Research On Data Transmission Mechanism In Opportunistic Mobile Networks

Recently, with the rapid proliferation of wireless portable devices (e.g., ipad, PDAs, smartphones and so on), Opportunistic Mobile Networks (OppNets) begin to emerge. With-out the constraint of real-time connectivity, OppNets are more suitable for the actual ad hoc network requirements. OppNets can be widely applied in wireless sensor networks, wildlife monitoring, vehicular networks, and providing network services in underdeveloped areas, etc. Being able to greatly improve people’s production and life style, OppNets have gained high attention from global researchers.In OppNets, it is hard to guarantee end-to-end path due to the time-varying network topology, and thus nodes with data to transmit have to exchange data with relay nodes within their communication range. This data exchange process is referred to as the store-carry-forward mechanism, which works as a basic strategy of data transmission in Opp-Nets. Many researchers have studied data transmission in OppNets, but the existing studies have two aspects of deficiencies:1) without consider the energy constraint of nodes in OppNets;2) lack of proper incentive schemes for data transmission in OppNets. Based on the latest results, this dissertation first investigates energy saving in neighbor discovery, then studies data forwarding in the duty-cycle mode and data dissemination in the selfish environment, and proposes the corresponding data forwarding strategy as well as incentive scheme for OppNets. The novelty and contributions are summarized as follows:1. A brief review on the background, overview, main characteristics, application field and related work of OppNets is provided.2. Exploring the trade-off between energy efficiency and the contact opportunities based on the Random Way-Point model in OppNets. In order to investigate this trade-off, this dissertation first proposes a model to quantify the detecting probability in Opp-Nets. Then, based on the proposed model, this dissertation analyzes the trade-off between energy efficiency and the total number of effective contacts under differ-ent situations. Simulation results show that the good trade-off points are obviously different when the speed of nodes is different.3. Exploring neighbor discovery in duty-cycle OppNets, and designing an energy-efficient adaptive working schedule for duty-cycle OppNets. The proposed adaptive work-ing schedule uses the past recorded contact histories to predict the future contact information, so as to adaptively configure the working schedule of each node in the network. Extensive simulations results demonstrate that the proposed adaptive work-ing schedule is superior to the random working schedule and the periodical working schedule algorithms in terms of the number of effect contacts, delivery ratio and delivery delay.4. Exploring the impact of duty-cycle operation on data forwarding in duty-cycle Opp-Nets, and designing an efficient data forwarding strategy for duty-cycle OppNets. The proposed forwarding strategy takes into account both the contact frequency and the contact duration, and manages to forward data copies along the opportunistic for-warding paths which maximize the data delivery probability in duty-cycle OppNets. Simulation results show that the proposed data forwarding strategy is close to Epi-demic Routing in terms of delivery ratio but with significantly reduced delivery cost. Additionally, the proposed strategy outperforms Bubble Rap and Prophet in terms of delivery ratio with reasonable delivery cost.5. Exploring data dissemination in selfish OppNets, and proposing an incentive-driven publish/subscribe (pub/sub) content dissemination scheme, called ConDis (Content Dissemination), for selfish OppNets. In ConDis, the Tit-For-Tat (TFT) scheme is em-ployed to deal with selfish behaviors of nodes in OppNets. ConDis also implements a novel content exchange protocol when nodes are in contact, and the objective is to maximize the utility of the content inventory stored in nodes’buffer. Extensive realistic trace-driven simulation results show that ConDis is superior to other ex- isting schemes in terms of total freshness value, total delivered contents, and total transmission cost.The conclusions and future work are depicted in the end of the dissertation.