DISSERTATION The Vehicular Radio Channel in the 5 GHz Band

In this thesis I present a methodology, in order to characterize the time-variant vehicular radio channel. The radio channel is part of the communication system, which the engineer cannot influence. Therefore it has to be characterized in a way that the transmitters and receivers can be well designed, for specific applications. For this characterization we carried out two vehicular radio channel measurement campaigns in Lund, Sweden. In both campaigns we used a 4 × 4 multiple-input multiple-output channel sounder in the 5GHz band. In general the radio channel can be described by the three main phenomena, pathloss, large-scale properties, i.e., shadowing, and small-scale properties, which I characterize by the concept of the Local Scattering Function (LSF). Pathloss models are developed for four different environments: rural, highway, urban, and suburban. For the rural environment a two-ray propagation model shows the best fit with the measurements. The pathloss for the other three environments is modeled via the classical power law model, with a pathloss exponent smaller than 2. The vehicular radio channel is highly time-variant, which is reflected in a non-Wide-Sense Stationary Uncorrelated Scattering (WSSUS) behavior. For the description of non-WSSUS radio channels, I use the concept of the LSF, which can be understood as a timeand frequency-variant scattering function. In this case the radio channel is assumed to be WSSUS for a limited region in the time domain (stationarity time) and frequency domain (stationarity bandwidth). I define and discuss the methodologies, in order to estimate the LSF from the measurement data. I observed a strong dependency of the stationarity time on the relative driving direction of the vehicles — in the range of double-digit milliseconds for vehicles driving in opposite directions and more than one second for vehicles driving in convoy. By investigations of the time-variant average power-delay profile and time-variant Doppler spectral density I observed that the most significant scatterers in vehicular environments are: traffic signs, trucks, bridges, and buildings. Beside the channel measurements and characterization we carried out a communication system performance measurement campaign in Tyrol, Austria. As system we used a prototype implementation of the draft standard IEEE 802.11p, which is expected to be soon ratified and implemented in commercial vehicular communication systems. The Roadside Unit (RSU) was configured as the transmitter and the Onboard Unit (OBU) as