Network Topology Mapping from Partial Virtual Coordinates and Graph Geodesics

For many important network types (e.g., sensor networks in complex harsh environments and social networks) physical coordinate systems (e.g., Cartesian), and physical distances (e.g., Euclidean), are either difficult to discern or inapplicable. Accordingly, coordinate systems and characterizations based on hop-distance measurements, such as Topology Preserving Maps (TPMs) and Virtual-Coordinate (VC) systems are attractive alternatives to Cartesian coordinates for many network algorithms. Herein, we present an approach to recover geometric and topological properties of a network with a small set of distance measurements. In particular, our approach is a combination of shortest path (often called geodesic) recovery concepts and low-rank matrix completion, generalized to the case of hop-distances in graphs. Results for sensor networks embedded in 2-D and 3-D spaces, as well as a social networks, indicates that the method can accurately capture the network connectivity with a small set of measurements. TPM generation can now also be based on various context appropriate measurements or VC systems, as long as they characterize different nodes by distances to small sets of random nodes (instead of a set of global anchors). The proposed method is a significant generalization that allows the topology to be extracted from a random set of graph shortest paths, making it applicable in contexts such as social networks where VC generation may not be possible.Comment: 17 pages, 9 figures. arXiv admin note: substantial text overlap with arXiv:1712.1006

Location-Quality-aware Policy Optimisation for Relay Selection in Mobile Networks

Relaying can improve the coverage and performance of wireless access networks. In presence of a localisation system at the mobile nodes, the use of such location estimates for relay node selection can be advantageous as such information can be collected by access points in linear effort with respect to number of mobile nodes (while the number of links grows quadratically). However, the localisation error and the chosen update rate of location information in conjunction with the mobility model affect the performance of such location-based relay schemes; these parameters also need to be taken into account in the design of optimal policies. This paper develops a Markov model that can capture the joint impact of localisation errors and inaccuracies of location information due to forwarding delays and mobility; the Markov model is used to develop algorithms to determine optimal location-based relay policies that take the aforementioned factors into account. The model is subsequently used to analyse the impact of deployment parameter choices on the performance of location-based relaying in WLAN scenarios with free-space propagation conditions and in an measurement-based indoor office scenario.Comment: Accepted for publication in ACM/Springer Wireless Network

Integrating Interactive Digital Maps into a Digital Library

Digital libraries and digital maps are two fast-growing technologies in the world of computing. In this thesis we have explored using digital maps to enhance the functionality of digital libraries. The Greenstone 3 digital library system was augmented though the use of the digital mapping system, Google Maps. An automatic place name recognition and disambiguation system was created to obtain geographical information from documents as they were viewed. This extracted information was presented as a map with markers showing the location of the places within the text of the document. We evaluated the system by performing a user study and an analysis of the speed, efficiency and accuracy of the place name recognition and disambiguation system. Participants in the user study completed most of the tasks easily and made comments expressing their satisfaction with the system. Analysis of the place recognition and disambiguation system was also positive, as the system was fast, relatively efficient and was highly accurate

Data capture of geometric data for local authorities' geographic information systems

Bibliography: leaves 64-65.This thesis describes research and development work which led to algorithms, procedures and computer programs which facilitate the cost effective and accurate capture of geometric data. The geometric data for a Geographical Information System (GIS) at a local authority or municipality consist of a number of different data sets. These include inter alia: the cadastral information, zoning information, servitudes, building lines, the outlines of improvements and the reticulation networks and the house connection points of the engineering services. The initial capture of the geometric data appears to be deceptively simple and is often not given the required consideration. The initial data capture phase of GIS projects is usually a difficult and time consuming process. This is even more so in the case of GIS for local authorities. The reason for this difficulty is the large volume of data coupled with the high accuracies required for the cadastral base map and the engineering services. Input facilities of most commercial GIS software packages generally do not provide the most efficient means of data capture. This problem warrants the development of techniques and procedures specific to local authority GIS applications which ensure that data capture can be done effectively and efficiently. The major benefit of these procedures is that they can be implemented on personal computers with low random access memory capacity. This eliminates the need for investment in costly equipment at the initial stage of data capture in the development of a GIS. It allows the capture of data on low cost technology and the postponement of the purchase of an expensive system or workstation until the data capture phase has been completed. The lowest personnel skills required are copy typing in contrast to the traditional methods of using CAD operators who command higher salaries and require more expensive training. The system developed by the author is more productive, both in quality and volume of work produced, than the CAD approach. It also permits the delay of purchase and training on expensive GIS software and hardware, which may be obsolete by the time the graphic database is established

