Large-system performance of iterative multiuser decision-feedback detection

Michael L. Honig*, Rapeepat Ratasuk

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


The large-system performance of iterative multiuser decision-feedback detectors (DFDs) is studied for synchronous coded direct-sequence code-division multiple access. Both successive and parallel demodulation of users are considered. The filters are optimized according to the minimum mean-squared error criteria, assuming perfect feedback. We first consider Viterbi decoding with hard decision feedback, and compute union bounds on the large-system error rate. We then consider maximum a posteriori (MAP) decoding with soft decision feedback, and evaluate the error rate semianalytically by assuming the log-likelihood ratios computed by the MAP decoder are Gaussian random variables. Performance is studied numerically as a function of noise level, spectral efficiency, and code rate. Results show that soft decision feedback gives substantial gains relative to hard decision feedback. At moderate spectral efficiencies (users divided by bandwidth expansion less than 0.9), the iterative DFDs with soft decision feedback based on a posteriori probabilities can achieve near-single-user performance at an Eb/No close to the large-system capacity bound.

Original languageEnglish (US)
Pages (from-to)1368-1377
Number of pages10
JournalIEEE Transactions on Communications
Issue number8
StatePublished - Aug 2003


  • Code-division multiple access (CDMA)
  • Decision feedback
  • Large-system analysis
  • Multiuser detection

ASJC Scopus subject areas

  • Electrical and Electronic Engineering

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