Donald C. Cox

910 MHz Urban Mobile Radio Propagation: Multipath Characteristics in New York City

Small scale statistics of multipath propagation in a heavily built-up urban mobile radio environment are presented. The statistics cover vehicle travel distances on the order of 30 m along streets. Measuring equipment time delay resolution is about 0.1 μs. In some locations, paths with significant amplitudes are observed with excess delays of 9 to 10 μs. The delay spreads ( \sqrt{second central moment of power delay profile} ) in this environment are on the order of 2 μs. Often the signal at fixed delays has a Rayleighdistributed amplitude but large departures from the Rayleigh distribution also occur. From the measurements it appears reasonable to model the urban mobile radio channel as a Gaussian quasi-wide-sense stationary uncorrelated scattering channel within a bandwidth of 10 MHz and for intervals along the street of up to 30 m.

Portable digital radio communications-an approach to tetherless access

The evolution of current technologies that provide either wireless exchange access or access and communications to people away from their own telephones is outlined. A description is given of a proposed use of digital radio technology as a drop/distribution/loop technology for local exchange access and the integration of this radio technology with network intelligence to provide the added functionality of portability. Issues surrounding portable digital radio as an exchange access technology are discussed.<<ETX>>

Antenna Diversity Performance in Mitigating the Effects of Portable Radiotelephone Orientation and Multipath Propagation

Antenna diversity can mitigate signal impairments caused by random angular orientation and multipath radio propagation when using portable radiotelephones. Cumulative distributions of signal-to-noise ratio ( S/N ) were determined for antenna diversity using realistic orientation and multipath propagation models. In a random orientation and multipath propagation environment with -6 dB average crosspolarization coupling, two-branch selection diversity with two perpendicular antennas yields an S/N distribution with the same slope as two-branch selection diversity in the fixed-oriented mobile radio environment. The distribution for random orientation is about 4.5 dB worse, however, than the mobile radio distribution.

Component Signal Separation and Recombination for Linear Amplification with Nonlinear Components

LINC is a technique that uses signal processing to produce linear amplification of bandpass signals with grossly nonlinear circuit components. Two important signal-processing functions of LINC are 1) forming two constant envelope phase-modulated signal components from the bandpass input signal and 2) recombining the amplified components to produce an amplified replica of the input signal. Two-tone laboratory tests of a LINC component separator and combiner, not including a limiter and envelope detector, show that, at full output, spurious levels 40 dB below tone level are achievable over a 1-MHz band. Because the laboratory model operated at relatively low frequencies (hundreds of megahertz), scaling up in frequency should result in a LINC with <40-dB spurious over a 10-MHz band. Spurious 30 dB below tone level should be achievable over a bandwidth of 50 to 100 MHz using the same technique of component signal separation. Lower spurious levels or greater bandwidths will require a sin-1phase modulator that is less sensitive to delay in a feedback loop.