Browsing by Author "Khalighi, M. A."

Now showing 1 - 5 of 5

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Bit-error-rate performance of an underwater wireless optical link under misalignment and turbulence effects
(IEEE, 2022) Ijeh, I. C.; Khalighi, M. A.; Elamassie, Mohammed; Hranilovic, S.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Underwater wireless optical communication (UWOC) links are highly susceptible to the degrading effects of oceanic turbulence and beam misalignment. In this paper, considering a silicon photo-multiplier at the receiver, we evaluate the link average bit-error rate (BER) performance, where an analytical expression is derived for its calculation, validated further by means of numerical simulations. We further investigate the impact of different system parameters on the link average BER.
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Capacity analysis of free space optical links for a partially coherent gaussian beam over a turbulent channel with pointing errors
(IEEE, 2013) Lee, I. E.; Ghassemlooy, Z.; Ng, W. P.; Khalighi, M. A.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we investigate the joint effects of beam width and the spatial coherence length in a partially coherent free-space optical (FSO) link from the information theory perspective, taking into account the combined influence of atmospheric turbulence and pointing errors. In addition, the effects of aperture-averaging on the average capacity of FSO links employing partially coherent beams (PCBs) are examined. Results show that PCBs are desirable in the weak-to-moderate turbulence regime, whereas highly coherent laser sources are preferred under strong fluctuations conditions; and there exist optimality in the optical beam parameters for different atmospheric channel conditions. Near-optimal average capacity is best achieved through the introduction of a larger receiver aperture and the joint beam width and spatial coherence length optimization technique, which effectively mitigates the effects of scintillation and pointing errors.
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Outage probability analysis of a vertical underwater wireless optical link subject to oceanic turbulence and pointing errors
(Optica Publishing Group, 2022-06-01) Ijeh, I. C.; Khalighi, M. A.; Elamassie, Mohammed; Hranilovic, S.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
The reliability of an underwater wireless optical communication (UWOC) network is seriously impacted by beam misalignment between transmitters (Txs) and receivers (Rxs). Also, the performance of UWOC systems can be affected by oceanic turbulence-induced fading due to fluctuations in the water refractive index as a result of variations in the pressure, water temperature, and salinity. In this work, we investigate the performance analysis of a vertical UWOC link subject to oceanic turbulence and pointing errors and further investigate the appropriate selection of link parameters to optimize link performance. This study is based on an accurate mathematical framework for link modeling while taking into account realistic Tx/Rx and channel parameters under different turbulence and beam misalignment conditions. We provide an analytical expression for calculating the link outage probability, whose accuracy is validated through numerical simulations. Last, the necessity of optimal Tx/Rx parameter selection to minimize the link outage is demonstrated. A laser beam is considered at the Tx, as well as an ultra-sensitive photodetector (silicon photo-multiplier) at the Rx to enable working at relatively long link ranges. The presented results give valuable insight into the practical aspects of deployment of UWOC networks.
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Practical implementation and performance study of a hard-switched hybrid FSO/RF link under controlled fog environment
(IEEE, 2014) Lee, I. E.; Ghassemlooy, Z.; Ng, W. P.; Gourdel, V.; Khalighi, M. A.; Zvanovec, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
The availability and performance of terrestrial free-space optical (FSO) communication systems are heavily deterred by the fluctuating conditions of the atmospheric channel, particularly in the presence of visibility-limiting fog effects. In this paper, we examine the viability of deploying hybrid FSO and radio frequency (RF) links through an experimental study, which takes advantage of a dedicated laboratory atmospheric chamber to emulate the fog scenarios encountered on outdoor environment. In particular, a root mean square power detector is developed and introduced in the system under study to monitor the signal quality of the primary FSO link. The quasi-linear output voltage characteristics of the power detector device is utilized as a useful decision metric to implement hard switching in a hybrid FSO/RF link based upon the changes in the visibility. Our measurement results reveal that the selection of a desirable threshold voltage is dependent upon the intended data rate and minimum achievable bit error rate, in order to enable effective switching between the FSO and RF links.
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Survey on free space optical communication: a communication theory perspective
(IEEE, 2014) Khalighi, M. A.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
Optical wireless communication (OWC) refers to transmission in unguided propagation media through the use of optical carriers, i.e., visible, infrared (IR), and ultraviolet (UV) bands. In this survey, we focus on outdoor terrestrial OWC links which operate in near IR band. These are widely referred to as free space optical (FSO) communication in the literature. FSO systems are used for high rate communication between two fixed points over distances up to several kilometers. In comparison to radio-frequency (RF) counterparts, FSO links have a very high optical bandwidth available, allowing much higher data rates. They are appealing for a wide range of applications such as metropolitan area network (MAN) extension, local area network (LAN)-to-LAN connectivity, fiber back-up, backhaul for wireless cellular networks, disaster recovery, high definition TV and medical image/video transmission, wireless video surveillance/monitoring, and quantum key distribution among others. Despite the major advantages of FSO technology and variety of its application areas, its widespread use has been hampered by its rather disappointing link reliability particularly in long ranges due to atmospheric turbulence-induced fading and sensitivity to weather conditions. In the last five years or so, there has been a surge of interest in FSO research to address these major technical challenges. Several innovative physical layer concepts, originally introduced in the context of RF systems, such as multiple-input multiple-output communication, cooperative diversity, and adaptive transmission have been recently explored for the design of next generation FSO systems. In this paper, we present an up-to-date survey on FSO communication systems. The first part describes FSO channel models and transmitter/receiver structures. In the second part, we provide details on information theoretical limits of FSO channels and algorithmic-level system design research activities to approach these limits. Specifi- topics include advances in modulation, channel coding, spatial/cooperative diversity techniques, adaptive transmission, and hybrid RF/FSO systems.