Underwater multi-target positioning method based on mixed spread spectrum waveform

Abstract

The invention discloses an underwater multi-target positioning method based on a mixed spread spectrum waveform, and the method comprises the following steps: generating an underwater multi-target chaotic spread spectrum sequence through a chaotic algorithm, sequentially carrying out the pulse forming, up-sampling and carrier modulation of a generated chaotic spread spectrum code, and generating a positioning signal of a u underwater target; the u-th underwater target carries out channel coding on the data stream containing the depth information to obtain a coded data stream, and sequentially carries out spread spectrum, pulse shaping and BPSK modulation on the coded data stream to obtain a communication signal of the u-th underwater target; mixing the positioning signal and the communication signal to obtain a mixed signal; generating a PWM signal based on the mixed signal, and sending the PWM signal to a positioning array; the positioning array carries out positioning resolving processing and communication demodulation processing in parallel based on the received signal to obtain positioning time delay and depth information, and uploads the depth information and the positioning time delay to a total base station; and the total base station obtains the coordinate information of the underwater target based on the positioning time delay and the depth information.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater positioning, and specifically relates to an underwater multi-cooperative target positioning method based on a hybrid spread spectrum waveform. Background Art

[0002] Safe operation in the underwater environment is inseparable from underwater acoustic positioning and underwater acoustic communication technologies. However, the complexity of the ocean environment poses severe challenges to underwater acoustic positioning and communication. The existing application method that uses two sets of independent devices to complete the positioning and communication functions can no longer meet the current requirements for low maintenance cost and low cost, and has the following disadvantages:

[0003] (1) Using repeated sequences of pseudo-random sequences such as m-sequences and gold codes as spreading codes, due to the periodic repetition characteristics of the spreading codes, the spread spectrum signals have obvious spectral characteristics, resulting in a decrease in the anti-frame capture and anti-interception capabilities of signal reception;

[0004] (2) A modulator with a pseudo-random sequence that completely changes with time as the spreading code has high implementation complexity and high cost in engineering;

[0005] (3) The traditional underwater acoustic spread spectrum communication frame structure is complex, and the synchronization signal is affected by the fast fading characteristics and multipath of the underwater acoustic channel, resulting in inaccurate synchronization;

[0006] (4) The realization of the positioning and communication functions is achieved through a time-sharing method. Therefore, the positioning and communication efficiency is extremely low. Summary of the Invention

[0007] Object of the Invention: To solve the defects existing in the existing application method that uses two sets of independent devices to complete the positioning and communication functions, the present invention proposes an underwater multi-cooperative target positioning method based on a hybrid spread spectrum waveform.

[0008] Technical Solution: An underwater multi-target positioning method based on a hybrid spread spectrum waveform, comprising the following steps:

[0009] Step 1: Use a chaos algorithm to generate an underwater multi-target chaos spread spectrum sequence. Among them, the chaos spread spectrum code of the u-th underwater target is expressed as In the formula, L is the code length of the chaos spread spectrum sequence, is the l-th code element of the chaos spread spectrum sequence of the u-th underwater target, and its value is 1 or -1;

[0010] Based on the generated chaos spread spectrum code p u , use a pulse shaping filter to perform pulse shaping on the chaos spread spectrum code;

[0011] Perform upsampling on the signal after pulse shaping, and then perform carrier modulation to generate the positioning signal of the u-th underwater target;

[0012] Step 2: The u-th underwater target performs channel coding on the data stream containing depth information to obtain the encoded data stream, and uses the chaotic spread spectrum code p generated in Step 1 u The encoded data stream is spread spectrum to obtain a spread spectrum signal. A pulse shaping filter is used to perform pulse shaping on the spread spectrum signal. BPSK modulation is adopted, and based on the local carrier, the pulse-shaped spread spectrum signal is encoded to obtain the communication signal of the u-th underwater target;

[0013] Step 3: The positioning signal and the communication signal are mixed to obtain a mixed signal; based on the mixed signal, a PWM signal is generated and sent to the positioning array, and the positioning array is composed of multiple buoy base stations;

[0014] Step 4: The positioning array performs positioning calculation processing and communication demodulation processing in parallel based on the received signal to obtain the positioning time delay and depth information, and uploads the depth information and the positioning time delay to the general base station;

[0015] Step 5: The general base station obtains the coordinate information of the underwater target based on the positioning time delay and the depth information.

