Abstract. Future mobile sensing systems are being designed using 802.15.4 low-power short-range radios for a diverse set of devices from embedded mobile motes to sensor-enabled cellphones in support, for example, of people-centric sensing applications. However, there is little known about the use of 802.15.4 in mobile sensor settings nor its impact on the performance of future communication architectures. We present a set of initial results from a simple yet systematic set of benchmark experiments that offer a number of important insights into the radio characteristics of mobile 802.15.4 person-to-person communication. Our results show that the body factor- that is to say, the human body and where sensors are located on the body (e.g., on the chest, foot, in the pocket)- has a significant effect on the performance of the communications system. While this phenomenon has been discussed in the context of other radios (e.g., cellular, WiFi, UWB) its impact on 802.15.4 based mobile sensor networks is not understood. Other findings that also serve to limit the communication performance include the effective contact times between mobile nodes, and, what we term the zero bandwidth crossing, which is a product of mobility and the body factor. This paper presents a set of initial findings and insights on this topic, and importantly, we consider the impact of these findings on the design of future communication architectures for mobile sensing. 1

The proliferation of wireless and mobile devices has fostered the demand of context aware applications. Location is one of the most significant contexts. Multilateration, as a basic building block of localization, however, have not yet overcome the challenges of (1) poor ranging measurement; (2) dynamic and noisy environments; (3) fluctuations in wireless communications. Hence, they often suffer poor accuracy and can hardly be employed in practical applications. In this study, we propose Quality of Trilateration (QoT) that quantifies the geometric relationship of objects and the ranging noise. Based on QoT, we design a confidence based iterative localization scheme, in which nodes dynamically select trilaterations with the highest quality for localization. To validate this design, a wireless sensor network prototype is deployed and results show that QoT well represents trilateration accuracy, and the proposed scheme significantly improve localization performances. 1.

Abstract—In this paper we consider the problem of how several observer nodes can cooperatively make reliable judgements about one mobile node. These judgments shall not only cover the mere presence or absence of the mobile node, but also include coarse indications about the distance of the mobile node to the observers. To this end, we present and investigate in this paper a scheme for distance classification. The results show that our scheme greatly reduces the number of times where the mobile node is classified as “absent ” and furthermore provides reliable classifications into one of a set of pre-defined distances, provided this pre-defined set is small enough. I.

Recent technological advances have enabled the development of low-cost, low-power, and multifunctional sensor devices. These nodes are autonomous devices with integrated sensing, processing, and communication capabilities. In general, wireless sensor networks intend to provide information on spatio-temporal characteristics of the observed physical world. Hence, it is necessary to associate sensed data with locations, making data geographically meaningful. A number of applications, such as object tracking, environment monitoring, inherently rely on location information. Besides, location information also supports fundamental network layer services, such as topology control, routing, clustering, and so on. Hence, Localization, a mechanism for autonomously discovering and establishing spatial relationships among sensor nodes, is of great importance in the development of wireless sensor networks. This survey reviews diverse physical measuring abilities of sensor nodes, discusses issues in localization algorithm design, presents the state-of-the-art localization techniques, and finally suggests future directions in localization studies. Many localization approaches are proposed based on diverse positioning principles, environmental constrains, accuracy requirements, etc., making them suitable/unsuitable for different applications. This survey in depth elaborates and compares existing approaches from two aspects: physical measurement and network-wide localization. The design tradeoffs of localization algorithms, as well as their advantages and disadvantages, are emphasized for comparison. Among these localization techniques, no specific algorithm is a clear favorite across the spectrum. In conclusion, localization is a new and exciting field, with new algorithms, hardware, and applications being developed at a feverish pace. A lot of work still needs to be done to realize practical applications for wireless sensor networks.

