Yazar "Ozen, Ali" seçeneğine göre listele

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    Öğe
    A Comparative Performance Analysis of Different Modulations in IM/DD Wireless Communication Systems
    (Ieee, 2023) Avci, Busra; Aykiri, Gazihan; Ozen, Ali
    In this paper, the performances of the ACO-OFDM waveform, one of the optical OFDM waveforms developed for IM/DD wireless communication systems, are analyzed in the multipath fading ceiling bounce optical channel environment with different modulations such as M-CSK and M-QAM modulations. Channel coding techniques such as Reed Solomon (RS) and 1/2 rate convolutional encoder (CC) are utilized to improve the bit error rate (BER) performance of the ACO-OFDM waveform. The performances of the RS and 1/2 CC encoded ACO-OFDM waveform using M-CSK and M-QAM modulations are compared over the BER-SNR performance metric in the 5-tap ceiling bounce wireless optical channel environment. From the produced numerical results, it is seen that nearly 2.5 dB SNR difference occurs between M-CSK and M-QAM modulations. Also, it is observed that 1/2 CC channel coding is approximately 2-3 dB better than RS channel coding.
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    Öğe
    A Novel DC Biasless Optical OFDM Waveform Design
    (Ieee, 2023) Kepezkaya, Talat; Ozen, Ali
    As a solution to the energy inefficiency problem of DC biased optical OFDM (DCO-OFDM) waveform, one of the optical OFDM (O-FDM) waveforms developed for new generation optical wireless communication systems, DC bias-free DCO-OFDM (DC Biasless O-OFDM) waveform is suggested by this study. The proposed waveform is compared with DCO-OFDM, NDC-O-OFDM and ACO-OFDM waveforms in AWGN and flat optic LOS channel environments over the BER-SNR and SE-SNR performance criteria. From the acquired performances, it is perceived that the recommended DC Biasless O-OFDM waveform gives an SNR gain of approximately 8 to 13 dB at 1E-4 BER value without sacrificing the spectral efficiency.
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    Öğe
    A novel Flip-OFDM optical communication system based on lazy lifting wavelet transform for intensity modulated direct detection
    (Natl Inst Optoelectronics, 2023) Temurtas, Sinem; Toprakci, Gamze; Ozen, Ali
    In this article, a novel optical OFDM (LLWT Flip-OFDM) waveform based on Lazy Lifting wavelet transform (LLWT) is recommended to enhance the success of Flip-OFDM communication system, which is one of the optical OFDM methods used in visible light communication systems. In the proposed scheme, superior advantages of LWT transform such as ICI and ISI suppression capabilities because of its good time-frequency localization properties and orthonormal structure are utilized, unlike fast Fourier transform (FFT). In order to confirm the success of the proposed waveform through the bit error rate (BER) achievement benchmark, computer simulation studies are executed in the indoor multipath optical channel and underwater multipath optical channel environment. It is perceived from the acquired results that with the suggested LLWT Flip-OFDM communication scheme, 7.5 dB SNR gain is achieved against the Flip-OFDM communication system and 22.5 dB SNR improvement is performed versus the VLC-OFDM communication system.
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    Öğe
    A novel optical OFDM waveform design for visible light communication system
    (Gazi Univ, Fac Engineering Architecture, 2024) Maras, Meryem; Ozen, Ali
    In this study, a new spread-based optical OFDM waveform is proposed for IM/DD communication systems. The proposed waveform is a combination of the spreading technique and the Flip OFDM waveform. Simulation studies are carried out to evaluate the performance of the proposed s-Flip-OFDM waveform and compare it with optical OFDM waveforms such as Flip OFDM, DCO-OFDM and VLC-OFDM. Figure A. The block diagram of the proposed spread optical OFDM waveform Purpose: The aim of this study is to combine optical OFDM waveforms with the spreading technique previously used in RF systems. The use of the spreading technique in the Flip-OFDM waveform, one of the multi-carrier optical wireless communication schemes, and in other optical OFDM waveforms such as DCO-OFDM and VLC-OFDM is proposed this study for the first time in the literature. Theory and Methods: The transmitter-receiver block diagram of the optical OFDM system using the proposed spreading method is shown in Figure A. In the transmitter side of the optical OFDM system shown in Figure A, randomly generated serial input data is subjected to propagation in the Spreading Block. The spreaded data is then modulated with BPSK modulation in the M-ary Modulator Block. The desired optical OFDM data packets are then generated in the Optical OFDM Modulator Block. In this study, Flip-OFDM waveform, one of the most important optical OFDM waveforms in the literature, is used. The generated flip OFDM data packets are transmitted via LEDs over a multipath fading optical channel and reach to the receiver after being corrupted by additive white Gaussian noise (AWGN). After the distorted signals reaching the receiver are restored with appropriate time domain or frequency domain equalizers, the reverse process is applied at the transmitter to obtain the signals decided at the output of the M-ary De-ModulatorBlock. Finally, the desired performance metrics such as BER and PAPR are calculated using the de-spreading data. Results: When the obtained simulation results are analyzed, from the numerical results, it is observed thatthe spreading technique provides SNR gains in the range of 5 to 10 dB to the performance of optical OFDM waveforms. It is found that the proposed s-Flip-OFDM waveform is approximately 10 dB better than the s-DCO-OFDM waveform and 15 dB better than the s-VLC-OFDM waveform in AWGN channel environment and diffuse multipath optical channel environments. Conclusion: In this article, significant gains were obtained in BER performances in all optical channel environments thanks to the proposed method. The hardware complexity of the proposed waveform is negligible compared to other waveforms. It can be concluded that the proposed s-Flip OFDM waveform may be one of the best waveform schemes for optical wireless communication systems for future 6G and beyond applications
