Section: 6.8C.5 Mapping to resource elements
Content: The mapping to resource elements is defined by operations on vectors of complex-valued symbols. Let denotes symbol vector and represents the signal for antenna port. The block of vectors , shall be mapped in sequence starting with to resource elements on the associated antenna port(s) which meet all of the following criteria: - they are part of the SREGs assigned for the SPDCCH transmission, and - they are assumed by the UE not to be used for cell-specific reference signals, where the positions of the cell-specific reference signals are given by clause 6.10.1.2 with the number of antenna ports and the frequency shift of cell-specific reference signals derived as described in clause 6.10.1.2 unless other values for these parameters are provided by clause 9.1.4.3 in TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [4], and - they are assumed by the UE not to be used for transmission of: - UE-specific reference signal associated with SPDCCH - zero-power CSI reference signals, where the positions of the CSI reference signals are given by clause 6.10.5.2. The configuration for zero power CSI reference signals is - obtained as described in clause 6.10.5.2 unless other values are provided by clause 9.1.4.3 in TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [4], and - obtained by higher-layer configuration of up to five reserved CSI-RS resources as part of the discovery signal configuration following the procedure for zero-power CSI-RS in clause 6.10.5.2. - non-zero-power CSI reference signals for CSI reporting with the configuration for non-zero power CSI reference signals for CSI reporting obtained as described in clause 6.10.5.2. - The set of indices of where the SPDCCH can be mapped to is dependent on if slot or subslot based SPDCCH is used, the subslot number, if CRS or DMRS based SPDCCH is configured and the number of symbols used for PDCCH. In case CRS based SPDCCH is configured, the set of indices is also dependent on the number of symbols, , configured by higher layers (see spdcch-NoOfSymbols in TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [9]), that the SPDCCH is mapped over. - For slot-SPDCCH and for frame structure type 1 and 2, the set of indices of for the second slot in the subframe is given in Table 6.8C.5-1. It can be noted that no SPDCCH is transmitted in the first slot of the subframe, where the DCI instead is carried in PDCCH, see [3]. - For subslot-SPDCCH and for frame structure type 1, the set of indices of for a given downlink subslot number in a subframe is given in Table 6.8C.5-2. It can be noted that for subslot number 0 where no SPDCCH is transmitted, and the DCI is instead carried in PDCCH, see [3]. If has been precoded according to clause 6.3.4.3 and if there is an uneven number of resource elements per PRB that fulfil all the above criteria, is not mapped to the resource element of the PRB with largest . Resource elements belonging to synchronization signals, the core part of PBCH, PBCH repetitions, or resource elements reserved for reference signals in the mapping operation of PBCH but not used for transmission of reference signals, shall be assumed available in the SPDCCH mapping but not used for transmission of SPDCCH. NOTE: For DMRS based SPDCCH, the UE is not required to use the PRGs of size 2 (see TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [4]) which is/are partially overlapped with PBCH/PSS/SSS for SPDCCH monitoring. For DMRS based SPDCCH, the mapping to resource elements on antenna port , meeting the criteria above, shall be in increasing order of first the index and then the index . For localized and distributed CRS based SPDCCH, the SREGs of a SPDCCH candidate are first interleaved according to step 1 below and then the modulated symbols are mapped to resource elements of the interleaved SREGs according to step 2 below. - Step 1: Perform a block interleaver on the SREGs building the SPDCCH candidate, where the number of rows equal to the number of SCCEs for the SPDCCH candidate and the number of columns equal to 4 (i.e. the number of SREGs in an SCCE). The SREGs are written into the matrix row by row and read out column by column. - Step 2: The modulated symbols are mapped in sequence starting with to resource elements on antenna port in increasing order of the index k, meeting the criteria above, over the interleaved SREGs in the order given by the block interleaver of step 1. Table 6.8C.5-1: Set of indices of for slot-SPDCCH Table 6.8C.5-2: Set of indices of for subslot-SPDCCH