CN104539569A - Orthogonal frequency division multiplexing coding underwater acoustic communication method based on parameter array - Google Patents

Abstract

The invention belongs to the field of underwater acoustic communication, and particularly relates to an orthogonal frequency division multiplexing coding underwater acoustic communication method based on a parameter array. The method comprises the steps that binary data to be transmitted by a transmitting end are mapped into a corresponding sequence of complex numbers; digital-to-analogue conversion is carried out on the sequence at intervals; receiving signals are sampled at intervals at a receiving end, and the discrete Fourier transformation is carried out; a modulated orthogonal frequency division multiplexing signal and a carrier signal serve as an original frequency wave of parameter array transmission; synchronous detection, series-to-parallel conversion and the circulation removing detection orthogonal frequency division multiplexing coding process are carried out, and then the information can be obtained. According to the communication scheme that the OFDM communication system widely applied and the parameter array are combined, the high communication rate can be achieved, reliable underwater acoustic communication can be achieved, and the high-directivity narrow beam can be obtained under the small size through the parameter array.

Description

A kind of method based on parametric array OFDM coding underwater sound communication

Technical field

The invention belongs to field of underwater acoustic communication, be related specifically to a kind of method based on parametric array OFDM coding underwater sound communication.

Background technology

OFDM (Orthogonal Frequency Division Multiplexing, OFDM) (see: Yin Changchuan, Luo Tao. multi-carrier broadband radio communication technology [M]. Beijing: publishing house of Beijing University of Post & Telecommunication, 2004:23.) be a kind of multi-carrier high-speed data modulation technique, high-speed data signal is converted to parallel low speed sub data flow, parallel transmission on modulates information to multiple orthogonal subcarrier effectively can be overcome frequency selective fading, be widely used in broadband connections.

Acoustic parametric arrays (see: He Zuoyong, Zhao Yufang. acoustic theory basis [M]. Beijing: National Defense Industry Press, be 1981:420-421.) utilize sound wave in the nonlinear effect of communication process medium, obtain difference frequency and involve and the small size acoustic emission device of the frequently sound wave such as ripple.Be characterized in low frequency, high directivity, be suitable for broadband signal use.In the communication process of sound wave, due to square being directly proportional of acoustical absorptivity and frequency of sound wave, the former frequency ripple that frequency is higher and and frequently wave attenuation very fast, after propagating a segment distance, the difference frequency signal that only remaining frequency is lower, this difference frequency signal is then the broadband signal of low frequency high directivity relative to former frequency signal.

The Some features of underwater acoustic channel determines the degree of difficulty of its communication, and the strong noise background of such as ocean, very strong Multi-path interference, communication frequency is lower and bandwidth is very limited.Multi-path interference is one of underwater sound communication significant obstacle, due to the complexity of underwater acoustic channel, super directive property ability under the small-bore of parametric array, from demodulation feature, and low frequency can to obtain very wide relative bandwidth be that the difficulty of underwater sound communication provides a possible solution.The high frequency sound wave signal using two frequencies close is as dominant frequency signal, and the difference frequency ripple that sound wave is formed due to nonlinear effect in communication process then has low frequency high directivity, can overcome Multi-path interference to a great extent.

Summary of the invention

The object of the present invention is to provide one can have good communication efficiency under complicated Underwater Acoustic Environment, can be applicable to the method based on parametric array OFDM coding underwater sound communication of secure communication.

The object of the present invention is achieved like this:

(1) first binary data to be transmitted for transmitting terminal is mapped to corresponding sequence of complex numbers { d ₀..., d _n-1, inverse discrete Fourier transform is carried out to this sequence of complex numbers, the sequence of complex numbers { S containing N number of element can be obtained ₀..., S _n-1;

(2) by sequence { S ₀..., S _n-1digital-to-analogue conversion is carried out for the time interval with Δ t, obtain continuous signal $x\left(t\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}d\left(n\right)\exp \left(j2\mathrm{\π}{f}_{n}t\right);$

(3) carry out to received signal sampling and carrying out discrete Fourier transform for the time interval with Δ t at receiving terminal, then can obtain sequence of complex numbers { d ₀..., d _n-1, and then recover binary data;

(4), after OFDM has been encoded, utilization single-side band modulation, using the former frequency ripple that orthogonal frequency-division multiplex singal and carrier signal after modulation are launched as parametric array;

(5) parametric array is utilized to transmit, because parametric array is from demodulation characteristics, receiving terminal obtains difference frequency signal and is lower frequency quadrature frequency-division multiplex singal, synchronously detects, serioparallel exchange, goes cycle detection OFDM decode procedure to obtain information to it.

