A Pixelated MIMO Wireless Optical Communication System

This paper introduces the pixelated wireless optical channel, which transmits data at high rates using a series of coded time-varying images. This multiple-input/multiple-output point-to-point wireless optical channel uses arrays of optical intensity transmitters and detectors to exploit the inherent spatial degrees of freedom and to realize significant gains in spectral efficiency over single-element systems. Spatial discrete multitone modulation is introduced as a means to combat low-pass spatial distortion and to alleviate spatial alignment problems of previous systems. The capacity of pixelated wireless optical channels is estimated by way of a water-pouring spectrum. A proof-of-concept experimental prototype is constructed using a $512\times 512$ pixel liquid crystal display panel and $154\times 154$ pixels of a charge-coupled device camera. A channel model is developed and the capacity estimated to be 22.4 kb/frame. An unoptimized multilevel code and multistage decoder is applied over the spatial frequency bins and shown to yield spectral efficiencies of approximately 1.7 $\text{kb}/\text{hz}$ over a range of 2 m.