Differential spread spectrum underwater acoustic remote control method capable of resisting channel interference and Doppler

Abstract

The invention relates to the field of underwater sound control, in particular to a differential spread spectrum underwater sound remote control method resistant to channel interference and Doppler. The invention provides a differential spread spectrum signal processing method based on an underwater sound remote control system, and provides a set of multipath interference resisting method combining peak searching and deconvolution aiming at a multipath effect. Aiming at the influence of noise and Doppler, a differential spread spectrum signal in a code element difference mode is used as a response signal of the UUV, a double-pulse method is firstly used for Doppler coarse compensation during resolving, and then an orthogonal receiver is used for orthogonal demodulation to obtain two paths of signals; finally, coefficients containing residual Doppler and sampling errors can be offset as much as possible in a differential solution link in a differential conjugate multiplication mode. A simulation result shows that compared with a traditional method, the anti-noise and anti-multipath capability is high, and when the relative movement speed between the UUV and the water surface mother ship is small, the bit error rate is lower.

Description

Technical Field

[0001] The invention belongs to the field of underwater acoustic remote control, and in particular relates to a differential spread spectrum underwater acoustic remote control method that is resistant to channel interference and Doppler. Background Art

[0002] As the only form of energy that can be transmitted over long distances underwater, sound waves are the information carrier of choice for most underwater acoustic systems. However, the extremely complex underwater environment still brings many challenges to information transmission. In underwater channels, there is always more than one propagation path between the transmitter and receiver, and its complex time-space frequency-varying characteristics further deepen the impact of multipath effects on the quality of underwater acoustic remote control communications. The underwater channel is manifested as a comb filter in the frequency domain, while in the time domain, the multipath effect will distort the amplitude and phase of the signal, which will not only weaken the correlation between the received signal and the local signal and reduce the spread spectrum gain, but also cause the waveforms of the previous and next code elements to be compressed or broadened to varying degrees, thereby generating inter-code crosstalk. Nowadays, there are many methods in the underwater acoustic field that can reduce the problem of reduced communication quality caused by multipath effects, including spread spectrum technology, orthogonal frequency division multiplexing technology, single carrier frequency domain equalization technology, etc. Among them, the spread spectrum signal has excellent correlation characteristics, so it has good anti-multipath capability. Common differential spread spectrum methods include code element differential and code chip differential. Due to the complexity of underwater channels, affected by noise and multipath, the spectrum of the received signal will be broadened, so the time correlation radius is usually small. However, the chip differential method requires the use of differential coherent demodulation at the receiving end, and the pulse width of a single chip is relatively narrow, so compared with the symbol differential method, its ability to resist multipath and noise interference is weaker.

[0003] Due to the low-speed propagation characteristics of sound waves in water, if there is relative motion between the transmitter and the receiver, the Doppler effect will cause the carrier frequency of the signal to shift, causing it to seriously mismatch with the local carrier and errors during demodulation. In addition, the signal is affected by Doppler and expanded or compressed in the time domain or frequency domain, thereby affecting the synchronization of code elements and increasing the bit error rate. The pseudo-random code used in the spread spectrum signal can broaden the spectrum of the modulated signal and reduce the sensitivity of the signal to Doppler, but its anti-Doppler performance is limited, so it is necessary to estimate the Doppler factor to improve the accuracy of synchronization.

[0004] Common Doppler estimation techniques include two types of processing methods: time domain and frequency domain.

[0005] The processing methods in the time domain mainly focus on designing the transmitted signal, and then use the local signal to cross-correlate with the received signal to obtain a rough estimate of the Doppler. Existing solutions use a multi-correlator Doppler compensation method based on variable sampling, which estimates the Doppler frequency shift by comparing the correlators with the largest correlation peaks. In the existing solutions, many signals that are insensitive to Doppler and have strong correlation are interpolated into the signal, and the Doppler frequency shift and residual are frequently estimated and iterated during the signal reception process. The Doppler estimation accuracy of these two time domain methods is limited by the duration of the received signal.

[0006] Signal processing methods in the frequency domain have developed more maturely, but the calculations of such methods are usually very complicated and need to be used according to actual environmental conditions. Signal processing method 1 in the frequency domain: First, the signal frequency is measured using the fitting approximation method in the frequency domain, and the signal is roughly compensated after obtaining the Doppler factor, and then fine compensation is performed using the method of multiple iterations in the detection domain. Method 2: Use EMD (Empirical Mode Decomposition, EMD) to decompose the frequency components of the signal and estimate the Doppler frequency deviation, and then use the WFFT (Wavelet-FFT, WFFT) Doppler suppression algorithm to compensate for the residual Doppler. Method 3: Perform a fast Fourier transform on the received signal after narrowband filtering, and then use the parabola method to fit and estimate the frequency offset.

[0007] All three methods require a trade-off between compensation accuracy and computational complexity. If higher compensation accuracy is required, the computational complexity will also increase.

[0008] In summary, when performing long-term missions, underwater unmanned vehicles (UUVs) are limited in their information collection and autonomous decision-making capabilities and are unable to cope with complex underwater environments. The host computer used in the underwater acoustic remote control system needs to query the working status of multiple UUVs at the same time and provide information support. Therefore, there is a problem in the existing technology that the underwater acoustic remote control cannot obtain accurate UUV status information due to channel interference and Doppler. Summary of the invention

[0009] The purpose of the present invention is to solve the problem that the prior art cannot obtain accurate UUV status information due to channel interference and Doppler resistance in underwater acoustic remote control. We propose a differential spread spectrum underwater acoustic remote control method that is resistant to channel interference and Doppler.

[0010] 1. The deployment and communication modes of the surface mother ship and underwater UUVs Figure 1As shown. The surface mother ship can carry GPS, passive sonar hydrometer and other equipment to obtain the position, distance and hydrological status parameters. Before launching, the UUV will store the frequency and structure of the broadcast signal emitted by the surface mother ship.

[0011] S1: The surface mother ship transmits a broadcast signal, and each underwater unmanned vehicle UUV receives the broadcast signal transmitted by the surface mother ship, wherein the broadcast signal contains status information;

[0012] S2: Each UUV obtains its own working status based on the broadcast signal transmitted by the surface mother ship;

[0013] The working status includes the position and speed information of the UUV, such as the longitude and latitude, movement direction, movement speed, etc. of the UUV.

