Performance of a free-space-optical relay-assisted hybrid RF/FSO system in generalized M-distributed channels

Abstract

This paper investigates the average symbol error rate (ASER) performance of a dual-hop hybrid relaying system relying on both radio frequency (RF) and free-space optical (FSO) links. Specifically, an RF link is used for supporting mobile communication, whereas an FSO link is adopted as the backhaul of the cellular infrastructure. Considering nonline-of-sight RF transmissions and a generalized atmospheric turbulence (AT) channel, the associated statistical features constituted of both exact and asymptotic moment-generating functions are derived in the closed form. They are then used for calculating the ASER of M -ary phase-shift keying (PSK), differentially encoded noncoherent PSK (DPSK), and noncoherent frequency-shift keying. A range of additional asymptotic expressions is also derived for all the modulation schemes under high signal-to-noise ratios (SNR). It is observed from the asymptotic analysis that the ASERs of all the modulation schemes are dominated by the average SNR of the RF link in the hybrid relaying system using a fixed relay gain, whereas in the relaying system using a dynamic channel-dependent relay gain, the ASERs of all the modulation schemes depend both on the average SNR and the AT condition of the FSO path. We also find that the fixed-gain relaying strategy achieves twice the diversity order of the channel-dependent relaying strategy, albeit at the cost of requiring a high power amplifier dynamic range at the relay node. Furthermore, by comparing the asymptotic ASERs, we calculate the SNR differences between the different modulation schemes in both the fixed-gain and channel-dependent relaying systems. Finally, simulation results are presented for confirming the accuracy of our expressions and observations

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ORCID for Lajos Hanzo: orcid.org/0000-0002-2636-5214

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