Impact of Atmospheric Turbulence, Pointing Error, and Traffic Pattern on the Performance of Cognitive Hybrid FSO/RF System

Abstract

Atmospheric turbulence conditions and mis-alignment in the free space optical (FSO) link are prime factors which necessitate the requirement of a back up radio frequency (RF) link to improve the link availability of the FSO systems. However, the utilization of this back-up RF link is limited. The RF channel which is meant chiefly as a back-up resource in case of FSO link failure, can be utilized more efficiently. In this work, it is attempted to improve the utilization of this RF resource. A second FSO link is converted to a Cognitive Hybrid FSO/RF link by accessing the already existing RF in the cognitive interweave mode. RF utilization factor is a measure of the efficiency with which the two FSO links utilize the same RF resource. The system performance is evaluated on the basis of RF utilization, outage probability and bit error rate (BER) under atmospheric turbulence and mis-alignment. Further, the impact of data traffic characteristics on system performance has been investigated. Closed form expressions for RF utilization, outage probability and BER have been derived for various traffic conditions. The analytical results have been verified through simulations. Results indicate improved system performance and better overall utilization of the RF resource.