Browsing by Author "Miramirkhani, Farshad"

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Citation Count: 7
Channel Modeling for Visible Light Communications
(Springer-Verlag Berlin, 2016) Miramirkhani, Farshad; Uysal, Murat; Panayırcı, Erdal
In this chapter, we present a novel and realistic channel modeling approach for visible light communications that overcomes the limitations of previous works. In our work, we consider wavelength dependency, effect of realistic light sources as well as different types of reflections such as specular and mixed cases of diffuse and specular. We use nonsequential ray tracing algorithms to calculate the detected power and path lengths from source to detector for each ray. These are then processed to yield the channel impulse responses for various indoor environments. We further present a channel characterization study where channel parameters such as channel DC gain, root mean square delay spread, coherence bandwidth, mean excess delay are calculated for different environments.
Citation Count: 0
Comparative Performance Evaluation of VLC, LTE and WLAN Technologies in Indoor Environments
(IEEE, 2021) Baykaş, Tunçer; Karbalayghareh, Mehdi; Miramirkhani, Farshad; Uysal, Murat; Baykas, Tuncer
Recent years have seen an exponential rise in the demand for indoor wireless connections that have driven future generation networks to aim for higher data rates with extended coverage and affordable rates. The two most prominent technologies for providing indoor wireless connections, WLAN and LTE, have their limitations and they can not coexist in a single band to form heterogeneous networks (HetNets). Visible light communication (VLC) has seen rapid growth in recent years as it has the capability to seamlessly merge with the existing technologies and provide wireless connections with high data rates. VLC based hybrid indoor network effectively combines the preferences of an end-user with the practicality of implementation. In this work, we investigate specific VLC/WLAN and VLC/LTE hybrid scenarios to perform a detailed analysis on the effect of user mobility on the performance of the system and how the performance of the network (in terms of throughput) can be maximized The study aims to show how different technologies complement each other in the best and even the worst-case scenarios.
Citation Count: 112
IEEE 802.15.7r1 Reference Channel Models for Visible Light Communications
(IEEE-Inst Electrical Electronics Engineers Inc, 2017) Baykaş, Tunçer; Narmanlıoğlu, Ömer; Baykas, Tuncer; Uysal, Murat; Panayırcı, Erdal
The IEEE has established the standardization group 802.15.7r1 "Short Range Optical Wireless Communications", which is currently in the process of developing a standard for visible light communication (VLC). As with any other communication system, realistic channel models are of critical importance for VLC system design, performance evaluation, and testing. This article presents the reference channel models that were endorsed by the IEEE 802.15.7r1 Task Group for evaluation of VLC system proposals. These were developed for typical indoor environments, including home, office, and manufacturing cells. While highlighting the channel models, we further discuss physical layer techniques potentially considered for IEEE 802.15.7r1.
Citation Count: 81
A Mobile Channel Model for VLC and Application to Adaptive System Design
(IEEE-INST Electrical Electronics Engineers Inc, 2017) Miramirkhani, Farshad; Narmanlıoğlu, Ömer; Uysal, Murat; Panayırcı, Erdal
In this letter we propose a realistic channel model for visible light communication (VLC) assuming a mobile user. Based on non-sequential ray tracing we first obtain channel impulse responses for each point over the user movement trajectories and then express path loss and delay spread as a function of distance through curve fitting. Our results demonstrate large variations in received power. In system design this necessitates the use of adaptive schemes where transmission parameters can be selected according to channel conditions. To demonstrate the benefits of link adaptation over a mobile VLC channel we propose an adaptive system with luminary selection and demonstrate improvements in spectral efficiency over non-adaptive systems.
Citation Count: 2
Modeling of Visible Light Channels and Performance Analysis of ACO-OFDM
(IEEE, 2015) Yeşilkaya, Anıl; Alsan, Hüseyin Fuat; Miramirkhani, Farshad; Panayırcı, Erdal; Şenol, Habib; Uysal, Murat
Spectrum scarcity of traditional radio communication has led communication engineers to find new alternatives. Indoor visible light communication is one alternative to solve this problem since its spectrum is not regulated and it has much wider bandwidth then traditional communication systems. This increased the research done in the field of visible light communications. However a proper indoor channel model is lacking and all previous studies assumes that only additive white Gaussian noise (AWGN) is present. Lack of proper channel model has motivated us to model a realistic indoor visible light channel. After modeling the indoor visible light channel the performance of an asymmetrically clipped optical OFDM (ACO-OFDM) system which is suitable for optical communications is investigated and compared to that of the AWGN optical channels.
