SU-MIMO = Single User MIMO
  • It is the most common form of MIMO.
  • Each user is served by only one BS and it occupies the resource exclusively, including
    time, frequency.
  • It can be applied in the uplink or downlink. But it is generally applied only in DL. The UE can easily have 2 antennas in reception but only 1 antenna can transmit

The Single User MIMO is used in DL and means that the 2 TB send by the 2 antennas using the same radio resources are for the same UE.
In UL, it is not possible to use this MIMO.

There are two operation modes in SU-MIMO spatial multiplexing: 
The closed-loop spatial multiplexing mode
  • The UE reports the CQI, the RI (Rank Indicator) and the PMI (Precoding Matrix indicator)
The open-loop spatial multiplexing mode
  • The reports only the CQI and the RI.
  • The RI (Rank Indicator) indicates the number of spatial layers (data streams) that can be supported by the current channel experienced at the UE.
  • The PMI (Precoding Matrix Indicator) is the UE feedback.

The required UE feedback for the MIMO are: 
  • RI, Rank Indicator. By this one the UE can indicate if it is able to separate 2 TB. If Yes the eNodeB can use the MIMO. If not it uses the TxDiv
  • PMI, Precoding Matrix indicator. It is used only for the Closed Loop MIMO. The UE indicates the eNodeB how to map the data on the 2 antennas to optimize the reception.