New Techniques for Geographic Routing

Unknown author (2006-06-14)

PhD thesis

As wireless sensor networks continue to grow in size, we are facedwith the prospect of emerging wireless networks with hundreds orthousands of nodes. Geographic routing algorithms are a promisingalternative to tradition ad hoc routing algorithms in this new domainfor point-to-point routing, but deployments of such algorithms arecurrently uncommon because of some practical difficulties.This dissertation explores techniques that address two major issues inthe deployment of geographic routing algorithms: (i) the costsassociated with distributed planarization and (ii) the unavailabilityof location information. We present and evaluate two new algorithmsfor geographic routing: Greedy Distributed Spanning Tree Routing(GDSTR) and Greedy Embedding Spring Coordinates (GSpring).Unlike previous geographic routing algorithms which require theplanarization of the network connectivity graph, GDSTR switches torouting on a spanning tree instead of a planar graph when packets endup at dead ends during greedy forwarding. To choose a direction on thetree that is most likely to make progress towards the destination,each GDSTR node maintains a summary of the area covered by the subtreebelow each of its tree neighbors using convex hulls. This distributeddata structure is called a hull tree. GDSTR not only requires an orderof magnitude less bandwidth to maintain these hull trees than CLDP,the only distributed planarization algorithm that is known to workwith practical radio networks, it often achieves better routingperformance than previous planarization-based geographic routingalgorithms.GSpring is a new virtual coordinate assignment algorithm that derivesgood coordinates for geographic routing when location information isnot available. Starting from a set of initial coordinates for a set ofelected perimeter nodes, GSpring uses a modified spring relaxationalgorithm to incrementally adjust virtual coordinates to increase theconvexity of voids in the virtual routing topology. This reduces theprobability that packets will end up in dead ends during greedyforwarding, and improves the routing performance of existinggeographic routing algorithms.The coordinates derived by GSpring yield comparable routingperformance to that for actual physical coordinates and significantlybetter performance than that for NoGeo, the best existing algorithmfor deriving virtual coordinates for geographic routing. Furthermore,GSpring is the first known algorithm that is able to derivecoordinates that achieve better geographic routing performance thanactual physical coordinates for networks with obstacles.