Performance Evaluations for Multiuser CQI Enhancements for LTE-Advanced

In LTE-Advanced, multiuser MIMO has been identified as a key technique for increasing system spectral efficiency in closed-loop MIMO. Transmission parameters like precoding and transmission rate are adapted based on finite rate feedback from the users. Switching between single user and multiuser transmission modes is possible without higher layer signaling, which means that the feedback should be designed to sustain efficiently both single user and multiuser transmissions. In this paper, performance of LTE-Advanced is evaluated with system level simulations. The focus is on studying the viability of an additional multiuser specific channel quality feedback. The baseline in the comparison is single stream single user feedback consisting of a preferred precoding vector and a channel quality feedback. This baseline is compared to feedback schemes that aim at improving the multiuser performance by an additional multiuser-specific CQI. Also, the gain from a user specific scaling for the channel quality feedback performed by the base station is evaluated.