What you lose when you snooze: intercontact times and power-saving mode in opportunistic networks

In opportunistic networks, putting devices in energy saving mode is crucial to preserve their battery, and hence to increase the lifetime of the network and to foster user cooperation. However, a side effect of duty cycling is to reduce the number of usable contacts for delivering messages, thus increasing intercontact times and delays. In order to understand the effect of duty cycling in opportunistic networks, in this paper we propose a general model for deriving the pairwise intercontact times when a duty cycling policy is superimposed on the original encounter process determined only by node mobility. We consider both the case of contacts with negligible duration and that of regular contacts. The model we propose is general, i.e., not bound to a specific distribution of intercontact time. We validate the model in the case of exponential and Pareto intercontact times, two popular assumptions in the related literature.