Construction and iterative decoding of LDPC codes over rings for phase-noisy channels

  • Authors:

  • Sridhar Karuppasami;William G. Cowley

  • Affiliations:

  • Institute for Telecommunications Research, University of South Australia, Mawson Lakes, SA, Australia;Institute for Telecommunications Research, University of South Australia, Mawson Lakes, SA, Australia

  • Venue:
  • EURASIP Journal on Wireless Communications and Networking - Advances in Error Control Coding Techniques
  • Year:
  • 2008

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Abstract

This paper presents the construction and iterative decoding of low-density parity-check (LDPC) codes for channels affected by phase noise. The LDPC code is based on integer rings and designed to converge under phase-noisy channels. We assume that phase variations are small over short blocks of adjacent symbols. A part of the constructed code is inherently built with this knowledge and hence able to withstand a phase rotation of 2π/M radians, where "M" is the number of phase symmetries in the signal set, that occur at different observation intervals. Another part of the code estimates the phase ambiguity present in every observation interval. The code makes use of simple blind or turbo phase estimators to provide phase estimates over every observation interval. We propose an iterative decoding schedule to apply the sum-product algorithm (SPA) on the factor graph of the code for its convergence. To illustrate the new method, we present the performance results of an LDPC code constructed over Z4 with quadrature phase shift keying (QPSK) modulated signals transmitted over a static channel, but affected by phase noise, which is modeled by the Wiener (random-walk) process. The results show that the code can withstand phase noise of 2° standard deviation per symbol with small loss.