DoA estimation and achievable rate analysis for 3D millimeter wave massive MIMO systems

Mobile data traffic is predicted to grow exponentially in the future. To address the challenge and consider the form factor limitation at the base station, 3D millimeter wave massive MIMO has been introduced as an enabling technology for 5G systems. In 3D millimeter wave massive MIMO systems, due to the large number of antennas and limited number of clusters, a base station will mainly rely on the uplink sounding signals instead of the feedback to figure out the channel knowledge to perform 3D MIMO operation. Accordingly, multi-dimensional channel estimation becomes critical for such systems to realize the predicted rate gains. In this paper, the performance of direction of arrival (DoA) estimation at the base station using ESPRIT method is characterized. The DoA estimation is further related to the underlying 3D MIMO achievable rate and the optimal transmission strategy is characterized. Finally, the impact of channel estimation error on the underlying achievable rate is analyzed. Our results suggest that DoA estimation is crucial for the transmit beam-forming of 3D millimeter wave massive MIMO systems. Furthermore, the optimal transmission strategy depends heavily on the performance of the underlying DoA estimation.