Uplink MIMO schemes for LTE will differ from downlink MIMO schemes to take into account terminal complexity issues. For the uplink, MU-MIMO can be used. Multiple user terminals may transmit simultaneously on the same resource block. This is also referred to as spatial division multiple access (SDMA).
The scheme requires only one transmit antenna at UE side which is a big advantage. The UEs sharing the same resource block have to apply mutually orthogonal pilot patterns.
To exploit the benefit of two or more transmit antennas but still keep the UE cost low, transmit antenna selection can be used. In this case, the UE has two transmit antennas but only one transmit chain and amplifier.
A switch will then choose the antenna that provides the best channel to the eNodeB.
This decision is made according to feedback provided by the eNodeB. The CRC parity bits of the DCI format 0 are scrambled with an antenna selection mask indicating UE antenna port 0 or 1. The support of transmit antenna selection is a UE capability.
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