Improvement And Performance Analysis Of Underwater Acoustic Communication System OFDM_UACS_v1 Based On OFDM

Underwater acoustic communication is the only form of communication which can carry out remote information transmission under water.It has very important significance in the protection and excavation of marine resources,monitoring of marine disasters and military communications.However,because of complex underwater environment and underwater acoustic channel with low transmission speed,transmission loss and time-varying characteristics of multipath and serious noise.Therefore,the design of un derwater acoustic communication system must be combined with the specific situation of underwater acoustic channel.As a multi carrier modulation technology,orthogonal frequency division multiplexing has been widely applied to underwater acoustic comm unication in recent years.Its advantages are high frequency band utilization and good anti multipath fading capability.The OFDM Underwater Acoustic Communication System version1 which researched by our laboratory was experimented in Qiandao Lake,and the bit error rate was about 0.1 and 0.2 when the distance is 260 m and 750 m.The result of bit error was larger.It is necessary to improve the related main modules.Therefore,the aims of this paper is to research the OFDM underwater acoustic communication system OFDM_UACS_v1.Then we improv e and optimize some main modules of the system OFDM_UACS_v1.It mainly includes channel coding,preamble signal,system synchronization,Doppler processing and channel estimation,and simulation under the simulated un derwater acoustic time-varying channel.According to the characteristics of underwater acoustic channel and the key technologies of OFDM,the improved communication system OFDM_UACS_v2 can realize high speed and reliable underwater communication.The experiment result of Qiandao Lake'15 shows that synchronization and Doppler are key factors affecting transmission.This paper focus on analysis of system performance of different synchronization method and Doppler method,according to the communication quality of three kinds of ocean channel environment by the simulation,experiment data of MACE 10 and experiment simulation of AUVFest 07.Then,we draw a conclusion that the specific methods suitable for different underwater acoustic channels.On this basis,the paper used the improved underwater acoustic communication system OFDM_UACS_v2 to carry out experiments under the Qiandao Lake named Qiandao Lake'17.The result of the experiment shows that the improved system can achieve reliable data transmission with bit error was below 10-5,when the distance is 3 km and the data rate is 2.6 kb/s.The result verified that the improved system is effective.In addition,it verifided the analysis and summary of the synchronization method and the Doppler processing method is correctness.As a result,the communication performance of improved system has been greatly improved.