基于分数阶Fourier变换的并行组合扩频Chirp水声通信系统研究

The Research in Parallel Combinatory Spread Spectrum Chirp Underwater Acoustic Communication Systems Based on Fractional Fourier Transform

Chirp信号具有较大的时宽带宽积,因此具有较强的抗多普勒扩展的能力,近年来在水下通信环境中得到广泛应用。但由于水声信道带宽非常有限,而Chirp信号又是一种宽带的信号,因此水下多载波Chirp系统中的的通信速率一般较低。利用Chirp信号在分数阶Fourier变换(Fractional Fourier Transform,FrFT)的最佳分数阶变换域的冲激特性,结合并行组合扩频(Parallel Combinatory Spread Spectrum,PCSS)技术,本文提出了一个基于FrFT的并行组合扩频Chirp水声通信系统。该系统的特点是:一方面充分利用Chirp信号的性质,在保证可靠性的同时,省去均衡环节,大大简化通信系统接收端结构;另一方面,通过并行组合多载波的选择方式有效提升了系统的速率,提高了系统的频带利用率。通过在计算机仿真和实验室水池实验验证了该系统的性能。

Because of the large time-bandwidth product, Chirp signal has the ability to resist the Doppler effect and is widely employed in underwater acoustic communication systems. Since the underwater acoustic channel is very bandwidth limited while the bandwidth of the Chirp signal has to be certain extent to keep the characteristics of the Chirp signal, the data rate of the underwater multicarrier chirp communication system is very low.Taldng advantage of the impulse characteristics of the Chirp signal in the best fractional Fourier transform domain, as well as the Parallel Combinatory Spread Spectrum（PCSS）algnrithm, a PCSS Chirp underwater acoustic communication system based on FrFT is proposed in this paper.On the one hand, this system makes full use of the characteristics of the Chirp signals, and simplifies the receiver of the system by removing the equalization module.On the other hand, data rate of the communication system could be increased by applying PCSS algorithm.The BER performance and data rate are verified by computer simulations and experiments of the pool.