Ranging and multipath-enhanced device-free localisation with densely-meshed ultra-wideband devices

Device-free localisation (DFL) is a prominent example of radio sensing and radio frequency (RF)-based passive localisation. RF-based passive localisation approaches determine the position of a non-cooperative user based on the user's impact on radio propagation. In this regard, DFL systems measure user-induced changes in the properties of the received RF signals. With multipath-enhanced device-free localisation (MDFL), a novel passive localisation approach which is taking the advantage of user-induced fading in the multipath signals, that is, reflected and scattered signals is introduced. In this work, the authors realise an MDFL system using low-cost ultra-wideband (UWB) devices. Specifically, the Qorvo (DecaWave) DW1000 module is used, for which how to access the channel impulse response is described in detail. Additionally, an overview of the required signal processing for MDFL is provided and a possible sequential Bayesian approach is introduced. Moreover, an efficient ranging scheme based on time-division multiple access (TDMA) and message broadcasting is outlined, which allows the deployment of a large number of interconnected UWB devices. Using an exemplary network of interconnected UWB devices, the localisation performance of both DFL and MDFL for an indoor scenario is evaluated. Thereby, MDFL is shown to clearly outperform DFL in terms of robustness and accuracy. Furthermore, a TDMA-based ranging scheme for active localisation is used, that is, for localising an UWB device carried by the user, allowing for a direct comparison between active and passive localisation. Achieving a sub-decimetre accuracy, the active localisation outperforms both DFL and MDFL, and thus, shows the possibility of using an active localisation device to initialize MDFL