Real-time vehicular channel emulator for future conformance tests of wireless ITS modems

In the vehicular communication channels, the mobility of the receiver (RX) and the transmitter (TX) along with the movements of interacting objects in the propagation environment result in significant non-stationary channel fading. The channel impulse response exhibits not just significant delay- and Doppler spreads, but also the delay- and Doppler spreads themselves are changing over the time- and frequency axes. In other words: the channel statistics change as the geometry of RX, TX, and interacting objects evolve over time. To account for this, the local stationary regions in time and frequency are specified and each one is modeled by a distinct local scattering function. We present an architecture for a real-time emulator capable of reproducing the input/output behavior of a non-stationary n-tap wireless vehicular propagation channel. The architecture is implemented as a virtual instrument on LabView and we benchmark the packet error ratio (PER) of a commercial off the shelf (COTS) vehicular IEEE 802.11p modem. The emulator architecture aims at a hardware implementation which features optimised hardware complexity while providing the required flexibility for calculating the non-stationary channel responses by reconfiguring the scattering model for each local stationary region. The National Instrument USRP-Rio 2953R is used as the Software-Defined Radio platform for implementation, however the results and considerations reported are general-purpose and can be applied to other platforms. Finally, we discuss the PER performance of a COTS modem for a vehicular non-stationary channel model derived for highway obstructed line of sight (LOS) scenario in the DRIVEWAY'09 measurement campaign.