[0014] S3: Each UUV generates a response signal according to the corrected working status, and each UUV uses a different response delay to transmit its own response signal to the surface carrier in turn;

[0015] S4: The UUV sends a reply signal at a fixed time interval. The processing system of the surface mother ship pairs the pilot code with the Doppler calibration code for each frame of the received reply signal. If the pairing is successful, S5 is performed. If the pairing is unsuccessful, the next frame of reply signal is waited for.

[0016] S5: The processing system of the surface mother ship obtains the working status of the UUV according to the content of the successfully matched response signal.

[0017] The present invention aims to detect and decode the response signal of the UUV in real time, thereby realizing more accurate control of the operating status of multiple UUVs.

[0018] The beneficial effects of the present invention are:

[0019] The present invention proposes a differential spread spectrum signal processing method based on an underwater acoustic remote control system, which can suppress Doppler, noise and multipath effects.

[0020] 1. The present invention proposes a set of anti-multipath interference methods that combine peak search with deconvolution for multipath effects. For the influence of noise and Doppler, the UUV's reply signal first uses a differential spread spectrum signal in a symbol differential mode, and first uses a double pulse method to roughly compensate for Doppler during the calculation, and then uses an orthogonal receiver for orthogonal demodulation to obtain two signals. Finally, the coefficients containing residual Doppler and sampling errors can be offset as much as possible in the form of differential conjugate multiplication in the differential process.

[0021] 2. Compared with the traditional method, the present invention has stronger anti-noise and anti-multipath capabilities, and when the relative movement speed between the UUV and the surface mother ship is small, the present invention has a lower bit error rate.

[0022] 3. The method proposed in the present invention can suppress the influence of Doppler, noise and multipath while having low computational complexity, so it has the characteristics of easy implementation, strong real-time performance and strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the working status of each surface and underwater platform of the present invention;

[0024] Figure 2 It is the algorithm flow chart of the present invention;

[0025] Figure 3 It is a schematic diagram of the response signal structure of the present invention;

[0026] Figure 4 is a schematic diagram of the peak search strategy of the present invention;

[0027] Figure 5 It is a schematic diagram comparing the anti-noise capabilities of different methods;

[0028] Figure 6 This is a schematic diagram of the relative motion mode between the UUV and the surface mother ship of the present invention.

[0029] Figure 7 Schematic diagram of signal waveform after differential solution by the method of the present invention;

[0030] Figure 8 This is a schematic diagram of the signal waveform after differential analysis using the conventional method;

[0031] Fig. 9 Schematic diagram of the effect of different movement speeds of the UUV of the present invention on the bit error rate;

[0032] Fig.10 This is a schematic diagram of the original response signal of the present invention.

[0033] Fig.11 This is a schematic diagram of the correlation peak envelope of the pilot code of the present invention.

[0034] Fig.12 is a schematic diagram of a channel function of the present invention;

[0035] Fig.13 It is a schematic diagram of the decoding situation without deconvolution of the present invention;

[0036] Fig.14 It is a schematic diagram of the decoding situation of deconvolution of the present invention. DETAILED DESCRIPTION

[0037] Specific implementation method 1: Combination Figure 1 The invention is described, comprising:

[0038] 1. The deployment and communication modes of the surface mother ship and underwater UUVs Figure 1 As shown. The surface mother ship can carry GPS, passive sonar hydrometer and other equipment to obtain the position, distance and hydrological status parameters. Before launching, the UUV will store the frequency and structure of the broadcast signal emitted by the surface mother ship.

[0039] S1: The surface mother ship transmits a broadcast signal, and each underwater unmanned vehicle UUV receives the broadcast signal transmitted by the surface mother ship, wherein the broadcast signal contains status information;

[0040] S2: Each UUV obtains its own working status based on the broadcast signal transmitted by the surface mother ship;

[0041] The working status includes the position and speed information of the UUV;

[0042] S3: Each UUV generates a response signal according to the corrected working status, and each UUV uses a different response delay to transmit its own response signal to the surface carrier in turn;

[0043] S4: The UUV sends a reply signal at a fixed time interval. The processing system of the surface mother ship pairs the pilot code with the Doppler calibration code for each frame of the received reply signal. If the pairing is successful, S5 is performed. If the pairing is unsuccessful, the next frame of reply signal is waited for.

[0044] S5: The processing system of the surface mother ship obtains the working status of the UUV according to the content of the successfully matched response signal.

[0045] The present invention aims to detect and decode the response signal of the UUV in real time, thereby achieving more accurate control of the operating status of a plurality of UUVs.

[0046] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that:

[0047] The specific process of each UUV making a response signal according to the corrected working status in S3 is:

[0048] S3.1: Each UUV encodes its own working status into an original information code in binary form, and then encodes the original information code in a differential encoding form to obtain a differential code;

[0049] S3.2: Perform spread spectrum processing on the differential code obtained in S3.1 to obtain a spread spectrum code;

[0050] S3.3: Modulate the spread spectrum code obtained in S3.2 to obtain an information code;

[0051] S3.4: Add an identical linear frequency modulation signal before and after the information code obtained in S3.3 to obtain a response signal; wherein the linear frequency modulation signal added before the information code is used as a pilot code, and the time gap between the pilot code and the information code is of duration t ld ;

[0052] The linear frequency modulation signal added after the information code is used as the Doppler calibration code. The time gap between the Doppler calibration code and the information code is the time length t ld .

[0053] The information code in the signal used in the present invention is in the form of differential coding, and then it is spread spectrum and modulated, and an identical linear frequency modulation signal is added before and after the information code as a pilot code and a Doppler calibration code. The response signal structure is as follows: Figure 2 Shown

[0054] The other steps and parameters are the same as those in the first specific implementation.

[0055] Specific implementation method three: This implementation method is different from the specific implementation method one in that:

[0056] In S4, the UUV sends a reply signal at a fixed time interval, and the processing system of the surface mother ship pairs the received reply signal with the pilot code and the Doppler calibration code once per frame. If the match is successful, S5 is performed. If the match is unsuccessful, the next frame of the reply signal is waited for. The specific process is as follows:

[0057] S4.1: Perform copy correlation processing on the reply signal received by the surface mother ship to obtain the correlation peak envelope;

[0058] S4.2: Perform peak search on the correlation peak envelope obtained in S4.1 to obtain the maximum peak, the first peak of the maximum peak, the second largest peak, and the first peak of the second largest peak;

[0059] S4.3: Pair the maximum peak, the first peak of the maximum peak, the second largest peak and the first peak of the second largest peak respectively; if there is a case where the calculated time delay difference is within the Doppler tolerance allowed by the design, that is, the pairing is successful, then proceed to S5 for subsequent calculations; if the calculated time delay differences in all cases are not within the Doppler tolerance allowed by the design, that is, the pairing fails, then no subsequent calculations are performed and wait for the arrival of the next frame of data, and the other steps and parameters are the same as those in one of the specific implementation methods one to two.

