Stijn Wielandt

Indoor Multipath Assisted Angle of Arrival Localization

Indoor radio frequency positioning systems enable a broad range of location aware applications. However, the localization accuracy is often impaired by Non-Line-Of-Sight (NLOS) connections and indoor multipath effects. An interesting evolution in widely deployed communication systems is the transition to multi-antenna devices with beamforming capabilities. These properties form an opportunity for localization methods based on Angle of Arrival (AoA) estimation. This work investigates how multipath propagation can be exploited to enhance the accuracy of AoA localization systems. The presented multipath assisted method resembles a fingerprinting approach, matching an AoA measurement vector to a set of reference vectors. However, reference data is not generated by labor intensive site surveying. Instead, a ray tracer is used, relying on a-priori known floor plan information. The resulting algorithm requires only one fixed receiving antenna array to determine the position of a mobile transmitter in a room. The approach is experimentally evaluated in LOS and NLOS conditions, providing insights in the accuracy and robustness. The measurements are performed in various indoor environments with different hardware configurations. This leads to the conclusion that the proposed system yields a considerable accuracy improvement over common narrowband AoA positioning methods, as well as a reduction of setup efforts in comparison to conventional fingerprinting systems.

Inductive charging of an EDLC powered wristband device for medical measurements

Electronic devices for measuring body parameters in healthcare environments generally exhibit hygienic problems. Furthermore, they require regular battery replacement or recharging. This paper presents an electronic wristband for medical measurements that can be charged wirelessly. Its power supply is equipped with a Qi compatible inductive power receiver, an Electrochemical Double-Layer Capacitor (EDLC) energy buffer and a series of voltage regulators that can be disconnected from the energy buffer by a microcontroller. Because the wireless power receiver was placed behind a display, a study was performed of the effects of the display on receiver coil characteristics and system performance. For the selection of the EDLC, a selection process is presented, making a tradeoff between device autonomy and charging time. The result is a completely sealable and thus sterilizable device that can be charged in less than 5 seconds while being worn on the wrist.

Design of an inductively coupled wireless power system for moving receivers

Present-day commercial wireless inductive power transfer systems rely on a low frequency alternating magnetic field, generated by a transmitter coil and picked up by a receiver coil. In general, these inductively coupled coils are perfectly aligned, in order to obtain a constant high coupling factor. In some cases though, the receiver can move on a regular basis above the transmitter. This paper discusses a method to wirelessly power a device moving on a surface. The transmitter consists of a single coil that is significantly smaller than the operation radius of the moving receiver. Therefore, the receiver is not always in the range of the transmitter and the power transfer occurs intermittent. In order to provide the receiver with a constant energy supply, a supercapacitor buffer is implemented. When the receiver approaches the transmitter, the buffer is charged in a short period of time. Furthermore, a communication channel is set up from the power receiver to the power transmitter, enabling receiver identification and power management.

Influence of magnetic design choices on the quality factor of off-the-shelf wireless power transmitter and receiver coils

In the design process of inductive wireless power systems, the quality factors of transmitter and receiver coils play an important role in the optimization of the link efficiency. In this work, the experimental evaluation of the quality factor of several commercially available transmitter and receiver coils is performed. The influence on the Q-factor of the following design choices is evaluated: an alignment aid magnet in the transmitter coil, the presence of ferrite at the receiver coil, electrical screening at both the transmitter and receiver coil and finally the effect of the proximity of the transmitter and receiver. The results of this research provide a clear overview of the impact of the studied magnetic design choices.

Performance simulations of a 2.4 GHz indoor angle of arrival system for multipath components

Multipath propagation is generally considered as an inconvenience in indoor radio frequency positioning systems, causing a degradation of localization accuracy. However, it is possible to exploit spatial information of reflected signals in a multipath assisted indoor positioning system, based on angle of arrival estimation. In order to assess the accuracy of the estimated angles and optimize system parameters, a simulation tool was developed. The tool simulates indoor line-of-sight signals and specular reflections of a 2.4 GHz signal, impinging on an antenna array. With this simulator, the performance of the MVDR, Beamscan, root MUSIC and ESPRIT algorithms for angle of arrival estimation is compared. Other investigated parameters include the position of the array in a square or rectangular room, the number of antennas, the number of signal decorrelation operations and the number of angles of arrival to be estimated. For each configuration, the spatial distribution of angular errors was evaluated, facilitating the design and dimensioning of an accurate indoor angle of arrival system.

