Spatial Multiplexing and Diversity Techniques for Multiple-Element Optical Wireless Links

Spatial degrees of freedom in optical wireless channels can be exploited to multiplex data or to improve reliability. A short-range MIMO optical wireless system is presented which combines spatial discrete multitone modulation with digital halftoning to produce binary-level transmit images. An experimental prototype pixelated wireless optical channel is constructed and a rate of 450 Mbps is predicted for a 1 m link with 0.5 megapixel arrays at a frame rate of 7 kiloframes/sec. In long-range turbulent links, a novel receiver based on digital micro-mirror devices (DMD) is presented to provide spatial diversity by estimating the focal-plane signal distribution due to atmospheric turbulence. The performance of the DMD receiver is analyzed on a time-varying channel model rather than the “frozen atmosphere” model conventionally used. Symbol-error rates are simulated for a photon counting channel and show an improvement of about 3 dBo over a single-detector receiver.