Bounds on Dynamic Modulation Scaling for Wireless Sensor Networks

Wireless communication is the most energy expensive operation for energy constrained wireless sensor networks. Dynamic modulation scaling (DMS) is a technique useful for optimizing transmission energy with respect to number of packets that need to be transmitted at that particular time intervals. In general, DMS trades off transmission energy against transmission delays. Multilevel (M-ary) modulation is the key aspect for dynamic modulation scaling. Dynamically varying the constellation size b (number of bits per symbol) with respect to number of packets that need to be transmitted helps in optimizing transmission power. In this scenario it is very important to decide minimum and maximum bounds on constellation size (scale of modulation) otherwise it may result in performance degradation. In this paper various factors affecting minimum and maximum limit of b are discussed and it is shown that the individual node can decide minimum limit on b but for deciding maximum limit it needs to consider network aspects such as network topology, node density, location of particular node etc. Only proper selection of these limits results in optimized power consumption with satisfactory performance. Otherwise trying to save energy without satisfying performance parameters will require retransmission and the energy cost for that will be much higher than what was saved earlier.