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

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Abstract
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.
Funding Information
  • project NOWIRE
  • Vienna Science and Technology Fund (WWTF)
  • NFN SISE (S10607)
  • Austrian Science Fund (FWF)
  • Austrian Government
  • City of Vienna
  • National Science Foundation

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