Delay spreads and channel dynamics measurements at ISM bands

Abstract

In 1985, the FCC authorized low power (less than 1 watt), license-free spread-spectrum radio transmissions in several ISM (Industrial, Scientific, and Medical) bands, resulting in a growing spread spectrum indoor radio industry. In order to understand the potential of indoor radio systems as communication media between portable computers and local area networks, we built a wideband indoor radio propagation measurement apparatus at IBM Yorktown Research Center. The apparatus operates in the ISM bands centered around 910 MHz, 2.44 GHz, and 5.8 GHz. We first briefly describe our measurement apparatus, our measurement procedures, and the measurement areas we chose in an academic environment, Columbia University. Complex multipath delay profiles were recorded in classrooms, small-room offices, open-layout offices, an auditorium, a library, and a machine room. From the multipath data we collected we found that most of the delay spreads are under 100 nscc, with a median level under 50 usec. Delay spread over all measurement areas shows a small dependence on distance. We have also measured channel dynamics. Here we observed a fast channel change when the transmitter antenna was being moved at a moderate speed of I ft/sec. The fast change of the propagation channel was identified to come from a fast change in the phase portion of the measured complex impulse response profiles. The effects of both delay spread and channel dynamics on designing high speed indoor radio data transmission scheme are discussed.