Barry M. G. Cheetham

RSA-based Certified Delivery of E-Goods Using Verifiable and Recoverable Signature Encryption

Delivering electronic goods over the Internet is one of the e-commerce applications that will proliferate in the coming years. Certified e-goods delivery is a process where valuable e-goods are exchanged for an acknowledgement of their reception. This paper proposes an efficient security protocol for certified e-goods delivery with the following features: (1) it ensures strong fairness for the exchange of e-goods and proof of reception, (2) it ensures non- repudiation of origin and non-repudiation of receipt for the delivered e-goods, (3) it allows the receiver of e-goods to verify, during the exchange process, that the e-goods to be received are the one he is signing the receipt for, (4) it uses an off-line and transparent semi-trusted third party (STTP) only in cases when disputes arise, (5) it provides the confidentiality protection for the exchanged items from the STTP, and (6) achieves these features with less computational and communicational overheads than related protocols.

DSP algorithm for cough identification and counting

Digital signal processing (DSP) is applied to the analysis of the acoustic properties of pathological cough sounds. This work emanates from a clinical study of asthmatic, cystic fibrosis and cryptogenic fibrosing alveolitis patients. The pathological vocalisations exhibit clinically inconsistent acoustic properties from one disease to another. We aim to analyse the individual cough characteristic to adapt a DSP algorithm for identifying particular coughs and distinguishing them from background noise over long periods. The application is to obtain long-term statistical measurements to allow objective assessment of the severity of cough. This will be used for comparing the effectiveness of various treatments as well as. to study the physiological characteristic of pulmonary diseases. In this work, cough identification and counting algorithm has been developed to detect and count coughs characteristic of asthma. Its accuracy has been assessed. A sensitivity of 70.5% and specificity of 98.3% were achieved.

Enhanced shape-invariant pitch and time-scale modification for concatenative speech synthesis

To preserve shape invariance when performing pitch or time-scale modification of sinusoidally-modelled voiced speech, the phases of the sinusoids used to model the glottal excitation are made to add coherently at estimated excitation points. Previous methods achieved this by estimating excitation phases at synthesis frame boundaries, disregarding the frequency modulation that may occur between the frame boundary and the nearest modified excitation point. This approximation can produce a significant misalignment of the excitation phases, leading to distortion of the temporal structure of the synthetic speech. In this paper, a shape-invariant technique is proposed which aligns the excitation phases at excitation points, whilst allowing for variations in the frequency of the sinusoidal components.

Speech monitoring of infective laryngitis

Many types of parameters have been proposed for the evaluation of vocal cord abnormalities by speech waveform analysis. However, none of them taken separately allows a reliable assessment of the presence and the degree of abnormality. We propose combining three different parameters which take into account different consequences of the hoarseness. To assess the effectiveness of the parameters, a group of subjects during and after acute infective laryngitis are compared with control subjects. The jitter, the glottal to noise excitation (GNE) and the normalised error prediction (NEP) are the parameters studied. Preliminary results indicate that reliable discrimination between normal and abnormal patients may be possible using these three parameters.

Phase modelling of speech excitation for low bit-rate sinusoidal transform coding

Sinusoidal transform coding (STC) techniques model speech as the sum of sine-waves whose frequencies, amplitudes and phases are specified at regular intervals. To achieve a low-bit rate representation, only the spectral envelope is encoded and the phases are regenerated according to a minimum phase assumption. In this paper, the inaccuracy of the minimum phase model is demonstrated. It is shown that the phase spectra of decoded speech segments may be corrected using either the parameters of a Rosenberg pulse model or a second order all-pass filter. Experiments have shown that by applying this correction, the phase accuracy increases and the speech quality improves.

Equation-Method for correcting clipping errors in OFDM signals

Orthogonal frequency division multiplexing (OFDM) is the digital modulation technique used by 4G and many other wireless communication systems. OFDM signals have significant amplitude fluctuations resulting in high peak to average power ratios which can make an OFDM transmitter susceptible to non-linear distortion produced by its high power amplifiers (HPA). A simple and popular solution to this problem is to clip the peaks before an OFDM signal is applied to the HPA but this causes in-band distortion and introduces bit-errors at the receiver. In this paper we discuss a novel technique, which we call the Equation-Method, for correcting these errors. The Equation-Method uses the Fast Fourier Transform to create a set of simultaneous equations which, when solved, return the amplitudes of the peaks before they were clipped. We show analytically and through simulations that this method can, correct all clipping errors over a wide range of clipping thresholds. We show that numerical instability can be avoided and new techniques are needed to enable the receiver to differentiate between correctly and incorrectly received frequency-domain constellation symbols.

Inverted Wrap-Around Limiting with Bussgang Noise Cancellation Receiver for OFDM Signals

Orthogonal frequency division multiplexing (OFDM) is a widely used multicarrier modulation technique. High peak-to-average power ratio (PAPR) is a major drawback of OFDM systems which leads to power inefficiency and signal distortions. The simplest approach is to clip the high amplitudes at some predefined threshold before the signal is applied to the amplifier. The clipping causes in-band distortion as well as out-of-band radiation. Though the out-of-band radiation is reduced using filtering, it causes peak regrowth. The peak regrowth is taken care of using the repeated clipping and filtering. This paper presents the use of a different form of limiting, inverted wrap-around (IWrap). IWrap is presented and evaluated in terms of PAPR reduction and peak regrowth. The results show that IWrap limiting is much better for PAPR reduction as compared to conventional clipping technique. The performance of the proposed limiting technique is investigated with Bussgang noise cancellation iterative receiver for OFDM signals. The results of this iterative receiver with IWrap limiting are presented in terms of bit error probabilities.

Dynamic Adaptive Mechanism in Learning Management System Based on Learning Styles

Learning management systems are widely and successfully used for the delivery of self-paced online courses. This paper is concerned with enhancing the capability of such systems by introducing adaptivity in the way the information is presented to the on-line learner. Adaptivity means that the presentation style is personalised to the preferred learning style of each student, as may be modelled by a Baysian Network. The modelling is based on learning theories that have been proven by much experience, and provide appropriate assessment procedures. Techniques for introducing two forms of adaptivity, static and dynamic are considered and two experiments, based on case-studies are devised for evaluating their potential.

A vibrating trachea

A case of relapsing polychondritis presenting as tracheomalacia is reported in which an unusual low pitched sound was heard at the mouth and over the chest wall during expiration. The sound was associated with expiratory airflow limitation and oscillation on the flow trace of approximately 50 Hz. Spectral analysis of the sound showed it to have the characteristics of sounds produced by flutter in flow limited flexible tubes. These observations suggest that the sound was produced by airflow induced flutter in the trachea and main airways and is further evidence in support of the dynamic flutter theory of wheeze production.

Clipping noise mitigating iterative receivers for OFDM

Orthogonal Frequency Division Multiplexing (OFDM) systems are susceptible to High Power Amplifier (HPA) nonlinearities because of the high Peak to Average Power Ratios (PAPR) in the symbols that are transmitted. Clipping or otherwise limiting these high peaks causes in-band and out-of-band distortion in the signals. This study focuses on clipping noise mitigation using iterative receivers based on Bussgang Noise Cancellation (BNC) and Decision-Aided Reconstruction (DAR). A modified DAR receiver is simulated with oversampled clipping and filtering. Both receivers are compared in terms of bit-error rate (BER) and number of iterations.