Optical communication using coherent detection with space-time coding in the presence of atmospheric turbulence

Space-time codes are of great interest for wireless communication systems as they can be used to improve the system performance. For optical wireless communications using coherent detection, atmospheric channels can induce fading as well as phase noise to degrade wireless link performance. In this paper, a space-time coded communication system is studied for a wireless optical link using coherent detection over atmospheric turbulence channels. An Alamouti-type space-time coded system structure is proposed when both turbulence-induced fading and phase noise from the channel and lasers are present. The error rate performance is analyzed for the proposed scheme over a wide range of turbulence conditions. Closed-form error rate expressions are derived for such systems for fast performance evaluation. In numerical case studies, the usefulness of the proposed optical wireless space-time coded system is demonstrated by a comparison to a single-input single-output optical wireless communication system.