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

TL;DR

This paper investigates the non-stationary time- and frequency-varying K-factor in vehicular channels, revealing its variability and proposing a Gaussian mixture model to accurately characterize it for safety-critical ITS scenarios.

Contribution

It provides the first detailed analysis of the K-factor's variability in vehicular channels and introduces a novel Gaussian mixture model to capture this variability.

Findings

K-factor varies significantly over time and frequency in vehicular channels.

First delay bin exhibits Ricean fading with a variable K-factor.

A Gaussian mixture model effectively captures K-factor variability.

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 Ricean 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 bi-modal Gaussian mixture model, that allows to capture the $K$-factor variability in time for safety-relevant ITS scenarios.