Beneficial effect of the present invention is: the communication plan ofdm communication system of extensive use combined with parametric array, higher traffic rate can be realized and reliable underwater sound communication, and because parametric array can obtain high directivity narrow beam under small size, the program also can be applicable to secure communication field.The method realizes simple, and can be widely used in underwater sound communication and secure communication, the present invention has certain application prospect.

Accompanying drawing explanation

Fig. 1 is the ofdm communication system block diagram based on parametric array.

Fig. 2 is launching and receiving end handling process.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described further:

The technical issues that need to address of the present invention are, for the complexity of complicated underwater acoustic channel, propose a kind of OFDM based on parametric array coding underwater acoustic communication method, the method.

The technical solution adopted in the present invention is as follows:

(1) in OFDM basis of coding, add source coding and channel coding, first utilize pseudo random sequence to carry out data scrambling, to data acquisition after scrambling with carrying out QPSK phase-modulation, QPSK adopts Gray code mode can avoid occurring continuous errors.

(2) insert pilot data and carry out period expansion, after expansion, IDFT conversion is done to data, use spread signal to fill protection interval and carry out period expansion, and control peak power ratio.

(3) carry out single-side band modulation to after this ofdm signal equalization filtering, the high frequency ofdm signal after modulation and carrier signal are together launched as the former frequency signal of parametric array.

(4) signal that receives of receiving terminal and low frequency ofdm signal, carries out OFDM decoding to it and can obtain transmitting information, carry out DFT conversion after first removing Cyclic Prefix.

(5) finally carry out that QPSK reflection is penetrated, deinterleaving successively, data can recover the binary data that transmitting terminal is launched after going to disturb.

The invention provides the method for a kind of OFDM based on parametric array coding underwater sound communication, the combination of OFDM coding techniques and parametric array, can be good at the Multi-path interference problem solving underwater sound communication, greatly enhance the reliability of communication system, and it is easy to implement the method, engineering can be applicable to underwater acoustic channel condition undesirable when, and the aspect such as secure communication.

Ofdm communication system is with reference to Fig. 1, and launching and receiving end handling process is with reference to Fig. 2.

Implementation process is as follows:

(1) binary data first utilizing pseudo random sequence to be transmitted to transmitting terminal carries out data scrambling, carries out error control in the mode of interweaving encoding to it.

(2) the data QPSK after intertexture is mapped to corresponding sequence of complex numbers, is expressed as { d ₀..., d _n-1, wherein N is element number.After inserting pilot tone, IDFT conversion is carried out to this sequence of complex numbers, the sequence of complex numbers containing identical element number can be obtained, be expressed as { S ₀..., S _n-1.

(3) to sequence { S after IDFT conversion ₀..., S _n-1add Cyclic Prefix and carry out period expansion.

(4) control peak power ratio and add synchronizing signal, synchronizing signal adopts linear FM signal.

(5) after OFDM has encoded, carry out single-side band modulation, modulation signal and carrier signal are launched as the former frequency ripple of parametric array.Because parametric array is from demodulation characteristics, receiving terminal obtains difference frequency signal and is low frequency ofdm signal.It is synchronously detected, goes the OFDM decode procedures such as cycle detection to obtain information.

(6) synchronously detect to received signal at receiving terminal, do DFT conversion after removing Cyclic Prefix and can obtain sequence of complex numbers { d ₀..., d _n-1.

(7) data after DFT conversion are carried out that QPSK reflection is penetrated, deinterleaving after going to disturb to data, and then recover the binary data that transmitting terminal launches.

Claims (1)

1., based on a method for parametric array OFDM coding underwater sound communication, it is characterized in that:

(1) first binary data to be transmitted for transmitting terminal is mapped to corresponding sequence of complex numbers { d ₀..., d _n-1, inverse discrete Fourier transform is carried out to this sequence of complex numbers, the sequence of complex numbers { S containing N number of element can be obtained ₀..., S _n-1;

(2) by sequence { S ₀..., S _n-1digital-to-analogue conversion is carried out for the time interval with Δ t, obtain continuous signal $x\left(t\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}d\left(n\right)\exp \left(j2\mathrm{\π}{f}_{n}t\right);$

(3) carry out to received signal sampling and carrying out discrete Fourier transform for the time interval with Δ t at receiving terminal, then can obtain sequence of complex numbers { d ₀..., d _n-1, and then recover binary data;

(4), after OFDM has been encoded, utilization single-side band modulation, using the former frequency ripple that orthogonal frequency-division multiplex singal and carrier signal after modulation are launched as parametric array;

(5) parametric array is utilized to transmit, because parametric array is from demodulation characteristics, receiving terminal obtains difference frequency signal and is lower frequency quadrature frequency-division multiplex singal, synchronously detects, serioparallel exchange, goes cycle detection OFDM decode procedure to obtain information to it.