Practical and Robust Power Management for Wireless Sensor Networks

Wireless Sensor Networks: WSNs) consist of tens or hundreds of small, inexpensive computers equipped with sensors and wireless communication capabilities. Because WSNs can be deployed without fixed infrastructure, they promise to enable sensing applications in environments where installing such infrastructure is not feasible. However, the lack of fixed infrastructure also presents a key challenge for application developers: sensor nodes must often operate for months or years at a time from fixed or limited energy sources. The focus of this dissertation is on reusable power management techniques designed to facilitate sensor network developers in achieving their systems\u27 required lifetimes. Broadly speaking, power management techniques fall into two categories. Many power management protocols developed within the WSN community target specific hardware subsystems in isolation, such as sensor or radio hardware. The first part of this dissertation describes the Adaptive and Robust Topology control protocol: ART), a representative hardware-specific technique for conserving energy used by packet transmissions. In addition to these single-subsystem approaches, many applications can benefit greatly from holistic power management techniques that jointly consider the sensing, computation, and communication costs of potential application configurations. The second part of this dissertation extends this holistic power management approach to two families of structural health monitoring applications. By applying a partially-decentralized architecture, the cost of collecting vibration data for analysis at a centralized base station is greatly reduced. Finally, the last part of this dissertation discusses work toward a system for clinical early warning and intervention. The feasibility of this approach is demonstrated through preliminary study of an early warning component based on historical clinical data. An ongoing clinical trial of a real-time monitoring component also provides important guidelines for future clinical deployments based on WSNs

Multi-Channel Reliability and Spectrum Usage in Real Homes: Empirical Studies for Home-Area Sensor Networks

Home area networks (HANs) consisting of wireless sensors have emerged as the enabling technology for important applications such as smart energy and assisted living. A key challenge faced by HANs is maintaining reliable operation in real-world residential environments. This paper presents two in-depth empirical studies on the wireless channels in real homes. The spectrum study analyzes the spectrum usage in the 2.4 GHz band where wireless sensor networks based on the IEEE 802.15.4 standard must coexist with existing wireless devices. We characterize the ambient wireless environment in six apartments through passive spectrum analysis across the entire 2.4 GHz band over seven days in each of the apartments. Notably, we find that the wireless conditions in these residential environments can be much more complex and varied than in a typical office environment. Moreover, while 802.11 signals play a significant role in spectrum usage, there also exist non-negligible noise from non-802.11 devices. The multi-channel link study measures the reliability of different 802.15.4 channels through active probing with motes. We discover that there is not always a persistently reliable channel over 24 hours; that reliability is strongly correlated across adjacent channels; and that link reliability does not exhibit cyclic behavior at daily or weekly timescales. Nevertheless, reliability can be maintained through a small number of channel hops per day, suggesting channel diversity as a key tool for designing robust HANs in residential environments. Our empirical studies provide important guidelines and insights for robust wireless sensor network design in residential environments

Energy-Efficient Low Power Listening for Wireless Sensor Networks in Noisy Environments

Low Power Listening (LPL) is a common MAC-layer technique for reducing energy consumption in wireless sensor networks, where nodes periodically wake up to sample the wireless channel to detect activity. However, LPL is highly susceptible to false wakeups caused by environmental noise being detected as activity on the channel, causing nodes to spuriously wake up in order to receive nonexistent transmissions. In empirical studies in residential environments, we observe that the false wakeup problem can significantly increase a node\u27s duty cycle, compromising the benefit of LPL. We also find that the energy-level threshold used by the Clear Channel Assessment (CCA) mechanism to detect channel activity has a significant impact on the false wakeup rate. We then design AEDP, an adaptive energy detection protocol for LPL, which dynamically adjust a node\u27s CCA threshold to improve network reliability and duty cycle based on application-specified bounds. Empirical experiments in both controlled tests and real-world environments showed AEDP can effectively mitigate the impact of noise on radio duty cycles, while maintaining satisfactory link reliability

ARCH: Practical Channel Hopping for Reliable Home-Area Sensor Networks

Home area networks (HANs) promise to enable sophisticated home automation applications such as smart energy usage and assisted living. However, recent empirical study of HAN reliability in real-world residential environments revealed significant challenges to achieving reliable performance in the face of significant and variable interference from a multitude of coexisting wireless devices. We propose the Adaptive and Robust Channel Hopping (ARCH) protocol: a lightweight receiveroriented protocol which handles the dynamics of residential environments by reactively channel hopping when channel conditions have degraded. ARCH has several key features. First, ARCH is an adaptive protocol that channel-hops based on changes in channel quality observed in real time. Second, ARCH is a distributed protocol that selects channels on a per-link basis, due to the large link-to-link variations in channel quality observed under empirical study. Third, ARCH is designed to be robust and lightweight. ARCH uses a practical hand-shaking approach to handle channel desynchronization and an efficient slidingwindow scheme that does not involve expensive calculations or modeling, and can be reasonably implemented on memoryconstrained wireless sensor platforms. Fourth, ARCH introduces minimal communication overhead for applications where packet acknowledgements are already enabled. We evaluate our approach through real deployment in real-life apartments with residents’ daily activity. Our results demonstrate that ARCH can reduce the number of packet retransmissions by a median of 42.3% compared to using a single, fixed wireless channel, and can enable up to a 2.2 improvement in delivery rate on the most unreliable links in our experiment. Under a multi-hop routing scenario, ARCH achieved an average 31.6% reduction in radio usage, by reducing the ETX along each path by up to 83.6%. Due to ARCH’s lightweight reactive design, most links achieve this improvement in reliability with 10 or fewer channel hops per day

