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.