Cooperative Relative Positioning of Mobile Users by Fusing IMU
Inertial and UWB Ranging Information
Ran Liu, Chau Yuen, Tri-Nhut Do, Dewei Jiao, Xiang Liu, and U-Xuan Tan
Abstract— Relative positioning between multiple mobile users
is essential for many applications, such as search and res-
cue in disaster areas or human social interaction. Inertial-
measurement unit (IMU) is promising to determine the change
of position over short periods of time, but it is very sensitive
to error accumulation over long term run. By equipping the
mobile users with ranging unit, e.g. ultra-wideband (UWB), it is
possible to achieve accurate relative positioning by trilateration-
based approaches. As compared to vision or laser-based sensors,
the UWB does not need to be with in line-of-sight and provides
accurate distance estimation. However, UWB does not provide
any bearing information and the communication range is
limited, thus UWB alone cannot determine the user location
without any ambiguity. In this paper, we propose an approach
to combine IMU inertial and UWB ranging measurement for
relative positioning between multiple mobile users without the
knowledge of the infrastructure. We incorporate the UWB and
the IMU measurement into a probabilistic-based framework,
which allows to cooperatively position a group of mobile users
and recover from positioning failures. We have conducted ex-
tensive experiments to demonstrate the benefits of incorporating
IMU inertial and UWB ranging measurements.
I. INTRODUCTION
Indoor positioning systems are essential to provide many
public, commercial, and military services. Many researchers
concentrate on the absolute positioning in a global coordinate
system with respect to a specific infrastructure, where many
reference anchors with known positions are deployed. The
user measures the received signal strength (RSS) [1], time
of arrival (ToA) [2], or angle of arrival (AoA) [3] to anchors
and infers its position in the environment. A typical system is
the global positioning system (GPS), which utilizes the satel-
lites as anchors to provide position information in outdoor
environments with an accuracy of several meters.
In some scenarios, for example fire rescue within a build-
ing, the global positioning is not possible, since anchors
may not be deployed or not functional due to the accident.
Therefore, relative positioning of users without any external
infrastructure is appealing, which is the focus of this paper. In
the context of relative positioning as shown in Fig. 1, all users
are considered as equal peers and are able to obtain the range
information of its neighbors if they are in communication
This work is supported by Temasek Lab under Indoor Relative Positioning
System project (No. IGDST1302024), National Science Foundation of
China (No. 61550110244, 61601381, and 61471306), and National Defense
Scientific Research of China (No. B3120133002).
R. Liu, C. Yuen, T. N. Do, and U-X. Tan are with the Engineer-
ing Product Development Pillar, Singapore University of Technology and
Design, 8 Somapah Rd, Singapore, 487372 {
ran liu, yuenchau,
trinhut
do, uxuan tan}@sutd.edu.sg.
D. Jiao and X. Liu are with the School of Software and Microelectronics,
Peking University, Beijing, China, 102600
xliu@ss.pku.edu.cn.
Fig. 1. Illustration of the relative positioning problem. We aim to
track the relative position of a group of mobile users by integrating the
inertial measurement provided by the IMU and the peer to peer ranging
measurement from the UWB. As our approach does not rely on any given
infrastructure, the environment is only used to validate our approach and
provide the ground truth. User1, User2, and User4 can range each other
using UWB, since they are close to each other. Due to the occlusion of the
concrete walls, User3 can not hear User1 through UWB. With the help of
IMU, we can cooperatively determine the relative positions of all users.
range. Additionally, the users carry inertial sensors, which
can measure their own movements. The goal is to determine
the relative position of all users in the network.
Dead reckoning (DR) [4] [5] determines one’s location
based on its previous position and speed, which is measured
by an IMU sensor or wheel encoder in the case of a mobile
robot. If the initial locations of the users are known, one
can use DR to determine the relative position of a group of
users. But the DR may not be accurate due to accumulative
error, which must be corrected or eliminated by other sources
of information. Anchors with known positions, for example,
can provide a measure to correct the positioning error, but
infrastructure-based anchors are not applicable in a number
of situations as mentioned previously. In this paper, we
propose using the peer to peer measurement to remove the
accumulative error for relative positioning estimation.
Many devices are able to provide peer to peer information,
for example camera, laser range finder, and wireless sensors.
Extensive research concerning relative positioning in a swam
behavior using vision or laser-based sensors have been done
in the area of robotics [6] [7]. The application of these
approaches are limited in uncontrolled environments, as it
is challenging for them to deal with the occlusions.
Due to the wide availability of RSS in many wireless
devices, a number of model-based or fingerprinting-based
techniques [8] [9] have been proposed to locate a device.
As compared to the visual-based sensors mentioned above,
the RSS is available even without line of sight. But the
2017 IEEE International Conference on Robotics and Automation (ICRA)
Singapore, May 29 - June 3, 2017
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