NLOS Mitigation Using Linear Programming in Ultrawideband Location-Aware Networks

In this paper, we propose a linear-programming (LP) approach to the problem of nonline-of-sight (NLOS) mitigation in ad hoc ultrawideband wireless networks. The locations of ldquounlocalizedrdquo nodes can be estimated using range or distance estimates from location-aware ldquoanchorrdquo nodes. In the absence of LOS between the unlocalized and anchor nodes, e.g., in indoor networks, the NLOS range estimates can be significantly biased. The direct incorporation of these biased range estimates into practical location estimators, such as the least squares estimator, without the mitigation of these bias errors, can potentially lead to severe degradation in the accuracy of node-location estimates. On the other hand, with certain geometries of anchor nodes, NLOS range estimates can be used to improve the accuracy of location estimation. Furthermore, discarding the biased range estimates may not be a viable option, as the number of range estimates available may be limited. We present a novel NLOS-bias mitigation scheme based on LP, that 1) allows us to incorporate NLOS range information into location estimation, but 2) does not allow NLOS bias errors to degrade node-localization accuracy.