Wireless infrared communications

The use of infrared radiation as a medium for high-speed, short-range wireless digital communication is discussed. Currently available infrared links and local-area networks are described. Advantages and drawbacks of the infrared medium are compared to those of radio and microwave media. Physical characteristics of infrared channels using intensity modulation with direct detection (IM/DD) are presented, including path losses and multipath responses. Natural and artificial ambient infrared noise sources are characterized. Strategies for designs of transmitters and receivers that maximize link signal-to-noise ratio (SNR) are described. Several modulation formats are discussed in detail, including on-off keying (OOK), pulse-position modulation (PPM), and subcarrier modulation. The performance of these techniques in the presence of multipath distortion is quantified. Techniques for multiplexing the transmissions of different users are reviewed. Performance of an experimental 50-Mb/s on-off-keyed diffuse infrared link is described.