Transmission subspace tracking for MIMO communications systems

This paper describes the benefits of transmission subspace tracking for multiple input multiple output communications systems, and applies the concepts of previous work on adaptive transmit antenna algorithms to this problem. A specific stochastic gradient technique of subspace or "multi-mode" tracking of the independent modes of the MIMO transfer function and the application to space time coding is considered. The technique provides gains by tracking the active modes when there are more transmit than receive antennas. With the proposed algorithm, the receiver generates binary feedback selecting preferred perturbed weights, which gives the transmitter a gradient estimate useful for subspace tracking. The capacity resulting from this approach is shown by simulation