Study On Low-Complexity Decoding Algorithms For Nonbinary Low-Density Parity-Check Coded-Modulation Systems

Channel coding is a necessary technique for reliable communication over noisy chan-nels. And the search for capacity-approaching channel coding schemes with practical complexity has been the focal point among the coding community. Last 20 years witness the phenomenal success of Turbo codes, which leads to the rediscovery of low-density parity-check (LDPC) codes. Recently, it has been shown that nonbinary LDPC codes can offer better error-correcting performance than their binary counterparts, especially when combined with higher-order modulations. However, the advantages of nonbinary LDPC codes are balanced by their higher decoding complexity. Over a decade, albeit the research and knowledge base for turbo codes and LDPC codes have been quite mature, more intensive research on theory and applications of nonbinary LDPC codes are required.This thesis investigates the decoding algorithms for nonbinary LDPC coded-modulation systems, with the emphasis on some low-complexity decoding methods. And we mainly address the reliability-based message passing algorithm for decoding nonbi-nary LDPC codes constructed based on finite fields/geometry. The main contents are as follows,(1) The definition and factor graph representation of nonbinary LDPC codes are intro-duced. The error-correcting performance of nonbinary LDPC codes decoded with sum-product algorithm is confirmed with simulations. Comparisons are performed with binary LDPC codes and turbo codes;(2) Extended min-sum (EMS) algorithm, which reduces the decoding complexity of non-binary LDPC codes with negligible performance loss is addressed. The effectiveness and feasibility of EMS algorithm are confirmed with simulations and complexity analysis;(3) The nonbinary LDPC coded-modulation systems are introduced. The capacity-approaching performance of the nonbinary LDPC coded-modulation systems is ver-ified by simulations;(4) A low-complexity iterative joint detection-decoding (IJDD) algorithm for nonbinary LDPC coded-modulation systems is developed. In the proposed scheme, signal de-tection and decoding are integrated as a whole. And the received signals are updated by the detector based on extrinsic information produced by hard decoder in an iter-ative manner. It is shown that the propose scheme can offer good error-correcting performance or even outperform QSPA with lower computational complexity.