Application of Single Carrier Fractional Fourier Domain Equalization in Underwater Acoustic Communication

摘要

Single carrier frequency domain equalization (SC-FDE) is an important means of high data rate communication. Considering frequency selective fading in the underwater acoustic channel, there are some disadvantages with respect to the traditional SC-FDE. When using Frequency Domain Linear Equalization (FD-LE), the equalizer based on zero-forcing rules may magnify noise at deep fading points of frequency domain, while the equalizer based on the least mean-square error rule cannot completely eliminate Inter-Symbol Interference (ISI). Frequency domain decision feedback equalization (FD-DFE) and frequency domain equalization noise prediction (FDE-NP) can make up this insufficiency, but the computational complexity of these methods is greater. With the aim of eliminating ISI and meanwhile minimizing mean-square error caused by noise, but without introducing the high computational complexity caused by complex technologies such as decision feedback, we propose a single carrier fractional Fourier domain equalization (SC-FrFDE) technique. With this technique, the channel response and equalizer coefficients in optimal-order fractional Fourier domain (FrFD) are calculated, turning the equalization to an FrFD with flat fading. In the simulation experiment, two underwater acoustic channels - the channel of a laboratory pool and Quangang Harbour - are chosen in order to test the performance of SC-FDE and SC-FrFDE, with reference to correlation, convergence and bit error rate. The simulation results demonstrate that both of these two methods have nearly the same effects when signals transmitted through the channel of a laboratory pool, while the performance of SC-FrFDE has significant improvement gains over traditional SC-FDE in the channel of Quangang Harbour, whose frequency selective fading is much more serious than the latter. The simulation results suggest that SC-FrFDE is suitable for underwater acoustic channels with frequency selective fading.