In MU-MIMO, multiple user terminals can transmit simultaneously on the same resource block. Only one transmit transmit antenna is required for mobile. This techniques is only possible with use of orthogonal SC-FDMA modulation on UL.
Uplink MIMO: MIMO schemes for LTE Uplink are different in comparison to Downlink. The Uplink (UL) is representative of a data link where Mobile is the transmitter and eNodeB is the receiver.
As we have already discussed, MIMO techniques are multi-antenna techniques to support
higher data rates on radio links. These techniques are ok for Downlink(DL) where
transmitter is eNodeB but in case of UL it gets complex for mobile entity.
So in order to reduce complexities in mobile UL path, a different antenna scheme
is used. This scheme is called MU-MIMO, where MU stands for Multiple Users.
SC-FDMA is single carrier FDMA technique to provide multi user orthogonality and
efficient frequency domain equalization. This transmit technique is also know as
DFT spread OFDM. So the main difference in this technique is involvement of DFT
Detailed processing of LTE uplink transmission is shown in block diagram below.