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. Then, we specialise this model when the original intercontact times are exponential (an assumption popular in the literature), and we show that, in this case, the intercontact times measured after duty cycling are, approximately, again exponential, but with a rate proportional to the inverse of the duty cycle.

Keywords: {mobile ad-hoc networks, opportunistic networks, duty cycling, intercontact times}