Design And Implementation Of Spread Spectrum Underwater Acoustic Communication System Based On DSP

Maritime security is related to national security.Underwater acoustic communication technology is not only an important technology to maintain maritime security,but also a key technology for the development of major powers in the world.Compared with underwater optical communication and underwater electromagnetic wave,underwater acoustic communication technology has the advantages of long transmission distance,small transmission loss and flexible use.It is widely used in underwater data transmission.However,underwater acoustic props sometimes have strong variability,accompanied by serious multipath effect and Doppler expansion,which is much more complex than terrestrial wireless channels.Direct sequence spread spectrum(DSSS)communication technology has the advantages of strong anti-interference performance,high confidentiality and strong selective addressing ability.It is widely used in the field of underwater communication.This paper adopts direct sequence spread spectrum communication technology,designs and implements the underwater acoustic communication system based on digital signal processing(DSP)and peripheral chips,independently completed the software and hardware of the underwater acoustic communication machine,and carried out many sea trials and lake trials to test the performance of the communication machine.The measured data show that the system has stable performance and strong anti-interference ability.This paper has mainly completed the following work:(1)In order to reduce the dependence of spread spectrum code synchronization technology on hardware and improve the anti noise performance of underwater acoustic communication machine,this paper makes some improvements on the basis of traditional spread spectrum code synchronization technology.The synchronization of spread spectrum code includes two stages:code acquisition and code tracking.In the code acquisition stage,the double zero filling method is used to expand the received signal and the local spread spectrum code sequence of the receiver to meet the requirements of radix-2 fast fourier transform operation;The combination of coherent accumulation and incoherent accumulation is used to process the received signal to improve the anti noise ability of the system;In the control logic part,the reservoir sampling algorithm is used to determine the calculation order of carrier frequency offset within the range,without traversing the carrier frequency offset within the range in a fixed order,so as to reduce the amount of calculation.In the code tracking stage,this paper adopts the full-time lead-lag incoherent correlated synchronous tracking loop and the design of double(?)value delay phase-locked loop,which expands the tracking range and reduces the probability of losing lock.Then the Costas loop is used to realize carrier recovery;Finally,the strong autocorrelation of Barker code is used to realize frame synchronization.A set of stable and reliable communication algorithm is designed.(2)Based on the design method of software radio,this paper realizes the underwater acoustic communication machine based on direct sequence spread spectrum technology by using high-performance DSP(TMS320C6747).C language is used to realize the communication algorithm,and it is optimized combined with the mathematical library;Dynamically manage the memory and make the most efficient use of the memory;According to the actual needs of underwater acoustic communication machine,formulate a detailed scheme,select appropriate interfaces and equipment,and finally realize it by software.Based on this technology,a direct sequence spread spectrum underwater acoustic communication machine is developed.From 2020 to 2022,sea trials and lake trials have been carried out in the Yellow Sea,Sanya South China Sea and Hubei Enshi Shuibuya reservoir for many times.The experimental results show that the symbol rate of the communication system is 40bps,the spread spectrum gain is127,and the bit error is lower than10^-4,showing high practical application value.The system can be mounted on wireless ocean observation equipment such as submarine buoy,buoy,unmanned underwater vehicle(UUV),autonomous underwater vehicle(AUV)and unmanned ship/boat to observe,detect and develop ocean information and realize wireless data transmission between underwater equipment;...