[0016] Further, assume that the signal received by the positioning array is expressed as:

[0017]

[0018] where r u (t) represents the signal of the u-th underwater target received, and s u (t) represents the mixed signal, h u (t) is the impulse response of the underwater acoustic channel, and n(t) is Gaussian white noise with a mean of zero and a variance of ;

[0019] The positioning calculation processing, the specific operations include:

[0020] First, for the u-th underwater target, perform the following related operations to obtain a related waveform, expressed as:

[0021]

[0022] In the formula, f u (t) is a matched filter composed of the chaotic spread spectrum sequence of the u-th user;

[0023] Perform three-point interpolation fitting on the related waveform R(τ u,n ) to obtain the positioning time delay τ of the u-th underwater target relative to the n-th buoy base station in the positioning array u,n ;

[0024] Secondly, perform the same operations as in the previous step on other underwater targets to obtain the positioning time delays of multiple users relative to each buoy base station in the positioning array.

[0025] Further, perform three-point interpolation fitting on the correlation waveform R(τ u,n ) to obtain the positioning time delay τ u,n of the u-th underwater target relative to the n-th buoy base station in the positioning array. The specific operations include:

[0026] Take the maximum point (t2, r2) of the detected correlation waveform R(τ u,n ) and the two points (t1, r1) and (t3, r3) before and after it. Then the following equations are satisfied:

[0027]

[0028] Calculate through the above equations to obtain:

[0029]

[0030] After arrangement, we get:

[0031] r3sinω r (t1 - t2) = r2sinω r (t1 - t3) - r1sinω r (t2 - t3)

[0032] where t3 - t2 = t2 - t1 = t s , t s is the sampling period;

[0033] We can obtain:

[0034] r3sin(ω r t s ) = 2r2sin(ω r t s )cos(ω r t s ) - r1 sin(ω r t s )

[0035] Since ω r ≈2πf0, and f s ≥2f0, so 0 < ω r t s < π, thus sin(ω r t s ) ≠ 0;

[0036] So we have:

[0037]

[0038] Thus, ω is estimated. r The value is:

[0039]

[0040] R(τ) is expressed as:

[0041]

[0042] Then when |R(τ)| reaches the maximum value, and thus the time delay is estimated:

[0043]

[0044] Because So there is:

[0045]

[0046] Estimate the exact position of the correlation waveform R(τ u,n ), and thus estimate the positioning time delay τ of the u-th underwater target relative to the n-th buoy base station in the positioning array u,n .

[0047] Furthermore, the communication demodulation process, the specific operations include:

[0048] Perform band-pass filtering on the mixed signal;

[0049] Intercept the signal from the band-pass filtered mixed signal, and use a decision feedback equalizer to perform phase estimation on the intercepted signal to obtain the phase-estimated signal;

[0050] Use the chaotic spreading code and local carrier of the u-th underwater target to demodulate and despread the phase-estimated signal, and then perform decision-making to obtain the depth information;

[0051] Upload the obtained depth information to the master base station.

[0052] Furthermore, in step 5, the master base station obtains the coordinate information of the underwater target based on the positioning time delay and depth information, and the specific operations include:

[0053] According to the positioning time delay and depth information of the signals sent by each underwater target to each buoy base station, and according to the relationship between the u-th underwater target and the positioning array, obtain their relative distances:

[0054]

[0055] Among them, is the true position of the u-th underwater target, that is, the coordinate information to be solved, is the coordinate of the m-th buoy base station, is the relative distance from the u-th underwater target to the m-th buoy base station, obtained through the speed of sound c and the positioning time delay;

[0056] The coordinate information of the underwater target is calculated using geometric methods.

