Research And Implementation Of A High Security DSSS Scheme Based On Variable-length PN

DSSS signals are the main work type in HF-VHF communication. Because of the characteristics such as keeping secret and low probabilities of intercept, DSSS signals have been widely used and the methods to acquire the PN sequence of DSSS signals are developmented rapidly. Those methods threat to keeping secrect of DSSS. Most of the methods to acquire the PN sequence of DS-SS signlas are divided into two steps: the first step is the period estimation and the second is the sequence estimation of PN sequence. Period estimation of PN sequence is the necessary condition for the estimation of PN sequence.Several usual methods to estimation of PN sequence are summed up, and the methods about period estimation are analyzed by computer simulation. In order to strength the secrecy of DSSS, a variable-length PN sequence DSSS based on adaptive threshold is proposed. In this system, different symsbols correspond to sequences of different lengths, because the randomness of the symsbols, the period estimation of PN sequence becomes very difficulty, so this system has a higher security. This system uses the adaptive threshold not the maximum correlation value, so the resisting-noise performance is not good as the fixed-length PN sequence DSSS and the simulation results are given. On the platform of Code Composer Studio, we finish the hardware implementation with processor TMS320C6713 in C language.