扩频系统中频率捕获精度改善算法研究

摘要

频率捕获精度影响系统的相干解调,从而影响通信系统的性能.基于FFT的频率估计速度快,实现简单,但FFT变换存在栅栏效应,所以直接利用FFT进行频率估计,会带来较大的测量误差.传统Rife算法在低信噪比或相对偏差较小时存在插值方向错误的问题,而传统的Quinn算法则可获得正确的插值方向,通过融合Rife算法和Quinn算法的优点,提出了一种Q-Rife算法,实现更高的精度估计.充分利用幅相联合内插算法在相对偏差较小时频率估计精度较高的特性,进一步综合Q-Rife算法和幅相联合内插算法的优势提出API-Q-Rife算法,可有效改善Q-Rife算法在较小相对偏差时的估计精度.利用MATLAB进行仿真,结果表明,改进的Q-Rife算法在减小频率估计误差的同时保证了算法的稳定性,而改进的API-Q-Rife算法可获得比Q-Rife更优的性能.%Frequency acquisition accuracy affects system coherent demodulation, thus affects the performance of communication system.FFT-based frequency estimation can be implemented with high speed and low complexity, but exists picket fence effect.Therefore, using FFT for frequency estimation directly will bring a greater measurement error.Traditional Rife algorithm has the problem of incorrect interpolation direction at low SNRs or with smaller relative offset, whereas traditional Quinn algorithm can obtain the correct interpolation direction.By combining the advantages of Rife algorithm and Quinn algorithm, a Q-Rife algorithm is proposed to achieve higher accuracy estimation.Further, making full use of higher accuracy estimation of joint amplitude-phase interpolation algorithm with small relative offset, an API-Q-Rife algorithm is put forward by combining the advantages of the above two algorithms, which can improve the estimation accuracy of Q-Rife algorithm with small relative offset.The simulation results based on MATLAB show that the improved Q-Rife algorithm can reduce the frequency estimation error while guaranteeing the stability of the algorithm, and the proposed API-Q-Rife algorithm can achieve better performance than Q-Rife algorithm.