Browsing by Author "Abdallah, M."

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Coordinated interference management for visible light communication systems
(IEEE, 2015-11) Kashef, M.; Abdallah, M.; Qaraqe, K.; Haas, H.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we consider the performance of a visible light communication (VLC) network with coordinated interference management. The VLC transmitters are allowed to coordinate their transmissions using one of two transmission schemes so as to maximize a network utility function. In the first technique, namely, orthogonal transmission, the utility function is maximized by optimally partitioning all resources. In the second technique, namely, power control, the transmitters are allowed to share the full spectrum while being allowed to control their power so as to maximize network performance. In particular, for each transmission technique, we optimize a general network utility function under the constraint of a desired illumination power for each VLC transmitter, taking into consideration the optical signal clipping effect due to the physical limitations of the VLC transmitters. For the power control transmission scheme, we develop a computationally efficient method for finding the optimal power values by deriving a computationally efficient way to obtain the achievable spectral efficiency region. Considering the summation and the proportional fairness utility functions, our simulation results show that the optimal transmission scheme depends on the location of the VLC users and the desired illumination power. Also, we show the superiority of the performance of the power control scheme over the orthogonal transmission scheme for low interference regions.
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Effect of eddy diffusivity ratio on underwater optical scintillation index
(The Optical Society, 2017-10-11) Elamassie, Mohammed; Uysal, Murat; Baykal, Y.; Abdallah, M.; Qaraqe, K.; Electrical & Electronics Engineering; UYSAL, Murat; Elamassie, Mohammed
The performance of underwater optical wireless communication systems is severely affected by the turbulence that occurs due to the fluctuations in the index of refraction. Most previous studies assume a simplifying, yet inaccurate, assumption in the turbulence spectrum model that the eddy diffusivity ratio is equal to unity. It is, however, well known that the eddy diffusivities of temperature and salt are different from each other in most underwater environments. In this paper, we obtain a simplified spatial power spectrum model of turbulent fluctuations of the seawater refraction index as an explicit function of eddy diffusivity ratio. Using the derived model, we obtain the scintillation index of optical plane and spherical waves and investigate the effect of the eddy diffusivity ratio.
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The impact of location errors on achievable rates in OFDM-based multi-user visible light communication systems
(IEEE, 2014) Kashef, M.; Abdallah, M.; Qaraqe, K.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
Visible light communication (VLC) is a communication technology in which data is transferred by modulating the visible light intensity. VLC signals degrade significantly due to the absence of the line of sight (LOS) between the transmitter and the receiver. Hence, any errors in determining the location of the users and equivalently the distance between the nodes can result in performance degradation. In this paper, we investigate the impact of location errors on performance of a VLC network exploiting power control. We consider the achievable rate region of two VLC communication pairs as the performance criterion. The system employs optical orthogonal frequency division multiplexing (O-OFDM) with power control. The power control algorithm exploits the receivers locations information to determine the distances between the transmitters and the receivers, which will be used to find the optimal transmission powers. We consider the case of random errors in the location estimation process modeled with a general error probability density function. In calculating the achievable rates of the communication pairs, the optical signal clipping effect is taken into consideration that results from the physical limitations at the transmitters. The numerical results show the effects of the system parameters including the location error variance, the desired illumination power and the relative positions of the receivers relative to the light emitting diodes (LED) transmitters on the achievable rate region.
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Indoor channel modelling and characterization for visible light communications
(IEEE, 2014) Sarbazi, Elham; Uysal, Murat; Abdallah, M.; Qaraqe, K.; Electrical & Electronics Engineering; UYSAL, Murat; Sarbazi, Elham
In this paper, we investigate channel modeling for visible light communications using ray tracing approach. The simulation environment is created in Zemax® and enables us to specify the geometry of the environment, the objects inside, the reflection characteristics of the surface materials as well as the specifications of the light sources and receivers. The received optical power and the delay of direct/indirect rays are computed for the specified indoor environment and the corresponding channel impulse response (CIR) is obtained through proper normalizations. Following this methodology, we present CIRs for a number of indoor environments and quantify multipath channel parameters gain for each environment.
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On the benefits of cooperation via power control in OFDM-based visible light communication systems
(IEEE, 2014) Kashef, M.; Abdallah, M.; Qaraqe, K.; Haas, H.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, the performance of a visible light communication (VLC) network exploiting power control is considered. The achievable rate region of two VLC communication pairs is characterized. The system employs optical orthogonal frequency division multiplexing (O-OFDM) with power control performed at the transmitters. The optical signal clipping effect is taken into consideration which results from the physical limitations at the transmitters. Also, the system is constrained by the desired illumination power for each transmitter. We prove that the achievable rate region is defined as the union of two regions where the boundary of each of these regions can be obtained by a single variable optimization problem. Our numerical results show the effects of the system parameters including direct current (DC) bias, the desired illumination power, clipping noise and the relative positions of the receivers relative to the LED transmitters on the achievable rate region of the two users. We show the enhancement in the performance resulted from using power control compared to orthogonal resource allocation techniques.