Automated Code Management for Service Oriented Computing in Ad Hoc Networks

Ad hoc networks are dynamic environments where fre-quent disconnections and transient interactions lead to de-coupled computing. Typically, participants in an ad hoc network are small mobile devices such as PDAs or cellu-lar phones that have a limited amount of resources avail-able locally, and must leverage the resources on other co-located devices to provide the user with a richer set of func-tionalities. Service-oriented computing (SOC), an emerging paradigm that seeks to establish a standard way of mak-ing resources and capabilities available for use by others in the form of services, is a useful model for engineering soft-ware that seeks to exploit capabilities on remote devices. This paper proposes an automatic code management sys-tem supporting SOC in ad hoc networks. The system is re-sponsible for ensuring that the binary code required to use a service on a remote machine is available on the local host only when required. To support this functionality, a local code base is maintained by discovering and installing code from remote hosts. Since the system is specifically designed for ad hoc networks, it incorporates additional features that help it withstand the inherent dynamism of the network. We present an architecture for our system supporting automatic code management and follow it with a discussion of a Java-based implementation

Context Aware Session Management for Services in Ad Hoc Networks

The increasing ubiquity of wireless mobile devices is promoting unprecedented levels of electronic collaboration among devices interoperating to achieve a common goal. Issues related to host interoperability are addressed partially by the service-oriented computing paradigm. However, certain technical concerns relating to reliable interactions among hosts in ad hoc networks have not yet received much attention. We introduce ”follow-me sessions”, where interaction occur between a client and a service, rather than a specific provider or server. We allow the client to switch service providers if needed. The redundancy offers scope for reliable communication in the presence of mobility induced disconnections. We exploit strategies involving the use of contextual information, strong process migration, context-sensitive binding, and location-agnostic communication protocols. We show how follow-me sessions mitigate issues related to proxy-based service-oriented architectures in ad hoc networks, making them more reliable

Extending BPEL for Interoperable Pervasive Computing

The widespread deployment of mobile devices like PDAs and mobile phones has created a vast computation and communication platform for pervasive computing applications. However, these devices feature an array of incompatible hardware and software architectures, discouraging ad-hoc interactions among devices. The Business Process Execution Language (BPEL) allows users in wired computing settings to model applications of significant complexity, leveraging Web standards to guarantee interoperability. However, BPEL\u27s inflexible communication model effectively prohibits its deployment on the kinds of dynamic wireless networks used by most pervasive computing devices. This paper presents extensions to BPEL that address these restrictions, transforming BPEL into a versatile platform for interoperable pervasive computing applications. We discuss our implementation of these extensions in Sliver, a lightweight BPEL execution engine that we have developed for mobile devices. We also evaluate a pervasive computing application prototype implemented in BPEL, running on Sliver

A Component Deployment Mechanism Supporting Service Oriented Computing in Ad Hoc Networks

Ad hoc networks are dynamic, open environments that exhibit decoupled computing due to frequent disconnections and transient interactions. Reliable deploy-ment of components in such demanding settings requires a different design approach for the mechanisms that perform these functions. Not only do the deployment mechanisms have to perform the traditional tasks of deploying, installing, integrating and activat-ing components, they must also be robust enough to handle the nuances of an ad hoc network. This paper proposes a mechanism for component deployment that is adapted for use in ad hoc networks, and, as such, can cope with the effects of disconnection and transient connectivity. We present the general architecture for the mechanism and follow it with a discussion of a Java-based implementation of the model

Towards Predictable Service Provision in Mobile Ad Hoc Networks

This paper considers the technical challenges associated with the development of applications designed to work over mobile ad hoc net-works (MANETs). The setting is one in which a miniature application core residing on a mobile host with limited resources is able to support a complex application in a changing open environment by exploiting ser-vices made available by other hosts it encounters. The proposed solution extends in a novel way the applicability of the service provision paradigm to the ad hoc wireless setting. The novelty of the approach rests with the accumulation and management of knowledge about the service structure and the mobility of hosts to ensure a degree of predictability during the service exploitation process

Knowledge-driven Interactions With Services Across Ad Hoc Networks

Service oriented computing, with its aim of unhindered in-teroperability, is an appropriate paradigm for ad hoc net-works, which are characterized by physical mobility of het-erogenous hosts and by the absence of standardized application level protocols. The decoupled nature of computing in ad hoc networks can result in disconnections at inoppor-tune times during the client-service interaction process. We introduce the notion of a priori selection of services to reduce the likelihood of disconnection during service usage. A client may specify the times when it requires certain ser-vices. A knowledge base of the physical motion profiles of various service providers is used to select instances of a ser-vice that are co-located with the client at the required time and least likely to disconnect. A system for constructing the knowledge base is presented in this paper, along with the implementation details and the algorithm used to deter-mine the service usage pattern