Time and Frequency Localized Pulse Shape for Resolution Enhancement in STFT-BOTDR

In systems using Orthogonal Frequency Division Multiplexed (OFDM) all transmitters in a radio broadcasting network may transmit identical signals in the same frequency block, forming a so called Single Frequency Network (SFN). The simultaneous transmission creates a severe artificial multipath propagation causing interference at the receiver. This interference consists not only by intersymbol interference (ISI), but also interchannel interference (ICI) due to orthogonality losses between OFDM scheme‘s subcarriers. A method that is often used to counter the ’’self-interference‘‘ is to insert a guard interval between consecutive OFDM frames combined with an increased symbol duration. The receiver in an SFN is normally experiencing a diversity gain of receiving several signals. Doubts concerning the performance has been raised due to the OFDM scheme‘s sensitivity to frequency errors. If the received signals are exposed to different carrier offsets it will lead to ICI, resulting into reduced coverage. In this paper we apply pulse shaping to reduce the effects of ISI and ICI. Pulse shaping of the transmitted OFDM signal is shown to give significant reductions in self-interference. It is hereby possible to achieve the same coverage with a reduced amount of transmitters. The system also becomes less sensitive to time and frequency synchronisation errors. A method to analyse the performance for time limited pulse shapes is presented using weight functions describing the amount of useful and interfering powers. In the receiver analysis, generalised expressions are given using Fourier transforms and series.

In tomoelastography, to achieve a final wave speed map by combining reconstructions obtained from all spatial directions and excitation frequencies, the use of weights is inevitable. Here, a new weighting scheme, which maximizes the signal-to-noise ratio (SNR) of the final wave speed map, has been proposed. To maximize the SNR of the final wave speed map, the use of squares of estimated SNR values of reconstructed individual maps has been proposed. Therefore, derivations of the SNR of the reconstructed wave speed maps have become necessary. Considering the noise on the complex MRI signal, the SNR of the reconstructed wave speed map was formulated by an analytical approach assuming a high SNR, and the results were verified using Monte Carlo simulations (MCSs). It has been assumed that the noise remains approximately Gaussian when the image SNR is high enough, despite the nonlinear operations in tomoelastography inversion. Hence, the SNR threshold was determined by comparing the SNR computed by MCSs and analytical approximations. The weighting scheme was evaluated for accuracy, spatial resolution and SNR performances on simulated phantoms. MR elastography (MRE) experiments on two different phantoms were conducted. Wave speed maps were generated for simulated 3D human abdomen MRE data and experimental human abdomen MRE data. The simulation results demonstrated that the SNR-weighted inversion improved the SNR performance of the wave speed map by a factor of two compared to the performance of the original (i.e., amplitude-weighted) reconstruction. In the case of a low SNR, no bias occurred in the wave speed map when SNR weighting was used, whereas 10% bias occurred when the original weighting (i.e., amplitude weighting) was used. Thus, while not altering the accuracy or spatial resolution of the wave speed map with the proposed weighting method, the SNR of the wave speed map has been significantly improved.

When compared to many other sensitive methods for material detection, such as inductively coupled mass spectroscopy and thermal ionization mass spectroscopy, laser-induced breakdown spectroscopy (LIBS) typically exhibits a lower signal-to-noise ratio (SNR), resulting in higher detection limits. Increasing the SNR of LIBS would improve the ability to characterize the sample composition with increased accuracy and speed and reduce the amount of material needed to perform analysis. We have been investigating the effect of simple ultrashort laser pulse shaping on the SNR of LIBS. Our goal is to control the dynamics of the ionization and recombination processes in the laser-produced plasma to favorably affect the SNR associated with the line emission from the plasma. Pulse shaping is performed using an acousto-optic programmable dispersive filter. An adaptive learning algorithm is being developed to automate the pulse shape optimization process for maximization of LIBS SNR in nuclear security-relevant material characterization scenarios. We report a 27 % increase of the SNR for non-gated LIBS measurements of uranium by utilizing simple pulse shaping limited exclusively to excess quadratic spectral phase of the laser pulse.