Open Access
Performance evaluation of LOS and NLOS vertical inhomogeneous links in underwater visible light communications
(IEEE, 2018-03-22) Anous, N.; Abdallah, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, underwater visible light communication (UWVLC) vertical links are modeled and evaluated, taking account of the inhomogeneous nature of underwater (UW) environment. An equivalent simplified model of stratified N layers is employed in which variations in refractive index and attenuation profiles across UW depth are considered. A generalized path loss expression is deduced which allows estimation of the vertical link loss prior to link design. Mathematical expressions of the received power for line-of-sight (LOS) and non-line-of-sight (NLOS) links between transmitters (Tx) and receivers are deduced. We evaluate the performance by computing the received power and bit error rate for inhomogeneous underwater links. Numerical examples are used to illustrate the proposed models. Deviations from expected results when considering a homogeneous underwater model are discussed. A simple underwater bilayer model is then introduced, which is considered a rough approximate model in comparison to the stratified N layers model. This model assists in estimating the UW link behavior without extensive calculations. The conditions necessary for applying this model are discussed and justified. Moreover, the effects of Tx orientation along with narrowing the transmitted light cone on LOS and NLOS vertical links are examined. A Tx power saving of 30%-50% in UWVLC links is proved to be achieved by rotating the Tx and narrowing its emitted light cone.
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Ray tracing based channel modeling for visible light communications
(IEEE, 2014) Sarbazi, Elham; Uysal, Murat; Abdallah, M.; Qaraqe, K.; Electrical & Electronics Engineering; UYSAL, Murat; Sarbazi, Elham
Bu bildiride, Zemax 13 yazılımı aracılığı ile görünür ışık haberleşmesi (visible light communication, VLC) kanalları karakterize edilecektir. Yaklaşımımızda, ölçülerini tanımlayacağımız iç mekân ortamı üçboyutlu olarak Zemax’da oluşturulmakta ve LED tabanlı ışık kaynakları uygun noktalara yerleştirilmektedir. Söz konusu yazılımım ışın izleme (ray tracing) araçları kullanılarak, alıcı tarafa doğrudan ve dolaylı yollardan (yansımalar) ulaşan sinyallerin gücü ve gecikme süreleri hesaplanmaktadır. Daha sonra bu bilgiler Matlab’a aktarılarak uygun normalleştirmeler aracılığı ile bu iç mekan propagasyonu ortamına karşılık gelen kanal dürtü cevabı elde edilmektedir. Bu yöntem izlenerek, değişik ebatlardaki odalarda farklı alıcı/verici yerleşimleri varsayımları altında kanal dürtü cevapları elde edilmiş ve gecikme yayılımı, DC kazancı vb kanal parametreleri hesaplanmıştır.
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Resource allocation for downlink OFDMA in underwater visible light communications
(IEEE, 2019-06) Elamassie, Mohammed; Karbalayghareh, Mehdi; Miramirkhani, Farshad; Uysal, Murat; Abdallah, M.; Qaraqe, K.; Electrical & Electronics Engineering; UYSAL, Murat; Elamassie, Mohammed; Karbalayghareh, Mehdi; Miramirkhani, Farshad
As a wireless connectivity solution with low latency and high capacity, visible light communication (VLC) is particularly attractive for high-speed underwater applications such as image or real-time video transmission. In this paper, we consider the downlink of an underwater sensor network (USN) where the communication between the central command unit and sensor nodes takes place through VLC. The system builds upon DC-biased-optical orthogonal frequency division multiple access (DCO-OFDMA) where subsets of subcarriers are assigned to different nodes. We propose a joint subcarrier allocation and bit loading algorithm in an effort to achieve identical data rate for each node in the USN while satisfying a targeted bit error rate (BER). We further present Monte Carlo simulation results to demonstrate the performance of the proposed adaptive algorithm.
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Single photon avalanche diode (SPAD) VLC system and application to downhole monitoring
(IEEE, 2014) Li, Y.; Videv, S.; Abdallah, M.; Qaraqe, K.; Uysal, Murat; Haas, H.; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, it is demonstrated for the first time that the problem of continuous downhole monitoring in the oil and gas industry is effectively addressed by the use of visible light communication (VLC). As a reliable, flexible and low-cost technique, VLC can fulfill a critical need of operators to maintain production efficiency and optimize gas well performance. The proposed VLC system makes use of a light emitting diode (LED) transmitter and a high sensitivity single photon detecting receiver referred to as single-photon avalanche diode (SPAD). The latter is instrumental in achieving long range communications, and the fact that ambient light is not present in a gas pipe is exploited. Specifically, the lack of ambient light enables high signal to noise ratio (SNR) at the receiver which operates in a photon counting mode. In this study, the bit error ratio (BER) performance of the system is simulated for a 4 kilometres long metal pipe. It is shown that the proposed system has superior power efficiency over conventional methods, which is important as it is assumed that the transmitter is battery operated. In addition, the theoretical BER performance is calculated and compared to the simulation results.
Open Access
Visible light channel modeling for gas pipelines
(IEEE, 2018-04) Miramirkhani, Farshad; Uysal, Murat; Narmanlıoğlu, Ömer; Abdallah, M.; Qaraqe, K.; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad; Narmanlıoğlu, Ömer
In this paper, we explore the use of visible light communication as a means of wireless monitoring in gas pipelines. In an effort to shed light on the communication limits in the presence of gas, we create a three-dimensional simulation platform where the pipeline size/shape, the reflection characteristics of the interior coating, gas specifications (i.e., temperature, density, refractive index, transmittance, etc.) and the specifications of the light sources and detectors (i.e., field of view, lighting pattern, etc.) are precisely defined. Based on ray tracing, we obtain channel impulse responses within the gas pipeline considering the deployment of different colored LEDs with various viewing angles. We further investigate the maximum achievable link range to ensure a given bit error rate.