Browsing by Author "Kazemi, Hossein"

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Multi-hop hybrid FSO/RF communication systems
(2014-08) Kazemi, Hossein; Uysal, Murat; Demiroğlu, Cenk; İlhan, H.; Department of Electrical and Electronics Engineering; Kazemi, Hossein
The reliability of free-space optical (FSO) links is severely restricted by weather-dependent atmospheric phenomena including absorption, scattering and turbulence. An efficient solution is to build hybrid links where a radio frequency (RF) link is incorporated in parallel to the FSO link. With respect to weather conditions, FSO links are mostly degraded by fog and turbulence-induced fading (scintillation) whereas RF links particularly suffer from rain scatter. Therefore, hybrid FSO/RF systems can offer significant enhancements in the system reliability for all weather conditions by means of the complementary nature of the underlying links. In this thesis, we investigate the outage performance of point-to-point hybrid FSO/RF systems as well as multi-hop hybrid FSO/RF systems with soft-switching. Starting from the point-to-point system, we model the link selection required for soft-switching between the FSO and RF channels in different weather conditions by a finite-state Markov chain (FSMC) process. Then, based on the proposed model, we derive a closed-form outage probability expression in terms of various system and weather-dependent parameters. Thereupon, we extend the scope of our analysis to multi-hop hybrid FSO/RF systems. We present the outage probability and diversity gain analysis for multi-hop hybrid FSO/RF systems. Our results clearly demonstrate the robust performance of the soft-switching hybrid FSO/RF systems deployed either as the point-to-point or multi-hop configuration in dealing with different weather conditions.
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Outage analysis of hybrid FSO/RF systems based on finite-state Markov Chain modeling
(IEEE, 2014) Kazemi, Hossein; Uysal, Murat; Touati, F.; Electrical & Electronics Engineering; UYSAL, Murat; Kazemi, Hossein
In this paper, we analyze the outage probability of a hybrid free-space optical/radio-frequency (FSO/RF) communication system with soft-switching. In soft-switching approach, either one of the links or both links can be active relying on their availabilities. We first model the link selection required for soft-switching between the FSO and RF channels in different weather conditions by a finite-state Markov chain (FSMC) process. Then, based on the proposed model, we derive a closed-form outage probability expression in terms of various system and weather condition parameters. Numerical results are provided to present the outage performance under various weather conditions.
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Outage performance of MIMO free-space optical systems in gamma-gamma fading channels
(IEEE, 2013) Kazemi, Hossein; Mostaani, Zohreh; Uysal, Murat; Ghassemlooy, Z.; Electrical & Electronics Engineering; UYSAL, Murat; Kazemi, Hossein; Mostaani, Zohreh
In this paper, we consider a MIMO Free-Space Optical (FSO) communication system over gamma-gamma turbulence channels and derive a closed-form analytical expression for the outage probability taking into account the effects of both the inner scale size of optical channel and the aperture averaging. Our results demonstrate that by increasing the number of transmit and/or receive apertures, the degrading effect of the inner scale size is effectively reduced by extracting the spatial diversity gain of the MIMO scheme. We further provide Monte Carlo simulation results to confirm the validity of the derived expression.
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Performance analysis of MIMO free-space optical communication systems with selection combining
(IEEE, 2013) Kazemi, Hossein; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Kazemi, Hossein
In this paper, we investigate the outage performance of a multi-input multi-output (MIMO) free-space optical (FSO) communication system with selection combining (SC). Under the assumption of log-normal distributed atmospheric turbulence, we first derive a closed-form outage probability expression, and then demonstrate the achievable diversity order. We further provide Monte Carlo simulation results to confirm the validity of the derived outage probability expression and present the corresponding diversity gains.