CN102170314A - Hyperbolic frequency-modulation spread spectrum acoustic communication method - Google Patents

Abstract

The invention discloses a hyperbolic frequency-modulation spread spectrum acoustic communication method, comprising the following steps: forming a basic waveform by two hyperbolic frequency-modulation signals which respectively have negative modulation rate and passive modulation rate; according to information to be sent and a preset shift step size, determining the shift of a carrier signal; carrying out cyclic shift on the carrier signal to realize multielement modulation; applying a pilot signal to the cyclic shift carrier signal to form a compound signal; sending the compound signal to an acoustic channel by a transmitting transducer; estimating the relevant output peak value position of the pilot signal and the carrier signal by the related duplicate technology on a receiving terminal; comparing the difference of relevant output peak value position of the pilot signal and the relevant output peak value position of the carrier signal with the shift step size; and looking up a table to code according to the preset multielement modulation of a transmitting terminal. The hyperbolic frequency-modulation spread spectrum acoustic communication method has small calculated amount and a simple receiver, and stability is improved.

Description

A kind of Hyperbolic Frequency Modulation spread-spectrum underwater sound communication method

Technical field

The invention belongs to the water sound communication technique field, be specifically related to a kind of spectrum spread communication method in the mobile underwater sound communication.

Background technology

Unmanned under water aircraft (UUV) is as the important tool of marine exploration, become the research focus in ocean engineering field, various countries, wherein, being applied to the mobile underwater sound communication in the UUV motion process, is to contain one of new and high technology of the countries in the world of marine technology and information technology being badly in need of.

Underwater acoustic channel generally can be characterized by limited bandwidth, multipath serious interference the time, frequently, the space-variant channel.Features such as the complicated multipath transmisstion of underwater acoustic channel, high background noise, deep fade have seriously limited the underwater sound communication performance.Especially, for mobile underwater sound communication, because the propagation velocity of sound wave in seawater is 1500m/s only, and the underwater movement velocity of aircraft is generally 1.5-15m/s.Comparatively speaking, time explanation or the compression that higher speed of related movement and sound wave lower propagation velocity in water have caused signal of communication between aircraft.

In recent years, the spread-spectrum underwater sound communication technology receives bigger concern, its reason: 1.. long-range (＞10km) in the underwater sound communication, received signal to noise ratio is lower, often below 0dB, and the related gain of spread-spectrum signal is big, can be so that it carries out the correct demodulation of signal under the condition below the 0dB; 2.. interference of its anti-multipath and channel fading ability are strong, and quilt is intercepted and captured with detection probability low, good confidentiality; 3.. spread spectrum is the technical foundation of the multi-user's underwater sound communication in the underwater sound communication network, and the finite bandwidth of underwater acoustic channel has limited the application of frequency division multiplexing (FDMA) technology in underwater acoustic network, and time division multiplexing (TDMA) needs strict simultaneous techniques.Generally believe that at present spread spectrum and CDMA (Code Division Multiple Access) (CDMA) are the multiple access access schemes that the shallow-sea underwater acoustic communication network has application prospect most.Multiple DS-CDMA scheme and the corresponding signal process technology that is used for underwater sound communication network now proposed.As seen, the spread-spectrum underwater sound communication technology has important application prospects.

At present spread-spectrum underwater sound communication method is mainly with pseudo random sequence, as m sequence, the Gold sequence communication mode as spreading code, is summarized as follows:

(1). direct sequence spread spectrum skill

Direct sequence spread spectrum (DSSS) underwater sound communication system, its transmitting terminal only distributes a frequency expansion sequence, if frequency expansion sequence length is L, each chip duration is T.Its information is then carried out demodulation according to the phase place of frequency expansion sequence by transmitting on the phase place that is modulated at frequency expansion sequence at receiving terminal.

