EXPERIMENTAL CHARACTERIZATION OF NON-DIRECTED INDOOR INFRARED CHANNELS

We have experimentally characterized nondirected indoor channels that use intensity modulation and direct detection of an infrared carrier a t a wavelength of 832 nm. At several locations in each of five differe nt rooms, we have studied line-of-sight and diffuse link configuration s, with and without shadowing, amounting to a total of approximately 1 00 different channels. We have measured channel frequency responses ov er the 2-300 MHz range by using a swept-modulation frequency technique , and from these data, we have computed channel impulse responses, pat h losses and r.m.s. delay spreads. Using channel impulse responses, we have calculated power penalties induced by multipath intersymbol inte rference in baseband on-off-keyed links operating at bit rates of 10, 30 and 100 Mb/s, considering unequalized links and those employing zer o-forcing decision-feedback equalization. Unshadowed line-of-sight con figurations generally have smaller path losses, r.m.s. delay spreads a nd power penalties than their unshadowed diffuse counterparts. Shadowe d line-of-sight configurations, however, generally exhibit larger valu es of all three parameters than the corresponding shadowed diffuse con figurations. We show that among the channels measured here, there is a strong correspondence between channel r.m.s. delay spread and multipa th power penalty. Finally, we provide an analysis indicating why non-d irected infrared channels using intensity modulation and direct detect ion do not exhibit multipath fading, and justifying their representati on as linear, time-invariant systems.