5G/NR - 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" >

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.

<  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