An Analysis Framework for Mobility Metrics in Mobile Ad Hoc Networks

Mobile ad hoc networks (MANETs) have inherently dynamic topologies. Under these difficult circumstances, it is essential to have some dependable way of determining the reliability of communication paths. Mobility metrics are well suited to this purpose. Several mobility metrics have been proposed in the literature, including link persistence, link duration, link availability, link residual time, and their path equivalents. However, no method has been provided for their exact calculation. Instead, only statistical approximations have been given. In this paper, exact expressions are derived for each of the aforementioned metrics, applicable to both links and paths. We further show relationships between the different metrics, where they exist. Such exact expressions constitute precise mathematical relationships between network connectivity and node mobility. These expressions can, therefore, be employed in a number of ways to improve performance of MANETs such as in the development of efficient algorithms for routing, in route caching, proactive routing, and clustering schemes

The Engineering Hubs and Spokes Project - institutional cooperation in educational design and delivery

The emergence of blended learning techniques that embrace a combination of face-to-face and online learning environments offers a raft of opportunity for flexibility in education. While much writing has focused on the opportunities for flexibility for the students and teachers, this paper focuses on the opportunities for effective sharing of expertise and effort between institutions. The Engineering 'Hubs and Spokes' project is a collaboration between The Australian National University and the University of South Australia. It draws on the strengths of each to improve the range and quality of educational opportunities for students. Two components of the project are underpinned by blended teaching and learning techniques: sharing of courses at the advanced undergraduate level; and development of an integrated graduate development program. We describe choices made, benefits identified, and the challenges encountered in the early stages of the project. We discuss recommendations for the future of cooperation in educational design and delivery, and comment on the opportunities that arise for structural reform of the higher education sector

Cache timeout strategies for on-demand routing in MANETs

Varying the route caching scheme can significantly change network performance for on-demand routing protocols in mobile ad hoc networks (MANETs). Initial route caching schemes retain paths or links until they are shown to be broken. However, stale routing information can degrade network performance with latency and extra routing overhead. Therefore, more recent caching schemes delete links at some fixed time after they enter the cache. This paper proposes using either the expected path duration or the link residual time as the link cache timeout. These mobility metrics are theoretically calculated for an appropriate random mobility model. Simulation results in NS2 show that both of the proposed link caching schemes can improve network performance in the dynamic source routing protocol (DSR) by reducing dropped data packets, latency and routing overhead, with the link residual time scheme out-performing the path duration scheme.IEEE, South Australian Sectio

On the minimum number of neighbours for good routing performance in MANETs

In a mobile ad hoc network, where nodes are deployed without any wired infrastructure and communicate via multihop wireless links, the network topology is based on the nodes’ locations and transmission ranges. The nodes communicate through wireless links, with each node acting as a relay when necessary to allow multihop communications. The network topology can have a major impact on network performance. We consider the impact of number and placement of neighbours on mobile network performance. Specifically, we consider how neighbour node placement affects the network overhead and routing delay. We develop an analytical model, verified by simulations, which shows widely varying performance depending on source node speed and, to a lesser extent, number of neighbour nodes

Decision region approximation by polynomials or neural networks

We give degree of approximation results for decision regions which are defined by polynomial and neural network parametrizations. The volume of the misclassified region is used to measure the approximation error, and results for the degree of L1 approximation of functions are used. For polynomial parametrizations, we show that the degree of approximation is at least 1, whereas for neural network parametrizations we prove the slightly weaker result that the degree of approximation is at least r, where r can be any number in the open interval (0, 1)

