CN103634262B - A kind of underwater acoustic coherent communication self adaptation phase compensating method - Google Patents

Abstract

The present invention relates to a kind of underwater acoustic coherent communication self adaptation phase compensating method, including: from each frame of received water sound communication signal, extract Chirp signal, carry out correlation computations for each Chirp signal, utilize calculated correlation peak location to seek the estimated value of the average speed of each frame, average acceleration；Utilize the estimated value of average speed in each frame duration, calculate relative Compression and Expansion coefficient, according to described relative Compression and Expansion coefficient calculations result, the reception waveform of water sound communication signal is carried out resampling, complete the compensation of average Doppler；Average acceleration estimated value is utilized to estimate the step sizes of self adaptation phase compensator；Self adaptation phase compensation is carried out by the signal after the compensation to average Doppler of the self adaptation phase compensator of employing step sizes.The present invention make full use of carrier relative movement to phase place change between relation, phase compensation will be made to become simpler, reliable.

Description

A kind of underwater acoustic coherent communication self adaptation phase compensating method

Technical field

The present invention relates to underwater acoustic coherent communication field, particularly to a kind of underwater acoustic coherent communication self adaptation phase compensation side Method.

Background technology

In communication process, the relative change of phase of received signal is caused in sending and receiving end, the athletic meeting of reflecting medium.With wireless Telecommunication is compared, and sound wave is little in water transmission speed, and doppler phenomenon is more serious；Underwater sound communication narrow bandwidth simultaneously, during symbol Between relatively long.Thus in underwater sound communication, the phase place change caused due to motion is the most serious.Underwater acoustic coherent communication needs Utilize the transmission of phase information of signal, therefore it is required that the phase place of signal is preferably followed the tracks of by receiving terminal.Lead at underwater sound coherent Letter needs utilize self adaptation Phase Compensation, overcome the phase place change that motion causes.

In prior art, the computational methods of phase compensation are had multiple, are respectively described as follows:

List of references 1:T.C.Yang delivered on IEEE Journal of Oceanic Engineering in 2004 Article " Differences between passive-phase conjugation and decision-feedback equalizer for underwater acoustic communications》.This article is pointed out, within 17 seconds, interval is carried out once Channel detection can realize demodulation, underwater acoustic channel close to time constant, channel phase changes linearly over time, obtains ratio according to data Value is 0.56rad/s, utilizes this linear relationship can realize phase compensation simply when demodulation.The scene of this article institute foundation Data obtain in the case of carrier stationary, and in whole process of the test, transmitting terminal and receiving terminal use laying of seabed subsurface buoy Mode.This research is not directly applicable the situation of carrier movement.

List of references 2:M.Stojanovic et al. in 1994 at IEEE Journal of Oceanic Document " Phase coherent digital communications for underwater is delivered on Engineering acoustic channels》.This article uses second order digital phase-locked loop to carry out the phase compensation in coherent communication.To difference Test data, use post processing mode estimate its Doppler's size, according to Doppler estimate regulate second order digital artificially The parameter of phase-locked loop (PLL), changes its bandwidth, to adapt to the phase place change under different Doppler's size.This method is one Determine in degree, to compensate the phase place change that carrier movement causes, but after needing the data collected are analyzed, artificially Phase compensator is carried out parameter regulation.This processing method can apply to data and processes, but actual available communication equipment is not The artificial parameter that participates in can be allowed to regulate.

List of references 3:B.Geller et al. in 1996 on IEEE Journal of Oceanic Engineering Publish an article: " Equalizer for video rate transmission in multipath underwater communications》.The phase place that article uses quick self-optimizing least mean square algorithm (FOLMS) to carry out in coherent communication is mended Repay.The compensation speed of phase compensator depends on its step-length, and estimation difference Partial derivative estimation is carried out by the size of step-length according to it Optimize.Adaptive step regulates, and estimation difference can be made to minimize, and then obtain on the premise of ensureing to follow the tracks of phase velocity Good phase compensation effect.But the problem that under still suffering from computationally intensive, nonstationary noise, self adaptation easily dissipates.

