Physical Sciences and Mathematics Commons^™

An Improved Channel Model For Adsl And Vdsl Systems, D. Franklin, Jiangtao Xi, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

This paper examines existing channel models used with xDSL systems and identifies a key shortcoming - namely, the implicit assumption that all impulse noise originates at the transmitter. Based on extensive data collected from the local loop, a new model is proposed which addresses this problem by combining a digital filter model of the transmission line with a distributed noise source. This better reflects the nature of a real telephone line, and thus provides a more solid basis for simulation and optimisation of xDSL systems.

Boundary Filters For Segmentation-Based Subband Coding, Alfred Mertins

Faculty of Informatics - Papers (Archive)

This paper presents design methods for boundary filters for the processing of finite-length signals. In particular, it is shown how vanishing moments can be imposed during the design. Applications are found in segmentation-based audio and shape-adaptive image compression.

On The Infomax Algorithm For Blind Signal Separation, Jiangtao Xi, Joe F. Chicharo, Ah Chung Tsoi, W. C. Siu

Faculty of Informatics - Papers (Archive)

This paper provides an analytical examination of the INFOMAX algorithm and establishes its effectiveness for blind signal separation using extensive simulation results. Results obtained show that the INFOMAX is not able to separate signal sources unless signal pre-processing is carried-out whereby the data to train the separating matrix is decorrelated. Further, results also show that if one uses the decorrelation pre-process alone it is able to effectively separate signal sources in many instances. Hence we conclude that the INFOMAX algorithm may not be a useful approach for signal separation.

An Examination Of Ip/Atm Cut-Through Forwarding In Dynamically Routed Networks, P. Boustead, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

Multiprotocol over ATM (MPOA), IP switching and multiprotocol label switching (MPLS) have distinctly different mechanisms for cut-through packet forwarding. MPOA and IP switching use flow-based cut-through (FBC) forwarding while MPLS uses routing table linked cut-through forwarding (TLC). This paper examines the sensitivity of each these cut-through forwarding mechanisms to changes in underlying routing tables. We examine a scenario where a congestion-sensitive dynamic routing protocol, such as OSPF optimised multipath, leads to frequently changing routing tables. We show that FBC forwarding reacts significantly worse than flow length distributions predict, taking up to 1200 seconds to react to route changes and forward …

Memory Truncation Receivers For Transmultiplexers, Alfred Mertins

Faculty of Informatics - Papers (Archive)

In this paper, the design of optimal receive filter banks for transmultiplexer-based data transmission over frequency selective channels is investigated. A new design strategy based on the principle of memory truncation, rather than equalization, is presented. Through the receive filters, each subchannel is truncated to a certain length, and the actual data detection is then carried out via low-complexity, independently operating Viterbi detectors. Design examples are presented for high-speed transmission over copper wires. The examples show that memory truncation allows significant performance improvements over MMSE equalization.

Shape-Vq-Based Lossless Hybrid Adpcm/Dct Coder, J. Wang, F. Naghdy

Faculty of Informatics - Papers (Archive)

The discrete cosine transform (DCT) has been shown as an optimum encoder for sharp edges in an image (Andrew and Ogunbona, 1997). A conventional lossless coder employing differential pulse code modulation (DPCM) suffers from significant deficiencies in regions of discontinuity, because the simple model cannot capture the edge information. This problem can be partially solved by partitioning the image into blocks that are supposedly statistically stationary. A hybrid lossless adaptive DPCM (ADPCM)/DCT coder is presented, in which the edge blocks are encoded with DCT, and ADPCM is used for the non-edge blocks. The proposed scheme divides each input image into …

Building Mlp Networks By Construction, Ah Chung Tsoi, M. Hagenbuchner, A. Micheli

Faculty of Informatics - Papers (Archive)

We introduce two new models which are obtained through the modification of the well known methods MLP and cascade correlation. These two methods differ fundamentally as they employ learning techniques and produce network architectures that are not directly comparable. We extended the MLP architecture, and reduced the constructive method to obtain very comparable network architectures. The greatest benefit of these new models is that we can obtain an MLP-structured network through a constructive method based on the cascade correlation algorithm, and that we can train a cascade correlation structured network using the standard MLP learning technique. Additionally, we show that …

