3,562 research outputs found
Multi-user lattice coding for the multiple-access relay channel
This paper considers the multi-antenna multiple access relay channel (MARC),
in which multiple users transmit messages to a common destination with the
assistance of a relay. In a variety of MARC settings, the dynamic decode and
forward (DDF) protocol is very useful due to its outstanding rate performance.
However, the lack of good structured codebooks so far hinders practical
applications of DDF for MARC. In this work, two classes of structured MARC
codes are proposed: 1) one-to-one relay-mapper aided multiuser lattice coding
(O-MLC), and 2) modulo-sum relay-mapper aided multiuser lattice coding
(MS-MLC). The former enjoys better rate performance, while the latter provides
more flexibility to tradeoff between the complexity of the relay mapper and the
rate performance. It is shown that, in order to approach the rate performance
achievable by an unstructured codebook with maximum-likelihood decoding, it is
crucial to use a new K-stage coset decoder for structured O-MLC, instead of the
one-stage decoder proposed in previous works. However, if O-MLC is decoded with
the one-stage decoder only, it can still achieve the optimal DDF
diversity-multiplexing gain tradeoff in the high signal-to-noise ratio regime.
As for MS-MLC, its rate performance can approach that of the O-MLC by
increasing the complexity of the modulo-sum relay-mapper. Finally, for
practical implementations of both O-MLC and MS-MLC, practical short length
lattice codes with linear mappers are designed, which facilitate efficient
lattice decoding. Simulation results show that the proposed coding schemes
outperform existing schemes in terms of outage probabilities in a variety of
channel settings.Comment: 32 pages, 5 figure
Tradeoff Analysis of Delay-Power-CSIT Quality of Dynamic BackPressure Algorithm for Energy Efficient OFDM Systems
In this paper, we analyze the fundamental power-delay tradeoff in
point-to-point OFDM systems under imperfect channel state information quality
and non-ideal circuit power. We consider the dynamic back- pressure (DBP)
algorithm, where the transmitter determines the rate and power control actions
based on the instantaneous channel state information (CSIT) and the queue state
information (QSI). We exploit a general fluid queue dynamics using a continuous
time dynamic equation. Using the sample-path approach and renewal theory, we
decompose the average delay in terms of multiple unfinished works along a
sample path, and derive an upper bound on the average delay under the DBP power
control, which is asymptotically accurate at small delay regime. We show that
despite imperfect CSIT quality and non-ideal circuit power, the average power
(P) of the DBP policy scales with delay (D) as P = O(Dexp(1/D)) at small delay
regime. While the impacts of CSIT quality and circuit power appears as the
coefficients of the scaling law, they may be significant in some operating
regimes.Comment: 30 page
Locating a Sound Source Using Single Microphone and Inertial Measurements
Locating a sound source in an indoor environment, e.g., a noise source, is difficult just based on human listening. While acoustic cameras with multiple microphone arrays can be used to locate the sound source, such equipment is expensive and unsuitable for many use cases. This disclosure describes techniques to identify the location of a sound source using a single built-in microphone and inertial measurement unit (IMU) sensor on a user device. Device motion and velocity data is obtained from the IMU. A baseline is established by recording sound without user movement to determine the frequency domain of sound. The user is prompted to record the sound again by moving the device in a particular direction and frequency shifts in the measured sound are detected to determine a direction of the sound source relative to the device location. The process is repeated at one or more additional locations. The intersection of the direction lines from the device locations to the noise source gives the location of the noise source
Investigation of dynamic ground effect
An experimental investigation of dynamic ground effect was conducted in the Univ. of Kansas wind tunnel using delta wings of 60, 70, 75 deg sweep; the XB-70 wing; and the F-104A wing. Both static and dynamic tests were made. Test data were compared to other test data, including dynamic flight test data of the XB-70 and F-104A. Limited flow visualization test were conducted. A significant dynamic effect was found for highly swept delta wings
Elastocapillary Levelling of Thin Viscous Films on Soft Substrates
A thin liquid film with non-zero curvature at its free surface spontaneously
flows to reach a flat configuration, a process driven by Laplace pressure
gradients and resisted by the liquid's viscosity. Inspired by recent progresses
on the dynamics of liquid droplets on soft substrates, we here study the
relaxation of a viscous film supported by an elastic foundation. Experiments
involve thin polymer films on elastomeric substrates, where the dynamics of the
liquid-air interface is monitored using atomic force microscopy. A theoretical
model that describes the coupled evolution of the solid-liquid and the
liquid-air interfaces is also provided. In this soft-levelling configuration,
Laplace pressure gradients not only drive the flow, but they also induce
elastic deformations on the substrate that affect the flow and the shape of the
liquid-air interface itself. This process represents an original example of
elastocapillarity that is not mediated by the presence of a contact line. We
discuss the impact of the elastic contribution on the levelling dynamics and
show the departure from the classical self-similarities and power laws observed
for capillary levelling on rigid substrates
Classification of Genes and Putative Biomarker Identification Using Distribution Metrics on Expression Profiles
BACKGROUND: Identification of genes with switch-like properties will facilitate discovery of regulatory mechanisms that underlie these properties, and will provide knowledge for the appropriate application of Boolean networks in gene regulatory models. As switch-like behavior is likely associated with tissue-specific expression, these gene products are expected to be plausible candidates as tissue-specific biomarkers. METHODOLOGY/PRINCIPAL FINDINGS: In a systematic classification of genes and search for biomarkers, gene expression profiles (GEPs) of more than 16,000 genes from 2,145 mouse array samples were analyzed. Four distribution metrics (mean, standard deviation, kurtosis and skewness) were used to classify GEPs into four categories: predominantly-off, predominantly-on, graded (rheostatic), and switch-like genes. The arrays under study were also grouped and examined by tissue type. For example, arrays were categorized as 'brain group' and 'non-brain group'; the Kolmogorov-Smirnov distance and Pearson correlation coefficient were then used to compare GEPs between brain and non-brain for each gene. We were thus able to identify tissue-specific biomarker candidate genes. CONCLUSIONS/SIGNIFICANCE: The methodology employed here may be used to facilitate disease-specific biomarker discovery
Light Flicker Detector
Light flickering can be detrimental to humans even if imperceptible. Headaches, migraine, and/or eye strain can result from exposure to flickering light. This disclosure describes techniques to detect and monitor light flicker. An ambient light sensor detects flickering in environmental lighting. Environmental light intensity is measured over a wide spectrum covering the human perceptive range. The peak flicker frequencies (and their magnitudes), flicker percentages, etc. are determined. If a substantial amount of flicker (greater than a threshold) is detected, an alert is provided. Furthermore, auto-generated instructions enable users to determine the light source that is the source of flickering
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