  DOA estimation for massive multiple-input multiple-output (MIMO) system can
provide ultra-high-resolution angle estimation. However, due to the high
computational complexity and cost of all digital MIMO systems, a hybrid analog
digital (HAD) structure MIMO was proposed. In this paper, a fast ambiguous
phase elimination method is proposed to solve the problem of direction-finding
ambiguity caused by the HAD MIMO. Only two-data-blocks are used to realize DOA
estimation. Simulation results show that the proposed method can greatly reduce
the estimation delay with a slight performance loss.
