CN1716840A - Precise frame synchronizing method in hydroacoustic communication - Google Patents

Abstract

The present invention relates to a method of the accurate frame synchronization for water sound communication mainly comprising the following steps: 1) digital processing of the received signals, respectively using the copy of Su (t) and Sd (t) to make a relevant processing of the copy of the received signal R (t) and respectively calculating the absolute values of the relevant functions |Cu (t)| and |Cd (t)|; 2) comparing |Cu (t)| & |Cd (t)| with one set threshold; if the result is smaller than the threshold, it will return to step 1) and make a relevant processing; if |Cu (t)| and |Cd (t)| surpasses the threshold, the result is regarded as the arrival of the synchronous pulse and then the calculation can turn to step 3; 3) calculating Tu and Td corresponding to the biggest value of |Cu (t)| and |Cd (t)| and also calculating the interval delta of the two relevant peak positions and then calculating relative Doppler beta; 4) calculating the central point of the two relevant peak positions and take it as the starting point of the time for the synchronous signals. The advantages of the invention are as follows: providing the accurate estimation values of the Doppler and the arrived time, which are very important to the water sound communications under certain conditions and can enhance the communication results. In addition, the invention can greatly reduce the volume of calculation for deciphering.

Description

The method of the accurate frame synchronization in a kind of underwater sound communication

Technical field

The present invention relates to the underwater sound communication field, mainly is the method for the accurate frame synchronization in a kind of underwater sound communication.

Background technology

Underwater sound communication is meant the relevant technologies that communicates with acoustically in the seawater medium, compare with wire communication with radio communication, underwater sound communication is a kind of more complicated communication mode, and its complexity mainly shows two aspects of dispersing of the broadening of time dimension of signal of communication and frequency dimension.Cause that signal comprises that in the factor of time dimension broadening multipath transmisstion effect, ocean current influence, energy are in the propagation in seabed etc., cause that signal comprises relative motion between transmit-receive platform, the kinetic scattering in influence, sea of ocean current (as morning and evening tides, interior ripple, whirlpool etc.), the signal fadeout in the seawater etc. in the factor that frequency dimension is dispersed, in fact owing to the time variation of channel, can not merely distinguish the energy dissipation of time dimension or frequency dimension.Because the propagation velocity of sound wave in seawater be slow (being about 1500m/s), the relative dobla of underwater sound communication channel is far longer than radio channel, even can reach magnitude more than 2%, and signal broadening in time may reach tens of to hundreds of milliseconds of magnitudes.For the signal that uses some form carries out underwater sound communication, must realize the Signal Matching under high dobla and the big time explanation application conditions, this just need make estimation accurately to relative dobla and signal due in earlier before to communication information decoding, to realize the decoding processing of low error rate.Similar with other communication mode, underwater sound communication comprise also that information sends and receiving terminal between shake hands, processes such as frame synchronization and information coding and decoding, the present invention is exactly a technology of carrying out accurate frame synchronization at dobla and time bidimensional of being developed at the frame synchronization link.

Frame synchornization method in the past mainly contains three kinds: a kind of method is to utilize a chirp pulse signal (brief note is the LFM signal) or pseudo random sequence signal (as the m sequence) as frame head, in receiving processing, LFM signal or m sequence signal are made process of pulse-compression, can extract the pulse due in like this, as shown in Figure 1, this method realizes simple, effectively, but can not estimate relative dobla value, only be applicable to low dobla occasion, is when transmitting the subaqueous survey data between buoy as sea bed base fixed platform to water surface anchor, because the relative motion speed between platform is very little, just can use this frame head and frame synchornization method.

Second method is to launch a LFM signal earlier, then launch a kind of pure-tone pulse signal (brief note is the CW pulse) again, in receiving processing,, the LFM signal can extract the pulse due in by being made process of pulse-compression, pulse is done spectrum analysis and can be measured the dobla frequency deviation value to CW, as shown in Figure 2, so just realized the accurate estimation synchronously of pulse due in and dobla frequency deviation, this method is also simpler in realization, but owing to will realize higher frequency spectrum resolving power, need to use the CW pulse wide than long pulse, in fact this taken call duration time, reduced traffic rate.

