Study On Data Forwarding And Buffer Scheduling For Opportunistic Networks

With the rapid development of the processor speed, mobile communication andbattery life, Computers evolve from completely wired to completey mobile.In the mostextreme case, even all nodes are mobile, only relying on available opportunities:traditional communication infrastructure and the mobility of intermediate nodes, thedata communication can realize between pair nodes. These are Opportunistic Networks(ONs). Moreover, the appearance of plenty of low-price intelligent devices equippedwith short-distance wireless communication interface boosts the fast rise ofopportunistic networks application in many extreme communication circumstances.Several typical characteristics in terms of data communication in ONs are shown asfollows.①Network topology dynamically change due to the mobility of nodes.End-to-end communication paths can not been established between pairs of nodes,which cause the low rate and high delay take place in data communication;②Successful rate of data forwarding mainly relies on the contact opportunitiesarising from the movement of nodes. Thus data forwarding policy made based onmeeting probability between pair nodes becomes the essential technique, whichinfluences the performance of data transmission.③Contention about the buffer space is very prominent in ONs when the networkresources are constrained. Due to a plenty of data that has not been forwarded timelystays in networks for long time，the storage space of nodes is consumed fast. Thus thenodal buffer is requested to obtain more efficient utilization.Data forwarding in opportunistic networks has two key challeges: theunpredictable mobility of nodes the network resouces constraints.With the limitedresources, Effective forwarding strategies and high-performance schedulingmanagement schemes become two key factors in the process of data transmission.Around such two key factors, study works in this thesis are shown as follows.Firstly, A delegation forwarding policy based on utility is proposed for ONs.Theforwarding policy computes a hybrid utility based on the information that containsnodal centrality, contact degree and similarity between pair nodes. The utility representsthe meeting probability between two nodes in the near future. Current node carryingmessages selects the best encountered node as delegation to forward message based on the utility. Simulation results show that the forwarding algorithm can select correctlythe appropriate carrying node for messages and improve the successful rate of deliverymessage for networks.Secondly, focus on the existence of partition in stationary opportunistic networks,stationary ferry route design for multiple ferries is proposed for ONs. The route designfor multiple ferries introduces two types of mobile entities which are called as LocalFerry (short as LF) and Global Ferry (short as GF). They are responsible for datacommunication within different areas respectively and provide forwarding message forstationary nodes that can not communicate directly. The route design makes LF and GFrealize online collaboration to delivery messages in order to improve the delivery rateand reduce latency for messages in patitioned ONs.In addition, aiming at the existence of partition in mobile opportunistic networks,dynamic ferry route design for local ferries is proposed for partitioned ONs. The ferryroute design utilizes traffic-aware heuristic to find the optimal movement path for localferries with the goal of minimizing message drops of nodes. At the same time,stationary relay nodes are used to complete asynchronous cooperative communicationbetween LF and GF. Finally simulation results demonstrate the multi-ferry routescheme can improve the performance of data transmission in partitioned ONsFinally, to solve the problem that nodes can not forward all buffered messagesduring limited contact duration because of intermittent connectivity of ONs, a bufferscheduling algorithm is proposed based on historical contact frequencies between pairnodes. The scheduling algorithm decides the forwarded priority for buffered messagesin current node based on historical contact frequencies between the encountered nodeand messages’ destinations. Furthermore, combining with dropping policy based onmessage copies, the utilization ratio of the nodal storage and the communication linkbandwidth get improvement，and the delivery efficiency for messages has beenheightened accordingly.In summary, this dissertation widely analyses data forwarding polices and bufferscheduling management policies in ONs. In order to overcome the limitations of theexisting strategies，a few data forwarding scheme and buffer scheduling policies abovementioned are proposed. Simulation experiments demonstrate that the above proposedmethods can significantly improve the performance of opportunistic networks in termsof the message delivery rate, message transmission delay and the network overheads.