Accurate, Critically Sampled Characteristic Waveform Surface Construction For Waveform Interpolation Decomposition, N. R. Chong-White, I. Burnett

Faculty of Informatics - Papers (Archive)

A waveform-matched waveform interpolation (WMWI) technique is presented which offers improved signal analysis over standard WI coders and, in the unquantised case, perfect reconstruction. In WMWI, an accurate representation of speech evolution is formed by extracting consecutive pitch periods of a time-warped, constant pitch residual. A pitch track optimisation technique is described which ensures that the critically sampled pitch periods can be effectively decomposed into a slowly evolving and rapidly evolving waveform, allowing efficient quantisation.

Performance Analysis Of Qos Mechanisms In Ip Networks, D. Jia, E. Dutkiewicz, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

Integrated services IP networks are expected to provide a variety of services with differentiated QoS. This requires the implementation of mechanisms that can discriminate service classes in terms of QoS. The IETF has recently proposed a differentiated services (Diffserv) framework for provision of QoS. In this paper we analyse the performance of two Diffserv mechanisms: threshold dropping and priority scheduling in terms of packet loss and mean packet delay. A comparison of the two mechanisms is carried out with the requirement that both mechanisms provide the same level of packet loss for the preferred flow. This comparison extends the results …

Multiparty Key Agreement Protocols, J. Pieprzyk, C. H. Li

Faculty of Informatics - Papers (Archive)

A class of multiparty key agreement protocols based on secret sharing is presented. The trust infrastructure necessary to achieve the intended security goals is discussed.

Differentiated Service Performance Analysis, L. V. Nguyen, A. Eyers, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

Differentiated service (DiffServ) has been proposed as an alternative for Integrated service. It aims to provide the same service to a group of flows that have similar quality of service requirements. Assured forwarding (AF) and expedited forwarding (EF) are two proposals for DiffServ provision. We present a performance analysis of an N drop-precedences threshold dropping (TD) queue, which is one of the proposed mechanisms for AF. In this analysis, traffic flows are assumed Poisson with exponentially distributed service time. We present simulation results that verify the analysis. This paper is an extension of the work attempted by Bolot et al. …

Connection Admission Control In Micro-Cellular Multi-Service Mobile Networks, R. S. Raad, E. Dutkiewicz, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

This paper investigates the use of fixed bandwidth reservation for multi-service mobile networks. In particular it extends previous fixed multi-service network results to the mobile scenario and presents analytical and simulation results for new and handover call blocking probabilities. It also investigates the performance sensitivity to different traffic load ratios as well as the cell dwell time distribution.

666 Or 616 (Rev. 13,18), M. G. Michael

Faculty of Informatics - Papers (Archive)

No abstract provided.

Parameter Tracking For Stochastic Time-Varying Systems, Zheng Li

Faculty of Informatics - Papers (Archive)

Describes a method for tracking fast time-varying parameters of dynamic systems under stochastic disturbances. Auxiliary information is used in addition to the plant input and output for better tracking accuracy.

Ip Forwarding Alternatives In Cell Switched Optical Networks, P. Boustead, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

Optical switching will enable core Internet packet switching to scale with future transmission rate increases. Currently proposed optical ATM switches do not allow packet reassembly, which is necessary for packet level forwarding. This results in the requirement to create end to end ATM virtual connections for flows even if they contain only one packet. In electronically switched networks MPOA and MPLS allow both cell and packet level forwarding to overcome this problem. This paper examines the feasibility of implementing such protocols over an optically switched network. Two different architectures are examined: use of an adjunct electrical router; and native optical …

Unfairness And Capture Behaviour In 802.11 Adhoc Networks, C. Ware, J. Judge, Joe F. Chicharo, E. Dutkiewicz

Faculty of Informatics - Papers (Archive)

We address issues with the performance of IEEE 802.11, when used in the adhoc mode, in the presence of hidden terminals. We present results illustrating the strong dependence of channel capture behavior on the SNR observed on contending hidden connections. Experimental work has illustrated that in a hidden terminal scenario, the connection having the strongest SNR is able to capture the channel, despite the use of the RTS-CTS-DATA-ACK 4-way handshake designed to alleviate this problem. Our results indicate that the near-far SNR problem may have a significant effect on the performance of an adhoc 802.11 network.

