1,484 research outputs found
Binary Message Passing Decoding of Product-like Codes
We propose a novel binary message passing decoding algorithm for product-like
codes based on bounded distance decoding (BDD) of the component codes. The
algorithm, dubbed iterative BDD with scaled reliability (iBDD-SR), exploits the
channel reliabilities and is therefore soft in nature. However, the messages
exchanged by the component decoders are binary (hard) messages, which
significantly reduces the decoder data flow. The exchanged binary messages are
obtained by combining the channel reliability with the BDD decoder output
reliabilities, properly conveyed by a scaling factor applied to the BDD
decisions. We perform a density evolution analysis for generalized low-density
parity-check (GLDPC) code ensembles and spatially coupled GLDPC code ensembles,
from which the scaling factors of the iBDD-SR for product and staircase codes,
respectively, can be obtained. For the white additive Gaussian noise channel,
we show performance gains up to dB and dB for product and
staircase codes compared to conventional iterative BDD (iBDD) with the same
decoder data flow. Furthermore, we show that iBDD-SR approaches the performance
of ideal iBDD that prevents miscorrections.Comment: Accepted for publication in the IEEE Transactions on Communication
Spread spectrum-based video watermarking algorithms for copyright protection
Merged with duplicate record 10026.1/2263 on 14.03.2017 by CS (TIS)Digital technologies know an unprecedented expansion in the last years. The consumer can
now benefit from hardware and software which was considered state-of-the-art several years
ago. The advantages offered by the digital technologies are major but the same digital
technology opens the door for unlimited piracy. Copying an analogue VCR tape was certainly
possible and relatively easy, in spite of various forms of protection, but due to the analogue
environment, the subsequent copies had an inherent loss in quality. This was a natural way of
limiting the multiple copying of a video material. With digital technology, this barrier
disappears, being possible to make as many copies as desired, without any loss in quality
whatsoever. Digital watermarking is one of the best available tools for fighting this threat.
The aim of the present work was to develop a digital watermarking system compliant with the
recommendations drawn by the EBU, for video broadcast monitoring. Since the watermark
can be inserted in either spatial domain or transform domain, this aspect was investigated and
led to the conclusion that wavelet transform is one of the best solutions available. Since
watermarking is not an easy task, especially considering the robustness under various attacks
several techniques were employed in order to increase the capacity/robustness of the system:
spread-spectrum and modulation techniques to cast the watermark, powerful error correction
to protect the mark, human visual models to insert a robust mark and to ensure its invisibility.
The combination of these methods led to a major improvement, but yet the system wasn't
robust to several important geometrical attacks. In order to achieve this last milestone, the
system uses two distinct watermarks: a spatial domain reference watermark and the main
watermark embedded in the wavelet domain. By using this reference watermark and techniques
specific to image registration, the system is able to determine the parameters of the attack and
revert it. Once the attack was reverted, the main watermark is recovered. The final result is a
high capacity, blind DWr-based video watermarking system, robust to a wide range of attacks.BBC Research & Developmen
On the Convergence Speed of Turbo Demodulation with Turbo Decoding
Iterative processing is widely adopted nowadays in modern wireless receivers
for advanced channel codes like turbo and LDPC codes. Extension of this
principle with an additional iterative feedback loop to the demapping function
has proven to provide substantial error performance gain. However, the adoption
of iterative demodulation with turbo decoding is constrained by the additional
implied implementation complexity, heavily impacting latency and power
consumption. In this paper, we analyze the convergence speed of these combined
two iterative processes in order to determine the exact required number of
iterations at each level. Extrinsic information transfer (EXIT) charts are used
for a thorough analysis at different modulation orders and code rates. An
original iteration scheduling is proposed reducing two demapping iterations
with reasonable performance loss of less than 0.15 dB. Analyzing and
normalizing the computational and memory access complexity, which directly
impact latency and power consumption, demonstrates the considerable gains of
the proposed scheduling and the promising contributions of the proposed
analysis.Comment: Submitted to IEEE Transactions on Signal Processing on April 27, 201
Low Complexity Belief Propagation Polar Code Decoders
Since its invention, polar code has received a lot of attention because of
its capacity-achieving performance and low encoding and decoding complexity.
Successive cancellation decoding (SCD) and belief propagation decoding (BPD)
are two of the most popular approaches for decoding polar codes. SCD is able to
achieve good error-correcting performance and is less computationally expensive
as compared to BPD. However SCDs suffer from long latency and low throughput
due to the serial nature of the successive cancellation algorithm. BPD is
parallel in nature and hence is more attractive for high throughput
applications. However since it is iterative in nature, the required latency and
energy dissipation increases linearly with the number of iterations. In this
work, we borrow the idea of SCD and propose a novel scheme based on
sub-factor-graph freezing to reduce the average number of computations as well
as the average number of iterations required by BPD, which directly translates
into lower latency and energy dissipation. Simulation results show that the
proposed scheme has no performance degradation and achieves significant
reduction in computation complexity over the existing methods.Comment: 6 page
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