ZoomOut Geographic Location Service (ZGLS): A Flat Quorum-based and Reliable Location Management Protocol for VANETs
URI: http://utpedia.utp.edu.my/21513/ , and https://khub.utp.edu.my/home/Record/utp-utpedia.25144
Dr. Halabi Bin Hasbullah
Associate Professor / Director, Intelligent Cities Mission-Oriented Research (MoR)
Universiti Teknologi PETRONAS, Malaysia.
By using position-based routing in VANET, a vehicle makes forwarding decision based on the geographic position of destination and single-hop neighbours. The position of a destination is obtained through location service, while the positions of single-hop neighbours are obtained through neighbour discovery. Location service is a process where a destination sends its location updates towards location server vehicles through hop-by-hop forwarding, and a source obtains this information from such location servers through location query. Neighbour discovery is a process where a vehicle advertises its position to all neighbours within a broadcast range. In many cases, adaptive neighbour discovery schemes are more suitable, but they suffer from high channel load and stale neighbour information. For location service, flooding-based model suffers from congestion, throughput and scalability problems due to global flooding; flat hashing-based model uses global hash function and suffers from network scalability due to delay, drop and overhead of location updates and queries; hierarchical hashing-based model also uses a global hash function and suffers from handover signalling, uneven load on higher level servers and query delay; hierarchical quorum-based model, which is having similar issues as the hierarchical model, suffers from non-intersection of update and query quorums. To overcome these problems, ZoomOut Geographic Location Service (ZGLS) introduces a flat quorum-based location service model. The neighbour discovery of ZGLS performs two tasks: first, it uses adaptive HELLO beacons to obtain neighbour table accuracy with least beacon load; second, every vehicle discovers two front and two behind neighbours, called relatives, that remain in its neighbour table for the longest time period. Thus, a chain of front relatives extends in front and a chain of behind relatives extends in behind direction. When a vehicle broadcasts location updates, all four relatives act as location servers, but only one on either side rebroadcasts them. When a source generates location query, a relative of destination in the single-hop proximity of source answers it. Reliability is achieved when a predecessor receives an echo acknowledgement of a location update from its relatives during the hop-by-hop forwarding. For evaluation of ZGLS, the performance of its neighbour discovery is compared against Connectivity-Aware Routing and Local Information-based Adaptive Hello protocols, and is found to produce higher neighbour table accuracy with reduced beacons. Also, the location update and query of ZGLS is compared against Region-Based Location Service Management Protocol and Hybrid Routing and Hierarchical Location Service protocols, and is found to produce much better results for signalling overhead, timeliness and probability of successful packet delivery.
