阅读说明：本技术 水声通信时变定时偏移迭代估计和补偿方法及装置 (Time-varying timing offset iterative estimation and compensation method and device for underwater acoustic communication ) 是由 武岩波 朱敏 于 2020-12-25 设计创作，主要内容包括：本发明公开了一种水声通信时变定时偏移迭代估计和补偿方法及装置。本发明通过迭代的方式生成本地同步信号,使其在到达时间和时变多普勒效应上,逐步与接收到的波形接近或达到一致。在迭代中,每次获得多个同步信号的定时偏移估计之后,通过样条插值法恢复出连续时间的定时偏移估计,进而对单载波调制符号进行定时补偿,获得符号速率采样率的接收波形之后,进行最小二乘信道估计及频域均衡器。本发明仅从重复出现的同步信号中恢复定时偏移,不需要借助符号判决反馈的信息,不需要逐符号更新均衡器系数,相对传统方法整体系统的计算复杂度更低。本发明的误符号率性能优于传统的平均多普勒补偿和自适应均衡器。(The invention discloses an underwater acoustic communication time-varying timing offset iterative estimation and compensation method and device. The invention generates the local synchronous signal in an iterative mode, so that the local synchronous signal is gradually close to or consistent with the received waveform on the arrival time and the time-varying Doppler effect. In iteration, after obtaining the timing offset estimation of a plurality of synchronous signals each time, recovering the timing offset estimation of continuous time through a spline interpolation method, further performing timing compensation on a single carrier modulation symbol, obtaining a received waveform of a symbol rate sampling rate, and then performing least square channel estimation and a frequency domain equalizer. The invention only recovers the timing offset from the repeated synchronous signals without the help of information fed back by symbol decision and updating the equalizer coefficient symbol by symbol, and has lower calculation complexity compared with the traditional method and the whole system. The symbol error rate performance of the invention is superior to that of the traditional average Doppler compensation and adaptive equalizer.)

1. An iterative estimation and compensation method for time-varying timing offset of underwater acoustic communication,

at a sending end, a sent data packet comprises a plurality of frames, each frame comprises a synchronous signal and a symbol segment, the synchronous signal adopts a linear frequency modulation signal, a blank segment is arranged between the synchronous signal and the symbol segment, the symbol segment comprises a training symbol, an information symbol and a tail blank segment, and the waveform of a transmitted signal is the real part of the signal after the synchronous signal and the symbol modulation waveform are superposed;

at a receiving end, receiving and processing a data packet, comprising:

s1: the steps of quadrature mixing and decimation:

sequentially performing band-pass sampling and quadrature frequency mixing on the received data packet, performing low-pass filtering and extraction processing to obtain a complex baseband form received waveform with baseband sampling frequency as an interval,

setting an initial value of a timing offset estimation value and an initial value of iteration times q, wherein the initial value of the timing offset estimation value is 0, and the initial value of the iteration times q is 1;

s2: and solving the residual integer multiple sampling point offset of the synchronous signal:

during the Q-th iteration, wherein Q is more than or equal to 1 and less than or equal to Q, and Q is the maximum iteration number, firstly, the complex baseband waveform of each synchronous signal is regenerated according to the estimated value of the timing offset obtained by the last iteration, then, the correlation function of each synchronous signal and the received waveform is respectively solved, and the offset of an integral multiple sampling point is obtained according to the position of the maximum value;

s3: and (3) solving the residual fraction multiple sampling point offset of the synchronous signal:

carrying out parabolic interpolation according to the obtained offset of the integral multiple sampling point, the corresponding maximum position and the correlation function amplitude of the front and rear positions of the maximum position to obtain fractional offset at the vertex, and combining the estimated value of the timing offset of the last iteration with the integral multiple timing offset and the fractional timing offset obtained at this time to obtain the timing offset at each frame head;

s4: and a step of spline interpolation according to the estimated values of the timing offsets of the plurality of synchronous signals:

taking the timing offset estimation value at the frame header as a control point constraint of spline interpolation, and solving according to the control point constraint of a spline function and the continuity of a derivative at a node to obtain the timing offset at each sampling point;

then, judging whether the iteration number reaches the maximum iteration number Q, if so, starting to execute the steps sequentially after the step S5, otherwise, increasing the iteration number Q by 1, and then jumping to the step S2 to start the sequential repeated processing;

s5: a step of calculating a reverse timing offset and compensating timing;

the timing offset of each sampling point is obtained through Q times of iteration, namely the sampling point-by-sampling point offset of the received waveform relative to the waveform of the transmitted signal is obtained, in the received waveform compensation, the time change process is inverted, the timing offset for resampling is further obtained, the timing offset for resampling is obtained through a linear interpolation inversion function mode, then the received waveform is resampled, and the influence caused by movement is eliminated.

