A large body of work has shown that ultra-wideband (UWB) technology enables accurate indoor localization and tracking thanks to its high time-domain resolution. Existing systems, however, are typically designed to localize only a limited number of tags, and involve the exchange of several messages following a given schedule. As a result, the scalability of current solutions in terms of tag density is limited, as well as their efficiency and responsiveness. In this paper, we present SnapLoc, a UWB-based indoor localization system that allows an unlimited number of tags to self-localize at a theoretical upper bound of 2.3 kHz. In SnapLoc, a tag obtains the responses from multiple anchors simultaneously. Based on these signals, the tag derives the time difference of arrival between anchors and estimates its position. Therefore, SnapLoc does not require tags to actively transmit packets, but to receive only a single message. This allows tags to passively localize themselves and ensures that the performance of SnapLoc does not degrade with high node densities. Moreover, due to the (quasi-)simultaneous responses, a tight clock synchronization between anchors is not needed. We have implemented SnapLoc on a low-cost platform based on the Decawave DW1000 radio and solved limitations in the transceiver's timestamp resolution to sustain a high localization accuracy. An experimental evaluation shows that SnapLoc exhibits a 90% error and median error of 33 cm and 18 cm, respectively, hence enabling decimeter-level accuracy at fast update rates for countless tags.

To enable future location-aware Internet of Things (IoT) applications, Ultra-wideband (UWB) technology provides centimeter-accurate distance estimations. In the common case of a non-synchronized network, at least N·(N-1) message exchanges are required to derive the distance between N nodes. Enabling concurrent ranging between an initiator and an arbitrary number of responders can drastically reduce the amount of necessary transmissions and hence increases the efficiency of UWB systems. Although the feasibility of concurrent ranging has been proven experimentally, several key challenges still need to be addressed to practically implement concurrent ranging in real-world UWB systems, such as the automatic detection of multiple responses, the identification of a responder, as well as the detection of overlapping responses (especially in the presence of multipath components). In this paper, we provide a concurrent ranging solution tackling the aforementioned challenges. Among others, our solution enables (i) to detect responses in the CIR reliably, (ii) to encode the responder ID in the CIR to allow personalized ranging, as well as (iii) to mitigate the impact of overlapping responses and multipath components. We further show how the proposed solution increases the scalability of concurrent ranging in real-world UWB-based distributed systems.

IoT localization systems based on ultra-wideband (UWB) technology require dependable communication links to reliably acquire and efficiently share the timestamps in the network. The communication performance of UWB radios, however, is still largely unexplored and strongly affected by the employed physical layer settings. In this work, we analyze the role of different UWB physical layer settings and propose a scheme that adapts them at runtime in order to maintain a highly reliable link while minimizing energy consumption. The proposed adaptation scheme exploits the channel impulse response provided by the UWB transceiver to estimate the link quality and to extract information about the surrounding environment, such as the presence of destructive interference.

Setting up indoor localization systems is often excessively time-consuming and labor-intensive, because of the high amount of anchors to be carefully deployed or the burdensome collection of fingerprints. In this paper, we present SALMA, a novel low-cost UWB-based indoor localization system that makes use of only one anchor and that does neither require prior calibration nor training. By using only a crude floor plan and by exploiting multipath reflections, SALMA can accurately determine the position of a mobile tag using a single anchor, hence minimizing the infrastructure costs, as well as the setup time. We implement SALMA on off-the-shelf UWB devices based on the Decawave DW1000 transceiver and show that, by making use of multiple directional antennas, SALMA can also resolve ambiguities due to overlapping multipath components. An experimental evaluation in an office environment with clear line-of-sight has shown that 90% of the position estimates obtained using SALMA exhibit less than 20 cm error, with a median below 8 cm. We further study the performance of SALMA in the presence of obstructed line-of-sight conditions, moving objects and furniture, as well as in highly dynamic environments with several people moving around, showing that the system can sustain decimeter-level accuracy with a worst-case average error below 34 cm.

Accurate indoor radio positioning requires high-resolution measurements to either utilize or mitigate the impact of multipath propagation. This high resolution can be achieved using large signal-bandwidth, leading to superior time resolution and / or multiple antennas, leading to additional angle resolution. To facilitate multiple antennas, phase-coherent measurements are typically necessary. In this work we propose to employ non-phase-coherent measurements obtained from directional antennas for accurate single-anchor indoor positioning. The derived algorithm exploits beam patterns to jointly estimate multipath amplitudes to be used in maximum likelihood position estimation. Our evaluations based on measured and computer generated data demonstrate only a minor degradation in comparison to a phase-coherent processing scheme.

Ultra-wideband (UWB) technology is increasingly used to build location-aware IoT applications because of its outstanding positioning accuracy. Its communication performance, however, is unexplored and strongly affected by the chosen physical layer settings as well as by the surrounding environment. Finding an effective way to increase the dependability of UWB communications is yet an open problem. In this paper, we study the performance of different UWB physical layer settings and use them as tuning knobs to increase the energy efficiency and robustness of communications. Towards this goal, we first experimentally quantify the reliability and energy cost of each setting, in order to understand which physical layer configuration to privilege depending on the application requirements. We then use the estimated channel impulse response-a unique feature of UWB transceivers-to accurately measure the link quality and to extract relevant information about the characteristics of the surrounding environment, such as the presence of destructive interference. Capitalizing on this information, we design a scheme that adapts the UWB physical layer settings at runtime. An experimental evaluation using the Decawave DW1000 radio shows the effectiveness of the proposed adaptive scheme, highlighting the increased communication robustness and energy efficiency.

In this demo, we present a low-cost indoor localization system based on the off-the-shelf ultra-wideband transceiver Decawave DW1000. To obtain an accurate position information, the system makes use of a single anchor and of multipath reflections from walls, hence removing the need of installing a network of anchors or any other additional infrastructure. The procedure of determining the position of a tag can be divided in four consecutive stages. First, the location of virtual anchors is computed by mirroring the anchor position at reflective surfaces. Using two-way ranging, the distance and channel impulse response (CIR) between anchor and tag is obtained. This actual CIR is compared with expected CIRs from possible tag locations using a maximum likelihood approach to estimate the tag's position. Finally, a switchable directional antenna can be exploited to improve the robustness of the system by suppressing undesired, interfering multipath components. By following this procedure, the proposed system can achieve a decimeter accuracy and react to position updates in real-time.