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Lte C Rnti Assignment Of Mortgage

 

 

 

RNTI

 

One of the other numbers which you would very frequently come accross is RNTI. RNTI stands for Radio Network Temporary Identifier.

As the name implies, it is a kind of Identification number. Normally we use indentification number to differntiate one thing from all other similar things. For example, your driver's license number let you identify yourself from all other drivers. Social Security number do the same thing as well.

 

Getting more specifically into LTE, this RNTI is used to indentify one specific radio channel from other radio channel and one user from another user. As you may recall, in WCDMA is a RNTI concept which is carried as part of MAC header to deferentiate one user to another while in communication state. and in WCDMA case it used special channelization code to deferentiate one radio channel from the other.

 

Putting it very simply, you can think of RNTI as a kind of UE ID for the traffic between UE and eNB lower layer. But it would be more accurate to think of it as '[UE ID] + DCI Type ID' since each of DCI message (more precisely the CRC bits of each DCI) is scrambled by a specific RNTI Value. [UE ID] (UE ID in bracket) means that some RNTI is dedicated for a specific UE and some RNTI is not.

 

Then you may notice that there are not so many different DCI types but there are a huge set of RNTI types and ask how a few DCI types can be mapped to such a big number of RNTI types. Actually this is one of the thing you have to (or will) figure out as you read along this page.

 

Followings are the list of topics that will be described in this page.

 

 

Types of RNTIs

 

What kind of RNTIs are there in LTE ?

The answer is A LOT -:). Followings are the brief summary of RNTIs being used in LTE. More detailed explanation will be updated continuously later.

  • P-RNTI : It stands for Paging RNTI. Used for Paging Message.
  • SI-RNTI : It stands for System Information RNTI. Used for transmission of SIB messages
  • RA-RNTI : It stands for Random Access RNTI. Used for PRACH Response.
  • C-RNTI : It stands for Cell RNTI. Used for the transmission to a specific UE after RACH.
  • T-CRNTI : It stands for Temporary C-RNTI. Mainly used during RACH
  • SPS-C-RNTI : It stands for Semi persistance Scheduling C-RNTI
  • TPC-PUCCH-RNTI : It stands for Transmit Power Control-Physical Uplink Control Channel-RNTI
  • TPC-PUSCH-RNTI : It stands for Transmit Power Control-Physical Uplink Shared Channel-RNTI
  • M-RNTI : It stands for MBMS RNTI
  • CC-RNTI : It stands for Common Control RNTI
  • G-RNTI : It stands for Group RNTI
  • SC-RNTI : It stands for Single Cell RNTI
  • SL-RNTI : It stands for Sidelink RNTI
  • SC-N-RNTI : It stands for Single Cell Notification RNTI
  • eIMTA-RNTI : It stands for Enhanced Interference Management and Traffic Adaptation - RNTI

 

Who issues these RNTI ?

Network issues RNTI.

 

Exactly what does RNTI do for each of those radio channel ? The detailed process differs with the types of RNTIs, but generally speaking all of these RNTI is used to scramble the CRC part of the radio channel messages. It implies that if UE does not know the exact RNTI values for each of the cases, it cannot decode the radio channel messages even though the message reaches the UE intact.

 

One of the most common questions that I got about RNTI is "There are a lot of different types of RNTI and I don't see any RNTI information on DCI or Higher layer signaling message. Then how can PHY layer know which RNTI it has to use to decode a data ?". The answer is "MAC or Layer 1 controller would instruct PHY on which RNTI it has to be used". Then a next questions comes out. "How MAC or Layer 1 controller would know which RNTI to be used ?". There is no explicit algorithm for this, MAC/L1 controller needs to figure it out "based on context". For example, if it is at the subframe where SIB is transmitted, it would instruct PHY to use SI-RNTI. if UE is in connected mode, it may instruct to use C-RNTI, TPC RNTI etc.

 

There are a lot of tables related to RNTI Type and Specific Physical/MAC layer operation. It would not be easy to make any sense out of these tables, but just look into these tables as often as possible. As your understanding / knoledge of LTE PHY procedure, you would make more sense out of these tables.

 

Following table from 36.321 shows the range of values which is allocated for each RNTI types.

 

< 36.321 - Table 7.1-1: RNTI values. >

 

 

Following table from 36.321 shows the types of RNTIs and it's usage.

