Space-time coding and transmission optimization for wireless channels

Space-time codes have been introduced to improve a mobile system´s performance in a multipath fading environment. We consider an L-multipath, m mobile-antenna system in which the base station has a phased n-antenna array (i.e. fading at the base station antennas is completely correlated). We show that when the channel has no ISI, then adaptive antennas, in the form of beamforming, can be combined with delay-diversity coding to achieve a diversity gain of mL and a large coding gain, whenever n/spl ges/L. When the channel has ISI, or for a rapid fading channel; beamforming can be used to achieve a coding gain over a SIMO system, although both have the same diversity gain. Novel concepts of beamforming are derived in the process.