在光通信中，采用高调制阶数可获得高功率利用率，但同时也会导致时隙速率增大。针对于此，文章研究了时隙速率对雪崩光电二极管(APD)直接检测接收机差错性能的影响。在给出接收机模型的基础上，以脉冲位置调制(PPM)为例，推导了差错概率解析式，并分析了产生影响的根本原因。数值结果表明，时隙速率的增大减弱了系统的抗噪声性能，当误码率为10-6时，调制阶数每增加1，需要增加约1 dBm的信号接收功率。

In optical communication, high modulation level (M) of a transceiver results in its high power efficiency, yet leading to the increase of time slot rate and affecting its error performance. In this paper, the effect of the time slot rate on the error performance of the APD-based direct detection receiver is studied. In the case of pulse position modulation, the code error rate versus time slot rate is derived and the root cause of effect production analyzed. Numerical results show that the increase of time slot rate weakens the system noise rejection performance and, for example, approximately 1 dBm more average signal power is required from M to M+1 with code error rate 10-6.