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Received Aug 17, 2017; Revised Jan 21, 2018; Accepted Feb 7, 2018
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1. Introduction
Optical wireless communication is receiving more and more attentions from many researchers in recent years. Due to the high demand of wireless technologies, wireless data traffic in telecom network is tremendously increasing, and overutilization of the conventional RF spectrum is becoming a big challenge. To tackle the challenge of this RF spectrum crunch, utilizing the optical spectrum for wireless communication is popularly considered to be a potential remedy. The optical spectrum intended for this application can offer wide unregulated bandwidth compared to the conventional RF spectrum. Moreover, optical wireless communication (OWC) is not easily affected by electromagnetic interference and has excellent security features [1]. The advancement of cost-effective solid state lighting technologies creates a huge motivation towards visible light communication along with illumination purpose at the same time [2]. Intensity modulation and direct detection (IM/DD) technique is the best candidate for developing low-cost OWC using the shelf transmitters and receivers.
Due to its potential of combating intersymbol interference (ISI), orthogonal frequency division multiplexing (OFDM) is confirmed as the best candidate for high speed OWC [3, 4]. The conventional complex bipolar OFDM scheme cannot be used directly for IM/DD-based OWC. Therefore, the conventional OFDM signal should be changed in to real and positive unipolar OFDM signal to make it suitable for the IM/DD system [4–9]. DCO-OFDM and ACO-OFDM are widely accepted unipolar OFDM schemes proposed for OWC on literatures [4–8]. Because of the imposed Hermitian symmetry in signal generation stage, both schemes waste 50% of the available bandwidth.
DCO-OFDM [4–6] uses additional DC bias to obtain a positive unipolar signal. But, adding a DC bias on the information signal reduces energy efficiency of the system; hence, DCO-OFDM is an energy inefficient modulation scheme. On the contrary, ACO-OFDM [6–8] avoids a DC bias and generates a positive unipolar signal by utilizing only odd subcarriers. Since all of the even subcarriers and half of the odd subcarriers are wasted on the process, ACO-OFDM provides poor spectral efficiency compared to DCO-OFDM. In [10], we proposed...