A new modulation scheme for space-time codes

A new modulation method for linear space-time codes is proposed based on using constellations of different sizes for different symbols. It is shown that the proposed method significantly reduces the complexity of the sphere decoding algorithm. Typically, a complexity reduction of one to two orders of magnitude can be achieved at the expense of about 3 dB coding gain. With a simple modification in our design, we reduce this loss to about 2 dB.