Anchor selection and Topology Preserving Maps in WSNs — A Directional Virtual Coordinate based approach

Virtual Coordinate Systems (VCS) characterize each node in a network by its hop distances to a subset of nodes called anchors. Performance of VCS based algorithms is highly sensitive to number of anchors and their placement. Extreme Node Search (ENS), a novel and efficient anchor placement scheme, is proposed that demonstrates significantly improved performance over state-of-the-art. ENS starts with two randomly placed anchors and then uses a Directional Virtual Coordinate (DVC) transformation, which restores the lost directionality in traditional VCS, to identify anchor candidates in a completely distributed manner. A vector-based representation is proposed for the DVC domain, which is then used to introduce the concept of angles between virtual directions in the transformed domain. Ability to specify cardinal directions and use angles is a radical change from the traditional VC system approaches. By selecting two anchor pairs with near orthogonal directional coordinates under the DVC transformation, a novel Topology Preserving Map (TPM) generation scheme is developed. This new TPM generation scheme requires significantly less computations than the existing PCA based method. Use of ENS significantly enhances the PCA based TPM generation as well. Simulation results for representative WSNs indicate that the ENS based anchor sets significantly improve performance of all prominent VC based routing schemes. For instance, Directional Virtual Coordinate Routing, when combined with ENS anchor placement strategy, outperforms even the geographic Greedy Perimeter Stateless Routing scheme that relies on exact physical node coordinates.