On exploiting contact patterns for data forwarding in duty-cycle opportunistic mobile networks

In this paper, we focus on investigating the impact of duty-cycle operation on data forwarding in duty-cycle opportunistic mobile networks (OppNets) and on designing an efficient data-forwarding strategy for duty-cycle OppNets. Some recent studies utilize node contact patterns to aid in the design of a data-forwarding strategy in OppNets. However, when duty-cycle operation is applied in OppNets, several node contacts will be missed when nodes are in the sleep state for energy saving, and it becomes challenging to design an efficient data-forwarding strategy based on exploitation of node contact patterns. To address this challenge, we first propose a model to investigate the contact process in dutycycle OppNets and to estimate the probability of contact discovery. We also experimentally validate the correctness of our proposed model. Second, based on this model, we propose a novel approach to improve the performance of data forwarding in duty-cycle OppNets. The proposed forwarding strategy takes into account both the contact frequency and contact duration and manages to forward data copies along the opportunistic forwarding paths, which maximize the data delivery probability. Finally, extensive real-trace-driven simulations are conducted to compare the proposed data-forwarding strategy with other recently reported dataforwarding strategies in terms of delivery ratio and cost. The simulation results show that our proposed data-forwarding strategy is close to the Epidemic Routing strategy in terms of delivery ratio but with significantly reduced delivery cost. Additionally, our proposed strategy outperforms the Bubble Rap and Prophet strategies in terms of delivery ratio with reasonable delivery cost.