[0060] Specific implementation method 4: This implementation method is different from specific implementation methods 1 to 3 in that:

[0061] In S4.1, the response signal received by the surface mother ship is subjected to copy correlation processing to obtain a correlation peak envelope; the specific process is:

[0062] S4.1.1: Input the reply signal received by the surface mother ship into the bandpass filter, and output the filtered reply signal.

[0063] S4.1.2: Input the filtered response signal obtained in S4.1.1 into the orthogonal filter and output the analytical signal;

[0064] S4.1.3: Perform copy correlation processing on the analysis signal obtained in S4.1.2 and the guide code saved by the surface mother ship, perform modulo processing on the result of the copy correlation processing to obtain the correlation peak envelope, and the other steps and parameters are the same as those in one of the specific implementation modes one to three.

[0065] Specific implementation method five: The difference between this implementation method and specific implementation methods one to four is that in S4.2, the peak value search is performed on the correlation peak envelope obtained in S4.1 to obtain the maximum peak, the first peak of the maximum peak, the second largest peak and the first peak of the second largest peak; the specific process is:

[0066] S4.2.1: Traverse all peaks of the relevant peak envelope and find the location and peak height of the maximum peak.

[0067] The maximum peak left and right t p1 The second is determined as the group where the maximum peak is located;

[0068] S4.2.2: t before the maximum peak position p2 In seconds, let t p1 >t p2 , the first peak that meets the search criteria found in chronological order is the first peak of the maximum peak.

[0069] The search condition is: the difference between the maximum peak height and the search peak height is within a set threshold;

[0070] S4.2.3: Exclude the group where the largest peak in the correlation peak envelope is located to obtain the remaining correlation peak envelope, traverse all peaks of the remaining correlation peak envelope, find the position and peak height of the largest peak among all peaks of the remaining correlation peak envelope, and use them as the position and peak height of the second largest peak;

[0071] S4.2.4: Before the next largest peak p2 Within seconds, t p1 >t p2 The first peak that meets the search conditions and is searched in chronological order is the first peak of the second largest peak, and the other steps and parameters are the same as those in one of the specific implementation modes one to four.

[0072] Specific implementation method 6: This implementation method is different from specific implementation methods 1 to 5 in that:

[0073] In S4.3, the maximum peak, the first peak of the maximum peak, the second largest peak, and the first peak of the second largest peak are paired respectively; if the delay difference calculated in all cases is not within the Doppler tolerance allowed by the design, that is, the pairing fails, no subsequent calculation is performed and the arrival of the next frame of data is waited; if the pairing is successful, S5 is performed for subsequent calculation; the specific process is:

[0074] S4.3.1: Calculate the absolute value of the time delay difference between the first peak of the maximum peak and the first peak of the second largest peak, and determine whether the absolute value of the time delay difference between the first peak of the maximum peak and the first peak of the second largest peak exceeds the Doppler tolerance. If the absolute value of the time delay difference between the first peak of the maximum peak and the first peak of the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, then save the pairing of the first peak of the maximum peak and the first peak of the second largest peak; if the absolute value of the time delay difference between the first peak of the maximum peak and the first peak of the second largest peak exceeds the Doppler tolerance, then do not save the pairing of the first peak of the maximum peak and the first peak of the second largest peak; the specific process is:

[0075] If d|E(a)-E(b)|<τ dt , then the pairing is successful and [E(a), E(b)] is saved, where d|·| is the absolute value of the delay difference between the two correlation peaks, τ dt represents the Doppler tolerance, and the [·] symbol indicates the preservation of the pairing situation; E(a) and E(b) represent the indices of the positions of the first peak of the largest peak and the first peak of the second largest peak, respectively;

[0076] If d|E(a)-E(b)|≥τ dt , then the pairing of the first peak of the largest peak and the first peak of the second largest peak will not be saved;

[0077] S4.3.2: Calculate the absolute value of the time delay difference between the maximum peak and the first peak of the second largest peak, and determine whether the absolute value of the time delay difference between the maximum peak and the first peak of the second largest peak exceeds the Doppler tolerance. If the absolute value of the time delay difference between the maximum peak and the first peak of the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, then the pairing of the maximum peak and the first peak of the second largest peak is saved; if the absolute value of the time delay difference between the maximum peak and the first peak of the second largest peak exceeds the Doppler tolerance, then the pairing of the maximum peak and the first peak of the second largest peak is not saved; the specific process is:

[0078] If d|R(A)-E(b)|<τ dt , the pairing is successful and [R(A), E(b)] is saved; R(A) represents the index of the position of the maximum peak;

[0079] If d|R(A)-E(b)|≥τ dt , then the pairing between the largest peak and the first peak of the second largest peak will not be saved;

[0080] S4.3.3: Calculate the absolute value of the time delay difference between the first peak of the maximum peak and the second largest peak, and determine whether the absolute value of the time delay difference between the first peak of the maximum peak and the second largest peak exceeds the Doppler tolerance. If the absolute value of the time delay difference between the first peak of the maximum peak and the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, then the pairing of the first peak of the maximum peak and the second largest peak is saved; if the absolute value of the time delay difference between the first peak of the maximum peak and the second largest peak exceeds the Doppler tolerance, then the pairing of the first peak of the maximum peak and the second largest peak is not saved; the specific process is:

[0081] If d|R(B)-E(a)|<τ dt , the pairing is successful and [R(B), E(a)] is saved; R(B) represents the index of the position of the second largest peak;

[0082] If d|R(B)-E(a)|≥τ dt , then the pairing of the largest peak and the second largest peak will not be saved;

[0083] S4.3.4: Calculate the absolute value of the time delay difference between the maximum peak and the second largest peak, and determine whether the absolute value of the time delay difference between the maximum peak and the second largest peak exceeds the Doppler tolerance. If the absolute value of the time delay difference between the maximum peak and the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, then the pairing of the maximum peak and the second largest peak is saved. If the absolute value of the time delay difference between the maximum peak and the second largest peak exceeds the Doppler tolerance, then the pairing of the maximum peak and the second largest peak is not saved. The specific process is as follows:

[0084] If d|R(A)-R(B)|<τ dt , then the pairing is successful and [R(A), R(B)] is saved;

[0085] If d|R(A)-R(B)|≥τ dt , the pairing of the largest peak and the second largest peak will not be saved.

