3,594 research outputs found
Refined Reliability Combining for Binary Message Passing Decoding of Product Codes
We propose a novel soft-aided iterative decoding algorithm for product codes
(PCs). The proposed algorithm, named iterative bounded distance decoding with
combined reliability (iBDD-CR), enhances the conventional iterative bounded
distance decoding (iBDD) of PCs by exploiting some level of soft information.
In particular, iBDD-CR can be seen as a modification of iBDD where the hard
decisions of the row and column decoders are made based on a reliability
estimate of the BDD outputs. The reliability estimates are derived using
extrinsic message passing for generalized low-density-parity check (GLDPC)
ensembles, which encompass PCs. We perform a density evolution analysis of
iBDD-CR for transmission over the additive white Gaussian noise channel for the
GLDPC ensemble. We consider both binary transmission and bit-interleaved coded
modulation with quadrature amplitude modulation.We show that iBDD-CR achieves
performance gains up to dB compared to iBDD with the same internal
decoder data flow. This makes the algorithm an attractive solution for very
high-throughput applications such as fiber-optic communications
Reliability Ratio Based Weighted Bit-Flipping Decoding for LDPC Codes
In this contribution, a novel reliability-ratio based weighted bit-flipping(RRWBF) algorithm is proposed for decoding Low Density Parity Check (LDPC) codes. The RRWBF algorithm proposed is benchmarked against the conventional weighted bit-flipping (WBF) algorithm [1] and the improved weighted bit-flipping (IWBF) algorithm [2]. More than 1 and 2 dB coding gain was achieved at an BER of 10-5 while invoking the RRWBF algorithm in comparison to the two benchmarking schemes, when communicating over an AWGN and an uncorrelated Rayleigh channel, respectively. Furthermore, the decoding complexity of the proposed RRWBF algorithm is maintained at the same level as that of the conventional WBF algorithm
Iterative Soft Input Soft Output Decoding of Reed-Solomon Codes by Adapting the Parity Check Matrix
An iterative algorithm is presented for soft-input-soft-output (SISO)
decoding of Reed-Solomon (RS) codes. The proposed iterative algorithm uses the
sum product algorithm (SPA) in conjunction with a binary parity check matrix of
the RS code. The novelty is in reducing a submatrix of the binary parity check
matrix that corresponds to less reliable bits to a sparse nature before the SPA
is applied at each iteration. The proposed algorithm can be geometrically
interpreted as a two-stage gradient descent with an adaptive potential
function. This adaptive procedure is crucial to the convergence behavior of the
gradient descent algorithm and, therefore, significantly improves the
performance. Simulation results show that the proposed decoding algorithm and
its variations provide significant gain over hard decision decoding (HDD) and
compare favorably with other popular soft decision decoding methods.Comment: 10 pages, 10 figures, final version accepted by IEEE Trans. on
Information Theor
Practical LDPC coded modulation schemes for the fading broadcast channel with confidential messages
The broadcast channel with confidential messages is a well studied scenario
from the theoretical standpoint, but there is still lack of practical schemes
able to achieve some fixed level of reliability and security over such a
channel. In this paper, we consider a quasi-static fading channel in which both
public and private messages must be sent from the transmitter to the receivers,
and we aim at designing suitable coding and modulation schemes to achieve such
a target. For this purpose, we adopt the error rate as a metric, by considering
that reliability (security) is achieved when a sufficiently low (high) error
rate is experienced at the receiving side. We show that some conditions exist
on the system feasibility, and that some outage probability must be tolerated
to cope with the fading nature of the channel. The proposed solution exploits
low-density parity-check codes with unequal error protection, which are able to
guarantee two different levels of protection against noise for the public and
the private information, in conjunction with different modulation schemes for
the public and the private message bits.Comment: 6 pages, 4 figures, to be presented at IEEE ICC'14 - Workshop on
Wireless Physical Layer Securit
Protograph-Based LDPC Code Design for Shaped Bit-Metric Decoding
A protograph-based low-density parity-check (LDPC) code design technique for
bandwidth-efficient coded modulation is presented. The approach jointly
optimizes the LDPC code node degrees and the mapping of the coded bits to the
bit-interleaved coded modulation (BICM) bit-channels. For BICM with uniform
input and for BICM with probabilistic shaping, binary-input symmetric-output
surrogate channels for the code design are used. The constructed codes for
uniform inputs perform as good as the multi-edge type codes of Zhang and
Kschischang (2013). For 8-ASK and 64-ASK with probabilistic shaping, codes of
rates 2/3 and 5/6 with blocklength 64800 are designed, which operate within
0.63dB and 0.69dB of continuous AWGN capacity for a target frame error rate of
1e-3 at spectral efficiencies of 1.38 and 4.25 bits/channel use, respectively.Comment: 9 pages, 10 figures. arXiv admin note: substantial text overlap with
arXiv:1501.0559
Efficient LLR Calculation for Non-Binary Modulations over Fading Channels
Log-likelihood ratio (LLR) computation for non-binary modulations over fading
channels is complicated. A measure of LLR accuracy on asymmetric binary
channels is introduced to facilitate good LLR approximations for non-binary
modulations. Considering piecewise linear LLR approximations, we prove
convexity of optimizing the coefficients according to this measure. For the
optimized approximate LLRs, we report negligible performance losses compared to
true LLRs.Comment: Submitted to IEEE Transactions on Communication
Iterative decoding for MIMO channels via modified sphere decoding
In recent years, soft iterative decoding techniques have been shown to greatly improve the bit error rate performance of various communication systems. For multiantenna systems employing space-time codes, however, it is not clear what is the best way to obtain the soft information required of the iterative scheme with low complexity. In this paper, we propose a modification of the Fincke-Pohst (sphere decoding) algorithm to estimate the maximum a posteriori probability of the received symbol sequence. The new algorithm solves a nonlinear integer least squares problem and, over a wide range of rates and signal-to-noise ratios, has polynomial-time complexity. Performance of the algorithm, combined with convolutional, turbo, and low-density parity check codes, is demonstrated on several multiantenna channels. The results for systems that employ space-time modulation schemes seem to indicate that the best performing schemes are those that support the highest mutual information between the transmitted and received signals, rather than the best diversity gain
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