Throughput of Self-Organizing Time Division Multiple Access MAC Layer for Vehicular Networks Based on Measured SNR Time-Series

IEEE802.11p is an approved amendment to the IEEE802.11 standard providing wireless access in vehicular environments (WAVE). It defines enhancements to the Physical layer (PHY) and Medium Access Control (MAC) for the support of Intelligent Transport Systems (ITS). This includes communication links between vehicles as well as between vehicles and a roadside infrastructure. The current MAC method uses randomized backoff in the case of access collisions which induces upredictable communication delays. It is known that such unpredictable delays severely limit the value of safety-related services. The most effective way forward is to design a protocol that suits vehicular traffic and safety- related service constraints and can coexist with the current IEEE802.11p MAC method. Self-Organizing Time Division Multiple Access (STDMA) is a suitable alternative, due to its structured channel access, predictable delay and periodic character. This contribution presents the time-evolution of throughput based on measured signal-to-noise ratio time-series of four vehicles driving on the same road joining the channel. These time-series were acquired during a real-world experiment in the 5.9 GHz band during 2010. Our results show that a collision-free access featuring predictable communication delay is feasible.