[0057] Furthermore, the steps of using BPSK modulation, based on the local carrier, to encode the spread-spectrum signal after pulse shaping to obtain a communication signal are as follows:

[0058] The encoded data stream is expressed as where N d is the total number of bits transmitted; the spread-spectrum signal is the product of the encoded data stream d and the chaotic sequence spreading code;

[0059] The spread-spectrum signal is used as the baseband signal, expressed as:

[0060]

[0061] In the formula, a n represents the data of each bit, T d represents the duration of a spreading code signal, p represents the spreading code sequence, f s represents the sampling frequency;

[0062] The baseband signal is modulated to the passband to obtain the communication signal of the u-th underwater target:

[0063] s[t] = g(t)cos(2πf c t), 0 < t < T c

[0064] In the formula, f c represents the carrier frequency, T c represents the duration of the spreading sequence symbol, cos(2πf c t) represents the local carrier.

[0065] Furthermore, the steps of intercepting the signal from the band-pass filtered mixed signal, using a decision feedback equalizer to perform phase estimation on the intercepted signal to obtain the phase-estimated signal, and using the chaotic spreading code and local carrier of the u-th underwater target to demodulate and despread the phase-estimated signal and then make a decision to obtain the depth information can be replaced with the following steps:

[0066] Intercept the signal from the band-pass filtered mixed signal;

[0067] Multiply each segment of the communication signal with the local signal s +1 (n) and the local signal s -1(n) Perform matched filtering to obtain the correlation results of 0 and the correlation results of 1;

[0068] If the correlation result of 1 is greater than the correlation result of 0, then this section of the communication signal is judged as 0, otherwise it is judged as 1; thus obtaining the depth information;

[0069] Among them, the local signal s +1 (n) and the local signal s -1 (n) are two groups of signals modulated to the passband after the data 0 and the data 1 go through the processes of mapping, spreading spectrum, and pulse shaping.

[0070] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0071] (1) The method of the present invention utilizes the good autocorrelation of chaotic spread-spectrum symbols to mix and superimpose the spread-spectrum sequence signals, making the transmitted signal frame structure short and effective, and effectively avoiding the serious multipath effect caused by the complex and lengthy signal frame structure;

[0072] (2) The method of the present invention uses an adaptive equalization algorithm to compensate the channel estimation tap coefficients, greatly improving the stability of positioning communication;

[0073] (3) The method of the present invention meets the integrated requirements of underwater acoustic positioning and communication technologies. On the basis of using chaotic sequences as spread-spectrum codes, on the one hand, a sufficiently long direct spread-spectrum signal can achieve a higher detection signal-to-noise ratio gain, which helps to improve the reliability of the system; on the other hand, the superimposed communication waveform can transmit data information while positioning, improving the spectrum utilization rate of the system. At the same time, the positioning waveform is an interference signal to the opponent, thereby improving the concealment of the system. Description of the Drawings

[0074] Figure 1 It is the workflow block diagram of a method for underwater multi-cooperative target positioning and communication based on a hybrid spread-spectrum waveform proposed in Embodiment 1;

[0075] Figure 2 It is the flow block diagram of the overlap-save method proposed by the present invention;

[0076] Figure 3 It is the composition block diagram of the hybrid waveform in the present invention;

[0077] Figure 4 It is the flow block diagram of the hybrid spread-spectrum communication proposed in Embodiment 2;

[0078] Figure 5 It is the three-point inset of the correlation peak in the present invention;

[0079] Figure 6 It is the chip-level feedback equalizer in the present invention. Detailed Embodiments

[0080] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0081] Embodiment 1:

[0082] This embodiment proposes an underwater multi-cooperative target positioning method based on a hybrid spread-spectrum waveform. As Figure 1 shown, it mainly includes the following steps:

