System performance of vehicle-roadside communications using asynchronous and synchronous MAC protocols

Vehicle-roadside communication (VRC) systems are expected to be an important element of a future integrated road transport environment (IRTE), which aims to enhance the safety and efficiency of road traffic. For the standardization of suitable communication protocols, choices between several options are made on the basis of performance evaluations. The results of a performance evaluation of VRC systems using different medium access control (MAC) schemes proposed for standardization are presented. The asynchronous protocol proposed within the European standardization group CEN TC 278 WG 9 is compared with a synchronous protocol being proposed for the IVHS communication architecture. After introducing the basic requirements for vehicle-roadside communications, the characteristics of both protocol options are presented. Next, reference scenarios are introduced, which take into account different system configurations (SDMA/TDMA vs. a pure TDMA solution), application profiles (AFC-like interactive dialogue combined with broadcast-oriented route guidance), traffic and channel characteristics. The results of simulations, which have been carried out based on these reference scenarios, are discussed in detail. It is shown, that, in the analysed scenarios, the asynchronous protocol achieves better results than the synchronous option, because it produces less overhead and is able to cope better with transmission errors.