The Study Of Carrier Tracking Based On FLL And PLL

The high dynamic environment will bring a lot of problems to the capturing and tracking of carrier in the receiver.The PLL can not maintain tracking because the problems of larger Dopper frequency shift and frequency ramp caused by high dynamic. And the carrier tracking loop will lost. Therefore, it is significantly to resolve the problem of carrier tracking in the high dynamic and low SNR environment. The main research works are as follow.First, as the rapid development of digital signal processing technology, the receiver is implemented by the methods of software radio more and more. Digital down converter is an important technology in this field, so it is designed in the paper.Second, I make study on the theory of phase-locked loop, the analysis of phase discriminator in the digital algorithms loop, the inference of the best loop filter, the design method of the digital loop filter and the analysis of the noise performance and dynamic tracking performance in the loop.Then, the paper investigates several methods of frequency estimation in tracking of spread spectrum signal in high dynamic environment and I also make compare and summary to these methods.The automatic frequency tracking loop which is the most commonly used has been researched depthly. By analyzing the pertormance of two methods of frequency discriminator, the paper points out their disadvantage and makes some improvments. The improved loop is compared with two commonly used loops.Finally, the FLL and PLL are analyzed and compared, conclusion is drawn that both tracking loops complement each other in thermal noise characteristics and dynamics characteristics. Integrated PLL and FLL strategy to track carrier frequency and phase is proposed. The FLL is used to track carrier frequency and PLL is used to compensate instantaneous phase. The simulation about the acquisition and tracking in high dynamic and low SNR environment is done through Matlab software. The simulation results show that the loop can tracking the signal on the conditions that the low SNR, the Dopper frequency shift for±300 kHz, the first order derivative for 0~30 kHz/s and the second order derivative for 0~3 kHz/s2. Therefore, the receiver can obtain better dynamics performance and tracking precision.