Research On Application Of FRFT In Orthogonal Multicarrier Underwater Acoustic Communication System

Underwater acoustic communication is the primary means of achieving the underwater integrated information perception and interaction. Underwater acoustic channel is the only physical medium which can transmit information over a long distance. It is different from the radio channel. Underwater acoustic channel is a very complex spatiotemporal frequency varying channel with the main characteristics of the variability, limited bandwidth and multiple effect.Therefore, underwater acoustic communication technology developed slowly. Orthogonal frequency-division multiplexing(OFDM) is widely used in high speed wireless communications,due to its high spectrum efficiency,high transfer rate, strong anti-multipath capability, etc. But when OFDM is applied to underwater acoustic communication system, it will be affected by a narrow frequency range and the comb amplitude frequency response characteristics of the underwater acoustic channel, not only not playing to its advantages, but also being sensitive to frequency offset and phase noise, leading to highlight its synchronization issues.To solve these problems, this paper proposed a overall program which using symmetrical triangular linear frequency modulation(STLFM) signal as the preamble to achieve orthogonal Multi-carrier underwater acoustic communication system based on fractional Fourier transform(FRFT). Through analyzing the energy convergence of STLFM signal in the fractional Fourier domain, it found that the STLFM signal can produce an energy peak of the signal respectively,when it’s made FRFT in1 p and2p order, in a signal cycle. It is greatly improving the target resolution and providing a good condition for the realization of the synchronization. Then I deduced the joint synchronization algorithms which adapts STLFM signal as the synchronization code, and estimated the algorithms of the sampling frequencysDf, carrier frequencycDf and symbol timing0 k in1p and2 p order, through researching the system model which adapts STLFM signal as the synchronous code. Finally, in order to prove the validity of the algorithm, I conducted simulation experiments and performance analysis to underwater acoustic communication system, which based on FRFT-OFDM, adopting synchronously bit error rate(BER) as evaluation indexes, analyzed and compared with traditional OFDM system which adapts linear frequency modulation(LFM) signals as the synchronous code. Through a large number of pool experiments verified that the underwater acoustic communication scheme whichbased on FRFT-OFDM is effective and feasible. It has a certain value.