Studies On The Dynamics Of Wireless Ad Hoc Network Topology

Because mobile Ad Hoc networks(MANETs) are decentralized; self-organizing networks and are capable of forming a communication network without relying on any fixed infrastructure, various demanding military, business and civilian applications are expected to be widely implemented in MANETs. The fundamental issue in MANETs is that performance degrades dramatically as the increase of path failures due to the complexity of user mobility. A sparse topology due to a sparse node density or a small wireless communication range may suffer disconnection, and/or may have a limited number of paths connecting nodes potentially leading to network congestion. This show the dynamics induced by node mobility, node density, wireless transmission range and node-pair distance affect the communication paths, the connectivity and performance of MANETs. Therefore, a study of the dynamic properties of MANETs is deemed crucial to provide reliable service. In this doctoral study, the following issues are investigated: First, in the performance evaluation for an MANET, it should be tested under realistic conditions including, but not limited to, a sensible transmission range, limited buffer space for the storage of messages, representative data traffic models, and realistic movements of the mobile users (i.e., a mobility model). We describe several mobility models that represent mobile nodes whose movements are independent of each other (i.e., entity mobility models) and several mobility models that represent mobile nodes whose movements are dependent on each other (i.e., group mobility models). The goal of surveying the mobility models that are used in the simulations of MANETs is in order to offer researchers more informed choices when they are deciding upon a mobility model to use in their performance evaluations. Moreover, by introducing several metrics, we present simulation results that illustrate the importance of choosing a mobility model in the simulation of an MANET. Specifically, we illustrate how the performance results of an MANET drastically change as a result of changing the mobility model simulated. In addition, by comparison of these presented mobility models, taking one with another, the SMS mobility is best which can model captures the transient user mobility according to the physical law of a smooth movement, and achieves the necessary stationary properties regarding stable average speed and uniform node distribution.Second, an important task of mobile Ad Hoc networks consisting of geographically dispersed nodes is to determine an appropriate topology over which high-level routing protocols are implemented. There is a need to evaluate the quality of topology. Based on the SMS mobility model, we investigate the path dynamics from three aspects:path stability, described by the expected k-hop path lifetime; path reliability, described by the expected k-hop path residual lifetime, k-hop path churn rate and k-hop path frequency; and path availability, described by the expected k-hop path available time. Moreover, we provide the closed-form expressions for the above all metrics considering the joint effects of various parameters in Ad Hoc networks, including node mobility, node density, wireless transmission range, and node-pair distance. The analytical results are validated by extensive simulations.Third, node degree is regarded as an important and convenient metric to measure the connectivity of MANETs. Existing studies are mainly based on the assumption that nodes are static and do not provide closed-form expressions for node degree. Upon a realistic radio channel fading model, we investigate several fundamental characteristics of a MANET:Its node degree distribution, its average node degree, the probability of isolated nodes, the connectivity, the distribution of its maximum node degree and its average maximum node degree experienced by the nodes during their movement. We introduce a novel mathematical model to derive analytical expressions in the presence of radio channel fading. These expressions can be readily used to study connectivity and impove algorithm complexity in evaluating the incentive protocols. Also, the results are of practical vale for researchers in this area, e.g., setting the parameters in a network-level simulation of a mobile Ad Hoc network or designing a wireless sensor network. In addition, we have investigated the node degree distribution for initial nodes location distributed following Exponential distribution, Gaussian distribution and Power law distribution.