Digital Measurement of Partial Discharge

Various new measurement techniques have been developed for a high voltage phenomenon referred to as partial discharge. Partial discharge is a localized breakdown of the high voltage insulation system which is observed as low level, random emissions. Both electrical and acoustic emissions have been measured in underground power cables, solid cast power transformers and in lumped specimens. Typical problems complicating the measurements are the randomness of the emission, high levels of interference and extreme distortion of the signal by the propagation path. Various signal processing techniques have been adapted to the measurement of partial discharge. The techniques investigated are capable of reducing noise in the measurements and have provided orders of magnitude improvement in sensitivity over ordinary methods. Some of the techniques studied are capable of providing information about the location of the partial discharge site

Code-timing synchronization in DS-CDMA systems using space-time diversity

The synchronization of a desired user transmitting a known training sequence in a direct-sequence (DS) asynchronous code-division multiple-access (CDMA) sys-tem is addressed. It is assumed that the receiver consists of an arbitrary antenna array and works in a near-far, frequency-nonselective, slowly fading channel. The estimator that we propose is derived by applying the maximum likelihood (ML) principle to a signal model in which the contribution of all the interfering compo-nents (e.g., multiple-access interference, external interference and noise) is modeled as a Gaussian term with an unknown and arbitrary space-time correlation matrix. The main contribution of this paper is the fact that the estimator makes eÆcient use of the structure of the signals in both the space and time domains. Its perfor-mance is compared with the Cramer-Rao Bound, and with the performance of other methods proposed recently that also employ an antenna array but only exploit the structure of the signals in one of the two domains, while using the other simply as a means of path diversity. It is shown that the use of the temporal and spatial structures is necessary to achieve synchronization in heavily loaded systems or in the presence of directional external interference.Peer ReviewedPostprint (published version

Getting the most out of C.O.AS.T

Chapter 1 is a review of developments in optical aperture synthesis and is not original work. Chapter 2 considers the techniques estimating of fringe visibilities from photon-noise- limited data and is mostly a review of previous work, although some of the analysis is my own. Chapters 3–6 are original except where otherwise stated. The delay line described in chapter 7 is based on the design developed by Connes [16], but the specific implementation is my own. Chapter 8 describes experiments which are a continuation of the work of Baldwin et al. [6] and Haniff et al. [37], but the specific work descibed here is my own. Chapter 9 is original except where otherwise stated

Hidden Markov models for radio localization in mixed LOS/NLOS conditions

Abstract—This paper deals with the problem of radio localization of moving terminals (MTs) for indoor applications with mixed line-of-sight/non-line-of-sight (LOS/NLOS) conditions. To reduce false localizations, a grid-based Bayesian approach is proposed to jointly track the sequence of the positions and the sight conditions of the MT. This method is based on the assumption that both the MT position and the sight condition are Markov chains whose state is hidden in the received signals [hidden Markov model (HMM)]. The observations used for the HMM localization are obtained from the power-delay profile of the received signals. In ultrawideband (UWB) systems, the use of the whole power-delay profile, rather than the total power only, allows to reach higher localization accuracy, as the power-profile is a joint measurement of time of arrival and power. Numerical results show that the proposed HMM method improves the accuracy of localization with respect to conventional ranging methods, especially in mixed LOS/NLOS indoor environments. Index Terms—Bayesian estimation, hidden Markov models (HMM), mobile positioning, source localization, tracking algorithms

A Study of Synchronization Techniques for Optical Communication Systems

The study of synchronization techniques and related topics in the design of high data rate, deep space, optical communication systems was reported. Data cover: (1) effects of timing errors in narrow pulsed digital optical systems, (2) accuracy of microwave timing systems operating in low powered optical systems, (3) development of improved tracking systems for the optical channel and determination of their tracking performance, (4) development of usable photodetector mathematical models for application to analysis and performance design in communication receivers, and (5) study application of multi-level block encoding to optical transmission of digital data