On transmit beamforming for multiantenna OFDM channels with finite-rate feedback

We propose two feedback methods for transmit beamforming in a point-to-point multiple-antenna OFDM channel. For the first method, a receiver with channel information quantizes and feeds back the optimal transmit beamforming vectors of a few selected subcarriers that are equally spaced. Based on those quantized vectors, the transmitter linearly interpolates the remaining beamforming vectors with different phase rotation whose expression is explicitly shown. For the second proposed method, a channel impulse response is quantized with a uniform scalar quantizer. At the transmitter, channel frequency response can be reconstructed from the quantized impulse response and the optimal beamforming vectors can then be computed. We show that switching between the two methods for different feedback-rate requirement outperforms existing methods in the literature.