Flexible channel feedback quantization in multiple antenna systems

We propose a new vector quantization (VQ) algorithm for reducing the bit rate used for channel state information feedback in a variety of multiple antenna systems on flat and frequency selective channels. We consider an approach where the receiver chooses an instantaneous capacity maximizing entry from a small finite set of predefined covariance matrices. The codebook of covariance matrices is constructed based on separate optimization of the channel eigenvectors and power allocation among them. If, for the given channel realization, one of the predefined covariance matrices provides higher capacity than equal power distribution, the indices of the two codebooks are fed to the transmitter; otherwise, the transmitter uses the open-loop approach. We implement the proposed algorithm on flat fading and frequency selective MIMO channels and show the influence of the feedback rate on system capacity. For the case of flat fading, the required feedback rates are approximately equal to the product of the number of transmit and receive antennas. Although much higher feedback throughput is needed for reliable channel state information feedback in OFDM systems, we show a simple clustering technique to lower the required bit rate.