Terms codeword, layer, and precoding have been taken to refer specifically to LTE signals and processing. The figure shows the processing steps to which they relate. The terms used in the following ways:
Codeword: codeword represents the user data before it is formatted for transmission. One or two code words, CW0 and CW1, may be used depending on the conditions of the channel and the use case. In the most common case of a single user MIMO (SU-MIMO), two codewords are sent to a single handset UE, but less common for downlink multi-user MIMO (MU-MIMO), each codeword is sent only one UE.
Layer: The term is synonymous with the current. For MIMO, the use of at least two layers. Up to four layers are allowed .The Number is always less than or equal to the number of antennas.
Precoding: Precoding layer modifies signals before transmission. This can be done diversity, spatial multiplexing, or beam direction. MIMO channel conditions may favor one layer (data stream) to another. If the base station (eNB) is given channel (e.g., the information sent back from the UE), the complex may be added to counter the imbalance cross-coupling in the channel. In arrangement 2 * 2, LTE uses a single stop 1 to 3 Precoding, which improves the performance if the channel has not changed too rapidly.