Electrical & Electronics Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10679/44

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Now showing 1 - 20 of 34

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Aerosol attenuation model for high altitude UAV-based FSO links
(IEEE, 2022) Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Free space optical (FSO) communication is well positioned to address connectivity needs in ground-UAV, inter-UAV and UAV-ground links. An accurate performance analysis of airborne FSO links requires the use of proper path loss models. While earlier studies have successfully modeled attenuation arising from rain, drizzle, fog, and snow, aerosols have received less attention. Aerosols are tiny particles suspended in the atmosphere. They can be found drifting in Earth's atmosphere from the stratosphere to the troposphere to the Earth's surface. In this paper, we conduct extensive simulations in MODTRAN to determine the extinction coefficient values for aerosol over the wavelength from 350 nm to 1550 nm including typical wavelengths (e.g., 690 nm, 780nm, 850nm, and 1550 nm) used in commercial FSO systems. Non-linear curve fitting is then used to obtain new closed-form expressions for extinction coefficients.
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Analysis and optimization of the network throughput in IEEE 802.15.13 based visible light communication networks
(IEEE, 2021) Bülbül, Yusuf; Elamassie, Mohammed; Baykas, T.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat; Bülbül, Yusuf
In line with the growing interest on visible light communication (VLC), IEEE has initiated standardization efforts on this emerging technology. In this work, we consider IEEE 802.15.13 Optical Wireless Personal Area Networks (OWPAN) standard draft. The underlying MAC protocol uses contention free and contention access periods. For a standard-compliant VLC network, we analyze the network load and propose an algorithm to improve the network throughput by proper selection of period lengths. Our suggested algorithm improves the network performance by at least 5% in the case of variable network traffic up to 15 active users.
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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.
Open Access
Capacity analysis of NOMA-enabled underwater VLC networks
(IEEE, 2021) Elamassie, Mohammed; Bariah, L.; Uysal, Murat; Muhaidat, S.; Sofotasios, P. C.; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Visible light communication (VLC) has recently emerged as an enabling technology for high capacity underwater wireless sensor networks. Non-orthogonal multiple access (NOMA) has been also proven capable of handling a massive number of sensor nodes while increasing the sum capacity. In this paper, we consider a VLC-based underwater sensor network where a clusterhead communicates with several underwater sensor nodes based on NOMA. We derive a closed-form expression for the NOMA system capacity over underwater turbulence channels modeled by lognormal distribution. NOMA sum capacity in the absence of underwater optical turbulence is also considered as a benchmark. Our results reveal that the overall capacity of NOMA-enabled Underwater VLC networks is significantly affected by the propagation distance in underwater environments. As a result, effective wireless transmission at high and moderate spectral efficiency levels can be practically achieved in underwater environments only in the context of local area networks. Moreover, we compare the achievable capacity of NOMA system with its counterpart, i.e., orthogonal frequency division multiple access (OFDMA). Our results reveal that NOMA system is not only characterized by achieving higher sum capacity than the sum capacity of its counterpart, OFDMA system. It is also shown that the distances between sensor nodes and the clusterhead for achieving the highest sum capacity in these two multiple access systems are different.
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Characterization of orbital angular momentum-multiplexed FSO channel in the presence of pointing errors
(IEEE, 2023) Elamassie, Mohammed; Tadayyoni, Hamed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat; Tadayyoni, Hamed
Free space optical communication (FSO) uses laser transmitters at near-infrared wavelengths for line-of-sight wireless communication. Through the use of advanced laser beams instead of the conventional Gaussian-shaped beam, orbital angular momentum (OAM) allows taking advantage of higher degrees of freedom in the FSO link design. OAM enables the simultaneous transmission of multiple data streams due to the orthogonality between beams of different spatial modes. However, in practice, atmospheric turbulence and pointing errors may destroy the orthogonality. Pointing errors may result in crosstalk between modes and power disparities as a result of shifting the received beam. In this paper, we consider Laguerre-Gaussian beams and investigate the effect of random pointing errors on crosstalk coefficients.
