Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleAçık Erişim2025Energy-Efficient 8-PAM Optical DAC Design for Visible Light Communication Systems
Başer, Oğuzhan; Küçük, Mehmet Ali; Albayrak, Cenk; Türk, Kadir
This paper presents a cost-effective and energy-efficient optical digital-to-analog converter (ODAC) transmitter scheme for visible light communication (VLC) systems. The proposed ODAC transmitter enables data transmission while providing lighting, as desired in VLC systems, unlike existing ODAC structures in the literature, by switching power LEDs at high speeds with a MOSFET-based switching circuit design. This paper also discusses the ODAC design stages and presents the points to be considered in detail. In addition, by implementing the hardware design of an ODAC transmitter with a 3-bit resolution, that is, capable of generating 8-PAM signals, based on the proposed ODAC architecture, experimental studies are conducted for energy efficiency and communication performance results via the established VLC system using the designed ODAC. Experimental results demonstrate that the proposed ODAC transmitter achieves a data transmission rate of 18.75 Mbps with a bit error rate (BER) below the forward error correction (FEC) limit at a communication distance of 4 m, while also exhibiting a high power efficiency of 94%.
- BildiriAçık Erişim2024Experimental Demonstration of an Optic-DAC Based Transmitter Structure
Baser, Oguzhan; Küçük, Mehmet Ali; Albayrak, Cenk; Türk, Kadir
In this paper, an optical-DAC (ODAC) based transmitter design is proposed for indoor visible light communication (VLC) applications. The proposed design is practically realized and the communication performance of the experimental VLC system is investigated. In the ODAC transmitter, multilevel communication signal can be generated optically by independently switching light emitting diode (LED) groups with different powers. In this way, multilevel modulation techniques in VLC systems can be realized through a simple transmitter structure that can be digitally driven. In the proposed transmitter design, unlike the existing ODAC-based VLC transmitters in the literature, metal oxide semiconductor field effect transistors (MOSFET) are used as switching elements in order to drive high-power LED for ambient illumination and communication. In the experimental studies, an offline VLC system using the designed ODAC-based transmitter with a power of approximately 10 W is tested at different switching speeds and distances. The results show that by implementing 8 PAM modulation in the proposed transmitter design, a data transmission rate of 6.264 Mbps is successfully achieved.
- BildiriAçık Erişim2024Reconfigurable Optical Filter Based Receiver Structure For Visible Light Communication
Küçük, Mehmet Ali; Albayrak, Cenk; Türk, Kadir
In this paper, a novel receiver structure is proposed to mitigate the inter-channel interference (ICI) effects that limit the data rate in multi-color visible light communication (MC-VLC) systems. Reconfigurable optical filters (ROFs) are used at the receiver side of MC-VLC systems to enable the separation of color channels. ROFs are optical elements that have the ability to electrically change their transmission spectrum. Utilizing this feature of ROFs, a receiver structure is developed that, unlike traditional receiver structures, can adaptively adjust the transmit spectrum based on channel state information. This adaptive adjustment is aimed at maximizing communication performance by effectively separating color channels in MC-VLC systems. The obtained results demonstrate that the proposed receiver structure achieves higher communication performance compared to traditional receivers.
- MakaleAçık Erişim2024Optical Filter Design for Multi-Color VLC in Reflective Environments with Multiple Lighting Sources
Kucuk, Mehmet A.; Albayrak, Cenk; Turk, Kadir; Yanikomeroglu, Halim
Multi-color visible light communication (MC-VLC) systems, which aim to transmit data in parallel with multi-color LEDs, use optical filters to separate color channels at the receiver side. However, the relatively wide spectrum of LEDs may cause inter-color interference (ICI). In addition, the passband of the optical filters shifts towards the blue wavelength depending on the angle of incidence (AoI) of the light, which may also increase ICI. In this paper, the problem of designing optical filters for MC-VLC systems in the presence of the blue-shift is investigated. The communication environment is assumed to be a typical room illuminated by multiple fixtures in accordance with lighting standards. Moreover, the walls in the room are reflective, resulting in non-line-of-sight (NLoS) components. The passband edges of the optical filter are optimized to maximize the average signal-to-interference-plus-noise ratio (SINR). The effect of the field-of-view (FOV) of the receiver on the system performance is also analyzed. Finally, a generic optical filter has been designed that can be used in standards-compliant environments for selected LEDs and a given FOV range. The results show that the designed optical filter provides a higher and uniform capacity than those in the literature.