By dividing the available spectrum into multiple bands, multi-band ultra-wideband (UWB) systems possess many advantages, such as the flexibility to eliminate possible interference and coexistence problems with available wireless standards. UWB channels have large delay spread, causing inter- symbol interference (ISI) in high rate systems. The RAKE receiver is often used to capture multipath energy, but it is incapable of ISI compensation, causing severe bit error rate (BER) degradation in practical UWB channels. This paper proposes an over-sampling multi-channel equalizer per sub-band for multi-band UWB. The performance of the proposed receiver is compared with the RAKE receiver through analytical and simulation studies. The proposed equalizer has been shown to be able to handle ISI under any channel conditions or data rate presented, with an acceptable BER. In addition, the rich multipath diversity of the UWB channels is harnessed by the over-sampling scheme, for output SNR improvement. one. Therefore, equalization receiver based on adaptive algorithms seems to be an effective way to recover the transmitted data. With this consideration, we propose an over-sampling multi-channel equalizer per sub-band for a multi-band UWB system, which provides more effective inter-symbol interference (ISI) suppression compared with the conventional RAKE receiver when operating in channels with large delay spread. Through detailed theoretical analysis and extensive simulations, we are able to show that the proposed 4-arm equalizer scheme is superior to a 4-arm conventional RAKE receiver in the presence of ISI at all signal-to-noise ratios (SNRs). Based on the method presented in (4), the simulated performance is shown to conform to analytical predictions. The RAKE receiver is incapable of ISI compensation, and a moderate level of ISI is shown to cause severe bit error rate (BER) degradation. The proposed over-sampling equalizer, on the other hand, is able to handle ISI under any channel conditions or data rate, with an acceptable BER. Over- sampling is shown to be able to achieve diversity gain, and improves the output SNR.

A vector sequential sequence estimator is proposed for multiple-channel systems with both intersymbol interference (ISI) and interchannel interference (ICI). Both finite ISI-ICI and infinite ISI-ICI are considered. The estimator consists of a multiple-dimensional whitened matched filter and a vector sequential decoder. The metric of the sequential algorithm is derived, and the algorithm's performance is analyzed. Computer simulation results for a two-dimensional finite ISI-ICI channel and a two-dimensional infinite ISI-ICI channel are presented. Analysis and simulation show that the symbol error probability of the vector sequential algorithm is essentially the same as for maximum-likelihood sequence estimation using the vector Viterbi algorithm, while its average computational complexity is much less, although computation per symbol is a random variable with the Pareto distribution. There exists a signal-to-noise ratio above which the ensemble average computation is bounded. An upper bound on this ratio is found.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A unified procedure to characterize the effect of interchannel and intersymbol interference, Doppler and fading in multicarrier modulation (MCM) systems, is presented. The effect of different waveform shapes is considered in order to check the possibility of utilizing MCM as a multiple access technique. The degradation of system performance due to time and frequency offsets typical of multi-user environments is evaluated. In order to compare in a concise way different schemes, graphs showing time-frequency signatures, are introduced. The effect of the number of subcarriers and sampling frequency offsets in FFT-based implementation is also taken into account.

In this chapter, various issues on pulse shaping waveform design for bandwidth efficient digital modulations will be addressed. Here what we concern about the pulse shaping waveforms is the physical appearances or shapes each information data bit or symbol take before carrier modulations. It is well known that the spectral characteristics of a carrier modulated signal can be uniquely determined by its baseband signal before modulation, and thus the waveform shape applied to pre-modulated signals is of ultimate importance to ensure overall bandwidth-efficiency of a wireless communication system. This chapter starts with an overview on the evolution of pulse shaping technologies from early digital modulation schemes to recently emerging new carrier modulations such as quadrature-overlapped modulations. The impact of the pulse shaping technologies on both bandwidth-efficiency and power-efficiency, which are two essential merit parameters of a digital modem, will also be discussed. The majority of the content in this chapter, however, is dedicated to the discussions on shaping pulse design methodology as well as performance analysis of a pulse-shaped digital modem, in which various shaping pulse design methods (including those commonly referred and those recently proposed in the literature) will be presented. To measure the effectiveness of the pulse-shaping techniques, different pulse shaped digital modulations will be evaluated and then compared in terms of their spectral characteristics, the sensitivity of their performance against synchronization timing jitter as well as their bit error rate performance, where the emphasis will be put on the pulse-shaped quadrature-overlapped (QO) modems under bandpass nonlinear channels, which usually exist in satellite and mobile cellular systems. Several new pulse shaped QO modulation schemes, which adopt various novel pulse shaping waveforms generated by time-domain convolution method, will be presented and their performance analysis will be carried out in comparison with other traditional digital modems, such as QPSK, OQPSK, MSK and so forth.

Proposal and analysis of a reconfigurable pulse shaping technique based on multi-arm optical differentiators

Spatial resolution and temporal resolution refer to the smallest distance and temporal change that can be differentiated. Signal-to-noise ratio (SNR) is a reflection of signal intensity with reference to the background noise. In cardiac MR imaging, it is desirable to acquire images that have adequate spatial resolution to resolve fine structures in the heart, sufficient temporal resolution to visualize cardiac motion, and high SNR for good image quality. This chapter first covers spatial resolution in MRI, its relationship to k-space, the difference between nominal and apparent spatial resolution, and factors that affect spatial resolution. The chapter then discusses temporal resolution and image acquisition methods that can be used to change/improve temporal resolution, including view-sharing, segmented imaging, and real-time imaging. Finally, the chapter covers SNR and sources of noise, factors affecting SNR, how to measure SNR, and the tradeoffs between SNR, spatial resolution and temporal resolution.