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Drizzle attenuation model for visible and infrared wavelengths
(IEEE, 2022) Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
In an outdoor environment, the transmitted optical signal is affected by the atmospheric particles that may scatter or absorb light such as drizzle, rain, snow, fog, and aerosols. Various earlier studies have attempted to provide models that accurately describe the attenuation caused by the propagation of light waves through different atmospheric conditions. While the rain attenuation models have received significant research efforts, the modeling of drizzle attenuation was not yet fully studied. In this paper, we conduct extensive simulations in MODTRAN to model drizzle attenuation over the wavelength from 350 nm to 1550 nm. Based on data fitting to simulation results, we further propose a closed-form expression for the drizzle extinction coefficient.
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Effect of sea waves on vertical underwater visible light communication links
(IEEE, 2023-04) Elamassie, Mohammed; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Underwater visible light communication (VLC) has been proposed to deal with emerging high bandwidth underwater applications. Initial research works on underwater VLC are based on the assumption that both transmitter and receiver are submerged, creating a horizontal link. In most of the vertical communication links, one of the transceiver nodes takes the form of a buoy and requires taking into the effect of the sea surface, which is inherently unsteady due to wind and waves. In this article, we consider a vertical underwater VLC link where the transmitter is in the form of a buoy at the sea surface, and the receiver is a submerged node at a certain depth. We assume sinusoidal waves and consider the fact that the buoy will fluctuate and oscillate, during drifting up and down, around its vertical axis. This effectively results in a 3-D displacement at the suspended transmitter. Building upon these assumptions of practical relevance, we propose an aggregate channel model, which includes a random path loss due to periodic changes of the transmission distance and a fading term induced by pointing errors with periodic changes of relative movement. Based on the proposed statistical model, we derive closed-form expressions for the exact and asymptotic bit error ratio and investigate the achievable diversity orders. We further present numerical results to confirm the analytical findings.
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Experimental characterization of multi-hop vehicular VLC systems
(IEEE, 2021) Mohamed, Bassam Aly Abdelrahman; Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; Mohamed, Bassam Aly Abdelrahman
In vehicular visible light communication (VLC), the reliable communication distance may be relatively short due to its dependence on many factors including the weather condition. This necessitates the use of relay-assisted systems to extend the transmission range. In this paper, we investigate experimentally the performance of vehicular multi-hop VLC systems in outdoor environments. Particularly, we first examine the effect of ambient noise on signal-to-noise ratio (SNR) during a whole day. Then, we conduct two multi-hop experiments, i.e., one at daytime and one at nighttime. We measure the bit error rate (BER) for each individual hop and then obtain the overall performance of the multi-hop system. We further compare experimental BER with theoretical BER to confirm our results.
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Experimental investigation of lens combinations on the performance of vehicular VLC
(IEEE, 2020) Mohamed, Bassam Aly Abdelrahman; Elamassie, Mohammed; Eldeeb, Hossıen Badr; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; ELDEEB, Hossien Badr Hossien; UYSAL, Murat; Mohamed, Bassam Aly Abdelrahman
With the increasing adoption of LEDs in outdoor light sources such as traffic lights, street lights and vehicle headlamps, visible light communication (VLC) has the promise to become a major enabler for vehicle-to-vehicle and vehicle-to-infrastructure communications. In this paper, we experimentally investigate the effect of using different lens combinations on vehicular VLC systems in outdoor environments. First, we measure the effective channel coefficient which includes the effect of both front-ends and propagation channel. Then, based on the estimated channel coefficients, we characterize the vehicular system performance in terms of signal-to-noise ratio and quantify improvements from utilizing different lens combinations.
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An experimental study of underwater visible light communication
(IEEE, 2022) Yıldız, Samet; Baǧlıca, İbrahim; Kebapçı, B.; Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; ELAMASSIE, Mohammed; Yıldız, Samet; Baǧlıca, İbrahim
Visible light communication (VLC) has emerged as a powerful high-data-rate alternative to conventional underwater acoustic technology for short and medium link distances. In this paper, we develop an experimental underwater VLC platform and present some initial performance results. Our set-up uses prerecorded voltage levels fed in the arbitrary waveform generator (AWG) at the transmitter side while an oscilloscope is used to measure the received electrical signal after photodetection. To speed up debugging and troubleshooting, both transmitter and receiver sides are connected to a controller PC. The test instruments are controlled via Standard Commands for Programmable Instruments (SCPI) commands executed by this controller computer with a Python code. Using this set-up, we demonstrate the successful transmission of 8-PAM symbols over an 8-meter-long underwater tank.
