Practical OFDM Signalling for Visible Light Communications Using Spatial Summation

Visible light communication (VLC) channels leverage solid-state illumination devices to provide a dual role as high-speed communication links. These channels are bandwidth-limited and can have high SNRs. Bandwidth-efficient intensity-modulated/direct-detection (IMlDD) orthogonal frequency-division multiplexing (OFDM) has been considered for VLC systems. Key drawbacks of OFDM in IM/DD channels are its high peak-to-average power ratio (PAPR) as well as the difficulty of implementing power efficient, high current, wideband drivers. In this paper, we propose a new form of IM/DD OFDM termed spatial optical OFDM (SO-OFDM) in which multiple narrowband OFDM signals are transmitted simultaneously from different LEDs and allowed to sum in space. In this way, a conventional OFDM receiver can be employed while having a series of lower power transmitters, each with improved PAPR. Simulation results show that in comparison with conventional IM/DD OFDM, SO-OFDM is more robust to amplifier nonlinearities and can be implemented with more efficient line driver topologies.