336 research outputs found
Rate-Flexible Fast Polar Decoders
Polar codes have gained extensive attention during the past few years and
recently they have been selected for the next generation of wireless
communications standards (5G). Successive-cancellation-based (SC-based)
decoders, such as SC list (SCL) and SC flip (SCF), provide a reasonable error
performance for polar codes at the cost of low decoding speed. Fast SC-based
decoders, such as Fast-SSC, Fast-SSCL, and Fast-SSCF, identify the special
constituent codes in a polar code graph off-line, produce a list of operations,
store the list in memory, and feed the list to the decoder to decode the
constituent codes in order efficiently, thus increasing the decoding speed.
However, the list of operations is dependent on the code rate and as the rate
changes, a new list is produced, making fast SC-based decoders not
rate-flexible. In this paper, we propose a completely rate-flexible fast
SC-based decoder by creating the list of operations directly in hardware, with
low implementation complexity. We further propose a hardware architecture
implementing the proposed method and show that the area occupation of the
rate-flexible fast SC-based decoder in this paper is only of the total
area of the memory-based base-line decoder when 5G code rates are supported
Re-proving Channel Polarization Theorems: An Extremality and Robustness Analysis
The general subject considered in this thesis is a recently discovered coding
technique, polar coding, which is used to construct a class of error correction
codes with unique properties. In his ground-breaking work, Ar{\i}kan proved
that this class of codes, called polar codes, achieve the symmetric capacity
--- the mutual information evaluated at the uniform input distribution ---of
any stationary binary discrete memoryless channel with low complexity encoders
and decoders requiring in the order of operations in the
block-length . This discovery settled the long standing open problem left by
Shannon of finding low complexity codes achieving the channel capacity.
Polar coding settled an open problem in information theory, yet opened plenty
of challenging problems that need to be addressed. A significant part of this
thesis is dedicated to advancing the knowledge about this technique in two
directions. The first one provides a better understanding of polar coding by
generalizing some of the existing results and discussing their implications,
and the second one studies the robustness of the theory over communication
models introducing various forms of uncertainty or variations into the
probabilistic model of the channel.Comment: Preview of my PhD Thesis, EPFL, Lausanne, 2014. For the full version,
see http://people.epfl.ch/mine.alsan/publication
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