A differential spread spectrum underwater acoustic remote control method against channel interference and Doppler

Abstract

The present application relates to the field of underwater acoustic control, especially to a differential spread spectrum underwater acoustic remote control method resisting channel interference and Doppler, and proposes a differential spread spectrum signal processing method based on an underwater acoustic remote control system, and proposes a set of peak search and deconvolution combined anti-multipath interference method for multipath effect, and for noise and Doppler influence, first, the response signal of the UUV uses a differential spread spectrum signal in a symbol differential mode, and when solving, first, a double pulse method is used for coarse compensation of the Doppler, and then a quadrature receiver is used for quadrature demodulation to obtain two signals, and finally, the differential conjugate multiplication form can be used in the differential solving link to try to offset the coefficients containing residual Doppler and sampling errors. Simulation results show that compared with the traditional method, the anti-noise and anti-multipath ability of the present application is stronger, and when the relative motion speed between the UUV and the surface mother ship is small, the present application has a lower bit error rate.

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 energy form currently capable of long-distance underwater propagation, sound waves are the information carrier of choice for most underwater acoustic systems. However, the extremely complex underwater environment still presents numerous challenges for information transmission. In underwater channels, there is always more than one propagation path between the transmitter and receiver. The complex spatiotemporal and frequency-varying characteristics of underwater channels exacerbate the impact of multipath on the quality of underwater acoustic remote control communications. Underwater channels behave like comb filters in the frequency domain. In the time domain, multipath distorts the amplitude and phase of the signal, weakening the correlation between the received signal and the local signal and reducing the spread spectrum gain. The waveforms of preceding and succeeding symbols also undergo varying degrees of compression or broadening, resulting in inter-symbol crosstalk. Numerous methods are currently available in the underwater acoustic field to mitigate the degradation of communication quality caused by multipath, including spread spectrum technology, orthogonal frequency division multiplexing, and single-carrier frequency domain equalization. Spread spectrum signals have excellent correlation characteristics, resulting in strong multipath immunity. Common differential spread spectrum methods include symbol differential and chip differential. Due to the complexity of underwater channels, the spectrum of the received signal is broadened by noise and multipath, resulting in a typically small temporal correlation radius. However, the chip differential method requires differential coherent demodulation at the receiver, and the pulse width of a single chip is relatively narrow, making it less robust to multipath and noise interference than the symbol differential method.

[0003] Due to the low-speed propagation of sound waves in water, if there is relative motion between the transmitting and receiving signals, the Doppler effect will cause the signal's carrier frequency to shift, resulting in a significant mismatch with the local carrier and errors during demodulation. Furthermore, the signal can be expanded or compressed in the time or frequency domain due to the Doppler effect, affecting symbol synchronization and increasing the bit error rate. The pseudorandom code used in spread-spectrum signals can broaden the modulated signal's spectrum, reducing the signal's sensitivity to Doppler, but its Doppler immunity is limited. Therefore, it is necessary to estimate the Doppler factor to improve synchronization accuracy.

[0004] Common Doppler estimation techniques include time domain and frequency domain processing methods.

[0005] Time-domain processing methods primarily focus on designing the transmitted signal, then cross-correlating the local signal with the received signal to obtain a rough Doppler estimate. Existing solutions utilize a multi-correlator Doppler compensation method based on variable sampling, estimating the Doppler shift by comparing the correlators with the largest correlation peaks. These existing solutions interpolate numerous Doppler-insensitive and highly correlated signals into the signal, frequently iterating the Doppler shift and residuals during signal reception. 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 are more mature, but the calculations of such methods are usually very complex and need to be used according to actual environmental conditions. Frequency domain signal processing method 1: First, use the fitting approximation method in the frequency domain to measure the signal frequency, obtain the Doppler factor, and then perform coarse compensation on the signal. Then, use a method with multiple iterations in the detection domain to perform fine compensation. Method 2: Use EMD (Empirical Mode Decomposition) to decompose the frequency components of the signal and estimate the Doppler frequency offset. Then, use the WFFT (Wavelet-FFT, WFFT) Doppler suppression algorithm to compensate for the residual Doppler. Method 3: Narrowband filter the received signal and perform a fast Fourier transform. 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 therefore 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 present invention aims to solve the problem in the prior art that underwater acoustic remote control cannot obtain accurate UUV status information due to channel interference and Doppler interference. We propose a differential spread spectrum underwater acoustic remote control method that is resistant to channel interference and Doppler interference.

