Finite-precision analysis of demappers and decoders for LDPC-coded M-QAM systems
IEEE TRANSACTIONS ON BROADCASTING
Autore/i: Baldi, Marco; Chiaraluce, Franco; Cancellieri, Giovanni
Classificazione: 1 Contributo su Rivista
Abstract: LDPC codes are state-of-art error correcting codes,
included in several standards for broadcast transmissions. Iterative
soft-decision decoding algorithms for LDPC codes reach excellent
error correction capability; their performance, however, is
strongly affected by finite-precision issues in the representation of
inner variables. Great attention has been paid, in recent literature,
to the topic of quantization for LDPC decoders, but mostly focusing
on binary modulations and analysing finite precision effects in a
disaggregrated manner, i.e., considering separately each block of
the receiver. Modern telecommunication standards, instead, often
adopt high order modulation schemes, e.g. M-QAM, with the aim
to achieve large spectral efficiency. This puts additional quantization
problems, that have been poorly debated in previous literature.
This paper discusses the choice of suitable quantization characteristics
for both the decoder messages and the received samples
in LDPC-coded systems using M-QAM schemes. The analysis
involves also the demapper block, that provides initial likelihood
values for the decoder, by relating its quantization strategy
with that of the decoder. A new demapper version, based on approximate
expressions, is also presented, that introduces a slight
deviation from the ideal case but yields a low complexity hardware
implementation.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51050 
