Cross-layer Energy Minimization 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 the energy-efficient joint routing, scheduling, and link adaptation strategies that maximize the network lifetime and 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 keeping the total energy consumption minimized. 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 more energy-efficient when only transmission energy is concerned, but single-hop transmissions may be more efficient when the circuit processing energy is considered.