[0010] 1. Deployment and communication mode of surface mother ship and underwater UUVs Figure 1The surface carrier can carry GPS, passive sonar hydrometers, and other equipment to obtain location, distance, and hydrological parameters. Before launching, the UUV will store prior information such as the frequency and structure of the broadcast signal emitted by the surface carrier.

[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 of the UUV, the moving direction, the moving speed, etc.

[0014] S3: Each UUV generates a response signal based on the corrected working status. Each UUV uses a different response delay and takes turns transmitting its own response signal to the surface carrier.

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

[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 signals of UUVs in real time, thereby achieving 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. This invention addresses multipath interference by proposing a method that combines peak search with deconvolution. To address noise and Doppler effects, the UUV's reply signal utilizes a differential spread spectrum signal using symbol differentials. During the decomposition process, a dual-pulse method is used for coarse Doppler compensation. Then, an orthogonal receiver performs orthogonal demodulation to obtain two signals. Finally, during the decomposition phase, differential conjugate multiplication is used to minimize the coefficients containing residual Doppler and sampling errors.

[0021] 2. 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.

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

[0023] Figure 1 This 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 This is a schematic diagram comparing the noise immunity 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 the signal waveform after the differential solution of 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] Figure 9 Schematic diagram of the effect of different movement speeds of the UUV on the bit error rate of the present invention;

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

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

[0034] Figure 12 It is a schematic diagram of the channel function of the present invention;

[0035] Figure 13 Schematic diagram of decoding without deconvolution of the present invention;

[0036] Figure 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 present invention is described, comprising:

[0038] 1. Deployment and communication mode of surface mother ship and underwater UUVs Figure 1 The surface carrier can carry GPS, passive sonar hydrometers, and other equipment to obtain location, distance, and hydrological parameters. Before launching, the UUV will store prior information such as the frequency and structure of the broadcast signal emitted by the surface carrier.

[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 based on the corrected working status. Each UUV uses a different response delay and takes turns transmitting its own response signal to the surface carrier.

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

[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 signals of UUVs in real time, thereby achieving more accurate control of the operating status of multiple UUVs.

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

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

[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 using differential coding 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 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] Other steps and parameters are the same as those in the first embodiment.

[0055] Specific embodiment three: This embodiment differs from specific embodiment one in that:

[0056] In S4, the UUV sends a response signal at a fixed time interval. The processing system of the surface mother ship pairs the pilot code and the Doppler calibration code of the received response signal once per frame. If the match is successful, S5 is performed. If the match is unsuccessful, the system waits for the response signal received in the next frame. 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 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 the next frame of data is waited for. The other steps and parameters are the same as those in one of the specific implementation methods one to two.

[0060] Specific embodiment 4: This embodiment differs from specific embodiments 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 the correlation peak envelope; the specific process is:

[0062] S4.1.1: Input the response signal received by the surface mother ship into the bandpass filter and output the filtered response 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 stored in the surface mother ship, perform modulo processing on the result of the copy correlation processing to obtain the correlation peak envelope. The other steps and parameters are the same as those in one of the specific implementation methods one to three.

[0065] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that, in S4.2, a peak 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 as follows:

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

[0067] The maximum peak on both sides of t p1 The second is determined as the group where the maximum peak is located;

[0068] S4.2.2: Before the maximum peak position t p2 In seconds, let t p1 >t p2 , the first peak that meets the search conditions found in the time sequence 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 cluster containing the largest peak in the correlation peak envelope to obtain the remaining correlation peak envelope, traverse all peaks of the remaining correlation peak envelope, and 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 found in chronological order is the first peak of the second largest peak. Other steps and parameters are the same as those in one of the specific implementation methods one to four.