[0083] Step 1: Use the chaos algorithm to generate the chaotic spread-spectrum sequences of underwater multi-targets. For a chaotic spread-spectrum system with a maximum number of users U, the chaotic spread-spectrum code of the u-th (u ∈ {1,..., U}) underwater target is expressed as In the formula, L is the code length of the chaotic spread-spectrum sequence, also known as the spreading gain, is the l-th symbol of the chaotic spread-spectrum sequence of the u-th underwater target, and its value is 1 or -1. The correlation characteristics between different chaotic spread-spectrum codes are low, which is used to distinguish different users. Select the passband range as f L ~f H , the bandwidth is B, select half of the bandwidth as the chip rate R c , the chip duration T c = 1 / R c , and satisfy the relationship of T d = NT c , T d represents the duration of a chaotic spread-spectrum sequence. The selection of the spread-spectrum code should at least follow the following principles: (1) having sharp autocorrelation characteristics; (2) the cross-correlation value is as small as possible; (3) having sufficient and diverse sequences; (4) having a long symbol period.

[0084] In this step, a square root raised cosine filter is used as the pulse shaping filter to reduce inter-symbol interference (ISI). The square root raised cosine filter k[t] is expressed as:

[0085]

[0086] In the formula, N PT is the order of the square root raised cosine filter, n PT ∈[-N PT / 2, L, N PT / 2] represents the sampling points of k(t), α is the roll-off factor, and T represents the number of sampling points per chip T = f s / R c .

[0087] Use the square root raised cosine filter k[t] to perform pulse shaping on the generated chaotic spread-spectrum code p u to obtain the pulse-shaped chaotic sequence spread-spectrum code p u(t), expressed as:

[0088]

[0089] In the formula, T c is the chip period, p i u represents the elements of the spreading code sequence, k[·] represents the pulse shaping filter, i represents the sequence number of the current spreading code element, and t represents the time domain.

[0090] After pulse shaping, the bandwidth B is obtained c expanded to R c (1 + α) and needs to satisfy B c ≤B.

[0091] Using BPSK modulation, the chaotic sequence spreading code p after pulse shaping u is carrier - modulated to obtain the pass - band signal s u (t) = g u (t)cos(2πf c t), 0 < t < T c ; f c represents the carrier frequency, g u (t) is the base - band signal, and the pass - band signal s u (t) here is the positioning delay signal s 1 (t);

[0092] Step 2: The underwater target encodes the data stream i = [i1, i2,..., i n containing depth information through channel coding to obtain a new data stream where n is the number of useful data bits and N d is the number of bits actually to be transmitted;

[0093] Based on the chaotic sequence spreading code obtained in Step 1 the new data stream d is spread - spectrum to obtain a spread - spectrum signal;

[0094] Similar to the pulse shaping and modulation steps in Step 1, the spread - spectrum signal is pulse - shaped to obtain a pulse - shaped spread - spectrum signal;

[0095] The pulse - shaped spread - spectrum signal is used as the base - band signal, expressed as:

[0096]

[0097] t = t s / f s ;

[0098] In the formula, d n represents the data bit, Td represents the duration of a chaotic spread - spectrum sequence, p u (t) represents the pulse - shaping function, f s represents the signal sampling frequency, t s ∈[0, T c *f s - 1] represents the sampling points.

[0099] After adopting BPSK modulation and modulating the spread - spectrum signal after pulse - shaping, the pass - band signal s u (t) = g(t)cos(2πf c t), 0 < t < N d T d ; f c represents the carrier frequency, N d represents the number of BPSK symbols for modulation. Here, the pass - band signal s u (t) is the communication signal cos(2πf c t) is the local carrier.

[0100] Step 3: As Figure 3 shown, mix the local carrier, the positioning delay signal and the communication signal to obtain the mixed signal S u (t);

[0101] Step 4: After synchronous triggering, the underwater target performs PWM transmission based on the mixed signal S u (t), and through the channel, it is received by the positioning array, which is composed of multiple buoy base stations.

[0102] Step 5: The positioning array performs positioning calculation processing and communication demodulation processing in parallel based on the received signal to obtain the positioning delay and depth information, and uploads the depth information and positioning delay to the master base station. Now, a further detailed description of the positioning calculation processing of the positioning array based on the received signal is given.

