5G/NR - RNTI  

 

 

 

RNTI

RNTI stands for Radio Network Temporary Identifier. This is exactly same concept as LTE RNTI. So I would suggest you to read LTE RNTI part first and get the general understandings on how this works.

In short, you can think of RNTI is the CRC mask that is required to decode DCI message. Each of the DCI needs its own specific RNTI for UE to decode it. There are some common RNTI that is shared by every UE (e.g, SI-RNTI, P-RNTI etc), but most of the DCI requires a specific RNTI that is assigned to a specific UE.

Is there any specific RNTI values for a specific UE  and Specific DCI type?

Some DCI uses (is masked by) a specific predefined RNTI that is common to every UE.  SI-RNTI, P-RNTI, MCCH-RNTI, PEI-RNTI belong to this category.

All other types of DCI uses (is masked by) a RNTI that is assigned to a specific individual UE or a specific group of UEs

<  38.321 v17.1 - Table 7.1-1: RNTI values. >

What kind of RNTI should be used ?

This is determined by the type of the DCI and Physical channel that a UE need to decode. These are well summarized by 3GPP specification as shown below.

<  38.202 v17.2 - Table 6.2-1: Downlink "Reception Types" >

Reception Type

Physical Channel

Monitored RNTI

Associated Transport Channel

Comment

A

PBCH

N/A

BCH

B

PDCCH+PDSCH

SI-RNTI

DL-SCH

Note 1

C0

PDCCH

P-RNTI

N/A

Note 1, Note 2

C1

PDCCH+PDSCH

P-RNTI

PCH

D0

PDCCH+PDSCH

RA-RNTI or Temporary C-RNTI or MsgB-RNTI

DL-SCH

Note 3

D1

PDCCH+PDSCH

C-RNTI, CS-RNTI, MCS-C-RNTI

DL-SCH

D2

PDCCH

C-RNTI, CS-RNTI, MCS-C-RNTI

DL-SCH

D3

PDCCH+PDSCH

G-RNTI, G-CS-RNTI

DL-SCH

Note 6

D4

PDCCH

G-CS-RNTI

N/A

Note 7

D5

PDCCH+PDSCH

MCCH-RNTI

DL-SCH

Note 8

D6

PDCCH+PDSCH

G-RNTI

DL-SCH

Note 9

E

PDCCH

C-RNTI

N/A

Note 4

F0

PDCCH

Temporary C-RNTI

UL-SCH

Note 3

F1

PDCCH

C-RNTI, CS-RNTI, MCS-C-RNTI

UL-SCH

G

PDCCH

SFI-RNTI

N/A

H

PDCCH

INT-RNTI

N/A

J0

PDCCH

TPC-PUSCH-RNTI

N/A

J1

PDCCH

TPC-PUCCH-RNTI

N/A

J2

PDCCH

TPC-SRS-RNTI

N/A

K

PDCCH

SP-CSI-RNTI

N/A

L0

PDCCH

SL-RNTI

SL-SCH

L1

PDCCH

SL-CS-RNTI

SL-SCH

M

PDCCH

SL Semi-Persistent Scheduling V-RNTI

SL-SCH

Note 5

N

PDCCH

PS-RNTI

N/A

O

PDCCH

AI-RNTI

N/A

P

PDCCH

CI-RNTI

N/A

Q

PDCCH

PEI-RNTI

N/A

Note 1

Note 1: These are received from PCell only.

Note 2: In some cases UE is only required to monitor the short message within the DCI for P-RNTI.

Note 3: These are received from PCell or PSCell.

Note 4: This corresponds to PDCCH-ordered PRACH.

Note 5: This corresponds to PDCCH scheduling LTE PC5.

Note 6: This is for multicast in RRC connected state.

Note 7: This corresponds to DL Semi-Persistent Scheduling release for multicast in RRC connected state.

Note 8: This is for broadcast MCCH.

Note 9: This is for broadcast MTCH. UE is not required to decode more than one PDSCH for MTCH simultaneously.

Should a UE has to try all different types of RNTI listed in the table above all the time to decode necessary DCIs ? It would be OK for UE to try all the RNTI, but it would be too much overhead and energy consuming. Usually there are only a few RNTI candiates for a specific call status. What kind of candidate RNTI is likely to be used for specific RRC States are summarized in 3GPP specification as shown below.

NOTE : Since the decoding of DCI is related to various search space, the note on SearchSpace would give you further insight

<  38.202 v17.2 - Table 6.2-2: Downlink Reception Type Combinations >

      q : the number of downlink component carriers configured for the UE

      j : the number of cell groups configured for the UE.

        j=1 indicates non-DC(non-Dual Connectivity)

        j=2 indicates NR-NR

Reference

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