NCD-SSB and CD-SSB BWP Use Case in REDCAP NR

Let’s discuss NCD-SSB and CD-SSB of REDCAP BWP UseCase. I already discuss the REDCAP NR Light use case and capabilities and REDCAP BWP in detail, please refer to the article read here.

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The InitialDownlinkBWP and InitialUplinkBWP are defined for RedCap and they are defined by initialDownlinkBWP-redcap and inititalUplinkBWP-redcap. The REDCAP UE is going to read these BWP’s and configured the parameters accordingly.

DownlinkConfigCommon field descriptions

frequencyInfoDL Basic parameters of a downlink carrier and transmission thereon.

initialDownlinkBWP The initial downlink BWP configuration for a serving cell. The network configures the locationAndBandwidth so that the initial downlink BWP contains the entire CORESET#0 of this serving cell in the frequency domain.

initialDownlinkBWP-RedCap If present, RedCap UEs use this DL BWP instead of initialDownlinkBWP. If absent, RedCap UEs use initialDownlinkBWP provided that it does not exceed the RedCap UE maximum bandwidth (see also clause 5.2.2.4.2).

UplinkConfigCommonSIB field descriptions

frequencyInfoUL Absolute uplink frequency configuration and subcarrier specific virtual carriers.

InitialUplinkBWP The initial uplink BWP configuration for a PCell (see TS 38.213 [13], clause 12).

initialUplinkBWP-RedCap If present, RedCap UEs use this UL BWP instead of initialUplinkBWP. If absent, RedCap UEs use initialUplinkBWP provided that it does not exceed the RedCap UE maximum bandwidth (see also clause 5.2.2.4.2).

If the REDCAP-specific BWPs are not present, then UE is working in Shared BWP mode which means the RedCap UE would also configure parameters based on InitialBWP’s (Non-RedCap).

Also Read:- What is REDCAP (Reduced Capability) in NR 3GPP R17 Release?

To conclude the configuration of BWP:

Shared BWP Mode: RedCap UE using the InitialBWP’s

Separate BWP Mode: RedCap UE using RedCap-specific InitialBWP’s

As per 3Gpp 38.331, Annex B-2 BWP Option 1 and Option 2 are below:

NCD SSB (non-Cell defining SSB) important IE’s for REDCAP UE.

Reference from 3GPP Specification 38.331 V17.3.0, below are the IE of the NCD SSB and CD SSB. you can see these IE in Logs of UE and Simulator logs to confirm that it’s correct.

Note:- CD-SSB IE is normal, SSB ie which are similar to SIB 1 SSB ie so here I have mentioned IE only for NCD-SSB.

NCD-SSB IE (Non-CellDefiningSSB) in RRC reconfiguration and RRC setup MSG

detailed IE for NCD-SSB in RRC reconfiguration and RRC setup MSG

NCD-SSB and CD-SSB BWP Use Case for Redcap or NR-Light.

-Initial Shared BWP with CD-SSB
-Initial Separate BWP without CD-SSB
-Initial Separate BWP with CD-SSB
-UE-Specific BWP with CD—SSB
-UE-Specific BWP with NCD-SSB

The current R17 version that REDCAP UEs in RRC_IDLE and RRC_INACTIVE states only monitor paging at the initial BWP associated with CD-SSB (which can be default BWP or REDCAP-specific BWP) and perform cell reselection by measuring CD-SSB. The definition of CD-SSB in the specification can be shown below.

If a REDCAP-specific initial UL BWP is configured, the REDCAP UE in the RRC_IDLE and RRC_INACTIVE states will only initiate RA on the Initial UL BWP.

Multiple NCD-SSB (Non-Cell Defining SSBs) can be configured for REDCAP UE, but each BWP can be configured with a maximum of one SSB. When RRC_CONNECTED, when the active BWP does not contain CD-SSB, you can configure RLM, BFD and service cell to measure NCD-SSB.

Initial Shared BWP with CD-SSB:

–Only Initial BWP is configured and initialRedcap BWP is configured because initial BWP bandwidth is <=20MHZ Redcap UE can still select this initial BWP.

– CD-SSB must locate inside the initial BWP.

Initial Separate BWP without CD-SSB

-Both initial BWP is configured and initialRedCap BWP is configured

-Initial BWP and Initial RedCap BWP are partially or not overlapped.

-CD-SSB must locate inside the initial BWP but not inside the initialRedCap BWP.

Initial Separate BWP with CD-SSB

-Both initial BWP is configured and initial Redcap BWP is configured

-Initial BWP and Initial RedCap BWP are partially or fully overlapped.

-CD-SSB must locate inside the initial BWP and inside the initial Redcap BWP.

UE-Specific BWP with CD SSB

-Both Initial BWP is configured, and initial RedCap BWP is configured.

-CD-SSB can locate inside and outside initial RedCap BWP.

-CD-SSB can locate inside a dedicated BWP.

-For Case A: CD-SSB locate inside initial RedCap BWP, initial RedCap BWP and dedicated BWP can be partially or fully overlapped.

-For Case B: CD-SSB locate outside initial RedCap BWP, initial RedCap BWP and dedicated BWP can be partially or not overlapped.

-BWP switch between dedicated BWP and initial RedCap BWP.

NCD-SSB with UE-Specific BWP

-Both initial BWP is configured, and initial RedCap BWP is configured.

-CD-SSB can locate inside or outside RedCap BWP.

-CD-SSB locate outside the dedicated BWP and NCD-SSB location inside the dedicated BWP.

Final Words for NCD-SSB and CD-SSB:-

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