The third method is to utilize to have certain hour two sub-frame-synchronizing impulses at interval to realize, as shown in Figure 3, each subframe frame head remains a LFM signal, the Transmission Time Interval of two subframe frame heads is that fix, known, at receiving terminal owing to be subjected to the influence of dobla effect, can change the time of advent of two subframes at interval, measures this variation and just can estimate the dobla frequency deviation, also can obtain the due in of each subframe simultaneously.This method has preferable performance, but has difficulties aspect realization, and mainly being needs to preserve earlier a complete subframe signal, can estimate the dobla frequency deviation value, shared like this calculator memory is very big, and especially when subframe was long, this problem was just more outstanding.

Summary of the invention

The present invention is directed to the deficiency of above three kinds of methods, and the method for the accurate frame synchronization in a kind of underwater sound communication is provided.This method can estimate relative dobla value and signal due in simultaneously, and only takies the width of a pulse signal, can not reduce traffic rate, and this method is also less to the occupancy of internal memory.

The technical solution adopted for the present invention to solve the technical problems.The method of the accurate frame synchronization in this underwater sound communication mainly may further comprise the steps:

1) make computer digit, to received signal and handle, establishing its sample rate is f _s, use s respectively _u(t) and s _d(t) copy r (t) is to received signal made the copy relevant treatment, and above-mentioned copy relevant treatment refers to a kind of correlation process method, and this method is finished following correlation function and calculated:

$C_u\left(\mathrm{\τ}\right)={\∫}_0^{T}r(t+\mathrm{\τ})s_u\left(t\right)\mathrm{dt}...\left(18\right)$

$C_d\left(\mathrm{\τ}\right)={\∫}_0^{T}r(t+\mathrm{\τ})s_d\left(t\right)\mathrm{dt}...\left(19\right)$

And the absolute value of calculating correlation function | C _u(τ) | and | C _d(τ) |;

2), | C _u(τ) |, | C _d(τ) | compare with a thresholding of setting,, then return step 1) and proceed relevant treatment if less than thresholding, if | C _u(τ) | and | C _d(τ) | surpass thresholding, then be judged to lock-out pulse and arrived, calculate and change step 3 over to;

3), calculate respectively | C _u(τ) | and | C _d(τ) the pairing time τ of | maximum _uAnd τ _d, and the interval delta of (20) formula of pressing calculating pairwise correlation peak position, calculate relative dobla β by (22) formula again;

Δ＝τ _u-τ _d (20)

Can obtain:

$\mathrm{\Δ}=\frac{2\mathrm{\β}{f}_c}{M}{f}_s...\left(21\right)$

After the alternate position spike of measuring the pairwise correlation peak, formula can be obtained relative dobla thus,

$\mathrm{\β}=\frac{\mathrm{\ΔM}}{2f_c{f}_s}...\left(22\right)$

4), calculate the mid point Λ of pairwise correlation peak position by (23) formula, and with this start time as synchronizing signal,

$\mathrm{\Λ}=\frac{{\mathrm{\τ}}_u+{\mathrm{\τ}}_d}{2}{f}_s...\left(23\right).$

Useful effect of the present invention is: the present invention is by carrying out suitable design to the frame-synchronizing impulse in the underwater sound communication, and provide corresponding processing method, can provide accurate dobla estimated value and the time of advent estimated value, this binomial estimated value is very important for the underwater sound communication under some condition.Nearly all underwater sound communication all needs the frame synchronization time is estimated, when carrying out high-speed communication, the estimated accuracy of frame synchronization time had higher requirements; Exist in the environment for use of relative motion between information transmission platform and message pick-up platform, most underwater sound communication modes need effectively be estimated the dobla value, can effectively improve communication efficiency like this, also can reduce the amount of calculation of decoding in addition greatly.

Compare with method in the past, method provided by the present invention have the frame-synchronizing impulse holding time short, calculate simple, committed memory is little, dobla and the high advantage of the estimated accuracy time of advent, the present invention is suitable for most of underwater sound communication environment and uses.

