In this thesis we study the free-space optical communication channel.
This channel is haracterized by inputs that are nonnegative
representing 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 on both their
average and peak power.

Our task is trying to find upper and lower bounds on the capacity of
this channel. We use a numerical approach to compute the channel
capacity and compare it with previous bounds. Based on the result of
this comparison, we try to derive improved analytical lower bounds on

Our numerical lower bounds are very close to previous upper bounds in
lower SNR region (below 5 dB) with improving performance if we loosen
the average-power constraint. Our analytical lower bounds are good in
medium SNR region (between 5 dB and 15 dB).

-||-   _|_ _|_     /    __|__   Stefan M. Moser
[-]     --__|__   /__\    /__   Senior Researcher & Lecturer, ETH Zurich, Switzerland
_|_     -- --|-    _     /  /   Adj. Professor, National Chiao Tung University (NCTU), Taiwan
/ \     []  \|    |_|   / \/    Web: http://moser-isi.ethz.ch/

Last modified: Wed Sep 10 11:09:18 UTC+8 2008