  Rate-Splitting Multiple Access (RSMA) is a flexible and robust multiple
access scheme for downlink multi-antenna wireless networks. RSMA relies on
multi-antenna Rate-Splitting (RS) at the transmitter and Successive
Interference Cancellation (SIC) at the receivers. In this work, we study the
performance of RSMA under the practical important setup of imperfect Channel
State Information at Transmitter (CSIT) originating from user mobility and
latency in the network. First, we derive a lower bound on the ergodic sum-rate
of RSMA for an arbitrary number of transmit antennas, number of users, user
speeds and transmit power. Then, we study the power allocation between common
and private streams and obtain a closed-form solution for the optimal power
allocation that maximizes the obtained lower bound. The proposed power
allocation greatly reduces precoder design complexity for RSMA. By Link-Level
Simulations (LLS), we demonstrate that RSMA with the proposed power allocation
is robust to degrading effects of user mobility and has significantly higher
performance compared to conventional multi-user (massive) Multiple-Input
Multiple-Output (MIMO) strategies. The work has important practical
significance as results demonstrate that, in contrast to conventional
multi-user (massive) MIMO whose performance collapse under mobility, RSMA can
maintain reliable multi-user connectivity in mobile deployments.