The present invention is carried out computer mould fitted sea trial, all confirmed result of use of the present invention.Computer simulation results shows that under the single channel condition, the dobla estimated accuracy can reach 0.01% magnitude relatively, and the time of arrival (toa) estimated accuracy can reach the 0.01ms magnitude; Be about the test of carrying out under the 6 joint conditions under the neritic environment in ship's speed; ship's speed is calculated by GPS; relative dobla that the present invention is estimated and ship's speed basically identical; the dobla estimated accuracy can reach 0.05% magnitude relatively; because the absolute time that signal arrives is unable to estimate; can only estimate the time interval between the consecutive frame lock-out pulse; this time interval estimated value comprehensively compares with the time interval that transmits and relative dobla estimated value; the estimated accuracy that can obtain the time interval can reach the 0.05ms magnitude; signal center frequency is 9600Hz during test, and bandwidth is 3600Hz.Utilize method of the present invention to make the underwater sound communication instrument, and carried out the sea trial checking, proved the practicality of method.

Description of drawings

Fig. 1 is the LFM pulse is used for the Measuring Time starting point as the underwater sound communication frame synchronizing signal a schematic diagram;

Fig. 2 is a schematic diagram of making frame synchronization difference Measuring Time starting point and dobla with LFM and CW pulse;

Fig. 3 is LFM frame-synchronizing impulse starting point estimated time and the dobla schematic diagram with two subframes;

Fig. 4 is accurate frame synchronization implementing procedure figure of the present invention;

Fig. 5 is a copy signal waveforms of the present invention;

Result of calculation schematic diagram when Fig. 6 is no dobla;

Fig. 7 is that relative dobla is-0.0035 o'clock a result of calculation schematic diagram.

Embodiment

The invention will be described further below in conjunction with drawings and Examples:

In the present invention, the frame synchronization head adopts two kinds of chirp pulse signal s _u(t) and s _d(t), they can be expressed as:

s _u(t)＝sin(2πf _lt+πMt ²) t∈[0，T] (1)

s _d(t)＝sin(2πf _ht-πMt ²) t∈[0，T] (2)

The centre frequency of two kinds of LFM signals is identical, is f _c, s _u(t) be the forward FM signal, its instantaneous frequency changes in time and raises, s _d(t) be the negative sense FM signal, its instantaneous frequency changes in time and descends, f in the following formula _lAnd f _hBe respectively the low side frequency and the high-end frequency of LFM signal, M is a frequency change rate, and T is a pulse duration, and signal bandwidth is B, has following relational expression to set up:

f _l＝f _c-MT/2 (3)

f _h＝f _c+MT/2 (4)

f _c＝(f _l+f _h)/2 (5)

B＝MT＝f _h-f _l (6)

Obtain signal s (t) behind these two kinds of LFM signal plus,

s(t)＝s _u(t)+s _d(t) (7)

S (t) is sent to transducer after linear power amplifier amplifies, acoustical signal is transmitted in the water.

Because have relative motion between the receiving terminal of underwater sound communication and the transmitting terminal, then received signal is put in place in time and stretches or compress, on frequency, produce the dobla frequency deviation, received signal can be expressed as:

r(t)＝r _u(t)+r _d(t) (8)

ru(t)＝sin(2πk?f _l(t-τ)+πMk ²(t-τ) ²) (9)

rd(t)＝sin(2πk?f _h(t-τ)+πMk ²(t-τ) ²) (10)

K represents time-stretching/compressibility factor respectively in the formula, represents relative dobla with β, k=1+ β then, the radially speed v between β and the transmitting-receiving two-end _rC is relevant with the velocity of sound,

$\mathrm{\β}=\frac{{2v}_r}{c}...11)$

The β value is much smaller than 1, and relative radial rate generally is lower than 10 joints between receiving and dispatching during underwater sound communication, and this moment, the β value was about 3.3 ‰.

Two kinds of instantaneous frequencys that transmit are respectively:

f _uT(t)＝f _l+Mt (12)

f _dT(t)＝f _h-Mt (13)

The instantaneous frequency of received signal is respectively:

f _uR(t)＝kf _l+k ²Mt≈f _uT(t)-β(f _l+2Mt) (14)

f _dR(t)＝kf _h-k ²Mt≈f _dT(t)-β(f _h-2Mt) (15)

Copy relevant treatment to received signal, can be owing to the coupling between life period and the dobla is blured and indeterminacy relevant peaks position, this is because except that signal time postponed, the skew of the dobla of frequency also can produce relevant time delay, can be referred to as the frequency deviation time delay.r _u(t) and r _d(t) frequency deviation time delay is respectively:

${\mathrm{\τ}}_u=\mathrm{\β}\frac{f_h}{M}...\left(16\right)$

${\mathrm{\τ}}_d=-\mathrm{\β}\frac{f_l}{M}...\left(17\right)$

Make computer digit to received signal and handle, establishing its sample rate is f _s, use s respectively _u(t) and s _d(t) copy r (t) is to received signal made the copy relevant treatment.So-called copy relevant treatment refers to a kind of cross correlation process method, and this method is finished following cross-correlation function and calculated:

$C_u\left(\mathrm{\τ}\right)={\∫}_0^{T}r(t+\mathrm{\τ})s_u\left(t\right)\mathrm{dt}...\left(18\right)$

$C_d\left(\mathrm{\τ}\right)={\∫}_0^{T}r(t+\mathrm{\τ})s_d\left(t\right)\mathrm{dt}...\left(19\right)$

Two copy correlation function absolute values | C _u(τ) | and | C _d(τ) the pairing position of | maximum difference τ _uAnd τ _d, their difference is:

Δ＝τ _u-τ _d (20)

Can obtain:

$\mathrm{\Δ}=\frac{2\mathrm{\β}{f}_c}{M}{f}_s...\left(21\right)$

After the alternate position spike of measuring the pairwise correlation peak, formula can be obtained relative dobla thus,

$\mathrm{\β}=\frac{\mathrm{\ΔM}}{2f_c{f}_s}...\left(22\right)$

Simultaneously, use τ _uAnd τ _dThe starting point that all right estimated signal arrives, the mid point of pairwise correlation peak position is Λ,

$\mathrm{\Λ}=\frac{{\mathrm{\τ}}_u+{\mathrm{\τ}}_d}{2}{f}_s...\left(23\right)$

Can be with the signal start time of this point midway, its precision is more than only using τ _uOr τ _dWant high as start point signal.

The method of the accurate frame synchronization in this underwater sound communication of the present invention, complete computational process as shown in Figure 4, concrete steps are as follows:

Step 1: input signal r (t) is used s respectively by (18), (19) formula _u(t) and s _d(t) make the copy relevant treatment, and calculate the absolute value of correlation function | C _u(τ) | and | C _d(τ) |.

Step 2:|C _u(τ) |, | C _d(τ) | compare with a thresholding of setting,, then return step 1 and proceed relevant treatment if less than thresholding, if | C _u(τ) | and | C _d(τ) | surpass thresholding, then be judged to lock-out pulse and arrived, calculate and change step 3 over to.

Step 3: calculate respectively | C _u(τ) | and | C _d(τ) the pairing time τ of | maximum _uAnd τ _d, and the interval delta of (20) formula of pressing calculating pairwise correlation peak position, calculate relative dobla β by (22) formula again.

Step 4:, calculate the mid point Λ of pairwise correlation peak position by (23) formula, and with this start time as synchronizing signal.

Concrete calculated examples:

The centre frequency of LFM pulse signal is f _c=4800Hz, the low side frequency f _l=3600Hz, high-end frequency f _h=6000Hz, pulse width T=50ms, frequency change rate M=48000Hz/s, signal bandwidth B=2400Hz.

Situation when at first considering no dobla frequency deviation, two copy signal s _u(t) and s _d(t) waveform as shown in Figure 5.S (t) is s _u(t) and s _d(t) sum, s (t) is for transmitting, and the starting point of s (t) pulse signal is 10.02ms.

If received signal r (t) is identical with s (t), the then waveform of r (t) and it and s _u(t) and s _d(t) copy correlation function C _u(τ), C _dEnvelope diagram (τ) is as shown in Figure 6:

Because received signal does not have dobla, so copy correlation function C _u(τ), C _dThe starting point of the equal directional signal in position of maximum correspondence (τ), the start point signal that estimates are 10.02ms, this moment the pairwise correlation peak position interval delta=0, so the relative dobla frequency deviation β that is calculated also is 0.

Having under the situation of dobla, is example with relative dobla β=-0.0035, and the start time of signal still is 10.02ms.Copy correlation function C _u(τ), C _dEnvelope diagram (τ) as shown in Figure 7, the situation during with no dobla is compared, skew has taken place in the pairwise correlation peak position, C _u(τ) that the peak value correspondence of envelope is τ _u=9.667ms, C _d(τ) that the peak value correspondence of envelope is τ _d=10.375ms, the interval delta of pairwise correlation peak position=-0.708ms, can estimate relative dobla value thus is-0.00354, the mid point of pairwise correlation peak position is Λ=10.02ms, therefore the start point signal that can estimate is at 10.02ms, and this is more than using τ u or τ _dWant high as the precision of start point signal.