[0072] Specific embodiment 6: This embodiment differs from specific embodiments 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 next frame of data is waited for. If the pairing is successful, S5 is performed for subsequent calculation. The specific process is as follows:

[0074] S4.3.1: Calculate the absolute value of the time delay difference between the first peak of the largest 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 largest 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 largest peak and the first peak of the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, and the pairing of the first peak of the largest peak and the first peak of the second largest peak is saved. If the absolute value of the time delay difference between the first peak of the largest peak and the first peak of the second largest peak exceeds the Doppler tolerance, the pairing of the first peak of the largest peak and the first peak of the second largest peak is not saved. The specific process is as follows:

[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 between 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, and 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, the pairing of the maximum peak and the first peak of the second largest peak is not saved. The specific process is as follows:

[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 maximum peak position;

[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, and 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, the pairing of the first peak of the maximum peak and the second largest peak is not saved. The specific process is as follows:

[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 between the largest peak and the second largest peak will not be saved;

[0083] S4.3.4: Calculate the absolute value of the delay difference between the maximum peak and the second largest peak, and determine whether the absolute value of the delay difference between the maximum peak and the second largest peak exceeds the Doppler tolerance. If the absolute value of the delay difference between the maximum peak and the second largest peak does not exceed the Doppler tolerance, that is, the pairing is successful, and the pairing of the maximum peak and the second largest peak is saved. If the absolute value of the delay difference between the maximum peak and the second largest peak exceeds the Doppler tolerance, 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 embodiment 7: This embodiment differs from specific embodiments 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 matched response signal. The specific process is as follows:

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

[0089] S5.2: intercept 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: Perform orthogonal demodulation on the deconvolved intercepted information code obtained in S5.3 to obtain a demodulated information code;

[0092] S5.5: Despread the demodulated information code obtained in S5.4 using a replica 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 and get signal A p2 ;

[0095] 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 judgment 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 the first to sixth embodiments.

[0098] Specific embodiment eight: This embodiment differs from specific embodiments 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 time delay 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 step S5.2, the information code is intercepted based on the Doppler influence factor calculated in step S5.1. The specific process is as follows:

[0103] S5.2.1: Calculate the time interval between the successfully matched preamble 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 pilot code and the 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 intercepted 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 intercepted information code, n is the number of 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 kth intercepted information code element at the receiving end, n(t k ) is Gaussian white noise,

[0110]

[0111] t k Indicates 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 step S5.3, a channel function is constructed and deconvolved with the information code intercepted in step S5.2 to obtain the deconvolved intercepted information code. The specific process is as follows:

[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 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 mapped one to 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 deconvolved intercepted information code. The specific process is as follows:

[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 embodiment 9: This embodiment differs from specific embodiments 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 as follows:

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

[0121] The intercepted information code y(t k ) is demodulated in two orthogonal ways through the cosine channel to obtain the signal I(t k );

[0122] S5.4.2: Convert 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 in the specific embodiments 1 to 8.

[0125] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that:

[0126] The intercepted information code y(tk ) Through the two-way 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 after quadrature demodulation through the cosine channel k Signal expression of code elements;

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

[0131] S5.4.2: Convert 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 is the demodulated information code. The specific process is:

[0138] Using Equation 7 and Equation 8 as the real part and imaginary part respectively to form a complex signal, the final orthogonal demodulation result, that is, the demodulated information code, is obtained, as shown in Equation 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 step S5.5, a copy correlator is used to despread the demodulated information code obtained in step S5.4 to obtain a despread information code. The specific process is as follows:

[0142] The spread spectrum code local signal 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] Because convolution requires continuous multiplication and accumulation operations, which consumes a lot of computing resources, the present invention uses fast Fourier transform to convert the received signal and the flipped local spread spectrum signal into frequency domain signals before performing the multiplication operation. This frequency domain-related method can significantly reduce computational complexity and more easily meet the requirements of real-time processing.

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

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

[0148] 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 Equation 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 obtain 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] 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 symbol is very short, it can be assumed that the difference in Doppler and sampling error between two adjacent symbols is very small, so it can be approximately obtained that

[0159]

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

[0161]

[0162] In step S5.7, the signal obtained in step S5.6 is subjected to symbol determination and peak search 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: Modulo processed signal D 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 or negative sign of the real part value corresponding to the peak point of the signal is 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 methods one to nine.

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

[0167] 1. Noise immunity

[0168] Assume the received signal has a 10kHz carrier frequency, a pseudo-random spreading code, and 1000 symbols. Compare the noise immunity of the symbol difference, chip difference, and the proposed method at different signal-to-noise ratios. Perform 300 Monte Carlo simulations for each condition, varying the signal-to-noise ratio from -26dB to -6dB in 2dB steps.

