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UYSAL, Murat

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Murat

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Now showing 1 - 10 of 350
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    Experimental evaluation of a software defined visible light communication system
    (IEEE, 2020) Mohamed, Bassam Aly Abdelrahman; Elamassie, Mohammed; Kebapçı, Burak; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Mohamed, Bassam Aly Abdelrahman; Kebapçı, Burak
    Visible light communication (VLC) allows the dual use of light-emitting diodes (LEDs) for illumination and communication purposes. With its large bandwidth and immunity to electromagnetic interference, VLC can be used as complementary and/or alternative to radio communications. In this paper, we present a comprehensive experimental evaluation of a software-defined VLC system with on-off keying for both line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios. The experimental set-up is based on a pair of modified National Instruments USRPs coupled with a custom design front-end. In the measurement campaign, we vary the distance between 1 to 3 meters with a step size of 0.5 m. For each point in this LOS scenario, we measure signal-to-noise ratio (SNR) and bit error rate (BER) with and without a lens. We also evaluate the effect of the reception angle (i.e, no strict alignment) on system performance. We further evaluate the SNR performance for NLOS scenarios and demonstrate a robust performance due to the wide field-of-view of the front-end.
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    Rate-adaptive OFDM MIMO VLC system
    (IEEE, 2018-01-19) Narmanlıoğlu, Ömer; Kızılırmak, R. Ç.; Miramirkhani, Farshad; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad; Narmanlıoğlu, Ömer
    In this paper, we investigate link adaptation for an orthogonal frequency division multiplexing (OFDM)-based multiple-input multiple-output (MIMO) visible light communication (VLC) system. The MIMO system under consideration employs repetition coding, therefore all the transmitters emit the same information. We propose a rate adaptation algorithm where the modulation size is selected among the available constellation sets. The receiver first calculates the instantaneous signal-to-noise ratio per subcarrier, then determines the maximum constellation size on each subcarrier that can be supported while satisfying a predefined target bit error rate. Our numerical results reveal that a peak data rate of more than 1.14 Gbits/sec can be achieved using LEDs with cut-off frequency of 10 MHz in typical office spaces.
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    Effect of partial coherence on MISO FSO systems
    (IEEE, 2015) Gökçe, M. C.; Baykal, Y.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    Multiple-input single-output (MISO) techniques are employed in free space optical (FSO) systems to mitigate the degrading effects of atmospheric turbulence and therefore the link reliability is improved. In this paper, we consider an incoherent radial array beams and a finite sized slow detector for MISO FSO systems. We have derived the average power and power correlation formulas on the finite sized slow detector using the Huygens Fresnel principle in weak atmospheric turbulence. This helps us to find the system performance, such as power scintillation and aperture averaging factor. Effect of system parameters such as the source size, the ring radius, the degree of coherence, the link distance, the structure constant and the receiver aperture radius are analyzed on the performance of MISO FSO systems.
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    Outage performance of multi-hop hybrid FSO/RF communication systems
    (IEEE, 2015) Kazemi, H.; Uysal, Murat; Touati, F.; Haas, H.; Electrical & Electronics Engineering; UYSAL, Murat
    In this paper, five scenarios are considered for the realization of a multi-hop hybrid free-space optical/radio frequency (FSO/RF) communication system with decode-and-forward (DF) relaying, and analytical outage probability expressions are derived. The scenarios have a different number of FSO and RF links. The aim is to identify an optimum scenario to effectively improve the end-to-end reliability of the multi-hop hybrid FSO/RF system. Outage performance is investigated for the scenarios under various weather conditions through numerical examples. It is identified that for a given link distance the end-to-end outage probability is minimized when using a hybrid FSO/RF link between every two successive nodes of the multi-hop system, and this requires the maximum number of FSO and RF links to be deployed.
