Point A
Point A serves as a common reference point for resource block grids and is obtained from:
- offsetToPointA for a PCell downlink where offsetToPointA represents the frequency offset between point A and the lowest subcarrier of the lowest resource block, which has the subcarrier spacing provided by the higher-layer parameter subCarrierSpacingCommon and overlaps with the SS/PBCH block used by the UE for initial cell selection, expressed in units of resource blocks assuming 15 kHz subcarrier spacing for FR1 and 60 kHz subcarrier spacing for FR2. Or,
- absoluteFrequencyPointA for all other cases where absoluteFrequencyPointA represents the frequency-location of point A expressed as in ARFCN.
Rules (TS 38.211 section 7.4.3.1):
- for SS/PBCH block type A, and with the quantities , and expressed in terms of 15 kHz subcarrier spacing
- for SS/PBCH block type B, and with the quantity expressed in terms of the subcarrier spacing provided by the higher-layer parameter subCarrierSpacingCommon and expressed in terms of 60 kHz subcarrier spacing
- the centre of subcarrier 0 of resource block coincides with the centre of subcarrier 0 of a common resource block with the subcarrier spacing provided by the higher-layer parameter subCarrierSpacingCommon. This common resource block overlaps with subcarrier 0 of the first resource block of the SS/PBCH block.
| Parameter | Value | Explanation | FR1 | FR2 |
|---|---|---|---|---|
| ssbSubcarrierSpacing | Subcarrier spacing of SSB | 15 or 30 kHz | 120 or 240 kHz | |
| subCarrierSpacingCommon | Subcarrier spacing of the CRB that overlaps with subcarrier 0 of the first RB of the SSB. It limits the possible values of . | 15 or 30 kHz | 60 or 120 kHz | |
| subcarrierSpacing for | 15 kHz | 15 kHz | subcarrierSpacing Common | |
| subcarrierSpacing for | 15 kHz | 15 kHz | 60 kHz | |
| (ssb-SubcarrierOffset) | subcarrier offset from subcarrier 0 in CRB to subcarrier 0 of the SSB | 0~23 | 0~11 | |
| (offsetToPointA) | expressed in terms of 15/60 kHz SCS for FR1/FR2. | |||
| From pointA to SSB start | 0.735MHz | |||
Common resource blocks
Common resource blocks are numbered from 0 and upwards in the frequency domain for subcarrier spacing configuration μ. The center of subcarrier 0 of common resource block 0 for subcarrier spacing configuration μ coincides with 'point A', where 'point A' serves as a common reference point for resource block grids.
The relation between the common resource block number in the frequency domain and resource elements (k, l) for subcarrier spacing configuration μ is given by , where k is defined relative to point A such that k=0 corresponds to the subcarrier centered around point A, . Every consecutive subcarriers in the frequency domain form a resource block.