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分析了相干光脉冲位置调制的信道容量及传信率最大化条件。通过分析光外差接收的脉冲位置调制信号具有的概率分布特性,推导出采用最大似然检测的相干脉冲位置调制信道具有的转移概率矩阵和信道容量,证明在检测器散粒噪声极限假设下,信道容量只取决于接收脉冲能量和脉冲位置调制阶数。利用Jensen不等式化简信道容量得到其下限,该下限能够近似实际通信链路的信道容量,基于此估计出达到最高传信率时的脉冲位置调制阶数同粒子数反转的重建时间之间的关系,给出了二者在一定范围内的一般映射。数值仿真表明,在接收能量使信道误码率优于10-2时,估算出的脉冲位置调制阶数能够使传信率接近最大值。
The channel capacity and the maximization of transmission rate of coherent optical pulse position modulation are analyzed. By analyzing the probability distribution characteristic of pulse position modulated signal received by optical heterodyne, the transition probability matrix and channel capacity of coherent pulse position modulated channel with maximum likelihood detection are deduced. It is proved that under the assumption of the detector shot noise limit, The channel capacity depends only on the received pulse energy and the pulse position modulation order. Jensen’s inequality is used to reduce the channel capacity to obtain the lower bound that approximates the channel capacity of the actual communication link. Based on this, it is estimated that between the pulse position modulation order and the reconstruction time of the population inversion when the highest transmission rate is reached Relationship, given a general mapping of the two within a certain range. The numerical simulation shows that when the received energy makes the channel bit error rate better than 10-2, the estimated pulse position modulation order can bring the transmission rate close to the maximum.