Visible Light Communications Using OFDM and Multiple LEDs

Visible-light communication (VLC) systems leverage solid-state illumination devices to create high-speed communication links. Orthogonal frequency-division multiplexing (OFDM) has been considered for these intensity-modulated/direct-detection (IM/DD) optical channels, however, it suffers from high peak-to-average power ratio (PAPR). Moreover, the implementation of linear, power-efficient, high-current, wideband drivers is challenging. In this paper, the concept of spatial summing is developed where wideband, high PAPR OFDM signals are partitioned into many low-PAPR narrowband signals that are transmitted from multiple LEDs. The signals from different LEDs are allowed to sum in space before being detected by a conventional OFDM receiver. Spatial optical-OFDM (SO-OFDM) is proposed in which filtered subsets of carriers are emitted by each LED. In addition, low-PAPR optical single-carrier FDMA (OSC-FDMA) is developed where different collections of LEDs act as virtual users in a multiple-access scheme. The different variations of SO-OFDM and OSC-FDMA are compared to conventional DC-biased optical (DCO) OFDM and are shown to achieve lower PAPR and more robustness to LED nonlinearities leading to error rate performance gains at high signal-to-noise ratios.