Browsing by Author "Yalcinkaya, A. D."

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    A 130 nm CMOS receiver for visible light communication
    (IEEE, 2022-06-15) Kısacık, Rıfat; Yagan, M. Y.; Uysal, Murat; Pusane, A. E.; Baykas, T.; Dundar, G.; Yalcinkaya, A. D.; Electrical & Electronics Engineering; UYSAL, Murat; Kısacık, Rıfat
    Visible light communication (VLC) is an emerging technology that has been gaining attention over the last few years. Transmission of data at higher rates in a VLC system is mainly limited by the modulation bandwidth of the employed LED. To alleviate this limitation, equalization is frequently employed. This is usually achieved by either using discrete circuit elements or in digital form. In this paper, we present a power-efficient VLC receiver as a system-on-chip, implemented in 130 nm CMOS technology. The proposed receiver supports LEDs with different bandwidths thanks to the switchable equalizer. We tested the proposed receiver using phosphorescent white LEDs with different bandwidths on an experimental VLC link. For each tested LED, around 20 fold improvement in data rate was achieved compared to the original bandwidth of the LED. For the LED with a modulation bandwidth of 1.6 MHz, data rates of 32 Mbps and 50 Mbps at a BER of 102 were obtained at a distance of 2 meters without and with a blue filter, respectively.
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    Characterization of LEDs for visible-light communications
    (SPIE, 2021-02) Kısacık, Rıfat; Yalcinkaya, A. D.; Pusane, A. E.; Baykas, T.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Kısacık, Rıfat
    Recent advances in solid-state technologies have enabled the development of light-emitting diodes (LEDs) with favorable features such as long life expectancy, low-power consumption, and reduced heat dissipation. Visible-light communication (VLC) is a short-range wireless access technology that deploys LEDs as wireless transmitters in addition to their primary task of illumination. The major limitation for the design of high-speed VLC systems is the electrical (modulation) bandwidth of the LED. In this study, we investigate the electrical characteristics of a number of off-the-shelf LEDs. Specifically, we determine their frequency responses and match them to their small-signal models. The electrical bandwidths of measured LEDs vary from 250 kHz to 20 MHz and depend on the emitted color and internal circuitry. As a verification of our measurements, we use the sample LEDs as a transmitter in a VLC system setup and determine the supported data rates. The equivalent circuit model is utilized to compare with the measured modulation characteristic of the LED. Furthermore, the bias current effect on the modulation bandwidth is presented.
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    Distance and power based experimental verification of channel model in visible light communication
    (IEEE, 2019) Kısacık, Rıfat; Efe, B. C.; Pusane, A. E.; Uysal, Murat; Baykas, T.; Dündar, G.; Yalcinkaya, A. D.; Electrical & Electronics Engineering; UYSAL, Murat; Kısacık, Rıfat
    In this work, a channel model for line-of-sight (LOS) in visible light communication is elaborated. In the proposed channel model, there is no optical component, such as filter or lens, between the transmitting LED and the receiving photodiode. Later, a suitable setup is built for emulation of the mentioned channel model. In the setup, the LED and the photodiode are located in a line-of-sight orientation. The change of the optical power on the photodiode is measured by varying the distance between the LED and photodiode. The measurement result is compared with the channel model. The channel model is in good agreement with the measurement results. Following that, the signal-to-noise ratio (SNR) at the output of the receiver, as a function of the distance, is measured. Measurement results indicate that the SNR value remains below 15 dB after exceeding a distance of 20 cm for the specific LED-Photodiode pair used in the experiment. The optical signal on photodiode drops to the noise level when the distance exceeds 50 cm.
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    Experimental validation of a novel RLL code for visible light communication
    (IEEE, 2020) Yagan, M. Y.; Kısacık, Rıfat; Erkinaci, T.; Pusane, A. E.; Uysal, Murat; Baykas, T.; Dundar, G.; Yalcinkaya, A. D.; Electrical & Electronics Engineering; Herencsar, N.; UYSAL, Murat; Kısacık, Rıfat
    Flicker arising in visible light communication (VLC) system is typically mitigated by run-length-limited (RLL) codes. The IEEE 802.15.7 standard proposes RLL codes according to the modulation type and data rate. In this paper, we propose a new RLL code and present the encoding and decoding operations for use in VLC systems. We provide experimental results for bit error rate (BER) for transmission of uncoded, 8B10B-coded and proposed code at different data rates in a VLC setup. We experimentally demonstrate that the proposed code performs close to the 8B10B code. The proposed code achieves a BER of 10(-5) at 50 Mbps where transmitting the uncoded data at the same rate results in the BER of 10(-3).
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    A new LED response model and its application to pre-equalization in VLC systems
    (IEEE, 2021-09-01) Kısacık, Rıfat; Yagan, M. Y.; Uysal, Murat; Pusane, A. E.; Yalcinkaya, A. D.; Electrical & Electronics Engineering; UYSAL, Murat; Kısacık, Rıfat
    With the growing interest in visible light communication (VLC), it is desired to transmit data at very high rates despite the LED's bandwidth becoming a bottleneck. The bandwidth of a white LED usually ranges between hundreds of kHz and a couple of MHz, limiting transmission rates dramatically in a VLC system. Successful design of an efficient equalizer for VLC systems heavily depends on the realistic modeling of LED's frequency response. In this letter, we first propose a new LED response model taking the parasitic effects appearing at higher frequencies into account. The proposed model provides better match with measurements of commercially available LEDs over a wide frequency range as compared to the existing models in the literature. Then, we design a digital equalizer in line with the proposed model and implement it as an offline digital system in Matlab. The designed equalizer yields an overall flat system response over a wide frequency range. As a demonstration, we present the measured eye diagrams and bit error rate performance results of the equalized VLC system with on-off keying modulation and demonstrate improvements in data rate in comparison to the LED bandwidth.