Research On Optimization Strategies Of Traffic Capacity In Complex Networks

The data is transmitted on the networks,which is the primary function of the networks.Modern society is in an information explosion age with the big data and large flow.For instance,with the rapid development of Internet,the network data are increasing rapidly.With the industry development and economic growth,vehicles have increased.Load of electric power network becomes more and more important heavy since the industrial electricity increased dramatically.Due to the above mentioned facts,traffic congestion occurs on current networks more frequently.The contradiction between network traffic capacity shortage and the increasing data flow is becoming more and more obvious.Enhancing traffic capacity of complex networks to reduce congestion has become a crucial problem to solve.Since the pioneering discovery of small-world phenomena and scale-free feature in the 1990 s,the study of complex networks has got considerable development.Complex network theory has become a powerful tool to understand the structure and functions of real network.Studies on the complex network dynamics contribute to understanding many kinds of phenomena emerging from real networks.Through investigating the dynamics of information traffic on complex networks,efficient strategies are proposed to enhance the network traffic capacity and alleviate its congestion.Traffic capacity is highly relevant to the underlying network structure and is also significantly affected by routing strategies and network resource allocation strategies.Therefore,in order to make the reasonable distribution of the average traffic load and the homogeneous information flow,this thesis focuses on optimizing strategies to enhance the traffic capacity of complex networks.(1)On the issue of optimizing network topology,a link-directed strategy based on the links' betweenness is proposed.This strategy enforce some undirected key links with heavy traffic load to be unidirectional so that the data packets pass the links with light traffic load,which results in the homogeneous information flow.This same link-directed strategy with non-random rule can enhance the overall traffic handling ability more than that with random rule.Although this link-directed strategy leads to a small increase of the average shortest path length,it can significantly enhance the network traffic capacity.In order to improve the overall performance of networks,an improved efficient linkadding strategy based on the node's local degree centrality and the shortest path length is proposed.The proposed link-adding strategy can bring better traffic capacity and other network performance.(2)As far as optimizing routing strategy concerned in the two-layer complex network,the traffic dynamics are analyzed and an efficient routing strategy is proposed which based on the betweenness of the logical and the physical layer nodes.In this strategy,the link weight is assigned based on the betweenness of nodes in both the logical and the physical layers.The optimal path with the minimum weight is chosen to deliver packets.Therefore,the routing paths can bypass hub nodes of both layers to make the information flow homogeneous and enhance the transport efficiency.For the purpose of balancing the transmitting capacity of the hub nodes and reducing computational complexity,an improved active routing strategy is proposed based on the degree of the logical and the physical layer nodes.In this strategy,the hub nodes also have an opportunity to be part of the optimal paths to deliver packets,which improves the utilization of network nodes.Since the cost function is based on degree,the proposed strategy has low computational complexity.Due to the significantly improved traffic performance,the active routing strategy can mitigate traffic congestion effectively.(3)On the issue of optimizing resource allocation,the average delivery capacity allocation strategy,which is susceptible to congestion,is widely applied according to the current research of two-layer complex networks.The average delivery capacity allocation strategy restricts the traffic capacity of two-layer complex networks.In case of fixed total delivery capacity,a reasonable allocation strategy is beneficial to improve the traffic performance.One efficient delivery capacity allocation strategy to optimize the traffic capacity of the two-layer complex networks is proposed.In this strategy,the delivering capacity of each node in the physical layer is assigned to the degree distributions of both the physical and logical layers.The results of theory analysis and simulations show the proposed strategy is more efficient than the average delivery capacity allocation strategy,and the traffic capacity of two-layer complex networks is actually enhanced.As the betweenness can reflect the traffic load more accurately,a betweenness-based efficient delivery capacity allocation strategy is proposed to optimize the traffic capacity of twolayer complex networks.The proposed strategy based on the betweenness can bring much better traffic capacity but need large calculations.