Imaging diversity receivers for high-speed infrared wireless communication

We discuss two modifications to the design of wireless infrared links that can yield significant performance improvements, albeit at the price of increased complexity. In line-of-sight and non-line-of-sight links, replacement of a single-element receiver by one employing an imaging light concentrator and a segmented photodetector can reduce received ambient light noise and multipath distortion. For a fixed receiver entrance area, such an imaging receiver can reduce transmit power requirements by as much as about 14 dB, depending on the link design and the number of photodetector segments. Imaging receivers also reduce co-channel interference, and may therefore enable infrared wireless networks to employ space- division multiplexing, wherein several transmitters located in close proximity can transmit simultaneously at the same wavelength. In nondirected non-line-of-sight links, replacement of the diffuse transmitter by one that projects multiple narrow beams can reduce the path loss, further reducing the transmit power requirement by several decibels. We describe the design of an experimental 100 Mb/s infrared wireless link employing a multibeam transmitter and a 37-pixel imaging receiver.