The Theoretical And Experimental Research On Time-Reversed OFDM Underwater Acoustic Communications

With the fast development of underwater acoustic communication, its engineering application is not only confined to the military, but also in commercial fields, including data acquisition, resource exploitation, environment monitoring, etc. With channel bandwidth limited, multipath, and unstable characteristics of the channel, traditional single carrier communication cannot achieve high rate.Compared with traditional single carrier communication, orthogonal frequency division multiplexing (OFDM) communication can achieve high spectrum efficiency, anti-multipath capability, high communication rate, and the hardware implementation is simple. But in the case of long multipath spread, the guard interval must be longer than multipath delay, resulting in significant reduction in the transmission efficiency of OFDM. With the space-time focus features, time reversal processing (TRP) can exploit multipath to improve signal-to-noise ratio at receiver. This thesis focuses on combination of TRP and OFDM for underwater acoustic communication.Based on the normal mode sound propagation model, the theory of TRP is discussed and its spatial-temporal focus capability is evaluated by numerical simulation and experimental data. On the basis of analysis of OFDM for underwater acoustic communication, Doppler estimation and compensation techniques are investigated. And the channel parameter are further estimated based on pilots. When TRP is used as equalization in OFDM for underwater acoustic communication, high-rate communication with a low error rate can be realized. The lab waveguide tank and Qiandaohu lake experimental results have shown the obvious advantage of TR-OFDM underwater acoustic communication.