  This work considers multiple-input multiple-output (MIMO) communication
systems using hierarchical modulation. A disadvantage of the maximum-likelihood
(ML) MIMO detector is that computational complexity increases exponentially
with the number of transmit antennas. To reduce complexity, we propose a
hierarchical modulation scheme to be used in MIMO trans- mission where base and
enhancement layers are incorporated. In the proposed receiver, the base layer
is detected first with a minimum mean square error (MMSE) detector which is
followed by ML detection of the enhancement layer. Our results indicate that
the proposed low complexity scheme does not compromise performance when design
parameters such as code rates and constellation ratio are chosen carefully.
