What is the BW part in NR? and useful cases?

The channel BW in case of LTE is max 20 (without CA) and with CA it can support up to 100mhz.
In case of 5G NR,Fr2 the maximum channel BW is 400Mhz(with 4CC). BWP feature in simple words the GNB restrict the certain PRB for the UE for scan in the frequency domain.

Here below are the two main reasons for which usage of BWP is required in Case of NR:

1. Cheaper devices may no want to support the whole BW.
2. A devices don’t need to monitor the whole bandwidth to reduce the battery power consumption.

Here below are the major points for the BWP:

1. With the BWP can handle different type of the UE’s which cannot support the large bandwidth.
2. BWP can be configured with different SCS within the same carrier each BWP part can support different services.
3. BWP reduce the UE power consumption because UE’s are scanning the small bandwidth portion(20MHZ etc..) instead of large BW (100MHZ etc..)
4. BWP is characterized by the numerology and CP.
5. A UE can configure up to 4 BWP in DL or in UL.
6. The BWP size should be more than the SSB size which is 20 PRB.
7. Each BWP has its own coreset and search space.
8. BWP switching can be triggered DCI based or BWP inactivity timer.

BWP Types:

1. Initial BWP: this BWP is common for all the UE which are latching with the network and reading SIB1 message which contain the initial BWP information. All RRC signaling is going through the initial BWP. In the RRC reconfiguration message the GNB decide if the BWP needs to keep the same or switch.
2. Default BWP: this is the BWP part for fall back ,where there is UE on different BWP and the inactivity timer get expire and the UE fall back to this default BWP.
3. First active BWP: The first BWP when the UE is active on, upon reception of the RRC message carrying the BWP ID.

Disadvantage:
There is no resources in UL and DL getting scheduled during the bandwidth part switching and latency can be effected.