On the use of the ZigBee protocol for wireless sensor networks

This project was developed within the ART-WiSe framework of the IPP-HURRAY group (http://www.hurray.isep.ipp.pt), at the Polytechnic Institute of Porto (http://www.ipp.pt). The ART-WiSe – Architecture for Real-Time communications in Wireless Sensor networks – framework (http://www.hurray.isep.ipp.pt/art-wise) aims at providing new communication architectures and mechanisms to improve the timing performance of Wireless Sensor Networks (WSNs). The architecture is based on a two-tiered protocol structure, relying on existing standard communication protocols, namely IEEE 802.15.4 (Physical and Data Link Layers) and ZigBee (Network and Application Layers) for Tier 1 and IEEE 802.11 for Tier 2, which serves as a high-speed backbone for Tier 1 without energy consumption restrictions. Within this trend, an application test-bed is being developed with the objectives of implementing, assessing and validating the ART-WiSe architecture. Particularly for the ZigBee protocol case; even though there is a strong commercial lobby from the ZigBee Alliance (http://www.zigbee.org), there is neither an open source available to the community for this moment nor publications on its adequateness for larger-scale WSN applications. This project aims at fulfilling these gaps by providing: a deep analysis of the ZigBee Specification, mainly addressing the Network Layer and particularly its routing mechanisms; an identification of the ambiguities and open issues existent in the ZigBee protocol standard; the proposal of solutions to the previously referred problems; an implementation of a subset of the ZigBee Network Layer, namely the association procedure and the tree routing on our technological platform (MICAz motes, TinyOS operating system and nesC programming language) and an experimental evaluation of that routing mechanism for WSNs

Collision-free beacon scheduling mechanisms for IEEE 802.15.4/Zigbee cluster-tree wireless sensor networks

The recently standardized IEEE 802.15.4/Zigbee protocol stack offers great potentials for ubiquitous and pervasive computing, namely for Wireless Sensor Networks (WSNs). However, there are still some open and ambiguous issues that turn its practical use a challenging task. One of those issues is how to build a synchronized multi-hop cluster-tree network, which is quite suitable for QoS support in WSNs. In fact, the current IEEE 802.15.4/Zigbee specifications restrict the synchronization in the beacon-enabled mode (by the generation of periodic beacon frames) to star-based networks, while it supports multi-hop networking using the peer-to-peer mesh topology, but with no synchronization. Even though both specifications mention the possible use of cluster-tree topologies, which combine multi-hop and synchronization features, the description on how to effectively construct such a network topology is missing. This paper tackles this problem, unveils the ambiguities regarding the use of the cluster-tree topology and proposes two collision-free beacon frame scheduling schemes. We strongly believe that the results provided in this paper trigger a significant step towards the practical and efficient use of IEEE 802.15.4/Zigbee cluster-tree networks

Feasibility of Indoor Localization using Angle of Arrival with Low Complexity Hardware

Owing to the enormous growth of the number of devices with wireless connectivity, for example smartphones and tablets but also healthcare monitors, object and device localization has become important. Besides the integration of Global Positioning System (GPS) sensors to localize objects and find locations outdoor, the number of applications collecting indoor location related information is uncountable. Currently developed applications are designed to incorporate indoor location depending functionality.nbsp;example one can use a mobile guide to accompany visitors in an exhibition, monitor elderly people at home or trace goods in a warehouse. The needed localization accuracy is strongly application dependent. This PhD intends to demonstrate the feasibility ofnbsp;Angle of Arrival localization algorithm to perform object localization within buildings. Therefore, a linear phased antenna array operating at 2.435 GHz is designed,nbsp;the intention to develop low complexity hardwarenbsp;on off-the-shelf components. The collected data samples are processed using different direction finding algorithms. Thenbsp;Multiple Signal Classification (MUSIC) and Estimation of Signal Parametersnbsp;Rotational Invariance Techniques (ESPRIT) algorithms are elaborated. Both the implemented algorithm as well asnbsp;antenna array architecture introduce inaccuraciesnbsp;determining the incident angle of a transmitting source. On one hand, the estimated direction will deviate from thenbsp;angle, it is callednbsp;angular measurement error. On the other hand, thenbsp;lobe of the total radiation patternnbsp;a certain beamwidth making the defined transmitternbsp;a markednbsp;instead of an exactnbsp;Both inaccuracies lead to undesired, but inevitable localization errors. Within the context ofnbsp;research two main tracksnbsp;followed. Firstly, this study investigates what interspacing is needed between multiple coherent sources to benbsp;to distinguish among them. Hence, the resolution of the measurement system is determined, based on the knowledge of the beamwidths. Through theoretical simulations and practical measurements, in the anechoic room, the feasible resolution is defined and shown to be related to thenbsp;dimensions andnbsp;source position. Secondly, it is intended to predict theoretically what localization errornbsp;be expected due to the angular measurement error whenever estimating the incident transmitter angle. Practical measurement results obtained in the anechoic roomnbsp;an empty room introducing reflections, must verify these predictions. Theynbsp;us to make statements concerning common angular measurement errors and thus localization errors feasible with Angle of Arrival localization deployed onto low complexity hardware.status: publishe

Analysis of the Realistic Resolution with Angle of Arrival for Indoor Positioning

The increasing importance of localizing objects in indoor environments is the motivation for much research on localization algorithms. This paper focuses on the maximum achievable resolution for Angle of Arrival as a means to position objects inside rooms using equipment within the field of wireless sensor networks, thus dealing with restricted resources. A clear view on beamforming using antenna arrays is represented and is proven to be useful in Angle of Arrival measurements. A detailed overview of a dedicated algorithm, leads the authors to draw conclusions concerning the resolution. A reference value is defined, which allows the authors to calculate the realistic resolution for all room dimensions. In order to verify these theoretical outcomes with practical results, the development of a quadrature demodulation based antenna array architecture, operating at 2.4 GHz, is presented. The latter is based on a study of different phase shifting technologies.status: publishe

Improving the performance of a RSS-based Location Estimation System, Study and Evaluation

status: publishe

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.status: publishe

Influence of Different Types of Metal Plates on a High Frequency RFID Loop Antenna: Study and Design

This paper presents our research on the influence of metal plates on a radio frequency identification (RFID) loop antenna operating at 13.56MHz. More specific we have tested different types of metal plates near a loop antenna in terms of resonance frequency. The performance of an RFID system strongly depends on the configuration of the antenna. The study shows that the resonance frequency will shift up in a metallic environment, resulting in a failing performance. A solution is presented to avoid the influence of a changing environment around a loop antenna. As an example a loop antenna is designed to prove the increase of stability.status: publishe