(2) .M unit spectrum spreading method

In order to improve the spread spectrum communication data transfer rate, can adopt the M element spread spectrum communication method.Its basic principle is: according to the binary message of the n bit that will transmit, choose some pseudo noise codes and carry out launching after the phase modulated in one group of set that comprises M=2n pseudo noise code.Receiving terminal comprises one group of matched filter, the sequence of each filter match in the pseudo random sequence group.According to the orthogonality of pseudo random sequence, the output that only is matched with the filter that transmits could surpass decision threshold, deciphers according to this, and data transfer rate improves log2M doubly.

(3) .M unit The parallel combined spread spectrum

Because the accurate orthogonality between the M unit pseudo noise code can be chosen k pseudo noise code simultaneously at transmitting terminal, carry out respectively launching simultaneously after the phase modulated, with further raising data transfer rate, be called The parallel combined M element spread spectrum communication.In the reality, usually M pseudo noise code is divided into the N group, according to information transmitted, selects a pseudo noise code from every group, total N pseudo noise code carried out phase modulated respectively, and after the stack, formation transmits.A kind of special case that can regard M element spread spectrum communication technology as The parallel combined M element spread spectrum communication, i.e. transmission means during N=1.

But, Doppler effect will appear during owing to the UUV motion, cause conventional underwater sound communication, and particularly above-mentioned underwater sound spread-spectrum communication systematic function based on pseudo random sequence will sharply descend.Its reason is: 1.. Doppler effect causes the phase place of signal of communication that serious variation takes place, and can't realize the correct demodulation of phase place, error rate height based on the underwater sound communication system of direct sequence spread spectrum; 2. spread-spectrum underwater sound communication system of .M unit adopts the size of the output peak value of one group of matched filter to carry out demodulation usually, and the pseudo random sequence phase-modulated signal has sharp-pointed ambiguity function figure, be that less Doppler frequency shift has decline with regard to the amplitude output signal that causes matched filter, the UUV motion has caused the matched filter mismatch of receiver, can't carry out correct demodulation; 3.. the multipath transmisstion of underwater acoustic channel complexity causes serious intersymbol interference, utilizes the coherent approach demodulation need accurately estimate underwater acoustic channel, system complexity height.

Summary of the invention

In order to overcome the deficiency that prior art causes the underwater sound communication system performance sharply to descend owing to Doppler effect, the invention provides a kind of Hyperbolic Frequency Modulation spread-spectrum underwater sound communication method, utilize the Hyperbolic Frequency Modulation signal correlation properties insensitive and good, can obtain the mobile spread-spectrum underwater sound communication method of higher rate, low complex degree Doppler effect.

The technical solution adopted for the present invention to solve the technical problems may further comprise the steps:

(1). form basic waveform by 2 Hyperbolic Frequency Modulation signals that are respectively positive and negative modulation rate, wherein, positive frequency modulation Hyperbolic Frequency Modulation signal is as carrier signal f (t), and negative frequency modulation Hyperbolic Frequency Modulation signal is as pilot signal p (t), these two signal nearly orthogonals, its cross-correlation function can be expressed as:

Wherein τ represents to postpone, and T represents the length of carrier signal and pilot signal;

(2). at the communication transmitting terminal, determine carrier signal f (t) shift size according to information to be sent and predefined shift step, and carrier signal is carried out cyclic shift, realize polynary modulation;

(3). on the carrier signal of superimposed pilot signal to the cyclic shift, form composite signal, and composite signal is transmitted into underwater acoustic channel by transmitting transducer;

(4). adopt the relevant output of duplicate correlation technique estimation pilot signals peak at receiving terminal;

(5). adopt the duplicate correlation technique to estimate the relevant output of carrier signal peak at receiving terminal;

(6). poor with the relevant output of pilot signal relevant output peak peak with carrier signal, compare with shift step, and the predefined polynary modulation decoding of tabling look-up according to transmitting terminal.

