Modulation Schemes

Authored by: Tamás Cseh , Sujan Rajbhandari , Gábor Fekete , Eszter Udvary

Visible Light Communications

Print publication date:  June  2017
Online publication date:  July  2017

Print ISBN: 9781498767538
eBook ISBN: 9781315367330
Adobe ISBN:

10.1201/9781315367330-4

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Abstract

The visible light communication (VLC) systems use intensity modulation and direct detection (IM/DD). For IM/DD systems, the optical intensity must be a real value and nonnegative. As a result of the constraints of IM/DD, modulation schemes that are advantageous in radio frequency (RF) communications that may not offer the same advantage in VLC. For example, the orthogonal frequency division multiplexing (OFDM) scheme does not offer the same spectral and energy efficiencies as in the RF domain [1,2]. Depending upon available signal-to-noise ratio (SNR) and system nonlinearity, it is experimentally shown in [2,3] that pulse amplitude modulation (PAM) with decision feedback equalizer (DFE) can outperform complex modulation schemes such as OFDM. As a result, the baseband modulation schemes like PAM and pulse position modulation (PPM) are often the prime candidates for standards and industrial applications. On the other hand, an OFDM scheme is inevitability often the first choice to maximize the system capacity because of the feasibility to match the system spectral profile with the constellation mapping using bit and power loading. This chapter provides an overview of the modulation schemes applied in VLC systems. The description includes baseband modulations, multicarrier modulations, and special color-shift keying (CSK) for VLC.

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