空间通信中GMSK信号的载波恢复与时钟同步

Carrier recovery and clock synchronization of GMSK signals in space communications

在空间通信中,过大的多普勒频移和多普勒变化率会造成相干解调接收机无法进行载波恢复与时钟同步。为此,针对高斯最小频移键控(GMSK)信号提出一种可靠且快速克服大多普勒频移的改进平方环方法。首先通过频率估计模块获取粗略载波频率,其次应用改进平方环结构实现GMSK信号的载波恢复和时钟同步。仿真结果显示,在输入信噪比Eb/N0=5 dB以及环路噪声带宽为50 kHz的条件下,载波恢复环路与时钟同步环路锁定时间约为3.6 ms。在低信噪比及大多普勒频移的条件下,该方法能够快速且稳定地实现GMSK信号在空间通信中的载波恢复与时钟同步。

Due to excessive Doppler shifts and Doppler rate in space communications,the coherent demodulation receiver fails to perform carrier recovery and clock synchronization.To this end,this paper proposed an improved square-loop method to overcome the large Doppler shifts reliably and quickly for the GMSK signal.This method could obtain the coarse carrier frequency by the frequency estimation module,and then realized the carrier recovery and clock synchronization by the improved square-loop.With loop noise bandwidth of 50 kHz and Eb/N0=5 dB,the simulation shows that the locked time of carrier-recovery loop and clock-synchronization loop is about 3.6 ms.In space communications,the method can implement carrier recovery and clock synchronization of GMSK signals quickly and stably under the conditions of low SNR and large Doppler shifts.