Mobility dependent feedback scheme for point-to-point MIMO systems

A MIMO diversity scheme that utilizes varying amounts of channel state information (CSI) for mobile users is presented. CSI at the transmitter is obtained through a time-duplexed feedback channel, and thus by varying the periodicity of feedback intervals, an optimal balance is struck between obtaining accurate CSI and minimizing the overhead of uplink transmission. The optimal feedback amount is shown to have a strong dependence on the user´s average SNR and Doppler spread. The proposed solution optimally switches between beamforming and orthogonal space-time block coding and has negligible loss of performance with respect to more complex optimal schemes.