Spatial diversity/Transmit diversity (e.g. TM2) or simply diversity improves the reliability of data by sending the same data over two or more transmit antennas. It is useful when radio conditions are not good or pathloss is high or the UE is in weak coverage areas. On the other hand, Spatial Multiplexing (e.g. TM3/TM4), sends parallel data streams over multiple antennas (2, 4 or 8) effectively increasing the data rate to 2x, 4x or 8x. This is only possible when the radio conditions (SINR) is very good.
