187,527 research outputs found
A programmable-load CMOS ring oscillator/inverter chain for propagation-delay measurements
A description is given of a test structure consisting of a combination of a ring oscillator and an inverter chain. The circuit can be used to carry out propagation delay measurements on two circuit types and under a number of load conditions. Full characterization only takes one test circuit. The elements of this structure are connected to a programmable load varying from a fan-in of 1 up to a fan-in of 15. In this way, the operating environment of the circuit can be simulated in hardware. The measurements can be carried out by means of a conventional automated digital measurement system providing AC and DC parametric measurement capabilities
Wall Compensation for Ultra Wideband Applications
Due to their low frequency contents, ultra wideband (UWB) signals have the ability to penetrate walls and obstacles. As the signal propagates through these obstacles, it gets attenuated, slows down, and gets dispersed. This paper demonstrates wall compensation for through-wall imaging, localization and communication receiver design purposes by first characterizing wave propagation through various building materials in the UWB frequency range. Knowledge of the walls obtained from the wall characterization is used to estimate and correct the position accuracy of a target object located behind the walls using three proposed methods namely; constant amplitude and delay (CDL), frequency dependent data (FFD), and data fitting methods (FIT). The obtained results indicated relatively acceptable measure of wall compensation for the three methods. Results from such work provide insight on how to develop algorithms for effective target position estimation in imaging and localization applications. They are also useful for channel modelling and link budget analysis
Common pulse retrieval algorithm: a fast and universal method to retrieve ultrashort pulses
We present a common pulse retrieval algorithm (COPRA) that can be used for a
broad category of ultrashort laser pulse measurement schemes including
frequency-resolved optical gating (FROG), interferometric FROG, dispersion
scan, time domain ptychography, and pulse shaper assisted techniques such as
multiphoton intrapulse interference phase scan (MIIPS). We demonstrate its
properties in comprehensive numerical tests and show that it is fast, reliable
and accurate in the presence of Gaussian noise. For FROG it outperforms
retrieval algorithms based on generalized projections and ptychography.
Furthermore, we discuss the pulse retrieval problem as a nonlinear
least-squares problem and demonstrate the importance of obtaining a
least-squares solution for noisy data. These results improve and extend the
possibilities of numerical pulse retrieval. COPRA is faster and provides more
accurate results in comparison to existing retrieval algorithms. Furthermore,
it enables full pulse retrieval from measurements for which no retrieval
algorithm was known before, e.g., MIIPS measurements
Phase retrieval via regularization in self-diffraction based spectral interferometry
A novel variant of spectral phase interferometry for direct electric-field
reconstruction (SPIDER) is introduced and experimentally demonstrated. Other
than most previously demonstrated variants of SPIDER, our method is based on a
third-order nonlinear optical effect, namely self-diffraction, rather than the
second-order effect of sum-frequency generation. On one hand, self-diffraction
(SD) substantially simplifies phase-matching capabilities for multi-octave
spectra that cannot be hosted by second-order processes, given manufacturing
limitations of crystal lengths in the few-micrometer range. On the other hand,
however, SD SPIDER imposes an additional constraint as it effectively measures
the spectral phase of a self-convolved spectrum rather than immediately
measuring the fundamental phase. Reconstruction of the latter from the measured
phase and the spectral amplitude of the fundamental turns out to be an
ill-posed problem, which we address by a regularization approach. We discuss
the numerical implementation in detail and apply it to measured data from a
Ti:sapphire amplifier system. Our experimental demonstration used 40-fs pulses
and a 500 m thick BaF crystal to show that the SD SPIDER signal is
sufficiently strong to be separable from stray light. Extrapolating these
measurements to the thinnest conceivable nonlinear media, we predict that
bandwidths well above two optical octaves can be measured by a suitably adapted
SD SPIDER apparatus, enabling the direct characterization of pulses down to
single-femtosecond pulse durations. Such characteristics appear out of range
for any currently established pulse measurement technique
How long delays impact TCP performance for a connectivity from Reunion Island ?
TCP is the protocol of transport the most used in the Internet and have a
heavy-dependence on delay. Reunion Island have a specific Internet connection,
based on main links to France, located 10.000 km away. As a result, the minimal
delay between Reunion Island and France is around 180 ms. In this paper, we
will study TCP traces collected in Reunion Island University. The goal is to
determine the metrics to study the impacts of long delays on TCP performance
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