Design Of Underwater Repeater Based On Orthogonal Frequency Division Multiplexing

Viewing the development of the technology for underwater acoustic communication all over the world, we have almost found practical solutions for low-bit-rate long-distance data transmission and high-speed short-distance data transmission, with lots of assistances of experimental systems and results. But we haven't found a satisfactory method to accomplish high-speed long-distance underwater data transmission.Relay transmission is a good method to achieve high-speed long-distance underwater data transmission. The repeater we designed in the paper is based on the thought, it realized high-speed long-distance underwater data transmission by the method likes to microwave relay transmission.In the paper, we discussed the hardware design and software realization of the system.1. Hardware design. Hardware design mainly contains two parts. The first one is how to reduce the power of the system. Two method had been done, one is to choose the low power devices, such as operational amplifier, A/D, D/A and the DSP; the other one is to design a circuit on duty. Only when the touch of the signal reaches and the identity is confirmed, the circuit on duty makes the digital processing flat power up and work. In the way, the system power is very low when it is free. The second part is to design a digital processing flat based on TMS320VC5509, which accomplished the arithmetic of the system. In the paper, we mainly discussed the interface and timing diagram between the DSP and the periphery devices.2. Software realization. For OFDM systems can overcome the problems of multi-path propagation and frequency selective fade effectively, in the paper, we introduced the foundational principle of orthogonal frequency division multiplexing (OFDM) and accomplished it on the digital processing flat by the language of C.At last, we did the experiments on the lake. The bit rate reached 2.88kb/ s under the bandwidth of 2kHz within 6000m with the bit error rate low than 10^-3, it reached the technique guideline of the system.