Energy Minimization and Delay Analysis in TDMA-based Sensor Networks

We consider sensor networks where energy is a limited resource so that energy consumption must be minimized while satisfying given throughput requirements. Moreover, energy consumption must take into account both the transmission energy and the circuit processing energy for short-range communications. In this context, we analyze energy-efficient joint routing, scheduling, and link adaptation strategies that maximize the network lifetime. We emphasize that the energy efficiency must be supported across all layers of the protocol stack through a cross-layer design. We start with the joint MAC and link layer optimization, and then extend the model to include routing optimization. The joint optimization minimizes the total energy consumption including both the transmission energy and the circuit processing energy across the network. We propose variable-length TDMA schemes where the slot length is optimally assigned according to the routing requirement while minimizing the energy consumption across the network. We show that the optimization problems can be transformed into or approximated by convex problems that can be efficiently solved using known techniques. The results show that multihop routing schemes are usually more energy-efficient when only transmission energy is considered, but single-hop transmission may be more efficient when the circuit processing energy is also taken into account. The delay performance of the optimal TDMA scheme is analyzed and an algorithm for minimum-delay scheduling is proposed. The delay analysis result can be applied to general networks based on TDMA transmissions.