Enhancing location service scalability with HIGH-GRADE

Location-based routing significantly reduces routing overheads in mobile ad hoc networks (MANETs) by utilizing position information of mobile nodes in forwarding decisions. A location service is therefore critical to location-based routing, the scalability of which hinges largely on the overheads of such a service. Although several location service schemes have been proposed, most of them focus only on one or two aspects of scalability in their performance evaluations, and a comprehensive comparative study is missing. We first explore the design space of location services and present a taxonomy of existing schemes. We then propose HIGH-GRADE, a new location service scheme that employs a multilevel hierarchical location server structure and a multi-grained location information organization. We develop a uniform theoretical framework to analyze HIGH-GRADE and four other existing schemes in terms of three metrics: location maintenance cost, location query cost, and storage requirement cost. We show that the design of a location service scheme involves tradeoffs among all three of these kinds of overhead. Further, in our theoretical analysis and simulation experiments, HIGH-GRADE demonstrates superior scalability, especially when a localized data traffic pattern is assumed.