The invention has the beneficial effects as follows: the present invention compares with the direct sequence spread spectrum underwater sound communication, has utilized the duplicate correlation technique to adjudicate and decipher, and need not to carry out phase demodulating, has improved stability; Compare with the first spread-spectrum underwater sound communication of M, owing to only adopt one road duplicate correlator, so amount of calculation is low; Because the Hyperbolic Frequency Modulation signal is moving insensitive to Doppler frequency shift, and pilot tone Hyperbolic Frequency Modulation signal can revise because the skew of the relevant peaks position that Doppler effect causes is applicable to mobile underwater sound communication; Owing to adopt non-coherent demodulation, need not to carry out channel estimating, receiver is simple.

Description of drawings

Fig. 1 is the invention flow chart;

Fig. 2 is the correlation properties figure of carrier wave Hyperbolic Frequency Modulation signal and pilot tone hyperbolic signal;

Fig. 3 is the correlation properties figure of pseudo noise code spread-spectrum signal under different Doppler frequency shifts;

Fig. 4 is the correlation properties figure of Hyperbolic Frequency Modulation signal under different Doppler frequency shifts;

Fig. 5 is the cyclic shift schematic diagram;

Fig. 6 is the Hyperbolic Frequency Modulation spread-spectrum underwater sound communication system block diagram of superimposed pilot signal;

Fig. 7 tests 1km underwater acoustic channel impulse response figure on the lake in the embodiment;

Fig. 8 is interpretation figure on the 1km Hyperbolic Frequency Modulation spread spectrum lake in the embodiment.

Embodiment

Below in conjunction with accompanying drawing and concrete embodiment to further detailed description of the present invention.

The present invention includes following steps:

(1). Hyperbolic Frequency Modulation signal and feature

The Hyperbolic Frequency Modulation signal expression is suc as formula (1):

In the formula, f ₀Be centre frequency, m is a coefficient of frequency modulation.The modulation bandwidth of Hyperbolic Frequency Modulation signal is

B＝|f _H-f _L|； (2)

In the formula, f _LAnd f _HBe respectively the lower frequency limit and the upper limiting frequency of Hyperbolic Frequency Modulation signal.

$f_0=\frac{{2f}_L{f}_H}{f_L+f_H};---\left(3\right)$

$m=\frac{{4f}_L{f}_H(f_H-f_L)}{T{(f_L+f_H)}^2};---\left(4\right)$

Positive frequency modulation o'clock is represented in m＞0; Negative frequency modulation o'clock is represented in m＜0.If positive frequency modulation Hyperbolic Frequency Modulation signal is a carrier signal, negative frequency modulation Hyperbolic Frequency Modulation signal is a pilot signal.Fig. 2 has provided the correlation properties of carrier signal and pilot signal, wherein Fig. 2 (a) provides the autocorrelogram of carrier wave Hyperbolic Frequency Modulation signal, Fig. 2 (b) provides the autocorrelogram of pilot tone Hyperbolic Frequency Modulation signal, Fig. 2 (c) provides the cross-correlogram of carrier wave Hyperbolic Frequency Modulation signal and pilot tone Hyperbolic Frequency Modulation signal, carrier signal and pilot signal all have good autocorrelation performance as can be seen, and both nearly orthogonals.The Hyperbolic Frequency Modulation signal is insensitive to Doppler effect, shown in Fig. 3 and 4, has provided the pseudo noise code spread-spectrum signal respectively at correlation properties figure under the different Doppler frequency shifts and the correlation properties figure of Hyperbolic Frequency Modulation signal under different Doppler frequency shifts; Fig. 3 represents that length is that 511 pseudo noise code (chip width 0.25ms) phase-modulated signal (symbol lengths is 0.128s) is respectively 0 in Doppler's factor (velocity of sound in UUV speed/seawater), 0.005 relevant output with 0.01 o'clock, can find, the pseudo noise code phase-modulated signal is very responsive to Doppler frequency shift, small Doppler's factor will cause relevant output amplitude to have decline, not have the correct restituted signal of sign indicating number; Fig. 4 represents be length be 0.1s positive frequency modulation Hyperbolic Frequency Modulation signal Doppler therefore be respectively 0,0.005 with 0.01 o'clock relevant output, can find, in Doppler's factor is 0.005 o'clock, during with respect to no Doppler effect, relevant output only has a delay, and changes in amplitude is faint; In Doppler's factor is 0.01, and relevant output amplitude drops to 0.7 times of amplitude peak.Relatively can find that the Hyperbolic Frequency Modulation signal is applicable to mobile environment by comparison diagram 3 and 4.

