Abstract
Orthogonal frequency division multiplexing (ofdm) systems have gained interest, especially in the case of bad propagation channels with severe multipath propagation and long delays. We will describe an ofdm system model and focus our attention on the estimation of the channel transfer function. Two different methods are presented which are analyzed and illustrated with regard to their mean squared error (mse). Then we will investigate the effects of an improper estimation on multilevel signal constellations. It reveals that avoiding signal points with high energy is very essential. Thus, we present a coding scheme which uses trellis shaping. Our simulations with ofdm over multipath channels give additional gains over those which are known for the additive white Gaussian noise (awgn) channel.
Résumé
Les systèmes ofdm s’appliquent à des canaux de transmission avec une propagation multitrajets très dégradés. Dans cet article, un modèle de système ofdm est présenté avec estimation de la fonction de transfert du canal. Deux méthodes sont décrites et comparées en fonction de ľerreur quadratique moyenne. Les effets ďune estimation incorrecte des constellations multiniveaux sont analysés; il apparaît qu’il faut éviter les points de signal à haute énergie, ďoù ľintérêt de la déformation du treillis. Les simulations canal multitrajets donnent un gain de 5 dB, ce qui est nettement plus élevé que les gains connus pour les canaux avec bruit additif gaussien blanc.
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This work was supported by Deutsche Forschungsgemeinschaft, Bonn, Allemagne.
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Bossert, M., Donder, A. On the effects of trellis shaping in OFDM systems. Ann. Télécommun. 52, 74–80 (1997). https://doi.org/10.1007/BF03001053
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DOI: https://doi.org/10.1007/BF03001053
Key words
- Frequency division multiplexing
- Orthogonal signal
- Trellis coding
- Multilevel signal
- Quadrature modulation
- Signal constellation
- Multipath propagation
- Statistical estimation