Channel estimation for super high bit rate massive MIMO systems using joint processing of analog fixed beamforming and CSI-based precoding

For the 5th generation (5G) mobile communication system, small cells using higher frequency bands with wider bandwidth will be introduced to achieve super high bit rate transmission of several tens of Gbps. Massive MIMO beamforming (BF) is one of promising technologies to compensate for larger path-loss in the higher frequency bands. We have proposed joint processing of analog fixed BF and channel state information (CSI)-based precoding (FBCP) for Massive MIMO systems to achieve large BF gain while reducing the number of baseband chains, which results in the cost reduction of the transceiver. To generate the precoding and postcoding matrices, both the transmitter and receiver have to estimate the equivalent MIMO channel (the multiplication of analog BF weight matrix and MIMO channel matrix). In this paper, the channel estimation (CE) scheme and the frame structure for Massive MIMO using FBCP is proposed. In the CE for FBCP, the accurate equivalent MIMO channel can be estimated because of the reference signal which obtains the BF gain by using the analog fixed BF. The throughput performances of FBCP with channel estimation are evaluated by the computer simulation and it is shown that the FBCP can achieve higher throughput than the fully digital Massive MIMO due to the reduced reference signal.