Investigation Of Topological Network Construction And Information Dissemination In Mobile Ad Hoc Networks

With the development of mobile communication technology,mobile ad hoc networks(MANETs)come into being as an important network.The MANETs are combinations of mobile communications and computer networks,and user terminals not only move freely in the MANETs,but also maintain their communications.The MANETs support rapid networking in the absence of fixed network infrastructures,and they support dynamic restructuring according to the change of the network environment.Hence it is a good solution to the communication problems of the mainstream wireless communication networks.The MANETs not only bring great convenience for the deployment and application due to the autonomy,distributed network control and scalability,but also lead to some problems,such as unpredictable topology change,low efficiency of information dissemination and other issues.Therefore,this thesis investigates network performance in different scenarios of MANETs,from perspectives of topological network construction and information dissemination,respectively.Specifically,this thesis focuses on the analysis of three fundamental metrics,i.e.,connectivity(from the aspect of topological network construction),throughput capacity and delay(from the aspect of information dissemination),the design of corresponding scheduling schemes,and discussions of the impact of network parameters on the above three metrics.The contributions of this thesis are summarized as follows:First,we investigate the impact of inhomogeneous correlated mobility on largescale clustered wireless networks.The inhomogeneity means that nodes move to different locations with different probabilities,and correlation means that the movements of nodes are not independent of each other.In particular,we consider three network states based on the degree of correlation among nodes,i.e.,cluster-sparse state(strong correlations),cluster-transitional state(medium correlations),and cluster-dense state(weak correlations).In each state,we focus on the following problems:(1)how to place cluster-head nodes to minimize the critical transmission range and(2)what is the corresponding minimum critical transmission range.We derive the optimal distribution of cluster-head nodes that minimizes the critical transmission range,and disclose the impact of inhomogeneous correlated mobility on network performance.Second,we study a hierarchical cooperation scheduling mechanism of large-scale cognitive radio networks(CRNs),where both primary and secondary networks coexist.To be specific,the primary network consists of static primary nodes,which have a higher priority to access the licensed spectrum.In contrast,the secondary network consists of mobile secondary nodes,which have opportunistic access to the licensed spectrum by employing their cognitive abilities.Motivated by the fact that cooperation between primary and secondary nodes leads to possible improvements on the performance of CRNs,as well as the fact that the heterogeneous moving regions of secondary nodes will bring about further improvements,we propose a novel hierarchical cooperative scheduling mechanism,where secondary nodes serve as relays for primary packet transmissions by exploiting their mobility heterogeneity and geographic information.According to the proposed hierarchical cooperative scheduling mechanism,we derive the throughput and delay of both primary and secondary networks.The results show that both primary and secondary networks obtain a near-optimal per-node throughput.Stronger mobility heterogeneity of secondary nodes leads to better delay performance of the primary network.And the delay of secondary source-destination pairs is determined by the moving speed of destination nodes.Third,we investigate the impact of correlated mobility on the throughput and delay performance of MANETs under information-centric environments,where the main concern of nodes is to retrieve contents stored by other nodes.Based on the degree of correlation among nodes,we consider two network regimes,i.e.,the cluster-dense regime and cluster-sparse regime.In each regime,we study two mobility time scales:(1)fast mobility,where node mobility is at the same time scale as packet transmissions,and(2)slow mobility,where node mobility is at a much slower time scale than packet transmissions.In each regime,we characterize the network performance under fast mobility and slow mobility,respectively.The results show that under fast mobility,correlated mobility improves delay performance at the cost of throughput performance.This is because under fast mobility,only one-hop transmission is feasible in a single time slot,and the enhancement of the correlation among nodes increases the density of nodes in each cluster.Hence,the correlation decreases the number of nodes that can be transmitted simultaneously,but reduces the average distance between the content requester and the content holder.Under slow mobility,correlated mobility has a negative impact on both throughput and delay performance when the movement of nodes is slow because of the long time spent on the relay movements towards the content holder.Correlated mobility improves delay performance but degrades throughput performance when the movement of nodes is relatively fast because of the relatively short time spent on the relay movements towards the content holder.Finally,we summarize research contents and innovation points of this thesis.Besides,we point out the shortcomings of the research,and provide some research directions of MANETs for future work.