Selva Muratoğlu Çürük

Bio: Selva Muratoğlu Çürük is an academic researcher from Mustafa Kemal University. The author has contributed to research in topics: Estimator & Mean squared error. The author has an hindex of 3, co-authored 10 publications receiving 15 citations. Previous affiliations of Selva Muratoğlu Çürük include Middle East Technical University.

A novel approach for the design of pulse shaping filters

Abstract: In this work, we propose a new class of pulses for PAM type digital signals. The pulses are designed based on minimization of a figure of merit that is the product of the Cramer-Rao bound of the timing jitter variance and the mean eye closure rate. The new pulses are seen to yield significantly better performances as compared to the classical ones

The Impact of Configuration on Channel Characteristics in Visible Light Communication

Abstract: A featured research topic, Visible Light Communication (VLC), is the idea of using Light Emitting Diodes (LEDs), that are used for illumination, for data communication. Reliable communication in VLC systems, as well as in other communication systems, necessitates accurate knowledge of the channel. In this paper we are interested in the characteristics of indoor VLC channels under various configurations. The channel model used in simulations is based on modified Monte Carlo ray tracing algorithm, which is capable of obtaining channel impulse responses. As case studies, we consider a number of room environments with different dimensions and surface materials. We further consider scenarios with different transmitter numbers placed in various layouts. For these circumstances, we obtain channel impulse and frequency responses and present a channel characterization study where channel root mean square (rms) delay spread, maximum bit rate and coherence bandwidth parameters are evaluated. It is shown that, although the contribution of reflections increases if the room size is decreased or the reflectivity of the walls is increased, the frequency selectivity of the channel does not changed considerably. But as the receiver moves away from the source, an appreciable attenuation is noticed. Multiple transmitter is the most forceful factor that has impact on the channel frequency characteristics. Thus, multiple sources cause a fluctuation in the frequency band, and the shape of the fluctuation is related to the configuration of sources.

A simplified MAP channel estimator for OFDM systems under Rayleigh fading

Abstract: This paper presents a simplified Maximum A Posteriori (SMAP) channel estimator to be used in orthogonal frequency division multiplexing (OFDM) systems under the Rayleigh fading assumption for the subchannels, using a parametric correlation model and assuming that the channel is frequency selective and slowly time varying. Expressions for the mean-square error (MSE) of estimations are derived to evaluate the performance of the estimator. The relation between the correlation of subchannels taps and error variance is investigated. Dependencies of the proposed estimator's performance on the correlation parameter estimation error and signal-to-noise ratios (SNR) estimation error are analysed. We provide approximations on the estimator algorithms in order to make the estimator practical. The simulations done using measured channel data show that the proposed estimator with approximations operates satisfactorily with negligible loss in performance. Finally, we investigate the symbol error rate (SER) performance of an OFDM system using quadrature phase-shift keying (QPSK) modulation, based on channel estimation modes (a) training sequence (b) decision feedback and (c) pilot subcarriers. The results have indicated that the proposed estimator performance is always better than maximum likelihood (ML) estimator, and as the subchannel correlation increases (large number of subcarriers) the performance comes very close to that of exactly known channel case. Copyright © 2010 John Wiley & Sons, Ltd.

Simplified MAP Estimator for OFDM Systems Under Fading

Abstract: This paper presents a simplified maximum a posteriori (MAP) estimator, which yields channel taps in OFDM systems under fading conditions using a parametric correlation model, assuming that the channel is frequency selective, slowly time varying and Gaussian. Expressions for the variance of estimation error are derived to evaluate the performance of the MAP estimator. The relation between the correlation of subchannels taps and error variance and the effect of signal to noise ratio (SNR) are investigated. The performance of the simplified MAP estimator is analyzed using measured channel data. Approximations are developed in order to make the MAP estimator practical. The simulations show that the proposed estimator operates satisfactorily.

Alignment of transmitters in indoor visible light communication for flat channel characteristics

Abstract: Visible light communication (VLC) systems incorporate ambient lighting and wireless data transmission, and the experienced channel in indoor VLC is a major topic that should be examined for reliable communication. In this study, it is realized that multiple transmitters in classical alignment are the forceful factors for channel characteristics. In the frequency band, fluctuations with sudden drops are observed, where the fluctuation shape is related to the source layout and receiver location. These varying frequency‐selective channels need solutions, especially for mobile users, because sustained channel estimation and equalization are necessary as the receiver changes its location. It is proven that using light‐emitting diodes (LEDs) with highly directional beams as sources or using a detector with a narrow field of view (FOV) in the receiver may help partially alleviate the problem; the frequency selectivity of the channel reduces in some regions of the room. For flat fading channel characteristics all over the room, LEDs should be aligned in hexagonal cellular structure, and detector FOV should be arranged according to the cell dimension outcomes.

