A High Integrity Positioning Method for Ad-Hoc Networks

R. Mautz, S. Feng, W. Ochieng, A. Kemp, B. Peng

Abstract:	The aim of this paper is to present the current status of the positioning algorithm for iPLOT (intelligent Pervasive Location Tracking) as an automatic, low-cost system that exploits current or near future wireless communications based on Bluetooth to enable continuous tracking of the location of devices in all environments. The proposed adhoc method has a full 3D positioning capability and set up for sensor networks. It is based on a lateration strategy to achieve high integrity positioning in wireless ranging networks. The local positioning method has the potential to complement GNSS (Global Navigation Satellite Systems) in terms of coverage. The novel positioning strategy proposed has three phases: (I) Creation of a rigid structure: The smallest redundant and rigid graph consists of 5 network nodes with distance constraints to each other. If such an initial cluster passes statistical tests, it is released for further expansion. Additional nodes are added consecutively using a novel multilateration technique which is based on a surplus of observations and carefully avoids flip ambiguities. (II) Merging of clusters: Experiments show that only a fraction of nodes can become a member of one single cluster. The remaining nodes are likely to make up their own clusters which may or may not be connected with neighbouring clusters. In case two clusters share an adequate number of nodes and/or range observations between them, they can be merged using an over-determinant 3 dimensional 6-parameter transformation. (III) Transformation of the cluster(s) into a reference coordinate system. The outcome of these three steps is a cluster of nodes with their coordinate positions and their error variances in a targeted reference system. Nodes with insufficient integrity or positional accuracy are strictly separated by delivering the corresponding integrity flag. Our simulations with large networks (e.g. 100 nodes) demonstrate the importance of carefully making decisions on folding ambiguities while creating rigid structures and expanding them by multilateration. Our simulations show that the algorithm is superior in terms of nodal reliability when compared with an established positioning tool such as Multidimensional Scaling (MDS). Only in case of extremely high inter-node connectivity (above 25), are the MDS position deviations of the same magnitude as in the proposed algorithm. We have studied networks with relatively large errors of up to 7.5% of the true ranges and shown that it is possible to achieve a position deviation that is of the size of the ranging error. A significant reduction in the quality output is hard to avoid if the measurement noise exceeds 5% of the ranges.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	134 - 144
Cite this article:	Mautz, R., Feng, S., Ochieng, W., Kemp, A., Peng, B., "A High Integrity Positioning Method for Ad-Hoc Networks," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 134-144.
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