Jawad A. Salehi

Prof. Dr. Jawad A. Salehi

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Academic Career Length

25Years (2002-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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21 December 2016 in IEEE Transactions on Communications
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Journal Article
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MJMohammad Vahid Jamali
Mohammad Vahid Jamali
JSJawad A. Salehi
Jawad A. Salehi
FAFarhad Akhoundi
Farhad Akhoundi
In this paper, we analytically study the performance of multiple-input multiple-output underwater wireless optical communication (UWOC) systems with ON-OFF keying modulation. To mitigate turbulence-induced fading, which is amongst the major degrading effects of underwater channels on the propagating optical signal, we use spatial diversity over UWOC links. Furthermore, the effects of absorption and scattering are considered in our analysis. We analytically obtain the exact and an upper bound bit error rate (BER) expressions for both optimal and equal gain combining. In order to more effectively calculate the system BER, we apply Gauss-Hermite quadrature formula as well as approximation to the sum of lognormal random variables. We also apply the photon-counting method to evaluate the system BER in the presence of shot noise. Our numerical results indicate an excellent match between the exact and upper bound BER curves. Also, a good match between the analytical results and numerical simulations confirms the accuracy of our derived expressions. Moreover, our results show that spatial diversity can considerably improve the system performance, especially for channels with higher turbulence, e.g., a 3×1 multiple-input single-output transmission in a 25 m coastal water link with a log-amplitude variance of 0.16 can introduce 8 dB performance improvement at the BER of 10 -9 .
31 May 2018 in IEEE Transactions on Communications
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Journal Article
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MJMohammad Vahid Jamali
Mohammad Vahid Jamali
AMAli Mirani
Ali Mirani
APAlireza Parsay
Alireza Parsay
BABahman Abolhassani
Bahman Abolhassani
PNPooya Nabavi
Pooya Nabavi
JSJawad A. Salehi
Jawad A. Salehi
Optical signal propagation through underwater channels is affected by three main degrading phenomena, namely, absorption, scattering, and fading. In this paper, we experimentally study the statistical distribution of intensity fluctuations in underwater wireless optical channels with random temperature and salinity variations, as well as the presence of air bubbles. In particular, we define different scenarios to produce random fluctuations on the water refractive index across the propagation path and, then, examine the accuracy of various statistical distributions in terms of their goodness of fit to the experimental data. We also obtain the channel coherence time to address the average period of fading temporal variations. The scenarios under consideration cover a wide range of scintillation index from weak to strong turbulence. Moreover, the effects of beam-expander-and-collimator (BEC) at the transmitter side and aperture averaging lens (AAL) at the receiver side are experimentally investigated. We show that the use of a transmitter BEC and/or a receiver AAL suits single-lobe distributions, such that the generalized Gamma and exponentiated Weibull distributions can excellently match the histograms of the acquired data. Our experimental results further reveal that the channel coherence time is on the order of 10 −3 s and larger which implies to the slow fading turbulent channels.
23 January 2017 in IEEE Photonics Technology Letters
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Journal Article
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MJMohammad Vahid Jamali
Mohammad Vahid Jamali
ACAta Chizari
Ata Chizari
JSJawad A. Salehi
Jawad A. Salehi
In this letter, we analytically evaluate the end-to-end bit error rate (BER) of point-to-point multi-hop underwater wireless optical communication (UWOC) systems with respect to all degrading effects of the UWOC channel, namely absorption, scattering, and turbulence-induced fading. To do so, we first derive the BER expression of a single-hop UWOC link as the building block for end-to-end BER evaluation. We also apply Gauss-Hermite quadrature formula to obtain the closed-form solution for the system BER in the case of lognormal underwater fading channel. Numerical results demonstrate that multi-hop transmission, by alleviating channel impairments, can significantly improve the system performance and extend the viable end-to-end communication distance.
20 July 2016 in Optics Letters
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Journal Article
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ACAta Chizari
Ata Chizari
SASajjad Abdollahramezani
Sajjad Abdollahramezani
MJMohammad Vahid Jamali
Mohammad Vahid Jamali
JSJawad A. Salehi
Jawad A. Salehi
In this Letter, we realize the concept of analog computing using an engineered gradient dielectric meta-reflect-array. The proposed configuration consists of individual subwavelength silicon nanobricks, in combination with a fused silica spacer and silver ground plane, realizing a reflection beam with full phase coverage of 2π degrees, as well as an amplitude range of 0 to 1. Spectrally overlapping electric and magnetic dipole resonances, such high-index dielectric metasurfaces can locally and independently manipulate the amplitude and phase of the incident electromagnetic wave. This practically feasible structure overcomes substantial limitations imposed by plasmonic metasurfaces such as absorption losses and low polarization conversion efficiency in the visible range. Using such CMOS-compatible and easily integrable platforms promises highly efficient ultrathin planar wave-based computing systems that circumvent the drawbacks of conventional bulky lens-based signal processors. Based on these key properties and the general concept of spatial Fourier transformation, we design and realize broadband mathematical operators such as the differentiator and integrator in the telecommunication wavelengths.
17 March 2017 in Optics Letters
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SASajjad Abdollahramezani
Sajjad Abdollahramezani
ACAta Chizari
Ata Chizari
ADAli Eshaghian Dorche
Ali Eshaghian Dorche
MJMohammad Vahid Jamali
Mohammad Vahid Jamali
JSJawad A. Salehi
Jawad A. Salehi
Leveraging subwavelength resonant nanostructures, plasmonic metasurfaces have recently attracted much attention as a breakthrough concept for engineering optical waves both spatially and spectrally. However, inherent ohmic losses concomitant with low coupling efficiencies pose fundamental impediments over their practical applications. Not only can all-dielectric metasurfaces tackle such substantial drawbacks, but also their CMOS-compatible configurations support both Mie resonances that are invariant to the incident angle. Here, we report on a transmittive metasurface comprising arrayed silicon nanodisks embedded in a homogeneous dielectric medium to manipulate phase and amplitude of incident light locally and almost independently. By taking advantage of the interplay between the electric/magnetic resonances and employing general concepts of spatial Fourier transformation, a highly efficient metadevice is proposed to perform mathematical operations including solution of ordinary differential and integro-differential equations with constant coefficients. Our findings further substantiate dielectric metasurfaces as promising candidates for miniaturized, two-dimensional, and planar optical analog computing systems that are much thinner than their conventional lens-based counterparts.
28 July 2016 in IEEE Access
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Journal Article
Open access
FAFarhad Akhoundi
Farhad Akhoundi
MJMohammad Vahid Jamali
Mohammad Vahid Jamali
NHNavid Bani Hassan
Navid Bani Hassan
HBHamzeh Beyranvand
Hamzeh Beyranvand
AMAmir Minoofar
Amir Minoofar
JSJawad A. Salehi
Jawad A. Salehi
Underwater wireless optical communications are an emerging solution to the expanding demand for broadband links in oceans and seas. In this paper, a cellular underwater wireless optical code division multiple-access network is proposed to provide broadband links for commercial and military applications. The optical orthogonal codes are employed as signature codes of underwater mobile users. Fundamental key aspects of the network, such as its backhaul architecture, its potential applications, and its design challenges, are presented. In particular, a promising underwater localization and positioning scheme based on this cellular network is presented. Furthermore, the proposed network is used as infrastructure of centralized, decentralized and relay-assisted underwater sensor networks for high-speed real-time monitoring. Finally, probable design challenges, such as cell edge coverage, blockage avoidance, power control, and network capacity, are addressed.