Wireless multiple-input single-output optical links with coherent detection

Coherent wireless optical communications (WOC) is a viable alternative to irradiance modulation with direct detection for atmospheric channels impacted by turbulence. Effective techniques such as channel coding and diversity can be introduced to mitigate the turbulence effects, but transmit diversity for coherent WOC has not been reported due to the phase noise imposed on the electric fields of multiple optical carriers. To understand this problem and facilitate multiple-input single-output (MISO) for coherent WOC, we propose a new MISO optical structure in this paper. Based on the proposed structure, several cases are studied by adopting this MISO technique. Error rates and outage probability are presented in closed-forms with equal gain combining. Significant performance improvement is seen by comparing MISO systems with the standard single-input single-output coherent WOC systems.