Impact of relay placement in three-hop buffer-aided FSO systems: An approximate performance analysis approach

Abstract

In this paper, we consider the problem of three-hop Free Space Optical (FSO) communications in the context of decode-and-forward (DF) buffer-aided (BA) relaying where the two relays are equipped with buffers of finite size. We adopt a Markov chain analysis for evaluating the outage probability (OP) and average packet delay (APD) of the considered serial relaying system that operates naturally in the full-duplex (FD) mode. Given the large number of states involved in the analysis and the large number of associated transitions resulting from the FD operation, we establish an approximate performance analysis approach following from the intractability of an exact analysis. The suggested framework improves over the existing asymptotic studies and provides closed-form approximate OP and APD expressions that are extremely close to the exact expressions in the average-to-high signal-to-noise ratio (SNR) range. Simulations over gamma–gamma atmospheric turbulence channels highlight on the accuracy of the adopted approximate approach irrespective of the underlying network setup. This accuracy is particularly appealing for predicting the APD performance since the gap between the exact APD and the existing asymptotic APD bounds can be huge for FSO networks with comparable hop distances.