Impact of tracking errors on dual diversity structure over the free space optics links

This paper analyzes the impact of tracking errors on the time diversity structure in relation to beam tracking over free-space optics (FSO) links. The paper proposes a time-diversity scheme with beam tracking introducing a powerfading model for an FSO system that utilizes beam tracking through atmospheric turbulence. Further, the paper derives a closed-form bit error rate (BER) for no-diversity and dual-diversity schemes, taking into account the tracking error, coherence of the diversity signals and photo detector noise. It is shown that time diversity is a clever mitigation technique for improving transmission reliability for the FSO system with beam tracking. Comparing with space diversity, time diversity is cost effective and easy to use in FSO.