Optimal training design for MIMO OFDM systems in mobile wireless channels

Imad Barhumi, Geert Leus, Marc Moonen

Research output: Contribution to journalArticlepeer-review

695 Citations (Scopus)


This paper describes a least squares (LS) channel estimation scheme for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems based on pilot tones. We first compute the mean square error (MSE) of the LS channel estimate. We then derive optimal pilot sequences and optimal placement of the pilot tones with respect to this MSE. It is shown that the optimal pilot sequences are equipowered, equispaced, and phase shift orthogonal. To reduce the training overhead, an LS channel estimation scheme over multiple OFDM symbols is also discussed. Moreover, to enhance channel estimation, a recursive LS (RLS) algorithm is proposed, for which we derive the optimal forgetting or tracking factor. This factor is found to be a function of both the noise variance and the channel Doppler spread. Through simulations, it is shown that the optimal pilot sequences derived in this paper outperform both the orthogonal and random pilot sequences. It is also shown that a considerable gain in signal-to-noise ratio (SNR) can be obtained by using the RLS algorithm, especially in slowly time-varying channels.

Original languageEnglish
Pages (from-to)1615-1624
Number of pages10
JournalIEEE Transactions on Signal Processing
Issue number6
Publication statusPublished - Jun 2003
Externally publishedYes


  • Channel estimation
  • MIMO
  • Multipath fading channels
  • OFDM

ASJC Scopus subject areas

  • Signal Processing
  • Electrical and Electronic Engineering


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