Experiments with a scheme of data reduction for television signals

Imperial Users onl

Analogue circuits for low power communication

Low power electronic circuits are required to extend the operational time of battery operated devices. They are also necessary to reduce the power consumption of equipment in general, especially as the world tries to cut energy usage. The first section of this thesis explores fundamental and implementation limits for low power circuits. The energy requirements of amplification are presented and a lower bound on the energy required to transmit information over a point to point link is proposed. It is evident from the low power limits survey that when a transistor is biased, significant thermodynamic energy is required to reduce the resistance of the channel. A transmitter is presented that turns on a transistor for 0.1 % of transmitted time. This transmitter approximates a Gaussian pulse by allowing the impulse response of two 2nd order transmitting elements to sum in free space. The transmitter is of low complexity and the receiver architecture ensures that no on-line tuning is required. Measured results indicate that by using coherent detection a 1 Mbps, 50 mm distance link with a bit error rate of 10−3 can be achieved. The bandwidth of the transmitted pulse is 30-37.5 MHz and 30 dB of out of band attenuation is provided. An analogue Gabor transform is described which splits a signal into parallel paths of a lower bandwidth. This enables post processing at lower clock rates, which can reduce energy dissipation. An implementation of the transform using sub-threshold CMOS continuous time filters is presented. A novel method for designing low power gmC filters using simple models of identical transconductors is used to specify transistor sizes. Measured results show that the transform consumes 7 μW for an input signal bandwidth of 4 kHz

Efficient automatic correction and segmentation based 3D visualization of magnetic resonance images

In the recent years, the demand for automated processing techniques for digital medical image volumes has increased substantially. Existing algorithms, however, still often require manual interaction, and newly developed automated techniques are often intended for a narrow segment of processing needs. The goal of this research was to develop algorithms suitable for fast and effective correction and advanced visualization of digital MR image volumes with minimal human operator interaction. This research has resulted in a number of techniques for automated processing of MR image volumes, including a novel MR inhomogeneity correction algorithm derivative surface fitting (dsf), automatic tissue detection algorithm (atd), and a new fast technique for interactive 3D visualization of segmented volumes called gravitational shading (gs). These newly developed algorithms provided a foundation for the automated MR processing pipeline incorporated into the UniViewer medical imaging software developed in our group and available to the public. This allowed the extensive testing and evaluation of the proposed techniques. Dsf was compared with two previously published methods on 17 digital image volumes. Dsf demonstrated faster correction speeds and uniform image quality improvement in this comparison. Dsf was the only algorithm that did not remove anatomic detail. Gs was compared with the previously published algorithm fsvr and produced rendering quality improvement while preserving real-time frame-rates. These results show that the automated pipeline design principles used in this dissertation provide necessary tools for development of a fast and effective system for the automated correction and visualization of digital MR image volumes

Analyse des Solitonengehaltes von optischen Impulsen in Glasfasern

Der Solitonengehalt von Lichtimpulsen in einer Glasfaser wird untersucht. Dabei wird ein neu entwickeltes Verfahren angewendet, welches auf der spektralen Analyse der Schwebunsstrukturen beruht. Dieses Verfahren ist in der Lage, den allemeinen Solitonengehalt zu bestimmen, sogar für nichtintegrable Systeme. Dies war bisher nur Näherungsweise möglich. Aus der vorgestellten Analyse wird ein Messprinzip abgeleitet, mit dem sich der Solitonengehalt bestimmen lässt. Dies wird anhand einer Beispielmessung demonstriert