25,401 research outputs found
Turbo Decoding and Detection for Wireless Applications
A historical perspective of turbo coding and turbo transceivers inspired by the generic turbo principles is provided, as it evolved from Shannon’s visionary predictions. More specifically, we commence by discussing the turbo principles, which have been shown to be capable of performing close to Shannon’s capacity limit. We continue by reviewing the classic maximum a posteriori probability decoder. These discussions are followed by studying the effect of a range of system parameters in a systematic fashion, in order to gauge their performance ramifications. In the second part of this treatise, we focus our attention on the family of iterative receivers designed for wireless communication systems, which were partly inspired by the invention of turbo codes. More specifically, the family of iteratively detected joint coding and modulation schemes, turbo equalization, concatenated spacetime and channel coding arrangements, as well as multi-user detection and three-stage multimedia systems are highlighted
A Belief Propagation Based Framework for Soft Multiple-Symbol Differential Detection
Soft noncoherent detection, which relies on calculating the \textit{a
posteriori} probabilities (APPs) of the bits transmitted with no channel
estimation, is imperative for achieving excellent detection performance in
high-dimensional wireless communications. In this paper, a high-performance
belief propagation (BP)-based soft multiple-symbol differential detection
(MSDD) framework, dubbed BP-MSDD, is proposed with its illustrative application
in differential space-time block-code (DSTBC)-aided ultra-wideband impulse
radio (UWB-IR) systems. Firstly, we revisit the signal sampling with the aid of
a trellis structure and decompose the trellis into multiple subtrellises.
Furthermore, we derive an APP calculation algorithm, in which the
forward-and-backward message passing mechanism of BP operates on the
subtrellises. The proposed BP-MSDD is capable of significantly outperforming
the conventional hard-decision MSDDs. However, the computational complexity of
the BP-MSDD increases exponentially with the number of MSDD trellis states. To
circumvent this excessive complexity for practical implementations, we
reformulate the BP-MSDD, and additionally propose a Viterbi algorithm
(VA)-based hard-decision MSDD (VA-HMSDD) and a VA-based soft-decision MSDD
(VA-SMSDD). Moreover, both the proposed BP-MSDD and VA-SMSDD can be exploited
in conjunction with soft channel decoding to obtain powerful iterative
detection and decoding based receivers. Simulation results demonstrate the
effectiveness of the proposed algorithms in DSTBC-aided UWB-IR systems.Comment: 14 pages, 12 figures, 3 tables, accepted to appear on IEEE
Transactions on Wireless Communications, Aug. 201
Gaussian Message Passing for Overloaded Massive MIMO-NOMA
This paper considers a low-complexity Gaussian Message Passing (GMP) scheme
for a coded massive Multiple-Input Multiple-Output (MIMO) systems with
Non-Orthogonal Multiple Access (massive MIMO-NOMA), in which a base station
with antennas serves sources simultaneously in the same frequency.
Both and are large numbers, and we consider the overloaded cases
with . The GMP for MIMO-NOMA is a message passing algorithm operating
on a fully-connected loopy factor graph, which is well understood to fail to
converge due to the correlation problem. In this paper, we utilize the
large-scale property of the system to simplify the convergence analysis of the
GMP under the overloaded condition. First, we prove that the \emph{variances}
of the GMP definitely converge to the mean square error (MSE) of Linear Minimum
Mean Square Error (LMMSE) multi-user detection. Secondly, the \emph{means} of
the traditional GMP will fail to converge when . Therefore, we propose and derive a new
convergent GMP called scale-and-add GMP (SA-GMP), which always converges to the
LMMSE multi-user detection performance for any , and show that it
has a faster convergence speed than the traditional GMP with the same
complexity. Finally, numerical results are provided to verify the validity and
accuracy of the theoretical results presented.Comment: Accepted by IEEE TWC, 16 pages, 11 figure
Estimating European volatile organic compound emissions using satellite observations of formaldehyde from the Ozone Monitoring Instrument
Emission of non-methane Volatile Organic Compounds (VOCs) to the atmosphere
stems from biogenic and human activities, and their estimation is difficult
because of the many and not fully understood processes involved. In order to
narrow down the uncertainty related to VOC emissions, which negatively
reflects on our ability to simulate the atmospheric composition, we exploit
satellite observations of formaldehyde (HCHO), an ubiquitous oxidation
product of most VOCs, focusing on Europe. HCHO column observations from the
Ozone Monitoring Instrument (OMI) reveal a marked seasonal cycle with a
summer maximum and winter minimum. In summer, the oxidation of methane and
other long-lived VOCs supply a slowly varying background HCHO column, while
HCHO variability is dominated by most reactive VOC, primarily biogenic
isoprene followed in importance by biogenic terpenes and anthropogenic VOCs.
The chemistry-transport model CHIMERE qualitatively reproduces the temporal
and spatial features of the observed HCHO column, but display regional
biases which are attributed mainly to incorrect biogenic VOC emissions,
calculated with the Model of Emissions of Gases and Aerosol from Nature
(MEGAN) algorithm. These "bottom-up" or a-priori emissions are corrected
through a
Bayesian inversion of the OMI HCHO observations. Resulting "top-down" or
a-posteriori isoprene emissions are lower than "bottom-up" by 40% over
the Balkans
and by 20% over Southern Germany, and higher by 20% over Iberian
Peninsula, Greece and Italy.
