Random Transmit Jitter Against Correlated Packet Collisions in Vehicular Safety Communications

Abstract

In Vehicular Safety Communication (VSC) vehicles periodically broadcast so called Cooperative Awareness Messages (CAM) to make neighboring vehicles being aware of their current status like position, speed and heading. Such periodic transmissions on top of the Dedicated Short Range Communication (DSRC) technology can cause temporal correlated (recurring) collisions. Whereas VSC applications may support the loss of individual CAMs, the loss of several subsequent messages increases the delay between consecutive awareness updates from a certain vehicle, which in turn significantly lowers the applications reliability. In this paper we propose to add a controlled random jitter to the nominal CAM broadcast interval at the application/facilities layer. Thus, we aim to make temporal correlated packet collisions more uncorrelated in time and by implication significantly decrease the delay between consecutive CAM updates (update delay or inter-reception time). The benefit of our approach has been demonstrated by simulating a multi lane highway scenario at different traffic/data load conditions. By adding a random transmit jitter we were able to reduce the amount of correlated collisions by more than factor 10, and by consequence to improve the update delay performance by up to two orders of magnitude.