Space-time codes for multiple access systems with low MMSE decoding complexity

We study a class of space-time codes constructed by linear dispersion encoding that allow low-complexity linear minimum mean square error (MMSE) decoding for a multiple access system. Considering that the information symbols are drawn from square QAM constellations, we optimize rate-one space time code designs with MMSE decoding to achieve minimum bit error rate (BER) for any channel realization. In addition, the performance is further improved with a simple MMSE successive interference cancellation (MMSE-SIC) method. Simulation results compare the proposed design with existing rate-one designs and show that simple rate-one circulant designs are also good candidates for deployment in multiple access systems.