Combined Human, Antenna Orientation in Elevation Direction and Ground Effect on RSSI in Wireless Sensor Networks

In this paper, we experimentally investigate the combined effect of human, antenna orientation in elevation direction and the ground effect on the Received Signal Strength Indicator (RSSI) parameter in the Wireless Sensor Network (WSN). In experiment, we use MICAz motes and consider different scenarios where antenna of the transmitter node is tilted in elevation direction. The motes were placed on the ground to take into account the ground effect on the RSSI. The effect of one, two and four persons on the RSSI is recorded. For one and two persons, different walking paces e.g. slow, medium and fast pace, are analysed. However, in case of four persons, random movement is carried out between the pair of motes. The experimental results show that some antenna orientation angles have drastic effect on the RSSI, even without any human activity. The fluctuation count and range of RSSI in different scenarios with same walking pace are completely different. Therefore, an efficient human activity algorithm is need that effectively takes into count the antenna elevation and other parameters to accurately detect the human activity in the WSN deployment region.Comment: 10th IEEE International Conference on Frontiers of Information Technology (FIT 12), 201

Key Generation in Wireless Sensor Networks Based on Frequency-selective Channels - Design, Implementation, and Analysis

Key management in wireless sensor networks faces several new challenges. The scale, resource limitations, and new threats such as node capture necessitate the use of an on-line key generation by the nodes themselves. However, the cost of such schemes is high since their secrecy is based on computational complexity. Recently, several research contributions justified that the wireless channel itself can be used to generate information-theoretic secure keys. By exchanging sampling messages during movement, a bit string can be derived that is only known to the involved entities. Yet, movement is not the only possibility to generate randomness. The channel response is also strongly dependent on the frequency of the transmitted signal. In our work, we introduce a protocol for key generation based on the frequency-selectivity of channel fading. The practical advantage of this approach is that we do not require node movement. Thus, the frequent case of a sensor network with static motes is supported. Furthermore, the error correction property of the protocol mitigates the effects of measurement errors and other temporal effects, giving rise to an agreement rate of over 97%. We show the applicability of our protocol by implementing it on MICAz motes, and evaluate its robustness and secrecy through experiments and analysis.Comment: Submitted to IEEE Transactions on Dependable and Secure Computin

Implementation of a herd management system with wireless sensor networks

This paper investigates an adaptation of Wireless Sensor Networks (WSNs) to cattle monitoring applications. The proposed solution facilitates the requirement for continuously assessing the condition of individual animals, aggregating and reporting this data to the farm manager. There are several existing approaches to achieving animal monitoring, ranging from using a store and forward mechanism to employing GSM-based techniques; these approaches only provide sporadic information and introduce a considerable cost in staffing and physical hardware. The core of this study is to overcome the aforementioned drawbacks by using alternative cheap, low power consumption sensor nodes capable of providing real-time communication at a reasonable hardware cost. In this paper, both the hardware and software has been designed to provide a solution which can obtain real-time data from dairy cattle whilst conforming to the limitations associated with WSNs implementations

Enhancing the Performance of Propagation Model-Based Positioning Algorithms

Object localization in wireless networks through Received Signal Strength (RSS) measurements requires a precise estimation of the signal attenuation model in order to produce meaningful results. The popular lognormal channel model, widely adopted to describe the signal strength attenuation as a function of the distance between nodes, turns out to be too simplistic when applied to a real scenario. In this paper, we analyze two possible improvements to this model: on one hand, we build a different channel model for each reference node in the network, with the aim of tackling the anisotropy of the environment. On the other hand, we explicitly append to the lognormal model a term to account for walls attenuation. A thorough experimental testbed demonstrates the potentials of the two approaches, with the second one being especially useful to counteract the effect of the limited sensitivity of practical wireless receivers

Performance of electromagnetic communication in underwater wireless sensor networks

Underwater wireless sensor networks (WSNs) composed of a number of sensor nodes that are deployed to conduct a collaborative monitoring task. Wireless signals are used for communication between the sensor nodes. Acoustic signals are the dominant signals used as a wireless communication medium in underwater WSNs due to the relatively low absorption in the underwater environments. Acoustic signals face a lot of challenges such as ambient noise, manmade noise, limited bandwidth, multipath and low propagation speed. Some of these challenges become more severe in shallow water environment where a high level of ambient and mankind noise, turbidity and multipath propagation are available. Therefore, electromagnetic signals can be applied as an alternative communication signal for underwater WSNs in the shallow water. In this project, the performance of EM communication in underwater WSNs is investigated for the shallow water environment. Theoretical calculations and practical experiments are conducted in fresh and seawater. It is shown that signals propagate for longer ranges in freshwater comparing to seawater. Theoretical results show that attenuation of electromagnetic communication in seawater is much higher than in fresh water. The attenuation is increasing with the increasing of frequency. In addition, velocity of the signal is increasing as the frequency is increasing while loss tangent is decreasing as the frequency increasing. Based on practical experiments, freshwater medium permits short ranges EM communication that does not exceed 25.1 cm for 2.4 GHz frequency. On the other hand, communication in seawater is very difficult to achieve for the same high frequency. Path loss exponent was estimated for freshwater environment based on logdistance path loss model. The estimation was achieved through a comparison between theoretical calculations and practical measurements. The path loss exponent for EM communication in fresh water was estimated to be in the range of 2.3 to 2.4

A realistic testing of a shipboard wireless sensor network

International audienceWireless Sensor Networks (WSN) may be a very useful technology for monitoring systems in hostile environments. Few works have treated the use of this technology in the particular metallic shipboard environment. This paper reports on the deployment of a WSN on board a ferry in realistic conditions. The network was tested during sailings and stopovers for several days. The results of our previous papers reporting on the radio wave propagation on board ships are recalled. Network performance and its topology evolution with respect to previous results are presented. In spite of the metallic structure of ferries and the dynamic movement of crew and passengers on board, the results show a significant network reliability and connectivity. The previous conclusions have been also confirmed by the topology evolution of the network and the analysis of RSSI levels of links between sensor nodes

Weighted Least Squares Techniques for Improved Received Signal Strength Based Localization

The practical deployment of wireless positioning systems requires minimizing the calibration procedures while improving the location estimation accuracy. Received Signal Strength localization techniques using propagation channel models are the simplest alternative, but they are usually designed under the assumption that the radio propagation model is to be perfectly characterized a priori. In practice, this assumption does not hold and the localization results are affected by the inaccuracies of the theoretical, roughly calibrated or just imperfect channel models used to compute location. In this paper, we propose the use of weighted multilateration techniques to gain robustness with respect to these inaccuracies, reducing the dependency of having an optimal channel model. In particular, we propose two weighted least squares techniques based on the standard hyperbolic and circular positioning algorithms that specifically consider the accuracies of the different measurements to obtain a better estimation of the position. These techniques are compared to the standard hyperbolic and circular positioning techniques through both numerical simulations and an exhaustive set of real experiments on different types of wireless networks (a wireless sensor network, a WiFi network and a Bluetooth network). The algorithms not only produce better localization results with a very limited overhead in terms of computational cost but also achieve a greater robustness to inaccuracies in channel modeling