Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleYalnız künye2026A comprehensive optimization framework for indoor laser-based optical wireless communication using gimbal-steered transmitters
Başer, Oğuzhan; Küçük, Mehmet Ali; Türk, Kadir
The growing demand for high-speed wireless communication, driven by data-intensive applications such as high-definition video streaming and augmented reality, has highlighted the limitations of the Radio Frequency (RF) spectrum. Optical Wireless Communication (OWC) has emerged as a promising complementary technology, offering wide bandwidth, license-free operation, high security, and immunity to electromagnetic interference. Among OWC transmitters, Laser Diodes (LDs) provide high modulation bandwidth and narrow divergence angles, enabling data rates of several tens of gigabits per second. However, the narrow beam of LDs requires precise Line-of-Sight (LoS) alignment, making beam steering essential. This study focuses on optimizing the positioning and orientation of gimbal- or galvo-based LD transmitters in indoor OWC systems to minimize outage probability under LoS constraints and physical obstructions. An outage probability model considering room geometry and device field-of-view angles is developed and analyzed for three scenarios within a 7 × 5 m room: an empty environment, a room with a 1 × 1 m column, and a user-occupancy-aware environment. The complex optimization problem is solved using multiple meta-heuristic algorithms, including Particle Swarm Optimization (PSO), L-SHADE, and Stochastic Fractal Search with Fitness-Distance Balance (FDB-SFS). The obtained results are subsequently validated through grid search approach. The proposed approach achieves significant outage reduction, demonstrating that incorporating obstacle and user-distribution information enables efficient coverage with fewer terminals, reaching outage probabilities as low as 0.4%.
- 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.
- MakaleYalnız künye2021Performance evaluation of IEEE 802.15.7 CSK modulation under blue shift effect of optical receiver filters
Küçük, Mehmet Ali; Türk, Kadir
In recent years, the use of light-emitting diodes (LEDs) in lighting, which has higher energy efficiency and longer-lasting environmentally friendly lighting compared to conventional lighting devices, has accelerated the development of a promising new technology for short-range wireless optical transmission called visible light communication (VLC). Besides other applications, VLC switches the LEDs at very high speeds to simultaneously realize indoor lighting and data transmission. But the intensity and color of the lighting may vary because of data transmission. Color shift keying (CSK) modulation defined in the IEEE 802.15.7 VLC standard guarantees constant light intensity and color. The CSK receiver uses a band-pass optical filter to separate the light channels. However, the transition band of optical filters shifts towards the blue wavelength depending on the incidence angle of the light which is called the blue shift effect. In this paper, the performance of the CSK receiver is investigated for the first time under the blue shift effect in the case of single and multiple transmitter LED cells. The numerical results show that the blue shift effect significantly decreases system performance. To eliminate the distorting effect, various methods and an adaptive equalizer-based CSK receiver are proposed. The proposed structures provide notable improvement.
- 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.