Smooth beamforming for OFDM

This paper investigates the combination of beamforming and channel state information (CSI) smoothing for OFDM. While both can offer significant performance gains, care must be taken when using both of them at the same time. Two different sets of beamforming weights can produce the same beamforming gains but be unsuitable for CSI smoothing due to sudden changes in the frequency domain. By using orthogonal iterations to compute the beamforming weights, it is shown that a smooth beamformer is produced which is suitable for CSI smoothing at the receiver. An additional benefit of this technique is that the beamforming weights are easy to compute by exploiting the frequency correlation of the channel. The performance is evaluated for an OFDM system based on the IEEE 802.11n draft standard for which the gains are quantified. We also present results obtained from a hardware test bed, which verify the performance of the proposed smooth beamforming technique.