Research And Implementation Of Tracking Algorithm For DS/FH Signal

DS/FH is a kind of spread spectrum communication technology combines direct sequence spread spectrum(DSSS)and frequency hopping spread spectrum(FHSS),which achieves the complementarity of advantages and disadvantages of DS and FH,and is the main technical system of next generation space TT&C system.The tracking technique of DS/FH signal is one of the key technologies for DS/FH hybrid spread spectrum TT&C system.Accurate tracking of signal is not only related to the demodulation of the data,but also affects the accuracy of distance and velocity measured of the system.Therefore,the research of tracking technology for DS/FH signal is of great significance.Based on the review of the research status of tracking algorithm for spread spectrum signal at home and abroad,firstly,the basic principle of spread spectrum communication is analyzed in this paper,and the models of DSSS,FHSS and DS/FH hybrid spread spectrum communication system are given,the characteristics of DSSS,FHSS and DS/FH hybrid spread spectrum communication are clarified.Then,the structure and design idea of general DSSS signal tracking loop are given,and the tracking errors of PLL,FLL and code loop are analyzed.Aiming at the characteristics of high jump rate and low carrier to noise ratio(CNR)of DS/FH signals in TT&C system,a tracking loop of the DS/FH signal is designed.The tracking performance of the DS/FH signal tracking loop is simulated and analyzed by MATLAB.Next,the signal generation module,tracking control module and NCO module are developed by the VHDL programming language on the FPGA(Field Programmable Gate Array)hardware platform,the function such as integrate dumping,discriminatting filtering are implemented.Finally,the function and performance of the DS/FH signal tracking algorithm are tested by the Chipscope online logic analyzer,and the test results show that the functions of the signal generation module,tracking control module,NCO module,integrate-dump module and discrimination filter module are operating well,the loop keeps track of static signal,constant velocity signal and constant acceleration signal when hopping ratio is 9000hops/s and CNR is 45dBHz.