 

< 36.321 - Table 7.1-2: RNTI usage. >

 

 

Following table from 36.312 shows the relationships between types of RNTIs and DCI Format. You would notice that some DCI format can be scrambled by many other types of RNTI type. Then you may ask how PHY layer figure out which RNTI types it has to use to decode a certain DCI type.  It depends on communication status. For example, DCI Format 1A can be scrambled by SI-RNTI, P-RNTI, C-RNTI. In this case, UE will try something like followings

  • UE will use SI-RNTI if it is in idle mode and within SI-transmission window
  • UE will use P-RNTI if it is in idle mode and it is at the PO (Paging Occasion) subframe
  • UE will use C-RNTI while it is in commuincation status

 

 

< 36.213 - Table 7.1-1: PDCCH and PDSCH configured by SI-RNTI >

 

 

< 36.213 - Table 7.1-1A: PDSCH configured by SI-RNTI >

 

 

< 36.213 - Table 7.1-2: PDCCH and PDSCH configured by P-RNTI >

 

 

< 36.213 - Table 7.1-3: PDCCH and PDSCH configured by RA-RNTI >

 

 

< 36.213 - Table 7.1-5: PDCCH and PDSCH configured by C-RNTI >

 

 

< 36.213 - Table 7.1-7: PDCCH and PDSCH configured by Temporary C-RNTI >

 

 

 

How/Who determines each types of RNTI ?

 

RA-RNTI : UE determines RA-RNTI as explained in here in the RACH page.

T-CRNTI : Network allocate T-CRNTI via RAR as shown in here in the RACH page.

C-RNTI : T-CRNTI becomes C-RNTI once Contention Resolution gets passed.

 

 

How RNTI value is informed  ?

 

How a RNTI value is informed to the other party of the communication ? If you are mainly working on higher layer or in WCDMA, you may expect there is a specific signaling message or MAC field that carries this ID. But in LTE, this ID is embedded and carried to the other party in much lower layer. Also, there is no specific field to carry RNTI value itself. It is combined with CRC field of each Physical layer data as shown below (This is only one example for PDCCH case).

 

 

 

How each of RNTI is used ?

 

Following is the quotes from 3GPP specification showing how RNTI is used for various cases.. for the exact details, you should see the specification but this partial quote would give you a rough idea of the usage of RNTI.

 

From 36.212 -----------------------------------------------------------------------------------------------

 

5.3.3 Downlink control information

  • A DCI transports downlink or uplink scheduling information, or uplink power control commands for one RNTI. The RNTI is implicitly encoded in the CRC.

 

 

5.3.3.1.3 Format 1A

  • Format 1A is used for random access procedure initiated by a PDCCH order only if format 1A CRC is scrambledwith C-RNTI
  • For distributed VRB: .. if the format 1A CRC is scrambled by RA-RNTI, P-RNTI, or SI-RNTI

 

 

5.3.3.2 CRC attachment

  • This section explain in detail on how CRC is scrambled by RNTI. Following is the summary of this process. As you see, RNTI is used to scramble CRC bits of PDCCH.

 

 

From 36.213 ------------------------------------------------------------------------------------------------

 

Following is some examples of 3GPP description related to RNTI. Just to focus which type of DCI is scrambled by which RNTI Type.

 

5.1.1.1 UE behaviour

  • δ_PUSCH is a UE specific correction value, also referred to as a TPC command and is included in PDCCH with DCI format 0 or jointly coded with other TPC commands in PDCCH with DCI format 3/3A whose CRC parity bits are scrambled with TPC-PUSCH-RNTI
  • if the TPC command PUSCH δ_PUSCH is included in a PDCCH with DCI format 0 where the CRC is scrambled by the Temporary C-RNTI
  • The UE attempts to decode a PDCCH of DCI format 0 with the UE�s C-RNTI or SPS CRNTI and a PDCCH of DCI format 3/3A with this UE�s TPC-PUSCH-RNTI in every subframe

 

5.1.2.1 UE behaviour

  • δ_PUCCH is a UE specific correction value, also referred to as a TPC command, included in a PDCCH with DCI format 1A/1B/1D/1/2A/2 or sent jointly coded with other UE specific PUCCH correction values on a PDCCH with DCI format 3/3A whose CRC parity bits are scrambled with TPC-PUCCH-RNTI.
  • The UE attempts to decode a PDCCH of DCI format 3/3A with the UE�s TPC-PUCCH-RNTI and oneor several PDCCHs of DCI format 1A/1B/1D/1/2A/2 with the UE�s C-RNTI or SPS C-RNTI on every subframe except when in DRX.
  • If the UE decodes a PDCCH with DCI format 1A/1B/1D/1/2A/2 and the corresponding detected RNTI equals the C-RNTI or SPS C-RNTI of the UE, the UE shall use the δ PUCCH provided in that PDCCH.

