Part 1: Optical Communication Over the Clear Turbulent Atmospheric Channel Using Diversity

TLDR

Optical communication over the clear atmosphere enables gigabit‑per‑second data rates over short distances, but atmospheric turbulence causes fades that can severely reduce data transmission. The study investigates using spatial and time diversity at the transmitter and receiver to mitigate short‑term signal loss. The authors derive outage probabilities for spatial and time diversity systems employing direct‑detection receivers and binary pulse‑position modulation with equal‑gain, optimal, and select‑max combining. The diversity schemes provide substantial power gain, with equal‑gain combining nearly matching optimal combining, indicating that diversity should be adopted to enhance clear‑atmosphere optical channel performance.

Abstract

Optical communication over the clear atmosphere provides a means for high data rate communication (gigabits per second) over relatively short distances (kilometers). However, turbulence in the atmosphere leads to fades of varying depths, some of which may lead to heavy loss of data. We consider spatial diversity at both the transmitter and receiver, as well as time diversity as a means to mitigate the short-term loss of signal strength. Using direct detection receivers and binary pulse position modulation as an example, we derive the outage probability of spatial diversity and time diversity systems that use equal gain combining (EGC), optimal combining, and select-max combining. The power gain of using these diversity systems is found to be substantial, and the performance of equal gain combining is found to be almost as good as optimal combining. Hence, we feel diversity should be considered as one of the system techniques to improve channel performance in clear atmospheric optical channels.