2. A method according to claim 1, wherein the modulation symbols of the symbol segment are in a quadrature phase shift keying, QPSK, scheme.

3. An underwater acoustic communication symbol equalization method, characterized in that, based on the time-varying timing offset iterative estimation and compensation method as claimed in claim 1 or 2, at the receiving end, the steps are performed:

s6, the least square channel estimation and frequency domain zero-forcing equalization steps:

according to the known training symbol and the received waveform after timing offset compensation, the least square estimation of channel impulse response is obtained, then by utilizing a zero-forcing equalization algorithm of frequency domain processing, the Fourier forward transformation is firstly carried out on the received information symbol sequence and the channel impulse response sequence, the two sequences are divided element by element in the frequency domain, and then the Fourier inverse transformation is carried out on the result, so that the information symbol estimation value of each frame is obtained.

4. An iterative estimation and compensation device for time-varying timing offset of underwater acoustic communication, based on the method of claim 1 or 2, characterized by comprising:

the orthogonal frequency mixing and extracting module is used for sequentially carrying out band-pass sampling and orthogonal frequency mixing on the received data packet, and then carrying out low-pass filtering and extracting processing to obtain a receiving waveform in a complex baseband form with baseband sampling frequency as an interval;

the iteration control module is used for setting an initial value of a timing offset estimation value to be 0 and an initial value of iteration times to be Q to be 1, judging whether the iteration times Q reach a maximum iteration time Q after each iteration, if so, finishing the iteration, otherwise, increasing the iteration times Q by 1, and then controlling a residual integral multiple sampling point offset solving module of a synchronous signal, a residual integral multiple sampling point offset solving module of the synchronous signal and a spline interpolation module to calculate, wherein Q is more than or equal to 1 and is less than or equal to Q, and Q is the maximum iteration times;

when the q-th iteration is performed, firstly, a complex baseband waveform of each synchronous signal is regenerated according to a timing offset estimation value obtained by the last iteration, then a correlation function of each synchronous signal and a received waveform is respectively solved, and the offset of an integral multiple sampling point is obtained according to the position of the maximum value;

a residual fractional sampling point offset calculation module of the synchronous signal, during the q-th iteration, according to the obtained offset of the integral multiple sampling point, the corresponding maximum value position and the correlation function amplitude of the front and rear positions thereof, parabolic interpolation is carried out to obtain the fractional offset at the vertex, the timing offset estimation value of the last iteration and the integral multiple and fractional timing offset obtained at the time are combined to obtain the timing offset at each frame header;

the spline interpolation module is used for taking the timing offset estimation value at the frame header as the control point constraint of the spline interpolation during the q-th iteration, and solving according to the control point constraint of the spline function and the continuity of the derivative at the node to obtain the timing offset at each sampling point;

the inverse timing offset solving and timing compensation module obtains the timing offset at each sampling point through Q times of iteration, namely the received waveform is offset relative to the sampling point by sampling point of the transmitted signal waveform, in the received waveform compensation, the time change process is solved, and then the timing offset used for resampling is obtained, the timing offset of resampling is obtained through a linear interpolation inversion function mode, and then the received waveform is resampled, so that the influence caused by movement is eliminated.

5. An underwater acoustic communication receiving device is characterized by comprising a timing offset estimation module, a least square channel estimation and frequency domain zero forcing equalization module; wherein

A timing offset estimation module, which adopts the underwater acoustic communication time-varying timing offset iterative estimation and compensation device as claimed in claim 4;

the least square channel estimation and frequency domain zero forcing equalization module obtains the least square estimation of channel impulse response according to the known training symbol and the received waveform after timing offset compensation, then uses the zero forcing equalization algorithm of frequency domain processing to firstly carry out Fourier forward transformation on the received information symbol sequence and the channel impulse response sequence, divides the two by elements in the frequency domain, and then carries out Fourier inverse transformation on the result, thereby obtaining the information symbol estimation value of each frame.

