Michael Rath

Using DecaWave UWB transceivers for high-accuracy multipath-assisted indoor positioning

Robust indoor positioning and location awareness at a sub-meter accuracy typically require highly accurate radio channel measurements to extract precise time-of-flight measurements. Emerging UWB transponders like the DecaWave DW1000 chip offer to estimate channel impulse responses with reasonably high bandwidth and excellent clock stability, yielding a ranging precision below 10 cm. The competitive pricing of these chips allows scientists and engineers for the first time to exploit the benefits of UWB for indoor positioning without the need for a massive investment into experimental equipment. This work investigates the performance of the DW1000 chip concerning position related information that can be extracted from its channel impulse response measurements. We evaluate the signal-to-interference-plus-noise ratio of the line-of-sight and reflected multipath components which is a key parameter determining the Cramér-Rao lower bound on the ranging error variance. We propose a novel and highly efficient positioning algorithm, which requires information from a single anchor only. Results demonstrate reliable and robust positioning at an accuracy below 0.5 m.

Message Scheduling Methods for Belief Propagation

Approximate inference in large and densely connected graphical models is a challenging but highly relevant problem. Belief propagation, as a method for performing approximate inference in loopy graphs, has shown empirical success in many applications. However, convergence of belief propagation can only be guaranteed for simple graphs. Whether belief propagation converges depends strongly on the applied message update scheme, and specialized schemes can be highly beneficial. Yet, residual belief propagation is the only established method utilizing this fact to improve convergence properties. In experiments, we observe that residual belief propagation fails to converge if local oscillations occur and the same sequence of messages is repeatedly updated. To overcome this issue, we propose two novel message update schemes. In the first scheme we add noise to oscillating messages. In the second scheme we apply weight decay to gradually reduce the influence of these messages and consequently enforce convergence. Furthermore, in contrast to previous work, we consider the correctness of the obtained marginals and observe significant performance improvements when applying the proposed message update schemes to various Ising models with binary random variables.

SALMA: UWB-based Single-Anchor Localization System using Multipath Assistance

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.

Dataset: single-anchor indoor localization with decawave DW1000 and directional antennas

Highly-accurate localization of wireless devices is a critical feature of future Internet-of-Things applications. Due to its superior time-domain resolution, ultra-wideband (UWB) technology allows centimeter-level positioning accuracy. Still, setting up an anchor-based UWB localization system requires extensive labour and costs. Recent works have shown that, instead of multiple physical anchors, the exploitation of multipath reflections from walls minimizes the required infrastructure to a single anchor. This dataset contains an extensive measurement campaign in two complex indoor environments with one anchor. It contains line-of-sight as well as non-line-of-sight situations. Furthermore, we have acquired datasets using directional antennas at the anchor to allow observing the impact of the angular domain on the localization performance.

Multipath-assisted indoor positioning enabled by directional UWB sector antennas

High-accuracy indoor radio positioning can be achieved by using high signal bandwidths to increase the time resolution. Multiple fixed anchor nodes are needed to compute the position or alternatively, reflected multipath components can be exploited with a single anchor. In this work, we propose a method that explores the time and angular domains with a single anchor. This is enabled by switching between multiple directional ultra-wideband (UWB) antennas. The UWB transmission allows to perform multipath resolved indoor positioning, while the directionality increases the robustness to undesired, interfering multipath propagation with the benefit that the required bandwidth is drastically reduced. The positioning accuracy and performance bounds of the switched antenna are compared to an omni-directional antenna. Two positioning algorithms are presented based on different prior knowledge available, one using floorplan information only and the other using additionally the beampatterns of the antennas. We show that the accuracy of the position estimate is significantly improved, especially in tangential direction to the anchor.

UWB-based Single-anchor Low-cost Indoor Localization System

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 tags 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.

Channel Capacity Analysis of Indoor Environments for Location-Aware Communications

Location awareness is a key factor for a wealth of wireless applications. Ultra-wideband (UWB)-based localization achieves centimeter-level accuracies in harsh indoor environments that are characterized as dense multipath propagation channels. Individual multi-path components (MPCs) can be resolved and used for accurate and robust positioning. In our previous research, tracking filters have been developed that can estimate the parameters of individual MPCs from measured channel impulse responses for this purpose. In this paper, we analyze the channel capacity of these individual propagation paths to assess the robustness of an indoor wireless link and its predictability by means of this resolved channel model. The relation between the capacity and the model parameters is evaluated through the analysis of experiment data. It is shown that the variability of the overall channel capacity can be closely approximated by the proposed statistical model.

Runtime adaptation of PHY settings for dependable UWB communications: poster abstract

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.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.