This paper presents analytical results of the effects of jitter and inter symbol interference (ISI) on a millimeter-wave impulse radio (IR) transceiver, compared with performance of the developed 10-Gb/s W-band IR transmitter prototype. The compact and cost-effective IR transmitter consists of a pulse generator (PG) that creates a short pulse with a duration of &#60;10 ps, a band-pass filter (BPF) that shapes the short pulse to the desired millimeter-wave pulse (wavelet), and a power amplifier (PA) which is deployed as an option. Jitters of the PG and ISI from the BPF are a great issue to make the IR transceiver robust and to obtain excellent performance. One analysis verified that, thanks to a novel retiming architecture, the random jitter and the data dependent jitter from the PG give only a small penalty of &#60;0.5-dB increase in signal to noise ratio (SNR) for achieving a bit error rate (BER) of &#60;10−12. The alternative analysis on the effect of ISI from the BPF indicated that using a Gaussian BPF enables transmission with a BER of &#60;10−12 up to a data rate of 1.4 times as large as a bandwidth of the BPF, whereas the ISI analysis suggested that mismatching of the skirt characteristics of the developed BPF to those of a Gaussian BPF causes tail lobes following the wavelet, resulting in an on/off ratio of &#60;15 dB and hence an SNR penalty of &#60;6 dB.

Even though breast cancer is a cancer with relatively easy early diagnostic and has an appropriate treatment, it has high mortality rates in Brazil. This is in part because the disease is diagnosed only in advanced stages, but also because the whole information contained in the mammograms is not used by physicians and radiologists. There are many parameters to be considered in assessing the quality of a mammogram image. Among these parameters are contrast, spatial resolution, the signal-to-noise ratio, and the efficiency of the applied dose. Even with the improvement of the quality of radiographs, many structures, such as small microcalcifications, are not always identified by radiologists in the images. To determine the lowest detectable structures in digital mammograms, we made a numerical analysis of a few digital mammography using simulators, determining the spatial and intensity resolutions, and studying the noise and its distribution. With this, we could determine the detection levels, quantifying the probability that any point is due to statistical noise or a real change in breast density. This is the first step towards early detection of microcalcifications. In our work, it was possible to detect even the smallest microcalcifications of the simulator, 0.18 mm in diameter, with false alarm probability smaller than 1/1000.

CNES is currently carrying out a Phase A study to assess the feasibility of a future hyperspectral imaging sensor (10 m spatial resolution) combined with a panchromatic camera (2.5 m spatial resolution). This mission focuses on both high spatial and spectral resolution requirements, as inherited from previous French studies such as HYPEX, HYPXIM, and BIODIVERSITY. To meet user requirements, cost, and instrument compactness constraints, CNES asked the French hyperspectral Mission Advisory Group (MAG), representing a broad French scientific community, to provide recommendations on spectral sampling, particularly in the Short Wave InfraRed (SWIR) for various applications.This paper presents the tests carried out with the aim of defining the optimal spectral sampling and spectral resolution in the SWIR domain for quantitative estimation of physical variables and classification purposes. The targeted applications are geosciences (mineralogy, soil moisture content), forestry (tree species classification, leaf functional traits), coastal and inland waters (bathymetry, water column, bottom classification in shallow water, coastal habitat classification), urban areas (land cover), industrial plumes (aerosols, methane and carbon dioxide), cryosphere (specific surface area, equivalent black carbon concentration), and atmosphere (water vapor, carbon dioxide and aerosols). All the products simulated in this exercise used the same CNES end-to-end processing chain, with realistic instrument parameters, enabling easy comparison between applications. 648 simulations were carried out with different spectral strategies, radiometric calibration performances and signal-to-noise Ratios (SNR): 24 instrument configurations × 25 datasets (22 images + 3 spectral libraries).The results show that spectral sampling up to 20 nm in the SWIR range is sufficient for most applications. However, 10 nm spectral sampling is recommended for applications based on specific absorption bands such as mineralogy, industrial plumes or atmospheric gases. In addition, a slight performance loss is generally observed when radiometric calibration accuracy decreases, with a few exceptions in bathymetry and in the cryosphere for which the observed performance is severely degraded. Finally, most applications can be achieved with a realistic SNR, with the exception of bathymetry, shallow water classification, as well as carbon dioxide and methane estimation, which require the optimistic SNR level tested. On the basis of these results, CNES is currently evaluating the best compromise for designing the future hyperspectral sensor to meet the objectives of priority applications.

