Exact and Asymptotic Analysis of Partial Relay Selection for Cognitive RF-FSO Systems With Non-Zero Boresight Pointing Errors

Abstract

In this paper, we investigate the performance of asymmetric radio frequency (RF) and free space optical (FSO) dual-hop cooperative relay network along with a direct RF link between source and destination. The FSO link experiences double generalized Gamma turbulence in the presence of the generalized non-zero boresight pointing errors, and RF links experience non-identically distributed Nakagami-m fading. Moreover, considering both cognitive radio and non-cognitive scenarios, a partial relay selection (PRS) strategy has been employed. Furthermore, both relay selection and underlay power restriction are governed with the outdated channel state information (CSI). We also assume both heterodyne and intensity modulation/direct detection methods in the FSO receiver. Under the assumption of amplify-and-forward relaying and PRS, we derive closed-form expressions for outage probability (OP) of both scenarios, while bit-error probability and ergodic capacity of the non-cognitive scenario are also obtained. The asymptotic expressions of OP and diversity order of this network are derived for both perfect CSI and outdated CSI cases. It is demonstrated that the diversity order is a function of the fading severity of the RF links, turbulence parameters of the FSO link, and pointing error, regardless of interference channel parameter of the primary user. INDEX TERMS Cognitive radio network, double generalized Gamma, free space optical communications, non-zero boresight pointing errors, outdated channel state information, partial relay selection. The associate editor coordinating the review of this manuscript and approving it for publication was Wei Wang. the log-normal, log-normal Rician, I-K distribution, Malaga, Gamma-Gamma (G 2) and Double-Weibull [2]. The G 2 is widespread distribution for modeling FSO turbulence channel in the literature, however, G 2 distribution is not completely match with experimental data particularly in tails [2]. Recently, a novel statistical model called Double Generalized Gamma (DGG) distribution has been introduced by [2], where irradiance fluctuations are given by production of small-scale and large-scale fluctuations, both of which are function of generalized Gamma distribution. This model precisely describes the signal propagation under all conditions, (i.e., from weak to strong turbulence conditions) added to the fact that it generalizes other distributions. B. NON-ZERO BORESIGHT MISALIGNMENT Additionally, the building sway phenomenon leads to the vibration of transmitter beam that causes a misalignment between transmitter and receiver known as pointing error.

Secrecy Performance Analysis of Mixed Hyper-Gamma and Gamma-Gamma Cooperative Relaying System

“…The authors also provided asymptotic analysis of OP, BER, and EC. An underlay cognitive RF-FSO system with multiple relays adopting PRS strategy was designed by the authors in [32]. In [33], a multiple-input single-output (MISO) RF-FSO underlay cognitive system was shown to reduce the OP based on a proposed power allocation model.…”

SIC-Coding Schemes for Underlay Two-Way Relaying Cognitive Networks

“…Suppose that P X,max ≫ I (e.g., the X nodes are near the PR node); hence, we can approximate P X by P X ≈ uI/g XPR . It is worth noting that this assumption is used in many published literatures, i.e., [12,26,[30][31][32][33][34][35][36].…”

“…Substituting (16) with k = 1 and l = 2 into the probability Pr fγ UTW-2TS-SC S 1 →x 2 < γ th g in (35) and performing similarly as (27), we have a result as Pr γ UTW-2TS-SC…”

Developing Cost-Effective and High-Speed 40 Gbps FSO Systems Incorporating Wavelength and Spatial Diversity Techniques

“…Often labeled as wireless optical fibers, optical wireless communication has huge potential to serve the ever-increasing demand for high-speed data services. Over the last few decades, the per capita demand for data has increased manifolds, and this pattern only seems to become more and more aggressive in the near future [1][2][3]. The recent surge in popularity of free-space optical (FSO) systems as a commercial alternative to radio-frequency (RF) systems is attributed to a wide range of advantages such as 1) massive bandwidth of the order of THz, 2) adaptability with present-day radio systems as RF/FSO systems [4,5], 3) license-free spectrum, 4) negligible interference from the adjacent carriers, and 5) plug-play character which makes the FSO systems very convenient to install and relocate [6,7].…”