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    Öğe
    Improving the BER and PAPR performances of conventional OFDM waveform with sequential LLWT-PTS-AC method
    (Gazi Univ, Fac Engineering Architecture, 2024) Tengizler, Bekir; Caliskan, Efe Kaan; Gulbaz, Alihan; Ozen, Ali
    Purpose: In this study, it is suggested to combine PTS and AC methods with LWT transform using Lazy wavelet to reduce PAPR in wireless communication systems using classical OFDM waveform. A new method combining the PAPR improvement provided by PTS and AC techniques on multi-carrier Communication systems and the BER performance provided by LWT is presented in this study. Theory and Methods: The proposed method is given in Figure A. In Figure A, randomly generated serial input data is modulated in the M-Ary Modulation Block. It is then propagated by applying the inverse Lifting wavelet transform to the data modulated in the ILWT Block. Next, in the PTS Block, the phases of emittedsymbols are changed. Then the phase-changed signals are subjected to IFFT processing. After the IFFT process, the signal with the lowest PAPR value is selected and transmitted to the AC Block by adding CP in the CP+ Block. The produced waveform after clipping processes in the AC Block is sent from the frequency selective channel and reaches the receiving side after the AWGN is distorted. The desired performance criteria are calculated by using the data obtained at the output of the M-Ary De-Modulation Block by applying the opposite of the operations on the transmitter side on the receiver side. Results: When the obtained PAPR results are analyzed, it is understood that the suggested waveform for the 1E-3 PAPR value is 0.5 dB better than the PTS-AC-OFDM waveform and 8 dB better than the K-OFDM waveform. In addition, when the BER performances are examined, it is observed that the suggested waveform for the 1E-4 BER level is 6 dB better than the PTS-AC-OFDM and K-OFDM waveforms. Conclusion: In this article, significant gains were obtained in both BER performances and PAPR performances thanks to the proposed method. Thus, despite the slightly increased computational complexity, the proposed LLWT-PTS-AC-OFDM method has yielded a high-performance next-generation OFDM waveform in this study.
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    Öğe
    Improving the BER and PAPR performances of optical OFDM with lazy lifting wavelet transform
    (Springer, 2023) Kepezkaya, Talat; Ozen, Ali
    Visible light communication (VLC), which is seen as an alternative and complementary technology to radio frequency (RF) communication systems, has emerged as a promising new generation system. Because of its potential to combat inter-symbol interference (ISI), orthogonal frequency division multiplexing (OFDM) has been validated as the best candidate for high-speed optical wireless communications (OWC). Asymmetrically clipped optical OFDM (ACO-OFDM), DC-biased optical OFDM (DCO-OFDM), and Flip-OFDM, which are made suitable for intensity modulation/direct detection (IM/DD) systems, are unipolar OFDM schemes widely accepted for OWC in the literature. In this study, it is proposed to combine the lifting wavelet transform (LLWT), which uses the lazy wavelet, with these three optical OFDM waveforms to increase the performance of the ACO-OFDM, DCO-OFDM, and Flip-OFDM systems proposed for OWC systems. In the environment where M-level color shift keying (M-CSK) and M-level quadrature amplitude modulation (M-QAM) modulations are used, proposed waveforms are tested with computer simulations for bit error rate (BER) and peak average power ratio (PAPR) performance measures. From the obtained simulation results, it is observed that the proposed transform technique performs an approximately 6 dB SNR improvement on the waveforms investigated in this study in both modulation methods for the 1E-4 BER value.
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    Öğe
    Improving the performance of non-DC-biased optical OFDM with lazy lifting wavelet transform
    (Springer, 2024) Ayvaz, Elif Nur; Ozen, Ali
    In recent years, the lifting wavelet transform (LWT) has been used in image and signal processing applications to overcome many of the shortcomings of the classical discrete wavelet transform (DWT). The LWT is a simplified and most efficient version of the classical discrete wavelet transform. To address the issue of energy inefficiency in the direct current-biased optical OFDM (DCO-OFDM) waveform, the literature proposes the use of the non-direct current-biased optical OFDM (NDC-O-OFDM) waveform, which does not require the addition of DC bias. Firstly, this paper proposes improving the performance of the NDC-O-OFDM waveform by combining it with the LWT using the lazy wavelet (LLWT). However, the literature proposes the use of the generalized LED index modulation OFDM (GLIM-OFDM) waveform as a solution to the spectrum inefficiency problem of the NDC-O-OFDM waveform. As a second contribution, this paper presents the combination of the GLIM-OFDM waveform with the LLWT transform to enhance the performance of the GLIM-OFDM waveform. Numerical simulations were performed to evaluate the performance of the proposed LLWT-NDC-O-OFDM and LLWT-GLIM-OFDM waveforms in terms of bit error rate (BER) in 2 x 2 and 4 x 4 optical MIMO channel environments. The results show that the proposed waveforms provide a gain of approximately 6.5 dB over both the NDC-O-OFDM and GLIM-OFDM waveforms, and a gain of 13.5 dB over the DCO-OFDM waveform, while maintaining the same BER requirement of 1E-4 and modulation order of BPSK in both 2 x 2 and 4 x 4 optical MIMO channel scenarios. Thus, despite some increase in computational complexity due to LWT implementation, a spectrum and energy efficient high performance optical OFDM waveform is achieved with the proposed LLWT transform in this work.