Markov chain analysis of alternative medium access control protocols for vehicle-roadside communications

Vehicle-roadside communication systems provide a very reliable communication link, which is able to support a great variety of ITS (intelligent transport systems) services, such as route guidance, automatic fee collection, driver information, and parking management. Different options for medium access control protocols have been proposed for a standardised communication architecture for vehicle-roadside communications: asynchronous and synchronous frame structures, different collision avoidance and recovery mechanisms (random delay counter vs. persist mechanism) and control parameters (maximum random delay counter, persist value, frame sizes, data rates). The results of a new, detailed analysis based on Markov chains of the proposed options are presented, including the harmonized European standardisation proposal developed within CEN TC 278 WG 9 for the dedicated short-range communications (DSRC) link and the open road frame being proposed for the IVHS communication architecture. Markov models are introduced, which allow one to determine the time span, which is needed in the connection phase to resolve data collisions involving up to three vehicles. Furthermore extended Markov models, which integrate the various models for special situations and are able to describe a complete transaction process, are introduced. As a result of the analysis, guidelines and recommendations for parameter choices are given in order to ensure optimal performance of the communication link in various scenarios and system configurations.