6. An underwater acoustic communication system comprising a transmitting device and a receiving device, wherein

The transmitting device, the data packet transmitted includes a plurality of frames, each frame includes synchronous signal and symbol section, the synchronous signal adopts linear frequency modulation signal LFM, the space section is behind the synchronous signal, the symbol section includes training symbol, information symbol and tail space section, the waveform of the transmitting signal is the signal after the synchronous signal and the symbol modulation waveform are superimposed,

receiving means employing the time-varying timing offset iterative estimation and compensation means of claim 4.

7. An underwater acoustic communication system comprising a transmitting device and a receiving device, wherein

The transmitting device, the data packet transmitted includes a plurality of frames, each frame includes synchronous signal and symbol section, the synchronous signal adopts linear frequency modulation signal LFM, the space section is behind the synchronous signal, the symbol section includes training symbol, information symbol and tail space section, the waveform of the transmitting signal is the signal after the synchronous signal and the symbol modulation waveform are superimposed,

a receiving apparatus using the receiving apparatus according to claim 5.

Technical Field

The invention belongs to the field of underwater acoustic communication, and particularly discloses a method and a device for iteratively estimating and compensating time-varying timing offset in underwater acoustic communication, a symbol equalization method and a symbol equalization device based on the method and the device, an underwater acoustic communication receiving device and an underwater acoustic communication system, aiming at the timing offset caused by movement in the underwater acoustic communication and based on a method for estimating a plurality of linear frequency modulation signals.

Background

In a vertical underwater acoustic communications channel, the effects of the channel on the transmitted signal typically include two parts, compression or tension variation (timing offset) and frequency selectivity. In the current underwater acoustic communication technology, a doppler estimation method or an average value estimation method of a doppler change rate is commonly used, but timing offset and frequency selectivity cannot be accurately separated, so that two-dimensional tracking and processing of time-varying channel impulse response on a time dimension and a delay dimension are required in subsequent processing, and a system is complex in structure, large in calculation amount and unstable in low signal-to-noise ratio.

The main reasons for inaccurate timing offset estimation are as follows: (1) the motion model during data packet transmission is incorrect, timing deviation is mainly caused by motion, and fluctuation of the water surface drives the communication platform to reciprocate, similar to simple harmonic motion and random. Therefore, the Doppler or Doppler change rate is subjected to piecewise constant estimation, so that the model error is large; (2) the timing offset estimation using the correlation function at non-constant speeds has a certain bias. Under the uniform motion, the deviation can be solved through a fuzzy function, but the deviation is difficult to offset under the condition that the speed is unknown or the motion process is complex, such as the acceleration is changed; (3) discrete time samples result in a limited time accuracy of the peak search, which is more pronounced when the sampling rate is close to the nyquist rate. Due to these problems, the conventional timing offset estimation can achieve the desired estimation effect, resulting in higher complexity and limited performance of the subsequent processing of the system.

Disclosure of Invention

The invention aims to realize accurate estimation of timing offset, meet the requirements of time-invariant frequency domain equalization on preceding-stage timing estimation and compensation, further realize time-invariant frequency domain equalization and reduce the computational complexity.

To achieve the above object, the present invention provides an iterative estimation and compensation method for time-varying timing offset in underwater acoustic communication, wherein

At a sending end, a sent data packet comprises a plurality of frames, each frame comprises a synchronous signal and a symbol segment, the synchronous signal adopts a linear frequency modulation signal, a blank segment is arranged between the synchronous signal and the symbol segment, the symbol segment comprises a training symbol, an information symbol and a tail blank segment, and the waveform of a transmitted signal is the real part of the signal after the synchronous signal and the symbol modulation waveform are superposed;

at a receiving end, receiving and processing a data packet, comprising:

s1: the steps of quadrature mixing and decimation:

sequentially performing band-pass sampling and quadrature frequency mixing on the received data packet, performing low-pass filtering and extraction processing to obtain a complex baseband form received waveform with baseband sampling frequency as an interval,

setting an initial value of a timing offset estimation value and an initial value of iteration times q, wherein the initial value of the timing offset estimation value is 0, and the initial value of the iteration times q is 1;

s2: and solving the residual integer multiple sampling point offset of the synchronous signal:

during the Q-th iteration, wherein Q is more than or equal to 1 and less than or equal to Q, and Q is the maximum iteration number, firstly, the complex baseband waveform of each synchronous signal is regenerated according to the estimated value of the timing offset obtained by the last iteration, then, the correlation function of each synchronous signal and the received waveform is respectively solved, and the offset of an integral multiple sampling point is obtained according to the position of the maximum value;

