IEEE 802.15.4a Ultra-wideband based wireless positioning has recently gained attention for precise localization. However, the multi-user scalability of those, mostly two-way ranging based, approaches is not considered. Due to the exchange of multiple frames per ranging, two-way ranging has significant downsides in terms of scalability. This paper proposes and validates a novel approach for a multi-user time-difference of arrival based localization system using wireless clock synchronization. The system accuracy is assessed using a complex experiment, covering robotic movement and an optical reference system for comparable results. It is shown, that the accuracies achievable by time-difference of arrival positioning with wireless clock synchronization are comparable to similar two-way ranging based approaches. All raw samples, reference data and processed positions are provided alongside this work.

ATLAS - an open-source TDOA-based Ultra-wideband localization system

In this demo, we present SnapLoc, a UWB-based indoor localization system that allows decimeter-accurate self-localization of mobile tags by listening to only a single message. To this end, SnapLoc leverages (quasi-)simultaneous responses of multiple anchors. Based on these responses, the tag derives the time difference of arrival between anchors and unambiguously estimates its position. Thanks to this principle, SnapLoc carries out passive localization and supports an unlimited number of tags at high update rates. Our SnapLoc implementation runs on the off-the-shelf Decawave DW1000 UWB transceiver. The latter suffers from a limited transmit timestamp resolution that affects the achievable localization accuracy when used in conjunction with concurrent anchor responses. Therefore, in this demo we also showcase techniques to overcome these limitations and achieve nevertheless a high localization accuracy.

SnapLoc: an ultra-fast UWB-based indoor localization system for an unlimited number of tags: demo abstract

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.

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

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 De-cawave 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.

SnapLoc: an ultra-fast UWB-based indoor localization system for an unlimited number of tags

Wireless positioning based on IEEE 802.15.4a has recently gained attention for precise localization. However, the multi-user scalability of those, mostly two-way ranging based, approaches is not considered. Due to the exchange of multiple frames per ranging, two-way ranging has significant downsides in terms of scalability. This paper proposes and validates a novel multi-user time-difference of arrival based localization approach using wireless clock synchronization to overcome the limitations of two-way ranging based positioning. The clock characteristics of the individual nodes are experimentally analyzed and the requirements and constraints for wireless clock synchronization are elaborated based on the experiments. The results show, that a clock synchronization rate of around 1 Hz is sufficient to achieve accuracies in the decimeter range. Experiments analyzing the multi-user capabilities of the system are conducted, highlighting the specific properties of multi-user access in the proposed time-difference of arrival based localization. The experiments show, that the system is capable of scaling gracefully under heavy load. However, clock synchronization suffers as it is degrading equally. Therefore, a novel approach is proposed and evaluated to prioritize the wireless clock synchronization to ensure load independent positioning accuracy. It is shown, that the proposed approach is capable of ensuring a synchronization receive ratio of around 90% independent of the system load.

Multi-user interference and wireless clock synchronization in TDOA-based UWB localization

Autonomy of vehicles is a widely discussed topic, increasing the need for low power, inexpensive and precise localization and navigation. Due to ongoing research and standardization in last decades, ultra-wideband (UWB) based localization technology is more and more ready for large scale usage. In this paper we propose an embedded UWB localization system, consisting of an inexpensive, low power hardware platform deploying an IEEE 802.15.4a-2011 UWB-PHY standard conform RF chip, enabling communication and localization, a software framework, and localization algorithms. The key contribution of the paper is this system concept and experimental results using a developed system in an underground parking garage. Within this system evaluation we show in an accuracy analysis an achievable positioning error of around 30 cm. Furthermore we show the useage of such an UBW localization system in an use case near scenario.

Kai Hildenbrand

Papers

Design of an embedded UWB hardware platform for navigation in GPS denied environments