大动态PCM/FM信号的载波频率同步

摘要

针对大动态脉冲编码-频率调制(PCM/FM)遥测信号的载波频率同步,提出了基于快速傅里叶变换(FFT)及频谱重心的载波频率估计方法,并采用了频谱叠加及频谱截取的优化方法提高算法估计精度.相对于其他基于FFT的频率估计算法,频谱重心法有着更高的估计精度及更好的抗噪声性能,而且复杂度代价很小.仿真的均方误差结果表明,基于FFT长度为2048和2块叠加以及保留信号99.9%能量的频谱截取方案有最好的估计性能.在最大多普勒频率、多普勒一阶变化率及二阶变化率分别为0.5倍、0.3倍及0.2倍符号率的大动态条件下,基于频谱重心法的二阶锁频环能够较好地完成载波频率跟踪.误码率曲线表明,经过频偏校正后的多符号非相干解调(MSD)性能与无频偏情况相比,无性能损失.%Frequency synchronizer based on the Fast Fourier Transform( FFT) and barycenter of frequency spectrum for large dynamic pulse-code modulation/frequency modulation( PCM/FM) signals is proposed. In order to improve the estimation performance,spectrum superposition and spectrum truncation are put for-ward. The spectrum -barycenter synchronizer has better anti-noise capability and tracking accuracy,but acceptable complexity increased compared with other algorithms based on FFT. The mean square error ( MSE) of simulations indicates that,the superposition scheme with 2048 FFT points and 2 blocks is the best. Meanwhile the spectrum truncation with 99. 9% of signal energy reserved has the best estimation per-formance . When the max offset,the first-order and the second-order acceleration of Doppler frequency are set as 0. 5,0. 3 and 0. 2 times of bit rate respectively,the second-order frequency locked loop(FLL) with spectrum-barycenter estimator can synchronize perfectly. The bit error rate(BER) curve shows that the multi-symbol detector( MSD) following proposed frequency offset correction,has no performance loss com-pared with the ideal situation without frequency offset.