@INPROCEEDINGS {4931,
author={N.S. Souto and J. C. Silva},
doi={},
booktitle={IEEE International Symp. on Communications and Information Technologies - ISCIT},
title={Efficient Channel Estimation for OFDM Systems with Hierarchical Constellations},
year={2007},
month={October},
volume={-},
pages={---} 
}