Design And Implementation On OFDM Underwater Acoustic Communication System

Underwater communication is one of key technologies of coastal defense,marine environmental monitoring,resource development and mineral exploration.As a specific kind of communication method,data rate of communication and communication resources cost are still limited by the Shannon's Law.Under certain signal to noise ratio,to ensure the communication rate,it must work with wide band.But in acoustic communication scenario,due to restrictions such as transducer size,transmission response,power consumption,it is difficult to operate in the low-frequency band to obtain wide frequency band,therefore,in order to realize high speed underwater communications,the higher work frequency is the inevitable choice.Firstly,this dissertation studied four kinds of modulation to realize OFDM in higher work frequency,including serial FFT modulation mode,direct digital synthesis modulation,mix-frequency modulation and Zoom FFT modulation.Furthermore,by comparing the four instruction cycles and cost of the algorithm,and according to the choice of frequency in high-frequency band,OFDM communication system with ZoomFFT as the core algorithm was determined.Then,through the simulation experiment,analyzed the main backgrounds of the high frequency acoustic underwater communication,which include ambient noise,transmission loss,channel of multiplicity and Doppler.In view of these effects,under the tradeoff consideration of the operation cost and system complexity,this dissertation used scrambling,separation of bandwidth and loophole carrier estimate,interference elimination methods to ensure the normal continuity for underwater acoustic communication.Moreover,simulations were done to verify their performance.At last,the codes transplant from simulation software based on PC to real time applicable software on TMS320C6713 and TMS320C6455,two high performance DSPs of TI's.Real time encoding and decoding are verified through the electrical debug in simulated channel condition with the inducing of additive noise and multipath effect.To test the performance of the communication algorithm in the field,trials had been carried out in Lianhua Lake,HeiLongJiang province and Qiandao Lake,ZheJiang province,respectively.During these trials,acquisited data were storage in disk for the further analysis when information series are transmitted.Results show that communication algorithm has some adaptability for different areas,different working conditions.