| Every physical event results in a natural information gradient in the proximity of the phenomenon. Many physical phenomena follow known diffusion laws. In wireless sensor networks, this natural gradient information can be exploited to design robust and energy efficient protocols. In this thesis, we design an information gradient-based active query routing framework for wireless sensor networks. In our analysis and design, we target scenarios where the event's effect can be sensed around the surrounding location of the event's source. To process user's query about events, we design protocols for three basic tasks: (1) query dissemination, (2) query processing, and (3) query reply. In these designs, we are interested to improve energy efficiency and robustness. These protocols reduce energy overhead by eliminating proactive phases and unnecessary flooding. Also, several robustness issues, such as noisy natural information gradient, region without information gradient i.e., flat information region, and environmental noise as well as lossy wireless links are modeled and considered in our analysis. In addition to mechanism design, we use simulations, analytical modeling and test-bed implementation for performance evaluation. From our results, it is found that the proposed protocols are significantly robust and energy efficient than the state of the art solutions.;More specifically, our current case studies include followings: (1) Design a multiple-path greedy mechanism to disseminate queries over noisy natural information gradient. Using analytical model and simulations, we analyze robustness and energy efficiency of the protocol in the presence of erroneous readings, environmental noise and region without information gradient as well as lossy wireless links. Also, we propose a new single-path approach for query routing in the presence of information gradient. Further, we compare both single-path and multiple-path approaches using analytical model and simulations.;(2) Develop an information gradient-based querying architecture that exploits geographical information and the perceivable gradient of an event's effect to reduce search overhead. We introduce virtual grid leveraging geographical information while the spread of the event's effect is used to determine the size of the grid cell. Then probing is used to identify the availability of required information before disseminating a query in a cell. We develop and evaluate algorithms for aggregate queries and combined query using this architecture.;(3) Design link loss tolerant data (or reply) routing protocol for multi-hop wireless sensor networks. The proposed data routing protocol effectively combines the benefits of wireless broadcast advantage with the traditional retransmission based data routing. Also, this protocol instantaneously adapts to network dynamics without periodic link quality maintenance. We evaluate the performance of the implementation of this protocol on a 56-node test-bed. In addition, we compare the performance of this protocol with that of hop-by-hop retransmission based routing with or without periodic link quality estimation, and the routing that exploits wireless broadcast advantage. |
