| The objective of this thesis is to investigate the role of protocol self organization at the Medium Access Control Layer in wireless ad hoc and sensor networks. Protocol self organization is defined as autonomous and self-calibrating communication state machines that can adjust their operating parameters and state machine logic as a reactive response to external operating environment such as network load, node crowding, topology changes due to mobility, energy depletion, infrastructure failure and communication errors. While the traditional wired networks continue to enjoy relatively stable operating environments, the emerging wireless and sensor networks suffer from the mentioned operating instabilities due to their ad hoc deployments, specialized applications and various resource constraints. The goal in this work is to utilize protocol reorganization as defined above in order to mitigate the effects of the mentioned instabilities. We propose a MAC self organization framework for both intra-MAC and inter-MAC as outlined below.;For infra-MAC self organization, we develop an In-band Self-Organized MAC (ISOMAC), for wireless sensor networks with arbitrary mesh topologies. The specific problems the mechanism attempts to solve are arbitrary ad hoc deployment, energy limitation, and network dynamics. The novelty of the proposed framework lies in its in-band control mechanism. Both analytical and simulation models show that in addition to the reasonably fast reorganization convergence, the energy penalty of the in-band information is quite negligible.;A cross-layer approach, Minimized Slot Misordered Routing (MSMR) with ISOMAC style MAC, is also developed. The self organizing TDMA MAC schedule is used as input to the routing protocol to generate routing paths.;As for validation and extension of the ISOMAC framework, an application adaptation in vehicular wireless networks is investigated. An adapted ISOMAC, Vehicular Self-Organizing MAC (VeSOMAC), which is capable of inter-vehicle message delivery with short and deterministic delay bounds has been developed. Through ns2 simulation experiments, the efficiency of self organizing abilities of VeSOMAC is demonstrated in the presence of fast topology variation in vehicular networks.;Finally, we propose an inter-MAC self organization framework in the form of dynamic MAC protocol switching. The problem we address with this framework is to make a network adaptable with dynamic network loading conditions while providing acceptable user perceived performance. The key concept is that a network node can autonomously switch across different MAC layer protocols as a response to network traffic heterogeneity. Therefore, the reorganization here is accomplished across multiple protocols. Both theoretical and experimental analyses support that the dynamic MAC protocol switching logic enhances the network-wide throughput in the presence of traffic heterogeneity. |
