Body Attenuation and Path Loss Exponent Estimation for RSS-Based Positioning in WSN

Abstract

The internet of things (IoT) is a vision consisting of a world where a large number of common objects used in a daily basis are imbued with computational and communication capabilities, efficiently automating innumerous tasks [1]. This vision is closely related to the ubiquitous computing vision from Mark Weiser, in which "technologies disappear into the background", facilitating daily tasks [2]. There are several institutions working in order to achieve this vision, not only in the form of standards creation and improvement, but also in the interaction between different standards, so a global network augmented by these objects can be realized [3]. Sensor networks have a central role in this ubiquitous computing vision, since they provide the connection to the real world through sensors and actuators. A plethora of different sensors can be applied to the most diverse scenarios and the information generated by these sensors can be used to achieve higher understanding or process efficiency. The terms IoT and ubiquitous computing, along with other terms such as ambient intelligence, pervasive computing and smart objects are related and sometimes used interchangeably in literature. A common feature shared between these visions, directly related to the data sensed from these smart objects, is the location from where the data is collected. Positioning technology is a key enabler for the ubiquitous computing vision due to the application opportunities that arise with the knowledge of the position of the user or device. In this work, the focus is on positioning capabilities in wireless sensor networks (WSN) applied to indoor environment, which is a major component of the ubiquitous computing vision. WSN nodes are sensing capable devices composed by a microcontroller and a wireless transceiver. WSN constraints nowadays relate to device cost, energy and computational capabilities, the latter of which trades-off with higher battery recharge frequencies. Positioning in WSN can be accomplished by using optical, acoustic or radio frequency (RF) technologies, to produce range, angle or pattern information. Using one of these measurements, or a combination of them, the location of a device can be computed. Ultrawideband (UWB) is a technology that enables ranging capabilities between devices and allows the detection of multipath components of transmitted signals by using large channel bandwidths. This technology holds the key to solve indoor positioning systems due to its sub-meter ranging accuracy. Yet, due to the existence of two versions of UWB standard competing among each other, a pulsed version and a frequency division version, standard acceptance has been very slow. Furthermore, the ranging capability feature is optional, not obligating manufacturers to implement it in order to comply with the standard. Due to the slow standard acceptance, there isn't yet a mass market in place, which in turn affects device cost for currently available off-the-shelf components. The inclusion of UWB in IEEE 802.15.4 standard [4] as a low po...

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