Browsing by Author "Safari, M."

Now showing 1 - 10 of 10

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All-optical amplify-and-forward relaying system for atmospheric channels
(IEEE, 2012-10) Aminikashani, Mohammadreza; Rad, M. M.; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Aminikashani, Mohammadreza
In this letter, we investigate the performance of a dual-hop free space optical link with an all-optical amplify-and-forward relay. We employ photon counting methodology and derive closed form expressions for the end-to-end signal-to-noise ratio and the outage probability. In our derivations, we consider either full or partial channel state information (CSI) at the relay and take into account practical limitations such as amplifier noise and filtering effects. Our results indicate significant performance improvements over direct transmission and furthermore demonstrate that semi-blind relaying (which depends only on statistical CSI) provides nearly identical performance to its full-CSI counterpart.
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Multi-hop quantum key distribution with passive relays over underwater turbulence channels
(The Optical Society, 2020-12-01) Raouf, Amir Hossein Fahim; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Raouf, Amir Hossein Fahim
Absorption, scattering, and turbulence experienced in underwater channels severely limit the range of quantum communication links. In this paper, as a potential solution to overcome range limitations, we investigate a multi-hop underwater quantum key distribution (QKD) where intermediate nodes between the source and destination nodes help the key distribution. We consider the deployment of passive relays that simply redirect the qubits to the next relay node or the receiver without any measurement. Based on the near-field analysis, we present the performance of a relay-assisted QKD scheme in terms of quantum bit error rate and secret key rate in different water types and turbulence conditions. We further investigate the effect of system parameters such as aperture size and detector field of view on the performance. Our results demonstrate under what conditions relay-assisted QKD can be beneficial and what end-to-end transmission distances can be supported with a multi-hop underwater QKD system.
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Multi-hop quantum key distribution with passive relays over underwater turbulence channels
(IEEE, 2020) Raouf, Amir Hossein Fahim; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Raouf, Amir Hossein Fahim
Absorption, scattering, and turbulence experienced in underwater channels severely limit the range of quantum communications. In this paper, to overcome range limitations, we investigate a multi-hop underwater quantum key distribution (QKD) where intermediate nodes help the key distribution between the source and destination nodes. We consider deployment of passive-relays which simply redirect the qubits to the next relay node or receiver without any measurement. Based on nearfield analysis, we present the performance of relay-assisted QKD scheme in clear ocean under different atmospheric conditions. We further investigate the effect of system parameters (aperture size and detector field-of-view) on the achievable distance.
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Multi-hop relaying over the atmospheric poisson channel
(IEEE, 2011) Safari, M.; Rad, M. M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we study the outage behavior of a decode-and-forward multi-hop free-space optical (FSO) system over a Poisson channel degraded by atmospheric turbulence. We assume that perfect channel side information (CSI) is available at the receiver side and consider both cases of perfect CSI and no CSI at the transmitter side. We solve the outage probability minimization problem subject to a peak power constraint as well as a short- or long-term average sum power constraint. As a result, optimal power control strategies are presented for different scenarios under consideration. A sub-optimal yet low-complexity solution is further proposed under the short-term power constraint. Our results demonstrate that multi-hop relaying yields significant performance improvements which are particularly important for long-range FSO links.
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Multi-hop relaying over the atmospheric poisson channel: outage analysis and optimization
(IEEE, 2012-03) Safari, M.; Rad, M. M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we study the outage behavior of a decode-and-forward multi-hop free-space optical (FSO) system over a Poisson channel degraded by atmospheric turbulence. We assume that perfect channel side information (CSI) is available at the receiver side and consider both cases of perfect CSI and no CSI at the transmitter side. We solve the outage probability minimization problem subject to a peak power constraint as well as a short- or long-term average sum power constraint. As a result, optimal power control strategies are presented for different scenarios under consideration. A sub-optimal yet low-complexity solution is further proposed under the short-term power constraint. Our results demonstrate that multi-hop relaying yields significant performance improvements which are particularly important for long-range FSO links.
