Spectrum sensing for free space optical communications in strong atmospheric turbulence channel

Abstract

One of the primary challenges in multi-user optical wireless communications (OWC) is to periodically sense the optical frequency spectrum at the receiver to detect whether the channel is occupied by other transceiver pairs in order to avoid interference. Spectrum sensing enables the user to continuously sense the channel prior to its access to the channel. In this paper, we propose the spectrum sensing of an unknown optical signal over strong atmospheric turbulence channel. The turbulent atmospheric channel causes fluctuations in the received signal intensity, resulting in power loss at the receiver. To mitigate this adverse effect, we present an energy detection based optical spectrum sensing scheme with the spatial diversity reception in the form of a square-law selection diversity. The intensity fluctuations are modeled by a negative exponential distribution. The analytical closed-form expressions for the probability of detection and the probability of false alarm are derived. Based on the derived expressions, we obtain the performance analysis as a function of the system parameters. It is also found that sensing capability is boosted with the square-law diversity scheme.