Is MSG4 in NR scrambled with TC-RNTI or C-RNTI?
It is TC-RNTI which becomes the C-RNTI for that UE after MSG4 onwards (if contention is resolved).
If UE has already a valid C-RNTI then MSG4 will be C-RNTI scremabled only.
Otherwise case TC-RNTI scrambled.
Id UE already have C-RNTI then why there will be an exchange of msg3 and msg4?
Do idle UE can have valid c-RNTI?
Only connected and inactive UE will have valid c-RNTI stored in UE, I guess.
Exactly that’s what my understanding is.
So UE won’t have a valid C-RNTI for MSG4.
Only case where UE can have valid C-RNTI is when RACH performed for UL sync purpose.
In all other cases, TC- RNTI will be there which then converted to C-RNTO in MSG4.
Only if the UE decodes msg4 successfully.