The Research Of Doppler Frequency Shift Compensation In OFDM Underwater Acoustic Communication System

The purpose of underwater acoustic communication is to reliably transport source of information to the destination in high-speed by the underwater acoustic channel. Therefore with the wide application in the national defense and development of marine resources of underwater acoustic communication technology, it has been paid more and more attention and studies. High-speed data transmission in underwater acoustic channel has become a hot research topic in the forefront of underwater communication technologies. However, due to the serious time-varying and frequency selective fading characteristics of underwater acoustic channel, the underwater acoustic communication channel was limited by bandwidth and multi-path effects.OFDM technology transmits numbers of orthogonal carriers which are modulated in parallel with high data rate, this technology has the advantages of against multi-path effects and high bandwidth utilization, and therefore it is valuable to apply OFDM technology in underwater acoustic communication in theoretical and practical. While with the increase of transmission distance, there appear more and more bad channel conditions, such as multipath and Doppler shift effects, So it is need to design an adaptive OFDM system and take effective measures to improve system performance.The main contents of this paper are as follows: firstly, the principle of OFDM technology and the application of this technology in underwater acoustic communication was researched and simulated, it can be found by simulation that the frequency offset has great impact on OFDM technology in the application of underwater acoustic com- munication. In actual Underwater Acoustic Channel the marine media is uniform and the relative motion of signal transmitter and the receiver making the Doppler shift is very serious which resulting the performance of OFDM in underwater acoustic communication appears a great fall.Secondly, this is to propose a solution for this question, which is based on the parallel correlators matched methods by operating on characteristics of the cyclic prefix OFDM signal to estimated and compensate the Doppler frequency shift, the algorithm requires a small amount of self-correlators to estimate Doppler factor for initial compensation, and then the second compensation was carried out. Which is complexity and easy to implement.Finally, a simulation platform based on the applications of OFDM underwater communication system and the Doppler estimation and compensation algorithm was built by using mixed programming of VC++ and MATLAB. This platform can facilitate future application of OFDM in underwater acoustic communication research and verification the corresponding algorithm.It can be found by simulation that the proposed algorithm can guarantee the receiver has a low error rate, and improve the system performance. The simulation platform provides a great help for further research.