PDCCH modulationV15.8.0

Control-channel element (CCE)

A physical downlink control channel consists of one or more control-channel elements (CCEs) as indicated in Table 7.3.2.1-1. I.e., the aggregation level equals number of CCEs per PDCCH. Higher level means lower coding rate, is more suitable for UEs with poor channel conditions.

A control-resource set consists of resource blocks in the frequency domain and symbols in the time domain.

A control-channel element consists of 6 resource-element groups (REGs) where a resource-element group equals one resource block during one OFDM symbol. Resource-element groups within a control-resource set are numbered in increasing order in a time-first manner, starting with 0 for the first OFDM symbol and the lowest-numbered resource block in the control resource set.

A UE can be configured with multiple control-resource sets. Each control-resource set is associated with one CCE-to-REG mapping only.

The CCE-to-REG mapping for a control-resource set can be interleaved or non-interleaved and is described by REG bundles:

• REG bundle i is defined as REGs {iL, iL+1,...,iL+L-1} where L is the REG bundle size, is the number of REGs in the CORESET
• CCE j consists of REG bundles { f(6j/L), f(6j/L+1),...,f(6j/L+6/L-1)} where f(·) is an interleaver.
  • For non-interleaved CCE-to-REG mapping, L = 6 and f(x) = x.
  • For interleaved CCE-to-REG mapping, and . The interleaver is defined bywhere R ∈ {2,3,6}.

The UE is not expected to handle configurations resulting in the quantity C not being an integer.

For a CORESET configured by the ControlResourceSet IE:

• is given by the higher-layer parameter frequencyDomainResources;
• is given by the higher-layer parameter duration, where is supported only if the higher-layer parameter dmrs-TypeA-Position (part of ServingCellConfigCommon) equals 3;
• interleaved or non-interleaved mapping is given by the higher-layer parameter cce-REG-MappingType;
• L equals 6 for non-interleaved mapping and is given by by the higher-layer parameter reg-BundleSize for interleaved mapping;
• R is given by the higher-layer parameter interleaverSize;
• n_shift ∈ {0,1,...,274} is given by the higher-layer parameter shiftIndex if provided, otherwise ; What it means: n_shift applies a cyclic shift to the interleaving pattern. The cyclic shift moves the CCE pattern upwards, with wraparound from the top to the bottom.
• for both interleaved and non-interleaved mapping, the UE may assume
  • the same precoding being used within a REG bundle if the higher-layer parameter precoderGranularity equals sameAsREG-bundle;
  • the same precoding being used across the all resource-element groups within the set of contiguous resource blocks in the CORESET, and that no resource elements in the CORESET overlap with an SSB or LTE cell-specific reference signals as indicated by the higher-layer parameter lte-CRS-ToMatchAround, if the higher-layer parameter precoderGranularity equals allContiguousRBs.
  What it means: PDCCH and DMRS are transmitted using a single antenna port (2000). 3GPP hasn't specified the precoding for PDCCH but base station can apply precoding to this antenna port to generate a beam in the direction of the UE. The precoding is transparent to the UE. The same precoding is applied to both PDCCH and DMRS so the UE can use the DMRS to estimate the composite impact of both the precoding and the propagation channel. UE shall know the freequency selectivity of the precoding applied by the base station.

For CORESET 0 configured by the ControlResourceSetZero IE:

• are defined by clause 13 of TS 38.213
• the UE may assume interleaved mapping
• L = 6;
• R = 2;
• the UE may assume normal cyclic prefix when CORESET 0 is configured by MIB or SIB1;
• the UE may assume the same precoding being used within a REG bundle.

Scrambling

The UE shall assume the block of bits b(0), ..., b(M_bit-1), where M_bit is the number of bits transmitted on the physical channel, is scrambled prior to modulation, resulting in a block of scrambled bits according to

where the scrambling sequence c(i) is given by scrambling. The scrambling sequence generator shall be initialized with

where

• for a UE-specific search space as defined in clause 10 of TS 38.213, n_ID ∈ {0,1,...,65535} equals the higher-layer parameter pdcch-DMRS-ScramblingID if configured
• otherwise

and where

• n_RNTI is given by the C-RNTI for a PDCCH in a UE-specific search space if the higher-layer parameter pdcch-DMRS-ScramblingID is configured, and
• n_RNTI=0 otherwise.

PDCCH modulation

The UE shall assume the block of bits to be QPSK modulated as described in modulation, resulting in a block of complex-valued modulation symbols d(0),...,d(M_symb-1).

Mapping to physical resources

The UE shall assume the block of complex-valued symbols d(0),...,d(M_symb-1) to be scaled by a factor β_PDCCH and mapped to resource elements (k,l)_p,μ used for the monitored PDCCH and not used for the associated PDCCH DMRS in increasing order of first k, then l. The antenna port p=2000.