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Öğe A Comparative Performance Analysis of Blind Equalization Algorithms in Single Carrier Visible Light Communications(Institute of Electrical and Electronics Engineers Inc., 2020) Yasar, Sabiha; Sinop, Hayriye; Tek, Yusuf İslam; Tuna, Elif Büşra; Karaerik, Kudret; Avci, Busra; Aykiri, GazihanIt is very important to estimate and equalize the multipath optical channel blindly in visible light communication (VLC) systems. It is recommended that it is used Constant Modulus Algorithm (CMA), modified CMA (M-CMA) and normalized CMA (N-CMA) algorithms, which are among the most commonly used blind equalization algorithms to eliminate inter-symbol interference (ISI) caused by a multipath optical channel in a closed environment in this paper. Computer simulations and comparative performance analysis of the algorithms mentioned above are performed over the Mean Square Error (MSE) and ISI performance metrics in stationary and non-stationary environment. It is observed that the best performances are obtained with M-CMA algorithm in MSE comparisons and the best performances are obtained with NCMA algorithm in ISI comparisons from the computer simulation results. © 2020 IEEE.Öğe A Novel ACO-OFDM System Based on Fast Walsh Hadamard Transform(Institute of Electrical and Electronics Engineers Inc., 2020) Avci, Busra; Aykiri, Gazihan; Karaerik, Kudret; Tuna, Elif Büşra; Yasar, Sabiha; Sinop, Hayriye; Tek, Yusuf İslamVisible Light Communication (VLC), an alternative to radio frequency (RF), was born as a promising technology. In VLC systems, orthogonal frequency division multiplexing (OFDM) has received much attention due to its high data rate, simple equalization and robustness against inter symbol interference (ISI). However, high peak to average power ratio (PAPR) and LED non-linearity have remarkable effects on the performance of indoor VLC-OFDM systems. Asymmetrically clipped optical OFDM (ACO-OFDM) is a technique that sacrifices spectral efficiency to transmit a unipolar frequency division multiplexed signal over a unipolar channel. In this study, fast Walsh Hadamard transform based ACO-OFDM (FWHT-ACO-OFDM) method is proposed to improve the performance of ACO-OFDM system by recovering this spectral efficiency. The performance of the proposed method is verified by computer simulation studies for bit error rate (BER) and PAPR performance criteria. From the simulation consequence, it is seen that the proposed method is better for both performance criteria than ACO-OFDM methods. © 2020 IEEE.Öğe A Novel Double Tree Complex Wavelet Transform OFDM Based on Fast Walsh Hadamard Transform(Institute of Electrical and Electronics Engineers Inc., 2020) Karaerik, Kudret; Tuna, Elif Büşra; Tek, Yusuf İslam; Sinop, Hayriye; Yasar, Sabiha; Avci, Busra; Aykiri, GazihanIn this paper, combining with the fast Walsh Hadamard transform (FWHT) to improve the performance of the double-tree complex wavelet transform (DTCWT) based OFDM technique developed to eliminate the disadvantages of the orthogonal frequency division multiplexing (OFDM) system is suggested. In order to test the achievement of the proposed DTCWT FWHT OFDM method, computer simulation studies are performed in AWGN and flat Rayleigh fading channel environments. In addition, peak to average power ratio (PAPR) simulations, which are one of the major disadvantages of the classical OFDM system, are also realized. From the achieved simulation results, it is seen that the suggested method has better performance than classical OFDM, Discrete Wavelet Transform (DWT) based OFDM and DTCWT OFDM techniques for both performance metrics. © 2020 IEEE.Öğe A Novel PAPR Improvement Approach for the Next Generation Waveforms(Institute of Electrical and Electronics Engineers Inc., 2020) Tek, Yusuf İslam; Tuna, Elif Büşra; Karaerik, Kudret; Sinop, Hayriye; Yasar, Sabiha; Avci, Busra; Aykiri, GazihanToday, the research for a new waveform for 5G and beyond wireless communication systems continues, with high spectral efficiency, high energy efficiency, low cost and less drawbacks of multi-carrier technologies. A novel peak to average power ratio (PAPR) improvement approach based on selected mapping (SLM) technique has been suggested in this paper. In this research, SLM technique is examined to improve the PAPR performance on alternative waveforms suggested in the literature for 5G and beyond. The examined method consists of a combination of alternative waveforms and selected mapping technique. This method has been tried on new generation waveforms for the PAPR reduction for the first time. In this study, the proposed method is applied to the zero-tail discrete Fourier transform spread OFDM (ZT DFT-S OFDM) and Unique Word OFDM (UW-OFDM) of alternative waveforms. Computer simulation works are executed to confirm and compare the proposed method on AWGN and flat Rayleigh fading channels. From the acquired simulation outcomes, it is seen that PAPR performance is improved. © 2020 IEEE.Öğe M-CSK and M-QAM Modulated DCO-OFDM for Visible Light Communication Systems(Institute of Electrical and Electronics Engineers Inc., 2022) Aykiri, Gazihan; Avci, Busra; Özen, AliVisible light communication (VLC), seen as an alternative and complementary technology to RF communication systems, has emerged as a promising new generation system. However, VLC systems face flicker problem. In this study, among the proposed methods for VLC systems, in order to increase the performance of a direct current biased optical OFDM (DCO-OFDM) system, DCO-OFDM with M level color shift keying (M-CSK) modulation, without flicker problem, (M-CSK DCO-OFDM) method is recommended. The proposed method is tested with computer simulations for bit error rate (BER) and peak to average power ratio (PAPR) achievement benchmark. From the acquired simulation outcomes, it is understood that the recommended scheme has better success than both M-CSK VLC-OFDM and M-QAM DCO OFDM schemes. © 2022 IEEE.
