摘要 :
We explore two fundamental questions at the intersection of sampling theory and information theory: how channel capacity is affected by sampling below the channel's Nyquist rate, and what sub-Nyquist sampling strategy should be em...
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We explore two fundamental questions at the intersection of sampling theory and information theory: how channel capacity is affected by sampling below the channel's Nyquist rate, and what sub-Nyquist sampling strategy should be employed to maximize capacity. In particular, we derive the capacity of sampled analog channels for three prevalent sampling strategies: sampling with filtering, sampling with filter banks, and sampling with modulation and filter banks. These sampling mechanisms subsume most nonuniform sampling techniques applied in practice. Our analyses illuminate interesting connections between undersampled channels and multiple-input multiple-output channels. The optimal sampling structures are shown to extract out the frequencies with the highest SNR from each aliased frequency set, while suppressing aliasing and out-of-band noise. We also highlight connections between undersampled channel capacity and minimum mean-squared error (MSE) estimation from sampled data. In particular, we show that the filters maximizing capacity and the ones minimizing MSE are equivalent under both filtering and filter-bank sampling strategies. These results demonstrate the effect upon channel capacity of sub-Nyquist sampling techniques, and characterize the tradeoff between information rate and sampling rate.
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This paper proposes a set-theoretic method to capture the effect of parametric uncertainty in reliability and performability indices obtained from Markov reliability and reward models. We assume that model parameters, i.e., compon...
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This paper proposes a set-theoretic method to capture the effect of parametric uncertainty in reliability and performability indices obtained from Markov reliability and reward models. We assume that model parameters, i.e., component failure and repair rates, are not perfectly known, except for upper and lower bounds obtained from engineering judgment or field data. Thus, the values that these parameters can take are constrained to lie within a set. In our method, we first construct a minimum volume ellipsoid that upper bounds this set, and hence contains all possible values that the parameters can take. This ellipsoid is then propagated via set operations through a second-order Taylor series expansion of the Markov chain stationary distribution, resulting in a set that provides approximate bounds on reliability and performability indices of interest. Case studies pertaining to a two-component shared load system with common-cause failures, and preventative maintenance of an electric-power distribution transformer, are presented.
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This paper presents a flexible ac distribution system device for microgrid applications. The device aims to improve the power quality and reliability of the overall power distribution system that the microgrid is connected to. The...
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This paper presents a flexible ac distribution system device for microgrid applications. The device aims to improve the power quality and reliability of the overall power distribution system that the microgrid is connected to. The control design employs a new model predictive control algorithm which allows faster computational time for large power systems by optimizing the steady-state and the transient control problems separately. Extended Kalman filters are also employed for frequency tracking and to extract the harmonic spectra of the grid voltage and the load currents in the microgrid. The design concept is verified through different test case scenarios to demonstrate the capability of the proposed device and the results obtained are discussed.
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Cholesteric liquid crystal (ChLC) bi-stable displays were fabricated on 100 $mu$m thick flexible glass front- and backplane substrates. The flexible glass substrates were ${hbox{250 mm}}times{hbox{300 mm}}$ in size, and the displa...
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Cholesteric liquid crystal (ChLC) bi-stable displays were fabricated on 100 $mu$m thick flexible glass front- and backplane substrates. The flexible glass substrates were ${hbox{250 mm}}times{hbox{300 mm}}$ in size, and the displays were fabricated using Gen2 equipment by temporarily attaching the substrates to processing carriers. No significant fabrication issues were encountered that would limit process optimization of these devices. Benefits of the flexible glass substrates observed compared to previously evaluated polymer film substrates include both thermal capability and dimensional stability. The fabricated flexible glass ChLC displays included both 5-inch color and 10.4-inch monochrome devices with resolutions of 80 ppi and 40 ppi, respectively. The displays had a total thickness of 204 $mu$m.
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The effect of TaO$_{rm x}$ capping layer on microstructures and magnetic properties of FePt thin films via annealing was studied. The structural ordering of FePt from face-centered cubic to face-centered tetragonal phases depends ...
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The effect of TaO$_{rm x}$ capping layer on microstructures and magnetic properties of FePt thin films via annealing was studied. The structural ordering of FePt from face-centered cubic to face-centered tetragonal phases depends strongly on the oxygen contents in the capping TaO$_{rm x}$ layer. The role of the TaO$_{rm x}$ layer is used to separate the FePt grains, as revealed by TEM. The annealed FePt/TaO$_{rm x}$ (15%O$_{2}$/Ar) exhibited the largest out-of-plane coercivity (${rm H}_{rm c}sim 4.2$ kOe) amongst all samples, compared to that (${sim}2.4$ kOe) in the reference FePt layer. At low oxygen content in FePt/TaO$_{rm x}$ bilayers, the Ta atoms may act as defects to obstruct the FePt ordering whereas at high oxygen contents, the excess oxygen atoms diffuse into the FePt layer and react with Fe to form iron oxides which give rise to the low coercivities, as characterized by the XPS depth profile and binding energy analysis.
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This letter presents a high-power amplifier (PA) matched by bandpass filter (BPF) for long term evolution (LTE) applications. The phase shift of the BPF is found to retain ${pm}90^{circ}$ at the working frequency. It can be emplo...
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This letter presents a high-power amplifier (PA) matched by bandpass filter (BPF) for long term evolution (LTE) applications. The phase shift of the BPF is found to retain ${pm}90^{circ}$ at the working frequency. It can be employed as the output impedance transformer which transforms 50 $Omega$ to the desired maximum power point. By using this method, the high-PA integrated with the BPF avoids extreme wide line and obtain three functions which could boost the radio signal, select the working frequency band and eliminate the harmonics at the same time. The system dimensions are consequently reduced as the following BPF after PA is omitted. A high-PA matched by BPF working at 2.6 GHz is designed. The analysis is given and the measured results and comparisons are presented. The good agreement confirms the validity of the proposed method.
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