Space-Time Coding versus Repetition Coding for Free-Space Optical Communication

In this paper, we investigate spatial diversity techniques for free-space optical (FSO) links with intensity modulation and direct detection (IM/DD) over log-normal atmospheric turbulence-induced fading channels. We consider the deployment of space-time block codes and repetition codes. Our performance analysis demonstrates that although both schemes are able to extract full diversity, repetition codes outperform their counterparts. The performance gap increases as the number of transmit apertures increases. Our findings clearly point out that deployment of space-time coding is not necessary for a FSO IM/DD link.