Study Of The Node Mobility Techniques In Wireless Ad Hoc Networks

In wireless ad hoc networks, due to mobility of network and unreliability of nodes and links, many techniques must be adopted to ensure network performance. Before network deployment, critical resources, configuration parameters and performance of major network protocols should be determined in advance through network simulations, and the node mobility model is among the most important related techniques. During network operation, to improve network performance, the network topology can be adjusted and constructed dynamically. In this thesis, we discuss node mobility techniques, including autonomous mobility and controlled mobility techniques, from three aspects: mobility models, movement deployment and movement topology control. The main contributions of this thesis are outlined as follows:1. In order to study influences of entrances of a terrain, the mobility model of RWP (Random Way Point) with entrances (RWPWE) is proposed. In this model, one or more entrances lie in the terrain. It is imperative for a node to pass through a certain entrance with a certain probability when it enters or exits from the terrain. The movement pattern of a node in a terrain can be described by RWP model. This model is a generalized form of RWP model and can be utilized in real-world environments with entrances. This model provides a theoretical and experimental basis for evaluations of the network performance in mobile ad hoc networks.2. In order to study influences of realistic terrains and to overcome problems of inaccuracy terrain modeling, bad scalability and large deviation in current related mobility models, the Terrain-Based Mobility Model (TBMM) is proposed, which includes terrain modeling and node mobility modeling. In terrain modeling, areas, area points, entrances, paths and crosses are included in its terrain component libraries and nested terrains are supported. In node mobility modeling, node movement is grouped into two classes: intra-terrain movement and inter-terrain movement. Intra-terrain movement is composed of several steps: selection of destination area, selection of routes and node movement on road. Inter-terrain movement allows different nodes move according to different mobility models. Any terrain can be modeled by different terrain components and different movement scenarios can be customized on demand. Furthermore, all the ideal mobility models and RWPWE are integrated into the frame architecture of TBMM.3. In order to improve the network coverage, Minimum Coverage Overlap (MCO) movement deployment algorithm is proposed, which increases the network coverage by minimizing the coverage overlap among different nodes. In MCO, after calculating the variation rate of coverage overlap based on the distribution of overlapped coverage arcs on its sensing circle, a node can determine its moving direction in which the variation rate of coverage overlap decreases the most prominent. This model can be executed independently in a fully decentralized manner by any node in the network. Simulation results show that MCO has advantages over Voronoi based algorithms in terms of coverage, moving distance, moving efficiency, deploying time and time efficiency.4. In order to improve the coverage uniformity, Multiple Minimum Coverage Overlap (MMCO) algorithm is proposed. In MMCO algorithm, coverage arcs with different overlaps are listed respectively when calculating the distribution of coverage overlaps on the sensing circle and the variation rate of multiple coverage overlap is the product of the single coverage overlap and the number of overlaps. Simulation results show that MMCO outperforms Voronoi based algorithms and SMCO in terms of both coverage and coverage uniformity.5. A group of MST based movement topology control algorithms are proposed to solve the problem of overlarge transmission power in wireless ad hoc networks. They are all composed of four steps: information collection, determination of addition links, determination of moving node candidates and movement of node candidates. Addition links are edges of the partition minimum spanning tree, which derives from the partition graph. In Partition Minimum Spanning Tree-Partition (PMST-P) algorithm, moving node candidates is determined by partition movement algorithm while in Partition Minimum Spanning Tree-Uncut Vertex (PMST-UV) algorithm by uncut vertex movement algorithm. With network connectivity and fairness considered, a moving node adopts three mobility styles: direct movement (DM) style, traced movement (TM) style and cascaded movement (CM) style. The distributed implementation of PMST-UV is given as Local Partition Minimum Spanning Tree- Local Uncut Vertices (LMST-LUV) algorithm. All MST algorithms can balance the transmission power dramatically. PMST-P and PMST-UV can also be utilized to solve the problem of network partitions.