Claims (3)

1, the method for the accurate frame synchronization in a kind of underwater sound communication is characterized in that: mainly may further comprise the steps:

1) make computer digit, to received signal and handle, establishing its sample rate is f _s, use s respectively _u(t) and s _d(t) copy r (t) is to received signal made the copy relevant treatment, and above-mentioned copy relevant treatment refers to a kind of correlation process method, and this method is finished following correlation function and calculated:

$C_u\left(\mathrm{\τ}\right)={\∫}_0^{T}r(t+\mathrm{\τ})s_u\left(t\right)\mathrm{dt}---\left(18\right)$

$C_d\left(\mathrm{\τ}\right)={\∫}_0^{T}r(t+\mathrm{\τ})s_d\left(t\right)\mathrm{dt}---\left(19\right)$

And the absolute value of calculating correlation function | C _u(τ) | and | C _d(τ) |;

2), | C _u(τ) |, | C _d(τ) | compare with a thresholding of setting,, then return step 1) and proceed relevant treatment if less than thresholding, if | C _u(τ) | and | C _d(τ) | surpass thresholding, then be judged to lock-out pulse and arrived, calculate and change step 3 over to;

3), calculate respectively | C _u(τ) | and | C _d(τ) the pairing time τ of | maximum _uAnd τ _d, and the interval delta of (20) formula of pressing calculating pairwise correlation peak position, calculate relative dobla β by (22) formula again;

Δ＝τ _u-τ _d (20)

Can obtain:

$\mathrm{\Δ}=\frac{2\mathrm{\β}{f}_c}{M}{f}_s---\left(21\right)$

After the alternate position spike of measuring the pairwise correlation peak, formula can be obtained relative dobla thus,

$\mathrm{\β}=\frac{\mathrm{\ΔM}}{2f_c{f}_s}---\left(22\right)$

4), calculate the mid point Λ of pairwise correlation peak position by (23) formula, and with this start time as synchronizing signal,

$\mathrm{\Λ}=\frac{{\mathrm{\τ}}_u+{\mathrm{\τ}}_d}{2}{f}_s---\left(23\right).$

2, the method for the accurate frame synchronization in the underwater sound communication according to claim 1 is characterized in that: described s _u(t) and s _d(t) be that the frame synchronization head adopts two kinds of chirp pulse signals, they can be expressed as:

s _u(t)＝sin(2πf _lt+πMt ²) t∈[0，T] (1)

s _d(t)＝sin(2πf _ht-πMt ²) t∈[0，T] (2)

The centre frequency of two kinds of LFM signals is identical, is f _c, s _u(t) be the forward FM signal, its instantaneous frequency changes in time and raises, s _d(t) be the negative sense FM signal, its instantaneous frequency changes in time and descends, f in the following formula _lAnd f _hBe respectively the low side frequency and the high-end frequency of LFM signal, M is a frequency change rate, and T is a pulse duration, and signal bandwidth is B, has following relational expression to set up:

f _l＝f _c-MT/2 (3)

f _h＝f _c+MT/2 (4)

f _c＝(f _l+f _h)/2 (5)

B＝MT＝f _h-f _l (6)。

3, the method for the accurate frame synchronization in the underwater sound communication according to claim 1 is characterized in that: received signal is put in place in time to be stretched or compresses, and produces the dobla frequency deviation on frequency, and received signal is expressed as:

r(t)＝r _u(t)+r _d(t) (8)

r _u(t)＝sin(2πkf _l(t-τ)+πMk ²(t-τ) ²) (9)

r _d(t)＝sin(2πkf _h(t-τ)+πMk ²(t-τ) ²) (10)

K represents time-stretching/compressibility factor respectively in the formula, represents relative dobla with β, k=1+ β then, the radially speed v between β and the transmitting-receiving two-end _rC is relevant with the velocity of sound,

$\mathrm{\β}=\frac{{2v}_r}{c}---\left(11\right).$

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