Vehicular communication channels are characterized by a nonstationary time-frequency-selective fading process due to rapid changes in the environment. The nonstationary fading process can be characterized by assuming local stationarity for a region with finite extent in time and frequency. For this finite region, the wide-sense stationarity and uncorrelated scattering assumption approximately holds, and we are able to calculate a time-frequency-dependent local scattering function (LSF). In this paper, we estimate the LSF from a large set of measurements collected in the DRIVEWAY'09 measurement campaign, which focuses on scenarios for intelligent transportation systems (ITSs). We then obtain the time-frequency-varying power delay profile (PDP) and the time-frequency-varying Doppler power spectral density (DSD) from the LSF. Based on the PDP and the DSD, we analyze the time-frequency-varying root-mean-square (RMS) delay spread and the RMS Doppler spread. We show that the distribution of these channel parameters follows a bimodal Gaussian mixture distribution. High RMS delay spread values are observed in situations with rich scattering, whereas high RMS Doppler spreads are obtained in drive-by scenarios.
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