High-accuracy Positioning for Indoor Applications: RFID, UWB, 5G, and beyond (Invited Paper) Klaus Witrisal, Stefan Hinteregger, Josef Kulmer, Erik Leitinger, and Paul Meissner Graz University of Technology, Austria email: {witrisal, stefan.hinteregger, kulmer, erik.leitinger, paul.meissner}@tugraz.at Abstract—Highly accurate and reliable indoor positioning— at accuracy levels in the 10 cm range—will enable a large a number of innovative location-based applications because such accuracy levels essentially allow for a useful real-time interaction of humans and cyber-physical systems. Activity recognition, navigation at “shelf” level, geofencing, process monitoring and process control are among the envisioned services that will yield numerous applications in various domains. This paper reviews the difficulties faced by indoor positioning systems, motivating the requirement for a large signal bandwidth and how a lack of bandwidth can be compensated by multi-antenna systems. The potential capabilities of upcoming generations of wireless systems will increasingly make high-accuracy positioning available in near future. I. I NTRODUCTION Robust and accurate indoor positioning is a key enabler for a wealth of future location-based services, ranging from supply-chain management and manufacturing to health-care and entertainment. For example in healthcare, application examples include behavioral monitoring to assess the physical and mental health of individuals, emergency (fall) detection to alert caretakers or emergency services, real-time assistance to provide context awareness to medication management systems (to remind— for instance—to take medications before/during/after meals) or as an orthotic and rehabilitation tool for individuals suffering from cognitive decline, geofencing for people with dementia, and even as a navigation aid for visually impaired (see [1], [2] and the references therein). In manufacturing and logistics, real-time positioning can be used to monitor the flow of items and hence the progress of processes. It can also be used to control processes in real time, for example the parametrization of tools has been envisioned, and hence to improve the efficiency and detect anomalies. Therefore, position information is a vital component of so- called smart factories [3]–[5]. However, sufficient reliability of the positioning service is required for that purpose. In a smart sales-floor, products and user devices can be localized to realize a recommender systems similar as in an internet store [6], [7]. In this scenario, the customer may be navigated to the desired items, matching accessories or alternative choices can be recommended, a real-time inventory function can be realized that ensures the shop owner always This work was supported by the Austrian Research Promotion Agency (FFG) within the project REFlex (project number: 845630). knows what items are still on stock, and last-but-not-least, theft control can be realized. To implement these functions, it will be of key importance to recognize interactions between cus- tomers and (identified) tracked objects, which is the challenge to be addressed in this scenario. These are a few specific examples that require cm or dm- level accuracies to yield robust activity recognition. Such a performance level cannot be achieved with current mass- market technologies. E.g. current RFID systems are already used for some of these applications, however with shortcom- ings concerning read range, false detections/missed detection due to multipath, and only imprecise positioning. Another difficulty is the heterogeneity of the scenarios and application environments. Therefore, as of today, the technologies for indoor localization have not converged towards a unique winning approach. Radiopositioning is—in principle—a very promising sens- ing method, because radio transceivers can be integrated in existing devices like smartphones and built at small form factors with low power consumption. Among the competing modalities [8]–[14], video cameras and microphones [15]– [17], for example, suffer from occlusions and a lack of acceptance because of privacy concerns. For radio systems, on the other hand, the influence of the dense multipath radio channel in indoor environments still makes accurate and robust positioning a challenging task. This paper first reviews the importance of a large signal bandwidth for accurate indoor positioning. We discuss the role of multi-antenna system configurations which can partly compensate for a lack of bandwidth. The diversity gains leveraged in MIMO (multiple-input multiple-output) radars [18], [19] can also be exploited in dense multipath channels, as faced in indoor environments, in order to obtain accurate positioning of RFID transponders [20]. Ultra-wideband (UWB) signals yield excellent accuracy, since they allow for a separation of the multipath components (MPCs) [21]–[24]. Hence, on the one hand, the direct signal path can be isolated from interfering MPCs; on the other hand, position-related information becomes accessible as well in later-arriving MPCs and turned into an advantage, as discussed in the second part of this paper. We will argue that with the advent of mm-wave communications in the 60 GHz band [25]– [27], a UWB localization system could operate synergetically with an existing communication system, e.g. using the IEEE