10.2.5 Narrowband physical downlink control channel

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

10.2.5.1 NPDCCH formats

The narrowband physical downlink control channel carries control information. A narrowband physical control channel is transmitted on an aggregation of one or two consecutive narrowband control channel elements (NCCEs), where a narrowband control channel element corresponds to 6 consecutive subcarriers in a subframe where NCCE 0 occupies subcarriers 0 through 5 and NCCE 1 occupies subcarriers 6 through 11. The NPDCCH supports multiple formats as listed in Table 10.2.5.1-1. For NPDCCH format 1, both NCCEs belong to the same subframe.

One or two NPDCCHs can be transmitted in a subframe.

Table 10.2.5.1-1: Supported NPDCCH formats

NPDCCH format	Number of NCCEs
0	1
1	2

10.2.5.2 Scrambling

Scrambling shall be done according to clause 6.8.2. The scrambling sequence shall be initialised at the start of subframe k₀ according to [4] Clause 16.6 and after every 4^th NPDCCH subframe with where is the first slot of the NPDCCH subframe in which scrambling is (re-)initialized.

10.2.5.3 Modulation

Modulation shall be done according to clause 6.8.3 using the modulation scheme in Table 10.2.5.3-1

Table 10.2.5.3-1: Modulation schemes

Physical channel	Modulation schemes
NPDCCH	QPSK

10.2.5.4 Layer mapping and precoding

Layer mapping and precoding shall be done according to clause 6.6.3 using the same set of antenna ports as the NPBCH.

10.2.5.5 Mapping to resource elements

The block of complex-valued symbols shall be mapped in sequence starting with to resource elements on the associated antenna port which meet all of the following criteria:

– they are part of the NCCE(s) assigned for the NPDCCH transmission, and

– they are not used for transmission of NPBCH, NPSS, or NSSS, and

– except in a special subframe when NPDCCH is transmitted in more than one subframe, they are assumed by the UE not to be used for NRS, and

– they are not overlapping with resource elements used for CRS as defined in clause 6 (if any), and

– the index in the first slot in a subframe fulfils where is given by clause 16.6.1 of TS 36.213 [4],

– in addition, for frame structure Type 2,

– in a special subframe where the NPDCCH is transmitted in one subframe, they are in DwPTS

– in a special subframe where the NPDCCH is transmitted in more than one subframe, they are not NRS locations when the subframe is not a special subframe.

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, starting with the first slot and ending with the second slot in a subframe. Denote as the complex-valued symbols that are mapped to resource elements meeting the criteria above in subframe , with the insertion of <NIL> elements in the locations of resource elements which are not part of the NCCE(s) assigned for the NPDCCH transmission.

If the NPDCCH is transmitted in more than one subframe, the resource elements in a special subframe that are not part of DwPTS are counted but not used in the mapping. When , the resource elements in a special subframe assumed by the UE for NRSs are counted but not used in the mapping if the NPDCCH is transmitted in more than one subframe.

For frame structure type 1,

– for NPDCCH associated with RA-RNTI, TC-RNTI or

– for P-RNTI and transmitted in an NB-IoT carrier configured by SystemInformationBlockType22-NB, or

– for NPDCCH associated with C-RNTI in an NB-IoT carrier configured by SystemInformationBlockType22-NB when RadioResourceConfigDedicted-NB is not configured by higher layer, or

– for NPDCCH associated with PUR-RNTI/G-RNTI/ SC-RNTI, or

– for NPDCCH associated with C-RNTI or SPS C-RNTI when interferenceRandomisationConfig is used according to [9], or

for frame structure type 2,

each complex-valued symbol , shall be multiplied with ,where

where the scrambling sequence is given by clause 7.2 and shall be initialized at the start of each subframe with .

The NPDCCH transmission can be configured by higher layers with transmissions gaps where the NPDCCH transmission is postponed. The configuration is the same as described for NPDSCH in clause 10.2.3.4.

The UE shall not expect NPDCCH in subframe if it is not a NB-IoT downlink subframe. In case of NPDCCH transmissions, in subframes that are not NB-IoT downlink subframes, the NPDCCH transmission is postponed until the next NB-IoT downlink subframe.

If higher layer parameter resourceReservationConfigDL is configured, then in case of NPDCCH transmission associated with C-RNTI or SPS C-RNTI using UE-specific NPDCCH search space,

– In a subframe that is fully reserved as defined in clause 16.4 in [4], the NPDCCH transmission is postponed until the next NB-IoT downlink subframe that is not fully reserved.

– In a subframe that is partially reserved, the reserved OFDM symbols shall be counted in the NPDCCH mapping but not used for transmission of the NPDCCH.