极大似然判决下大气无线光脉冲位置调制差错性能

Error Performance for Pulse Position Modulation under Turbulence Based on Maximum-likelihood Detection

大气湍流对无线光通信系统影响较大,基于高斯信道及门限判决方法的大气无线光通信脉冲位置调制(PPM)的误码特性分析存在局限性。针对于此,推导了湍流大气中无线光PPM系统在极大似然判决(MLD)下的差错性能计算模型,并运用蒙特卡洛方法验证了理论计算模型的有效性。仿真分析表明,MLD下PPM具有更好性能,但也较易受湍流影响,为使弱湍流信道中PPM的误比特率不高于10-6,调制阶数每增加1阶,须提高平均接收信噪比0.67dB以上。对于峰值功率恒定PPM系统,应根据器件性能和具体通信条件,在差错性能和功率利用率之间作出平衡。

Atmospheric turbulence can greatly degrade the performance of Free Space Optical （FSO） Communication system. With Gauss channel model and threshold detection, studies about Pulse Position Modulation （PPM） under turbulence have limitation in describing its characteristic. Mathematical calculation expressions about Symbol Error Rate （SER） and Bit Error Rate （BER） of PPM under turbulence channel based on Maximum-likelihood Detection （MLD） are deduced. Monte Carlo methods verify the presented theoretic calculation models. Simulations show that, PPM based on MLD will present better performance, which is also easily influenced by turbulence. The PPM receiver requires average received Signal Noise Ratio （SNR） gain not less than 0.67 dB when the modulation level is increased one level with BER 10-6 in weak turbulence atmosphere environment. For fixed peak power PPM system, synthesized devices capability and communication conditions, proper compromise should be made between the error performance and the power efficiency.