 

6.1 Physical non-synchronized random access procedure

  • A preamble index, a target preamble received power (PREAMBLE_RECEIVED_TARGET_POWER), a corresponding RA-RNTI and a PRACH resource are indicated by higher layers as part of the request.
  • Detection of a PDCCH with the indicated RA-RNTI is attempted during a window controlled by higher layers

7.1 UE procedure for receiving the physical downlink shared channel

  • If a UE is configured by higher layers to decode PDCCH with CRC scrambled by the SI-RNTI, the UE shall decode the PDCCH and the corresponding PDSCH according to any of the combinations defined in table 7.1-1. The scrambling initialization of PDSCH corresponding to these PDCCHs is by SI-RNTI. // SI-RNTI scrambles the DCI for SIB messages.
  • If a UE is configured by higher layers to decode PDCCH with CRC scrambled by the P-RNTI, the UE shall decode the PDCCH and the corresponding PDSCH according to any of the combinations defined in table 7.1-2. The scrambling initialization of PDSCH corresponding to these PDCCHs is by P-RNTI. // P-RNTI scrambles the DCI for Paging message.
  • If a UE is configured by higher layers to decode PDCCH with CRC scrambled by the C-RNTI, the UE shall decode the PDCCH and any corresponding PDSCH according to the respective combinations defined in table 7.1-5. The scrambling initialization of PDSCH corresponding to these PDCCHs is by C-RNTI.
  • If a UE is configured by higher layers to decode PDCCH with CRC scrambled by the Temporary C-RNTI and is not configured to decode PDCCH with CRC scrambled by the C-RNTI, the UE shall decode the PDCCH and the corresponding PDSCH according to the combination defined in table 7.1-7. The scrambling initialization of PDSCHcorresponding to these PDCCHs is by Temporary C-RNTI.

 

What is RNTI?

RNTI stands for Radio Network Temporary Identifier. RNTIs are used to differentiate/identify a connected mode UE in the cell, a specific radio channel, a group of UEs in case of paging, a group of UEs for which power control is issued by the eNB, system information transmitted for all the UEs by the eNB etc…

There are a several RNTI types in LTE such as SI-RNTI, P-RNTI, C-RNTI, Temporary C-RNTI, SPS-CRNTI, TPC-PUCCH-RNTI, TPC-PUSCH-RNTI, RA-RNTI, and M-RNTI. Each RNTI’s usage, its value range etc…are discussed in detail below



SI-RNTI (System Information RNTI)

  • SI-RNTI is used for broadcast of system information.
  • It is a common RNTI meaning that, it is not allocated to any UE explicitly.
  • SI-RNTI is of 16-bit in length and its value is fixed to 65535 (0xFFFF). A single SI-RNTI is used to address SystemInformationBlockType1 as well as all SI messages
  • Broadcast of System Information uses BCCH logical channel which is then mapped to DL-SCH transport channel which intern mapped to PDSCH physical channel. The UEs should know the scheduling information for PDSCH which is carrying System Information. The required scheduling information is contained in DCI (Downlink Control Information) whose CRC is scrambled by SI-RNTI
  • DCI Formats which carries scheduling information for System Information are DCI Format 1A and DCI Format 1C in common search space
  • The UE starts decoding PDCCH scrambled with SI-RNTI at the start of SI-Window (for the concerned SI message) until the end of the SI-window, or until the SI message was received excluding the following subframes. 
          - subframe #5 in radio frames for which SFN mod 2 = 0
          - any MBSFN subframes
          - any uplink subframes in TDD

  • If the SI message was not received by the end of the SI-window, the UE repeats reception at the next SI-window occasion for the concerned SI message

P-RNTI (Paging RNTI)