We conclude that OMI
satellite observations of HCHO can provide a quantitative "top-down"
constraint on the European "bottom-up" VOC inventories
Reduced-complexity non-coherent soft-decision-aided DAPSK dispensing with channel estimation
Differential Amplitude Phase Shift Keying (DAPSK), which is also known as star-shaped QAM has implementational advantages not only due to dispensing with channel estimation, but also as a benefit of its low signal detection complexity. It is widely recognized that separately detecting the amplitude and the phase of a received DAPSK symbol exhibits a lower complexity than jointly detecting the two terms. However, since the amplitude and the phase of a DAPSK symbol are affected by the correlated magnitude fading and phase-rotations, detecting the two terms completely independently results in a performance loss, which is especially significant for soft-decision-aided DAPSK detectors relying on multiple receive antennas. Therefore, in this contribution, we propose a new soft-decision-aided DAPSK detection method, which achieves the optimum DAPSK detection capability at a substantially reduced detection complexity. More specifically, we link each a priori soft input bit to a specific part of the channel's output, so that only a reduced subset of the DAPSK constellation points has to be evaluated by the soft DAPSK detector. Our simulation results demonstrate that the proposed soft DAPSK detector exhibits a lower detection complexity than that of independently detecting the amplitude and the phase, while the optimal performance of DAPSK detection is retained
Coarse-to-Fine Adaptive People Detection for Video Sequences by Maximizing Mutual Information
Applying people detectors to unseen data is challenging since patterns distributions, such
as viewpoints, motion, poses, backgrounds, occlusions and people sizes, may significantly differ
from the ones of the training dataset. In this paper, we propose a coarse-to-fine framework to adapt
frame by frame people detectors during runtime classification, without requiring any additional
manually labeled ground truth apart from the offline training of the detection model. Such adaptation
make use of multiple detectors mutual information, i.e., similarities and dissimilarities of detectors
estimated and agreed by pair-wise correlating their outputs. Globally, the proposed adaptation
discriminates between relevant instants in a video sequence, i.e., identifies the representative frames
for an adaptation of the system. Locally, the proposed adaptation identifies the best configuration
(i.e., detection threshold) of each detector under analysis, maximizing the mutual information to
obtain the detection threshold of each detector. The proposed coarse-to-fine approach does not
require training the detectors for each new scenario and uses standard people detector outputs, i.e.,
bounding boxes. The experimental results demonstrate that the proposed approach outperforms
state-of-the-art detectors whose optimal threshold configurations are previously determined and
fixed from offline training dataThis work has been partially supported by the Spanish government under the project TEC2014-53176-R
(HAVideo
Terrain analysis using radar shape-from-shading
This paper develops a maximum a posteriori (MAP) probability estimation framework for shape-from-shading (SFS) from synthetic aperture radar (SAR) images. The aim is to use this method to reconstruct surface topography from a single radar image of relatively complex terrain. Our MAP framework makes explicit how the recovery of local surface orientation depends on the whereabouts of terrain edge features and the available radar reflectance information. To apply the resulting process to real world radar data, we require probabilistic models for the appearance of terrain features and the relationship between the orientation of surface normals and the radar reflectance. We show that the SAR data can be modeled using a Rayleigh-Bessel distribution and use this distribution to develop a maximum likelihood algorithm for detecting and labeling terrain edge features. Moreover, we show how robust statistics can be used to estimate the characteristic parameters of this distribution. We also develop an empirical model for the SAR reflectance function. Using the reflectance model, we perform Lambertian correction so that a conventional SFS algorithm can be applied to the radar data. The initial surface normal direction is constrained to point in the direction of the nearest ridge or ravine feature. Each surface normal must fall within a conical envelope whose axis is in the direction of the radar illuminant. The extent of the envelope depends on the corrected radar reflectance and the variance of the radar signal statistics. We explore various ways of smoothing the field of surface normals using robust statistics. Finally, we show how to reconstruct the terrain surface from the smoothed field of surface normal vectors. The proposed algorithm is applied to various SAR data sets containing relatively complex terrain structure
Point Process Algorithm: A New Bayesian Approach for Planet Signal Extraction with the Terrestrial Planet Finder
The capability of the Terrestrial Planet Finder Interferometer (TPF-I) for
planetary signal extraction, including both detection and spectral
characterization, can be optimized by taking proper account of instrumental
characteristics and astrophysical prior information. We have developed the
Point Process Algorithm (PPA), a Bayesian technique for extracting planetary
signals using the sine-chopped outputs of a dual nulling interferometer. It is
so-called because it represents the system being observed as a set of points in
a suitably-defined state space, thus providing a natural way of incorporating
our prior knowledge of the compact nature of the targets of interest. It can
also incorporate the spatial covariance of the exozodi as prior information
which could help mitigate against false detections. Data at multiple
wavelengths are used simultaneously, taking into account possible spectral
variations of the planetary signals. Input parameters include the RMS
measurement noise and the a priori probability of the presence of a planet. The
output can be represented as an image of the intensity distribution on the sky,
optimized for the detection of point sources. Previous approaches by others to
the problem of planet detection for TPF-I have relied on the potentially
non-robust identification of peaks in a "dirty" image, usually a correlation
map. Tests with synthetic data suggest that the PPA provides greater
sensitivity to faint sources than does the standard approach (correlation map +
CLEAN), and will be a useful tool for optimizing the design of TPF-I.Comment: 17 pages, 6 figures. AJ in press (scheduled for Nov 2006
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