Reducing MIMO Detection Complexity via Hierarchical Modulation
  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. 
Yigit Ugur and Ali Ozgur Yilmaz
cs.IT math.IT