A Positioning System Based on Low-Frequency Magnetic Fields

Abstract

This paper describes the design and the realization of a low frequency AC-magnetic-field-based indoor positioning system. The system operation is based on the principle of inductive coupling between wire loop antennas. Specifically, due to the characteristics of the AC artificially generated magnetic fields, the relation between the induced voltage and the distance is modeled with a linear behavior in a bi-logarithmic scale when a configuration with coplanar, thus equally oriented, antennas is used. In this case the distance between a transmitting antenna and a receiving one is estimated using measurements of the induced voltage in the latter. For a high operational range, the system makes use of resonant antennas tuned at the same nominal resonant frequency. The quality factors act as antenna gain increasing the amplitude of the induced voltage. The low operating frequency is the key factor for improving robustness against non-line-of-sight (NLOS) conditions and environment influences with respect to other existing solutions.The realized prototype, which is implemented using off-theshelf components, exhibits an average and maximum positioning error respectively lower than 0.3 m and 0.9 m in an indoor environment over a large area of 15 m × 12 m in NLOS conditions. Similar performance is obtained in an outdoor environment over an area of 30 m × 14 m. Furthermore, the system does not require any type of synchronization between the nodes and can accommodate an arbitrary number of users without additional infrastructure.

An interactive system for exhibitions in a science and technology center

“…An infrastructure consisting of four knownposition transmitting coils (anchors) is deployed. Each anchor transmits a sinusoidal signal and is characterized by a unique operating frequency; thus, the system operates in frequency division multiplexing mode [5]. The user wears a receiving coil mounted on a badge (mobile node), which is equipped with a microcontroller that digitizes the received signal and transfers the samples to the PC via a Bluetooth connection.…”

“…If the assumption that the receiver and transmitter coils lie on the same plane is not applicable, i.e. for arbitrary orientations, a different model must be used, which is more computationally burdensome and prone to numerical issues [5]. In the developed system, we apply the simple power-law model in (1), due to its computational advantages.…”

“…Therefore, the core of the realized system is a positioning subsystem based on an infrastructure of knownposition nodes deployed in the exhibition area and a sensor, which is worn by the user. The principle of operation of the positioning system is based on inductive coupling of resonating coils [5], [6]. The position measurement results are used by a software application to implement the interaction functionality and game mechanics of the interactive exhibition.…”

Robust Indoor Mobile Localization with a Semantic Augmented Route Network Graph

“…The outdoor localization services can be provided by GPS with a reliable accuracy, but in indoor spaces which are GPS-denied, alternative technology needs to be explored. Many existing indoor localization methods rely on dedicated infrastructure such as Wi-Fi access points [1], ultrasonic networks [2], synthetic aperture radar (SAR) [3], Bluetooth [4], ultra-wideband (UWB) [5,6], or magnetic fields [7]. However, this is often expensive and labor-intensive for large-scale deployment and suffers from discontinuous tracking during pedestrian movement.…”

Accurate estimation of a coil magnetic dipole moment

“…Then, by measuring a set of physical quantities that depend on the transmitted signal, ranging and positioning can be performed using fitting techniques on a known propagation model. Among PSs, those based on measurement of AC magnetic fields, generated by either mobile nodes or fixed beacons are often mentioned in the recent literature, because this approach is both easily implemented and robust to most environmental factors, such as the presence of obstacles and the static geomagnetic field [7]-12].…”