguity for the kth symbol

[0139]

[0140] Among them, T s is the symbol pulse width;

[0141] Step 47: Calculate the fuzzy velocity v caused by M-order phase modulation and limited phase measurement range a :

[0142]

[0143] Step 48: According to v a To calculate The fuzziness

[0144]

[0145] Step 49: Utilize fuzziness right Defuzzification is performed to obtain the unambiguous Doppler estimation result

[0146]

[0147] Step 5: Based on the unambiguous Doppler estimation results Calculate the phase deviation caused by time-varying Doppler Combined Benefit

[0148] With phase deviation Phase information Compensate and get the compensated phase

[0149] The specific process of step five is:

[0150] Step 5.1: Based on the unambiguous Doppler estimation result Calculate the phase difference of the kth symbol caused by time-varying Doppler

[0151] Bit deviation

[0152]

[0153] Where c represents the speed of sound in water, is the unambiguous Doppler estimation result of the mth symbol;

[0154] Step 52: Using the phase deviation of the kth symbol Phase information of the kth symbol To make compensation:

[0155]

[0156] in, is the phase of the kth symbol after compensation.

[0157] Step 6: Phase of the kth symbol after compensation Demodulate and get the kth original bit

[0158] Experimental part

[0159] The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication based on a time-varying Doppler channel proposed in the present invention is simulated and verified. The basic signal parameters are shown in Table 1:

[0160] Table 1 Simulation signal parameters

[0161] parameter set up communication system direct expansion communication Modulation method BPSK Center frequency 12.5kHz bandwidth 2.5kbps Spread spectrum sequence N=255 length m sequence

[0162] The simulation of the transmitting and receiving nodes is carried out in a sinusoidal motion with an amplitude of 0.12m and a period of 1.2s. This simulates a scenario where the transmitting node is anchored on the seabed and the receiving node is affected by waves and oscillates on the sea surface. Under these simulation conditions, the Doppler estimation of underwater direct-spread communication in a time-varying Doppler channel can estimate the velocity change within a frame of signal. The estimation results are shown in the figure below. Figure 3 The bit error rate curves before and after time-varying Doppler phase compensation are shown in Figure 4 As shown in the figure, under such a fast time-varying channel, traditional direct spread communication will fail, but after compensation by the present invention, the bit error rate is significantly reduced.

[0163] The proposed Doppler estimation and compensation method for underwater direct-spread spectrum communication in a time-varying Doppler channel was verified by field data processing. The field test and simulation had the same signal parameters. The receiving ship was anchored, and the transmitting ship moved at a speed of 1.5 m / s to a distance of 1 km. During the movement, the transmitting transducer was constantly oscillating due to the impact of the water flow. The bit error rate and packet loss rate are shown in Table 2.

[0164] Table 2 Field data processing results

[0165] Time-varying Doppler estimation and compensation method Traditional DS-Series Demodulation Method Bit Error Rate 0 0.43 Packet loss rate 0 / 48 47 / 48

[0166] Results show that by estimating the time-varying Doppler within the DSSS signal, the present invention can determine the motion of the transmitting and receiving nodes within a frame of the signal, estimate the time-varying Doppler within the signal, and compensate for the phase effect it causes. After compensation, the phase effect of the time-varying Doppler on the DSSS signal is eliminated, significantly improving communication performance. By removing the ambiguity caused by communication modulation in Doppler estimation, communication quality is improved. The present invention's time-varying Doppler estimation method not only maintains low system complexity but also provides more efficient signal processing performance, possessing important practical application value and broad prospects.

[0167] The above examples are merely illustrative of the calculation model and process of the present invention and are not intended to limit the embodiments of the present invention. Persons skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. This list of embodiments is not exhaustive; however, any obvious variations or modifications derived from the technical solution of the present invention remain within the scope of protection of the present invention.

Claims

1. A Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel, characterized in that: The method specifically comprises the following steps: Step 1: Frame synchronization of the received underwater acoustic direct-spread signal to obtain the signal start time and the initial Doppler estimation result Step 2: According to the signal start time Intercept the direct spread communication signal y(t) from the received signal and demodulate the signal y(t) to baseband to obtain the baseband signal Step 3: Based on the initial Doppler estimation results Generate a local baseband reference signal and then use the local baseband reference signal and baseband signal The kth symbol of Perform matching correlation to obtain the despread correlation signal r k (τ), k=1,2,…,K, K is the baseband signal The number of symbols in the Then extract the relevant signal r k The position where the maximum correlation peak appears in (τ) and the phase information corresponding to the maximum correlation peak is calculated based on the position where the maximum correlation peak appears Step 4: Calculate the baseband signal separately The rough Doppler estimation result of the kth symbol in according to Calculate the phase difference between the kth symbol and the adjacent symbol Reuse Obtain a detailed estimate with fuzziness And Defuzzification is performed to obtain the unambiguous Doppler estimation result Step 5: Based on the unambiguous Doppler estimation results Calculate the phase deviation caused by time-varying Doppler And using phase deviation Phase information Compensate and get the compensated phase 2. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 1, characterized in that: In the step 1, the copy correlation method is used to perform frame synchronization on the received underwater acoustic direct-spread signal.

3. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 1, characterized in that: The specific process of step one is: Step 11: Obtain the synchronization header reference signal corresponding to each speed according to the speed search list; Step 1 and 2: Matching correlation is performed on the synchronization head reference signal corresponding to each speed with the received underwater acoustic direct spread signal to obtain the matching correlation peak corresponding to each synchronization head reference signal; Step 13: determine the highest matching correlation peak and the synchronization header reference signal corresponding to the highest matching correlation peak; The position where the highest matching correlation peak appears is taken as the signal start time The speed corresponding to the determined synchronization head reference signal is the initial Doppler estimation result.

4. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 1, characterized in that: The signal y(t) is demodulated to baseband to obtain a baseband signal Specifically: Where LPF(·) stands for low-pass filtering, e is the base of the natural logarithm, j is the imaginary unit, t is time, and f c is the carrier frequency.

5. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 1, characterized in that: In step 3, according to the initial Doppler estimation result Generate a local baseband reference signal and then use the local baseband reference signal and baseband signal The kth symbol of Perform matching correlation to obtain the despread correlation signal r k (τ); specifically: According to the initial Doppler estimation results and the spreading code c(t) to generate the local baseband reference signal Using local baseband reference signal and the kth symbol of the baseband signal Perform matching correlation to obtain the despread correlation signal r k (τ): where τ is the time delay.

6. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 5, characterized in that: The extracted correlation signal r k The position where the maximum correlation peak appears in (τ) and the phase information corresponding to the maximum correlation peak is calculated based on the position where the maximum correlation peak appears Specifically: Extract the relevant signal r k The position where the maximum correlation peak appears in (τ) Calculate position Corresponding phase information in, It's location In the correlation signal r k The corresponding value in (τ) is yes The imaginary part of yes The real part of .

7. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 6, characterized in that: The specific process of step 4 is as follows: Step 4.1: Baseband signal Downsampling is performed to obtain Among them, T c is the baseband signal The chip length, λ is the oversampling rate, n is the nth point of downsampling, is the signal value corresponding to the nth point of downsampling; Step 42: According to the speed search list, calculate the signal window length N corresponding to each search speed v l ; Where N is the spread spectrum code length, c is the speed of sound in water, Indicates rounding down; Step 4.3: Calculate the autocorrelation result R corresponding to the kth symbol at different speeds based on the signal window length calculation result. k (v), k = 1, 2, ..., K; Step 4. Calculate the rough Doppler estimation result of each symbol based on the autocorrelation result in, is the rough Doppler estimation result of the kth symbol; Step 4.5: According to The corresponding autocorrelation results Calculate the phase difference between the kth symbol and the adjacent symbol in, yes The imaginary part of yes The real part of Step 46: Pass Calculate the Doppler fine estimate with ambiguity for the kth symbol Among them, T s is the symbol pulse width; Step 47: Calculate the fuzzy velocity v caused by M-order phase modulation and limited phase measurement range a : Step 48: According to v a To calculate The fuzziness Step 49: Utilize fuzziness right Defuzzification is performed to obtain the unambiguous Doppler estimation result 8. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 7, characterized in that: The specific process of step 43 is as follows: Among them, |·| means taking the absolute value, Indicates taking The conjugate of is the signal value corresponding to the downsampled point i+λkN, i=0,1,…,N l -1, is the downsampled i+λkN+N l The signal value corresponding to each point.

9. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 8, characterized in that: The specific process of step five is: Step 5.1: Based on the unambiguous Doppler estimation result Calculate the phase deviation of the kth symbol caused by time-varying Doppler Where c represents the speed of sound in water, is the unambiguous Doppler estimation result of the mth symbol; Step 52: Using the phase deviation of the kth symbol Phase information of the kth symbol To make compensation: in, is the phase of the kth symbol after compensation.

10. The Doppler estimation and compensation method for underwater acoustic direct spread spectrum communication in a time-varying Doppler channel according to claim 1, characterized in that: The method further includes step six, which is specifically: The phase of the kth symbol after compensation Demodulate and get the kth original bit

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