[0086] Specific implementation method 7: This implementation method is different from specific implementation methods 1 to 6 in that:

[0087] In S5, the processing system of the surface mother ship obtains the working status of the UUV according to the content of the successfully matched response signal. The specific process is as follows:

[0088] S5.1: Calculate the Doppler influence factor;

[0089] S5.2: intercepting the reply signal according to the Doppler influence factor calculated in S5.1 to obtain an interception information code;

[0090] S5.3: construct a channel function, and deconvolve the channel function with the information code intercepted in step S5.2 to obtain the intercepted information code after deconvolution;

[0091] S5.4: performing orthogonal demodulation on the intercepted information code after deconvolution obtained in S5.3 to obtain a demodulated information code;

[0092] S5.5: Despread the demodulated information code obtained in S5.4 using a copy correlator to obtain a despread information code;

[0093] S5.6: Remove the last code element from the despread information code obtained in S5.5 to obtain signal A p1 ;

[0094] Remove the first code element from the despread information code obtained in S5.5 to obtain signal A p2 ;

[0095] The signal A p1 and signal A p2 After approximate processing and conjugate multiplication, we get the signal D p ;

[0096] S5.7: Signal D obtained from S5.6 p Modulo, peak search and symbol decision processing are performed to obtain the final N-1-bit information code, and the working status of the UUV is obtained according to the content of the final N-1-bit information code.

[0097] The other steps and parameters are the same as those in Specific Embodiments 1 to 6.

[0098] Specific implementation eight: This implementation differs from specific implementations one to seven in that:

[0099] The Doppler influence factor is calculated in S5.1; the specific process is:

[0100]

[0101] Among them, t ld is the delay interval between the pilot code and the Doppler calibration code in the reply signal transmitted by the UUV, t' ld The time interval between the successfully matched pilot code and Doppler calibration code;

[0102] In S5.2, the information code is intercepted according to the Doppler influence factor calculated in S5.1; the specific process is:

[0103] S5.2.1: Calculate the time interval between the successfully matched guide code and information code. The specific process is as follows:

[0104] t' lm =t lm *(1-P) (3)

[0105] Among them, t lmis the time interval between the guidance code and information code of the UUV transmission signal, * represents multiplication, t' lm The time interval between the successfully matched guide code and information code;

[0106] S5.2.2: Based on the position of the peak with the smaller delay value among the two correlation peaks saved in step S4.3 and the time interval t' between the successfully matched pilot code and information code lm , intercept the response signal and obtain the interception information code y(t)=[x(t1),x(t2),...,x(t k )],k∈[1,N]

[0107] The expression of the intercepted information code is:

[0108]

[0109] Among them, x(t k ) represents the expression of intercepting the kth code element of the information code, d(t k ) represents the polarity of the k-th bit intercepted information code, n is the number of code chips in a code element, C n (t k ) represents the kth intercepted information code element with n code chips, w represents the carrier frequency affected by Doppler, Δw k represents the residual Doppler of the kth intercepted information code element after Doppler compensation, is the sampling error of the receiving end for the kth intercepted information code element, n(t k ) is Gaussian white noise,

[0110]

[0111] t k It represents the time length of the kth intercepted information code symbol, T1 is the number of cycles occupied by a code chip in the intercepted information code symbol after being modulated, k∈[1,N], N is the total number of intercepted information code symbols;

[0112] In said S5.3, a channel function is constructed, and the channel function is deconvolved with the information code intercepted in step S5.2 to obtain the intercepted information code after deconvolution; the specific process is:

[0113] S5.3.1: Record the range T after the pilot code correlation peak X The size and index of the relevant peak envelope within, the index set is t est , T X The range is determined by the actual channel.

[0114] S5.3.2: Construct the channel function h(t est ), the specific process is:

[0115] The relevant peak envelope size and index obtained in step 5.3.1 are matched one by one, and the index without index is set to 0.

[0116] S5.3.3: Deconvolve the channel function obtained in S5.3.2 with the information code intercepted in step S5.2 to obtain the intercepted information code after deconvolution; the specific process is:

[0117] y(t k )=x(t k )*h(-t est ) (4), other steps and parameters are the same as those in any one of the specific implementation modes one to seven.

[0118] Specific implementation method 9: This implementation method is different from specific implementation methods 1 to 8 in that:

[0119] In S5.4, the deconvolved intercepted information code obtained in S5.3 is orthogonally demodulated to obtain a demodulated information code; the specific process is:

[0120] S5.4.1: The deconvolved intercepted information code y(t k ) is demodulated through the sinusoidal channel to obtain the signal Q(t k );

[0121] The deconvolution information code y(t k ) is demodulated by two orthogonal channels of the cosine channel to obtain the signal I(t k );

[0122] S5.4.2: Obtain the signal Q(t k ) is processed by a low-pass filter to obtain the signal Q'(t k );

[0123] S5.4.1 obtains the signal I(t k ) is processed by a low-pass filter to obtain the signal I'(t k );

[0124] S5.4.3: Transform the signal Q'(t k ) as the imaginary part, the signal I'(t k ) as the real part to form a complex signal, and obtain the final orthogonal demodulation result, the complex signal formed is the demodulated information code. The other steps and parameters are the same as those of the specific implementation methods one to eight.

[0125] Specific implementation method 10: This implementation method is different from specific implementation methods 1 to 9 in that:

[0126] In S5.4.1, the interception information code y(tk ) Through the orthogonal demodulation of the sine channel and the cosine channel, the two signals after orthogonal demodulation are obtained, namely, equation 5 and equation 6. The specific process is:

[0127]

[0128]

[0129] Among them, I(t k ) is the tth k Signal expression of code elements;

[0130] Q(t k ) is the tth k Signal expression of code elements;

[0131] S5.4.2: Obtain the signal Q(t k ) is processed by a low-pass filter to obtain the signal Q'(t k );

[0132] S5.4.1 obtains the signal I(t k ) is processed by a low-pass filter to obtain the signal I'(t k ); the specific process is:

[0133] In S5.4.2, the two signals after orthogonal demodulation obtained in S5.4.1 are processed by low-pass filters respectively to obtain two signals processed by low-pass filters, that is, the second term in equation 5 and equation 6 is removed to obtain equation 7 and equation 8.