Abstract—Networked sensors and actuators for purposes from production monitoring and control to home automation are in increasing demand. Until recently, the main focus laid on wired systems, althoughtheirdeployment requirescareful planningand expensive infrastructure that may be difficultto install or modify. Hence, solutions based on wireless sensor networks (WSNs) are gaining popularity to reduce cost and simplify installation. Clearly, one of the key issues rising from the switch to wireless communication lies in security; while an air gap is among the most effective security measures in wired networks, wireless communication is not as easy to isolate from attack. In this paper, we propose a system leveraging the peculiarities of the wireless medium, such as the broadcast nature of wireless communication and the unpredictability of indoor signal propagation to achieve effective protection against attacks based on the injection of fake data. Using a real-world WSN deployment and a realistic implementation of an attacker, we analyze this protection scheme and demonstrate that neither position change, transmission power manipulation, nor complete knowledge of wireless parameters can help an attacker to successfully attack the network. As a result, this work demonstrates how the chaotic nature of radio communication, which is often considered a disadvantage in regard to security objectives, can be used to enhance protection and support implementation of lightweight security mechanisms.

We present empirical data of communication between 802.15.4 devices in static and mobile scenarios. We evaluate the body factor between two devices in a cycling environment and show it has a significant impact on communication. Our findings show that RSSI is severly hampered as an indicator of reception quality and that LQI serves as a much more reliable indicator in a mobile setting. Additionally, we show that different bicycling speeds do not adversely affect 802.15.4 communication. 1

Recent years have witnessed the emergence of novel application paradigms such as the Wireless Sensor Network and Context Aware computing. Among the challenges posed by these applications, localization – i.e. the process of locating people and/or devices – has emerged as a key problem that has found only partial answers. Although GPS receivers are common on many consumer electronic devices, alternative solutions are needed when locating devices that strive to be small and inexpensive, as in sensor networks, or when supporting indoor positioning. This dissertation focuses on radio-based positioning schemes suitable for applications where GPS is not a viable solution. The first part of this work addresses schemes that use proximity constraints inferred from radio connectivity. A novel solution based on the Self-Organizing Map (SOM) formalism is proposed. Using extensive simulations, the SOM approach is shown to achieve a low localization error using limited computational resources. Comparison with other schemes demonstrate favorable results, especially in sparse deployments and when few (or none) of the nodes are located at known positions. The second part focuses on theoretical analysis of the results. Two broad families of positioning schemes are analyzed: 1) Range-free schemes that use radio proximity information, as in the SOM approach; and 2) Range-based schemes that measure the attenuation of the Radio-Frequency (RF) signal to estimate

This paper discusses our experience in designing and deploying a 994-node sensor network to measure the social contact network of a high school over one typical day. The system aims to capture interactions of human subjects for the study of infectious disease spread. We describe unique challenges posed by a large-scale network that is heavily affected by humans. We present techniques to address challenges such as frequent node reboots and global timestamps. The end result of the deployment is a dataset of 792 traces which can be used to calculate the school population’s contact network and the rough location where interactions occurred. 1

Abstract-Although the characteristics of RF transmissions are physically well understood at the lowest levels of communication design, accurately incorporating power and interference effects is one of the most challenging tasks in designing efficient wireless network algorithms. The most noteworthy approaches are the circular transmission and interference "ranges " that do not apply to antennae packages that are not omnidirectional, as well as to non line-of-sight environments of many low power wireless sensor and mesh network. In this paper we experimentally investigate and then model the transmission interference of low power 802.15.4 based transceiver nodes by relying not only on distance but also on the transmit power, orientations, and the relative positions of the transmitter, receiver, and interfering nodes. The experimentally validated power/interference model is then used as the basis for an optimization algorithm that schedules nodes to minimize interference and maximize throughput from a set of senders to a set of receivers. I.

Abstract—In this paper we analyse the accuracy of indoor localization measurement based on a Wireless Sensor Network (WSN). The position estimation procedure is based on the Received Signal Strength (RSS) measurements collected in a real indoor environment. Two different classes of low computational effort algorithms based on the centroid concept are considered, namely the Weighted Centroid Localization (WCL) method and the Relative Span Exponential Weighted Localization (REWL) method. In particular, different sources of measurement uncertainty are analysed by means of theoretical simulations and experimental results. Index Terms—Wireless Sensor Networks, localization, centroid algorithm, propagation model.