6.3.4 Precoding

36.2113GPPEvolved Universal Terrestrial Radio Access (E-UTRA)Physical channels and modulationRelease 17TS

The precoder takes as input a block of vectors, from the layer mapping and generates a block of vectors, to be mapped onto resources on each of the antenna ports, where represents the signal for antenna port.

6.3.4.1 Precoding for transmission on a single antenna port

For transmission on a single antenna port, precoding is defined by

where is the number of the single antenna port used for transmission of the physical channel and , .

6.3.4.2 Precoding for spatial multiplexing using antenna ports with cell-specific reference signals

Precoding for spatial multiplexing using antenna ports with cell-specific reference signals is only used in combination with layer mapping for spatial multiplexing as described in clause 6.3.3.2. Spatial multiplexing supports two or four antenna ports and the set of antenna ports used is or, respectively.

6.3.4.2.1 Precoding without CDD

Without Cyclic Delay Diversity (CDD), precoding for spatial multiplexing is defined by

where the precoding matrix is of size and , .

For spatial multiplexing, the values of shall be selected among the precoder elements in the codebook configured in the eNodeB and the UE. The eNodeB can further confine the precoder selection in the UE to a subset of the elements in the codebook using codebook subset restrictions. The configured codebook shall be selected from Table 6.3.4.2.3-1 or 6.3.4.2.3-2.

6.3.4.2.2 Precoding for large delay CDD

For large-delay CDD, precoding for spatial multiplexing is defined by

where the precoding matrixis of size and , . The diagonal size-matrix supporting cyclic delay diversity and the size- matrix are both given by Table 6.3.4.2.2-1 for different numbers of layers .

The values of the precoding matrix shall be selected among the precoder elements in the codebook configured in the eNodeB and the UE. The eNodeB can further confine the precoder selection in the UE to a subset of the elements in the codebook using codebook subset restriction. The configured codebook shall be selected from Table 6.3.4.2.3-1 or 6.3.4.2.3-2.

For 2 antenna ports, the precoder is selected according to where denotes the precoding matrix corresponding to precoder index 0 in Table 6.3.4.2.3-1.

For 4 antenna ports, the UE may assume that the eNodeB cyclically assigns different precoders to different vectors on the physical downlink shared channel as follows. A different precoder is used every vectors, where denotes the number of transmission layers in the case of spatial multiplexing. In particular, the precoder is selected according to , where is the precoder index given by and denote precoder matrices corresponding to precoder indices 12,13,14 and 15, respectively, in Table 6.3.4.2.3-2.

Table 6.3.4.2.2-1: Large-delay cyclic delay diversity

Number of layers
2
3
4

6.3.4.2.3 Codebook for precoding and CSI reporting

For transmission on two antenna ports, , and for the purpose of CSI reporting based on two antenna ports or , the precoding matrix shall be selected from Table 6.3.4.2.3-1 or a subset thereof. For the closed-loop spatial multiplexing transmission mode defined in TS 36.213 [4], the codebook index 0 is not used when the number of layers is .

Table 6.3.4.2.3-1: Codebook for transmission on antenna ports and for CSI reporting based on antenna ports or

Codebook index	Number of layers
	1	2
0
1
2
3		–

For transmission on four antenna ports, , the precoding matrix shall be selected from Table 6.3.4.2.3-2 or a subset thereof. For the purpose of CSI reporting based on four antenna ports or , the precoding matrix shall be selected from Table 6.3.4.2.3-2 or a subset thereof except for alternativeCodeBookEnabledFor4TX-r12 =TRUE in which case the precoding matrix shall be selected from Tables 7.2.4-0A, 7.2.4-0B, 7.2.4-0C, 7.2.4-0D in [4] or a subset thereof, and except for advancedCodebookEnabled = TRUE in which case the precoding matrix shall be selected from Table 7.2.4-17C in [4] or a subset thereof. The quantity denotes the matrix defined by the columns given by the set from the expression where is the identity matrix and the vector is given by Table 6.3.4.2.3-2.

Table 6.3.4.2.3-2: Codebook for transmission on antenna ports and for CSI reporting based on antenna ports or

Codebook index		Number of layers
		1	2	3	4
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

For the purpose of CSI reporting for 8, 12, 16, 20, 24, 28, and 32 CSI reference signals the codebooks are given in clause 7.2.4 of TS 36.213 [4].

6.3.4.3 Precoding for transmit diversity

Precoding for transmit diversity is only used in combination with layer mapping for transmit diversity as described in clause 6.3.3.3. The precoding operation for transmit diversity is defined for two and four antenna ports.

For transmission on two antenna ports, , the output , of the precoding operation is defined by

for with .

For rank=1 transmission on two antenna ports, , the output , of the precoding operation is defined by

where .

For transmission on four antenna ports,, the output , of the precoding operation is defined by

for with .

6.3.4.4 Precoding for spatial multiplexing using antenna ports with UE-specific reference signals

Precoding for spatial multiplexing using antenna ports with UE-specific reference signals is only used in combination with layer mapping for spatial multiplexing as described in clause 6.3.3.2. Spatial multiplexing using antenna ports with UE-specific reference signals supports up to eight antenna ports.

If the higher-layer parameter dmrs-tableAlt is set to TRUE and the set of antenna ports is used for two layers transmission, the precoding operation for transmission on the two antenna ports is defined by

where , .

If the higher-layer parameter semiOpenLoop is set to TRUE for subframe PDSCH or the higher-layer parameter semiOpenLoop-STTI is set to TRUE for slot/subslot PDSCH and the set of antenna ports is used for rank=2 transmission, the precoding operation for transmission on the two antenna ports is defined by

where and .

If the number of codewords is two and the DCI associated with the scheduled PDSCH is of Format 2D and the ‘PDSCH RE Mapping and Quasi-Co-Location indicator’ field in the DCI indicates a higher-layer configured PDSCH-RE-MappingQCL containing two sets of parameters, the precoding operation for transmission on antenna ports is defined by

where , and set of antenna ports used is given by Table 6.3.4.4-1.

Table 6.3.4.4-1: Layer-to-port mapping for two-codeword transmission when PDSCH-RE-MappingQCL contains two sets of parameters

Number of layers	Layer-to-port mapping
2
3
4
5
6
7
8

Otherwise, the set of antenna ports used is and the precoding operation for transmission on antenna ports is defined by

where , .