s3: and (3) solving the residual fraction multiple sampling point offset of the synchronous signal:

carrying out parabolic interpolation according to the obtained offset of the integral multiple sampling point, the corresponding maximum position and the correlation function amplitude of the front and rear positions of the maximum position to obtain fractional offset at the vertex, and combining the estimated value of the timing offset of the last iteration with the integral multiple timing offset and the fractional timing offset obtained at this time to obtain the timing offset at each frame head;

s4: and a step of spline interpolation according to the estimated values of the timing offsets of the plurality of synchronous signals:

taking the timing offset estimation value at the frame header as a control point constraint of spline interpolation, and solving according to the control point constraint of a spline function and the continuity of a derivative at a node to obtain the timing offset at each sampling point;

then, judging whether the iteration number reaches the maximum iteration number Q, if so, starting to execute the steps sequentially after the step S5, otherwise, increasing the iteration number Q by 1, and then jumping to the step S2 to start the sequential repeated processing;

s5: a step of calculating a reverse timing offset and compensating timing;

obtaining timing offset at each sampling point through Q times of iteration, namely the sampling point-by-sampling point offset of a received waveform relative to a transmitted signal waveform, inverting the time change process in received waveform compensation to further obtain the timing offset for resampling, obtaining the timing offset for resampling in a linear interpolation inversion function mode, and resampling the received waveform to eliminate the influence caused by movement;

furthermore, the modulation symbols of the symbol segment adopt a four-phase shift keying QPSK mode.

The invention also provides an underwater acoustic communication symbol equalization method, which is based on the time-varying timing offset iterative estimation and compensation method and comprises the following steps at a receiving end:

s6, the least square channel estimation and frequency domain zero-forcing equalization steps:

according to the known training symbol and the received waveform after timing offset compensation, the least square estimation of channel impulse response is obtained, then by utilizing a zero-forcing equalization algorithm of frequency domain processing, the Fourier forward transformation is firstly carried out on the received information symbol sequence and the channel impulse response sequence, the two sequences are divided element by element in the frequency domain, and then the Fourier inverse transformation is carried out on the result, so that the information symbol estimation value of each frame is obtained.

The invention also provides an underwater acoustic communication time-varying timing offset iterative estimation and compensation device, which is based on the method of claim 1 or 2 and is characterized by comprising the following steps:

the orthogonal frequency mixing and extracting module is used for sequentially carrying out band-pass sampling and orthogonal frequency mixing on the received data packet, and then carrying out low-pass filtering and extracting processing to obtain a receiving waveform in a complex baseband form with baseband sampling frequency as an interval;

the iteration control module is used for setting an initial value of a timing offset estimation value to be 0 and an initial value of iteration times to be Q to be 1, judging whether the iteration times Q reach a maximum iteration time Q after each iteration, if so, finishing the iteration, otherwise, increasing the iteration times Q by 1, and then controlling a residual integral multiple sampling point offset solving module of a synchronous signal, a residual integral multiple sampling point offset solving module of the synchronous signal and a spline interpolation module to calculate, wherein Q is more than or equal to 1 and is less than or equal to Q, and Q is the maximum iteration times;

when the q-th iteration is performed, firstly, a complex baseband waveform of each synchronous signal is regenerated according to a timing offset estimation value obtained by the last iteration, then a correlation function of each synchronous signal and a received waveform is respectively solved, and the offset of an integral multiple sampling point is obtained according to the position of the maximum value;

a residual fractional sampling point offset calculation module of the synchronous signal, during the q-th iteration, according to the obtained offset of the integral multiple sampling point, the corresponding maximum value position and the correlation function amplitude of the front and rear positions thereof, parabolic interpolation is carried out to obtain the fractional offset at the vertex, the timing offset estimation value of the last iteration and the integral multiple and fractional timing offset obtained at the time are combined to obtain the timing offset at each frame header;

the spline interpolation module is used for taking the timing offset estimation value at the frame header as the control point constraint of the spline interpolation during the q-th iteration, and solving according to the control point constraint of the spline function and the continuity of the derivative at the node to obtain the timing offset at each sampling point;

the inverse timing offset solving and timing compensation module obtains the timing offset at each sampling point through Q times of iteration, namely the received waveform is offset relative to the sampling point by sampling point of the transmitted signal waveform, in the received waveform compensation, the time change process is solved, and then the timing offset used for resampling is obtained, the timing offset of resampling is obtained through a linear interpolation inversion function mode, and then the received waveform is resampled, so that the influence caused by movement is eliminated.

