Browsing by Author "Kashef, 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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    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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    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.