Showing papers by "Theodore S. Rappaport published in 1990"

900-MHz multipath propagation measurements for US digital cellular radiotelephone

Abstract: The results of multipath power delay profile measurements of 900-MHz mobile radio channels in Washington, DC, Greenbelt, MD, Oakland, CA, and San Francisco, CA, are presented. The measurements have focused on acquiring worst-case profiles for typical operating locations. The data reveal that at over 98% of the measured locations, root mean square (RMS) delay spreads are less than 12 mu s. Urban areas typically have RMS delay spreads on the order of 2-3 mu s and continuous multipath power out to excess delays of 5 mu s. In hilly residential areas and in open areas within a city, RMS delay spreads are slightly larger, typically having values of 5-7 mu s. In very rare instances, reflections from city skylines and mountains can cause RMS delay spreads in excess of 20 mu s. The worst-case profiles show resolvable diffuse multipath components at excess delays of 100 mu s and amplitudes 18 dB below that of the first arriving signal. >

Indoor wideband radiowave propagation measurements at 1.3 GHz and 4.0 GHz

Abstract: Measured impulse response estimates of radio channels have been used to determine time delay spread and path loss characteristics inside four buildings using different antenna heights at 1.3 GHz and 4.0 GHz. RMS delay spread values were found to be dependent on building and local topography, but generally independent of frequency and antenna height. Path loss values were found to be nearly independent of frequency.

Effects of path loss and fringe user distribution on CDMA cellular frequency reuse efficiency

Abstract: Expressions that quantitatively describe the impact of path loss and user distribution on CDMA (code division multiple access) cellular radio system performance are determined. Path loss in typical microcellular and cellular channels is shown to increase exponentially with distance, to between the second and third power, as opposed to the commonly quoted fourth power law. Two performance measures, frequency reuse efficiency and bit error rate probability, are evaluated for CDMA cellular systems. Values for frequency reuse efficiency are derived for the uplink using different propagation rules and spatial distributions of subscribers in adjacent cells. Bit error rate probabilities are found as a function of the number of users for a two-cell downlink model that assumes the subscriber is straddling the cell boundaries. >

Path loss and multipath delay statistics in four European cities for 900 MHz cellular and microcellular communications

Abstract: Typical and worst case channel path loss, RMS delay spreads, and excess delay spreads (10dB down) at 900MHz in four European cities using typical cellular and microcellular antenna locations are presented. It is shown that a change in reference distance from 1 km to 100 m can change the perceived propagation power law exponent from 3.0 to 2.7, where free space propagation is assumed from the transmitter to the reference distance. This is a significant result, since the path loss directly affects the frequency reuse efficiency in CDMA spread spectrum systems. Measured data show that for microcellular sites, RMS delay spreads are less than 2 μs, with excess delay spreads (10dB) less than 6 μs. At typical cellular locations with high base antennas, RMS delay spreads are generally less than 8 μs and excess delay spreads (10dB) are less than 16 μs. Worst case measurements resulted in a RMS delay spread of 19.6 μs and an excess delay spread of 51.3 μs.

Simulation of UHF indoor radio channels for open-plan building environments

Abstract: A software channel simulator for UHF indoor radio channels in open-plan buildings is introduced. The simulator is based on wideband statistical models of individual multipath component amplitudes and delays. The simulator creates closely spaced channel impulse responses for both line-of-sight (LOS) and obstructed (OBS) topographies. The effects of transmitter-receiver (T-R) distance and the correlation of individual multipath component amplitudes over time and space are incorporated in the simulation. the simulator has been extended to yield narrowband fading over small distances by synthesizing the phases of multipath components. Multipath power delay profiles, RMS delay spread distributions, and narrowband fading distributions produced by the simulator accurately portray typical radio channels in a variety of open-plan building environments. >

Indoor wideband radio propagation measurement system at 1.3 GHz and 4.0 GHz

Abstract: The development and operation of a dual-band time-domain radar system used to measure indoor multipath propagation characteristics in several office buildings and factories are described. The system operates at 1.3 GHz and 4.0 GHz and uses 4-ns RMS pulses to provide estimates of indoor radio channel impulse responses. The effects of antenna diversity, frequency scaling, and topography on indoor radio system design are quantified through analyses of measured propagation data. The data are used to develop and refine wideband channel models for multipath propagation in factories and open-plan office buildings and provide insight into the validity of geometric modeling techniques for predicting channel characteristics. >

Development of an autonomous guided vehicle for indoor propagation measurements

Abstract: At Virginia Tech, an autonomous guided vehicle (AGV) has been developed for use in indoor propagation measurements and for a research/teaching tool in the Computer Integrated Manufacturing Laboratory. The AGV design strategy, navigation methodology, and a calibration technique used to minimize path errors caused by unequal wheel radii in dead-reckoning navigation are described. The basic geometry of dead-reckoning navigation is developed, with a particular emphasis on the use of a calibration run to yield exact wheel radii and steering correction factors for use in navigation. These techniques were used on an actual AGV, and measurements were taken under operating conditions to determine navigation accuracy. The major limitation in dead reckoning comes from improper estimates of wheel radii. This can be compensated for with a calibration run, but the tire radius may still change due to dynamic conditions such as redistribution of vehicle weight during cornering, and inexact manufacturing of the tires themselves. Measurements of vehicle position through use of calibrated dead reckoning show accurate vehicle position to within a few cm along a 10 m path. >

A single-hop F/sub 2/ propagation model for frequencies above 30 MHz and path distances greater than 4000 km

Abstract: Standard textbook explanations of ionosphere propagation suggest that 30 MHz and 4000 km are the limiting frequency and distance for single-hop communications. During the peak of sunspot cycle 22, however, there have been hundreds of reports of F/sub 2/ communications exceeding great-circle distance of 4200 km at 50 MHz. It is shown that parabolic F/sub 2/ ionospheric models explain this propagation irregularity, although textbooks and reference books fail to show that such long distances at VHF are possible. >