[0103] The signal received by the buoy base station is expressed as:

[0104]

[0105] In the formula, P represents the amplitude of the received signal, τ represents the one - way propagation delay of the signal, r u (t) represents the signal of the u - th underwater target received, s u (t) represents the mixed signal, h u (t) is the impulse response of the underwater acoustic channel, and n(t) is Gaussian white noise with a mean of zero and a variance of .

[0106] S1: Filter the received signal using a band-pass filter to obtain the filtered signal;

[0107] S2: For the u-th underwater target, perform matched filtering through the overlap-save method to obtain the correlation waveform, expressed as:

[0108]

[0109] where f u (t) is the matched filter constituted by the chaotic spreading sequence of the u-th user;

[0110] Perform three-point interpolation fitting on the correlation waveform R(τ u,n ) to obtain the positioning delay τ u,n of the u-th underwater target relative to the n-th buoy base station in the positioning array;

[0111] Secondly, perform the same operation as the previous step on other underwater targets to obtain the positioning delays of multiple users relative to each buoy base station in the positioning array.

[0112] Among them, the specific operation of the overlap-save method adopted is:

[0113] As Figure 2 shown, assume that the length of the local reference signal h(t) is N1, divide the system received signal x(n) into many segments, each segment has a length of N2, and the i-th segment x(n) sequence is expressed as:

[0114] x i (n) = x(n), iN2 ≤ n ≤ (i + 1)N2 - 1

[0115] Then the expression of the received signal is:

[0116] x(n) = ∑x i (n)

[0117] The sequence expression after correlation is:

[0118] y(n) = x(n) * h(n) = ∑x i (n) * h(n) = Σy i (n)

[0119] where y i (n) = x i (n) * h(n) is the process of segmented convolution. The overlap-save method is equivalent to performing circular convolution on x i (n) and h(n), and splicing the last N1 - 1 points in the previous frame data t i-1 (n) with the x i (n) data to form a new x i with a length of N1 + N2 - 1(n), and then perform an FFT of N1+N2-1 points on x i (n), and multiply it point by point with the FFT of N1+N2-1 points of the local reference signal h(n). Perform an IFFT on the result after point multiplication to complete the convolution. Then discard the first N1-1 points of each convolution result, retain the overlapping part, and output y i (n). Finally, splice y i (n) is equivalent to dividing it into several correlation sequences y(n) of length N2.

[0120] Among them, the three-point interpolation fitting adopted specifically includes:

[0121] In the positioning system, perform autocorrelation on the received spread-spectrum signal, and the output waveform can be expressed as:

[0122] R(τ) = B(τ)cosω0(τ - t0)

[0123] It reaches the maximum value when τ = t0, where B(τ) is the envelope of the correlation function and can be fitted to a cosine function. Express it in the form of a cosine function:

[0124] R(τ) = A r cosω r τ + B r sinω r τ.

[0125] As Figure 5 shown, take the maximum value point (t2, r2) of the detected correlation peak and its two adjacent points (t1, r1) and (t3, r3), then the following equation is satisfied:

[0126]

[0127] Calculated through the above equation:

[0128]

[0129] After arrangement:

[0130] r3sinω r (t1 - t2) = r2sinω r (t1 - t3) - r1sinω r (t2 - t3)

[0131] Among them, t3 - t2 = t2 - t1 = t s , t s is the sampling period.

[0132] It can be obtained that:

[0133] r3sin(ω r ts ) = 2r2sin(ω r t s )cos(ω r t s ) - r1sin(ω r t s )

[0134] Since ω r ≈ 2πf0, and f s ≥ 2f0, so 0 < ω r t s < π, thus sin(ω r t s ) ≠ 0.

[0135] Then there is:

[0136]

[0137] Thus, the value of ω r is estimated as:

[0138]

[0139] R(τ) can be expressed as:

[0140]

[0141] Then when , |R(τ)| takes the maximum value, thus estimating the time delay:

[0142]

[0143] Because So there is:

[0144]

[0145] Estimate the exact position of the correlation peak, thus estimating the exact arrival time of the signal, that is, the time delay value τ0.

