Under low SNR condition rapidly varying Doppler frequency offset influence on carrier frequency acquisition and simulation analysis

摘要

The Quickly changed Doppler frequency offset is calculated and researched under low SNR during mobile satellite communications receiver carrier capture process. Firstly, current carrier frequency offset calculation technology is introduced, and the influence of the Doppler shift caused by the carrier capture is analyzed; Secondly, carrier frequency offset acquisition affected by changing rate of Doppler frequency offset is analyzed. It's mainly considered that first order changing rate and second order changing rate affect carrier acquisition. The changing rate would seriously reduces non-coherent accumulation number during carrier frequency offset estimation at low SNR; Finally, carrier frequency offset caused by the rate of change of the first order and second-order Doppler shift is analyzed and researched. It is demonstrated that "platform effort" caused by Doppler frequency offset can be improved, and the efficiency of the carrier capture increased through sampling points N reasonable by MATLAB simulation. In the mobile satellite communication system, due to the rapid relative motion of the transmitter and the receiver, the received signal will be affected by "Doppler effect", so that the received signal carrier Doppler frequency shift, a change rate change or secondary pseudo-code rates and relatively large frequency offset, using conventional methods not to achieve capture chip carrier and simultaneously capture. Such a signal would be called "high dynamic signal." Especially for LEO satellite constellation communication, the dynamic effect of the received signal is more significant. This paper studies the receiving end of carrier synchronization in the Doppler shift of the carrier acquisition impact. The receiving end for satellite mobile communication system Doppler shift is estimated for GPS navigation and positioning system, Doppler shift estimation has been studied by the satellite position and velocity of the resulting estimate of a satellite sometime Doppler frequency shift[1] [3] [5] [9]; Documents presented, does not depend on the symbol synchronization based on differential detection method of Doppler frequency shift, could apply to more than the symbol rate estimation of Doppler frequency shift, and compensation[2]. Literature by analyzing the different propagation modes in the ionosphere Doppler frequency shift signal changes with the radial distance, get a different transmission mode variation of Doppler frequency shift some conclusions[4]. Document infers a link from relative speed variation rate as a new method for calculating Doppler frequency shift, and the simulation [8].