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Radio Network Temporary Identifier (RNTI) in 5G-NR

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

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