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Feedback-free adaptive modulation selection algorithm for FSO systems
(IEEE, 2021-09) Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; ELAMASSIE, Mohammed
Free space optical (FSO) communication systems experience turbulence-induced fading. As a possible solution to mitigate the effects of fading, adaptive transmission that allows the adjustment of transmission parameters such as transmit power and modulation size can be used. Most of the existing works on adaptive FSO systems assume the presence of full channel state information (CSI) at the transmitter side. In practice, incomplete/outdated CSI may prevent the complete extraction of the theoretical gain expected from adaptive systems. In this letter, to avoid the difficulties associated with feedback, we propose a feedback-free adaptive modulation selection algorithm for FSO systems. We formulate the design as an optimization problem where average throughput is maximized by selecting the largest modulation order under the constraint that the required transmit power for a targeted bit error rate (BER) value does not exceed the maximum transmit power. We further present numerical results to confirm the superiority of the proposed adaptive algorithm.
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Finite-SNR diversity gain analysis of FSO systems over gamma-gamma fading channels with pointing errors
(IEEE, 2021-06) Elamassie, Mohammed; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Free space optical (FSO) communication systems are subject to turbulence-induced fading as a result of fluctuations in the refractive index. Gamma-Gamma (GG) distribution is commonly used in the literature to characterize moderate-to-strong turbulence conditions. The performance of FSO systems is further degraded by pointing error-induced fading as a result of building sways. While the asymptotic analysis presented in earlier works is important to understand the maximum diversity gains of FSO systems attainable over fading channels, such gains might not be available in practical range of signal-to-noise ratio (SNR). Furthermore, different systems with the same asymptotic slope may have different slopes in the range of finite SNR values. In this paper, we consider a multiple-input multiple-output (MIMO) FSO system with intensity modulation and direct detection (IM/DD). We derive approximate expression for the finite-SNR diversity order over GG turbulence channels in the presence of pointing errors. We also investigate convergence speed to full diversity. We provide numerical results to demonstrate the accuracy of our derivations and corroborate on our analytical findings.
Open Access
Free space optical communication: An enabling backhaul technology for 6G non-terrestrial networks
(MDPI, 2023-11) Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
The deployment of non-terrestrial networks (NTNs) is envisioned to achieve global coverage for 6G and beyond. In addition to space nodes, aerial NTN nodes such as high-altitude platform stations (HAPSs) and rotary-wing unmanned aerial vehicles (UAVs) could be deployed, based on the intended coverage and operational altitude requirements. NTN nodes have the potential to support both wireless access and backhauling. While the onboard base station provides wireless access for the end users, the backhauling link connects the airborne/space-borne base station to the core network. With its high data transmission capability comparable to fiber optics and its ability to operate in the interference-free optical spectrum, free space optical (FSO) communication is ideally suited to backhauling requirements in NTNs. In this paper, we present a comprehensive tutorial on airborne FSO backhauling. We first delve into the fundamentals of FSO signal transmission and discuss aspects such as geometrical loss, atmospheric attenuation, turbulence-induced fading, and pointing errors, all of which are critical for determining received signal levels and related link budget calculations. Then, we discuss the requirements of airborne backhaul system architectures, based on use cases. While single-layer backhaul systems are sufficient for providing coverage in rural areas, multi-layer designs are typically required to establish connectivity in urban areas, where line of sight (LoS) links are harder to maintain. We review physical layer design principles for FSO-based airborne links, discussing both intensity modulation/direct detection (IM/DD) and coherent modulation/coherent demodulation (CM/CD). Another critical design criteria for airborne backhauling is self-sustainability, which is further discussed in our paper. We conclude the paper by discussing current challenges and future research directions. In this context, we discuss reconfigurable intelligent surfaces (RIS) and spatial division multiplexing (SDM), for improved performance and an extended transmission range. We emphasize the importance of advanced handover techniques and scalability issues for practical implementation. We also highlight the growing role of artificial intelligence/machine learning (AI/ML) and their potential applications in the design and optimization of future FSO-based NTNs.
