MIMO schemes in LTE

SU-MIMO (Single User MIMO)

• This is an example of downlink 2x2 single user MIMO with precoding.
• Two data streams are mixed (precoded) to best match the channel conditions.
• The receiver reconstructs the original streams resulting in increased single-user data rates and corresponding increase in cell capacity.
• 2x2 SU-MIMO is mandatory for the downlink and optional for the uplink

MU-MIMO (Multiuser MIMO)

• Example of uplink 2x2 MU-MIMO.
• In multiple user MIMO the data streams come from different UE.
• There is no possibility to do precoding since the UE are not connected but the wider TX antenna spacing gives better de-correlation in the channel.
• Cell capacity increases but not the single user data rate.
• The key advantage of MU-MIMO over SU-MIMO is that the cell capacity increase can be had without the increased cost and battery drain of two UE transmitters.
• MU-MIMO is more complicated to schedule than SU-MIMO