(2). the cyclic shift modulation system

The cyclic shift modulation is carried out cyclic shift to carrier frequency Hyperbolic Frequency Modulation signal f (t) and is obtained displacement waveform g (t) according to the binary message of input, and its relation is as follows:

$g\left(t\right)=\left\{\begin{array}{cc}f(t+\mathrm{k\&Delta;\&tau;}),& 0\&le;t\&le;T-\mathrm{k\&Delta;\&tau;}\\ f(t-T+\mathrm{k\&Delta;\&tau;}),& T-\mathrm{k\&Delta;\&tau;}<t\&le;T\end{array}\right.---\left(5\right)$

Represent that wherein T is Hyperbolic Frequency Modulation signal duration, Δ τ is a shift step, and k determines according to the binary message of input.If utilize M different step length of cyclic shift can differentiating to represent information, then each displacement waveform g (t) can represent log ₂M bit information.According to input information, utilize (5) formula to produce displacement waveform signal g (t).Its shift step Δ τ depends on the precision that time delay is estimated.Cyclic shift modulation principle figure as shown in Figure 5.

(3). the superimposed pilot signal

Doppler and multipath transmisstion are bigger to the time delay estimation effect, in order to alleviate this influence, adopt the cyclic shift modulation technique of superimposed pilot signal.In this modulation system, s emission signal s (t) is displacement waveform g (t) and pilot signal p (t) sum, is shown below:

s(t)＝g(t)+p(t)， 0≤t≤T (6)

Transmitting terminal is that acoustical signal emission enter in seawater by power amplifier and transmitting transducer with electrical signal conversion with mixed signal s (t).

(4). handle with the circular correlation of carrier signal

Receiving terminal at first is converted to the signal of telecommunication by hydrophone with the acoustical signal that obtains, and calculates the relevant output with carrier wave Hyperbolic Frequency Modulation signal f (t) of received signal r (t), estimates the position of correlation peak simultaneously, can be expressed as

y ₁(t)＝|IDFT(DFT ^*(f(t))×DFT(r(t)))|

(7)

${\mathrm{\&tau;}}_1=\arg \underset{t}{\max }\left(y_1\left(t\right)\right)$

Wherein f (t) is stored in local receiver, and DFT/IDFT is corresponding Fourier transform.() ^*Be conjugate operation.

(5). handle with the circular correlation of pilot signal

Calculate the relevant output of received signal r (t), estimate the position of correlation peak simultaneously, can be expressed as with pilot tone Hyperbolic Frequency Modulation signal p (t)

y ₂(t)＝|IDFT(DFT ^*(p(t))×DFT(r(t)))|

(8)

${\mathrm{\&tau;}}_2=\arg \underset{t}{\max }\left(y_2\left(t\right)\right)$

Wherein p (t) is stored in local receiver, and DFT/IDFT is corresponding Fourier transform.() ^*Be conjugate operation.

(6). delay inequality relatively reaches decoding

The delay inequality of more top two relevant peaks correspondence positions, promptly

$\widehat{\mathrm{\&tau;}}=|{\mathrm{\&tau;}}_1-{\mathrm{\&tau;}}_2|---\left(9\right)$

To make comparisons with shift step, decipher.

Below in conjunction with Fig. 6, the signal flow according to the cyclic shift spread-spectrum of superimposed pilot signal is communicated by letter describes in further detail the present invention in conjunction with concrete embodiment.

