SU-MIMO Combined MU-MIMO SU-MIMO Combined MU-MIMO SNR 10dB SNR 0dB Number of Users Figure 5.6 Performance for a 4 X 4 MIMO. SU-MIMO uses MMSE-SIC and four code words per UE. MU-MIMO uses MMSE and one code word per UE. 5.4 Physical Channel Procedures Supporting MIMO UE is semistatically configured via higher-layer signaling to receive the physical downlink shared channel based on one of the following transmission modes [4]: single-antenna port; transmit diversity; open-loop spatial multiplexing; closed-loop spatial multiplexing; and multiuser MIMO. 5.4.1 UE Procedure for Reporting Channel Quality Indication, Precoding Matrix Indicator, and Rank The time and frequency resources that can be used by the UE to report CQI, pre- coding matrix indicator (PMI), and rank indication (RI) are controlled by the eNB. For spatial multiplexing, as given in reference 3, the UE determines an RI cor- responding to the number of useful transmission layers. For transmit diversity, as given in reference 3, RI = 1. © 2009 by Taylor & Francis Group, LLC MIMO OFDM Schemes for 3GPP LTE Performance Comparison Between 2x2 SU-MIMO and MU-MIMO in a Correlated Precoded Channel SU-MIMO Combined SNR 10 dB MU-MIMO SU-MIMO Combined MU-MIMO SNR = 0 dB Number of Users Figure 5.7 Performance for a 2 X 2 MIMO. SU-MIMO uses MMSE-SIC and two code words per UE. MU-MIMO uses MMSE and one code word per UE. The chan- nel is correlated and precoded. CQI, PMI, and RI reporting is periodic or aperiodic. A UE transmits CQI, PMI, and RI reporting on a physical uplink control channel (PUCCH) for subframes with no physical uplink shared channel (PUSCH) allocation. A UE transmits CQI, PMI, and RI reporting on a PUSCH for those subframes with PUSCH allocation for (a) scheduled PUSCH transmissions with or without an associated scheduling grant or (b) PUSCH transmissions with no uplink shared channel (UL-SCH). The CQI transmissions on PUCCH and PUSCH for various scheduling modes are sum- marized in Table 5.7. If both periodic and aperiodic reporting occur in the same 