The invention also provides an underwater acoustic communication receiving device, which comprises a timing offset estimation module, a least square channel estimation and frequency domain zero forcing equalization module; wherein

The timing offset estimation module adopts the underwater acoustic communication time-varying timing offset iterative estimation and compensation device;

the least square channel estimation and frequency domain zero forcing equalization module obtains the least square estimation of channel impulse response according to the known training symbol and the received waveform after timing offset compensation, then uses the zero forcing equalization algorithm of frequency domain processing to firstly carry out Fourier forward transformation on the received information symbol sequence and the channel impulse response sequence, divides the two by elements in the frequency domain, and then carries out Fourier inverse transformation on the result, thereby obtaining the information symbol estimation value of each frame.

The invention also provides an underwater acoustic communication system which comprises a transmitting device and a receiving device, wherein

The transmitting device, the data packet transmitted includes a plurality of frames, each frame includes synchronous signal and symbol section, the synchronous signal adopts linear frequency modulation signal LFM, the space section is behind the synchronous signal, the symbol section includes training symbol, information symbol and tail space section, the waveform of the transmitting signal is the signal after the synchronous signal and the symbol modulation waveform are superimposed,

and the receiving device adopts the time-varying timing offset iterative estimation and compensation device.

The invention also provides an underwater acoustic communication system, a transmitting device and a receiving device, wherein

The transmitting device, the data packet transmitted includes a plurality of frames, each frame includes synchronous signal and symbol section, the synchronous signal adopts linear frequency modulation signal LFM, the space section is behind the synchronous signal, the symbol section includes training symbol, information symbol and tail space section, the waveform of the transmitting signal is the signal after the synchronous signal and the symbol modulation waveform are superimposed,

the receiving device adopts the receiving device.

Advantageous effects

In order to eliminate the estimation deviation, the invention generates the local synchronization signal in an iterative mode, so that the local synchronization signal is gradually close to or consistent with the received waveform on the arrival time and the time-varying Doppler effect. In the iteration, after the timing offset estimation of a plurality of synchronous signals is obtained, the timing offset estimation of continuous time is recovered by a spline interpolation method. And after the iteration times are reached, performing timing compensation on the single-carrier modulation symbol, obtaining a received waveform of a symbol rate sampling rate, and performing least square channel estimation and a frequency domain equalizer. The invention provides a timing offset estimation and compensation method under the condition of continuous time and a symbol equalization method of single carrier underwater acoustic communication, which only recovers the timing offset from a repeatedly appeared synchronous signal, does not need to update equalizer coefficients symbol by symbol, does not need to use information fed back by symbol decision, and has lower calculation complexity compared with the traditional method. The test result shows that the symbol error rate performance of the invention is superior to the receiving scheme of the traditional average Doppler compensation and adaptive equalizer.

Drawings

FIG. 1 is a schematic diagram of the packet composition of the present invention.

Fig. 2 is a block diagram of the receive timing and equalization scheme of the present invention.

Fig. 3 is a graph of the displacement, velocity and acceleration obtained from the timing offset estimate obtained after 4 iterations in the sea test data.

Fig. 4 is a comparison graph of output constellations of the conventional method and the method of the present invention.

Detailed Description

The following describes in detail embodiments of the present invention with reference to the drawings.

In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.

Typical parameters and values used in the present invention are as follows:

the packet transmission structure is shown in fig. 1, where the number of frames in each packet is N_Frm. Each frame containing a synchronisation signal of duration T_SyncFollowed by a length T_GapBlank of (2). Including N in the symbol segment_TSA training symbol and N_ISInformation symbols and spaces. The modulation symbols are in a Quadrature Phase Shift Keying (QPSK) manner. Linear Frequency Modulation (LFM) is used as a synchronization signal, and the expression is:

wherein g (T) is defined as [0, T ]_Sync]The unit amplitude gate on the interval gates pulses. Within a transmitted packet there are a plurality of synchronization signals, denoted

The modulated waveform of training symbol and information symbol in a transmitting packet is recorded as

Wherein f is_CIs the carrier frequency, g_S() is a shaped pulse waveform; s_TS[m]For the m-th training symbol, s, of each frame_IS[m，k]M information symbols for the k-th frame; t is t_TS[m，k]For m training symbol transmission instants, t, of the k-th frame_IS[m，k]The m information symbol transmission time instants of the kth frame can be directly obtained according to the packet structure. Finally, the transmitted waveform is the same asThe real part of the superposition of the step signal and the symbol-modulated waveform, i.e.