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FSO-based backhauling for airborne THz base stations
(IEEE, 2023) Elamassie, Mohammed; Edemen, Çağatay; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; EDEMEN, Çağatay; UYSAL, Murat
Airborne nodes in the form of high-altitude platform stations (HAPSs) or unmanned aerial vehicles (UAVs) can be used for backhauling and wireless access. In this paper, we investigate the cascaded free space optical (FSO)/terahertz (THz) link in which the FSO link serves as a backhaul between the gateway and the airborne node. In contrast, the THz link provides wireless communication between the airborne node and the user. We present channel models, including the atmospheric attenuation, geometrical loss, and fading effect. The FSO sub-system builds upon intensity-modulation direct-detection (IM/DD), while the THz sub-system employs coherent modulation and demodulation. Under the assumption of decode-and-forward relaying, we derive the end-to-end bit error rate (BER). We present numerical results to demonstrate the performance of cascaded airborne links.
Open Access
Hybrid RF/VLC systems: A comprehensive survey on network topologies, performance analyses, applications, and future directions
(IEEE, 2021) Abuella, H.; Elamassie, Mohammed; Uysal, Murat; Xu, Z.; Serpedin, E.; Qaraqe, K. A.; Ekin, S.; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Wireless communications refer to data transmissions in unguided propagation media through the use of wireless carriers such as radio frequency (RF) and visible light (VL) waves. The rising demand for high data rates, especially, in indoor scenarios, overloads conventional RF technologies. Therefore, technologies such as millimeter waves (mmWave) and cognitive radios have been adopted as possible solutions to overcome the spectrum scarcity and capacity limitations of the conventional RF systems. In parallel, visible light communication (VLC) has been proposed as an alternative solution, where a light source is used for both illumination and data transmission. In comparison to RF links, VLC links present a very high bandwidth that allows much higher data rates. VLC exhibits also immunity to interference from electromagnetic sources, has unlicensed channels, is a very low power consumption system, and has no health hazard. VLC is appealing for a wide range of applications including reliable communications with low latency such as vehicle safety communication. Despite the major advantages of VLC technology and a variety of its applications, its use has been hampered by its cons such as its dependence on a line of sight connectivity. Recently, hybrid RF/VLC systems were proposed to take advantage of the high capacity of VLC links and better connectivity of RF links. Thus, hybrid RF/VLC systems are envisioned as a key enabler to improve the user rates and mobility on one hand and to optimize the capacity, interference and power consumption of the overall network on the other hand. This paper seeks to provide a detailed survey of hybrid RF/VLC systems. This paper represents an overview of the current developments in the hybrid RF/VLC systems, their benefits and limitations for both newcomers and expert researchers.
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IEEE 802.11BB reference channel models for light communications
(IEEE, 2023-12-01) Miramirkhani, F.; Baykas, T.; Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Increasing industrial attention to visible light communications (VLC) technology led the IEEE 802.11 to establish the task group 802.11bb 'Light Communications' (LC) for the development of a VLC standard. As a part of the standard development process, the development of realistic channel models according to possible use cases is of critical importance for physical layer system design. This article presents the reference channel models for the mandatory usage models adopted by IEEE 802.11bb for the evaluation of system proposals. The use cases include industrial, medical, enterprise, and residential scenarios. Channel impulse responses and corresponding frequency responses are obtained for each use case using a ray tracing approach based on realistic specifications for transmitters and receivers, and optical characterization of the environment.