[0134]

[0135]

[0136] Among them, I'(t k ) is I(t k ) after passing through the low-pass filter k The signal expression of code elements, Q'(t k ) is Q(t k ) after passing through the low-pass filter k Signal expression of code elements;

[0137] S5.4.3: Transform the signal Q'(t k ) as the imaginary part, the signal I'(t k ) as the real part to form a complex signal, and obtain the final orthogonal demodulation result. The complex signal formed is the demodulated information code. The specific process is:

[0138] Formula 7 and Formula 8 are used as the real part and imaginary part to form a complex signal, and the final orthogonal demodulation result, that is, the demodulated information code, is obtained, as shown in Formula 9.

[0139] S p (t k )=I'(t k )+i·Q'(t k ) (9)

[0140] Among them, S p (t k ) is the signal expression of the kth code element of the demodulated information code, i represents the imaginary unit, S p (t k ) is the orthogonal demodulation result of the kth symbol corrected by the Doppler factor P,

[0141] In S5.5, the demodulated information code obtained in S5.4 is despread using a copy correlator to obtain a despread information code; the specific process is:

[0142] The local signal of the spread spectrum code stored by the surface mother ship is copied and correlated with the demodulated information code obtained in S5.4 to obtain the despread information code. The specific process is as follows:

[0143]

[0144] Among them, A p (t k ) represents the kth code element of the despread information code, and <·> is the copy correlation operation. Since the spreading code is uncorrelated with the noise, the influence of the noise can be ignored.

[0145] Since convolution requires continuous multiplication and accumulation operations, which occupy a large amount of computing resources, the present invention uses the fast Fourier transform method to convert the received signal and the flipped local spread spectrum signal into frequency domain signals respectively, and then perform multiplication operations. This frequency domain related method can reduce a lot of computational complexity and more easily meet the requirements of real-time processing.

[0146] In S5.6, the last code element of the despread information code obtained in S5.5 is removed to obtain signal A. p1 ;

[0147] Remove the first code element from the despread information code obtained in S5.5 to obtain signal A p2 ;

[0148] The signal A p1 and signal A p2 After approximate processing and conjugate multiplication, we get the signal D p ; The specific process is:

[0149] S5.6.1: The despread information code {A p (t1),A p (t2),…,A p (t N )} Remove the last code element to get signal A p1 , signal A p1 The formula is formula 11:

[0150] A p1 ={A p (t1),A p (t2),…,A p (t N-1 )} (11)

[0151] S5.6.2: The despread information code {A p (t1),A p (t2),…,A p (t N )} Remove the first code element to get signal A p2 , signal A p2 The formula is Equation 12:

[0152] A p2 ={A p (t2),…,A p (t N-1 ),A p (t N )} (12)

[0153] The signal A p1 and signal A p2 After approximate processing and conjugate multiplication, we get the signal D p ; The specific process is:

[0154] D p =A p1 .*conj(A p2 ) (13)

[0155] Among them, A p1 .Indicates signal A p1 The conjugate signal of

[0156] Among them, signal A p1 and signal A p2 In the approximate processing, since the spreading codes used by different symbols are the same,

[0157] C n (t k )=C n (t k+1 )

[0158] If the duration of each code element is very short, it can be assumed that the Doppler and sampling errors between two adjacent code elements are very small, so it can be approximately obtained that

[0159]

[0160] Since the length of the code element is a periodic signal of integer length, the final signal D is p The expression of a single code unit is:

[0161]

[0162] In S5.7, the signal obtained in S5.6 is subjected to symbol judgment and peak search processing to obtain a final information code. The specific process of obtaining the working status of the UUV according to the content of the final information code is as follows:

[0163] S5.7.1: For signal D p Perform modulo processing to obtain the signal D after modulo processing p1 ;

[0164] S5.7.2: Signal D after modulo processing p1 Perform peak search to obtain the signal D after modulo processing p1 N-1 peak points;

[0165] S5.7.3: Determine the signal D after modulo processing p1 The positive and negative signs of the real part values ​​corresponding to the peak points are determined. If the real part value is positive, the code element is judged to be 1; if the real part value is negative, the code element is judged to be 0, and the final N-1-bit information code is obtained. The processing system of the surface mother ship obtains the working status of the UUV according to the content of the final N-1-bit information code. The other steps and parameters are the same as those in the specific implementation modes one to nine.

[0166] Combining the simulation analysis of specific implementation methods one to ten

[0167] 1. Noise immunity

[0168] Assume that the carrier of the received signal is 10kHz, the spread spectrum code is a pseudo-random sequence, and the signal has 1000 code elements. Compare the anti-noise capabilities of the code element difference, the code chip difference and the method of the present invention under different signal-to-noise ratios. Let the signal-to-noise ratio change from -26dB to -6dB in steps of 2dB, and perform 300 Monte Carlo simulations.

[0169] like Figure 5As shown in the figure, when the signal-to-noise ratio is above -6dB, the three methods perform well. As the signal-to-noise ratio gradually decreases, the bit error rate of the code difference method increases rapidly. When the signal-to-noise ratio drops below -15dB, the anti-noise ability of the method of the present invention is slightly improved compared with the traditional code difference method.

[0170] 2. Anti-Doppler capability:

[0171] The relative motion mode between the surface mother ship and the UUV is as follows: Figure 6 As shown. At the initial moment, the UUV is 200m away from the surface mother ship, and the UUV moves away from the surface mother ship at a uniform speed v. Assuming that the time length of each code element is very short, the Doppler effect on each code element is determined by the movement speed of the surface mother ship when it starts to receive the code element, and the influence of sampling error is ignored.

[0172] The center frequency of the two linear frequency modulation signals is 3kHz, the bandwidth is 2kHz, the duration is 0.015 seconds, and the pilot code and Doppler calibration code are separated by 0.03 seconds from the differential spread spectrum signal. The spread spectrum signal is the same as that in Section 4.1.

[0173] Figure 7 and Figure 8 The signal waveforms after demodulation, despreading and dedifferentiation of the method of the present invention and the conventional method are compared. Figure 7 It can be seen that the present invention has a better effect on Doppler compensation. coefficient, so in Figure 7 The influence of the uncompensated Doppler factor on the signal waveform can be clearly seen.

[0174] Let the UUV's speed change from 0m / s to 10m / s, and calculate the final bit error rate every 0.5m / s. Fig. 9 The anti-Doppler performance of the method of the present invention and the conventional method is compared in FIG. The conventional method uses only a single channel for demodulation, and adopts the form of offset multiplication for the final differential solution. Both methods use the double pulse method to compensate for Doppler. The blue curve and the red curve are the bit error rate curves of the conventional method and the method of the present invention, respectively. It can be seen that the Doppler tolerance of the present invention is relatively high, and when the movement speed of the UUV is within 10m / s, the bit error rate is maintained at a low level.

