Browsing by Author "Panayirci, E."

Now showing 1 - 9 of 9

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Channel modeling for visible light communications
(Springer Science+Business Media, 2016) Miramirkhani, Farshad; Uysal, Murat; Panayirci, E.; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad
In this chapter, we present a novel and realistic channel modeling approach for visible light communications that overcomes to 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 non-sequential 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.
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Generalized LED index modulation optical OFDM for MIMO visible light communications systems
(IEEE, 2016) Başar, E.; Panayirci, E.; Uysal, Murat; Haas, Harald; Electrical & Electronics Engineering; UYSAL, Murat; Haas, Harald
In this paper, we propose a generalized light emitting diode (LED) index modulation scheme for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) visible light communications (VLC) systems. The proposed scheme generalizes the LED index modulation concept by using the spatial multiplexing principle to transmit complex OFDM signals through VLC channels by separating these signals into their real-imaginary and positive-negative parts. The maximum a posteriori (MAP) estimator of the proposed scheme, which relies on quadratic programing (QP) problem, is presented for flat VLC channels. It is shown via computer simulations that the proposed scheme achieves considerably better error performance than the existing VLC-MIMO-OFDM systems due to its power efficiency and improved transceiver structure.
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IEEE 802.15.7r1 reference channel models for visible light communications
(IEEE, 2017) Uysal, Murat; Miramirkhani, Farshad; Narmanlioglu, Ömer; Baykas, T.; Panayirci, E.; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad; Narmanlioglu, Ömer
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.
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Information theoretical performance analysis and optimisation of cooperative underwater acoustic communication systems
(IEEE, 2016-05) Nouri, Hatef; Uysal, Murat; Panayirci, E.; Electrical & Electronics Engineering; UYSAL, Murat; Nouri, Hatef
In this study, the authors investigate the information theoretical limits on the performance of single-carrier cooperative underwater acoustic communication systems in the presence of intersymbol interference. The authors assume decode-and-forward relaying and consider orthogonal half-duplex cooperation. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise, the authors derive expressions for bounds on the individual and achievable rates for both cases where channel state information is available at the transmitter or not. Using these expressions, the authors optimise input signalling and relay location to maximise average achievable rates.
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A mobile channel model for vlc and application to adaptive system design
(IEEE, 2017-05) Miramirkhani, Farshad; Narmanlıoğlu, Ömer; Uysal, Murat; Panayirci, E.; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad; Narmanlıoğlu, Ömer
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.
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Optical MIMO-OFDM with generalized LED index modulation
(IEEE, 2017-08) Yesilkaya, A.; Basar, E.; Miramirkhani, Farshad; Panayirci, E.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad
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.
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Performance of MIMO enhanced unipolar OFDM with realistic indoor visible light channel models
(IEEE, 2016) Yesilkaya, A.; Miramirkhani, Farshad; Basar, E.; Panayirci, E.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad
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 multipleinput multiple-output (MIMO) transmission scenario, using nonsequential 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 (MIMOeU-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.
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Performance of MIMO enhanced unipolar OFDM with realistic indoor visible light channel models
(IEEE, 2016) Yesilkaya, A.; Miramirkhani, Farshad; Basar, E.; Panayirci, E.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad
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.
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Sparse channel estimation for OFDM-based underwater acoustic systems in rician fading with a new OMP-MAP algorithm
(IEEE, 2019-03-15) Panayirci, E.; Altabbaa, M. T.; Uysal, Murat; Poor, H. V.; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, a new channel estimation algorithm is proposed that exploits channel sparsity in the time domain for an orthogonal frequency division multiplexing (OFDM)-based underwater acoustical (UWA) communications systems in the presence of Rician fading. A path-based channel model is used, in which the channel is described by a limited number of paths, each characterized by a delay, Doppler scale, and attenuation factor. The resulting algorithm initially estimates the overall sparse channel tap delays and Doppler shifts using a compressed sensing approach, in the form of the orthogonal matching pursuit (OMP) algorithm. Then, a computationally efficient and novel channel estimation algorithm is developed by combining the OMP and maximum a posteriori probability (MAP) techniques for estimating the sparse complex channel path gains whose prior densities have complex Gaussian distributions with unknown mean and variance vectors, where a computationally efficient maximum likelihood algorithm is proposed for their estimation. Monte Carlo simulation results show that the mean square error and symbol error rate performances of the OMP-MAP algorithm uniformly outperforms the conventional OMP-based channel estimation algorithm, in case of uncoded OFDM-based UWA communications systems.