Cross-Validation of DSRC Radio Testbed and NS-2 Simulation Platform for Vehicular Safety Communications

One of the most important challenges for DSRC deployment is maintaining high performance under heavy channel load. The study of congestion control mechanisms will be impractical if it requires hundreds of physical radios deployed on vehicles. In this paper we demonstrate two important results that together suggest a strategy for investigating congestion control. First, we show that the NS-2 simulator accurately models the MAC and PHY associated with an IEEE 802.11 hardware implementation. This opens the door to using simulation as the primary investigative tool. Second, we show that a technique in which one radio emulates N vehicles can produce results quite similar to the case in which a larger number of distinct vehicles exist. This will allow selective validation tests with tens of physical radios emulating hundreds of vehicles. The means by which we demonstrate these results is a cross-validation technique. We show that three test approaches produce consistently similar results: physical radios with emulation, NS-2 with emulation, and NS-2 without emulation. The close agreement among these results validates both the radio emulation technique and the NS-2 implementation of the 802.11 MAC and PHY protocols. We use this cross-validation technique to compare results for a wide variety of transmit power, message rate, data rate, channel bandwidth, message size and EDCA settings.