Phase measurements and characterization of mobile radio channels

A channel phase measurement system based on stable quartz oscillators at the transmitter and at an I and Q receiver is presented. Observations of the phase behavior over a 910-MHz mobile radio channel in urban and semi-urban areas are made and related to the signals physical parameters. A method to characterize channel phase variations is proposed that corresponds to taking the second difference on the phase. Standard deviations of this phase variation measure are found to increase more or less linearly with distance in built-up areas, with a slope as high as 10° per km. Comparisons between measured and theoretical statistical distributions of the phase variations are made: while not meeting the χ-square test criteria, quadratic error tests supported by visual observation show that a Student´s t distribution with two degrees of freedom, of the type used to describe the statistical characteristics of random FM, offers for practical purposes a useful statistical description of the measured phase variations