Design and evaluation of UWB sensors for mobile positioning

Abstract

As ultra-wideband (UWB) becomes more widely available in smartphones (e.g., over 1 billion active iPhones) and other handheld devices, new opportunities emerge for Internet of Things applications and more accurate UWB-based indoor positioning. However, existing research is limited and does not address issues such as the compatibility of UWB anchors with smartphones and the orientation dependence of UWB devices. To address these issues, this paper first presents a custom UWB anchor design that is compatible with UWB-equipped iPhones. Second, unlike traditional positioning methods that require at least three anchors in range, this paper presents positioning use cases with one and two anchors. We provide a formal proof that if one follows the direction estimated with a UWB anchor and the relative-angle error is under 60°, one still moves closer to the anchor. We also empirically demonstrate that sub-metre-level accuracy can be achieved even with two anchors. Third, the paper evaluates the accuracy of multilateration and our positioning vector framework for direction inference for different numbers of sensors in range and multilateration time intervals. This can provide a channel-impulse-response-free solution to UWB phase ambiguity in smartphones and may be especially useful for the visually impaired. The experimental results show that multilateration with higher numbers of anchors in range yields better accuracy (up to 80%). Finally, we provide comprehensive experimental results on distance and relative-angle accuracy in a large indoor environment using iPhones and DWM3001CDK-based sensors that have not been previously studied.