The FCC uses the simultaneous multi-round auction (SMA) to assign spectrum licenses.
Congress mandated that the SMA be compared to an auction that allows combinatorial
bids. We review the theoretical and experimental evidence relevant to the SMA procedures
and their inherent defects. Results from experiments evaluating the SMA in comparison
to a combinatorial auction designed by Charles River and Associates show that several
of the SMA rules hinder efficiency and create a trade-off between efficiency and
auction length. The combinatorial auction outperforms the SMA when license values
are superadditive, but requires more time to complete and is not robust.