[0146] Now, a further detailed description is given for the communication demodulation process of the positioning array based on the received signal.

[0147] Perform band-pass filtering on the mixed signal;

[0148] Intercept the signal from the band-pass filtered mixed signal, and use a decision feedback equalizer to perform phase estimation on the intercepted signal to obtain the phase-estimated signal;

[0149] Use the chaotic spreading code and local carrier of the u-th underwater target to demodulate and despread the phase-estimated signal, and then perform decision-making to obtain the depth information;

[0150] Upload the obtained depth information to the master base station.

[0151] Among them, a decision feedback equalizer is used to perform phase estimation on the intercepted signal to obtain the signal after phase estimation. The specific operations include:

[0152] S1: Intercept the complete mixed waveform according to the correlation peak of the synchronization signal. Since the spread spectrum gain of the communication signal is low and it is more severely affected by multipath and phase, the situation of the multipath fast time-varying channel needs to be considered. When the transmission time is nT a at this time, the transmitted symbol is D(n), and the user spreading code is then the spreading sequence at this time is

[0153]

[0154] When the signal passes through the multipath fast time-varying channel, the signal received at the receiving end is

[0155]

[0156] In the formula, C p (t) is the time-varying complex-valued gain under the Pth propagation path, τ p is the propagation delay under this path, θ(t) is the phase shift that occurs after signal propagation. n(t) is the channel noise superimposed at the receiving end;

[0157] S2: The signal r(t) enters the feedforward filter a H (k), and the filter outputs once every chip interval. After passing through the feedforward filter, the chip estimate is obtained

[0158]

[0159] In the formula, a′ is the tap vector of the feedforward filter; b′ is the tap vector of the feedback filter; is the phase estimation value of the phase-locked loop; r(k) = [..., r(kT c +T s ), r(kT c ), r(kT c -T s ),...] T is the received signal vector passing through the feedforward filter ff at time kT c where T s is the ADC sampling period T s = T c / 2, T c is the chip period, is the chip decision value vector passing through the feedback filter fd.

[0160] S3: The chips after despreading are estimated as:

[0161]

[0162] S4: Obtain the optimal decision:

[0163]

[0164] S5: Under the minimum mean square error criterion, the parameters of the equalizer are updated through NLMS at the chip rate R c Update the error function:

[0165]

[0166] Weighting coefficient:

[0167]

[0168] In the formula, ε is a constant to prevent the denominator from being zero.

[0169] S6: Update the phase estimate through the phase-locked loop:

[0170]

[0171] In the formula,

[0172] The proportional integral of the phase-locked loop k1 = μk L ;

[0173] The constant integral k2 = μk L α;

[0174] Proportional coefficient

[0175]

[0176] The optimal damping factor ζ = 0.707.

[0177] S7: Repeat steps S1 - S7, and the equalization system updates the equalization parameters in real time until all chips are decided. The bit after decision is the demodulated depth information.

[0178] Step 6: The master base station stores the longitude and latitude information (EW, SN) of each buoy base station, and receives the positioning delay information and depth information from each buoy base station; specifically:

[0179] The system obtains the relative distances between them based on the positioning delay information of the signals sent by the underwater target to each buoy base station, and then uses geometric methods to calculate the target position to achieve the positioning of the underwater target. According to the buoy base station and the delay information, the following relational formula can be obtained:

[0180]

[0181] Among them, is the true position of the u-th underwater target, that is, the coordinate position to be solved. is the coordinate of the m-th buoy base station. is the relative distance from the underwater target to the m-th buoy base station, which can be obtained by the speed of sound c and the positioning time delay obtained.

[0182] Combined with the longitude and latitude information (EW, SN), it is converted into geodetic coordinates to achieve precise positioning of multiple underwater targets.

