Contents 1. Introduction
There has been a steadily growing interest concerning optical wireless communications by use of light in recent years. This technology is frequently referred to as visible-light communications (VLC). Research on VLC was pioneered by the group of Nakagawa at the Keio University, Japan, and the maturity of this technology recently triggered global standardization efforts within IEEE 802.15 [1]. High-speed data transmission by use of white LEDs gained interest after the advent of high-power white LEDs [2]–[4], and 100 Mbit/s transmission over short distances was recently demonstrated [5]. The modulation bandwidth of white LEDs is limited to 20 MHz and less [4], so that such high data rates can only be achieved by equalization [6], multiplexing, multi-level modulation [4], or a combination of all three. Furthermore, LEDs are notoriously nonlinear, a fact that affects the performance of such systems. The objective of the work presented here was to assess the impact of LED transfer function nonlinearity on VLC for quadrature amplitude modulation (QAM) on discrete-multitone (DMT) modulation by use of numerical simulations.
