Adaptive transmitting antenna methods for multipath environments

Adaptive transmitting antenna arrays hold great promise for increasing the capacity of mobile radio networks by reusing a channel among several users. To reuse bandwidth, a transmitting antenna array requires feedback information from the mobile receivers in order to track changes in the multipath environment. When the mobile is moving rapidly, the required feedback rates can become significant. We present a new method for transmission beamforming, which, by exploiting the subspace structure present in the spatial channel, requires much lower feedback data rates than previous methods.