Nonlinear parameter estimation in classification problems

A nonlinear generalisation of the perceptron learning algorithm is presented and analysed. The new algorithm is designed for learning nonlinearly parametrised decision regions. It is shown that this algorithm can be viewed as a stepwise gradient descent of a certain cost function. Averaging theory is used to describe the behaviour of the algorithm, and in the process conditions guaranteeing convergence of the algorithm are established. These conditions are hard to test, so some simpler sufficient are derived using the directional derivative of the instantaneous cost. A number of simulation examples and applications are given, showing the variety of situations in which the algorithm can be used. In the initial analysis, a great deal of a priori knowledge about the decision region to be learnt has been assumed-in particular, it is assumed that the decision region is parametrised by some known (nonlinear) function. Often in applications, a general class of decision regions must be assumed, in which case the best approximate from the class is sought. It is shown that function approximation results can be used to derive degree of approximation results for decision regions. The approximating classes of decision regions considered are described by polynomial and neural network parametrisations. One shortcoming of all gradient descent type algorithms, such as the online learning algorithm discussed in the first part of this thesis, is that estimates may be attracted to local minima of the cost function. This is a problem because local minima occur in many interesting cases. Therefore a modified version of the algorithm, which avoids local minima traps, is presented. In the new algorithm, a number of parameter estimates ( called a congregation) are kept at any one time, and periodically all but the best estimate are restarted. Convergence of the new algorithm is established using the averaging theory that was used for the first algorithm. A probabilistic result concerning the expected time to convergence of the algorithm is given, and the effect of different population sizes is investigated. Again, a number of simulation examples are presented, including the application to the CMA algorithm for blind equalisation

International Wildlife Law : Understanding and Enhancing Its Role in Conservation

We gratefully acknowledge valuable input by Kees Bastmeijer, Sanja Bogojevic, Jennifer Dubrulle, and Han Somsen.Peer reviewedPublisher PD

Evaluating the boundary and covering degree of planar Minkowski sums and other geometrical convolutions

AbstractAlgorithms are developed, based on topological principles, to evaluate the boundary and “internal structure” of the Minkowski sum of two planar curves. A graph isotopic to the envelope curve is constructed by computing its characteristic points. The edges of this graph are in one-to-one correspondence with a set of monotone envelope segments. A simple formula allows a degree to be assigned to each face defined by the graph, indicating the number of times its points are covered by the Minkowski sum. The boundary can then be identified with the set of edges that separate faces of zero and non-zero degree, and the boundary segments corresponding to these edges can be approximated to any desired geometrical accuracy. For applications that require only the Minkowski sum boundary, the algorithm minimizes geometrical computations on the “internal” envelope edges, that do not contribute to the final boundary. In other applications, this internal structure is of interest, and the algorithm provides comprehensive information on the covering degree for different regions within the Minkowski sum. Extensions of the algorithm to the computation of Minkowski sums in R3, and other forms of geometrical convolution, are briefly discussed

The impact of education, country, race and ethnicity on the self-report of postpartum depression using the Edinburgh Postnatal Depression Scale

Background Universal screening for postpartum depression is recommended in many countries. Knowledge of whether the disclosure of depressive symptoms in the postpartum period differs across cultures could improve detection and provide new insights into the pathogenesis. Moreover, it is a necessary step to evaluate the universal use of screening instruments in research and clinical practice. In the current study we sought to assess whether the Edinburgh Postnatal Depression Scale (EPDS), the most widely used screening tool for postpartum depression, measures the same underlying construct across cultural groups in a large international dataset. Method Ordinal regression and measurement invariance were used to explore the association between culture, operationalized as education, ethnicity/race and continent, and endorsement of depressive symptoms using the EPDS on 8209 new mothers from Europe and the USA. Results Education, but not ethnicity/race, influenced the reporting of postpartum depression [difference between robust comparative fit indexes (∆*CFI) < 0.01]. The structure of EPDS responses significantly differed between Europe and the USA (∆*CFI > 0.01), but not between European countries (∆*CFI < 0.01). Conclusions Investigators and clinicians should be aware of the potential differences in expression of phenotype of postpartum depression that women of different educational backgrounds may manifest. The increasing cultural heterogeneity of societies together with the tendency towards globalization requires a culturally sensitive approach to patients, research and policies, that takes into account, beyond rhetoric, the context of a person's experiences and the context in which the research is conducted