I. Introduction
MASSIVE multiple-input multiple-output (MIMO) has emerged as one of the key technologies for the next generation of wireless communication systems where a number of user equipments (UEs) have to be reliably served by a base station (BS) equipped with a large number of antennas [1], [2]. The benefits of massive MIMO greatly relies on the quality of channel estimates acquired by the base-station (BS). Therefore, the robustness of the channel estimation technique is crucial in determining how well the system caters to the service requirements of all its users [3].