Improved Performance of M-ary PPM Free-Space Optical Communication Systems in Atmospheric Turbulence due to Forward Error Correction

The performance of a free-space optical (FSO) communication system is limited by light intensity fluctuations induced by atmospheric turbulence. To improve the system performance, one effective way is to use forward error correction (FEC). Pulse position modulation (PPM) is a power- efficient modulation scheme employed in FSO systems. So this paper evaluates the performance improvement of an FSO system with M-ary PPM due to FEC in atmospheric turbulence. The FEC scheme are based on Reed-Solomon (RS) codes, and the results show that FEC can decrease the required average signal light intensity for a high bit rate FSO system to keep a BER below 10"9, and that with the FEC scheme, the system is tolerant of the noise resulted from the background light stronger than the desired signal light. Furthermore, we also found that FEC can remarkably increase the system tolerance for intensity fluctuations caused by atmospheric turbulence.