Random Relay Jamming in Cooperative Free Space Optical Systems

Relay-assisted free space optical (FSO) systems offer several advantages such as cooperative diversity, mitigating turbulence-induced fading, and broad coverage area. Despite these manifold advantages, they can still be affected by unfavorable activities of jammer. Therefore, it is of high importance and need to investigate random jamming specially for security-constrained cooperative FSO communication protocol. This article develops a new system model of relay-assisted FSO system and studies a novel mathematical framework to analyze the performance of decode-and-forward protocol-based cooperative FSO system in presence of random relay jamming effects. In presence of jammer, the probability density functions (pdfs) of different additive noises, i.e., a mixture of negative exponential and Gaussian random variables (RVs) and mixture of negative exponential RVs are derived. A closed-form expression of the average bit error rate (ABER) is analytically evaluated by using the derived pdfs in the presence of random relay jamming effects. In presence of jammer, an approximate and simple expression of a threshold-based detector is obtained. By studying the ABER performance comparison, it is shown that the proposed approximate detector works satisfactorily compared to the maximum-likelihood detector in presence of random relay jammers. In addition to that, ABER performance of a general relay FSO system with an arbitrary number of relays is also obtained.