[0175] 3. Anti-multipath capability

[0176] Fig.10 This is the actual response signal collected in a lake test in 2023, and the receiving and sending distance is approximately 600 meters. Fig.11It can be seen from the correlation peak envelope of the pilot code that the actual underwater channel conditions are extremely complex, and the correlation peak height of the multipath signal after coherent superposition has exceeded that of the direct signal. Therefore, when the channel conditions are more complex, it is necessary to search for multiple correlation peaks and try to match them multiple times. Since the signal length used in this experiment is relatively short, the multipath structure after the pilot code and the information code can be considered to be consistent. Therefore, no matter whether the final match is successful for the multipath signal or the direct signal, the final solution result is likely to be correct.

[0177] The purpose of deconvolution is to focus the energy of multipath signals on the direct signal. Fig.12 is the channel function obtained from the pilot code, and Fig.13 and Fig.14 The decoding results of the original signal before and after deconvolution are shown respectively. The red dotted line indicates the peak search range. The decoding result of the signal is (0,0,1,0,0,1). It can be seen that Fig.13 Decoding failed. Fig.14 The decoding was successful and the effect was significant.

[0178] The present invention proposes a differential spread spectrum signal processing method based on an underwater acoustic remote control system, which can suppress Doppler, noise and multipath effects. In view of the multipath effect, the present invention proposes a set of anti-multipath interference methods that combine peak search with deconvolution. In view of the influence of noise and Doppler, the UUV's reply signal first uses a differential spread spectrum signal in a symbol differential mode, and when solving, the double pulse method is first used to roughly compensate for the Doppler, and then an orthogonal receiver is used for orthogonal demodulation to obtain two signals, and finally the coefficients containing residual Doppler and sampling errors can be offset as much as possible in the form of differential conjugate multiplication in the differential solution link. The simulation results show that compared with the traditional method, the present invention has stronger anti-noise and anti-multipath capabilities, and when the relative motion speed between the UUV and the surface mother ship is small, the present invention has a lower bit error rate.

[0179] The method proposed in the present invention can suppress the influence of Doppler, noise and multipath while having low computational complexity, and therefore has the characteristics of being easy to implement, having strong real-time performance and strong anti-interference capability, and is a practical and reliable method in engineering.

[0180] The above only describes the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the above specific implementation methods. Although the present invention has been disclosed as above in the preferred embodiments, it is not used to limit the present invention. Any technician familiar with the profession can make some changes or modify the technical contents disclosed above into equivalent embodiments with equivalent changes without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A differential spread spectrum underwater acoustic remote control method resistant to channel interference and Doppler, characterized in that: The following steps are involved: S1: The surface mother ship transmits a broadcast signal, and each underwater unmanned vehicle UUV receives the broadcast signal transmitted by the surface mother ship, wherein the broadcast signal contains the working status information of each UUV; S2: Each UUV obtains its own working status based on the broadcast signal transmitted by the surface mother ship; The working status includes the position and speed information of the UUV; S3: Each UUV generates a response signal according to the acquired working status. Each UUV uses a different response delay and transmits its own response signal to the surface carrier in turn; S4: The UUV sends a reply signal at a fixed time interval. The surface mother ship pairs the pilot code with the Doppler calibration code for each frame of the reply signal received. If the pairing is successful, S5 is performed. If the pairing is unsuccessful, the next frame of reply signal is waited for. S5: The surface mother ship obtains the working status of the UUV according to the content of the successfully matched response signal.

2. The differential spread spectrum underwater acoustic remote control method against channel interference and Doppler according to claim 1, characterized in that: The specific process of each UUV making a response signal according to the corrected working status in S3 is: S3.1: Each UUV encodes its own working status into an original information code in binary form, and then encodes the original information code in a differential encoding form to obtain a differential code; S3.2: Perform spread spectrum processing on the differential code obtained in S3.1 to obtain a spread spectrum code; S3.3: Modulate the spread spectrum code obtained in S3.2 to obtain an information code; S3.4: Add an identical linear frequency modulation signal before and after the information code obtained in S3.3 to obtain a response signal; wherein the linear frequency modulation signal added before the information code is used as a pilot code, and the time gap between the pilot code and the information code is of duration t ld ; The linear frequency modulation signal added after the information code is used as the Doppler calibration code. The time gap between the Doppler calibration code and the information code is the time length t ld .

3. The differential spread spectrum underwater acoustic remote control method against channel interference and Doppler according to claim 2, characterized in that: In S4, the UUV sends a reply signal at a fixed time interval, and the processing system of the surface mother ship pairs the received reply signal with the pilot code and the Doppler calibration code once per frame. If the match is successful, S5 is performed. If the match is unsuccessful, the next frame of the reply signal is waited for. The specific process is as follows: S4.1: Perform copy correlation processing on the reply signal received by the surface mother ship to obtain the correlation peak envelope; S4.2: Perform peak search on the correlation peak envelope obtained in S4.1 to obtain the maximum peak, the first peak of the maximum peak, the second largest peak, and the first peak of the second largest peak; S4.3: Pair the maximum peak, the first peak of the maximum peak, the second largest peak, and the first peak of the second largest peak respectively; if the calculated delay difference is within the Doppler tolerance allowed by the design, that is, the pairing is successful, then proceed to S5 for subsequent calculations; if the calculated delay differences in all cases are not within the Doppler tolerance allowed by the design, that is, the pairing fails, then no subsequent calculations are performed and wait for the arrival of the next frame of data.

4. The differential spread spectrum underwater acoustic remote control method against channel interference and Doppler according to claim 3, characterized in that: In S4.1, the response signal received by the surface mother ship is subjected to copy correlation processing to obtain a correlation peak envelope; the specific process is: S4.1.1: Input the reply signal received by the surface mother ship into the bandpass filter, and output the filtered reply signal. S4.1.2: Input the filtered response signal obtained in S4.1.1 into the orthogonal filter and output the analytical signal; S4.1.3: Perform copy correlation processing on the analysis signal obtained in S4.1.2 and the guide code stored in the surface mother ship, and perform modulo processing on the result of the copy correlation processing to obtain the correlation peak envelope.

