中文说明：
研究多进制脉冲位置调制和关闭键控在直接检测光无线通信系统中存在的大气影响，比较了ook与PPM调制方式的区别。
English Description：
The atmospheric effects of M-ary pulse position modulation and turn off keying in direct detection optical wireless communication system are studied, and the differences between ook and PPM modulation modes are compared