Yazar "Abdulkafi, Ayad Atiyah" seçeneğine göre listele

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    A new precoding scheme for spectral efficient optical OFDM systems
    (Elsevier Science Bv, 2018) Hardan, Saad Mshhain; Bayat, Oğuz; Abdulkafi, Ayad Atiyah
    Achieving high spectral efficiency is the key requirement of 5G and optical wireless communication systems and has recently attracted much attention, aiming to satisfy the ever increasing demand for high data rates in communications systems. In this paper, we propose a new precoding/decoding algorithm for spectral efficient optical orthogonal frequency division multiplexing (OFDM) scheme based visible light communication (VLC) systems. The proposed coded modulated optical (CMO) based OFDM system can be applied for both single input single output (SISO) and multiple input multiple-output (MIMO) architectures. Firstly, the real OFDM time domain signal is obtained through invoking the precoding/decoding algorithm without the Hermitian symmetry. After that, the positive signal is achieved either by adding a DC-bias or by using the spatial multiplexing technique. The proposed CMO-OFDM scheme efficiently improves the spectral efficiency of the VLC system as it does not require the Hermitian symmetry constraint to yield real signals. A comparison of the performance improvement of the proposed scheme with other OFDM approaches is also presented in this work. Simulation results show that the proposed CMO-OFDM scheme can not only enhance the spectral efficiency of OFDM-based VLC systems but also improve bit error rate (BER) performance compared with other optical OFDM schemes.
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    Öğe
    Efficient DC biased-PAM based OFDM for visible light communication system
    (Springer, 2022) Zaidan, Zahraa Mustafa; Bayat, Oğuz; Abdulkafi, Ayad Atiyah
    The need of high spectral efficiency to increase bandwidth utilization have been the main drivers for next generation optical wireless communication including visible light communication (VLC) systems. However, conventional optical techniques adopted Hermitian symmetry to satisfy the real and positive constraints of intensity modulation with direct detection based VLC systems on the cost of spectral efficiency loss. In this paper, a new direct current biased- pulse amplitude modulated based orthogonal frequency division multiplexing (DC-PAM-OFDM) is proposed to utilize all subcarriers without using Hermitian symmetry and hence provide more spectral efficiency for VLC systems. The proposed scheme ensures the real-valued optical signals by inserting PAM signal in frequency domain side of OFDM system, clipping, splitting, and rearranging the time domain signal instead of using Hermitian symmetry. This results in improving spectral efficiency by 100% compared to PAM based discrete multitoned modulation (DMT). In addition, theoretical analyses show that the proposed DC-PAM based OFDM scheme is more energy efficient than the PAM-DMT. Furthermore, simulation results show that the proposed scheme has better bit error rate performance and reduces the Peak-to-Average Power Ratio when compared with the existing methods under same spectral efficiency conditions.
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    Öğe
    Multilayered optical OFDM for high spectral efficiency in visible light communication system
    (Springer, 2019) Abdulkafi, Ayad Atiyah; Hardan, Saad Mshhain; Bayat, Oğuz; Uçan, Osman Nuri
    This paper presents two new schemes for improving the spectral efficiency of an optical orthogonal frequency-division multiplexing-based visible light communication (OFDM-VLC) system. The proposed schemes employed the generalized spatial modulation (GenSM) along with multi-input multi-output (MIMO) techniques as well as modified the coded modulation optical OFDM (CMO-OFDM) approach to attain more bandwidth utilization and higher spectral efficiency. The proposed multilayered/enhanced CMO-OFDM (LeCMO-OFDM) systems ensure the real-valued optical OFDM signals without using Hermitian symmetry and utilize the redundant codes existed in CMO-OFDM for further improvements in system's spectral efficiency while ensuring acceptable bit error rate (BER) performance. LeCMO-OFDM scheme transmits multilayer optical signals after converting them to unipolar form either by using DC bias (DC-LeCMO-OFDM) or by separating them through employing the GenSM with no DC bias (NDC-LeCMO-OFDM). We present analytical and simulation results to evaluate the effectiveness of the proposed systems and demonstrate the additional capacity gain in terms of spectral efficiency. In addition, the impact of the spacing distance between the light emitting diodes has been addressed. Detailed performance comparison in terms of spectral efficiency and BER between the proposed techniques and other recent works is provided for validation purpose. Finally, results show that our schemes can achieve better spectral and power efficiencies performance with acceptable BER performance when compared with the related methods.