  This paper investigates the performance of reconfigurable intelligent surface
(RIS)-aided massive multiple-input multiple-output (MIMO) systems with direct
links, and the phase shifts of the RIS are designed based on the statistical
channel state information (CSI). We first derive the closed-form expression of
the uplink ergodic data rate. Then, based on the derived expression, we use the
genetic algorithm (GA) to solve the sum data rate maximization problem. With
low-complexity maximal-ratio combination (MRC) and low-overhead statistical
CSI-based scheme, we validate that the RIS can still bring significant
performance gains to traditional massive MIMO systems.
