Research Of Underwater Acoustic Speech Communication System Based On 600b/s MELP

With the development of ocean strategy, the unique advantage of underwater acoustic communication is more and more irreplaceable. As the most direct and convenient means of communication, speech communication plays an important role under waters. In the ocean channel, band is precious. The usage of speech coding makes communication more effective.It has great effect on the smaller channel capacity in ocean environment. So the research of low rate speech coding is increase but no decrease.The Mixed Excitation linear Prediction (MELP) speech coding in 2.4kb/s, which has good voice in quality and low bitrate, has been widely used in all kinds of speech communication. But the lower rate of algorithm must be used for channel which lacks frequency resource. Orthogonal Frequency Division Multiplexing (OFDM) is more suitable for the characteristic of underwater acoustic channel. Because its sub-carrier orthogonality makes frequency overlap and fully used.Based on MELP technology, this paper researches the lower rate of algorithm and finally reaches the coding rate in 600b/s after three speech frames are compressed then transmit and vector quantization technology are widely used to reduce more transmission bit. Besides,combining OFDM technology, it adds the cyclic prefix to overcome the effects of multipath of underwater acoustic channel, and adds synchronization, channel estimation and scrambling technology to ensure a good and stable communication. Finally,on the processing board of fixed-point DSP chip DM642, it achieves real-time underwater voice communication. The entire communication system is passed by simulation test and tank test and the recovery voice reaches good quality. It's close to the 1.2kb/s MELP algorithm. The whole communication process is relatively stable and has practical applications.