List of references 4: Zhu Weiqing et al. was published an article on acoustic journal in 2007: " high speed underwater acoustic transmission of image is believed Number processing method ".This article to described in list of references 2, list of references 3 and two kinds of phase compensation modes contrasted, Point out that the tolerance limit of phase compensation (FOLMSPC) based on FOLMS is than second order PLL 5 times.This is owing to the step-length of FOLMSPC exists One symbol intervals inner iteration once, adapts to the change of Doppler frequency shift, and the second order parameter in second order PLL is fixing, Adaptation ability to differ from.This achievement in research has been successfully applied to the underwater acoustic communication set of China " flood dragon number " manned underwater vehicle, and Obtain gratifying test effect.

In sum, PLL method of the prior art carries out phase place discriminating to each sampled point, loop filtering calculates, FOLMSPC method carries out step-length regulating calculation to each sampled point.These calculating need hardware platform to have higher calculating energy Power is supported, is not easy to the miniaturization of underwater sound communication node, low-power consumption.FOLMSPC has carried in tracking ability relative to PLL It is high, it is not necessary to artificial regulation parameter, but there is problems: if algorithm is based on additive Gaussian noise it is assumed that noise Unstable, such as channel occurs spike noise, step-length will become very big moment, be easily caused dissipating of calculating；Step-length is maximum Value is chosen and is used the mode of test data post processing to provide, as being adjusted according to communication bandwidth, mid frequency, and step-length maximum The test data combined under new traffic parameter is needed to be set.

Summary of the invention

It is an object of the invention to overcome existing phase compensating method to calculate complicated, the insecure defect of compensation effect, Thus a kind of phase compensating method simple, reliable is provided.

To achieve these goals, the invention provides a kind of underwater acoustic coherent communication self adaptation phase compensating method, including:

Step 1), from each frame of received water sound communication signal extract Chirp signal, believe for each Chirp Number carry out correlation computations, utilize calculated correlation peak location to ask the average speed of each frame and the estimated value of average acceleration；

Step 2), utilize step 1) estimated value of average speed in each frame duration of obtaining, calculate and relatively draw Stretch coefficient of compressibility, according to described relative Compression and Expansion coefficient calculations result, the reception waveform of water sound communication signal is heavily adopted Sample, completes the compensation of average Doppler；

Step 3), utilize step 1) to estimate the step-length of self adaptation phase compensator big for the average acceleration estimated value that obtains Little；

Step 4), by using step 3) estimate that the self adaptation phase compensator of step sizes obtained is to step 2) obtain Signal after the compensation of average Doppler carries out self adaptation phase compensation.

In technique scheme, the step 2 described) in, according to described relative Compression and Expansion coefficient calculations result pair Water sound communication signal receive that waveform carries out that the method for resampling uses in following methods any one: first-order linear interpolation side Method, parabolic interpolation, Farrow wave filter resampling method.

In technique scheme, described step 3) including:

Step 3-1), after obtaining the average acceleration estimated value of each frame, be first according to equation below and find out the most greatly Speed absolute value:

a_max=max{ | a_i|, i=2 ... L；

Step 3-2), according to step 3-1) the peak acceleration absolute value a that obtains_max, frame length time T, signal wavelength lambda, from Sample rate Fs that adaptation processes, calculates the step size mu of self adaptation phase compensation:

$\mathrm{\μ}=\frac{50a_{max}T}{\mathrm{\λ}Fs}$

Wherein, frame length time T, signal wavelength lambda, sample rate Fs of self-adaptive processing are all given values.

In technique scheme, described step 4) including:

Step 4-1), described self adaptation phase compensator use a upper moment phase estimation value current sign is carried out phase Position compensates, and its computing formula is as follows:

Wherein, r_kFor the symbol after the compensation of average Doppler, also it is the symbol before self adaptation phase compensation simultaneously,For Symbol after self adaptation phase compensation, step 3) estimate that the step sizes obtained affected the phase estimation value in a upper moment's Calculate；

Step 4-2), after obtaining the result of phase compensation, utilize the self adaptation that is connected with self adaptation phase compensator to sentence The current sign expected value that certainly feedback equalizer is given, calculates the phase estimation value of current time according to equation below, when The phase estimation value in front moment is used for the phase compensation of subsequent time and calculates:

Wherein, Im () for asking imaginary part to calculate,For symbol expected valueConjugate.

It is an advantage of the current invention that:

The present invention make full use of carrier relative movement to phase place change between relation, phase compensation will be made to become simpler Single, reliable.