[0169] like Figure 5As shown in the figure, above -6dB, the three methods perform well. As the signal-to-noise ratio gradually decreases, the bit error rate of the chip difference method increases rapidly. When the signal-to-noise ratio drops below -15dB, the noise immunity of the method of the present invention is slightly improved compared to the traditional symbol 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 in Figure 1, the UUV is initially 200 meters away from the surface carrier and moves away from the carrier at a constant speed v. Assuming that each symbol is short, the Doppler effect on each symbol is determined by the speed of the surface carrier when it first receives the symbol, and the influence of sampling error is ignored.

[0172] The two linear frequency modulation signals have a center frequency of 3 kHz, a bandwidth of 2 kHz, and a duration of 0.015 seconds. The pilot code and Doppler calibration code are separated from the differential spread spectrum signal by 0.03 seconds. 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 from the figure that the present invention has a better effect on Doppler compensation. coefficient, so in Figure 7 The influence of the incompletely compensated Doppler factor on the signal waveform can be clearly seen in the figure.

[0174] Let the UUV's speed change from 0m / s to 10m / s, and calculate the final bit error rate every 0.5m / s. Figure 9 The figure compares the Doppler tolerance of the method of the present invention and a conventional method. The conventional method uses only a single channel for demodulation and employs a staggered multiplication method for the final differential solution. Both methods use a dual-pulse method to compensate for Doppler. The blue and red curves are the bit error rate curves for the conventional and the method of the present invention, respectively. It can be seen that the Doppler tolerance of the present invention is relatively high, and the bit error rate remains low when the UUV's movement speed is within 10 m / s.

[0175] 3. Anti-multipath capability

[0176] Figure 10 This is the actual response signal collected during a lake test in 2023, with a sending and receiving distance of approximately 600 meters. Figure 11The correlation peak envelope of the pilot code reveals the extremely complex underwater channel conditions. After coherent superposition, the correlation peak height of the multipath signal exceeds that of the direct signal. Therefore, when channel conditions are complex, it is necessary to search for multiple correlation peaks and conduct multiple matching attempts. Since the signal length used in this experiment was relatively short, the multipath structures after the pilot code and the information code can be assumed to be identical. Therefore, regardless of whether the multipath signal or the direct signal is ultimately matched, the final solution is likely to be correct.

[0177] The purpose of deconvolution is to focus the energy of multipath signals onto the direct signal. Figure 12 is the channel function obtained from the pilot code, and Figure 13 and Figure 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 Figure 13 Decoding failed and Figure 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 response to the multipath effect, the present invention proposes a set of anti-multipath interference methods that combine peak search with deconvolution. In response to the influence of noise and Doppler, the UUV's response signal first uses a differential spread spectrum signal in a symbol differential manner, and when solving the problem, 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. 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. Simulation results show that compared with traditional methods, 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 has low computational complexity and can suppress Doppler, noise and multipath effects. Therefore, it has the characteristics of being easy to implement, having strong real-time performance and strong anti-interference ability, 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-mentioned specific implementation methods. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent replacements and improvements 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 scope of protection 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. 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 based on the acquired working status. Each UUV uses a different response delay and takes turns transmitting its own response signal to the surface carrier. The specific process is as follows: S3.1: Each UUV encodes its own working status into an original information code in binary form, and then encodes the original information code using differential coding 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 t ld ; S4: The UUV sends a response signal at a fixed time interval. The surface mother ship pairs the pilot code with the Doppler calibration code for each frame of the response signal received. If the pairing is successful, it proceeds to S5. If the pairing is unsuccessful, it waits for the next frame of the response signal. 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; the specific process is as follows: S4.2.1: Traverse all peaks of the relevant peak envelope and find the location and height of the maximum peak. The maximum peak on both sides of t p1 Seconds are determined as the group where the maximum peak is located; S4.2.2: Before the maximum peak position t p2 In seconds, let t p1 >t p2 , the first peak that meets the search conditions found in the time sequence 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 cluster containing the largest peak in the correlation peak envelope to obtain the remaining correlation peak envelope, traverse all peaks of the remaining correlation peak envelope, and 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 conditions found in the time sequence is 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 the next frame of data is waited for. This includes: S4.3.1: Calculate the absolute value of the time delay difference between the first peak of the largest 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 largest peak and the first peak of the second largest peak exceeds the Doppler tolerance. S4.3.2: Calculate the absolute value of the time delay difference between the largest peak and the first peak of the second largest peak, and determine whether the absolute value of the time delay difference between the largest peak and the first peak of the second largest peak exceeds the Doppler tolerance. S4.3.3: Calculate the absolute value of the time delay difference between the first peak of the largest peak and the second largest peak, and determine whether the absolute value of the time delay difference between the first peak of the largest peak and the second largest peak exceeds the Doppler tolerance. S4.3.4: Calculate the absolute value of the delay difference between the largest peak and the second largest peak, and determine whether the absolute value of the delay difference between the largest peak and the second largest peak exceeds the Doppler tolerance; 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 resistant to channel interference and Doppler according to claim 1, characterized in that: In S4.1, the response signal received by the surface mother ship is subjected to copy correlation processing to obtain the correlation peak envelope; the specific process is: S4.1.1: Input the response signal received by the surface mother ship into the bandpass filter and output the filtered response 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 pilot 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; In S5, the processing system of the surface mother ship obtains the working status of the UUV according to the content of the matched response signal. The specific process is as follows: S5.1: Calculate the Doppler influence factor; S5.2: intercept 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: Perform orthogonal demodulation on the deconvolved intercepted information code obtained in S5.3 to obtain a demodulated information code; S5.5: Despread the demodulated information code obtained in S5.4 using a replica 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 and get signal A p2 ; 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 judgment 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.

