对于基于脉冲位置调制(PPM)的光子探测阵列接收的深空光通信系统, 提出了一种直接预测频偏和初始相偏的PPM时隙同步方法。该方法首先测量每个支路各个光子的到达时间, 进而得到每个光子到达时间相对于PPM时隙位置的偏移量, 统计得到不同偏移量处的光子分布。然后利用前、后半帧数据光子分布峰值点对应时隙位置差值即半帧数据频偏累积值的原理对频偏进行估计; 根据频率估计值修正光子达到时间数据后, 再根据修正后一帧数据光子分布统计图峰值位置相对于理想同步位置的偏移量大小估计出初始相偏。仿真结果表明, 在计数时钟频率大于等于四倍时隙时钟频率情况下, 该方法均能实现时隙同步。

For the deep space optical communication system based on pulse position modulation (PPM) and photon detection array, a PPM slot synchronization method that directly predicted frequency offset and initial phase offset was proposed. In this method, the arrival time of each photons was measured firstly, and in this way, it can get the offset of every photon′s arrival time relative to PPM slot position and draw out the photon distribution diagram of different offsets of the half-frame forward and backward. Then, the frequency offset was evaluated by using the offset of the photon distribution between the half-frame forward and backward(i.e. the cumulative value of frequency offset in the half frame data). After correcting the data of the arrival time of photons according to the frequency estimation value, the initial phase offset can be estimated by calculating the offset between the frequency corrected photon distribution and that of the ideal synchronization. The simulation result shows, when the counting clock frequency in the receiver is equal or greater than 4 times that of the PPM slot, this method can realize PPM slot synchronization.