  • P-RNTI is used by the UEs for the reception of paging.
  • It is a common RNTI meaning that it is not allocated to any UE explicitly.
  • P-RNTI is of 16-bit in length and its value is fixed to 65534 (0xFFFE).
  • Paging message is carried by PCCH logical channel which is mapped to PCH transport channel. The PCH transport channel is mapped to PDSCH physical channel. The eNB scrambles PDCCH’s CRC with P-RNTI for transmission of PDSCH that carries paging information
  • DCI Formats which carries scheduling information for paging are DCI Format 1A and DCI Format 1C in common search space

RA-RNTI (Random Access RNTI)

  • As part of Random Access procedure, the eNB’s MAC generates Random Access Response (RAR) as a response to the Random Access Preamble transmitted by the UE. RAR is transmitted on DL-SCH transport channel which intern is mapped to PDSCH. The eNB scrambles PDCCH’s CRC with RA-RNTI for transmission of PDSCH that carries RAR(s).
  • RA-RNTI can be addressed to multiple UEs, i.e., multiple UEs might decode PDCCH scrambled by the same RA-RNTI.
  • RA-RNTI unambiguously identifies which time-frequency resource was utilized by the UE to transmit the Random Access preamble (explained below)
  • RA-RNTI is of 16-bit in length and its value is derived from the below equation where t_id is the index of the first subframe of the specified PRACH (0≤ t_id <10), and f_id is the index of the specified PRACH within that subframe, in ascending order of frequency domain (0 ≤ f_id< 6).
                                              RA-RNTI= 1 + t_id+10*f_id
  • For FDD there is at most one PRACH resource per subframe ⇨ f_id = 0 ⇨ RA-RNTI range is 1 to 10 whereas for TDD, the RA-RNTI ranges from 1 to 60
  • The values corresponding to the RA-RNTI values of a cell’s PRACH configuration are not used in the cell for any other RNTI (C-RNTI, Semi-Persistent Scheduling C-RNTI, Temporary C-RNTI, TPC-PUCCH-RNTI or TPC-PUSCH-RNTI)
  • DCI Formats which carries scheduling information for RAR are DCI Format 1A and DCI Format 1C in common search space

Temporary C-RNTI

  • As part of Random Access procedure, the eNB’s MAC generates Random Access Response (RAR) as a response to the Random Access Preamble transmitted by the UE. The MAC RAR contains Temporary C-RNTI
  • Temporary C-RNTI is of 16-bit in length and its value can range from 1 to 65523 (0x0001 to 0xFFF3).
  • During contention based random access procedure, the UE stores received Temporary 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 Temporary C-RNTI for scrambling of msg3 (PUSCH corresponding to RAR grant) and it’s retransmissions
  • During contention based RA procedure, the UE monitors PDCCH scrambled with Temporary C-RNTI for DCI0 in common search space (This DCI0 monitoring is for possible retransmission of msg3)
  • In downlink, UE Contention Resolution (UE Contention Resolution Identity MAC Control Element) is on PDSCH for which PDCCH will be scrambled by Temporary C-RNTI. This is applicable only if UE has included CCCH SDU (RRC Connection Request or RRC Connection Re-establishment) in Msg3
  • DCI Format which carriers scheduling information for Contention Resolution in the downlink can be either DCI Format 1A in Common and UE specific search space or DCI Format 1 in UE specific search space
  • The Temporary C-RNTI is promoted to C-RNTI for a UE which detects RA success and does not already have a C-RNTI. It is dropped by others (for which contention is not successful)
  • A UE which detects RA success and already has a C-RNTI, resumes using its C-RNTI and discards Temporary C-RNTI

C-RNTI (Cell RNTI)