5. The differential spread spectrum underwater acoustic remote control method against channel interference and Doppler according to claim 4, characterized in that: In S4.2, the peak value of the correlation peak envelope obtained in S4.1 is searched to obtain the maximum peak, the first peak of the maximum peak, the second largest peak and the first peak of the second largest peak; the specific process is: S4.2.1: Traverse all peaks of the relevant peak envelope and find the location and height of the maximum peak. The maximum peak left and right t p1 The second is determined as the group where the maximum peak is located; S4.2.2: t before the maximum peak position p2 In seconds, let t p1 >t p2 , the first peak that meets the search criteria found in chronological order is the first peak of the maximum peak. The search condition is: the difference between the maximum peak height and the search peak height is within a set threshold; S4.2.3: Exclude the group where the largest peak in the correlation peak envelope is located to obtain the remaining correlation peak envelope, traverse all peaks of the remaining correlation peak envelope, find the position and peak height of the largest peak among all peaks of the remaining correlation peak envelope, and use them as the position and peak height of the second largest peak; S4.2.4: Before the next largest peak p2 Within seconds, t p1 >t p2 , the first peak that meets the search criteria found in chronological order is the first peak of the second largest peak.

6. A differential spread spectrum underwater acoustic remote control method resistant to channel interference and Doppler according to claim 5, characterized in that: In S4.3, the maximum peak, the first peak of the maximum peak, the second largest peak, and the first peak of the second largest peak are paired respectively; if the delay difference calculated in all cases is not within the Doppler tolerance allowed by the design, that is, the pairing fails, no subsequent calculation is performed and the arrival of the next frame of data is waited; if the pairing is successful, S5 is performed for subsequent calculation; the specific process is: S4.3.1: Calculate the absolute value of the time delay difference between the first peak of the maximum peak and the first peak of the second largest peak, and determine whether the absolute value of the time delay difference between the first peak of the maximum peak and the first peak of the second largest peak exceeds the Doppler tolerance. If the absolute value of the time delay difference between the first peak of the maximum peak and the first peak of the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, then save the pairing of the first peak of the maximum peak and the first peak of the second largest peak; if the absolute value of the time delay difference between the first peak of the maximum peak and the first peak of the second largest peak exceeds the Doppler tolerance, then do not save the pairing of the first peak of the maximum peak and the first peak of the second largest peak; the specific process is: If d|E(a)-E(b)|<τ dt , then the pairing is successful and [E(a), E(b)] is saved, where d|·| is the absolute value of the delay difference between the two correlation peaks, τ dt represents the Doppler tolerance, and the [·] symbol indicates the preservation of the pairing situation; E(a) and E(b) represent the indices of the positions of the first peak of the largest peak and the first peak of the second largest peak, respectively; If d|E(a)-E(b)|≥τ dt , then the pairing of the first peak of the largest peak and the first peak of the second largest peak will not be saved; S4.3.2: Calculate the absolute value of the time delay difference between the maximum peak and the first peak of the second largest peak, and determine whether the absolute value of the time delay difference between the maximum peak and the first peak of the second largest peak exceeds the Doppler tolerance. If the absolute value of the time delay difference between the maximum peak and the first peak of the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, then the pairing of the maximum peak and the first peak of the second largest peak is saved; if the absolute value of the time delay difference between the maximum peak and the first peak of the second largest peak exceeds the Doppler tolerance, then the pairing of the maximum peak and the first peak of the second largest peak is not saved; the specific process is: If d|R(A)-E(b)|<τ dt , the pairing is successful and [R(A), E(b)] is saved; R(A) represents the index of the position of the maximum peak; If d|R(A)-E(b)|≥τ dt , then the pairing between the largest peak and the first peak of the second largest peak will not be saved; S4.3.3: Calculate the absolute value of the time delay difference between the first peak of the maximum peak and the second largest peak, and determine whether the absolute value of the time delay difference between the first peak of the maximum peak and the second largest peak exceeds the Doppler tolerance. If the absolute value of the time delay difference between the first peak of the maximum peak and the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, then the pairing of the first peak of the maximum peak and the second largest peak is saved; if the absolute value of the time delay difference between the first peak of the maximum peak and the second largest peak exceeds the Doppler tolerance, then the pairing of the first peak of the maximum peak and the second largest peak is not saved; the specific process is: If d|R(B)-E(a)|<τ dt , the pairing is successful and [R(B), E(a)] is saved; R(B) represents the index of the position of the second largest peak; If d|R(B)-E(a)|≥τ dt , then the pairing of the largest peak and the second largest peak will not be saved; S4.3.4: Calculate the absolute value of the time delay difference between the maximum peak and the second largest peak, and determine whether the absolute value of the time delay difference between the maximum peak and the second largest peak exceeds the Doppler tolerance. If the absolute value of the time delay difference between the maximum peak and the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, then the pairing of the maximum peak and the second largest peak is saved. If the absolute value of the time delay difference between the maximum peak and the second largest peak exceeds the Doppler tolerance, then the pairing of the maximum peak and the second largest peak is not saved. The specific process is as follows: If d|R(A)-R(B)|<τ dt , then the pairing is successful and [R(A), R(B)] is saved; If d|R(A)-R(B)|≥τ dt , the pairing of the largest peak and the second largest peak will not be saved.

7. A differential spread spectrum underwater acoustic remote control method resistant to channel interference and Doppler according to claim 6, characterized in that: In S5, the processing system of the surface mother ship obtains the working status of the UUV according to the content of the successfully matched response signal. The specific process is as follows: S5.1: Calculate the Doppler influence factor; S5.2: intercepting the reply signal according to the Doppler influence factor calculated in S5.1 to obtain an interception information code; S5.3: construct a channel function, and deconvolve the channel function with the information code intercepted in step S5.2 to obtain the deconvolved intercepted information code; S5.4: performing orthogonal demodulation on the intercepted information code after deconvolution obtained in S5.3 to obtain a demodulated information code; S5.5: Despread the demodulated information code obtained in S5.4 using a copy correlator to obtain a despread information code; S5.6: Remove the last code element from the despread information code obtained in S5.5 to obtain signal A p1 ; Remove the first code element from the despread information code obtained in S5.5 to obtain signal A p2 ; The signal A p1 and signal A p2 After approximate processing and conjugate multiplication, we get the signal D p ; S5.7: Signal D obtained from S5.6 p Modulo, peak search and symbol decision processing are performed to obtain the final N-1-bit information code, and the working status of the UUV is obtained according to the content of the final N-1-bit information code.

