A novel limited feedback mechanism based on mixed reciprocity and codebook in large scale 3D-MIMO systems

3D-MIMO, using two dimensional antenna array at base station, demonstrates promising throughput gain over conventional antenna system during recent academic and industry studies. To realize the performance gain, accurate channel state information (CSI) feedback is one essential aspect. However, traditional feedback method, either codebook based or reciprocity based, suffers from overhead and partial reciprocity issues, respectively. In this paper, a novel mixed feedback mechanism is proposed, in which reciprocity based feedback is complemented with minimal codebook based feedback, to enable full rank MIMO transmission but with minimal reference signal and CSI reporting overhead. The mechanism is optimized for the case with cross-polarized antenna at base station and two receive/one transmit antenna at UE, which is the most practical LTE cellular system configuration. Numerical evaluations verify that the mixed feedback mechanism can realize 3D-MIMO performance with minimal reference signal overhead, CSI reporting overhead and UE complexity.