Energy-efficient protocols and topologies for sensor and personal-area networks

We study energy-efficient topologies and protocols in Wireless Sensor Networks (WSN) and Personal Area Networks (PAN). In both networks, energy-efficiency is the primary objective for designing communication protocols since the deployed devices are usually battery-powered and resource-constrained. We also identified network performance requirements (e.g., end-to-end delay, throughput, etc.), and improve energy-efficiency without sacrificing network performance. We identify WSN's distinct requirements on the Medium Access Control (MAC) protocol and trade-offs among delay, energy, and throughput. Based on these requirements and trade-offs, we propose ECR-MAC (for Energy-efficient Contention-Resilient MAC) which employs a Dynamic Forwarder Selection technique to improve both energy-efficiency and delay without requiring additional synchronization or radio hardware support, and efficiently handle spatially-correlated contention. Besides conserving independent node's energy in ECR-MAC, we also study the "energy hole" problem in WSN, and propose a differential duty cycle assigning approach to balance energy consumption overall the network. Results show that ECR-MAC provides significant energy-savings, low delay and high network throughput, and our differential duty cycle assigning approach can further improve network lifetime without sacrificing network performance. To provide a short bounded end-to-end delay for WSN's real-time sensor applications that may not be satisfied by ECR-MAC, we propose a sleep-based topology control technique, which facilitates to implement an efficient wakeup scheduling method by leveraging time synchronization and localization. Through analysis and simulations, we show that our topology control and wakeup scheduling can provide the end-to-end delay that is generally bounded by a small factor to a fully-active approach, achieve higher throughput than ECR-MAC, and conserve more energy. To address energy-efficiency problems in personal area networks, we propose a multi-hop energy-aware scatternet (EMTS) formation technique for Bluetooth-based PAN, and further design a local reorganization approach that maintains scatternets' energy-efficient features to extend scatternet lifetime. Our scatternet formation technique balances devices' energy consumption by assigning roles to devices that suit their workload and energy resources, and efficiently form the scatternets with short links and small network diameter to reduce energy consumption. The lightweight reorganization can extend scatternet lifetime further. Experimental results confirm that the generated scatternets have a significantly longer lifetime than others.