Oversampled Gabor representation for transient signals

Considers the Gabor representation that uses a one-sided exponential window for detection and analysis of transient signals. Earlier results on the critically sampled case are extended to the more practically useful oversampled case. For oversampling by an integer factor, the authors derive an explicit analytical expression for the dual window (dual frame) function required for computing the Gabor representation. Based on this expression they develop an efficient procedure for computing the Gabor coefficients. Finally, they demonstrate the performance of the method by numerical examples     

Realizable lower bounds for time delay estimation

The accuracy of time delay estimates obtainable in active localization systems is studied, focusing on the effect of ambiguities in the time delay estimates. Such ambiguities occur when the transmitted signal has small relative bandwidth. Then, for signal to noise ratios below a certain threshold, the commonly used Cramer-Rao lower bound is not realizable. The study concentrates on the region of intermediate SNR values, where the Cramer-Rao bound is no longer achievable, but useful information on time delays can still be obtained from the measurement. Realizable bounds for the single and two echo cases are obtained by deriving a new form of the Barankin (1949) bound for active time delay estimation. This form maintains the realizability property of the most general form, but is of reasonable complexity. New bounds are derived for the multiple echo case. Examples are presented to illustrate the dependence of the bound on parameters such as SNR, relative bandwidth, and echo separation     

A low bias algorithm to estimate negative SNRs in an AWGN channel

Signal-to-noise ratio (SNR) is an important parameter in many receivers. In this letter, we derive a maximum-likelihood estimate of the amplitude of a binary phase-shift keying modulated signal and develop an iterative SNR search algorithm. Low bias is achieved for low SNR.     

Direction of arrival estimation using parametric signal models

We consider the problem of estimating the directions-of-arrival (DOAs) of narrowband sources with known center frequency. The paper evaluates the potential improvement in estimation accuracy by using spatial-temporal processing for signals obeying a deterministic parametric model. One would expect that prior information about the temporal structure of the signals will yield some gain in performance. By deriving the Cramer-Rao bound (CRB) on the DOA estimates, we quantify this gain and identify the cases for which the gain is significant. We show that for the single-source case, spatial-temporal processing does not yield any gain in performance relative to conventional spatial processing. For multiple noncoherent signals, incorporating temporal processing can achieve the single-source performance, yielding a significant gain for the case of multiple sources with small spatial separation relative to the beamwidth of the array. However, spatial-temporal processing cannot yield any gain in performance for multiple coherent signals     

Direction finding with time-varying arrays

This paper considers the problem of finding the directions of narrowband signals using a time-varying array, whose elements move during the observation interval in an arbitrary but known way. Assuming a Gaussian signal model, we derive the Cramer-Rao bound (CRB) and the maximum likelihood estimator for the directions of arrival. The single source case is studied in detail. Time-varying arrays are shown to be more robust to ambiguity errors than static arrays of comparable dimensions     

Detection of broadband signals in frequency and time dispersivechannels

A major problem for active sonar systems operating in shallow water is reverberation. High time-bandwidth waveforms and coherent matched filtering are often used to improve detection performance in reverberation. However, an active sonar echo undergoes distortion during the two-way propagation and reflection from the target. As a result, the full performance gain is not achievable, and this approach is severely limited. In this case, more robust detectors are needed. We evaluate the detection performance of several commonly used detectors in an ideal nondistorting channel, a fast-fading distortion (FFD) channel, and a channel with time-spreading distortion (TSD). We examine the robustness of the various detectors by evaluating the performance in the case of mismatch between the detector and the channel parameters. Studying the relation between the FFD model and the TSD, we show that, under certain conditions, the TSD and FFD channels have an equivalent effect on the waveform     

Work measurement for estimating food preparation time of a bioregenerative diet

During space missions, such as the prospective Mars mission, crew labor time is a strictly limited resource. The diet for such a mission (based on crops grown in a bioregenerative life support system) will require astronauts to prepare their meals essentially from raw ingredients. Time spent on food processing and preparation is time lost for other purposes. Recipe design and diet planning for a space mission should therefore incorporate the time required to prepare the recipes as a critical factor. In this study, videotape analysis of an experienced chef was used to develop a database of recipe preparation time. The measurements were highly consistent among different measurement teams. Data analysis revealed a wide variation between the active times of different recipes, underscoring the need for optimization of diet planning. Potential uses of the database developed in this study are discussed and illustrated in this work.     

High precision processing of flexible P3HT/PCBM modules with geometric fill factor over 95%

Flexible OPV modules, based on P3HT:PCBM as absorber layer, were manufactured with a power conversion efficiency over 3% and for a total area of 3500 mm² consisting of 14 in series interconnected cells. The modules utilize the excellent mechanical and the outstanding optical properties of sputtered transparent ITO-Metal-ITO (IMI) electrodes deposited on the PET foil on the one hand, and the combination of large area slot-die coating with high resolution ultrafast laser patterning on the other hand. The manufacturing of modules with outstanding performance was found to be reproducible. The right combination of innovative electrodes and smart roll-to-roll compatible processing technologies demonstrates a viable path towards high efficient industrial module technology.     

Pseudo-Wigner distribution for analysis of pulsed Dopplerultrasound

Existing pulsed Doppler ultrasound systems apply the spectrogram as a tool for analysis and display of signals scattered from the blood. The spectrogram is a time-frequency representation (TFR) of a signal that maps a one-dimensional signal of time into a two-dimensional function of time and frequency. The analysis of Doppler ultrasound signals requires application of a two-dimensional TFR rather than one-dimensional spectral representations due to the nonstationary nature of the signals scattered from blood. The classical spectrogram is a smoothed Wigner distribution (SWD) with a specific smoothing function. For this smoothing function, the smoothing, and hence the resolution in time and frequency, cannot be controlled independently. The purpose of this study is to examine the application of other SWD's to analysis and display of Doppler ultrasound signals. The present paper concentrates on the pseudo-Wigner distribution (PWD). The PWD and the spectrogram are examined and compared as analysis tools for nonstationary Doppler ultrasound signals. The performance of these two TFR's as a function of Doppler bandwidth is evaluated and compared for time-varying flow