UE and Network Identifiers
- NR UE uses temporary identifiers to communicate gNB.
- RNTI is 16-bit identifier and its value depends on type of RNTI.
- Many RNTI of LTE and NR are same.
- Below are the identifiers as per 38.321 for NR :
C-RNTI: Cell RNTI A unique UE identification used as an identifier of the RRC connection and for scheduling purposes. The gNB assigns different C-RNTI values to different UEs. CRNTI is used by gNB to differentiate uplink transmissions (e.g. PUSCH, PUCCH) of a UE from others.
SI-RNTI: System Information RNTI is used for broadcasting System information.SI-RNTI is of 16 bit length. Broadcast of SI uses BCCH-DL-SCH-PDSCH.
P-RNTI: Paging RNTI is used by UE reception of paging. It is not allocated to any UE explicitly. It is of 16-bit in length. Paging message is carried by PCCH-PCH-PDSCH.
RA-RNTI: RA-RNTI is used for Random Access procedure .gNB’s MAC generates Random Access Response (RAR) as a response to the Random Access Preamble transmitted by the UE.RA-RNTI can be addressed to multiple UEs, i.e., multiple UEs might decode PDCCH scrambled by the same.
TC-RNTI: This RNTI is also used in Random access procedure. gNB’s MAC generates Random Access Response (RAR) as a response to the Random Access Preamble transmitted by the UE. MAC RAR contains Temporary C-RNTI. During contention based random access procedure, the UE stores received Temp C-RNTI (received in RAR) and uses it during random access procedure. The UE shall discard the Temporary C-RNTI value received in RAR during non-contention based random access procedure. The UE shall use Temp C-RNTI for scrambling of msg3.
TPC RNTI : This TPC RNTI is knows as Transmit Power Control RNTI. This RNTI is basically used for uplink power control purpose.
This TPC-RNTI is assigned to a group of UEs.TPC-RNTI is divided into 3 types :
- TPC-PUCCH-RNTI :Transmit Power Control-PUCCH – RNTI
- TPC-PUSCH-RNTI :Transmit Power Control-PUSCH – RNTI
- PC-SRS-RNTI : Transmit Power Control-Sounding Reference Symbols – RNTI
MCS-C-RNTI : This MCS-C-RNTI is knows as Modulation and Coding Scheme Cell RNTI.
CS-RNTI: This RNTI is know as Configured Scheduling RNTI.
INT-RNTI: This RNTI is know as Interruption RNTI. This is an identification of preemption in downlink.
SFI-RNTI: This RNTI is know as Slot Format Indication RNTI.
SP-CSI- -RNTI: This RNTI is know as Semi-Persistent CSI RNTI reporting on PUSCH.
Radio network temporary identifiers (RNTIs) in NR and their usage