Square-Wave Spatial Optical Orthogonal Frequency-Division Multiplexing

Visible light communication (VLC) systems leverage illumination devices, such as light-emitting diodes (LEDs), to serve a dual role as indoor high-speed communication downlinks. Though high data rates are possible using orthogonal frequency-division (OFDM) in VLC systems, the impact on the complexity and luminous efficacy of the luminaire remain among the key challenges. In this paper, square-wave spatial optical OFDM (SW-SO-OFDM) is proposed which transmits an OFDM signal using $G$ square-wave subcarriers from $G$ LED groups and allowing them to sum in space. Using a binary-level square-wave carrier signal eliminates the need for digital-to-analog conversion, non-linear pre-distortion hardware and the transmitter inverse Fourier transform, thereby greatly reducing the complexity of the transmitter in the luminaire. Further, by coordinating the binary transmissions from pairs of LED groups, SW-SO-OFDM can transmit multi-level constellations, which further improves the bandwidth efficiency. Through simulation and experiment, SW-SO-OFDM is shown to provide communication performance comparable to SO-OFDM and to significantly outperform conventional DC-biased (DCO)-OFDM at high signal-to-noise ratios, while considerably reducing the overall transmitter complexity in the luminaire.