Accompanying drawing explanation

During Fig. 1 is " flood dragon number " manned underwater vehicle dive, underwater acoustic communication set is utilized to gather the Doppler that waveform obtains Estimated value graph of a relation over time；

Fig. 2 is the schematic diagram of the relevant device of water sound communication signal receiving terminal closely-related with the inventive method；

Fig. 3 is the flow chart of the underwater acoustic coherent communication self adaptation phase compensating method of the present invention；

Fig. 4 is the schematic diagram of the water sound communication signal received by receiving terminal；

Fig. 5 is that the planisphere not doing phase compensation (uses QPSK modulation system, SNR=10dB, a_max=1m/s², T= 0.5s, Fs=5kHz, λ=0.15m)；

Fig. 6 is the planisphere (same Fig. 5 of condition, step-length is 0.033) after using the method for the present invention to do phase compensation；

Fig. 7 is the change curve schematic diagram (same Fig. 5 of condition, step-length is 0.033) of true phase, phase estimation and error；

Fig. 8 is set to that (the same Fig. 5 of condition, step-length is respectively for the schematic diagram of different step-length phase positions estimation difference curve 0.033、0.01、0.1)。

Detailed description of the invention

In conjunction with accompanying drawing, the invention will be further described.

By the content disclosed by list of references 1 it is recognised that the phase place that water body medium causes itself is unconspicuous, if It can be avoided that the relative motion of carrier, phase compensation can be the simplest.But in actual applications, underwater acoustic communication set use hull or Person's buoy is transferred, and hull, buoy have certain horizontal movement speed, and is risen and fallen by the water surface to be affected and have certain hanging down Straight movement velocity, causes simple phase compensation way in underwater sound communication to lose efficacy.Fig. 1 is " flood dragon number " manned underwater vehicle dive process In, utilize underwater acoustic communication set to gather Doppler's estimated value graph of a relation over time that waveform obtains, the vertical coordinate in this figure Representing Doppler's estimated value, abscissa represents frame number, is spaced half second between frame and frame.As can be seen from this figure: Doppler estimates Value is not simple constant, hence it is evident that have the feature of fluctuating.Thus, carrier phase is not the most linear, simply Utilize linear phase compensate be not all right.Meanwhile, the cycle that the cycle that Doppler rises and falls at sea rises and falls with ship is consistent, Demonstrate doppler phenomenon to be caused by ship motion.

Phase compensating method of the prior art is based entirely on phase place change speed in collection waveform, sets phase place artificially The parameter of compensator, or utilize the parameter of the error amount adaptive change phase compensator after compensating, carry out Phase Tracking, And do not take in from the angle of carrier movement rule.In this application, make full use of carrier relative movement phase place is changed Between relation, regulate step-length by the acceleration of carrier movement so that the realization of phase compensation become simpler, Reliably.

Before the method for the present invention is elaborated, technical background required when first the inventive method being realized Illustrate.

Underwater acoustic communication set includes two parts, and a part is water sound communication signal transmitting terminal, and another part is underwater sound communication Signal receiving end.Water sound communication signal transmitting terminal therein is used for launching water sound communication signal, the water sound communication signal launched For the coherent modulation waveform at least provided with linear FM signal (Chirp)；Water sound communication signal receiving terminal therein is used for receiving Water sound communication signal.Described water sound communication signal transmitting terminal generates the public affairs that process is those skilled in the art of water sound communication signal Know general knowledge, it is not described in detail.Figure 2 illustrates underwater sound communication closely-related with the inventive method The schematic diagram of the relevant device of signal receiving end.As it can be seen, water sound communication signal receiving terminal includes: receive transducer, AD adopts Storage, average Doppler compensator, self adaptation phase compensator, adaptive decision feedback equalizer and movement velocity detection Device.Wherein, described reception transducer, AD harvester, average Doppler compensator, self adaptation phase compensator, self adaptation are sentenced Certainly feedback equalizer is sequentially connected with, the outfan of described adaptive decision feedback equalizer also with described self adaptation phase compensator Input connect.The outfan of AD harvester is connected to the input of movement velocity detector, movement velocity detector defeated Go out end and be connected respectively to average Doppler compensator, the input of self adaptation phase compensator.

On the basis of the said equipment, below with regard to water sound communication signal receiving terminal after receiving water sound communication signal how The method realizing phase compensation is illustrated.

With reference to Fig. 3, the underwater acoustic coherent communication self adaptation phase compensating method of the present invention comprises the following steps:

Step 1), from each frame of received water sound communication signal extract Chirp signal, believe for each Chirp Number carry out correlation computations, utilize calculated correlation peak location to ask the average speed of each frame and the estimated value of average acceleration.