Linear Prediction Incorporating Simultaneous Masking, J Lukasiak, I. S. Burnett, Joe F. Chicharo, M. M. Thomson

Faculty of Informatics - Papers (Archive)

Whilst linear prediction is the cornerstone of most modern speech coders, few of these coders incorporate the perceptual characteristics of hearing into the calculation of the linear predictor coefficients (LPCs). This paper proposes a method of incorporating simultaneous masking into the calculation of the LPCs. This modification requires only a modest increase in computational complexity and results in the linear predictor removing more perceptually important information from the input speech signal. This results in a filter that better models the formants of the input speech spectrum. The net effect is that an improvement in quality is achieved for a given …

The Second International Symposium On Constructing Software Engineering Tools (Coset2000), J. Gray, L. Scott, I. Ferguson

Faculty of Informatics - Papers (Archive)

No abstract provided.

Computing Running Dcts And Dsts Based On Their Second-Order Shift Properties, Jiangtao Xi, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

This paper presents a set of second-order recursive equations which are referred to as the second-order shift (SOS) properties of the discrete cosine transform (DCT) and the discrete sine transform (DST). The proposed SOS properties enable independent updating of the respective DCT and DST coefficients. This is in direct contrast with existing methodology for computing the running DCT and DST where there is an inherent interdependency between the DCT and DST coefficients. The SOS properties provide more efficient algorithms in terms of computational burden and memory requirements when implementing running DCTs and DSTs.

A New Waveform Interpolation Coding Scheme Based On Pitch Synchronous Wavelet Transform Decomposition, N. R. Chong, I. Burnett, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

This correspondence uses a pitch synchronous wavelet transform (PSWT) as an alternative characteristic waveform decomposition method for the waveform interpolation (WI) paradigm. The proposed method has the benefit of providing additional scalability in quantization than the existing WI decomposition to meet desired quality requirements. The PSWT is implemented as a quadrature mirror filter bank and decomposes the characteristic waveform surface into a series of reduced time resolution surfaces. Efficient quantization of these surfaces is achieved by exploiting their perceptual importance and inherent transmission rate requirements. The multiresolution representation has the additional benefit of more flexible parameter quantization, allowing a more …

Bounds On The Maximum Determinant For (1,-1) Matrices, C Koukouvinos, M Mitrouli, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We suppose the Hadamard conjecture is true and an Hadamard matrix of order 4t, exists for all t ≥ 1. We use the results for the equivalent SBIBD(4t –1, 2t–1, t–1) to establish the maximum determinant or a lower bound for the maximum determinant for all ±1 matrices. In particular we give numerical results for all orders ≤100.

A New And Efficient Fail—Stop Signature Scheme, Willy Susilo, R. Safavi-Naini, M. Gysin, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

Security of ordinary digital signature schemes relies on a computational assumption. Fail-stop signature schemes provide security for a sender against a forger with unlimited computational power by enabling the sender to provide a proof of forgery, if it occurs. In this paper, we give an efficient fail-stop signature scheme that uses two hard problems, discrete logarithm and factorisation, as the basis of receiver's security. We show that the scheme has provable security against adaptively chosen message attack and is the most efficient scheme with respect to the ratio of the message length to the signature length. The scheme provides an …

Modelling Multi-Player Games Traffic, R. A. Bangun, E. Dutkiewicz

Faculty of Informatics - Papers (Archive)

The growing popularity of delay-sensitive multi-player games over the Internet is creating a need for proper characterisation of such traffic. We are currently developing source models for game traffic, on a per-player basis, with the intended use being to scale the models to simulate scenarios involving large numbers of players, which will enable us to observe the effects of game traffic on the network. We outline the procedure used, and we show that for certain cases, relatively simple source models are able to provide sufficiently accurate results (in terms of mean delay and mean buffer occupancy).

