A Comparison of Single- and Multi-hop Beaconing in VANETs

Optimizing vehicular communication strategies is important for an efficient usage of the available wireless bandwidth and also critical for the success of VANETs. In this paper we address the fundamental and practical question whether the load on the wireless channel can be reduced if periodic beacon messages are transmitted over multiple hops with reduced transmit power instead of being transmitted over one hop with high transmit power. In particular, we look at the possible bandwidth savings that can be achieved by piggybacking forwarded messages into the own next beacon transmission. For that matter, we first propose an analytical model to compute a lower bound for the resulting channel load when single- or multi-hop dissemination of beacons is performed. In this model we assume optimal channel conditions and perfect relaying and piggybacking decisions to show that a reduction of the load by multi-hop is possible and closely related to piggybacking. Further, we show that the possible savings depend on the ratio between the size of the header and the payload of a beacon and that a reduction of the load is theoretically possible if the header is larger than the payload - what would be the case in VANETs if security overheads are considered part of the header. ... mehrWe then perform a simulative comparison of single- and multi-hop beaconing to evaluate the impact of effects such as packet collisions and channel fading. We show that the possible savings of multi-hop beaconing are difficult to exploit under non-perfect channel conditions and suboptimal relaying decisions.