8. The differential spread spectrum underwater acoustic remote control method against channel interference and Doppler according to claim 7, characterized in that: The Doppler influence factor is calculated in S5.1; the specific process is: Among them, t ld is the delay interval between the pilot code and the Doppler calibration code in the reply signal transmitted by the UUV, t l ' d The time interval between the successfully matched pilot code and Doppler calibration code; In S5.2, the information code is intercepted according to the Doppler influence factor calculated in S5.1; the specific process is: S5.2.1: Calculate the time interval between the successfully matched guide code and information code. The specific process is as follows: t′ lm =t lm *(1-P)(3) Among them, t lm is the time interval between the guidance code and information code of the UUV transmission signal, * represents multiplication, t′ lm The time interval between the successfully matched guide code and information code; S5.2.2: Based on the position of the peak with the smaller delay value among the two correlation peaks saved in step S4.3 and the time interval t′ between the successfully matched pilot code and information code lm , intercept the response signal and obtain the interception information code y(t)=[x(t1),x(t2),...,x(t k )],k∈[1,N] The expression of the kth code element of the intercepted information code is: Among them, x(t k ) represents the expression of intercepting the kth code element of the information code, d(t k ) represents the polarity of the k-th bit intercepted information code, n is the number of code chips in a code element, C n (t k ) represents the kth intercepted information code element with n code chips, w represents the carrier frequency affected by Doppler, Δw k represents the residual Doppler of the kth intercepted information code element after Doppler compensation, is the sampling error of the receiving end for the kth intercepted information code element, n(t k ) is Gaussian white noise, t k It represents the time length of the kth intercepted information code symbol, T1 is the number of cycles occupied by a code chip in the intercepted information code symbol after being modulated, k∈[1,N], N is the total number of intercepted information code symbols; S5.3: construct a channel function, and deconvolve the channel function with the information code intercepted in step S5.2 to obtain the deconvolved intercepted information code; the specific process is: S5.3.1: Record the range T after the pilot code correlation peak X The size and index of the relevant peak envelope within, the index set is t est , S5.3.2: Construct the channel function h(t est ), the specific process is: The correlation peak envelope size obtained in step 5.3.1 is matched with the index one by one, and the index without index is set to 0; S5.3.3: Deconvolve the channel function obtained in S5.3.2 with the information code intercepted in step S5.2 to obtain the deconvolved intercepted information code y(t k ); the specific process is: y(t k )=x(t k )*h(-t est ) (4)。 9. The differential spread spectrum underwater acoustic remote control method against channel interference and Doppler according to claim 8, characterized in that: In S5.4, the deconvolved intercepted information code obtained in S5.3 is orthogonally demodulated to obtain a demodulated information code; the specific process is: S5.4.1: The deconvolved intercepted information code y(t k ) is demodulated through the sinusoidal channel to obtain the signal Q(t k ); The deconvolution information code y(t k ) is demodulated by two orthogonal channels of the cosine channel to obtain the signal I(t k ); S5.4.2: Obtain the signal Q(t k ) is processed by a low-pass filter to obtain the signal Q'(t k ); S5.4.1 obtains the signal I(t k ) is processed by a low-pass filter to obtain the signal I'(t k ); S5.4.3: Transform the signal Q'(t k ) as the imaginary part, the signal I'(t k ) as the real part to form a complex signal, and obtain the final orthogonal demodulation result. The composed complex signal is the demodulated information code.

10. A differential spread spectrum underwater acoustic remote control method resistant to channel interference and Doppler according to claim 9, characterized in that: The intercepted information code y(t k ) is demodulated through the sinusoidal channel to obtain the signal Q(t k ); The deconvolution information code y(t k ) is demodulated by two orthogonal channels of the cosine channel to obtain the signal I(t k ); the specific process is: Among them, I(t k ) is the tth k The signal expression of code element; Q(t k ) is the tth k Signal expression of code elements; In said S5.4.2, the signal Q(t k ) is processed by a low-pass filter to obtain the signal Q'(t k ); S5.4.1 obtains the signal I(t k ) is processed by a low-pass filter to obtain the signal I'(t k ); the specific process is: Among them, I'(t k ) is I(t k ) after passing through the low-pass filter k The signal expression of code elements, Q'(t k ) is Q(t k ) after passing through the low-pass filter k Signal expression of code elements; In S5.4.3, the signal Q'(t k ) as the imaginary part, the signal I'(t k ) as the real part to form a complex signal, and obtain the final orthogonal demodulation result. The complex signal formed is the demodulated information code. The specific process is: S p (t k )=I'(t k )+i*Q'(t k ) (9) Among them, S p (t k ) is the signal expression of the kth code element of the demodulated information code, i represents the imaginary unit, In S5.5, the demodulated information code obtained in S5.4 is despread using a copy correlator to obtain a despread information code; the specific process is: The local signal of the spread spectrum code stored by the surface mother ship is copied and correlated with the demodulated information code obtained in S5.4 to obtain the despread information code. The specific process is as follows: Among them, A p (t k ) represents the kth code element of the despread information code, <·> is the copy correlation operation, In S5.6, the last code element of the despread information code obtained in S5.5 is removed to obtain signal A. p1 ; Remove the first code element from the despread information code obtained in S5.5 to obtain signal A p2 ; The signal A p1 and signal A p2 After approximate processing and conjugate multiplication, we get the signal D p ; The specific process is: The despread information code {A p (t1),A p (t2),…,A p (t N )} Remove the last code element to get signal A p1 , the specific process is: A p1 ={A p (t1),A p (t2),…,A p (t N-1 )} (11) The despread information code {A p (t1),A p (t2),…,A p (t N )} Remove the first code element to get signal A p2 , the specific process is: A p2 ={A p (t2),…,A p (t N-1 ),A p (t N )} (12) The signal A p1 and signal A p2 After approximate processing and conjugate multiplication, we get the signal D p ; The specific process is: D p =A p1 .*conj(A p2 ) (13) Among them, A p1 .Indicates signal A p1 The conjugate signal of ; conj(·) represents the conjugate function; Signal D p The expression of a single code unit is: In S5.7, the signal obtained in S5.6 is subjected to modulus extraction, peak search and symbol determination processing to obtain the final information code. The specific process of obtaining the working status of the UUV according to the content of the final information code is as follows: S5.7.1: For signal D p Perform modulo processing to obtain the signal D after modulo processing p1 ; S5.7.2: Signal D after modulo processing p1 Perform peak search to obtain the signal D after modulo processing p1 N-1 peak points; S5.7.3: Determine the signal D after modulo processing p1 The positive and negative signs of the real part values ​​corresponding to the peak points are determined. If the real part value is positive, the code element is judged to be 1. If the real part value is negative, the code element is judged to be 0, and the final N-1-bit information code is obtained. The processing system of the surface mother ship obtains the working status of the UUV according to the content of the final N-1-bit information code.

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