Channel Smoothing for 802.11ax Beamformed MIMO-OFDM

Channel smoothing is a powerful technique that improves the channel estimation of orthogonal frequency division multiplexing (OFDM) systems by exploiting the correlation or smoothness among the frequency-domain channel responses. However, it can’t be applied to WiFi beamformed MIMO systems because the beamforming vectors provided by the beamforming receiver are disruptive and consequently make the beamformed channels disruptive. We propose a scheme that enables the transmitter to generate smooth beamforming vectors from the disruptive beamforming vectors provided by the receiver. As a result, the beamformed channel becomes smooth so that the powerful channel smoothing can be applied again for more than 2 dB gain. The objective function for smoothing the beamforming vectors is formulated first and then the optimal solution to this optimization problem is derived. The performance gain is finally verified by simulations.