Research And Design Of OFDM Underwater Communication

The ocean is an important part of the earth,and it is rich in resources.However,human exploration of the ocean is still in its infancy.With the transitional development of terrestrial resources,humans are more aware of the importance of researching and utilizing marine resources.Information transfer in the marine environment is critical when researching and utilizing marine resources.Therefore,high-speed and high-reliability information transmission in the marine environment has become the main goal of research.Among various communication methods,sound waves are considered to be the only way to achieve medium-to-long-range wireless communication in the marine environment.Therefore,underwater acoustic communication has been highly valued by scientific research institutions all over the world.The underwater acoustic channel has the characteristics of strong multipath,large attenuation,high noise and strict band limit.Therefore,a modem with high multi-path and high frequency band utilization is needed.The OFDM modulation sub-bands are orthogonal to each other and half overlap,and the spectrum utilization rate is very high.At the same time,a guard interval can be inserted between the symbol blocks,which can well resist multipath fading;in addition,multi-carrier is compared with the single carrier transmission mode.The transmission method can increase the system capacity and increase the communication rate.This is very suitable for underwater acoustic communication.In this context,this paper mainly studies and designs the OFDM-based underwater acoustic communication system.The following are the main contents of the research:1.Firstly,by analyzing the characteristics of underwater acoustic channel and the source of noise,it is concluded that the underwater acoustic channel is a very complex channel with time variation,spatial variation and frequency variation,with strong multipath,fast fluctuation,large attenuation,high noise and strict band.The characteristics of the limit,and the corresponding solutions and channel theory models are given.Then,combined with the communication sonar equation,the optimal operating frequency of the transducer and the estimation method of the transmit power and the gain interval of the receiving circuit are analyzed.The channel test scheme uses LFM pulse signals to obtain real-time channel characteristics.2.For the above-mentioned underwater acoustic communication channel,this paper adopts OFDM modulation technology.The implementation and technical characteristics of OFDM modulation technology are demonstrated in detail,including the use of conjugate symmetric sequence modulation method,LFM pulse signal to solve synchronization problem,cyclic prefix andcyclic suffix for inter-symbol interference,PN sequence scrambling,subcarrier randomization.Phase scrambling and clipping methods reduce the system's high peak-to-average ratio.3.Firstly,the BELLHOP model is used to simulate the underwater acoustic communication channel.By analyzing the simulated underwater acoustic channel,a specific underwater acoustic communication system is designed,including OFDM parameters,frame structure,overall structure and software flow.Then the communication distance and sonar are realized.The equation estimates the specific transmit power and receive circuit gain interval of the underwater acoustic communication system.Finally,the specific hardware platform and hardware are designed by using the estimated transmit power,the receive circuit gain interval,and the system structure and function.Finally,the reliability and effectiveness of the communication system are verified by simulation and experiment.The main work is done in three aspects: firstly,the system simulation is carried out under Gaussian channel and multipath channel,and the reliability and effectiveness of the system are verified.Then the correctness,reliability and effectiveness of the system are verified by the silencer pool experiment.The next step of the lake test can be carried out;finally,the lake test is carried out in Qiandao Lake,which verifies the reliability and effectiveness of the system.