Utilising temporal signal features in adverse noise conditions: Detection, estimation, and the reassigned spectrogram

Visual displays in passive sonar based on the Fourier spectrogram are underpinned by detection models that rely on signal and noise power statistics. Time-frequency representations specialised for sparse signals achieve a sharper signal representation, either by reassigning signal energy based on temporal structure or by conveying temporal structure directly. However, temporal representations involve nonlinear transformations that make it difficult to reason about how they respond to additive noise. This article analyses the effect of noise on temporal fine structure measurements such as zero crossings and instantaneous frequency. Detectors that rely on zero crossing intervals, intervals and peak amplitudes, and instantaneous frequency measurements are developed, and evaluated for the detection of a sinusoid in Gaussian noise, using the power detector as a baseline. Detectors that rely on fine structure outperform the power detector under certain circumstances; and detectors that rely on both fine structure and power measurements are superior. Reassigned spectrograms assume that the statistics used to reassign energy are reliable, but the derivation of the fine structure detectors indicates the opposite. The article closes by proposing and demonstrating the concept of a doubly reassigned spectrogram, wherein temporal measurements are reassigned according to a statistical model of the noise background

The Impact of the Nanoscale on Computing Systems

Nanoscale technologies provide both challenges and opportunities. We show that the issues and potential solutions facing designers are technology independent and arise mainly from shrinking device sizes and an increase in the number of devices available. We explore how it is possible to use some of the devices that will be available to help ease design complexity as well as overcome process related challenges such as limited layout freedom, increased defect densities, timing constraints, and power dissipation