Communications Through Non-Line-of-Sight Solar-Blind Ultraviolet Scattering Channels

Abstract

A recent exciting application in free-space optical communication systems is to use atmospheric scattering to establish non-line-of-sight (NLOS) links in the solar-blind ultraviolet (SB-UV) band. Such scattering links enable communications to take place in rough terrain where the line-of-sight is blocked. NLOS SB-UV links are of great interest in many potential civilian and military operations especially for applications with low data rate and short coverage range requirements. This thesis proposes a fundamental approach to design NLOS SB-UV communication systems that takes into consideration the unique characteristic of this type of link.

An analytical geometrical scattering propagation model is developed that generalizes the classical model under the assumption of first-order scattering. The generalized model considers the impact of finite receiver aperture size to overcome the inaccuracies when significant scattering takes place near the receiver. In addition, it handles the noncoplanar geometry case where it relaxes the restriction that transmitter and receiver axes have to lie in a common plane. The accuracy of this analytical model is verified by a stochastic Monte Carlo method that shows a close agreement. Next, a rigorous communication channel model is defined that combines both the temporal dispersion due to the multipath propagation and the stochastic impairments due to the random arrival of the scattered photons. Unlike previous work, system performance is investigated by numerically computing the achievable channel information rates for binary-inputs. Practical error control coding is applied, and a message passing decoding technique is outlined in order to approach the fundamental channel rates. Finally, to improve the system performance in terms of the information rates, an array of multiple receiver elements is considered to make use of the information in photon spatial arrival-locations on the detecting surface. A spatial diversity receiver for a multipath compensation and a noise suppression is designed. Information rates under equally likely are computed where a significant gain in rate over a single-element receiver is achieved especially in the case of a narrow transmitter beam.