The purpose of this study was to investigate the optimal spatial resolution and temporal resolution of dynamic improved motion-sensitized driven-equilibrium steady-state free precession for visualization of respiratory-driven cerebrospinal fluid (CSF) dynamics. We investigated the differences in the visualization using the midsagittal cross-sections of nine healthy volunteers by three imaging conditions. (A: spatial resolution 0.49×0.49×5 mm, temporal resolution 1000 ms; B: 0.49×0.49×5 mm, 430 ms; and C: 0.78×0.78×5 mm, 200 ms). First, we calculated the CSF of the third and fourth ventricles and the signal-to-noise ratio (SNR) of the pons. Next, we calculated the signal intensity ratio (SIR) of the CSF flowing at 10 cm/s or more and the CSF flowing at 10 cm/s or less due to respiration. We also calculated the difference between the inspiration and expiration SIR. Furthermore, 1) the presence of flow in the third and fourth ventricles centered on the cerebral aqueduct and 2) the change in flow due to respiration was investigated by a three-point scale visual assessment by seven radiological technologists. The SNR was the highest in A, the next highest in B, and the lowest in C in all cases. There were significant differences between A and B, and A and C in CSF of the third and fourth ventricles. However, there was no significant difference between B and C. The CSF signal intensity changed with respiration. The SIR of the third ventricle was higher on inspiration and lower on expiration. Conversely, the SIR of the fourth ventricle was lower on inspiration and higher on expiration. There was a significant difference between A and C and B and C in each SIR (p<0.05). The difference between inspiration and expiration SIR was the highest in B, the next highest in A, and the lowest in C in both the third and fourth ventricles. Significant differences were found between A and C, and between B and C (p<0.05). There was no significant difference in the presence of flow in the third and fourth ventricles centered on the cerebral aqueduct (p=0.264). On the other hand, there was a significant difference between the imaging conditions in the change in flow due to respiration, with B having a higher value than the others (p<0.001). The optimal spatial and temporal resolutions were 0.49×0.49×5 mm and 430 ms, respectively. The results also suggest that it is important to carefully set the imaging conditions for the spatial and temporal resolutions because of the use of phase dispersion in this method.

Approaches for designing surface acoustic wave (SAW) filters used in pulsed quadrature binary modulation (QBM) systems are presented. Several previously defined pulse shapes were implemented by a SAW filter and showed good QBM system performance with respect to modulation envelope nonuniformity (AM) and intersymbol interference (ISI). A new approach to QBM pulse shape definition using both frequency- and time-domain design criteria is described. This approach allows families of new pulse shapes having various levels of AM and spectral confinement to be designed. The approaches to the design equations are presented, and examples of specific pulse shapes and their implementation using SAW filters are given. Time- and frequency-domain results of iteratively designed pulse shapes for application to QBM systems are also presented, showing good performance.

We sought to compare objectively computed tomography (CT) scanner performance for three clinically relevant protocols using a task-based image quality assessment method in order to assess the potential for radiation dose reduction. Four CT scanners released between 2003 and 2007 by different manufacturers were compared with four CT scanners released between 2012 and 2014 by the same manufacturers using ideal linear model observers (MO): prewhitening (PW) MO and channelized Hotelling (CHO) MO with Laguerre-Gauss channels for high-contrast spatial resolution and low-contrast detectability (LCD) performance, respectively. High-contrast spatial resolution was assessed using a custom-made phantom that enabled the computation of the target transfer function (TTF) and noise power spectrum (NPS). Low-contrast detectability was assessed using a commercially available anthropomorphic abdominal phantom providing equivalent diameters of 24, 29.6, and 34.6cm. Three protocols were reviewed: a head (trauma) and an abdominal (urinary stones) protocol were applied to assess high-contrast spatial resolution performance; and another abdominal (focal liver lesions) protocol was applied for LCD. The liver protocol was tested using fixed and modulated tube currents. The PW MO was proposed for assessing high-contrast detectability performance of the various CT scanners. Compared with older generation CT scanners, three newer systems displayed significant improvements in high-contrast detectability over that of their predecessors. A fourth, newer system had lower performance. The CHO MO was appropriate for assessing LCD performance and revealed that an excellent level of image quality could be obtained with newer scanners at significantly lower dose levels. This study shows that MO can objectively benchmark CT scanners using a task-based image quality method, thus helping to estimate the potential for further dose reductions offered by the latest systems. Such an approach may be useful for adequately and quantitatively comparing clinically relevant image quality among various scanners.