Multi-Panel MIMO in 5G

Massive MIMO is one of the key enabling technologies in 5G wireless communications. A large number of antenna elements bring extra degrees of freedom for increasing the throughput and considerable beamforming gains for improving the coverage. In practice, a large number of antenna elements can be assembled into multiple antenna panels for the purpose of cost reduction and power saving. Multi-panel MIMO is expected to become promising for millimeter-wave massive MIMO systems. This article gives an overview of multi-panel MIMO systems, including downlink, uplink, and non-coherent transmissions, and discuss research challenges and future directions of multi-panel MIMO. We also propose new multi-panel codebook design and corresponding CSI feedback design for 5G systems as well as non-coherent MIMO transmission.