12,306 research outputs found
A survey of outlier detection methodologies
Outlier detection has been used for centuries to detect and, where appropriate, remove anomalous observations from data. Outliers arise due to mechanical faults, changes in system behaviour, fraudulent behaviour, human error, instrument error or simply through natural deviations in populations. Their detection can identify system faults and fraud before they escalate with potentially catastrophic consequences. It can identify errors and remove their contaminating effect on the data set and as such to purify the data for processing. The original outlier detection methods were arbitrary but now, principled and systematic techniques are used, drawn from the full gamut of Computer Science and Statistics. In this paper, we introduce a survey of contemporary techniques for outlier detection. We identify their respective motivations and distinguish their advantages and disadvantages in a comparative review
Generalized Spatial Modulation in Large-Scale Multiuser MIMO Systems
Generalized spatial modulation (GSM) uses transmit antenna elements but
fewer transmit radio frequency (RF) chains, . Spatial modulation (SM)
and spatial multiplexing are special cases of GSM with and
, respectively. In GSM, in addition to conveying information bits
through conventional modulation symbols (for example, QAM), the
indices of the active transmit antennas also convey information bits.
In this paper, we investigate {\em GSM for large-scale multiuser MIMO
communications on the uplink}. Our contributions in this paper include: ()
an average bit error probability (ABEP) analysis for maximum-likelihood
detection in multiuser GSM-MIMO on the uplink, where we derive an upper bound
on the ABEP, and () low-complexity algorithms for GSM-MIMO signal detection
and channel estimation at the base station receiver based on message passing.
The analytical upper bounds on the ABEP are found to be tight at moderate to
high signal-to-noise ratios (SNR). The proposed receiver algorithms are found
to scale very well in complexity while achieving near-optimal performance in
large dimensions. Simulation results show that, for the same spectral
efficiency, multiuser GSM-MIMO can outperform multiuser SM-MIMO as well as
conventional multiuser MIMO, by about 2 to 9 dB at a bit error rate of
. Such SNR gains in GSM-MIMO compared to SM-MIMO and conventional MIMO
can be attributed to the fact that, because of a larger number of spatial index
bits, GSM-MIMO can use a lower-order QAM alphabet which is more power
efficient.Comment: IEEE Trans. on Wireless Communications, accepte
On the deployment of on-chip noise sensors
The relentless technology scaling has led to significantly reduced noise margin and complicated functionalities. As such, design time techniques per se are less likely to ensure power integrity, resulting in runtime voltage emergencies. To alleviate the issue, recently several works have shed light on the possibilities of dynamic noise management systems. Most of these works rely on on-chip noise sensors to accurately capture voltage emergencies. However, they all assume that the placement of the sensors is given. It remains an open problem in the literature how to optimally place a given number of noise sensors for best voltage emergency detection. The problem of noise sensor placement is defined at first along with a novel sensing quality metric (SQM) to be maximized.
The threshold voltage for noise sensors to report emergencies serves as a critical tuning knob between the system failure rate and false alarms. The problem of minimizing the system alarm rate subject to a given system failure rate constraint is formulated. It is further shown that with the help of IDDQ measurements during testing which reveal process variation information, it is possible and efficient to compute a per-chip optimal threshold voltage threshold.
In the third chapter, a novel framework to predict the resonance frequency using existing on-chip noise sensors, based on the theory of 1-bit compressed sensing is proposed. The proposed framework can help to achieve the resonance frequency of individual chips so as to effectively avoid resonance noise at runtime --Abstract, page iii
High-Rate Space-Time Coded Large MIMO Systems: Low-Complexity Detection and Channel Estimation
In this paper, we present a low-complexity algorithm for detection in
high-rate, non-orthogonal space-time block coded (STBC) large-MIMO systems that
achieve high spectral efficiencies of the order of tens of bps/Hz. We also
present a training-based iterative detection/channel estimation scheme for such
large STBC MIMO systems. Our simulation results show that excellent bit error
rate and nearness-to-capacity performance are achieved by the proposed
multistage likelihood ascent search (M-LAS) detector in conjunction with the
proposed iterative detection/channel estimation scheme at low complexities. The
fact that we could show such good results for large STBCs like 16x16 and 32x32
STBCs from Cyclic Division Algebras (CDA) operating at spectral efficiencies in
excess of 20 bps/Hz (even after accounting for the overheads meant for pilot
based training for channel estimation and turbo coding) establishes the
effectiveness of the proposed detector and channel estimator. We decode perfect
codes of large dimensions using the proposed detector. With the feasibility of
such a low-complexity detection/channel estimation scheme, large-MIMO systems
with tens of antennas operating at several tens of bps/Hz spectral efficiencies
can become practical, enabling interesting high data rate wireless
applications.Comment: v3: Performance/complexity comparison of the proposed scheme with
other large-MIMO architectures/detectors has been added (Sec. IV-D). The
paper has been accepted for publication in IEEE Journal of Selected Topics in
Signal Processing (JSTSP): Spl. Iss. on Managing Complexity in Multiuser MIMO
Systems. v2: Section V on Channel Estimation is update
Manipulating Highly Deformable Materials Using a Visual Feedback Dictionary
The complex physical properties of highly deformable materials such as
clothes pose significant challenges fanipulation systems. We present a novel
visual feedback dictionary-based method for manipulating defoor autonomous
robotic mrmable objects towards a desired configuration. Our approach is based
on visual servoing and we use an efficient technique to extract key features
from the RGB sensor stream in the form of a histogram of deformable model
features. These histogram features serve as high-level representations of the
state of the deformable material. Next, we collect manipulation data and use a
visual feedback dictionary that maps the velocity in the high-dimensional
feature space to the velocity of the robotic end-effectors for manipulation. We
have evaluated our approach on a set of complex manipulation tasks and
human-robot manipulation tasks on different cloth pieces with varying material
characteristics.Comment: The video is available at goo.gl/mDSC4
Scherk-Schwarz orbifolds at the LHC
We examine orbifold theories of Grand Unification with Scherk-Schwarz
twisting, performing a renormalisation group analysis and applying low energy
experimental constraints. We rule out the minimal SU(5) models, and consider
simple extensions including additional fields, such as an additional scalar
field, or additional symmetries, such as or . We find
that it is very difficult to generate a large enough Higgs mass while
simultaneously passing LHC experimental search constraints.Comment: 26 pages, 12 figures; v3: Version accepted for publication; v4: Typos
correcte
The ultra high resolution XUV spectroheliograph: An attached payload for the Space Station Freedom
The principle goal of the ultra high resolution XUV spectroheliograph (UHRXS) is to improve the ability to identify and understand the fundamental physical processes that shape the structure and dynamics of the solar chromosphere and corona. The ability of the UHRXS imaging telescope and spectrographs to resolve fine scale structures over a broad wavelength (and hence temperature) range is critical to this mission. The scientific objectives and instrumental capabilities of the UHRXS investigation are reviewed before proceeding to a discussion of the expected performance of the UHRXS observatory
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