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    Performance analysis of cooperative diversity networks with imperfect channel estimation over Rician fading channels
    (IEEE, 2010) Ikki, S. S.; Feteiha, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    In this paper, we examine the effect of channel estimation error on the error and outage probabilities of a multi-relay system with amplify-and-forward relaying over frequency-flat Rician fading channel. We consider orthogonal relaying and study both conventional cooperative systems (i.e., all relays participate in the relaying phase) and opportunistic cooperative systems (i.e., only the best relay participates in the relaying phase). Based on the derivation of effective signal-to-ratio (SNR) at the receiver taking into account channel estimation error, we obtain closed-form expressions for error and outage probabilities in high SNR regime. Such closed form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. Computer simulations are used to validate our analytical results.
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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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    Non-orthogonal multiple access (NOMA) for indoor visible light communications
    (IEEE, 2015) Kizilirmak, R. C.; Rowel, C. R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    Providing multiple access support to visible light communication (VLC) systems requires new networking architecture. Non-orthogonal multiple access (NOMA) is a proposed multiple access technique for future cellular systems. In this work, based on a realistic indoor channel conditions, we apply NOMA to indoor VLC channels and demonstrate its superior performance over orthogonal frequency division multiple access (OFDMA).
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    Görünür ışık kanalların modellenmesi ve ACO-OFDM için başarım analizi
    (IEEE, 2015) Yeşilkaya, A.; Alsan, H. F.; Miramirkhani, Farshad; Panayırcı, E.; Şenol, H.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad
    Spectrum scarcity of traditional radio communication has led communication engineers to find new alternatives. Indoor visible light communication is one alternative to solve this problem since its spectrum is not regulated and it has much wider bandwidth then traditional communication systems. This increased the research done in the field of visible light communications. However a proper indoor channel model is lacking and all previous studies assumes that only additive white Gaussian noise (AWGN) is present. Lack of proper channel model has motivated us to model a realistic indoor visible light channel. After modeling the indoor visible light channel, the performance of an asymmetrically clipped optical OFDM (ACOOFDM) system which is suitable for optical communications is investigated and compared to that of the AWGN optical channels.
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    Broadcasting brake lights with MIMO-OFDM based vehicular VLC
    (IEEE, 2016) Turan, B.; Narmanlıoğlu, Ömer; Coleri Ergen, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
    Inter-vehicular connectivity to enhance road safety and enable highly autonomous driving is increasingly becoming popular. Despite the prevalent works on radio-frequency (RF) based vehicular communication schemes, visible light communication (VLC) is considered to be a promising candidate for vehicular communications due to its low complexity and RF interference-free nature. This paper investigates applicability of VLC to enhance road safety based on real world measurements. Deployment of multiple light emitting diodes (LEDs) enables multiple-input multiple-output (MIMO) transmission in the context of vehicular VLC. We consider direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) based MIMO transmission scheme and evaluate the performances of different MIMO modes including repetition code (RC) and spatial multiplexing (SM), different modulation orders and different transmitter-receiver selection. The results reveal that selection of the closest transmitters to the receivers, provide better performance due to high signal-to-noise-ratio (SNR) requirements for RC mode. However, usage of all possible transmitters does not always yield better performance due to power division at the transmitter side. Moreover, SM suffers from channel correlation whereas the performance of RC shows more degradation on higher-order modulations that are required to yield the same throughput with SM.
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    Outage capacity regions of multicarrier DF relaying in underwater acoustic channels
    (IEEE, 2012) Al-Dharrab, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    In this paper, we investigate the information theoretical limits on the performance of cooperative multicarrier underwater acoustic (UWA) communication systems. We assume decode-and-forward (DF) relaying and consider non-orthogonal half-duplex cooperation. Under the assumptions of sparse and frequency-selective Rician fading channel and correlated Gaussian ambient noise, we derive the maximum achievable sum-rate and common/individual outage capacity regions for the cooperation protocol under consideration. We further investigate the effect of several parameters such as underwater temperature, carrier frequency, etc. on the outage capacity regions.