Low complexity direction of arrival (DoA) estimation for 2D massive MIMO systems

Mobile data traffic is expected to almost double every year from 2012 to 2016. In order to address the challenge, “massive MIMO” has been proposed as one of the enabling technologies to significantly increase the spectral-efficiency of a wireless system. In “massive MIMO” systems, a base station will rely on the uplink sounding signals from mobile stations to figure out the channel knowledge to perform MIMO beam-forming. Accordingly, direction-of-arrival estimation at the base station becomes crucial for “massive MIMO” systems to realize the predicted capacity gains. In this paper, we study DoA estimation for two-dimensional (2D) “massive MIMO” systems in mobile wireless systems. To be specific, we derive the Cramer-Rao lower bound for 2D “massive MIMO” systems and introduce a low complexity direction-of-arrival estimation algorithm to jointly estimate elevation and azimuth angles of the arrived signals based on unitary transformation. Results suggest that the dimension of the antenna array at the base station plays an important role in the estimation performance. It is also found that azimuth estimation is more vulnerable compared to elevation estimation. These insights will be useful for designing practical “massive MIMO” systems in future mobile wireless communications.