Encounter gossip: a high coverage broadcast protocol for MANET

PhD ThesisMobile Ad-hoc Networks (MANETs) allow deployment of mobile wireless devices or nodes in a range of environments without any fixed infrastructure and hence at a minimal setup cost. Broadcast support that assures a high coverage (i.e., a large fraction of nodes receiving a broadcast) is essential for hosting user applications, and is also non-trivial to achieve due to the nature of devices and mobility. We propose Encounter Gossip, a novel broadcast protocol, which holds minimal state and is unaware of network topology. Coverage obtained can be made arbitrarily close to 1 at a moderate cost of extra message tra c, even in partition-prone networks. Under certain simplifying assumptions, it is shown that a high coverage is achieved by making a total of O(n ln n) broadcasts, where n is the number of nodes, and the time to propagate a message is O(ln n). The e ect of various network parameters on the protocol performance is examined. We then propose modifications to minimise the number of redundant transmissions without compromising the achieved coverage. Two approaches are pursued: timer based and history based. The e ectiveness of each of these approaches is assessed through an extensive set of simulation experiments in the context of two mobility models. Specifically, we introduce a new heuristic alpha policy which achieves significant reduction in redundancy with negligible reduction in coverage. A generalisation to multiple broadcasts proceeding in parallel is proposed and the protocol is refined to reduce problems that can occur due to the effects of high mobility when transmitting a large number of messages. Finally, we implement and validate Encounter Gossip in the context of a real-life mobile ad-hoc network. All these investigations suggest that the protocol, together with the proposed modifications and re nements, is suited to MANETs of varying degrees of node densities and speeds

Geometrical modelling and graphics display of stratigraphic orebodies.

In this research project the author introduces the use of geometrical modelling techniques alongside geostatistical methods to model a stratigraphic orebody and to present a graphics display system developed as a fIrst step towards a general integrated system for computer aided design and planning in mining. Geometrical modelling techniques and geostatistical methods are combined to carry out the process of modelling a stratigraphic orebody. From a mining point of view, there are two main features of interest in a stratigraphic ore-body: a-The modelling of the geometry of the orebody. b- The modelling (estimation) of the physical properties (grades, etc ... ) of the orebody. The first feature is the subject of this research project. Modelling methods and techniques developed elsewhere and for different applications, such as Computer Aided Design, have been applied successfully to model the geometry of stratigraphic orebodies. The modelling process consists of the applications of surface modelling techniques to represent the hangingwall and the footwall of the stratigraphic orebody and thereby to produce the space where the physical properties are geostatistically to be estimated. The graphics display system is presented to highlight the use of computer graphics techniques to communicate graphically all sorts of information concerning the modelling of stratigraphic orebodies and also to display the end product of the modelling process, such as cross-sections, plane-sections, wireframe and solid models of the orebody. The graphics system itself is part of a computer based system for mine design and planning similar to computer aided design systems used mainly in the manufacturing industry. The presentation of the research project in this thesis started by the review of the literature of some existing ore reserves estimation methods in the mineral industry, particularly geostatistical methods. Then an overview and the scope of this research project have been given. The second chapter describes the type of data which could be encountered while building a geometrical model of a stratigraphic orebody and a description of data from a nickel vein deposit used as a case study for this research project. The accumulations have been estimated geostatistically subject to geometrical control. The geometrical control concept and surface modelling techniques are presented in chapter three together with the numerical application of modelling a nickel vein deposit using two different surface modelling techniques. Chapter four describes the graphics display system developed to display several geometric features of stratigraphic orebodies in two and three dimensions. The summary of this research project and some concluding remarks are given in chapter fiv

Integrated modelling for 3D GIS

A three dimensional (3D) model facilitates the study of the real world objects it represents. A geoinformation system (GIS) should exploit the 3D model in a digital form as a basis for answering questions pertaining to aspects of the real world. With respect to the earth sciences, different kinds of objects of reality can be realized. These objects are components of the reality under study. At the present state-of-the-art different realizations are usually situated in separate systems or subsystems. This separation results in redundancy and uncertainty when different components sharing some common aspects are combined. Relationships between different kinds of objects, or between components of an object, cannot be represented adequately. This thesis aims at the integration of those components sharing some common aspects in one 3D model. This integration brings related components together, minimizes redundancy and uncertainty. Since the model should permit not only the representation of known aspects of reality, but also the derivation of information from the existing representation, the design of the model is constrained so as to afford these capabilities. The tessellation of space by the network of simplest geometry, the simplicial network, is proposed as a solution. The known aspects of the reality can be embedded in the simplicial network without degrading their quality. The model provides finite spatial units useful for the representation of objects. Relationships between objects can also be expressed through components of these spatial units which at the same time facilitate various computations and the derivation of information implicitly available in the model. Since the simplicial network is based on concepts in geoinformation science and in mathematics, its design can be generalized for n-dimensions. The networks of different dimension are said to be compatible, which enables the incorporation of a simplicial network of a lower dimension into another simplicial network of a higher dimension.The complexity of the 3D model fulfilling the requirements listed calls for a suitable construction method. The thesis presents a simple way to construct the model. The raster technique is used for the formation of the simplicial network embedding the representation of the known aspects of reality as constraints. The prototype implementation in a software package, ISNAP, demonstrates the simplicial network's construction and use. The simplicial network can facilitate spatial and non spatial queries, computations, and 2D and 3D visualizations. The experimental tests using different kinds of data sets show that the simplicial network can be used to represent real world objects in different dimensionalities. Operations traditionally requiring different systems and spatial models can be carried out in one system using one model as a basis. This possibility makes the GIS more powerful and easy to use