Research On Positioning Techniques In Mobile Ad Hoc Networks

Wireless networks provide users with the capability of ubiquitous communicating and access to information at anytime and keeping connections valid in continuous movement. In traditional mobile communication systems users are generally connected to the network via base stations that are usually connected by a wired backbone. A mobile ad hoc network (MANET) is a special wireless network that is self-organized by mobile nodes. These mobile nodes communicate each other using distributed protocols. Such a network can function without fixed routing infrastructures, e.g. base stations. When the wired network is not available, as in battlefield communications and emergency search-and-rescue operations, mobile ad hoc networks can provide a feasible means for ground communications and information access.A MANET has such basic characteristics as self-organization, mobility and independency. All nodes in a MANET can move with unlimited mobility. Traditional positioning techniques rely totally or partially on Global Positioning System(GPS), fixed grids or base stations, and the positioning results are planar. All these limit the successfully utilization of traditional positioning techniques in MANET. New positioning techniques are needed. To implement a GPS-free and fixed-grids-independent three-dimensional positioning system is challenging in multi-hop wireless networks. In this dissertation, three-dimensional positioning techniques are studied in MANETs with flat structure. A self-organized GPS-free three-dimensional positioning system, ANGEPS, is presented with a series of positioning algorithms.ANGEPS consists of three main parts: local positioning, global positioning and dynamic positioning. It can position nodes in MANET from single-hop to multi-hop, from static to dynamic. Each part is not only the base of its sequential parts but also can be applied independently.Local positioning is the basis of ANGEPS. It solves the problem of providing nodes' three-dimensional coordinates in a single-hop MANET. When nodes are communicated via omni-directional antenna, the problem can be reduced as setting up a three-dimensional coordinate system by only using distances and/or angles between nodes. On the basis of distances and angles measured by RSSI/AOA, according to trigonometry and solid geometry theory, a three-dimensional coordinate system can be built up by four un-coplanar nodes. Then other nodes can be positioned while some mirror image need to be rejected. Basic datum algorithm, building-up coordinate system algorithm and local nodes positioning algorithm are introduced and validated in the dissertation. Using the network simulator ns-2, factors which affect the precision of positioning are discussed.Global positioning is the extension of local positioning in multi-hop MANET. A multi-hop MANET can be viewed as a combination of several single-hop MANETs. By local positioningand conditional flooding, global positioning extends positioning space to the entire network gradually. And the whole network will be united as a single coordinate system by means of coordinate transformation. A central and a distributed global positioning algorithm as well as their optimized forms are presented in the dissertation. Three kinds of simple conditional flooding algorithms and coordinate transformation algorithm are also presented. All algorithms together can successfully solve the problem of positioning nodes in multi-hop MANET. Through simulation, performances of different conditional flooding algorithms are compared and precision of positioning is studied.In order to reduce the cumulative errors in global positioning and to improve system's precision, dew-flooding global positioning is brought forwarded. Dew-flooding is an extension of simple conditional flooding. It utilizes multiple starting points to carry out simple conditional flooding, which improves system's timing performance greatly. By converging different flooding regions-, cumulative errors are reduced and the system's precision can thus be improved greatly. Nodes' distribution an...