@article{eroglu_anjinappa_guvenc_pala_2021, title={Slow Beam Steering and NOMA for Indoor Multi-User Visible Light Communications}, volume={20}, ISSN={["1558-0660"]}, url={https://doi.org/10.1109/TMC.2019.2960495}, DOI={10.1109/TMC.2019.2960495}, abstractNote={Visible light communication (VLC) is an emerging technology that enables broadband data rates using the visible spectrum. In this paper, considering slow beam steering where VLC beam directions are assumed to be fixed during a transmission frame, we find the steering angles that simultaneously serve multiple users within the frame duration and maximize the data rates. This is achieved by solving a non-convex optimization problem using a grid-based search and majorization-minimization (MM) procedure. Subsequently, we consider multiple steerable beams with a larger number of users in the network and propose an algorithm to cluster users and serve each cluster with a separate beam. We optimize the transmit power of each beam to maximize the data rates. Finally, we propose a non-orthogonal multiple access (NOMA) scheme for the beam steering and user clustering scenario, to further increase the data rates of the users. The simulation results show that the proposed beam steering method can efficiently serve a high number of users, and with power optimization, a sum rate gain up to thirteen times is possible. The simulation results for NOMA suggests an additional 10 Mbps sum rate gain for each NOMA user pair.}, number={4}, journal={IEEE TRANSACTIONS ON MOBILE COMPUTING}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Eroglu, Yusuf Said and Anjinappa, Chethan Kumar and Guvenc, Ismail and Pala, Nezih}, year={2021}, month={Apr}, pages={1627–1641} }
 @article{eroglu_yapici_guvenc_2019, title={Impact of Random Receiver Orientation on Visible Light Communications Channel}, volume={67}, ISSN={["1558-0857"]}, url={https://doi.org/10.1109/TCOMM.2018.2879093}, DOI={10.1109/TCOMM.2018.2879093}, abstractNote={Visible light communications (VLC) has been studied thoroughly in recent years as an alternative or complementary technology to radio frequency communications. The reliability of VLC channels highly depends on the availability and alignment of line of sight links. In this paper, we study the effect of random receiver orientation for mobile users over VLC downlink channels, which affects the existence and quality of line of sight links. Based on the statistics of the receiver location and relative orientation with respect to the transmitter LED, we develop an analytical framework to characterize the statistical distribution of VLC downlink channels, which is then utilized to obtain the outage probability and the bit error rate. Our analysis is generalized for arbitrary distributions of relative orientation and location for a single transmitter, and extended to multiple transmitter case for some certain scenarios. Extensive Monte Carlo simulations show a perfect match between the analytical and the simulation data in terms of both the statistical channel distribution and the resulting bit error rate. Our results also characterize the channel attenuation due to random receiver orientation and location for various scenarios of interest.}, number={2}, journal={IEEE TRANSACTIONS ON COMMUNICATIONS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Eroglu, Yusuf Said and Yapici, Yavuz and Guvenc, Ismail}, year={2019}, month={Feb}, pages={1313–1325} }
 @article{mushfique_palathingal_eroglu_yuksel_guvenc_pala_2018, title={A Software-Defined Multi-Element VLC Architecture}, volume={56}, ISSN={["1558-1896"]}, DOI={10.1109/mcom.2018.1700306}, abstractNote={In the modern era of radio frequency (RF) spectrum crunch, visible light communication (VLC) is a recent and promising alternative technology that operates at the visible light spectrum. Thanks to its unlicensed and large bandwidth, VLC can deliver high throughput, better energy efficiency, and low cost data communications. In this article, a hybrid RF/VLC architecture is considered that can simultaneously provide light- ing and communication coverage across a room. Considered architecture involves a novel multi-element hemispherical bulb design, which can transmit multiple data streams over light emitting diode (LED) modules. Simulations considering various VLC transmitter configurations and topologies show that good link quality and high spatial reuse can be maintained in typical indoor communication scenarios.}, number={2}, journal={IEEE COMMUNICATIONS MAGAZINE}, author={Mushfique, Sifat Ibne and Palathingal, Prabath and Eroglu, Yusuf Said and Yuksel, Murat and Guvenc, Ismail and Pala, Nezih}, year={2018}, month={Feb}, pages={196–203} }
 @article{eroglu_guvenc_sahin_yapici_pala_yuksel_2018, title={Multi-Element VLC Networks: LED Assignment, Power Control, and Optimum Combining}, volume={36}, ISSN={["1558-0008"]}, DOI={10.1109/jsac.2017.2774378}, abstractNote={Visible light communications (VLCs) are a promising technology to address the spectrum crunch problem in radio frequency networks. A major advantage of VLC networks is that they can use the existing lighting infrastructure in indoor environments, which may have large number of LEDs for illumination. While LEDs used for lighting typically have limited bandwidth, presence of many LEDs can be exploited for indoor VLC networks, to serve each user by multiple LEDs for improving link quality and throughput. In this paper, LEDs are grouped and assigned to the users based on received signal strength from each LED, for which different solutions are proposed to achieve maximum throughput, proportional fairness, and quality of service. Additionally, power optimization of LEDs for a given assignment is investigated, and the Jacobian and Hessian matrices of the corresponding optimization problem are derived. Moreover, for multi-element receivers with LED grouping at the transmitter, an improved optimal combining method is proposed. This method suppresses interference caused by simultaneous data transfer of LEDs and improves the overall signal-to-interference-plus-noise-ratio by 2–5 dB. Lastly, an efficient calculation of channel response is presented to simulate multipath VLC channel with low computational complexity.}, number={1}, journal={IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS}, author={Eroglu, Yusuf Said and Guvenc, Ismail and Sahin, Alphan and Yapici, Yavuz and Pala, Nezih and Yuksel, Murat}, year={2018}, month={Jan}, pages={121–135} }