[0183] Embodiment 2:

[0184] The difference between this embodiment and Embodiment 1 is that the step of completing the decision of phase estimation in Embodiment 1 is changed to a matching filtering-related decision process similar to the synchronization signal as Figure 4 shown. The steps are as follows:

[0185] Step 1: According to the synchronization result, intercept each segment of the communication signal in the backup signal, and perform matching filtering with two groups of local signals s +1 (n) and s -1 (n) respectively. s +1 (n) and s -1 (n) are two groups of signals modulated to the passband after data 0 and data 1 are mapped, spread spectrum processed, and pulse shaped.

[0186] Step 2: After matching filtering, compare and discriminate the maximum values of the two groups of correlation peaks. If the value of the correlation peak made by correlating with s +1 (t) is larger, then the bit data is judged as 0, otherwise it is judged as 1.

[0187] Embodiment 3:

[0188] The difference between this embodiment and Embodiment 1 is that the spreading code used to generate the synchronization and communication signals in Step 1 of this embodiment also needs to satisfy the relationship that the cross-correlation between the spreading code sequence used in each communication segment and the corresponding local spreading code when it is mixed with its synchronization signal is low. This avoids interference between the synchronization signal and the communication signal and further improves the stability of the system.

Claims

1. An underwater multi-target positioning method based on a hybrid spread-spectrum waveform, characterized in that: It includes the following steps: Step 1: Generate an underwater multi-target chaotic spread spectrum sequence using a chaotic algorithm. Among them, the chaotic spread spectrum code of the u-th underwater target is expressed as where L is the code length of the chaotic spread spectrum sequence, is the l-th code element of the chaotic spread spectrum sequence of the u-th underwater target, and its value is 1 or -1; Use a pulse shaping filter to perform pulse shaping on the chaotic spreading code p u ,; Upsample the signal after pulse shaping, and then perform carrier modulation to generate the positioning signal of the u-th underwater target; Step 2: The u-th underwater target performs channel coding on the data stream containing depth information to obtain the encoded data stream, and uses the chaotic spreading code p generated in Step 1 u The encoded data stream is spread spectrum to obtain a spread spectrum signal. A pulse shaping filter is used to perform pulse shaping on the spread spectrum signal. BPSK modulation is adopted, and based on the local carrier, the spread spectrum signal after pulse shaping is encoded to obtain the communication signal of the u-th underwater target; Step 3: Mix the positioning signal and the communication signal to obtain a mixed signal; based on the mixed signal, generate a PWM signal and send it to the positioning array, where the positioning array is composed of multiple buoy base stations; Step 4: The positioning array performs positioning calculation processing and communication demodulation processing in parallel based on the received signal to obtain the positioning delay and depth information, and uploads the depth information and the positioning delay to the master base station; Step 5: The master base station obtains the coordinate information of the underwater target based on the positioning delay and depth information; Assume that the signal received by the positioning array is expressed as: where r u (t) represents the signal of the u-th underwater target received, s u (t0 represents the mixed signal, h u (t) is the underwater acoustic channel impulse response, and n(t) is Gaussian white noise with a mean of zero and a variance of ; The specific operations of the positioning calculation processing include: First, for the u-th underwater target, perform the following related operations according to the following formula to obtain a related waveform, expressed as: where f u (t) is a matched filter formed by the chaotic spreading sequence of the u-th user; Interpolate and fit the relevant waveform R(τ u,n ) with three-point interpolation to obtain the positioning delay τ u,n ; Secondly, perform the same operations as the previous step on other underwater targets to obtain the positioning delays of multiple users relative to each buoy base station in the positioning array; The specific operations of the communication demodulation processing include: Perform band-pass filtering on the mixed signal; Intercept the signal from the band-pass filtered mixed signal, and use a decision feedback equalizer to perform phase estimation on the intercepted signal to obtain the phase-estimated signal; Use the chaotic spreading code and local carrier of the u-th underwater target to demodulate and despread the phase-estimated signal, and then perform decision-making to obtain the depth information; Upload the obtained depth information to the master base station.

