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合适的编码方案可以减小通信系统的误码率,在自由空间光通信中显得尤为重要.空时编码技术是一种空间域和时间域相结合的分组编码方式,它能有效抵抗衰落,改善系统的误码性能.文中首先将Alamouti空时码的正交性和Q-PPM调制技术相结合,提出了一种适合于强度调制/直接检测式光通信的编码方法.其次分析了该系统在无衰落无背景辐射、有衰落无背景辐射、无衰落有背景辐射和有衰落有背景辐射时的误码性能.最后,通过Monte-Carlo仿真实验进一步证明了该理论的正确性.结果表明:采用该编码方法不仅能实现1速率传输,而且能有效抵抗衰落,克服大气湍流所产生的闪烁效应.当误字率为2×10~(-3)时,相对于1×1系统而言,2×1系统的发送功率被节约了约3.5 dBJ,2×2系统的发送功率被节约了约9 dBJ.
Appropriate coding scheme can reduce the bit error rate of the communication system, and it is especially important in the free space optical communication.Space-time coding is a combination of spatial and temporal packet coding, which can effectively resist the decline, improve System.Firstly, by combining the orthogonality of Alamouti space-time codes with the Q-PPM modulation technique, a coding method suitable for intensity modulation / direct detection optical communication is proposed.Secondly, No fading without background radiation, fading without background radiation, without fading background radiation and fading with background radiation.Finally, the Monte-Carlo simulation experiment further proves the correctness of the theory.The results show that: The encoding method can not only achieve 1-rate transmission, but also effectively resist the fading and overcome the flickering effect of atmospheric turbulence. When the error rate is 2 × 10 -3, compared with 1 × 1 system, 2 The transmission power of the × 1 system is saved by about 3.5 dBJ, and the transmission power of the 2 × 2 system is saved by about 9 dBJ.