An Application-Oriented Evaluation of LTE-V's Mode 4 for V2V Communication

Future vehicles are envisaged to periodically exchange status updates to improve traffic safety. Among the wireless access technologies, WLAN-based contenders like ITS-G5 or DSRC have already been extensively evaluated. Recently, LTE-V mode 3 and 4 have been published to support V2V communication. Mode 4 is the most important baseline because mode 3 relies on cellular coverage. We present an application-oriented evaluation of LTE-V's mode 4 and outline possible problems with its MAC protocol. We argue that LTE-V's semi-persistent scheduling is disadvantageous under application-centric considerations, because packet collisions with the same vehicles carry forward in time and the MAC protocol reacts slowly to changes of the wireless channel. In this paper, options to improve the responsiveness of the MAC protocol and to limit the time of semi-persistent collisions are presented and evaluated using the European C-ITS framework in a large-scale system-level simulation with an application-oriented metric. The results of the simulative evaluation reveal that the proposed modifications can lead to significant improvements of the cooperative awareness, while the packet delivery ratio does not improve. This indicates that LTE-V mode 4 is optimized for traditional communication metrics instead of cooperative awareness itself. The awareness is more important for traffic safety and we deduce the necessity for additional evaluations using application-oriented metrics.