Pairwise Node Localization From Differences in Their UWB Channels to Observer Nodes

We consider the problem of localization and distance estimation between a pair of wireless nodes in a multipath propagation environment, but not the usual way of processing a channel measurement between them. We propose a novel paradigm which compares the two nodes' ultra-wideband (UWB) channels to other nodes, called observers. The key principle is that the channel impulse responses (CIRs) are similar at small inter-node distance $d$ and differ increasingly with increasing $d$. We present distance estimators which utilize the rich location information contained in the delay differences of extracted multipath components (MPCs). Likewise, we present estimators for the relative position vector which process both MPC delays and MPC directions. We do so for various important cases: with and without clock synchronization, delay measurement errors, and knowledge of the MPC association between the two CIRs. The estimators exhibit great technological advantages: they do not require precise time-synchronization, line-of-sight conditions, or knowledge about the observer locations or the environment. We study the estimation accuracy with a numerical evaluation based on random sampling and, additionally, with an experimental evaluation based on measurements in an indoor environment. The proposal shows the potential for great accuracy in theory and practice. Integrating the paradigm into existing localization algorithms and systems could enable low-cost localization of wireless users or networks in dynamic multipath settings.