Adaptive antennas for space-time coding over block-time invariant multipath fading channels

Space-time codes have been introduced to improve mobile systems performance in a multipath fading environment. We consider the downlink of an L-multipath, m mobile-antenna system in which the base station has a phased n-antenna array (i.e. outdoor wireless). We show that when the channel has no ISI, then adaptive antennas, in the form of beamforming, can be combined with space-time coding to achieve a diversity of mL and a large signal processing (SNR) gain, whenever n⩾L. When the channel has ISI, beamforming can be used to achieve an SNR gain over a SIMO system, although both have the same diversity gain. Novel concepts of beamforming are derived in the process