Flexible Multi-User MIMO with Limited Feedback

In a Multi-User MIMO (MU-MIMO) spatial multiplexing scheme, multiple users are scheduled in the same resource block (RB). However, due to the wide fluctuation of realistic traffic patterns, it could often occur that only a single or few users have active data that need to be sent. In 3GPP Long Term Evolution (LTE), Single-User MIMO (SU-MIMO) rank one preceding based Channel Quality Indicator (CQI) reporting mechanism is reused for MU-MIMO. This is optimum for MU-MIMO if single user is served. Based on SU-MIMO Rank one reporting, CQI re-calculations at the Basestation (BS) are derived for Space Division Multiple Access (SDMA) mode and Zero-Forcing (ZF) mode respectively. A novel flexible MU-MIMO scheme with rank and mode adaptation is thus proposed for the first time with this limited feedback information. Simulation examples are provided to confirm the advantage of proposed flexible MU-MIMO scheme over SU-MIMO with 3GPP LTE framework.