Achievable capacity region of a Gaussian optical wireless relay channel

Congested and expensive radio spectrum coupled with an insatiable demand for higher throughput in the last mile makes optical wireless an attractive alternative. The limitation of coverage area of optical wireless links is compensated by their ultrahigh bandwidth and unregulated spectrum. Cooperative relay strategies can further enhance the capacity and availability of optical wireless. A number of researchers have studied how the capacity of an optical relay channel is effected by fading processes. However, the capacity of an optical wireless relay channel (OWRC) has received little attention. This paper attempts to delineate the achievable capacity region of a Gaussian OWRC. Decode and forward, compress and forward, and amplify and forward relay strategies are used to determine the capacity bounds that constitute the achievable region. High and low signal asymptotes of the bounds are developed. The probability of outage under fading induced by turbulence and pointing error is also discussed. The results presented in this paper will facilitate the design of optical wireless relay networks in terms of choice of relaying strategy and input distribution.