An approximately MAI-free multiaccess OFDM system in fast time-varying channels

Layla Tadjpour*, Shang-Ho Tsai, C. C.Jay Kuo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


A new multiuser orthogonal frequency division multiplexing (OFDM) transceiver with preceding, called the precoded multiuser OFDM (PMU-OFDM) system, was recently introduced by Tsai et al. (2005). The PMU-OFDM system can reduce multiaccess interference (MAI) due to the carrier frequency offset (CFO) to a negligible amount by preceding the data of each user with a codeword selected from either even or odd Hadamard-Walsh codes. The performance of the PMU-OFDM system in a mobile environment, where the channel response varies within one OFDM symbol due to the Doppler effect, is evaluated in this paper. It is shown by analysis and simulation that the use of even or odd Hadamard-Walsh codewords can greatly reduce the MAI effect due to the Doppler effect as well. Generally, all Hadamard-Walsh codewords except for the all-one codeword result in considerable suppression of intercarrier interference (ICI) induced by the Doppler effect. Furthermore, we discuss codeword priority schemes to minimize ICI as much as possible. Finally, simulations results are given to demonstrate the advantage of PMU-OFDM over OFDMA with a codeword priority scheme in the Doppler environment. We show that the PMU-OFDM system with odd Hadamard-Walsh codewords outperforms a half-loaded OFDMA system in a mobile environment.

Original languageAmerican English
Pages (from-to)3787-3799
Number of pages13
JournalIEEE Transactions on Signal Processing
Issue number7 II
StatePublished - Jul 2007


  • Carrier frequency offset (CFO)
  • Doppler effect
  • Fast fading
  • Multiaccess interference (MAI)
  • Multiuser orthogonal frequency division multiplexing (OFDM)
  • Precoded multiuser OFDM (PMU-OFDM)
  • Precoding
  • Time varying


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