What is CLSM (Closed Loop Spatial Multiplexing)?

Closed Loop Spatial Multiplexing form of LTE MIMO is the same as the open-loop version, but as the name demonstrates it has feedback joined to close the loop. A PMI, Precoding Matrix Indicator is fed back from the UE to the base station. This empowers the transmitter to pre-code the information to improve the transmission and empower the receiver to more easily separate the various information streams.