The (in-) validity of the WSSUS assumption in vehicular radio channels

The assumption of wide-sense-stationarity (WSS) and uncorrelated scattering (US) of wireless propagation channels is widespread for the design and analysis of wireless propagation channels. However, the assumption is only valid within a limited range. In this paper, we investigate the extension of this range not only in time (WSS), but also in frequency (US), for measured vehicular propagation channels. We do this by using the collinearity of the local scattering function, which is a bounded spectral distance metric, and thus allows us to set an indicative threshold, which in turn enables a WSS and a US test. We prove that the fading process in vehicular communications is strongly non-WSS, which agrees with results previously reported in the literature. Furthermore, for the first time (to the authors' knowledge), we show their non-US behavior as well, mainly in scenarios with rich scattering. The dimensions of the minimum stationarity region are on the order of 40 ms in time and 40MHz in frequency.