Upper and lower bounds on the capacity of wireless optical intensity channels

Abstract — This paper finds asymptotically exact upper and lower bounds on the channel capacity of power and band-limited optical intensity channels corrupted by white Gaussian noise. This work differs from the oft investigated case of the Poisson photon counting channel in that not only are rectangular pulse amplitude schemes considered, but general results for all time-disjoint intensity modulation schemes are presented. The role of bandwidth is expressed by way of the effective dimension of the set of signals and together with an average optical power constraint is used to determine bounds on the spectral efficiency of time-disjoint optical intensity signalling schemes. The signal independent, additive white Gaussian noise model is realistic for indoor free-space optical channels. The bounds show that at high optical signal-to-noise ratios the use of bandwidth efficient pulse sets is essential to achieve high spectral efficiencies. This result can be considered as an extension of previous work on photon counting channels which more closely model low optical intensity channels. I