Hierarchical map-based location service for VANETs in urban environments

Vehicular Ad-hoc Network is gaining the attention of researchers because of the technological advancements for developing an Intelligent Transportation System (ITS). The dynamic nature of vehicles (nodes) leads to frequent path breaks and network fragmentation. Therefore, routing has become a critical issue in inter-vehicle communication. Location management in VANETs is considered as a critical issue in position based routing protocol. For this purpose we have proposed novel distributed map-based location service scheme that uses mobility pattern and density of the vehicles in the region. In the proposed location service mechanism, the geographical region is divided into segments and each segment is further fragmented into cells. For exchanging the routing information among vehicles across network, the location of destination node should be discovered within the cell. In case the destination is not discovered in the cell, the request for location search migrates to the segment. The information extracts from the digital map database helps to select location server in high traffic point regions in the entire area. The location service uses minimum speed aware policy to select location server at high traffic density waypoint and dynamic location updates are sent to location server based on threshold distance. In order to reduce the location discovery delay, adjacent level hierarchy is used for location query sent by the location servers. Simulation results obtained with different scenarios are used to demonstrate the performance of HLS, EMBL and HMLS in terms of location query answer and location update strategy. Simulation results show that HMLS achieve outperforms others in urban environments.