The Design And Realization Of PDS Mode In The UWA Communication Experimental System

The characteristic of the underwater acoustic(UWA) channel displays in five pieces, which are limited communication bandwidth, multipath interference, non-stationary ocean ambient noises and local noises, time-variation, randomness and Doppler effect. They have certain influence on underwater acoustic communicate performance. There are a lot of similar characteristic between the underwater acoustic channels and the wireless channels, much wireless communication technology now can be used for reference. In this subject the PDS system is used to realize UWA communication. The PDS system uses the time delay of LFM to encode in the sender system, and uses the Time Delay Estimation technology in the receiver system. Different time delay values represent different information. PDS uses a kind of multidimensional channel coding technique, which makes use of code structure to realize multidimensional channel coding and uses the good linear compression properties of linear frequency modulation. So the system has excellent ability of anti-multipath interference and overcomes intersymbol interference and outersymbol interference. It can realize signal detection in the condition of low signal-to-noise ratio. Multi-bit encoding can improve the communication rate. And it also resolves the synchronization problem. In this subject, the signal mode is designed in the first place. Appropriate pattern number and pattern signal are choosed to improve the ability of anti-multipath interference and communication rate. In the second place, under the frame system of the software radio, the whole receiver system is designed. In the course of it, downsampling processing can improve the calculating speed of the system without sacrificing the algorithm performance. Adaptive method of the synchronization detectation was adopted to adapt to the change of the environment. So the position of synchronization peak value can be captured. At the same time, the second position-fixing process which takes use of the signal mode in a frame can get the frame's accurate position ulteriorly. During the decoding process, the processing of the two orthogonal channels and the operation of plurality correlation was adopted to eliminate the phase error. On the basis of classical PDS theory, a new fast Time Delay Estimation algorithm was used. This algorithm which can decode with much less calculations improves the calculation speed a lot. Finally, the whole real time receiving system was realized. Studies have show that PDS has its great potential as a new kind of coding system。Through the realization of this coding method, we can find out the PDS system has very good development prospects.