Browsing by Author "Kizilirmak, R. Ç."

Now showing 1 - 5 of 5

Metadata only
Centralized light access network (C-LiAN): a novel paradigm for next generation indoor VLC networks
(IEEE, 2017) Kizilirmak, R. Ç.; Narmanlıoğlu, Ömer; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Visible light communication (VLC) builds upon the idea of using existing lighting infrastructure for wireless data transmission. In a conventional VLC network, each light fixture acts as an access point (AP) which are connected to each other through electrical grid as well as data backbone. These VLC-enabled fixtures consist baseband unit (BBU) followed by the optical front-end (OFE). In this paper, we propose the so-called centralized light access network (C-LiAN) which aggregates all AP computational resources into a central pool that is managed by a centralized controller. Unlike the distributed architecture where each light fixture performs both baseband processing and optical transmission/reception, the centralized architecture employs “dummy”fixtures with a VLC OFE. Moving the baseband processing to a central pool reduces the associated cost and complexity of each VLC-enabled LED luminary. It further enables joint processing of signals from different APs making possible an efficient implementation of joint processing, offloading, handover, interference management, scheduling, and resource management algorithms. As an example to demonstrate the virtues of C-LiAN, we further present the performance of coordinated multipoint transmission and enhanced inter-cell interference coordination with almost blank subframe techniques originally proposed for Long Term Evolution-Advanced in the context of indoor VLC networks.
Metadata only
Cooperative visible light communications with full-duplex relaying
(IEEE, 2017-06) Narmanlıoğlu, Ömer; Kizilirmak, R. Ç.; Miramirkhani, Farshad; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad; Narmanlıoğlu, Ömer
In this paper, we investigate cooperative visible light communication (VLC) system where an intermediate light source acts as a relay terminal. We assume that relay terminal operates in full-duplex mode. In contrast to radio frequency counterparts, full-duplex VLC terminal is relatively easier to implement due to directive propagation characteristic of light. We first model VLC relay terminal taking into account loop interference channel based on ray tracing simulations. Then, we investigate error rate performance of the relay-assisted VLC system. Our performance evaluations demonstrate the superiority of full-duplex relaying over half-duplex counterpart especially for high modulation sizes.
Metadata only
FSO link attenuation measurement in extreme winter conditions for secure 5G applications
(SPIE, 2023) Khamidullin, A.; Kizilirmak, R. Ç.; Uysal, Murat; Ukaegbu, I. A.; Electrical & Electronics Engineering; UYSAL, Murat
The functionality of Free Space Optical (FSO) communication links is highly influenced by meteorological conditions such as precipitation, snowfall, and fog. In this study, we establish an FSO link and conduct experimental measurements to evaluate the link performance under extreme winter conditions in the city of Astana, with the goal of facilitating secure 5G applications. During the measurement period, the lowest recorded temperature was -19.3 °C, with an average of -7 °C. We present the path loss for a link with a distance of 212 meters under various weather conditions (snow, clear sky, cloudy, overcast), visibility, humidity, and air pressure levels. We also record wind speed and snowfall rate. The obtained path loss data is subsequently compared with analytical approximations previously reported in the literature.
Metadata only
Pilot-aided channel estimation on SC-PAM based visible light communications
(IEEE, 2018-07-02) Narmanlıoğlu, Ömer; Turan, B.; Kizilirmak, R. Ç.; Ergen, S. C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Estimation of the time-varying optical wireless channel response is crucial in order to decode received signals coherently. In this work, we investigate symbol-error-rate and mean absolute error performance of different interpolation techniques including linear, nearest, spline, and piece-wise cubic Hermite interpolating polynomial (pchip), which are used in pilot-aided channel estimation process for visible light communication. The performance of interpolators is evaluated in realistic time-varying channel model, generated on Zemax software and compared with each other under the consideration of different modulation orders, different pilot symbol periods, and different user equipment (UE) speeds through Monte Carlo simulations. The results reveal that spline and pchip techniques are more robust to low pilot symbol transmission rate and fast time-varying channel conditions as a consequence of high UE speeds. However, low complex linear interpolation technique can be chosen for highly rated pilot signal transmission cases or when optical channel varies slowly over the time.
Metadata only
Unmanned-aerial-vehicle-assisted cooperative communications for visible light communications-based vehicular networks
(SPIE, 2019-08) Kalikulov, N.; Kizilirmak, R. Ç.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
We propose and investigate cooperative visible light communications (VLC) enabled vehicular network architecture with an unmanned aerial vehicle (UAV) relay. In the proposed system, a UAV equipped with an onboard photodetector and light-emitting diodes is used as a relay in a vehicular VLC link. The advantage of having a flying UAV relay is its great mobility and ease of deployment. The performance of UAV-assisted cooperative VLC is investigated for amplify and forward and decode and forward protocols with half duplex and full duplex modes. Moreover, location of the UAV relay is optimized in order to maximize the signal-to-noise ratio at the destination vehicle. The active light beam tracking technique is further employed to increase the reliability of the proposed VLC system. Our results reveal that a UAV relay can significantly improve the transmission performance of conventional VLC-based vehicular networks.