System parameters and operational environment are as follows: system bandwidth 4kHz, carrier frequency 10kHz, sample frequency 40kHz; The width of Hyperbolic Frequency Modulation signal is 50ms, and the size of shift step is 25/16 of the Hyperbolic Frequency Modulation deration of signal, is about 1.56ms; Then each cyclic shift waveform is represented 5 bit informations, and data transfer rate can reach 100bit/s.

1.. at transmitting terminal and receiving terminal, generate carrier wave Hyperbolic Frequency Modulation signal f (t) and pilot tone Hyperbolic Frequency Modulation signal p (t) in advance, be kept in the local storage, f (t) and p (t) nearly orthogonal; To the binary message that will send, divide into groups, per 5 bits are one group; The binary message group becomes one-to-one relationship with corresponding cyclic shift size; As binary message group b=[0 001 0] corresponding cyclic shift size is 3.12ms;

2.. according to the binary message group after the grouping, carrier signal f (t) is carried out circulative shift operation according to Fig. 5.As, if binary message group b=[0 001 0]; Then need carrier wave Hyperbolic Frequency Modulation signal 3.12ms data shift is foremost formed the displacement waveform signal to least significant end.Pilot signal p (t) is added on the displacement waveform signal, and sends in the underwater acoustic channel by transducer by power amplifier.

3.. at receiving terminal, the signal that hydrophone is received passes through band pass filter, carries out the A/D sampling behind the agc circuit and obtains digital signal.To the digital signal that obtains, carry out earlier synchronously, and cut apart by symbol width.

4.. the signal after cutting apart according to each symbol width, utilize the FFT/IFFT technology to carry out quick cyclic correlation, its local reference waveform is carrier signal f (t), its circular correlation output waveform is carried out peak value detect.According to the circular correlation characteristic of basic waveform, have only the position of corresponding cyclic shift size maximum correlation peak just to occur.

5.. the signal after cutting apart according to each symbol width, utilize the FFT/IFFT technology to carry out quick cyclic correlation, its local reference waveform is pilot signal p (t), its circular correlation output waveform is carried out peak value detect, and provide the position of its peak value correspondence.

6.. the relevant peaks position that top two correlations obtain poor, according to binary message with cyclic shift size one-to-one relationship, judge 5 binary message group b=[0 0010 that sent].The communication system block diagram is tested the 1km channel impulse response as shown in Figure 7 on the lake as shown in Figure 6.Fig. 8 provides circular correlation and handles output and corresponding time delay evaluated error.The last figure of Fig. 8 has provided the cross-correlation output of carrier wave Hyperbolic Frequency Modulation signal, and figure below has provided the cross-correlation output of pilot tone Hyperbolic Frequency Modulation signal, and relatively pairwise correlation peak outgoing position is poor, can try to achieve delay inequality.

Claims (1)

1. Hyperbolic Frequency Modulation spread-spectrum underwater sound communication method is characterized in that may further comprise the steps:

(1). form basic waveform by 2 Hyperbolic Frequency Modulation signals that are respectively positive and negative modulation rate, wherein, positive frequency modulation Hyperbolic Frequency Modulation signal is as carrier signal f (t), and negative frequency modulation Hyperbolic Frequency Modulation signal is as pilot signal p (t), these two signal nearly orthogonals, its cross-correlation function Wherein τ represents to postpone, and T represents the length of carrier signal and pilot signal;

(2). at the communication transmitting terminal, determine carrier signal f (t) shift size according to information to be sent and predefined shift step, and carrier signal is carried out cyclic shift, realize polynary modulation;

(3). on the carrier signal of superimposed pilot signal to the cyclic shift, form composite signal, and composite signal is transmitted into underwater acoustic channel by transmitting transducer;

(4). adopt the relevant output of duplicate correlation technique estimation pilot signals peak at receiving terminal;

(5). adopt the duplicate correlation technique to estimate the relevant output of carrier signal peak at receiving terminal;

(6). poor with the relevant output of pilot signal relevant output peak peak with carrier signal, compare with shift step, and the predefined polynary modulation decoding of tabling look-up according to transmitting terminal.

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