Time-and Frequency-Varying K-Factor of Non-Stationary Vehicular Channels for Safety-Relevant Scenarios

Vehicular communication channels are characterized by a non-stationary time-and frequency-selective fading process due to fast changes in the environment. We characterize the distribution of the envelope of the first delay bin in vehicle-to- vehicle channels by means of its Rician K-factor. We analyze the time-frequency variability of this channel parameter using vehicular channel measurements at 5.6 GHz with a bandwidth of 240 MHz for safety-relevant scenarios in intelligent transportation systems (ITS). This data enables a frequency-variability analysis from an IEEE 802.11p system point of view, which uses 10 MHz channels. We show that the small-scale fading of the envelope of the first delay bin is Rician distributed with a varying K-factor. The later delay bins are Rayleigh distributed. We demonstrate that the K-factor cannot be assumed to be constant in time and frequency. The causes of these variations are the frequency-varying antenna radiation patterns, as well as the time-varying number of active scatterers, and the effects of vegetation. We also present a simple but accurate bimodal Gaussian mixture model, which allows to capture the K-factor variability in time for safety-relevant ITS scenarios.