Off-network control processing for scalable routing in very large sensor networks

Although wireless sensor networks have demonstrated a promising future, there are still a significant number of challenges to be overcome before they become reality. The prime research issues involve fault tolerance, network scalability, cost, hardware design, topology management, and power consumption. In this thesis we investigate two problems concerning wireless sensor networks: (A) energy efficient medium access control and (B) scalable routing architecture for very large wireless sensor networks.;Regarding problem A, we propose a Self Reorganizing Slot Allocation (SRSA) mechanism for a TDMA-based medium access control (MAC) protocol in wireless sensor networks. With SRSA, a node can achieve significant energy savings by remaining active only during allocated slots for transmissions and receptions. In multi-cluster networks, it is often necessary for nodes to use either CDMA or FDMA for preventing TDMA slots across neighboring clusters from interfering with each other. Using FDMA or CDMA incurs costs in terms of spectrum usage as well as hardware complexity. Our goal is to provide an alternative design that can reduce inter-cluster TDMA interference without having to use CDMA or FDMA. The primary contribution of our work is to demonstrate that with adaptive slot allocation algorithms, it is possible to minimize such interference under low traffic loading conditions. The second contribution is to design a feedback-based adaptive allocation protocol that can minimize those interferences without relying on any global synchronization mechanisms. We present the design of SRSA and provide a detailed simulation-based characterization of the protocol.;In the second problem, we motivate an architectural solution to address the problem of scalable routing in very large sensor networks. The control complexities of the existing sensor routing protocols, both node-centric and data-centric, do not scale well for large networks with potentially hundreds of thousands of embedded sensor devices. We develop a routing solution Off-Network Control Processing (ONCP) that achieves control scalability in large sensor networks by shifting a certain amount of routing functions to an "off-network" server. A tiered hybrid routing approach, consisting of "coarse grain" server-based global routing, and distributed "fine grain" local routing is proposed for achieving scalability by avoiding network-wide control message dissemination. We present the ONCP architectural concepts and analytically characterize its performance in relations to both flat and hierarchical routing architectures. Through an ns2-based simulation model, the experimental results indicate that for large sensor networks with realistic data models, the packet drop, latency and energy performance of ONCP can be significantly better than those for a flat sensor routing protocol such as Directed Diffusion and hieratical cluster-based protocol like CBRP We also incorporate the sink mobility into routing architecture, and investigate its impacts on the ONCP, Directed Diffusion, and CBRP routing protocols.