BWP concept is introduced in 5G because in most cases 5G will operate in very wide band. A Bandwidth Part is a set of attached Common Resource Blocks. A Bandwidth Part may include all Common Resource Blocks within the channel bandwidth, or a subset of Common Resource Blocks.
A UE can be configured with up to 4 DL BWP per carrier and up to 4 UL BWP per carrier. Only a single Bandwidth Part per carrier can be active in each direction. UE receives the PDCCH/PUCCH and PDSCH/PUSCH info only within an active DL & UL Bandwidth Part.
A UE uses an ‘Initial’ BWP when first accessing a cell. The Initial DL BWP will be sent within SIB1 using the initialDownlinkBWP parameter. If the parameter is not provided to a UE then the Initial DL BWP is defined by the set of Resource Blocks belonging to the Control Resource Set (CORESET) for the Type0 PDCCH Common Search Space.
BWP selection or switching will occur during UL grant by PDCCH, due to BWP Inactivity timer if the timer is defined, during RACH procedure. A specific BWP can become active depending on various situations in the call processing.
Source: Mohammed Saifuddin
Linkedin Profile: https://www.linkedin.com/in/mohammed-saifuddin-5a75b614/