Abstract
In visible light communications (VLC), dimming control constitutes an indispensable technique to comply with various illumination necessities and with different energy consumption constraints. Therefore, a novel dimming compatible hybrid optical orthogonal frequency division multiplexing (DCHO-OFDM) is conceived in this paper to fulfil the requirements from communications and illuminations. Explicitly, the signal branch of the unclipped asymmetrically clipped O-OFDM (ACO-OFDM) and the down/upper-clipped pulse-amplitude-modulated discrete multitone (PAM-DMT) are adaptively amalgamated in order to increase the spectrum efficiency. For the sake of precisely achieving dimming control, the chromaticity-shift-free and industry-preferred pulse width modulation (PWM) is further invoked to the hybrid signal, assisted by a time-varying biasing scheme to mitigate the non-linear distortion. As the different signal components in DCHO-OFDM are beneficially combined in an interference-orthogonal approach, the transmitted symbols are able to be readily detected upon relying on a standard OFDM receiver, as that of ACO-OFDM. Our simulations demonstrate that a high spectrum efficiency of the conceived DCHO-OFDM scheme can be achieved with less fluctuation in a wide dimming range.
Highlights
Driven by the rapid development of light emitting diodes (LED), visible light communication (VLC) constitutes a promising part of next-generation wireless communications [1,2,3]
In order to evaluate the non-linear distortion, a pair of scaling factors β ACO and β PAM are defined as β ACO = ( Ih − Il )/σACO and β PAM = ( Ih − Il )/σPAM, where σACO and σPAM denote the standard variance of the unclipped ACO-OFDM and pulse-amplitude-modulated discrete multitone (PAM-DMT), respectively
Unlike the HACO-OFDM, the proposed OFDM scheme is capable of alleviating the undesired non-linear distortion in the presence of the non-linear transfer characteristic of LED
Summary
Driven by the rapid development of light emitting diodes (LED), visible light communication (VLC) constitutes a promising part of next-generation wireless communications [1,2,3]. To improve the spectrum efficiency, a negative HACO-OFDM (NHACO-OFDM) scheme was conceived in [22] for combining with the high level of PWM signal, which is further amalgamated with. As mentioned above, both the HACO-OFDM and LACO-OFDM require a successive demodulation operation, suffering from an increased receiver complexity Against this background, a novel dimming compatible hybrid optical OFDM (DCHO-OFDM) is conceived in this paper incorporating the PWM technique to realize high-spectral-efficiency transmission under various dimming levels, where the transmitted signal can be readily recovered upon relying on a standard receiver. The symbols transmitted by the proposed DCHO-OFDM can be readily detected upon relying on a standard OFDM receiver, which significantly reduces the complexity at receiver compared to the existing advanced transmission schemes, such as HACO-OFDM and LACO-OFDM.
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