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Recent studies suggest that Self-organizing Time-Division Multiple Access (STDMA) might be a better medium access strategy in inter-vehicle communication networks than Carrier Sense Multiple Access (CSMA), especially when considering safety focused applications. Although it is necessary to completely understand a protocol and the effect of its 'turning knobs' on performance before adoption, STDMA has not yet been subjected to such rigorous treatment in the literature. In order to address this shortcoming we perform and present an in-depth analysis and evaluation of STDMA's fundamental principles. In particular, we contribute a detailed and complete description of the STDMA protocol, followed by the analysis and evaluation of two key questions: How can packet collisions occur in STDMA and whether packet collisions are 'contagious'. We further perform a fair comparison with CSMA on the basis of which we provide recommendations on the configuration of STDMA. Our results show that STDMA coordinates multiple access effectively -even in highly congested situations -as long as all transmitted packets are decoded successfully. When non-decodable (but still carrier-sensible) transmissions are present, STDMA effectiveness drops below that achieved by CSMA due to the lack of control information. To ensure reproducibility and encourage further inquiry we release the STDMA implementation used in this paper to the wireless networks research community.

Motivated by the idea to reduce deployment costs and to dynamically regulate vehicular traffic flows at intersections, inter-vehicle communications based virtual traffic lights are envisioned to replace traditional infrastructure based traffic lights. According to recent studies, virtual traffic lights are expected to increase traffic flow by up to 60 %. Yet, those studies were based on the assumption of a perfectly reliable communication, i.e., notification messages which signal a traffic light were always received by vehicles located within a certain distance to the sender. Hence, effects such as signal fading or non-line-of-sight conditions due to buildings were neglected. Such effects, however, can have a negative impact on the dissemination of the notification messages. This poster paper therefore studies whether these effects lead to significantly larger dissemination delays or not, and whether this increase is crucial for the feasibility of virtual traffic lights. According to the results of this study, the delay is not significantly larger, and virtual traffic lights seem to be feasible under such challenging conditions.

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Vehicular ad hoc networks are conceived as a means to increase traffic safety. Primary means to demonstrate their beneficial impact before deployment are computer simulations that comprise communication models, mobility models of vehicles and models of VANET applications. In particular, the movement behavior of vehicles poses questions when evaluating traffic safety since driver models typically do not allow accidents to happen. In this paper we address modifications to the popular Wiedemann model and present an integration of the modified driving behavior to the traffic simulator VISSIM which thus enables simulations containing accidents. Finally, we show in a simulative study how locally available information on the current traffic situation can contribute to safer road traffic. Our contributions represent a first step on how to assess VANETs with respect to traffic safety.