| Underwater acoustic technology was initially mainly used in the military field to achieve the detection,positioning,and identification of underwater targets,and then gradually developed to the service stage of communication and navigation.Underwater communication technology can be applied to underwater vehicles,frogmen,and other military applications,with the increase of human marine activities and the improvement of the utilization of marine resources,underwater communication technology can also be applied to maritime scientific investigation,underwater resource detection,and other civilian fields.Different from the wireless communication system on the ground,the noise in underwater communication,the multipath effect,and the complexity of the underwater environment will have a very adverse impact on the reliability of underwater wireless communication,so how to improve the speed and quality of underwater communication is an important issue.In recent years,OFDM technology has been widely used in underwater communication due to its higher spectrum utilization and better anti-multipath interference performance,and the light waves and electromagnetic waves of terrestrial wireless communication are relatively attenuated in seawater,so sound waves have become the best carrier for underwater wireless communication.There are many reefs,irregular ocean undercut ents,and inhomogeneiseawater water attenuation in the marine environment,the underwater acoustic channel model is very complex,OFDM technology is very sensitive to synchronization,and it is necessary to strictly ensure the orthogonality between subcarriers,so high-performance symbolic timing synchronization is a prerequisite for OFDM communication system.The main work of this paper is summarized as follows:1,The traditional symbolic timing synchronization algorithm is simulated and analyzed,and an improved Park algorithm is proposed to improve the synchronization accuracy.Aiming at the problem that the sub-peaks on both sides of the positive time point in the Park algorithm are too high,the structure of the training sequence in the Park algorithm is improved,and the proportion of sub-peaks to the main peak is reduced by 0.6444 when SNR=15,which weakens the interference of the sub-peaks.The normalization factor in the timing metric function is improved,the value of the timing measure function when the timing position is positively determined is increased,and the RMSE of the synchronization algorithm is reduced.The RMSE and accuracy of the improved symbolic timing synchronization algorithm under different signal-to-noise ratio are simulated,and the simulation results show that the improved algorithm is greatly improved compared with the traditional Park algorithm.The symbolic timing synchronization accuracy of the improved algorithm exceeds 98% when the SNR is 0d B,corresponding to the accuracy of the Park algorithm reaching 98%,and the signal-to-noise ratio required is 5d B,the RMSE of the improved algorithm is close to 10 when the signal-to-noise ratio is 0d B,while the RMSE of the Park method reaches 20 when the SNR is 0d B,and the gain of the improved algorithm compared with the classical Park algorithm is 3d B when the RMSE is 1.2.The underwater acoustic channel model in the shallow marine environment is analyzed,and the BELLHOP underwater acoustic channel model is selected to simulate the improved symbolic timing synchronization algorithm.The improved algorithm has an accuracy of more than 98% at a signal-to-noise ratio of 10 d B,while the Park algorithm has an accuracy of more than 98% at 20 d B.Compared with the Gaussian white noise channel,when the accuracy of the improved algorithm exceeds 98%,the SNR is reduced by 10 d B,which corresponds to the Park algorithm by 15 d B.The simulation results show that compared with the classical Park algorithm,the timing synchronization estimation of the improved algorithm has higher accuracy and better anti-timing interference.3.A hydroacoustic OFDM transceiver system was built,and the improved synchronization algorithm was verified with Park.The center frequency of the communication system is 35 KHz,and the transmit and receive controls are designed on the computer side based on MATLAB.Experimental results show that compared with the Park algorithm,it has higher synchronization estimation accuracy,and the system bit error rate is smaller than that the of Park algorithm,which proves the feasibility of the improved symbolic timing synchronization algorithm in underwater acoustic channels. |