A Survey of Channel Modeling Techniques for Visible Light Communications

Abstract: Visible Light Communication (VLC) is a subset of Optical Wireless Communication (OWC) originally based on Light Emitting Diodes (LEDs) for data transmission in an imperceptible way to human vision. Thanks to its wide license-free bandwidth, high security, and its low cost, VLC becomes a revolutionary alternative to the Radio Frequency (RF) networks. This paper presents a comprehensive survey of VLC channel modeling techniques. It describes the main VLC channel components. It gives different channel models in indoor, outdoor, underwater, and underground environments. It draws a synthesis comparing the algorithms proposed in each environment. Moreover, the paper gives concluding remarks and future research directions for VLC channel models.

I-Q diagram utilization in a novel modulation classification technique for cognitive radio applications

Abstract: We report here on the utilization of signal in-phase-quadrature (I-Q) diagrams in a novel modulation classification (MC) technique. This MC technique is able to classify linear digital single-carrier modulations as well as multi-carrier modulations. The method uses the waveforms’ I-Q diagrams and, by employing a combination of k-center and k-means algorithms, determines the type of modulation. Implementation and refinement of the novel single-carrier modulation classification technique using the I-Q diagrams are discussed in detail. Further, a model for classification of multi-carrier signals is presented, including Gaussianity, cyclostationarity, and autocorrelation tests for further extracting orthogonal frequency division multiplexing signal parameters. Finally, results of this method are presented and compared to other classification methods, and the considerations for implementing the method in hardware are briefly discussed. As a future direction of this research, the performance of the algorithm in fading channels is an interesting topic to pursue.

Non-Line of Sight Visible Light Communications: A Technical and Application based Survey

Abstract: Visible Light Communication (VLC) do not suffer from electromagnetic interference and can be safely used in sensitive environments such as chemical plants, aircrafts and hospitals, as well as in high vehicle density VLC systems advantages of have high speed, greater power efficiency and a high spatial reuse ratio makes it a promising candidate for object allocation detection and V2V communication. This work review the need to assess the Non-Line of Sight propagation in VLC systems as the real applications have Line of Sight (LoS) and Non Line of Sight (NLoS) transmission. The challenges in VLC development and implementation are highlighted, and channel modelling of the NLoS VLC systems to ensure accuracy of channel capacity is discussed. Optimizing the configurations of VLC networks is important to overcome the challenges in VLC implementation and channel modelling. MIMO configurations in NLoS VLC systems coupled with suitable equalization techniques may be required to mitigate the high interference. BER, SNR and channel impulse response are some parameters that should be investigated to assess the performance of the NLoS VLC system.

A simplified MAP channel estimator for OFDM systems under Rayleigh fading

Abstract: This paper presents a simplified Maximum A Posteriori (SMAP) channel estimator to be used in orthogonal frequency division multiplexing (OFDM) systems under the Rayleigh fading assumption for the subchannels, using a parametric correlation model and assuming that the channel is frequency selective and slowly time varying. Expressions for the mean-square error (MSE) of estimations are derived to evaluate the performance of the estimator. The relation between the correlation of subchannels taps and error variance is investigated. Dependencies of the proposed estimator's performance on the correlation parameter estimation error and signal-to-noise ratios (SNR) estimation error are analysed. We provide approximations on the estimator algorithms in order to make the estimator practical. The simulations done using measured channel data show that the proposed estimator with approximations operates satisfactorily with negligible loss in performance. Finally, we investigate the symbol error rate (SER) performance of an OFDM system using quadrature phase-shift keying (QPSK) modulation, based on channel estimation modes (a) training sequence (b) decision feedback and (c) pilot subcarriers. The results have indicated that the proposed estimator performance is always better than maximum likelihood (ML) estimator, and as the subchannel correlation increases (large number of subcarriers) the performance comes very close to that of exactly known channel case. Copyright © 2010 John Wiley & Sons, Ltd.