  Recent works on massive multiple-input multiple-output (MIMO) have shown that
a potential breakthrough in capacity gains can be achieved by deploying a very
large number of antennas at the basestation. In order to achieve the
performance that massive MIMO systems promise, accurate transmit-side channel
state information (CSI) should be available at the basestation. While
transmit-side CSI can be obtained by employing channel reciprocity in time
division duplexing (TDD) systems, explicit feedback of CSI from the user
terminal to the basestation is needed for frequency division duplexing (FDD)
systems. In this paper, we propose an antenna grouping based feedback reduction
technique for FDD-based massive MIMO systems. The proposed algorithm, dubbed
antenna group beamforming (AGB), maps multiple correlated antenna elements to a
single representative value using pre-designed patterns. The proposed method
modifies the feedback packet by introducing the concept of a header to select a
suitable group pattern and a payload to quantize the reduced dimension channel
vector. Simulation results show that the proposed method achieves significant
feedback overhead reduction over conventional approach performing the vector
quantization of whole channel vector under the same target sum rate
requirement.
