Research On Modulation Algorithm And Application Of Transmission Signal In Acoustic Parameter Array

The acoustic parametric array can generate the difference frequency wave signal through the nonlinear effect of the sound wave in the medium,and the difference frequency wave has the characteristics of low frequency and narrow directivity.At the same time,the size of the transmitting transducer is relatively small.In underwater acoustic communication,a narrower directional transmission limits the sound line to a smaller angle range,which can reduce the number of multiple channel.Therefore,the parametric array,which emits a narrower directivity signal,has certain application advantages in the field of underwater acoustic communication.However,in the parametric array theory,the relationship between the original excitation signal and the difference frequency wave is nonlinear.If the difference frequency wave obtained at the receiving terminal is expected to be the same as the preset signal to be transmitted,the preset signal needs to be pre-modulated before it is transmitted.Then after the modulated signal is self-demodulated by the aqueous medium,the preset signal that was originally intended to be transmitted can be obtained without distortion at the receiving terminal.Therefore,this paper studies the key technology of modulation algorithm for parametric array transmit signals and its application in parametric array communication.Based on Berktay's theory that the difference frequency wave is proportional to the quadratic derivative of the square of the original excitation signal envelope,four parametric array emission signal modulation algorithms are studied.Through theoretical derivation and simulation,it is found that using the parametric array to transmit a signal modulated by conventional modulation algorithm,such as full amplitude modulation algorithm and the suppression carrier double-band modulation algorithm,there is a certain degree of distortion on difference frequency wave at the receiving terminal,which means the preset signal that is expected to be transmitted cannot be obtained.But the double integral squared modulation algorithm and the recursive filtered parameter modulation algorithm can generate the difference frequency wave with the preset signal form that is desired to be transmitted without distortion.Based on the simulation of modulation algorithm,this paper simulates the channel structure corresponding to the narrow directional transmission method and the transmission method with larger emission angle,and verifies that the narrow directional transmission can suppress multiple channels and simplify the channel structure.Finally,this paper combines the modulation technology of the parametric array transmit signal with the Differential Pattern time Delay Shift coding(DPDS)communication system and introduces the specific parametric array transmission communication method with the full amplitude modulation algorithm,the suppression carrier double-band modulation algorithm,the double-integral squared modulation algorithm and the recursive filtered parameter modulation algorithm respectively.At the receiving terminal,the correlation between local copy and received signal is used to demodulate the delay difference between adjacent Pattern and the communication effects of four parametric array transmit signal modulation algorithms in different SNR environments are analyzed by simulation.In this paper,the four parametric array emission signal modulation algorithms are tested in the pool firstly.The experiments show that the double integral squared modulation algorithm and the recursive filtering parameter modulation algorithm are better than the other two algorithms in performance.In addition,in the communication experiment based on parametric array,the effects of parametric array communication under different modulation algorithms are tested in the Songhua River.The experimental results show that the performance of DPDS communication based on parametric array can be great,and the error rate of communication system is related to the modulation algorithm of parametric array transmission signal.The underwater acoustic communication effect under the double integral open square modulation algorithm and the recursive filter parameter modulation algorithm is significantly better than the underwater acoustic communication effect under the traditional modulation algorithm.