Where Re (×) represents the real part operation.

The receiver steps of the present invention are described in detail below.

Step 1: quadrature mixing and decimation in a conventional manner

For received waveforms, sampling frequency T in band-pass_PBSampling for intervals, followed by quadrature mixing at a frequency of-f_CThen low-pass filtering and extracting processing are carried out to obtain a baseband sampling frequency T_BBThe received waveform in the form of spaced complex baseband is

Wherein the content of the first and second substances,LPF { } represents a Low Pass Filter (LPF) process for the received waveform bandpass waveform at time t. The initial estimate of the timing offset is set to 0, i.e.And taking the initial iteration number as q-1.

Step 2: method for calculating residual integral multiple sampling point offset of synchronous signal

In the Q-th iteration, wherein Q is more than or equal to 1 and less than or equal to Q, firstly, the timing offset obtained in the last iteration is usedRegenerating the complex baseband waveform of the kth sync waveform, i.e.

Then, the correlation function between the received waveform and the plurality of synchronous signals is obtained, and the correlation function is as follows:

obtaining the offset of the integral multiple sampling point according to the position of the maximum value, and recording the offset as

And step 3: residual fractional sampling point offset of synchronous signal is calculated

According to the offset of an integer multiple of the sampling point and the magnitude of the correlation function before and after it, i.e.

Parabolic interpolation is carried out to obtain fractional offset of the vertex as

Combining the offset of the last iteration and the integer and fractional timing offsets obtained this time to obtain the timing offsets of each frame head:

and 4, step 4: spline interpolation according to a plurality of synchronous signal offsets

According to the timing offset at the frame head as the control point constraint of the spline interpolation, the order of the spline interpolation is recorded as N_DegTaking the location t of the l-th node_lIs composed of

The following piecewise functions constitute the required spline functions:

and has t_l≤t＜t_l+1，

WhereinAnd solving the coefficients of the piecewise function according to the constraint of the control points of the spline interpolation and the continuity of the derivatives at the nodes.

For the nth sampling point in a data packet, the value range isThe serial number of the corresponding spline node is marked as l_nSatisfy the following requirementsThen find out l_n. The timing offset of the sample point is obtained by a spline function, i.e.

And calculating all sampling points in the data packet to obtain the timing offset of each sampling point in the data packet.

After steps 2, 3 and 4 are sequentially executed, the step 2 is skipped to start the sequential repeated processing; the iteration number q is increased by 1; after reaching the maximum iteration number Q, the 5 th step and the subsequent steps are started.

And 5: determination of inverse timing offset and timing compensation based on resampling and phase rotation at baseband

Obtaining timing offset by Q iterationsI.e. the offset of the received waveform relative to the sampling point by sampling point of the transmitted signal, but in the received waveform compensation, the time variation process needs to be inverted, and then the timing offset for resampling is obtained. Here, the inverse timing offset is obtained by means of a linear interpolation inverse function, and the obtained inverse timing offset is:

wherein the second term at the right end of the equation represents a relation function of the sampling time sequence at the transmitting end and the sampling time sequence at the receiving endLinear interpolation is carried out to obtain nT_BBThe value of (c) is as follows. The resampling process for the received waveform is as follows:

wherein Farrow { } denotes a Farrow filter, which is a resampled filter.Representing a function of the relation between the sequence of sampling instants at the receiving end and the received waveformResampling the symbol interval, each sampling point nT_SymIs offset by Representing the phase compensation for this offset. The effects of motion have been eliminated by the base band waveform based on resampling and phase rotation compensation.

