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LTE Transmission Mode:
Transmission mode 1: Single-antenna transmission.
Transmission mode 2: Transmit diversity, SFBC(Space-Frequency Block Coding)based.
Transmission mode 3: Open-loop codebook-based precoding in the case of more than one layer, degraded to transmit diversity in the case of rank-one transmission. (SU-MIMO)
Transmission mode 4: Closed-loop codebook-based precoding. (SU-MIMO).
Transmission mode 5: Multi-user MIMO version of transmission mode 4 (up to max 2 users/layers).
Transmission mode 6: Special case of closed-loop codebook-based precoding limited to single layer transmission, also called beam-forming for single user.
Transmission mode 7: Release-8 non-codebook-based precoding supporting only single-layer transmission per UE, it is also called beam-forming here for single layer per UE.
Transmission mode 8: Release-9 non-codebook-based precoding supporting up to two layers per UE.
Transmission mode 9: Release-10 non-codebook-based precoding supporting up to eight layers per UE.
Codebook based mode means the precoding matrix can only be selected from known(predefined) cookbook.
Non-codebook based mode requests different demodulation/UE specific reference signals to be inserted in the allocated RBs of PDSCH before precoding and the precoding matrix is completely selected by randomly. This mode supports up to 8 transmission layers(ranks) per UE in Release10.
Closed-loop precoding is assumed that the network selects the precoder matrix based on feedback(CSI-PMI/RI) from the terminal.
Open-loop precoding does not rely on any detailed precoder recommendation being reported by the terminal and does not require any explicit network signaling of the actual precoder used for the downlink transmission. Instead, the precoder matrix is selected in a predefined and deterministic way known to the terminal in advance. One use of open-loop precoding is in high-mobility scenarios where accurate feedback is difficult to achieve due to the l******cy in the PMI reporting.