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    Spectrally efficient hybrid radio frequency and visible light communication based on hermitian symmetery free with direct current biasing
    (Altınbaş Üniversitesi / Lisansüstü Eğitim Enstitüsü, 2023) Zaidan, Zahraa Mustafa Zaidan; Bayat, Oğuz
    To tackle the rapidly increasing demand for Internet services from mobile devices, network convergence is envisaged by integrating various technology domains. A recently proposed and promising strategy to indoor wireless communications is integrating the wireless fidelity (WiFi) and light fidelity (LiFi) namely a hybrid WiFi and LiFi networks (HWLNs). Such type of networks can handle the short comes of each standalone technology such as the spectrum congestion of WiFi and the limited area coverage of LiFi. In HWLNs, the WiFi sub-network follows the IEEE.802.11series standard applying quadrature amplitude modulation with orthogonal frequency division multiplexing QAM-OFDM to support high speed. While LiFi sub-network follows IEEE.802.11bb standard where OFDM-based modulation approaches are applied. In LiFi technology, light emitted diodes (LEDs) are applied as transmitters then only the signal intensity can be used to encode the information. Consequently, the signal needs to be real and unipolar at the input of LEDs. There are few spatialized approaches which account for this, including the most common PAM based discrete multitoned modulation (PAM-DMT) and direct current biased optical OFDM (DCO-OFDM). However, all of them achieve the real signal representation on the cost of halving the spectral efficiency as they impose the Hermitian symmetry. In this work, an optical OFDM approach named Hermitian symmetry free with direct current biasing (HSFDC) is proposed to increase the spectral efficiency of LiFi subnetwork by 100%. The proposed HSF-DC scheme applies clipping, splitting, and reordering on the pulse amplitude modulation based OFDM (PAM-OFDM) instead of imposing Hermitian symmetry to achieve the real signal representation, then a suitable DC-biasing is added to ensure the positivity of the signal. The energy efficiency of HSF-DC is manifested in the fact that it has the least Peak-to-Average Power Ratio (PAPR) and the best Bit Error Rate (BER) compared with the counterparts. The proposed HSF-DC is then integrated with QAM-OFDM to build a spectrally efficient HWLN with gain of 1.3 over QAM-OFDM/PAM-DMT and QAMOFDM/DCO. Finally, computer simulations show that the proposed hybrid QAMOFDM/HSF-DC has the best BER performance over stand-alone QAM-OFDM, hybrid QAM-OFDM/DCO and QAM-OFDM/PAM-DMT.