Hybrid CQI estimation method for higher order MU-MIMO in LTE-A systems

This paper addresses the problem of estimating the Multi-User Multiple Input Multiple Output (MU-MIMO) Channel Quality Indicator (CQI) from the reported Single-User MIMO rank-1 CQI. A hybrid MU-MIMO CQI estimation algorithm is proposed. Proposed algorithm applies a fixed back off offset to compensate the power sharing among co-scheduled users and a dynamic offset for Multi-User (MU) interference. Dynamic offset is estimated according to a closed-form formula in terms of MU Zero-Forcing Beamforming (ZFBM) pre-coders at each MU scheduling instant. Simulation results show that proposed scheme achieves significant outperformance than conventional estimation methods. Furthermore, the algorithm shows efficient performance balance between cell median and cell edge users. The proposed algorithm is tested under different MU ranks with emphasis on the received Block Error Rates and Modulation & Coding Schemes.