Structure-Aware Sampling: Flexible and Accurate Summarization

In processing large quantities of data, a fundamental problem is to obtain a summary which supports approximate query answering. Random sampling yields flexible summaries which naturally support subset-sum queries with unbiased estimators and well-understood confidence bounds. Classic sample-based summaries, however, are designed for arbitrary subset queries and are oblivious to the structure in the set of keys. The particular structure, such as hierarchy, order, or product space (multi-dimensional), makes range queries much more relevant for most analysis of the data. Dedicated summarization algorithms for range-sum queries have also been extensively studied. They can outperform existing sampling schemes in terms of accuracy on range queries per summary size. Their accuracy, however, rapidly degrades when, as is often the case, the query spans multiple ranges. They are also less flexible - being targeted for range sum queries alone - and are often quite costly to build and use. In this paper we propose and evaluate variance optimal sampling schemes that are structure-aware. These summaries improve over the accuracy of existing structure-oblivious sampling schemes on range queries while retaining the benefits of sample-based summaries: flexible summaries, with high accuracy on both range queries and arbitrary subset queries

Network Topology Mapping from Partial Virtual Coordinates and Graph Geodesics

For many important network types (e.g., sensor networks in complex harsh environments and social networks) physical coordinate systems (e.g., Cartesian), and physical distances (e.g., Euclidean), are either difficult to discern or inappropriate. Accordingly, Topology Preserving Maps (TPMs) derived from a Virtual-Coordinate (VC) system representing the distance to a small set of anchors is an attractive alternative to physical coordinates for many network algorithms. Herein, we present an approach, based on the theory of low-rank matrix completion, to recover geometric properties of a network with only partial information about the VCs of nodes. In particular, our approach is a combination of geodesic recovery concepts and low-rank matrix completion, generalized to the case of hop-distances in graphs. Distortion evaluated using the change of distance among node pairs shows that even with up to 40% to 60% of random coordinates missing, accurate TPMs can be obtained. TPM generation can now also be based on different context appropriate VC systems or measurements as long as they characterize each node with distances to a small set of random nodes (instead of a global set of anchors). The proposed method is a significant generalization that allows the topology to be extracted from a random set of graph geodesics, making it applicable in contexts such as social networks where VC generation may not be possible.Comment: A more recent version uploade

The Development of Web-Based Interface to Census Interaction Data

This project involves the development of a Web interface to origin-destination statistics from the 1991 Census (in a form that will be compatible with planned 2001 outputs). It provides the user with a set of screen-based tools for setting the parameters governing each data extraction (data set, areas, variables) in the form of a query. Traffic light icons are used to signal what the user has set so far and what remains to be done. There are options to extract different types of flow data and to generate output in different formats. The system can now be used to access the interaction flow data contained in the 1991 Special Migration Statistics Sets 1 and 2 and Special Workplace Statistics Set C. WICID has been demonstrated at the Origin-Destination Statistics Roadshows organised by GRO Scotland and held during May/June 2000 and the Census Offices have expressed interest in using the software in the Census Access Project

Data DNA: The Next Generation of Statistical Metadata

Describes the components of a complete statistical metadata system and suggests ways to create and structure metadata for better access and understanding of data sets by diverse users