The schematic diagram of water sound communication signal received by receiving terminal, described water sound communication signal bag are presented in Fig. 4 it Including multiple frame, each frame includes a Chirp signal and a coherent modulation frame, and described Chirp signal is positioned at water sound communication signal frame Beginning.Time span T of transmitting terminal water sound communication signal frame_iRepresent, in this application, different water sound communication signal frames Time span is identical, i.e. T₁=T₂=...=T_L=T.The width R of the water sound communication signal frame received_iRepresent.

When the average speed calculated in each frame duration, calculated in each frame duration by equation below The estimated value of average speed:

$v_i=\frac{R_i-R_{i-1}}{T}c,i=1,2,\mathrm{...}L---\left(1\right)$

Wherein, c=1500m/s is sound wave spread speed in water.

After calculating the estimated value of average speed, it is also possible to calculate the average acceleration in each frame duration further The estimated value of degree:

$a_i=\frac{v_i-v_{i-1}}{T}=\frac{R_i+R_{i-2}-2R_{i-1}}{T^2}c,i=2,...L---\left(2\right)$

Step 2), utilize step 1) estimated value of average speed in each frame duration of obtaining, calculate and relatively draw Stretch coefficient of compressibility, according to relative Compression and Expansion coefficient calculations result, the reception waveform of water sound communication signal is carried out resampling, complete Become the compensation of average Doppler.

In the present embodiment, water sound communication signal receives waveform carrying out the method for resampling is first-order linear interpolation side Method, but in other embodiments, it is possible to use such as parabola interpolation, the method for Farrow wave filter resampling.

Step 3), utilize step 1) to estimate the step-length of self adaptation phase compensator big for the average acceleration estimated value that obtains Little.This step specifically includes:

Step 3-1), in step 1) in obtained the average acceleration estimated value of each frame after, be first according to equation below Find out peak acceleration absolute value.

a_max=max{ | a_i|, i=2 ... L (3)

Step 3-2), according to peak acceleration absolute value a_max, frame length time T, signal wavelength lambda, the sampling of self-adaptive processing Rate Fs, calculates the step size mu of self adaptation phase compensation:

$\mathrm{\μ}=\frac{50a_{max}T}{\mathrm{\λ}Fs}---\left(4\right)$

In above-mentioned formula, frame length time T, signal wavelength lambda depend on mid frequency, sample rate Fs of self-adaptive processing depends on In character rate, these three value when Communication System Design it has been determined that be all given value.

The derivation of above-mentioned formula (4) is as follows:

Hereinafter the formula (6) equivalent equation under small-signal model assumed condition is:

Wherein,For the phase estimation value of kth sampled point, x_kPhase place actual value for kth sampled point.

When carrier carries out relative motion with v speed in certain period, enter the sequence phase change sequence of phase compensator It is classified as:

x_k=Bk, k >=0

WhereinNow phase compensator is output as:

Thus, maximum phase estimated difference is

For coherent communication, phase error is less thanTime, little to the Control of Bit Error Rate of demodulation.Thus, order maximum Phase estimation is poorObtainThis formula is exactly the formula (4) being previously mentioned before.

Step 4), by using step 3) estimate that the self adaptation phase compensator of step sizes obtained is to step 2) obtain Signal after the compensation of average Doppler carries out self adaptation phase compensation.

Described self adaptation phase compensator is to step 2) signal after the compensation of average Doppler that obtains carries out self adaptation During phase compensation, using the phase estimation value in a upper moment that current sign is carried out phase compensation, its computing formula is as follows:

Wherein, r_kFor the symbol after the compensation of average Doppler, also it is the symbol before self adaptation phase compensation simultaneously,For Symbol after self adaptation phase compensation, step 3) estimate that the step sizes obtained affectsCalculating.

After obtaining the result of phase compensation, utilize the adaptive decision-feedback equalization being connected with self adaptation phase compensator The current sign expected value that device is given, can calculate the phase estimation value of current time, current time according to equation below (6) Phase estimation value can be used for subsequent time phase compensation calculate:

Wherein, Im () for asking imaginary part to calculate,For symbol expected valueConjugate.

It is above the description of the self adaptation phase compensating method to the present invention.The method using the present invention has good effect Really.

