An alternative congestion control using an enhanced contention based forwarding for vehicular networks

Abstract

Many ITS (Intelligent Transportation Systems) applications require multi-hop forwarding of Decentralised Event Notification Message (DENM). If not well designed, multi-hop forwarding algorithms provide negative impact on the IEEE 802.11p vehicular systems, which already suffer from channel congestion caused by e.g., Cooperative Awareness Messages (CAM). In this paper, we propose an enhancement of the contention based forwarding (CBF) by a congestion control functionality. Specifically, we propose CBF2C packet forwarding algorithm, which is designed to fit into the distributed congestion control (DCC) framework specified by ETSI. In order to efficiently utilise the channel, CBF2C adapts retransmission count based on channel load status. Extensive simulation evaluations on communication performances and channel utilisation are carried out targeting scenarios, where the wireless channel is shared by DENM and CAM packets. The performances of CBF2C is compared against those of an enhanced flooding and an ETSI-standardised scheme, CBF-RT. Moreover, two cases, with and without congestion control on the CAM rate, are considered in the performance evaluations. The simulation results show a positive impact of the dual DCC, CAM rate control at the facilities layer and DENM retransmission count control at the networking layer.