Barend Jacobus van Wyk

Online Estimation of the Approximate Posterior Cramer-Rao Lower Bound for Discrete-Time Nonlinear Filtering

Although it is difficult to assess the achievable performance of nonlinear tracking applications, it nevertheless remains extremely important to do so. This paper illustrates how the mean and covariance of the estimated online state can be used to recursively calculate an approximate posterior Cramer-Rao lower bound (CRLB). Most CRLB implementations require the true state, but this is impractical except for appropriately designed experiments or simulations where the exact value of the state is given as prior knowledge. The performance of the approximate posterior CRLB (PCRLB) used in conjunction with the extended Kalman filter (EKF) and the unscented Kalman filter (UKF) for online state estimation are investigated. To test the validity of the proposed method, it was applied to the problem of tracking a ballistic object on reentry. Simulation results confirm the theory and reveal that the proposed approximate PCRLB is sufficiently accurate and that the PCRLB approximations obtained using different state filters are in general very close to each other.

A 3-D four-wing attractor and its analysis

In this paper, several three dimensional (3-D) four-wing smooth quadratic autonomous chaotic systems are analyzed. It is shown that these systems have a number of similar features. A new 3-D continuous autonomous system is proposed based on these features. The new system can generate a four-wing chaotic attractor with less terms in the system equations. Several basic properties of the new system is analyzed by means of Lyapunov exponents, bifurcation diagrams and Poincare maps. Phase diagrams show that the equilibria are related to the existence of multiple wings.

Difference Histograms: A new tool for time series analysis applied to bearing fault diagnosis

A powerful tool for bearing time series feature extraction and classification is introduced that is computationally inexpensive, easy to implement and suitable for real-time applications. In this paper the proposed technique is applied to two rolling element bearing time series classification problems and shown that in some cases no data pre-processing, artificial neural network or nearest neighbour approaches are required. From the results obtained it is clear that for the specific applications considered, the proposed method performed as well as or better than alternative approaches based on conventional feature extraction.

Dynamic Power Control for Wireless Backbone Mesh Networks: a Survey

With the tremendous growth of wireless networks into the next generation to provide better services, Wireless Mesh Networks (WMNs) have emerged to offer ubiquitous communication and seamless broadband applications. WMNs are hybrid networks composed of a mixture of static Wireless Mesh Routers (WMRs) and mobile Wireless Mesh Clients (WMCs) interconnected via wireless links to form a multi-hop wireless Ad Hoc network (WANET). WMNs are self-organized, self-configured, and reliable against single points of failures, and robust against RF interference, obstacles or power outage. This is because WMRs forming wireless backbone mesh networks (WBMNs) are built on advanced physical technologies. Such nodes perform both accessing and forwarding functionality. They are expected to carry huge volumes of traffic and be “on power” at all times. While trying to increase network capacity, problems of the dynamic transmission power control (DTPC) arise in such networks. Such problems include RF Interference, Connectivity and energy-depletion. While there are numerous studies on this topic, contributions in the context of WBMNs are still challenging but interesting research areas. This paper provides an overview of the DTPC algorithms central to the WBMNs framework. The open issues are also highlighted.

Bilateral mesh filtering

The paper presents a new graph-based implementation of bilateral filtering. Based on the Laplacian mesh smoothing framework, the proposed filter mimics the behaviour of the classical mesh filter while retaining some of the interesting properties of mesh smoothing. The comparison between the filters is twofold. First of all, the two filters are benchmarked according to their ability to denoise complex synthetic image transitions. The respective performance of the filters are then assessed in a multiresolution denoising scheme for grayscale images, combining wavelet decomposition, shrinkage and bilateral filtering. The results obtained are encouraging and shows that the BMF is a viable alternative to classical bilateral filtering.

Measuring Straight Line Segments Using HT Butterflies

This paper addresses the features of Hough Transform (HT) butterflies suitable for image-based segment detection and measurement. The full segment parameters such as the position, slope, width, length, continuity, and uniformity are related to the features of the HT butterflies. Mathematical analysis and experimental data are presented in order to demonstrate and build the relationship between the measurements of segments and the features of HT butterflies. An effective method is subsequently proposed to employ these relationships in order to discover the parameters of segments. Power line inspection is considered as an application of the proposed method. The application demonstrates that the proposed method is effective for power line inspection, especially for corner detection when they cross poles.

Joint queue-perturbed and weakly coupled power control for wireless backbone networks

Abstract Wireless Backbone Networks (WBNs) equipped with Multi-Radio Multi-Channel (MRMC) configurations do experience power control problems such as the inter-channel and co-channel interference, high energy consumption at multiple queues and unscalable network connectivity. Such network problems can be conveniently modelled using the theory of queue perturbation in the multiple queue systems and also as a weak coupling in a multiple channel wireless network. Consequently, this paper proposes a queue perturbation and weakly coupled based power control approach forWBNs. The ultimate objectives are to increase energy efficiency and the overall network capacity. In order to achieve this objective, a Markov chain model is first presented to describe the behaviour of the steady state probability distribution of the queue energy and buffer states. The singular perturbation parameter is approximated from the coefficients of the Taylor series expansion of the probability distribution. The impact of such queue perturbations on the transmission probability, given some transmission power values, is also analysed. Secondly, the inter-channel interference is modelled as a weakly coupled wireless system. Thirdly, Nash differential games are applied to derive optimal power control signals for each user subject to power constraints at each node. Finally, analytical models and numerical examples show the efficacy of the proposed model in solving power control problems in WBNs.

Autonomous Transmission Power Adaptation for Multi-Radio Multi-Channel Wireless Mesh Networks

Multi-Radio Multi-Channel (MRMC) systems are key to power control problems in WMNs. Previous studies have emphasized throughput maximization in such systems as the main design challenge and transmission power control treated as a secondary issue. In this paper, we present an autonomous power adaptation for MRMC WMNs. The transmit power is dynamically adapted by each network interface card (NIC) in response to the locally available energy in a node, queue load, and interference states of a channel. To achieve this, WMN is first represented as a set of Unified Channel Graphs (UCGs). Second, each NIC of a node is tuned to a UCG. Third, a power selection MRMC unification protocol (PMMUP) that coordinates Interaction variables (IV) from different UCGs and Unification variables (UV) from higher layers is proposed. PMMUP coordinates autonomous power optimization by the NICs of a node. The efficacy of the proposed method is investigated through simulations.

Performance evaluation of IEEE 802.11p MAC protocol in VANETs safety applications

VANETs are becoming more and more popular as a way to increase the traffic safety and comfort. The IEEE 802.11p standard, especially the 802.11p MAC protocol, has attracted much attention as part of the WAVE protocol in VANETs. Safety applications, as one of the main categories of applications in VANETs, is very challenging for the design of a MAC protocol due to their low latency and high reliability requirements. The CCH interval is also a key parameter for the 802.11p MAC protocol since it can affect the performance of safety message delivery significantly. In this paper, a simulation based evaluation is proposed to evaluate the performance of the 802.11p MAC protocol with various vehicle densities and CCH interval settings. The evaluation results indicate that the 802.11p MAC protocol can be improved via extending the CCH interval. However, the reliability is still very challenging due to high collision rates.

Optimal Control of Transmission Power Management in Wireless Backbone Mesh Networks

Wireless Mesh Networks, Book edited by: Nobuo Funabiki, ISBN: 978-953-307-519-8, Publisher: InTech, Publishing date: January 2011