LDPC Bit Permutation for High-Order QAM SNR Improvement

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Solution Overview

Problem

The existing LDPC codes used in the DVB-S2 standard for digital television broadcasting over cable networks, when combined with QAM modulations, do not provide a satisfactory signal-to-noise ratio (SNR) for achieving the Quasi Error Free (QEF) condition, particularly for 1024QAM and 4096QAM modulations.

Innovation Solution

A method is introduced that improves the association between bits outputted by the LDPC encoder and constellation coordinates for QAM modulations by employing a specific permutation scheme in the 'Demux' block, using a matrix interleaver and mapping bits to constellation points in a way that optimizes bit arrangement for 1024QAM and 4096QAM modulations, specifically by rearranging and interlacing bits within the in-phase and quadrature portions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If LDPC codes from DVB-S2 standard are used with QAM modulations for cable network broadcasting, then the system can support high-order modulations (1024QAM, 4096QAM), but the signal-to-noise ratio required to achieve Quasi Error Free condition is not satisfactory

Engineering Contradiction:

Improvesupport for high-order QAM modulationsVSAvoidsignal-to-noise ratio performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The bit stream from LDPC encoder is segmented and permuted through multiple stages: first separating information bits and parity bits, then applying different permutation patterns to different bit groups. This segmentation allows optimization of bit-to-symbol mapping for QAM constellations, improving error performance while maintaining compatibility with high-order modulations

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Bit permutation is performed in advance before QAM mapping to optimize the association between coded bits and constellation points. The permutation patterns are designed beforehand to ensure that bits mapping to the same constellation symbol are well-distributed across different LDPC code positions, improving robustness against channel errors before the actual modulation occurs

Inventive Principle:

Principle #10Preliminary action

2Device complexity

If standard LDPC encoding without bit permutation is used, then the system implementation is simpler, but the association between encoded bits and constellation coordinates is not optimized for QAM modulations

Engineering Contradiction:

Improveimplementation simplicityVSAvoidbit-to-constellation association performance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

A bit permutation intermediary stage is introduced between the LDPC encoder and the QAM mapper. This intermediary applies predetermined permutation patterns to rearrange bits before mapping, optimizing the association between encoded bits and constellation coordinates without adding complex adaptive processing, thus maintaining implementation simplicity while improving performance

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP2294738B1Permutation of LDPC coded bits to be applied before QAM constellation mapping

Publication Date: 2013.10.23 RAI-RADIOTELEVISIONE ITALIANA SPA

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AI summary

The present invention relates to a method for processing digital signals and to a transmission/reception system implementing said method; the present invention is based on the use of LDPC codes, in particular the LDPC code of the DVB-S2 standard, in combination with a QAM modulation, in particular the 1024QAM and 4096QAM modulations; in transmission, a bit permutation (Demux) is carried out prior to the QAM constellation mapping function; in reception, the bit permutation is carried out after the QAM constellation demapping function.