Research On Key Techniques Of Digital Iterative Receive For M-ary Differential Chaos Shift Keying Modulation System

Due to the inherent characteristics of chaos signal,such as wideband spectra,high auto-correlation and low correlations between different signals,chaotic communication systems which use noise-like chaotic signals as the carrier,have strong anti-inference ability for multi-path fading and high communication security.Moreover,they also can co-exist with other conventional narrowband communication systems.Therefore,as a kind of candidate modulation scheme for Ultra-Wideband(UWB)technique,chaotic modulation schemes can be employed in some power constrained communication systems,e.g.Wireless Body Area Network(WBAN),for providing high data rate communication service over complicated multi-path fading channel.In this dissertation,in order to improve the reliability of M-ary Differential Chaos Shift Keying(DCSK)system,and to reduce the convergence threshold and processing delay of this system,the key technologies of digital iterative receiver based on M-ary DCSK,which includes modified Low Density Parity Check(LDPC)codes decoding algorithm,joint demodulation and decoding iterative receiver(IR)design and double ptotograph LDPC codes based joint source and channel decoder(DP-JSCD)design,are systemic studied.Main contributions of the dissertation include the following aspects:It has been found that when decoding medium or short length LDPC codes,BP algorithm will be stuck in some trapping sets.Therefore,those nodes which delong to trapping sets or connect to them.can be defined as unreliable nodes.In order to improve the performance of BP algorithm,a Reliability-wise BP(RW-BP)algorithm,is introduced.By means of an extra reliability index,the reliability of each node and its Log-Likelihood Ratio(LLR)is labeled and transmitted during decoding procedure.Consequently,the unreliable nodes are identified,and the negative impact of them on decoding algorithm can be reduced by dynamic reweighted method.The simulation results suggest that RW-BP algorithm outperforms BP one at high signal to noise ratio(SNR)region over different channels,e.g.,additive white Gaussian noise(AWGN)channel and partial response(PR)channel.Meanwhile,compared with standard BP algorithm,the computation complexity of this proposed one is increased due to extra addition and multiplication.In order to reduce the convergence threshold of the non-coherent M-ary DCSK system,iterative receiver(IR)structure has been introduced in M-ary DCSK system.In this dissertation,the soft metrics of non-coherent M-ary DCSK have been derived over multi-path fading channel with channel state information(CSI)and without CSI.An extrinsic information transfer(EXIT)technique based on Monte Carlo method has been used to investigate the iteration behavior of this IR structure over different channels.The simulation results suggest that IR structure overall outperforms non-IR one at the aspect of bit error rate(BER)and convergence threshold.Meanwhile,the comparison curves of achievable rate also indicate that a gain can be obtained through an iterative processing.These simulation results also reveal that there is an optimal rate of non-coherent DCSK which depends on the channel.In order to further reduce M-ary DCSK system's convergence threshold,joint source and channel decoder based on double photograph LDPC codes(DP-JSCD)also can be employed.Meanswhile,a question is raised:which design,DP-JSCD or Iterative receiver with source decoder(IR-SD),can provide more iterative gains to M-ary DCSK system.The EXIT analysis and simulation results suggest that DP-JSCD design outperforms IR-SD one on the aspects of BER,convergence threshold and processing delay under M-ary DCSK system over multi-path fading channel,when source information with relatively constant statistic transmitted.This research also can be considered as a reference for designing multilevel iterative receiver to other systems.In this chapter,RW-BP algorithm is also modified and employed in DP-JSCD system.The simulation results suggest that this algorithm also improves the BER performance and convergence speed of this system at high SNR region.