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Two-Dimensional (2-D) Spatial Domain Modulation Methods for Unipolar Pixelated Optical Wireless Communication Systems

Pixelated two-dimensional (2-D) optical wireless communication systems (OWCS), with intensity-modulation and direct-detection (IM/DD), modulate the data to be transmitted, into image intensities at the transmitter. The image is passed through an optical channel, and is captured at the receiver, then demodulated into received data. In traditional one-dimensional (1-D) IM/DD OWCS, the proposed schemes modulate the output signal either in the time-domain, such as in single-carrier modulation, or in the frequency-domain, such as in orthogonal frequency-division multiplexing (OFDM). In contrast to 1-D systems, the previously proposed 2-D pixelated OWCS, use frequency-domain modulation (FDM) only, overlooking space-domain modulation (SDM). FDM benefits from the ability to control the output signal's spectrum, though suffers from high peak-to-average power ratio (PAPR), and high computational complexity at the transmitter. In this study, we propose a new SDM-based, 2-D pixelated OWCS, which maintains low PAPR and low computational-complexity at the transmitter side, while enabling efficient spectral-control of its output signal. After a definition of a general scheme for the proposed SDM, we present three signal examples, suitable for three typical channels. Analysis of the spectral content of those output signals is performed, demonstrating the spectral control ability, and their resulted lower PAPR. Simulation results of the proposed SDM methods, as well as a common reference FDM method, the spatial asymmetrically-clipped optical OFDM, are presented. Although showing minor performance disadvantage for typical average power limited channels, the proposed SDM methods show significant performance advantage for peak limited channels, while maintaining, in all cases, flexibility in dimensions, to meet the target screen size, significantly lower PAPR, and lower transmitter side computational complexity.