Study On The Key Technologies Of Subset Based Coherent Fast Frequency Hopping Communication Systems

Fast frequency hopping(FFH) has the characteristic of transmitting a modulation symbol by more than one hop with wide interval. As a mainstream technology in wireless communications, FFH has been widely used due to its advantages in anti-jamming, antimultipath fading, anti-Intercept and anti-reconnaissance.Due to the signal properties above-mentioned, it is difficult for FFH to implement channel estimation. Incoherent FFH system is widely used since it does not require channel estimation, but it has limitations of incoherent diversity combined loss, low spectral efficiency, and insufficient scalability. Therefore it is urgent to apply coherent modulation and demodulation techniques to FFH systems.This thesis focuses on key technologies in Subset Based Coherent Fast Frequency Hopping system(S-CFFH). This technologies include system design and frame format design of S-CFFH system, reception processing technology under non-interference environment, anti-jamming combining schemes and interference suppression under interference environment.The major work of this thesis are summarized as follows.Firstly, this thesis proposed the S-CFFH scheme. By solving the channel estimation problem, the S-CFFH has high spectral efficiency and good expandability, without compromise in anti-jamming and anti-Intercept ability.Secondly, this thesis analyzes the reception processing technologies of S-CFFH system under non-interference environment including channel estimation, interpolation algorithm and coherent combining, and implement simulation analysis of these different algorithms in many different channels. The simulation results show that S-CFFH/QPSK system has better performance in BER and spectral efficiency,compared to FFH/4FSK system.Thirdly, this thesis analyzes the anti-jamming combining schemes of S-CFFH system. Based on the theoretical analysis, this thesis implements simulation of ideal channel estimation and ML(Maximum Likelihood) anti-jamming combining schemes of S-CFFH system under partial band noise jamming and multi-tone interference environment, both in AWGN channel and typical suburban channel. The results show that the ML combing scheme has better anti-jamming performance than MRC(Maximum Ratio Combining) whether it is under ideal or non-ideal channel estimation.Finally, this thesis studies the interference suppression techniques in S-CFFH system, especially the pulse interference suppression technology based on the group detection and frequency domain interference suppression based on maximum likelihood. The simulation result shows that both two techniques can suppress pulse jamming, multitone jamming and partial band noise jamming effectively. With coding, the ML amplitude limiting has a better performance than zero setting. The interference suppression techniques in S-CFFH system greatly enhance the anti-jamming performance without increased complexity.