Design And Simulation Of Low Complexity Frequency Hopping Systems Using LDPC Codes

Frequency-hopping(FH) wireless communication systems were initially developed as a military application to permit reliable and safe communications in the face of an enemy interferer,especially in a poor electromagnetic environment.So the FH systems are of a great military significance.Due to the good anti-jamming performance and multiple access ability of FH technique, FH systems are also widely used in civilian communications.At present,FH communications have been improved with faster hopping rate,higher jamming resistance capabilities and lower implementation complexity.And channel coding technique in a FH system is not only a key technique to improved system performance but also a part with high complexity.This thesis proposes two feasible schemes to reduce the complexity of FH systems with a little performance degradation.The first scheme aims to diminish system complexity by simplifying the encoder and decoder.It replaces LDPC codes constructed by PEG algorithm(PEG-LDPC codes) with EG-LDPC codes which have lower implementation complexity.Our simulations show that EG-LDPC codes perform worse than PEG-LDPC codes about 0.4dB to 0.6dB both over partial-band noise jamming channel and Rayleigh flat fading channel(BER=10^-6).As a consequence the scheme is suitable for a system with low complexity requirements.The second scheme aims to reduce the overall complexity of the FH system.It substitutes GLDPCH codes coded FH(GLDPCH-FH) system for LDPC codes coded hybrid FH with DS spread spectrum(LDPC-FH/DS) system.Because the extremely low rate codes are used,GLDPCH-FH system can decrease the system complexity owing to the absence of some complicated technique in receivers.Our simulations figure out that over partial-band noise jamming channel,when the system code rate is 0.05, GLDPCH-FH system outperforms LDPC-FH/DS system with 0.1dB,while,the number increases to 0.3dB when the system code rate is 0.02.But for Rayleigh flat fading channel,GLDPCH-FH system has worse performance compared with LDPC-FH/DS system with the same system code rate. Fortunately,we can choose some system code rate carefully to approach the performance of LDPC-FH/DS system.In words,over partial-band noise jamming channel the second scheme can be considered as a candidate for a system desiring better performance and lower complexity.Meanwhile over flat fading channel,the second scheme can meet the low complexity requirements of a system.Therefore,these two schemes have a theoretical significance to promote the practical application of LDPC codes in FH systems.