279,029 research outputs found
EXIT Chart Based Joint Code-Rate and Spreading-Factor Optimisation of Single-Carrier Interleave Division Multiple Access
Abstract—In this paper, we consider the joint code-rate and spreading-factor optimisation of turbo-style iterative joint detection and decoding assisted single-carrier interleave division multiple access (SC-IDMA) systems using different-rate convolutional codes and Extrinsic Information Transfer (EXIT) charts, when communicating over Additive White Gaussian Noise (AWGN) channels. More explicitly, we study the extrinsic information exchange between two serial concatenated components and maximise the number of users supported by the SC-IDMA system under the constraint of a fixed bandwidth expansion factor, while maintaining a predefined Bit Error Ratio (BER) versus Eb/N0 performance. We found that an optimum coderate and spreading-factor combination can be found for the SC-IDMA system at low Eb/N0 values, where maintaining a low BER inevitably requires the employment of channel coding. By contrast, at high Eb/N0 the system performs best, when no channel coding is used, i.e. DS-spreading is the only means of bandwidth expansion
Observation of Terahertz Radiation via the Two-Color Laser Scheme with Uncommon Frequency Ratios
In the widely-studied two-color laser scheme for terahertz (THz) radiation
from a gas, the frequency ratio of the two lasers is usually fixed at
1:2. We investigate THz generation with uncommon frequency
ratios. Our experiments show, for the first time, efficient THz generation with
new ratios of 1:4 and 2:3. We observe that the THz
polarization can be adjusted by rotating the longer-wavelength laser
polarization and the polarization adjustment becomes inefficient by rotating
the other laser polarization; the THz energy shows similar scaling laws with
different frequency ratios. These observations are inconsistent with multi-wave
mixing theory, but support the gas-ionization model. This study pushes the
development of the two-color scheme and provides a new dimension to explore the
long-standing problem of the THz generation mechanism.Comment: 6 pages, 3 figure
An Algorithm for Probabilistic Alternating Simulation
In probabilistic game structures, probabilistic alternating simulation
(PA-simulation) relations preserve formulas defined in probabilistic
alternating-time temporal logic with respect to the behaviour of a subset of
players. We propose a partition based algorithm for computing the largest
PA-simulation, which is to our knowledge the first such algorithm that works in
polynomial time, by extending the generalised coarsest partition problem (GCPP)
in a game-based setting with mixed strategies. The algorithm has higher
complexities than those in the literature for non-probabilistic simulation and
probabilistic simulation without mixed actions, but slightly improves the
existing result for computing probabilistic simulation with respect to mixed
actions.Comment: We've fixed a problem in the SOFSEM'12 conference versio
Rhythmic firing patterns in SCN: The role of circuit interactions
The suprachiasmatic nucleus (SCN) is believed to contain the main generator of circadian rhythmicity in mammals. In order to obtain further functional details of this, electrophysiological extracellular measurements in vitro were made. By means of an interspike interval distribution analysis, it is shown that there is a novel kind of neuronal firing pattern: the harmonic pattern. From these observations, we have developed a theoretical model based on possible filtering processes occurring during synaptic transmission. The model suffices to infer that regular ultradian oscillators could be an emergent property of circuit interactions of cells in the suprachiasmatic nucleus
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