Modal analysis/filtering to estimate time-varying MIMO-OFDM channels

In the multipath multiple-input multiple-output (MIMO) channel, long-term/large-scale properties (e.g., delays, angles, powers) remain approximately constant over many coherence times (i.e., over many Doppler periods) and define the structural terms of the propagation channel referred as delay (powers and delays) and angular (powers and angles of departure and arrival) modes of the channel. Effective improvement of the channel estimate is obtained by estimating delay and angular modal spaces via modal analysis and by filtering the (original) least squares channel estimates as projection onto the modal spaces. The paper also provides experimental validation of the overall method with realistic channel models.