On the Convenience of Turning Off the Radio Interface and using Multiple Transmission Power Levels in Sensor Networks Applying Geographical Forwarding

Energy is a precious resource in wireless sensor networks. Accordingly, several approaches have been proposed in the literature to increase energy efficiency. In some of such approaches radio interface is periodically turned off. As a consequence, the energy spent by each node is expected to decrease. In this paper we argue that this is not always true if geographical forwarding is applied. In fact, periodically turning off the radio interface results in a decrease of the actual node density observed in the network, which causes a decrease in energy efficiency. Another important issue that will be investigated in this paper regards the advantages of using multiple levels of transmission power depending on the current network conditions. This involves the adoption of more complex and expensive hardware, but achieves much higher energy efficiency. In this paper an analytical framework is derived which allows to evaluate the effects of the above solutions on the overall energy efficiency of a sensor network where geographical forwarding is applied. Numerical results demonstrate that to achieve high energy efficiency a minimum observed node density must be guaranteed and that this minimum value increases as the number of transmission power levels that can be selected by a relaying node increases.