High Dynamic Dsss Signal Carrier Synchronization Technology

This dissertation mainly focused on discussing the carrier synchronization of signals with high Doppler shifts in the spread spectrum TT&C (Track, Telemetry and Control) system. In high dynamic circumstances, Doppler shifts are from several tens kHz to more than one hundred kHz, due to the high velocity of the aero craft. PN code and carrier synchronization is crucial in spread spectrum receivers for it is the requirement of correctly getting data from the modulated signals. But, because of the large Doppler shifts, the correlation of PN code decrease severely and the receiver can't detect the synchronous PN code. Consequently, PLL is hard to acquire and track carrier signals. In a word, large Doppler shifts make the performance of receiver get worse.This dissertation proposed some technique on PN code and carrier synchronization to promote the performance of the conventional receiver and formed a whole scheme for carrier synchronization in high dynamic circumstances. The scheme is processed by three steps. At the first step, a fast code acquisition scheme is designed to acquire the phase of PN code while tuning the carrier NCO to make the residual carrier frequency error not affect the work of DPLL, that's called the coarse acquisition of carrier frequency. At the second step, the residual carrier frequency error is decreased again so that it's within the fast acquisition range of PLL to make it fast lock, that's called the fine acquisition of carrier frequency. At the third step, PLL is used to track the carrier frequency and phase.For the coarse acquisition of carrier frequency, a fast PN code acquisition technique called partial correlation based on FFT was discussed and then an improved technique was proposed to speed up acquisition and decrease acquisition time. The new technique takes segmented matched filter to replace partial correlator, so it's called segmented matched filter technique based on FFT. After that, the thesis proposed some scheme to reduce scalloping loss due to FFT and the impact of data modulation for improving the probability of detection. At last, quadratic interpolation was taken to improve the accuracy of frequency estimation which has the advantage of small amount of calculation.For the fine acquisition of carrier frequency, FFT, as an aided frequency acquisition technique, was combined with PLL to scan carrier frequency range at a smaller frequency interval. Considering the impact of data modulation on error SNR, this dissertation compared the performance of four phase detectors of costas loop, according to that the proper arm filter would be chosen.At last, an FPGA design for fine acquisition loop of carrier frequency performed in Quartus II was given in this dissertation to testify the performance of the system.