Semantic Modeling For Video Content-Based Retrieval Systems, L. A. Al Safadi, J. R. Getta

Faculty of Informatics - Papers (Archive)

This work proposes a semantic data model for video documents based on the story-line structure powerful enough to express various human interpretations of video documents, and introduces a formal query language for video retrieval that facilitates retrieval of users' heterogeneous queries based on the proposed model. The paper identifies the elementary semantic units, composite semantic units, associations and abstraction mechanisms necessary for symbolic modeling of semantic video contents. The method is independent of presentation media and it has its origins in symbolic modeling systems developed for database and complex software systems design.

Software Engineering Tools, J. Gray

Faculty of Informatics - Papers (Archive)

Automated tools play an important role in the promotion and adoption of software engineering methods and processes. The development of these tools is itself a significant software engineering task, requiring a considerable investment of time and resources. There are a large number of different kinds of automated software engineering tools, variously known as CASE, CAME, IPSE, SEE, and metaCASE tools. Although these tools differ in the particular methods, activities, and phases of the software development cycle to which they are applied, constructors of these tools often face similar implementation issues. Decisions about host computing platform, implementation language, conformance with standards …

Asymptotic Properties Of Maximum (Composite) Likelihood Estimators For Partially Ordered Markov Models, Hsin-Cheng Huang, Noel A. Cressie

Faculty of Informatics - Papers (Archive)

Partially ordered Markov models (POMMs) are Markov random fields (MRFs) with neighborhood structures derivable from an associated partially ordered set. The most attractive feature of POMMs is that their joint distributions can be written in closed and product form. Therefore, simulation and maximum likelihood estimation for the models is quite straightforward, which is not the case in general for MRF models. In practice, one often has to modify the likelihood to account for edge components; the resulting composite likelihood for POMMs is similarly straightforward to maximize. In this article, we use a martingale approach to derive the asymptotic properties of …

Minimum Phi Divergence Estimator And Hierarchical Testing In Loglinear Models, Noel A. Cressie, Leandro Pardo

Faculty of Informatics - Papers (Archive)

In this paper we consider inference based on very general divergence measures, under assumptions of multinomial sampling and loglinear models. We define the minimum phi divergence estimator, which is seen to be a generalization of the maximum likelihood estimator. This estimator is then used in a phi divergence goodness-of-fit statistic, which is the basis of two new statistics for solving the problem of testing a nested sequence of loglinear models.

Relationships Between Boolean Functions And Symmetric Groups, Chengxin Qu, Jennifer Seberry, Josef Pieprzyk

Faculty of Informatics - Papers (Archive)

We study the relations between boolean functions and symmetric groups. We consider elements of a symmetric group as variable transformations operators for boolean functions. Boolean function may be fixed or permuted by these operators. We give some properties relating the symmetric group S_n and boolean functions on V_n.

Growth In Gaussian Elimination For Weighing Matrices W(N,N-1), C. Koukouvinos, M. Mitrouli, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We consider the values for large minors of a skew-Hadamard matrix or conference matrix W of order n and find maximum n x n minor equals to (n-1)ⁿ/₂, maximum (n-1) x (n-1) minor equals to (n-1)ⁿ/₂-1, maximum (n-2) x (n-2) minor equals 2(n-1)ⁿ/₂-2, and maximum (n-3) x (n-3) minor equals to 4(n-1)ⁿ/₂-3.

This leads us to conjecture that the growth factor for Gaussian elimination of compeletely pivoted skew-Hadamard or conference matrices and indeed any completely pivoted weighing matrix or order n and weight n-1 …

Bounds On The Maximum Determinant For (1,-1) Matrices, C. Koukouvinos, M. Mitrouli, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We suppose the Hadamard conjecture is true and an Hadamard matrix of order 4t, exists for all t ≥ 1. We use the results for the equivalent SBIBD(4t-1,2t-1,t-1) to establish the maximum determinant or a lower bound for the maximum determinant for all ±1 matrices. In particular we give numerical results for all orders ≤100.