Information Technology Reference
In-Depth Information
In traditional MANETs, if a path to destination can't be found, the message will be
dropped, which means Message Life Time is 0. However, a Spatial-Temporal path
allows a message to be stored and carried by a node for a certain time T until being
forwarded. From Fig. 6, when Message Life Time T=10s, the two-dimensional Ran-
dom Direction Model has the probability of 97% to be at least 1-Reachability, 70% to
be at least 2-Reachability and 10% to be at least 3-Reachability. K-Reachability offers
more flexibility to describe a communication system, and can provide more Spa-
tial-Temporal paths for delivering messages.
6
Conclusions
In this paper, we bring time dimension into graph theory to build a Spatial-Temporal
graph. “Spatial-Temporal Reachability” is proposed to describe the probability of a
message reaching its destination in time of validity in DTNs. Through mathematical
analysis, we get K-Reachability for a network from some basic local information such
as Message Life Time T, node moving speed V and transmitting range r. Simulations
are also done to prove the correctness of our analytical results. By bringing
time-dimension into consideration, we argue that Spatial-Temporal Reachability is a
better concept of studying a communication system's delivery ratio, robustness and
efficiency rather than traditional “Connectivity”. Furthermore, we get the probability of
a network being at least K-Reachable for each Message Life Time. Therefore,
K-Reachability tells a network's robustness in a quantitative fashion, giving guidance
to constructing high performance challenged networks. In the future, we plan to utilize
our analytical approach in different mobility models, further applications of Spa-
tial-Temporal Reachability are also considered.
Acknowledgements.
This work is supported by following projects: The National
Natural Science Foundation Project under Grant No. 61300173 and 61170295; Na-
tional Foundation Research Project; The Project of Aeronautical Science Foundation of
China under Grant No.2011ZC51024; The Co-Funding Project of Beijing Municipal
education Commission under Grant No.JD100060630; and the Fundamental Research
Funds for the Central Universities No. YWF-12-LXGY-001.
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