Recerca: articles, congressos, llibres
http://hdl.handle.net/10230/5542
2018-12-08T14:08:40ZAdvanced decoding algorithms for satellite broadcasting
http://hdl.handle.net/10230/36019
Advanced decoding algorithms for satellite broadcasting
Lamarca, Meritxell; Sala, Josep; Rodríguez, Eduardo; Martínez, Alfonso
The evaluation of the union bound for theber of Reed-Solomon/Convolutional concatenated codes indicates that their performance might largely improve through the application of soft iterative decoders. This paper presents an iterative decoding algorithm for concatenated codes consisting of an outer Reed-Solomon code, a symbol interleaver and an inner convolutional code. The performance improvement for iterative and non-iterative decoders is evaluated. Existing solutions for the different decoding stages and their interfaces are discussed and their performance is compared. A new procedure is proposed to define the feedback signal from the output of the Reed-Solomon decoder to the input of the convolutional decoder, which captures the reliability information that can be inferred from errors-and-era-suresrs decoders and includes the “state pinning” approach as a particular case. The decoding schemes are applied to the specificdvb-s concatenated code.
2005-01-01T00:00:00ZExtremes of error exponents
http://hdl.handle.net/10230/36018
Extremes of error exponents
Guillén i Fàbregas, Albert; Land, Ingmar; Martinez, Alfonso
This paper determines the range of feasible values of standard error exponents for binary-input memoryless symmetric channels of fixed capacity C and shows that extremes are attained by the binary symmetric and the binary erasure channel. The proof technique also provides analogous extremes for other quantities related to Gallager's E 0 function, such as the cutoff rate, the Bhattacharyya parameter, and the channel dispersion.
2013-01-01T00:00:00ZMismatched decoding: error exponents, second-order rates and saddlepoint approximations
http://hdl.handle.net/10230/36017
Mismatched decoding: error exponents, second-order rates and saddlepoint approximations
Scarlett, Jonathan; Martinez, Alfonso; Guillén i Fàbregas, Albert
This paper considers the problem of channel coding with a given (possibly suboptimal) maximum-metric decoding rule. A cost-constrained random-coding ensemble with multiple auxiliary costs is introduced, and is shown to achieve error exponents and second-order coding rates matching those of constant-composition random coding, while being directly applicable to channels with infinite or continuous alphabets. The number of auxiliary costs required to match the error exponents and second-order rates of constant-composition coding is studied, and is shown to be at most two. For independent identically distributed random coding, asymptotic estimates of two well-known non-asymptotic bounds are given using saddlepoint approximations. Each expression is shown to characterize the asymptotic behavior of the corresponding random-coding bound at both fixed and varying rates, thus unifying the regimes characterized by error exponents, second-order rates, and moderate deviations. For fixed rates, novel exact asymptotics expressions are obtained to within a multiplicative 1+o(1) term. Using numerical examples, it is shown that the saddlepoint approximations are highly accurate even at short block lengths.
2014-01-01T00:00:00ZExpurgated random-coding ensembles: exponents, refinements and connections
http://hdl.handle.net/10230/36016
Expurgated random-coding ensembles: exponents, refinements and connections
Scarlett, Jonathan; Peng, Li; Merhav, Neri; Martinez, Alfonso; Guillén i Fàbregas, Albert
This paper studies expurgated random-coding bounds and exponents for channel coding with a given (possibly suboptimal) decoding rule. Variations of Gallager's analysis are presented, yielding several asymptotic and nonasymptotic bounds on the error probability for an arbitrary codeword distribution. A simple nonasymptotic bound is shown to attain an exponent of Csiszár and Körner under constant-composition coding. Using Lagrange duality, this exponent is expressed in several forms, one of which is shown to permit a direct derivation via cost-constrained coding that extends to infinite and continuous alphabets. The method of type class enumeration is studied, and it is shown that this approach can yield improved exponents and better tightness guarantees for some codeword distributions. A generalization of this approach is shown to provide a multiletter exponent that extends immediately to channels with memory.
2014-01-01T00:00:00Z