2. The underwater multi-target positioning method based on a hybrid spread spectrum waveform according to claim 1, wherein: The relevant waveform R(τ u,n ) is subjected to three-point interpolation fitting to obtain the positioning delay τ u,n of the u-th underwater target relative to the n-th buoy base station in the positioning array. The specific operations include: Take the maximum point (t2, r2) of the detected relevant waveform R(τ u,n ), and the two points (t1, r1) and (t3, r3) before and after it, then the following equations are satisfied: In the formula, the subscript t represents the sampling point, and the subscript r represents the amplitude; Calculated through the above equation: where A r and B r are coefficients to be solved for; After arrangement: r3 sinω r (t1 - t2) = r2 sinω r (t1 - t3) - r1 sinω r (t2 - t3) where, t3 - t2 = t2 - t1 = t s , t s is the sampling period; It can be obtained: r3 sin(ω r t s ) = 2r2 sin(ω r t s ) cos(ω r t s ) - r1 sin(ω r t s ) Since ω r ≈ 2πf0, and f s ≥ 2f0, so 0 < ω r t s < π, thus sin(ω r t s ) ≠ 0; So there is: Thus, ω is estimated r The value is: R(τ) is expressed as: Then when occurs, |R(τ)| takes the maximum value, and thus the time delay is estimated: Because Therefore, there is: Estimate the exact position of the relevant waveform R(τ u,n ), and thus estimate the positioning delay τ u,n of the u-th underwater target relative to the n-th buoy base station in the positioning array.

3. A method for underwater multi-target positioning based on a hybrid spread-spectrum waveform according to claim 1, characterized in that: In step 5, the master base station obtains the coordinate information of the underwater target based on the positioning delay and depth information. The specific operations include: According to the positioning delays and depth information of the signals sent by each underwater target to each buoy base station, and according to the relationship between the u-th underwater target and the positioning array, obtain the relative distance between them: Among them, is the true position of the u-th underwater target, that is, the coordinate information to be solved. is the coordinate of the m-th buoy base station. is the relative distance from the u-th underwater target to the m-th buoy base station, which is obtained through the sound speed c and the positioning time delay. Use geometric methods to calculate the coordinate information of the underwater target.

4. The underwater multi-target positioning method based on a hybrid spread-spectrum waveform according to claim 1, wherein: The BPSK modulation, encoding the spread spectrum signal after pulse shaping based on the local carrier to obtain the communication signal, all include the following steps: The encoded data stream is represented as where N d is the total number of bits transmitted; the spread-spectrum signal is the product of the encoded data stream d and the chaotic-sequence spreading code; Take the spread spectrum signal as the baseband signal, expressed as: where a n represents the data of each bit, T d represents the duration of a spread-spectrum code signal, p represents the spread-spectrum code sequence, f s represents the sampling frequency; Modulate the baseband signal to the passband to obtain the communication signal of the u-th underwater target: s[t]=g(t)cos(2πf c t), 0 < t < T c where f c represents the carrier frequency, T c represents the spreading sequence symbol duration, and cos(2πf c t) represents the local carrier.

5. The underwater multi-target positioning method based on a hybrid spread-spectrum waveform according to claim 1, wherein: The operation of intercepting the signal from the band-pass filtered mixed signal, using a decision feedback equalizer to perform phase estimation on the intercepted signal to obtain the phase-estimated signal, and using the chaotic spreading code and local carrier of the u-th underwater target to demodulate and despread the phase-estimated signal, and then perform decision-making to obtain the depth information; can be replaced with the following steps: Intercept the signal from the band-pass filtered mixed signal; Match each communication signal with the local signal s +1 (n) and the local signal s -1 (n) through matched filtering to obtain the correlation results of 0 and the correlation results of 1; If the correlation result of 1 is greater than the correlation result of 0, then judge this segment of communication signal as 0, otherwise judge it as 1; thus obtain the depth information; Among them, the local signal s +1 (n) and the local signal s -1 (n) are two groups of signals modulated to the passband after the data 0 and data 1 go through the processes of mapping, spreading spectrum, and pulse shaping.

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