Bidirectional Iterative Reception Algorithm Based On Frequency Domain Equalization Over Time-varying Underwater Acoustic Channels

In recent years,with the increasing attention to the marine resources,the requirement of underwater acoustic communication(UWAC)technology is getting higher and higher.Underwater acoustic(UWA)channel is one of the most complex wireless communication channels.It has the characteristics of time-varying,severe multipath effect,Doppler effect,complex background noise,extremely narrow available bandwidth are all obstacles to the development of high speed and reliable UWAC technology.Single carrier frequency-domain equalization(SC-FDE)is an effective technique in resisting multipath effect.Because it has the equalizer with low computational complexity,has lower peak to average ratio and good performance in resisting frequency offset compared with multicarrier communication system.SC-FDE is one of the common techniques in UWAC.This paper mainly researches SC-FDE equalization algorithm in UWAC and verifies the feasibility of the algorithms through simulation analysis and practical experiments.The main works are summarized as follows:1.This paper begins with introducing the physical characteristics of UWA channel and analyzing the channel characteristics,contrasts the wireless communication channel with the UWA channel.Then,this paper introduces the basic principle,system model and frame structure of SC-FDE system,and presents the parameter design of UWA SC-FDE system according to the characteristics of UWA channel.2.This paper studies the most important part of SC-FDE system:channel equalization and channel estimation.Then,introduces the principle of traditional linear equalization algorithm,Turbo equalization,the commonly used channel estimation algorithms and the selection of training sequences.All these algorithms are simulated in Rayleigh fading channel and these algorithms'performance are analyzed.3.In order to deal with the complex characteristics of UWA channel,this paper proposes a new bidirectional iterative receiving algorithm based on firequency-domain equalization.Then,based on this algorithm,the idea of Turbo equalization is used to improve it.Moreover,this paper proposes a banded frequency-domain matrix iterative equalization algorithm according to the characteristics of Doppler frequency shift of UWA channel.All these algorithms are simulated in Rayleigh fading channel and these algorithms'performance are analyzed.4.This paper studies two typical UWA channels and analyzes the multipath effect and time-varying characteristics.The algorithms which are proposed above are simulated in these UWA channels.This paper analyzes the performance of the algorithms in UWA channels.Moreover,using the proposed algorithms,the actual UWAC experiment was performed in the pool and lake.The experimental results show algorithms can be applied to the UWAC system.