User pilot scheduling in massive MIMO systems

One bottleneck of the massive multi-input multi-output (MIMO) systems is the pilot contamination caused by users sharing the non-orthogonal pilots. The pilot contamination contributes significantly to the channel estimation error at the base station (BS) and finally results in the saturation of user rates. This paper firstly analyzes the mean square error (MSE) of the channel estimation at the BS. Inspired by the results, this paper then proposes a user pilot scheduling algorithm which preferentially minimizes the channel estimation MSE of users with poorer channel qualities. Simulation results show that the algorithm significantly improves the achievable rates of the poorer users as well as the system sum rate compared with the conventional way.