Degradation of Transmission Range

Reliability is one of the key requirements for intervehicle com-munication in order to improve safety in road traffic. This pa-per describes the difficulties of intervehicle communication. We focus on an analysis of the state-of-the art MAC protocol draft IEEE P802.11p and its limitations in high load situations. For our analysis we consider a particular safety scenario: An emergency vehicle is approaching a traffic jam. In a simu-lation experiment, we highlight that severe packet loss can occur. The reliable transmission range can be reduced by up to 90%. The main reason for this degradation is interference caused by transmissions of other vehicles within the traffic jam. In the study, we focus on the vehicle at the very end of the traffic jam. There, we measure the number of packets per second that are successfully received from the emergency vehicle. The key observation is that only a small fraction of the warning lead time remains which will also reduce the time for the driver to react on this information on an approaching emergency vehicle.