241 research outputs found
Fast Decoder for Overloaded Uniquely Decodable Synchronous Optical CDMA
In this paper, we propose a fast decoder algorithm for uniquely decodable
(errorless) code sets for overloaded synchronous optical code-division
multiple-access (O-CDMA) systems. The proposed decoder is designed in a such a
way that the users can uniquely recover the information bits with a very simple
decoder, which uses only a few comparisons. Compared to maximum-likelihood (ML)
decoder, which has a high computational complexity for even moderate code
lengths, the proposed decoder has much lower computational complexity.
Simulation results in terms of bit error rate (BER) demonstrate that the
performance of the proposed decoder for a given BER requires only 1-2 dB higher
signal-to-noise ratio (SNR) than the ML decoder.Comment: arXiv admin note: substantial text overlap with arXiv:1806.0395
On generalized LDPC codes for ultra reliable communication
Ultra reliable low latency communication (URLLC) is an important feature in
future mobile communication systems, as they will require high data rates, large
system capacity and massive device connectivity [11]. To meet such stringent
requirements, many error-correction codes (ECC)s are being investigated; turbo
codes, low density parity check (LDPC) codes, polar codes and convolutional codes
[70, 92, 38], among many others. In this work, we present generalized low density
parity check (GLDPC) codes as a promising candidate for URLLC.
Our proposal is based on a novel class of GLDPC code ensembles, for which
new analysis tools are proposed. We analyze the trade-o_ between coding rate and
asymptotic performance of a class of GLDPC codes constructed by including a
certain fraction of generalized constraint (GC) nodes in the graph. To incorporate
both bounded distance (BD) and maximum likelihood (ML) decoding at GC nodes
into our analysis without resorting to multi-edge type of degree distribution (DD)s,
we propose the probabilistic peeling decoding (P-PD) algorithm, which models the
decoding step at every GC node as an instance of a Bernoulli random variable with
a successful decoding probability that depends on both the GC block code as well
as its decoding algorithm. The P-PD asymptotic performance over the BEC can
be efficiently predicted using standard techniques for LDPC codes such as Density
evolution (DE) or the differential equation method. We demonstrate that the
simulated P-PD performance accurately predicts the actual performance of the
GLPDC code under ML decoding at GC nodes. We illustrate our analysis for
GLDPC code ensembles with regular and irregular DDs.
This design methodology is applied to construct practical codes for URLLC.
To this end, we incorporate to our analysis the use of quasi-cyclic (QC) structures,
to mitigate the code error floor and facilitate the code very large scale integration
(VLSI) implementation. Furthermore, for the additive white Gaussian noise
(AWGN) channel, we analyze the complexity and performance of the message
passing decoder with various update rules (including standard full-precision sum product and min-sum algorithms) and quantization schemes. The block error rate
(BLER) performance of the proposed GLDPC codes, combined with a complementary
outer code, is shown to outperform a variety of state-of-the-art codes, for
URLLC, including LDPC codes, polar codes, turbo codes and convolutional codes,
at similar complexity rates.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Juan José Murillo Fuentes.- Secretario: Matilde Pilar Sánchez Fernández.- Vocal: Javier Valls Coquilla
Layer-Aware Forward Error Correction for Mobile Broadcast of Layered Media
The bitstream structure of layered media formats such as scalable video coding (SVC) or multiview video coding (MVC) opens up new opportunities for their distribution in Mobile TV services. Features like graceful degradation or the support of the 3-D experience in a backwards-compatible way are enabled. The reason is that parts of the media stream are more important than others with each part itself providing a useful media representation. Typically, the decoding of some parts of the bitstream is only possible, if the corresponding more important parts are correctly received. Hence, unequal error protection (UEP) can be applied protecting important parts of the bitstream more strongly than others. Mobile broadcast systems typically apply forward error correction (FEC) on upper layers to cope with transmission errors, which the physical layer FEC cannot correct. Today's FEC solutions are optimized to transmit single layer video. The exploitation of the dependencies in layered media codecs for UEP using FEC is the subject of this paper. The presented scheme, which is called layer-aware FEC (LA-FEC), incorporates the dependencies of the layered video codec into the FEC code construction. A combinatorial analysis is derived to show the potential theoretical gain in terms of FEC decoding probability and video quality. Furthermore, the implementation of LA-FEC as an extension of the Raptor FEC and the related signaling are described. The performance of layer-aware Raptor code with SVC is shown by experimental results in a DVB-H environment showing significant improvements achieved by LA-FEC. © 2011 IEEE.Hellge, C.; Gómez Barquero, D.; Schierl, T.; Wiegand, T. (2011). Layer-Aware Forward Error Correction for Mobile Broadcast of Layered Media. IEEE Transactions on Multimedia. 13(3):551-562. doi:10.1109/TMM.2011.2129499S55156213
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