In future smart environments, wireless sensor networks will play a key role in sensing, collecting, and disseminating information about environmental phenomena. Sensing applications represent a new paradigm for network operation, one that has different goals from more traditional wireless networks. This paper examines this emerging field to classify wireless micro-sensor networks according to different communication functions, data delivery models, and network dynamics. This taxonomy will aid in defining appropriate communication infrastructures for different sensor network application sub-spaces, allowing network designers to choose the protocol architecture that best matches the goals of their application. In addition, this taxonomy will enable new sensor network models to be defined for use in further research in this area.

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Routing in Ad hoc networks is a challenging problem because nodes are mobile and links are continuously being created and broken. Existing on-demand Ad hoc routing algorithms initiate route discovery only after a path breaks, incurring a significant cost in detecting the disconnection and establishing a new route. In this work, we investigate adding proactive route selection and maintenance to on-demand Ad hoc routing algorithms. More specifically, when a path is likely to be broken, a warning is sent to the source indicating the likelihood of a disconnection. The source can then initiate path discovery early, potentially avoiding the disconnection altogether. A path is considered likely to break when the received packet power becomes close to the minimum detectable power (other approaches are possible). Care must be taken to avoid initiating false route warnings due to fluctuations in received power caused by fading, multipath effects and similar random transient phenomena. Experiments demonstrate that adding proactive route selection and maintenance to DSR and AODV (on-demand ad hoc routing protocols) significantly reduces the number of broken paths, with a small increase in protocol overhead. Packet latency and jitter also goes down in most cases. Because preemptive routing reduces the number of broken paths, it also has a secondary effect on TCP performance -unnecessary congestion handling measures are avoided. This is observed for TCP traffic under different traffic patterns (telnet, ftp and http). Additionally, we outline some problems in TCP performance in Ad hoc environments.

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Localization is a fundamental operation in mobile and self-configuring networks such as sensor networks and mobile ad hoc networks. For example, sensor location is often critical for data interpretation; moreover, network protocols, such as geographic routing and geographic storage require individual sensors to know their coordinates. Existing research focuses on localization mechanisms: algorithms and infrastructure designed to allow the sensors to determine their location. In a mobile environment, a related problem exists: when nodes are mobile, the underlying localization mechanism must be invoked repeatedly to maintain accurate location information. We propose and investigate adaptive and predictive protocols that control the frequency of localization based on sensor mobility behavior to reduce the energy requirements for localization while bounding the localization error. In addition, we evaluate the energyaccuracy tradeoffs that arise: intuitively, higher the frequency of localization, the lower the error introduced because of mobiliy. However, localization is a costly operation since it involves both communication and computation. Since energy is at a premium in wireless devices, it is important to perform localization in an energy efficient fashion. Our results indicate that the proposed protocols reduce the localization energy significantly without sacrificing accuracy.

Routing in Ad hoc networks is a challenging problem because nodes are mobile and links are continuously being created and broken. Existing on-demand Ad hoc routing algorithms initiate route discovery only after a path breaks, incurring a significant cost in detecting the disconnection and establishing a new route. In this work, we investigate adding proactive route selection and maintenance to on-demand Ad hoc routing algorithms. More specifically, when a path is likely to be broken, a warning is sent to the source indicating the likelihood of a disconnection. The source can then initiate path discovery early, potentially avoiding the disconnection altogether. A path is considered likely to break when the received packet power becomes close to the minimum detectable power (other approaches are possible). Care must be taken to avoid initiating false route warnings due to fluctuations in received power caused by fading, multipath effects and similar random transient phenomena. Experiments demonstrate that adding proactive route selection and maintenance to DSR and AODV (on-demand ad hoc routing protocols) significantly reduces the number of broken paths, with a small increase in protocol overhead. Packet latency and jitter also goes down in most cases. Because preemptive routing reduces the number of broken paths, it also has a secondary effect on TCP performance -unnecessary congestion handling measures are avoided. This is observed for TCP traffic under different traffic patterns (telnet, ftp and http). Additionally, we outline some problems in TCP performance in Ad hoc environments.

Visual sensor networks are becoming increasingly popular in a number of application domains. A distinguishing characteristic of VSNs is to self-configure to minimize the need for operator control and improve scalability. One of the areas of self-configuration is camera coverage control: how should cameras adjust their field-of-views to cover maximum targets? This is an NP-hard problem. We show that the existing heuristics have a number of weaknesses that influence both their coverage and their overhead. Therefore, we first propose a computationally efficient centralized heuristic that provides near-optimal coverage for small-scale networks. However, it requires significant communication and computation overhead, making it unsuitable for large scale networks. Thus, we develop a distributed algorithm that outperforms the existing distributed algorithm with lower communication overhead, at the cost of coverage accuracy. We show that the proposed heuristics guarantee to cover at least half of the targets covered by the optimal solution. Finally, to gain benefits of both centralized and distributed algorithms, we propose a hierarchical algorithm where cameras are decomposed into neighborhoods that coordinate their coverage using an elected local coordinator. We observe that the hierarchical algorithm provides scalable near-optimal coverage with networking cost significantly less than that of centralized and distributed solutions.

In a sensor network, the infrastructure (in terms of the sensor capabilities, number of sensors, and deployment strategy) plays a significant role in determining the performance of the network. In this paper, we study the effect of infrastructure decisions on the performance of a sensor network. We study the effect of the infrastructure for two types of network delivery models (phenomenon driven and continuous) and different network protocols (DSR, DSDV and AODV). We show the performance both in terms of network efficiency as well as meeting the application accuracy and latency demands. By exploring the criteria for effective infrastructure configurations, we open the door for network optimizations that control the effective topology to better achieve the application requirements.