53,410 research outputs found
Systematic polar coding
Cataloged from PDF version of article.Polar codes were originally introduced as a class
of non-systematic linear block codes. This paper gives encoding
and decoding methods for systematic polar coding that preserve
the low-complexity nature of non-systematic polar coding while
guaranteeing the same frame error rate. Simulation results are
given to show that systematic polar coding offers significant
advantages in terms of bit error rate performance
Hybrid Polar Encoding with Applications in Non-Coherent Channels
In coding theory, an error-correcting code can be encoded either
systematically or non-systematically. In a systematic encode, the input data is
embedded in the encoded output. Conversely, in a non-systematic code, the
output does not contain the input symbols. In this paper, we propose a hybrid
encoding scheme for polar codes, in which some data bits are systematically
encoded while the rest are non-systematically encoded. Based on the proposed
scheme, we design a joint channel estimation and data decoding scheme. We use
the systematic bits in the hybrid encoding scheme as pilots for channel
estimation. To mitigate the code rate loss caused by the pilots and to provide
additional error detecting capability, we propose a dynamic pilot design by
building connections between the systematic bits and non-systematic bits.
Simulation results show that the performance of the proposed scheme approaches
that of the traditional non-systematic polar coding scheme with perfect channel
state information (CSI) with the increase of SNR.Comment: 12 pages, 5 figure
Eye position modulates retinotopic responses in early visual areas: a bias for the straight-ahead direction
Even though the eyes constantly change position, the location of a stimulus can be accurately represented by a population of neurons with retinotopic receptive fields modulated by eye position gain fields. Recent electrophysiological studies, however, indicate that eye position gain fields may serve an additional function since they have a non-uniform spatial distribution that increases the neural response to stimuli in the straight-ahead direction. We used functional magnetic resonance imaging and a wide-field stimulus display to determine whether gaze modulations in early human visual cortex enhance the blood-oxygenation-level dependent (BOLD) response to stimuli that are straight-ahead. Subjects viewed rotating polar angle wedge stimuli centered straight-ahead or vertically displaced by ±20° eccentricity. Gaze position did not affect the topography of polar phase-angle maps, confirming that coding was retinotopic, but did affect the amplitude of the BOLD response, consistent with a gain field. In agreement with recent electrophysiological studies, BOLD responses in V1 and V2 to a wedge stimulus at a fixed retinal locus decreased when the wedge location in head-centered coordinates was farther from the straight-ahead direction. We conclude that stimulus-evoked BOLD signals are modulated by a systematic, non-uniform distribution of eye-position gain fields
Polar Coding for the Large Hadron Collider: Challenges in Code Concatenation
In this work, we present a concatenated repetition-polar coding scheme that
is aimed at applications requiring highly unbalanced unequal bit-error
protection, such as the Beam Interlock System of the Large Hadron Collider at
CERN. Even though this concatenation scheme is simple, it reveals significant
challenges that may be encountered when designing a concatenated scheme that
uses a polar code as an inner code, such as error correlation and unusual
decision log-likelihood ratio distributions. We explain and analyze these
challenges and we propose two ways to overcome them.Comment: Presented at the 51st Asilomar Conference on Signals, Systems, and
Computers, November 201
Concatenated Polar Codes
Polar codes have attracted much recent attention as the first codes with low
computational complexity that provably achieve optimal rate-regions for a large
class of information-theoretic problems. One significant drawback, however, is
that for current constructions the probability of error decays
sub-exponentially in the block-length (more detailed designs improve the
probability of error at the cost of significantly increased computational
complexity \cite{KorUS09}). In this work we show how the the classical idea of
code concatenation -- using "short" polar codes as inner codes and a
"high-rate" Reed-Solomon code as the outer code -- results in substantially
improved performance. In particular, code concatenation with a careful choice
of parameters boosts the rate of decay of the probability of error to almost
exponential in the block-length with essentially no loss in computational
complexity. We demonstrate such performance improvements for three sets of
information-theoretic problems -- a classical point-to-point channel coding
problem, a class of multiple-input multiple output channel coding problems, and
some network source coding problems
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