Evaluation of angle of arrival estimation for localization in multiple indoor environments

The performance of indoor localization systems based on angle of arrival strongly depends on the environment. Consequently, a characterization of localization errors in different environments is necessary to correctly assess the accuracy of these systems. This paper focuses on the localization errors in multiple environments using basic 2.4 GHz linear antenna arrays. First, a theoretical algorithm is elaborated to predict the expected localization error in various environments. Subsequently, this algorithm is tested in practical tests performed in an anechoic room, an empty room and a room with obstacles. In these tests, various techniques for error minimization are evaluated, as well as the Beamscan, ESPRIT and MUSIC angle of arrival algorithms. It is shown that the accuracy in an anechoic room can also be obtained in an empty room for certain configurations. This is not the case for a room with obstacles preventing line-of-sight connections. For this case, a new type of localization system is proposed.

Study of wireless power systems with two-dimensionally moving receivers

The advantages of wirelessly powering electronic devices are numerous, but the technology is generally not being applied to moving devices because existing solutions are complex or offer poor efficiency. This paper describes a wireless power system for receivers moving between uniformly distributed points in a rectangular area. The proposed solution consists of a single small wireless power transmitter, offering both low complexity and high efficiency. Simulations were performed to determine the optimal transmitter location, shape and transmitted power. Also a statistical analysis of the receiver buffer size was performed. As a result of these simulations, a design flow was proposed that permits the use of existing technologies for the considered setup.

2.4 GHz single anchor node indoor localization system with angle of arrival fingerprinting

Location prevails as a piece of crucial information for decision-making processes. Whereas positioning in outdoor environments can be mainly attributed to Global Navigation Satellite Systems, no single technology can be appointed for accurate indoor localization. Many approaches exist, mostly relying on line-of-sight propagation from a mobile node to multiple anchor nodes. These solutions not only require complex installations, but in many cases they also make inapplicable assumptions about indoor environments. This paper investigates an indoor localization system with a single anchor node, estimating the position of an omnidirectional mobile transmitter by fingerprinting angle of arrival data. Measurements were taken with a 10-elements uniform linear antenna array at a 2.47 GHz carrier frequency. Three different scenarios were defined for the evaluation of localization errors and the influence of spatial smoothing, a technique for signal decorrelation.

Multipath-assisted angle of arrival indoor positioning system in the 2.4 GHz and 5 GHz band

Angle of arrival localization systems generally rely on multiple antenna arrays, estimating the position of a mobile node by measuring the line-of-sight directions. However, indoor multipath effects tend to deteriorate system performance. In this paper, an alternative system for in-room positioning is proposed and tested, consisting of a mobile transmitter and a single antenna array for angle of arrival estimation of direct and reflected signals. With the help of a floor plan of the room and a ray tracing algorithm, antenna array outputs can be calculated for every possible position of the mobile node. These simulation outputs are compared to the measurement results to determine the position of the transmitter. The system is evaluated in an extreme multipath environment, being a 2.25 m × 3 m room with metallic walls. Measurements are performed with a 2.45 GHz and a 5.2 GHz 8-element antenna array, followed by an MVDR beamforming algorithm with a variable number of spatial smoothing operations. Two distinct localization algorithms are tested, as well as the influence of various parameters on localization accuracy, resulting in an optimal setup with an average localization error under 1 m.

Resolving positions of coherent sources using linear antenna arrays at 2.4 GHz

In this paper we intend to find out what resolution can be achieved with two-dimensional Angle of Arrival localization when using linear antenna arrays at 2.4 GHz. A theoretical resolution calculation method is presented. Room dimensions, number of cooperating anchor nodes (provided with a linear antenna array) which track the position of a mobile node and number of antenna elements can be chosen. These theoretical calculations lead to the definition of a reference value which can be used to calculate the expected resolution for all rectangular shaped rooms with the desired variable settings. It is also shown that square rooms result in the best resolution and adding extra antenna elements improves the resolution. The design and calibration of a practical linear antenna array, with four linearly positioned 2.4 GHz antenna elements and inter distance of λ/2, is presented. Measurements of practical beam patterns, and the corresponding -3dB beam widths, for different incident angles show that influences such as mutual coupling and reflections can not be neglected. The practical resolutions are compared with expected theoretical values and it is shown that besides I/Q and phase offset calibration, manifold calibration is necessary.