How much energy saving does topology control offer for wireless sensor networks? - A practical study

Topology control is an important feature for energy saving, and many topology control protocols have been proposed. Yet, little work has been done on quantitatively measuring practical performance gains that topology control achieves in a real sensor network. This is because many existing protocols either are too complex or make too impractical assumptions for a practical implementation and analysis. A rule of thumb or a practical upper bound on the energy saving gains achievable by topology control would assist engineers in estimating the overall energy budget of a real sensor system. This paper proposes a new topology control protocol simple enough to permit a straightforward stochastic analysis and also a real implementation in Mica2. This protocol is currently deployed in our testbed network of 42 Mica2 nodes. Our contribution is not on the novelty of this protocol but on a practical performance bound we can study using this protocol. The stochastic analysis reveals that topology control can achieve a power gain proportional to network density divided by a factor of eight to ten. Our experiment result from the real testbed tests confirms this finding. We also find a tradeoff in terms of throughput loss due to reduced density by topology control which amounts to about 50% throughput loss. These performance figures represent rough rules of thumb on energy efficiency achievable even by a very simple, unoptimized protocol. (C) 2007 Elsevier B.V. All rights reserved.