High-speed non-directional infrared communication for wireless local-area networks

The use of wide-area infrared beams to establish high-speed digital links between portable terminals and a base station, allowing construction of in-building wireless local-area networks, is discussed. Key impairments to high-speed communication using nondirectional infrared links, namely, small received power in the face of potentially intense ambient infrared radiation and intersymbol interference caused by multipath optical propagation, are examined. Transmitter and receiver design strategies to achieve a high signal-to-noise ratio are discussed. Experimental measurements of multipath dispersion are presented, and the performance of two communication techniques that attempt to counter multipath distortion are evaluated. They are baseband on-off keying with adaptive decision-feedback equalization and multiple-subcarrier modulation