High Dynamic Environments In Multi-band Spread Spectrum System With Synchronous Technology Research

Direct Sequence Spread Spectrum (DSSS) technology is widely applied in modern communication system because of its advantages on anti-jamming and high security. But in the case of band-limited environment, conventional DSSS system may not works well, so it's critical to improve the spectrum efficiency. It has been proved that M-ary spread spectrum technology is an efficient solution in theory and practice.In high dynamic environment, the received signal has high Doppler, high Doppler rate and jerk. In consideration about these above characteristics, the acquisition algorithm and carrier tracking algorithm for M-ary spread spectrum communication are researched in high dynamic environment in the dissertation.In the dissertation, the acquisition algorithm based on Fast Fourier Transform (FFT) technology is researched. The structure and the performance of the FFT-based acquisition method are analyzed and several techniques for improving the performance are also discussed. The code phase is searched and the carrier Doppler is coarsely estimated with error less than half of the FFT precision, so the former two-dimensional acquisition process becomes a one-dimensional process, which can significantly accelerate the acquisition process and reduce the acquisition time. In the tracking process, three algorithms including Most Likelihood Estimation (MLE), Kalman Filter and Extended Kalman Filter (EKF) are researched. In addition, the despreading programme is researched for the QPSK modulation scheme used in the system. The tracking performance and Bit-error ration (BER) performance are achieved by the MATLAB simulation with coherent and noncoherent dispreading respectively.The dissertation presents an introduction about the related concepts and background knowledge firstly. Then the synchronization algorithms in acquisition and tracking process are carried out orderly and a new noncoherent despreading algorithm is presented for M-ary spread spectrum system with QPSK modulation scheme. The last chapter summarizes the thesis and makes a prospect about the further research.