  • C-RNTI is a unique identification used for identifying RRC Connection and scheduling which is dedicated to a particular UE.
  • The eNB assigns different C-RNTI values to different UEs. When Carrier Aggregation is configured, same C-RNTI applies to all serving cells.
  • The eNB uses C-RNTI to allocate a UE with uplink grants, downlink assignments, PDCCH orders etc.
  • The eNB also uses C-RNTI to differentiate uplink transmissions (e.g. PUSCH, PUCCH) of a UE from others.
  • C-RNTI is of 16-bit in length and its value can range from 1 to 65523 (0x0001 to 0xFFF3).
  • After connection establishment or re-establishment the Temporary C-RNTI (as explained above) is promoted to C-RNTI.
  •  During Handovers within E-UTRA or from other RAT to E-UTRA, C-RNTI is explicitly provided by the eNB in MobilityControlInfo container with IE newUE-Identity
  • DCI Formats 0 and 1A in Common and UE specific search space and DCI Formats 1, 1B, 1D, 2, 2A, 2B, 2C, and 4 in UE specific search space will be transmitted on PDCCH with CRC scrambled by the C-RNTI
  • The scrambling initialization of PDSCH corresponding to the PDCCHs with DCI Formats 1, 1A, 1B, 1D, 2, 2A, 2B, and 2C is by C-RNTI
  • The scrambling initialization of the PUSCH corresponding to the PDCCHs with DCI Format 0/4 and the PUSCH retransmission for the same transport block is by C-RNTI

SPS C-RNTI (Semi-Persistent Scheduling C-RNTI)

  • SPS C-RNTI identifies semi-persistent grants/assignments. 
  • SPS C-RNTI is a dedicated RNTI and is configured by RRC. eNB configures the UE with a SPS C-RNTI as part of sps-Config as discussed in detail here
  • The CRC parity bits obtained for the PDCCH payload are scrambled with the SPS C-RNTI for SPS activation, release, re-activation and retransmission
  • SPS C-RNTI is of 16-bit in length and its value can range from 1 to 65523 (0x0001 to 0xFFF3).
  • For SPS activation/re-activation/retransmission in downlink, DCI Format 1A (common and UE specific search space) and DCI Formats 1/2/2A/2B/2C (UE specific search space) with PDCCH’s CRC is scrambled by SPS C-RNTI are used. The scrambling initialization of PDSCH corresponding to these PDCCHs and PDSCH without a corresponding PDCCH is by SPS C-RNTI
  • For SPS release in downlink, DCI Format 1A (common and UE specific search space) with PDCCH’s CRC is scrambled with SPS C-RNTI is used
  • For SPS activation/re-activation/retransmission/release in uplink, DCI Format 0 (common and UE specific search space) with PDCCH’s CRC is scrambled by SPS C-RNTI is used.The scrambling initialization of PUSCH corresponding to these PDCCHs and PUSCH retransmission for the same transport block is by SPS C-RNTI. The scrambling initialization of initial transmission of PUSCH without a corresponding PDCCH and the PUSCH retransmission for the same transport block is by SPS C-RNTI.
  • UE monitors SPS C-RNTI only on PCell

TPC RNTI (Transmit Power Control RNTI)

  • TPC RNTI is used for uplink power control purpose. There are two types, TPC-PUSCH-RNTI and TPC-PUCCH-RNTI
  • Normally TPC RNTI is assigned to a group of UEs. eNB may configure the UE with TPC-PUSCH-RNTI and TPC-PUCCH-RNTI via RRC signalling
  • TPC-PUSCH-RNTI/TPC-PUCCH-RNTI is of 16-bit in length and its value can range from 1 to 65523 (0x0001 to 0xFFF3).
  • DCI format 3/3A (common search space) whose CRC is scrambled with TPC-PUCCH-RNTI is used for the transmission of TPC commands for PUCCH
  • DCI format 3/3A (common search space) whose CRC is scrambled with TPC-PUSCH-RNTI is used for the transmission of TPC commands for PUSCH
  • DCI format 3 is used for the transmission of TPC commands for PUCCH and PUSCH with 2-bit power adjustments. DCI format 3A is used for the transmission of TPC commands for PUCCH and PUSCH with single bit power adjustments.
  • The notation 3/3A implies that the UE shall receive either DCI format 3 or DCI format 3A depending on the configuration

M-RNTI (MBMS RNTI)

  • Indication of an MBMS specific RNTI, the M-RNTI, on PDCCH is used to inform UEs in RRC_IDLE and UEs in RRC_CONNECTED about an MCCH information change
  • The DCI format 1C (common search space) with M-RNTI is used for notification and includes an 8-bit bitmap to indicate the one or more MBSFN Area(s) in which the MCCH change(s)
  • M-RNTI is of 16-bit in length and its value is fixed to 65533 (0xFFFD)

Reference 3GPP TS 36.300, 36.331, 36.211, 36.212, 36.213, 36.321

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