Joint modulation and multiple access optimization under energy constraints

We consider radio applications in sensor networks where energy is a limited resource so that energy consumption must be minimized while satisfying given delay and throughput requirements. In this context, we analyze energy-efficient data collection strategies where we minimize the total energy consumption necessary for collecting a certain amount of data from multiple sensors. The total energy consumption includes both the transmission energy and the circuit energy consumption. We propose a variable-length TDMA scheme where the slot length is adaptively assigned according to the number of bits in the transmitting queues and the distance between the transmitting nodes and the collecting node. The underlying goal is to finish the collection of information bits from the multiple sensor nodes before a deadline T with minimum energy cost. We show that the problem can be efficiently solved by convex relaxation methods, and in some special cases simple analytical solutions can be derived.