| Underwater acoustic communication (UAC) Technology plays an important role in marine resource exploitation and national security etc. With the rapid development of marine resource exploitation and urgent demand of National Ocean security, UAC Technology has been paid more and more attention. However, underwater acoustic (UWA) channel is expressed as a complex channel which is randomly variable in time-space-frequency, coupled with its high noise, narrow bandwidth, low carrier frequency, large fluctuation, and transmission latency, which bring a great difficult to UAC. Strong multi-path effect and large amplitude fluctuation is the main factor that it will lead to signal fading and severe inter-symbol interference (ISI).Urgent actual demand recently, underwater acoustic network becomes a research hotspot, in which a reliable and robust point-to-point communication is the precondition. This paper is just put forward in such circumstances, combined with the national 863 specific subject "Distribute UAC Technology research in ocean".Consulted abundant domestic and foreign relevant references, according to physical characteristics of UWA channel, the paper uses Matlab to make a transmission characteristics simulation to UWA channel based on the ray theory. Through the simulation results, we can see that multi-path effect will cause receive signal fading, frequency spreading and ISI, which are main obstacles for reliable high-speed UAC, so all possible anti-strong multi-path interference measures must be studied. As spread spectrum (SS) technology in anti-ISI-interference has excellent properties, frequency-hopping (FH) technology is proposed as a concrete realization of the system through analysis of the various SS technology.How to detect synchronized signal quickly, accurately and effectively is one of key techniques of FH communication in UWA channel. A synchronized scheme suitable for UWA channel is proposed in the paper, which uses Synchronized-head method combined with spectrum estimation to capture synchronization, and cross-correlation detection chirp signal to complete synchronization tracking.According to rapid development of high speed digital signal processing (DSP) technology, this paper concentrates on DSP-based embedded acoustic FH communications system, which based on the UWA channel of analysis, focusing on decoding and synchronization technology. Through experiments both in the laboratory's pool and in Xiamen Harbor, this system can realize high reliable transmission in a certain transmission rate, 3km transmission distance is confined in the shallow sea (2～12m), with transfer rate up to 200 bit/s, and the bit error rate (BER) is about 10-3. |
