Statistical Model for Amplitude and Delay of Selective Fading

Abstract

The transmission performance of digital radio systems is controlled by spectral distortion caused by multipath fading. To evaluate this performance for digital systems with high-order modulation schemes, a statistical model for frequency-selective fading is needed. New propagation data obtained in Gainesville, Florida, were used to generalize Rummler's model to include group delay response. The introduction of the delay response data into the model of the fading channel enabled the classification of the fades as minimum phase and nonminimum phase. We found that 24 percent of all fades have significant delay distortion, and can be characterized as being minimum phase or non-minimum phase. In the range of practical interest, there are as many minimum phase as nonminimum phase fades. The results of this work will facilitate a better understanding of the fading channel, which will be beneficial in the engineering of radio routes and digital radio design. The results also demonstrate the need for a description of the geographical occurrence of dispersion, which will differ from that for multipath fading at a single frequency. This is based on the observation, presented in this paper, that the relative amount of dispersive fading is significantly greater in Gainesville, Florida, than in Palmetto, Georgia. The availability of a dispersive fading map will facilitate the accurate engineering of digital radio routes.