Citation Count: 11
Novel Channel Models For Visible Light Communications
(Spie-Int Soc Optical Engineering, 2015) Miramirkhani, Farshad; Uysal, Murat; Panayırcı, Erdal
In this paper we investigate channel modeling for visible light communications (VLC) using non-sequential ray tracing simulation tools. We create three dimensional realistic simulation environments to depict indoor scenarios specifying the geometry of the environment the objects inside the reflection characteristics of the surface materials as well as the characteristics of the transmitter and receivers i.e. LED sources and photodioes. Through ray tracing simulations we compute the received optical power and the delay of direct/indirect rays which are then used to obtain the channel impulse response (CIR). Following this methodology we present CIRs for a number of indoor environments including empty/furnished rectangular rooms with different sizes and wall/object materials (e.g. plaster gloss paint wood aluminum metal glass) assuming deployment of both single and multiple LED transmitters. We further quantify multipath channel parameters such as delay spread and channel DC gain for each configuration and provide insights into the effects of indoor environment parameters (e.g. size wall/object materials etc.) transmitter/receiver specifications (e.g. single vs. multiple transmitters location rotation etc.) on the channel.
Citation Count: 92
Optical MIMO-OFDM With Generalized LED Index Modulation
(IEEE-INST Electrical Electronics Engineers Inc, 2017) Yeşilkaya, Anıl; Basar, Ertugrul; Miramirkhani, Farshad; Panayırcı, Erdal; Uysal, Murat; Haas, Harald
Visible light communications (VLC) is a promising and uncharted new technology for the next generation of wireless communication systems. This paper proposes a novel generalized light emitting diode (LED) index modulation method for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based VLC systems. The proposed scheme avoids the typical spectrum efficiency losses incurred by time- and frequency-domain shaping in OFDM signals. This is achieved by exploiting spatial multiplexing along with LED index modulation. Accordingly real and imaginary components of the complex time-domain OFDM signals are separated first then resulting bipolar signals are transmitted over a VLC channel by encoding sign information in LED indexes. As a benchmark we demonstrate the performance analysis of our proposed system for both analytical and physical channel models. Furthermore two novel receiver designs are proposed. Each one is suitable for frequency-flat or selective channel scenarios. It has been shown via extensive computer simulations that the proposed scheme achieves considerably better bit error ratio versus signal-to-noise-ratio performance than the existing VLC-MIMO-OFDM systems that use the same number of transmit and receive units [LEDs and photo diodes (PDs)]. Compared with the single-input single-output (SISO) DC biased optical (DCO)-OFDM system both spectral efficiency and DC bias can be doubled and removed respectively simply by exploiting a MIMO configuration.
Citation Count: 0
Performance of MIMO Enhanced Unipolar OFDM With Realistic Indoor Visible Light Channel Models
(Institute of Electrical and Electronics Engineers Inc., 2016) Yeşilkaya, Anıl; Miramirkhani, Farshad; Basar, Ertugrul; Panayırcı, Erdal; Uysal, Murat
Visible light communication (VLC) involves the dual use of illumination infrastructure for high speed wireless access. Designing such optical based communication systems realistic indoor optical channel modeling becomes an important issue to be handled. In this paper first we obtain new realistic indoor VL channel characterizations and models in a multiple-input multiple-output (MIMO) transmission scenario using non-sequential ray tracing approach for the channel impulse responses (CIRs). Practical issues such as number of light emitting diode (LED) chips per luminary spacing between LED chips objects inside the room and cabling topology are also investigated. On the other hand since indoor optical channels exhibit frequency selectivity multi-carrier communication systems particularly orthogonal frequency division multiplexing (OFDM) is used to handle the resulting inter-symbol interference in VLC systems. Hence we propose a new MIMO-OFDM based VLC system called MIMO enhanced unipolar OFDM (MIMO-eU-OFDM) by combining MIMO transmission techniques with the recently proposed eU-OFDM scheme. The bit error rate (BER) performance of the proposed system is investigated in the presence of the 2×2 and 4×4 realistic MIMO VLC channels and its BER performance is compared with the reference optical MIMO-OFDM systems. © 2016 IEEE.