12,859 research outputs found
Blind Detection of Polar Codes
Polar codes were recently chosen to protect the control channel information
in the next-generation mobile communication standard (5G) defined by the 3GPP.
As a result, receivers will have to implement blind detection of polar coded
frames in order to keep complexity, latency, and power consumption tractable.
As a newly proposed class of block codes, the problem of polar-code blind
detection has received very little attention. In this work, we propose a
low-complexity blind-detection algorithm for polar-encoded frames. We base this
algorithm on a novel detection metric with update rules that leverage the a
priori knowledge of the frozen-bit locations, exploiting the inherent
structures that these locations impose on a polar-encoded block of data. We
show that the proposed detection metric allows to clearly distinguish
polar-encoded frames from other types of data by considering the cumulative
distribution functions of the detection metric, and the receiver operating
characteristic. The presented results are tailored to the 5G standardization
effort discussions, i.e., we consider a short low-rate polar code concatenated
with a CRC.Comment: 6 pages, 8 figures, to appear at the IEEE Int. Workshop on Signal
Process. Syst. (SiPS) 201
On the Tradeoff Between Accuracy and Complexity in Blind Detection of Polar Codes
Polar codes are a recent family of error-correcting codes with a number of
desirable characteristics. Their disruptive nature is illustrated by their
rapid adoption in the -generation mobile-communication standard, where
they are used to protect control messages. In this work, we describe a
two-stage system tasked with identifying the location of control messages that
consists of a detection and selection stage followed by a decoding one. The
first stage spurs the need for polar-code detection algorithms with variable
effort to balance complexity between the two stages. We illustrate this idea of
variable effort for multiple detection algorithms aimed at the first stage. We
propose three novel blind detection methods based on belief-propagation
decoding inspired by early-stopping criteria. Then we show how their
reliability improves with the number of decoding iterations to highlight the
possible tradeoffs between accuracy and complexity. Additionally, we show
similar tradeoffs for a detection method from previous work. In a setup where
only one block encoded with the polar code of interest is present among many
other blocks, our results notably show that, depending on the complexity
budget, a variable number of undesirable blocks can be dismissed while
achieving a missed-detection rate in line with the block-error rate of a
complex decoding algorithm.Comment: 5 pages, 4 figures, fixes typo in Sect. IV-D; presented at the
International Symposium on Turbo Codes & Iterative Information Processing
(ISTC) 201
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
Fast-SSC-Flip Decoding of Polar Codes
Polar codes are widely considered as one of the most exciting recent
discoveries in channel coding. For short to moderate block lengths, their
error-correction performance under list decoding can outperform that of other
modern error-correcting codes. However, high-speed list-based decoders with
moderate complexity are challenging to implement. Successive-cancellation
(SC)-flip decoding was shown to be capable of a competitive error-correction
performance compared to that of list decoding with a small list size, at a
fraction of the complexity, but suffers from a variable execution time and a
higher worst-case latency. In this work, we show how to modify the
state-of-the-art high-speed SC decoding algorithm to incorporate the SC-flip
ideas. The algorithmic improvements are presented as well as average
execution-time results tailored to a hardware implementation. The results show
that the proposed fast-SSC-flip algorithm has a decoding speed close to an
order of magnitude better than the previous works while retaining a comparable
error-correction performance.Comment: 5 pages, 3 figures, appeared at IEEE Wireless Commun. and Netw. Conf.
(WCNC) 201
Fermi pulsar revolution
2009 has been an extraordinary year for gamma-ray pulsar astronomy and 2010
promises to be equally good. Not only have we registered an extraordinary
increase in the number of pulsars detected in gamma rays, but we have also
witnessed the birth of new sub-families: first of all, the radio-quiet gamma
pulsars and later an ever growing number of millisecond pulsars, a real
surprise. We started with a sample of 7 gamma-ray emitting neutron stars (6
radio pulsars and Geminga) and now the Fermi-LAT harvest encompasses 24
"Geminga-like" new gamma-ray pulsars, a dozen millisecond pulsars and about
thirty radio pulsars. Moreover, radio searches targeted to LAT unidentified
sources yielded 18 new radio millisecond pulsars, several of which have been
already detected also in gamma rays. Thus, currently the family of gamma-ray
emitting neutron stars seems to be evenly divided between classical radio
pulsars, millisecond pulsars and radio quiet neutron stars.Comment: High Time Resolution Astrophysics IV - The Era of Extremely Large
Telescopes-HTRA-IV Agios Nikolaos, Crete, Greece May 5-7 2010 to be published
in Po
The KATRIN Pre-Spectrometer at reduced Filter Energy
The KArlsruhe TRItium Neutrino experiment, KATRIN, will determine the mass of
the electron neutrino with a sensitivity of 0.2 eV (90% C.L.) via a measurement
of the beta-spectrum of gaseous tritium near its endpoint of E_0 =18.57 keV. An
ultra-low background of about b = 10 mHz is among the requirements to reach
this sensitivity. In the KATRIN main beam-line two spectrometers of MAC-E
filter type are used in a tandem configuration. This setup, however, produces a
Penning trap which could lead to increased background. We have performed test
measurements showing that the filter energy of the pre-spectrometer can be
reduced by several keV in order to diminish this trap. These measurements were
analyzed with the help of a complex computer simulation, modeling multiple
electron reflections both from the detector and the photoelectric electron
source used in our test setup.Comment: 22 pages, 12 figure
- …