Approximation of multiuser rates in MIMO OFDM downlink systems
The authors propose a new limited feedback scheme for the downlink of multiuser multiple input multiple output orthogonal frequency division multiplexing (MIMO OFDM) systems based on fixed linear beamforming, i.e. the linear beamforming vectors are chosen from a fixed transmit codebook. The proposed feedback method allows the base station to uniformly approximate all multiuser rates for any selection of users and any combination of beamforming vectors defined by the transmit codebook; thus providing all degrees of freedom for the user selection. The approximation of the multiuser rates is enabled by using an additional codebook for the feedback. Which has the advantage that the transmit codebook can be designed independent of the feedback codebook. The authors show how feedback codebooks can be designed for arbitrary environments using the Linde-Buzo-Gray (LBG) algorithm. In the simulations we demonstrate that our proposed method outperforms other methods within the long term evolution (LTE) context.