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Implementation of software-defined adaptive DCO-OFDM for vehicular visible light communication
(IEEE, 2023) Tettey, D. K.; Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
With its high data rates and electromagnetic interference-free operation capability, visible light communication (VLC), has emerged as a potential candidate for 6G and beyond networks. In this work, we present the preliminary experimental results of our rate-adaptive OFDM vehicular VLC implemented on software-defined platform. The physical layer of the system builds upon direct current biased optical OFDM (DCO-OFDM) and supports adaptive transmission with different modulation schemes/levels including BPSK, 4-QAM, 16-QAM and 64-QAM. For switching between different modulation schemes, a feedback link with on/off keying modulation is used to send channel state information (CSI) to the OFDM transmitter. Based on the CSI, the OFDM transmitter adapts its next transmission by selecting a modulation scheme/level which maximizes the spectral efficiency while satisfying a predefined error performance target of 3.8×10-3
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Infrastructure-to-vehicle visible light communications: Channel modelling and performance analysis
(IEEE, 2022-03) Eldeeb, Hossien Badr Hossien; Elamassie, Mohammed; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat; Eldeeb, Hossien Badr Hossien
Visible light communication (VLC) has emerged as a potential wireless connectivity solution for infrastructure-to-vehicle (I2V) communications. In this paper, we investigate the performance of I2V VLC systems with access points in the form of streetlights. Particularly, we consider a typical two-lane highway road where the light poles are located at both roadsides and uniformly separated from each other. Based on non-sequential ray tracing simulations, we first propose a closed-form path loss expression as a function of transceiver and infrastructure parameters. Then, we statistically analyze the path loss and derive a closed-form expression for its probability distribution function (PDF). Utilizing the derived PDF, we derive an approximate closed-form bit error rate (BER) expression. We confirm the accuracy of derived BER expression through comparison with Monte Carlo simulation results and demonstrate the effect of transceiver and infrastructure parameters such as receiver aperture, pole height, car height, lateral shift, and spacing between light poles on the BER performance.
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Non-orthogonal multiple access-based underwater VLC systems in the presence of turbulence
(IEEE, 2022-02) Bariah, L.; Elamassie, Mohammed; Muhaidat, S.; Sofotasios, P. C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; ELAMASSIE, Mohammed
The promising potential of underwater applications in visible light communication (VLC) systems has recently gained considerable research attention, as an efficient technology for enabling high data rate, massive connectivity, and ultra-low latency. Different from indoor VLC, underwater wireless communications experience harsh environmental challenges, yielding a degraded performance. Non-orthogonal multiple access (NOMA) was introduced to enhance spectral efficiency and connectivity of underwater VLC communications. In this paper, we develop a mathematical framework to evaluate the performance of NOMA-enabled underwater VLC systems in the presence of turbulence. Specifically, we derive a closed-form expression for the outage probability of NOMA over lognormal channels, while considering the effect of path loss and turbulence. The derived analytical results with the corresponding numerical results demonstrate that the transmission distance between laser diode and sensor nodes (SNs) has a high impact on the outage performance of the SNs, due to the increased turbulence level with increased distance. Moreover, the presented results show the effect of the water type on the outage performance of the SNs and on the optimum values of the power coefficients.
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Operation altitude optimization of solar-powered rotary-wing UAVs for FSO backhauling
(IEEE, 2023) Mahmoodi, Khadijeh Ali; Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat; Mahmoodi, Khadijeh Ali
Free space optical communication (FSO) has emerged as an alternative backhauling technology. It provides a line-of-sight (LOS) link with a capacity comparable to fiber optics and much higher than those that can be supported by radio counterparts. Rotary-wing unmanned aerial vehicles (UAVs) equipped with FSO terminals can be positioned as a complementary aerial solution to the terrestrial backhaul links in dense areas with high-peak traffic demands. In this paper, we consider a solar-powered rotary-wing UAV equipped with an FSO terminal that provides backhaul link to a ground base station in an urban area. We first quantity the energy consumption and energy harvesting of a rotary-wing solar-powered UAV. Then, we formulate an optimization problem to determine the optimal operation altitude with the goal of maximizing the net energy of UAV while satisfying the LOS requirements critical for the FSO link. Our results show that the selection of operation altitude is highly dependent on the weight of the UAV as well as the size and efficiency of the solar panel.

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