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Optimal relay placement and diversity analysis of relay-assisted free-space optical communication systems
(IEEE, 2013-01) Kashani, M. A.; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
Relay-assisted free-space optical (FSO) transmission exploits the fact that atmospheric turbulence fading variance is distance dependent and yields significant performance gains by taking advantage of the resulting shorter hops. In this paper, we investigate how to determine optimal relay locations in serial and parallel FSO relaying so as to minimize the outage probability and quantify performance improvements obtained through optimal relay placement. We further present a diversity gain analysis for serial and parallel FSO relaying schemes and quantify their diversity advantages in terms of the number of relays and channel parameters.
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Optimal relay placement in cooperative free-space optical communication systems
(IEEE, 2012) Aminikashani, Mohammadreza; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Aminikashani, Mohammadreza
Relay-assisted free-space optical (FSO) transmission exploits the fact that atmospheric turbulence fading variance is distance dependent and yields significant performance gains by taking advantage of the resulting shorter hops. In this paper, we first investigate how to determine optimal relay locations in serial and parallel FSO relaying as to minimize the outage probability and then quantify performance improvements obtained through optimal relay placement.
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Performance analysis of decoy state quantum key distribution over underwater turbulence channels
(Optica Publishing Group, 2022-06-01) Raouf, Amir Hossein Fahim; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Raouf, Amir Hossein Fahim
Decoy state quantum key distribution protocols have been studied for atmospheric, fiber, and satellite links; however, those results are not directly applicable to underwater environments with different channel characteristics. In this paper, we investigate the fundamental performance limits of decoy state BB84 protocol over turbulent underwater channels and provide a comprehensive performance characterization.We adopt a near field analysis to determine the average power transfer over a turbulent underwater path and use this to obtain a lower bound on the secret key rate.We quantify the performance of decoy BB84 protocol in different water types assuming various turbulence conditions.We further investigate the effect of system parameters such as transmit aperture size and detector field of view on the performance.
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Performance analysis of quantum key distribution in underwater turbulence channels
(The Optical Society, 2020) Raouf, Amir Hossein Fahim; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Raouf, Amir Hossein Fahim
The current literature on quantum key distribution is limited mainly to transmissions over fiber optic, atmospheric, or satellite links and is not directly applicable to underwater environments with different channel characteristics. In this paper, we analyze the quantum bit error rate (QBER) and secret key rate (SKR) performance of the well-known BB84 protocol in underwater channels. As a path loss model, we consider a modified version of the Beer-Lambert formula, which takes into account the effect of scattering. We derive a closed-form expression for the wave structure function to determine the average power transfer over a turbulent underwater path and use this to obtain an upper bound on QBER as well as a lower bound on SKR. Based on the derived bounds, we present the performance of the BB84 protocol in different water types including dear, coastal, and turbid and under different atmospheric conditions such as clear, hazy, and overcast. We further investigate the effect of system parameters such as aperture size and detector field of view on QBER and SKR performance metrics.
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Vehicular visible light communications with SPAD receivers
(IEEE, 2019) Karbalayghareh, Mehdi; Miramirkhani, Farshad; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Karbalayghareh, Mehdi; Miramirkhani, Farshad
Light emitting diodes (LEDs) are increasingly used in automotive exterior lighting. The expected wide availability of LED-based front and back lights makes visible light communication (VLC) a natural vehicular connectivity solution. A major challenge in vehicular VLC systems is their relatively poor performance in adverse weather conditions such as severe fog. In this paper, we propose the use of single-photon avalanche diode (SPAD) for vehicular VLC systems. With their higher sensitivity in comparison to conventional photodetectors, SPADs can be efficiently used to detect weak signals. Under the assumption of on-off keying (OOK), we present the error rate performance of vehicular VLC systems. Since the SPAD output is modelled by Poisson statistics, the bit error rate (BER) takes the form of a semi-infinite summation. Based on Anscombe transformation, we approximate Poisson noise as Gaussian and derive a closed-form BER expression. Using this expression, we obtain a closedform expression for maximum achievable link distance to ensure a targeted BER. We present an extensive numerical study to validate our derivations and demonstrate the performance of vehicular VLC system under different weather conditions.