An IMM-based Decentralized Cooperative Localization with LoS and NLoS UWB Inter-agent Ranging

This paper studies the global localization of a group of communicating mobile agents via an ultra-wideband (UWB) inter-agent ranging aided dead-reckoning system. We propose a loosely coupled cooperative localization algorithm that acts as an augmentation atop the local dead-reckoning system of each mobile agent. This augmentation becomes active only when an agent wants to process a relative measurement it has taken. The main contribution of this paper is to address the challenges in the proper processing of the UWB range measurements in the framework of the proposed cooperative localization. Even though UWB offers a decimeter level accuracy in line-of-sight (LoS) ranging, its accuracy degrades significantly in non-line-of-sight (NLoS) due to the significant unknown positive bias in the measurements. Thus, the measurement models for the UWB LoS and NLoS ranging conditions are different, and proper processing of NLoS measurements requires a bias compensation measure. On the other hand, in practice, the measurement modal discriminators determine the type of UWB range measurements with only some level of certainty. To take into account the probabilistic nature of the NLoS identifiers, our proposed cooperative localization employs an interacting multiple model (IMM) estimator. The effectiveness of our proposed method is demonstrated via an experiment for a group of pedestrians who use UWB relative range measurements among themselves to improve their geolocation using a shoe-mounted INS system.