An example is given below, and water sound communication signal uses QPSK modulation system, SNR=10dB, a_max=1m/s²,T =0.5s, Fs=5kHz, λ=0.15m, then be calculated step-length according to formula (4)

Fig. 5 is the planisphere not doing phase compensation, and Fig. 6 is the constellation after using the method for the present invention to do phase compensation Figure.From the comparison of the two figure this it appears that: Fig. 5 does not sees the feature that QPSK planisphere is distributed, this is because channel Phase place change causes.This it appears that QPSK planisphere feature in Fig. 6, the point on Fig. 6 is mainly distributed on 4 regions, right Answer 4 states that QPSK modulates, illustrate that its phase compensation is suitable.

Fig. 7 is the change curve of true phase, phase estimation and error.Fig. 8 is given and is set to that different step-length phase position is estimated Meter curve of error, step-length value 0.033,0.01,0.1 respectively.Can be seen that when step-length less (step-length is 0.01), curve becomes Change slowly, it is impossible to perfect tracking phase place changes.When step-length relatively big (step-length is 0.1), curvilinear motion quickly, due to channel additivity The phase noise that noise causes well is not suppressed.This demonstrate that the application motion conditions according to reality, by calculating The step-length estimated is rational.

It should be noted last that, above example is only in order to illustrate technical scheme and unrestricted.Although ginseng According to embodiment, the present invention is described in detail, it will be understood by those within the art that, the technical side to the present invention Case is modified or equivalent, and without departure from the spirit and scope of technical solution of the present invention, it all should be contained in the present invention Right in the middle of.

Claims (4)

1. a underwater acoustic coherent communication self adaptation phase compensating method, including:

Step 1), from each frame of received water sound communication signal extract Chirp signal, enter for each Chirp signal Row correlation computations, utilizes calculated correlation peak location to ask the average speed of each frame and the estimated value of average acceleration；

Step 2), utilize step 1) estimated value of average speed in each frame duration of obtaining, calculate and relatively stretch pressure Contracting coefficient, carries out resampling according to described relative Compression and Expansion coefficient calculations result to the reception waveform of water sound communication signal, Complete the compensation of average Doppler；

Step 3), utilize step 1) the average acceleration estimated value that obtains estimates the step sizes of self adaptation phase compensator；

Step 4), by using step 3) estimate that the self adaptation phase compensator of step sizes obtained is to step 2) obtain average Signal after the compensation of Doppler carries out self adaptation phase compensation.

Underwater acoustic coherent communication self adaptation phase compensating method the most according to claim 1, it is characterised in that in described step Rapid 2), in, according to described relative Compression and Expansion coefficient calculations result, water sound communication signal is received waveform and carry out resampling Method uses any one in following methods: first-order linear interpolation method, parabolic interpolation, Farrow wave filter resampling Method.

Underwater acoustic coherent communication self adaptation phase compensating method the most according to claim 1, it is characterised in that described step 3) including:

Step 3-1), after obtaining the average acceleration estimated value of each frame, be first according to equation below and find out peak acceleration Absolute value:

a_max=max{ | a_i|, i=2 ... L；

Step 3-2), according to step 3-1) the peak acceleration absolute value a that obtains_max, frame length time T, signal wavelength lambda, self adaptation Sample rate Fs processed, calculates the step size mu of self adaptation phase compensation:

$\mathrm{\μ}=\frac{50a_{max}T}{\mathrm{\λ}Fs}$

Wherein, frame length time T, signal wavelength lambda, sample rate Fs of self-adaptive processing are all given values.

Underwater acoustic coherent communication self adaptation phase compensating method the most according to claim 1, it is characterised in that described step 4) including:

Step 4-1), described self adaptation phase compensator use a upper moment phase estimation value current sign is carried out phase place benefit Repaying, its computing formula is as follows:

Wherein, r_kFor the symbol after the compensation of average Doppler, also it is the symbol before self adaptation phase compensation simultaneously,For adaptive Answer the symbol after phase compensation, step 3) estimate that the step sizes obtained affected the phase estimation value in a upper momentCalculating；

Step 4-2), after obtaining the result of phase compensation, utilize anti-with the self-adaptive decision that self adaptation phase compensator is connected The current sign expected value that feedback equalizer is given, calculates the phase estimation value of current time, time current according to equation below The phase estimation value carved is used for the phase compensation of subsequent time and calculates:

Wherein, Im () for asking imaginary part to calculate,For symbol expected valueConjugate.