3. The differential spread spectrum underwater acoustic remote control method resistant to channel interference and Doppler according to claim 2, characterized in that: The Doppler influence factor is calculated in S5.1; the specific process is: Among them, t ld is the time delay 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; In step S5.2, the information code is intercepted based on the Doppler influence factor calculated in step S5.

1. The specific process is as follows: S5.2.1: Calculate the time interval between the successfully matched preamble 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 pilot code and the 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: The time interval t′ between the position of the peak with the smaller delay value among the two correlation peaks saved in step S4.3 and the successfully matched pilot code and information code lm , intercept the response signal and obtain the intercepted 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 intercepted information code, n is the number of 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 kth intercepted information code element at the receiving end, n(t k ) is Gaussian white noise, t k Indicates 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 as follows: 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 t est , S5.3.2: Construct the channel function h(t est ), the specific process is: The corresponding indexes are mapped to the corresponding envelope sizes obtained in step 5.3.

1. If there is no index, set it 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)。 4. The differential spread spectrum underwater acoustic remote control method resistant to channel interference and Doppler according to claim 3, 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 as follows: S5.4.1: The deconvolution-derived information code y(t k ) is demodulated through the sinusoidal channel to obtain the signal Q(t k ); The intercepted information code y(t k ) is demodulated in two orthogonal ways through the cosine channel to obtain the signal I(t k ); S5.4.2: Convert 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 complex signal is the demodulated information code.

5. The differential spread spectrum underwater acoustic remote control method resistant to channel interference and Doppler according to claim 4, characterized in that: The intercepted information code y(t k ) is demodulated through the sinusoidal channel to obtain the signal Q(t k ); The intercepted information code y(t k ) is demodulated in two orthogonal ways through the cosine channel to obtain the signal I(t k ); the specific process is: Among them, I(t k ) is the tth after quadrature demodulation through the cosine channel k The signal expression of code elements; 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 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 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 step S5.5, a copy correlator is used to despread the demodulated information code obtained in step S5.4 to obtain a despread information code. The specific process is as follows: The spread spectrum code local signal 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 step S5.6, the last code element of the despread information code obtained in step S5.5 is removed to obtain signal A. p1 ; Remove the first code element from the despread information code obtained in S5.5 and get signal A p2 ; 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 obtain signal A p2 The specific process is: A p2 ={A p (t2),…,A p (t N-1 ),A p (t N )} (12) 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 step S5.7, the signal obtained in step S5.6 is subjected to modulus extraction, peak search, and symbol determination 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: S5.7.1: For signal D p Perform modulo processing to obtain the signal D after modulo processing p1 ; S5.7.2: Modulo processed signal D 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 or negative sign of the real part value corresponding to the peak point is 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 based on the content of the final N-1-bit information code.

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