| Summary: | 碩士 === 國立中央大學 === 通訊工程學系 === 105 === In delay tolerant networks (DTNs), persistent end-to-end route paths from the source to the destination are not truely existed. The DTN technology aims to solve the challenges and obstacles of data transmission caused by environmental factors, such as long distance transmission, uncertain network topology, sparse node density and high mobility.
Unlike conventional routing protocols in DTNs, the geographic routing strategy is the only one that does not need the network addresses of nodes to obtain the information of the route paths in a network. Nodes use the satellite positioning system or other positioning
systems to decide a routing mode and the next relay node, which is chosen to transfer messages based on the store-carry-and-froward scheme. However the geographic routing
model is difficult to predict the follow-up movement of nodes based on historical records of node movement in high dynamic network environments. This situation affects the policy of choosing the next relay node and decreases the opportunity to deliver messages to the destination. In addition, the constrained buffer space of nodes makes the congestion problem more possible.
This thesis proposes a modified geographic routing scheme which is suitable in high dynamic DTN environment.
1. This scheme uses the encounter node’s moving direction and base line which is
established between source and destination to get the encounter node’s moving
angle.
2. After getting the moving angle, this scheme will follow specific conditions to choose the next relay node.
3. At last, according to the size of the Euclidean distance between an encounter node and base line, this scheme will row the queue of the message transmission.
Accordingly, the modified geographic routing scheme will give different copy payoffs to increase the probability of successful delivery according to the routing strategy. Furthermore, this thesis designs an optimal buffer management to maximize the average message delivery rate. We focus on one key issue: messages should be dropped first when the buffer is full. We develop a utility function using local network information to optimize
per-message of average delivery rate. Messages will be dropped or kept according to their utility values. Finally, we use the ONE simulator to examine the performance of our scheme in comparison with other schemes. The results indicate that the delivery rate of
our proposed scheme approximately has 70% and higher average delay in different value sets of parameters in simulation.
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