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Abstract-Geographic stateless routing schemes such as GPSR have been widely adopted to routing in Vehicular Ad Hoc Networks (VANET). However, due to the particular urban topology and the non-uniform distribution of cars, the greedy routing mode often fails and needs a recovery strategy such as GPSR's perimeter mode to deliver data successfully to the destination. It has been shown that the cost of planarization, the non-uniform distribution of cars, and radio obstacles make GPSR's perimeter mode inefficient in urban configurations. Some enhancements have been proposed such as GPCR, which uses the concept of junction nodes to control the next road segments that packets should follow. However, the concept of junction nodes itself is problematic and hard to maintain in a dynamic urban environment.In this paper, we describe GpsrJ+, a solution that further improves the packet delivery ratio of GPCR with minimal modification by predicting on which road segment its neighboring junction node will forward packets to. GpsrJ+ differs from GPCR as decisions about which road segment to turn does not need to be made by junction nodes. Moreover, GpsrJ+ does not need an expensive planarization strategy since it uses the natural planar feature of urban maps. Consequently, GpsrJ+ reduces the hop count used in the perimeter mode by as much as 200% compared to GPSR. It therefore allows geographic routing schemes to return to the greedy mode faster.

Abstract-In this paper, we introduce a routing solution called "Landmark Overlays for Urban Vehicular Routing Environments" (LOUVRE), an approach that efficiently builds a landmark overlay network on top of an urban topology. We define urban junctions as overlay nodes and create an overlay link if and only if the traffic density of the underlying network guarantees the multi-hop vehicular routing between the two overlay nodes. LOUVRE contains a distributed traffic density estimation scheme which is used to evaluate the existence of an overlay link. Then, efficient routing is performed on the overlay network, guaranteeing a correct delivery of each packet. We evaluate LOUVRE against the benchmark routing protocols of GPSR and GPCR and show that LOUVRE performs higher in packet delivery and achieves lower hop count.

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