MU-MIMO in LTE: Performance and the challenges for future enhancement

We consider the performance and improvement of Multi-User MIMO (MU-MIMO) in 3GPP LTE. In particular, we build on academic guidance, demonstrating the link between channel state information (CSI) accuracy and MU-MIMO performance, by considering MU-MIMO with practical CSI estimation and feedback within an actual system design under practical channels. Link-Level simulations are provided to model the interplay of such factors in the LTE design. We also propose a practical codebook structure to support increased CSI feedback. The results show that for some scenarios, in particular those with sufficient channel coherence and low antenna correlation, that MU-MIMO can be significantly improved by increased CSI feedback. Such conditions may be indicative of “small-cell” scenarios, an important scenario for future network capacity enhancement. The results also point to other issues that merit further consideration including CSI feedback granularity in frequency, CSI estimation, and improved MU-MIMO processing.