A research of carrier tracking loop for high hopping rate DS/FH receiver
Chen Tianwu, Ju Wang, Fan Xing, Yue Yingying, Miao Chunhui · 2013
High hopping rate DS/FH (Direct Sequence/ Frequency Hopping) hybrid spread spectrum system has the advantages of both advanced anti-jamming capabilities and high security, which is one of the directions of the frequency hopping communication system in the future. After deriving a mathematical model of DS/FH hybrid spread spectrum receiver, first, analyze the influence on loop integrating gain caused by frequency hopping asynchrony and point out the problem of traditional frequency locked loop (FLL) existed in the high hopping hybrid spread spectrum system. Second, discuss influence on receiver carrier tracking loop since spatial channel nonlinear group delay leads to random initial phase of different frequency hopping period. At last, propose a method to reduce the impact on the tracking loop caused by above problems. It related the PN code to the FH code in the DS/FH signal, and replaced FLL by velocity locked loop (VLL) with the help of frequency hopping pattern. The effectiveness of the proposed method was verified by simulation.