On the capacity of free-space optical intensity channels

Abstract

New upper and lower bounds are presented on the capacity of the freespace optical intensity channel. This channel is characterized by inputs that are nonnegative (representing the transmitted optical intensity) and by outputs that are corrupted by additive white Gaussian noise (because in free space the disturbances arise from many independent sources). Due to battery and safety reasons the inputs are simultaneously constrained in both their average and peak power. For a fixed ratio of the average power to the peak power the difference between the upper and the lower bounds tends to zero as the average power tends to infinity, and the ratio of the upper and lower bounds tends to one as the average power tends to zero.The case where only an average-power constraint is imposed on the input is treated separately. In this case, the difference of the upper and lower bound tends to 0 as the average power tends to infinity, and their ratio tends to a constant as the power tends to zero.

Capacity bounds for a Gaussian optical wireless relay channel

“…For˛> 1 2 , the capacity approaching measure is the discrete uniform probability distribution function on the interval OE0, A. It is further shown [19,Lemma 2] that in case of the discrete uniform distribution with mean A 2 , the capacity…”

“…The continuous uniform measure q 2 .x/ is suggested [19] to be used for developing inner bounds when˛> 1 2 .…”

“…Selected output measures and Gaussian channel law meet the enabling conditions (18,19) for use of (17)…”

“…where ı and are free parameters such that ı > 0 and > 0 and U is the peak power of the output signal. Application of (17) to this measure is shown to yield the following upper bound on the capacity of a single-input single-output optical wireless channel [19].…”

“…The continuous uniform measure q 2 .x/ [19] is used for developing lower bound when˛> 1 2 as discrete uniform measure is the maximum entropy measure in this case [22].…”