Hybrid Massive-MIMO and Its Practical Beamforming Implementation

Multiple-input multiple-output (MIMO) becomes a prevailing technology to significantly strengthen the channel capacity by employing multiple antennas at both transmitter (Tx) and receiver to explore multipath radio propagation channels. The expected huge path losses will be compensated by more antenna elements which can provide sufficiently high beamforming and multiplexing gain. This chapter presents the system model of hybrid massive-MIMO (m-MIMO), which followed with a discussion on the three hybrid m-MIMO architectures and their associated design algorithms for seeking optimized hybrid precoders. An efficient iterative hybrid beamformer algorithm is developed based on classical block coordination descent methods. Fixed subarray m-MIMO aims to maximize energy efficiency with reduced hardware complexity while suffering lower spectral efficiency. The dynamic subarray can be constructed with various degrees of reconfigurability of connecting radio frequency chains and Tx antenna elements/subarrays. The implementation of the reconfigurable power divider improves the performance of the fixed subarray.