- BildiriYalnız künye2018Experimental Channel Measurement for Indoor Office Visible Light Communication
Yazgan, Ayhan; Simsek, Cemaleddin; Albayrak, Cenk; Tugcu, Emin; Turk, Kadir; Herencsar, N.
Channel measurement for visible light communication (VLC) is theoretically and experimentally performed in a real office platform. Six armatures composed of phosphor based white LED arrays are fed by designed analog LED drivers. Measurements are taken in a 6m x 7.8m office room which is formed as 10×13 matrix with 60 cm grid distance for both simulation and experiment studies. The link distance between LED arrays and optical receiver is kept minimum 2.5 meters for each measurement. Experimental results are generally in good agreement with simulation results, which are obtained using Barry's theoretical channel model.
- BildiriYalnız künye2018Performance of Visible Light Communication with Colour Shift Keying Modulation and Polar Code
Simsek, Cemaleddin; Tugcu, Emin; Albayrak, Cenk; Yazgan, Ayhan; Turk, Kadir; Herencsar, N.
Visible light communication (VLC) is an emerging technology to fulfill both illumination and communication purposes considered as either an alternative or a support system for some of scenarios carried by RF communication systems. Colour shift keying (CSK) is the modulation given in IEEE 802.15.7 VLC standard which proposes Reed-Solomon as error correction code. Polar code is the first theoretically proven capacity achieving error correction code with low encoding and decoding complexities. Performance of Polar code with belief propagation decoder has not been studied under VLC CSK scheme. In this study we investigate performance of Polar code with belief propagation decoder under VLC CSK scheme and compare it with performance of Reed-Solomon code. Result show that Polar code with belief propagation decoder outperforms Reed-Solomon code by at least 1.5dB.
- BildiriYalnız künye2017Hardware Friendly Early Stopping Structure For Polar Code
Simsek, Cemaleddin; Albayrak, Cenk; Türk, Kadir
Polar code has become a major milestone in information theory field in recent times. Researchers are still observing more efficient encoding and decoding structures. In this study, a new WIB based structure is proposed which reduces the computational complexity of WIB introduced as an early termination method for BP polar decoder in literature. Both proposed and WIB methods are implemented with VHDL and hardware complexities are compared via XILINX ISE synthesis tool. Most important complexity reduction came with removing unnecessary addition operations which make early termination method possible to implement only with hit-wise logical operations. Results show that along with complexity reduction proposed approach can also acquire same performance in half time compared to previous counterpart with fewer logic gates.
- BildiriYalnız künye2017Sign Alterations of LLR Values Based Early Termination Method for LT BP Decoder
Albayrak, Cenk; Simsek, Cemaleddin; Türk, Kadir
In this letter, a new early termination method is proposed for Luby transform (LT) belief propagation (BP) decoder. The proposed method is decided whether BP decoder output converges to original data bits by observing only sign alterations of log-likelihood ratio (LLR) messages in BP decoder structure. Simulation results and complexity analyzes show that proposed method has low computational complexity and small average iteration amounts compared to conventional early termination methods in literature. In addition to this, the proposed method doesn't cause any performance degradation in BP decoder. The method can be easily applied to code families which can be decoded by BP algorithm such as low density parity check (LDPC) codes, polar codes and Raptor codes.
- MakaleYalnız künye2017Low-complexity early termination method for rateless soft decoder
Albayrak, Cenk; Simsek, Cemaleddin; Turk, Kadir
We propose a new early termination method (ETM) with low computational complexity for Luby transform belief propagation (BP) decoder. The proposed method, which we call least reliable messages (LRM) ETM, observes only sign alterations of a small cluster in log-likelihood ratio messages passing between nodes in BP decoder. Simulation results and complexity analyzes show that LRM ETM has quite low computational complexity and small average iteration amounts without any performance degradation compared with conventional ETMs in literature. The method can be applied to code families which can be decoded by BP such as low density parity check codes, polar codes, and Raptor codes.