Measurement of time-varying multiple-input multiple-output channels

We derive a criterion on the measurability/identifiability of multiple-input multiple-output (MIMO) channels based on the size of the so-called spreading support of its subchannels. Novel MIMO transmission techniques provide high-capacity communication channels in time-varying environments and exact knowledge of the transmission channel operator is of key importance when trying to transmit information at a rate close to channel capacity.