Step 6: least square channel estimation and frequency domain zero forcing equalization

Assume that the channel impulse response at the nth tap position of the kth frame is h_k[n]The range of action is-N_h≤n≤N_hIn which N is_hIs the single-sided length of the channel impulse response. The vector form of the channel impulse response is noted as

h_k＝[h_k[-N_h]，h_k[1-N_h]，…，h_k[N_h]]^T。

Obtaining a Least Squares (LS) estimate of the channel impulse response based on the known training symbols and the timing offset compensated received waveform

Wherein the matrix formed by the training symbols is recorded as

The compensated received waveform vector is recorded as

r′_TS，k＝[r′(t_TS[N_h，k])，r′(t_TS[N_h+2，k])，…，r′(t_TS[N_TS-N_h-1，k]))^T。

Obtaining channel impulse responseThen, using the zero forcing equalization algorithm of frequency domain processing, firstly carrying out Fourier forward transformation on the received information symbol sequence and channel impulse response sequence, dividing the two element by element in the frequency domain, then carrying out Fourier inverse transformation on the result to obtain the information symbol estimated value of the frame, wherein the whole equalization process is expressed as

Wherein N is_ZFIs the time domain unilateral equivalent length of the zero forcing equalizer, and takes the value of N_ZF＝10N_h，N_FFTIs the number of points of Fourier transform, and takes the value as Representing a rounding up operation.

The traditional receiving framework combines average Doppler compensation with an adaptive equalizer with phase tracking, improves the adaptive optimization method in the traditional equalizer method, the sparse structure of the equalizer and the joint iteration of a decoding equalizer, has good application effect on underwater acoustic communication systems of a flood dragon manned submersible and a deep sea warrior manned submersible, still needs an adaptive mode to compensate residual timing error, has large calculation amount and is sensitive to burst noise.

Using the method of the invention, the order of the spline function takes the value N_Deg3, namely common third-order spline interpolation (cubic spline), so that the acceleration corresponding to the fitted motion curve is a piecewise linear function, a variable acceleration scene can be well approximated, and the method has obvious advantages compared with the constant speed assumption in the traditional method, thereby providing a good timing compensation basis for the application of time-invariant frequency domain equalization of symbol rate sampling. The method provided by the invention is used for processing the experimental acquisition waveform with the flood dragon number of 7 months in 2011 and the water depth of 5000 meters. Fig. 3 shows the displacement, velocity and acceleration in the sea test data obtained from the timing offset estimation of 4 iterations, with the vertical line representing the starting position of the synchronization signal. The displacement is obtained by multiplying the timing offset by the sound speed, and then the first derivative and the second derivative are obtained to obtain the speed and the acceleration. The method of the invention is further verified in the figure by the fact that the acceleration has a large variation between two adjacent synchronization signals.

Fig. 4 is a comparison of star maps after equalization by different methods, and respectively shows the performance of the adaptive equalization method used in the flood dragon sea test, the performance of frequency domain equalization performed after 1 iteration timing, and the performance of frequency domain equalization performed after 2 iteration timings. It can be seen that the traditional method is sensitive to noise because each symbol needs adaptive adjustment, and the constellation diagram is more severely diffused although no obvious phase rotation exists; after 1 time of iterative timing, the amplitude distribution of a constellation diagram is concentrated, but the phase rotation is serious due to the large error of timing estimation; the method eliminates the phase rotation phenomenon after 2 times of iterative timing, and has the advantages of less noise influence on the equalizer, concentrated amplitude and phase of constellation points and obvious performance advantage due to the adoption of the channel estimation-based method. The necessity of adopting a high-order spline model as timing estimation is fully illustrated by sea test data, and the performance of iterative timing estimation and the performance advantage of frequency domain equalization compared with the traditional adaptive equalization are verified.

Based on the same inventive concept, the specific embodiment of the invention also provides a time-varying timing offset iterative estimation and compensation device in underwater acoustic communication, an underwater acoustic communication receiving device based on the time-varying timing offset iterative estimation and compensation device and an underwater acoustic communication system. The time-varying timing offset iterative estimation and compensation device in the underwater acoustic communication comprises an orthogonal frequency mixing and extraction module, an iterative control module, a residual integral multiple sampling point offset calculation module of a synchronous signal, a residual integral multiple sampling point offset calculation module of the synchronous signal, a spline interpolation module and an inverse timing offset calculation and timing compensation module. The underwater acoustic communication receiving device based on the device comprises a timing offset estimation module, a least square channel estimation module and a frequency domain zero forcing equalization module. The underwater acoustic communication system based on the device comprises a transmitting device and a receiving device. The modules and the corresponding equipment which are formed by the modules complete the corresponding functions of the time-varying timing offset iterative estimation and compensation method and the symbol equalization method in the underwater acoustic communication.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.