829 research outputs found
Partitioned List Decoding of Polar Codes: Analysis and Improvement of Finite Length Performance
Polar codes represent one of the major recent breakthroughs in coding theory
and, because of their attractive features, they have been selected for the
incoming 5G standard. As such, a lot of attention has been devoted to the
development of decoding algorithms with good error performance and efficient
hardware implementation. One of the leading candidates in this regard is
represented by successive-cancellation list (SCL) decoding. However, its
hardware implementation requires a large amount of memory. Recently, a
partitioned SCL (PSCL) decoder has been proposed to significantly reduce the
memory consumption. In this paper, we examine the paradigm of PSCL decoding
from both theoretical and practical standpoints: (i) by changing the
construction of the code, we are able to improve the performance at no
additional computational, latency or memory cost, (ii) we present an optimal
scheme to allocate cyclic redundancy checks (CRCs), and (iii) we provide an
upper bound on the list size that allows MAP performance.Comment: 2017 IEEE Global Communications Conference (GLOBECOM
On the Decoding of Polar Codes on Permuted Factor Graphs
Polar codes are a channel coding scheme for the next generation of wireless
communications standard (5G). The belief propagation (BP) decoder allows for
parallel decoding of polar codes, making it suitable for high throughput
applications. However, the error-correction performance of polar codes under BP
decoding is far from the requirements of 5G. It has been shown that the
error-correction performance of BP can be improved if the decoding is performed
on multiple permuted factor graphs of polar codes. However, a different BP
decoding scheduling is required for each factor graph permutation which results
in the design of a different decoder for each permutation. Moreover, the
selection of the different factor graph permutations is at random, which
prevents the decoder to achieve a desirable error-correction performance with a
small number of permutations. In this paper, we first show that the
permutations on the factor graph can be mapped into suitable permutations on
the codeword positions. As a result, we can make use of a single decoder for
all the permutations. In addition, we introduce a method to construct a set of
predetermined permutations which can provide the correct codeword if the
decoding fails on the original permutation. We show that for the 5G polar code
of length , the error-correction performance of the proposed decoder is
more than dB better than that of the BP decoder with the same number of
random permutations at the frame error rate of
Polar Codes with Dynamic Frozen Symbols and Their Decoding by Directed Search
A novel construction of polar codes with dynamic frozen symbols is proposed.
The proposed codes are subcodes of extended BCH codes, which ensure
sufficiently high minimum distance. Furthermore, a decoding algorithm is
proposed, which employs estimates of the not-yet-processed bit channel error
probabilities to perform directed search in code tree, reducing thus the total
number of iterations.Comment: Accepted to ITW201
Throughput-based Design for Polar Coded-Modulation
Typically, forward error correction (FEC) codes are designed based on the
minimization of the error rate for a given code rate. However, for applications
that incorporate hybrid automatic repeat request (HARQ) protocol and adaptive
modulation and coding, the throughput is a more important performance metric
than the error rate. Polar codes, a new class of FEC codes with simple rate
matching, can be optimized efficiently for maximization of the throughput. In
this paper, we aim to design HARQ schemes using multilevel polar
coded-modulation (MLPCM). Thus, we first develop a method to determine a
set-partitioning based bit-to-symbol mapping for high order QAM constellations.
We simplify the LLR estimation of set-partitioned QAM constellations for a
multistage decoder, and we introduce a set of algorithms to design
throughput-maximizing MLPCM for the successive cancellation decoding (SCD).
These codes are specifically useful for non-combining (NC) and Chase-combining
(CC) HARQ protocols. Furthermore, since optimized codes for SCD are not optimal
for SC list decoders (SCLD), we propose a rate matching algorithm to find the
best rate for SCLD while using the polar codes optimized for SCD. The resulting
codes provide throughput close to the capacity with low decoding complexity
when used with NC or CC HARQ
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