5G-RNTI-有解無憂

- RNTI，Radio Network Temporary Identifier，是一種標識，兩類用途：用于加擾DCI的CRC，UE只有使用正確的RNTI才能對接收到的訊息解碼；基站用于識別UE，UE發送的RRC message會攜帶自己專用的RNTI值，

- 5G中有多種型別的RNTI，可分為公共的和專用的兩類：公共的RNTI取值是固定的，所有UE都一樣（SI-RNTI,P-RNTI），專用的RNTI取值不是固定的，UE需要根據基站指示或者通過相關狀態計算得到（如RA-RNTI是通過UE發送Preambles的RACH Occasion計算的）

RNTI的取值

為16bit，取值范圍如下：

TS38.321 Table 7.1-1: RNTI values.

	Value (hexa-decimal)	RNTI
-	0000	N/A
專用的	0001–FFF2 （1~65522）	RA-RNTI, MSGB-RNTI, Temporary C-RNTI, C-RNTI, CI-RNTI, MCS-C-RNTI, CS-RNTI, TPC-PUCCH-RNTI, TPC-PUSCH-RNTI, TPC-SRS-RNTI, INT-RNTI, SFI-RNTI, SP-CSI-RNTI, PS-RNTI, SL-RNTI, SLCS-RNTI SL Semi-Persistent Scheduling V-RNTI, and AI-RNTI
-	FFF3–FFFD （65523~65533）	Reserved
公共的	FFFE（65534）	P-RNTI
公共的	FFFF（65535）	SI-RNTI

RNTI的用途以及與信道的映射關系

TS38.321 Table 7.1-2: RNTI usage.

RNTI	Usage	Transport Channel	Logical Channel
P-RNTI	Paging and System Information change notification	PCH	PCCH
SI-RNTI	Broadcast of System Information	DL-SCH	BCCH
RA-RNTI	Random Access Response	DL-SCH	N/A
MSGB-RNTI	Random Access Response for 2-step RA type	DL-SCH	CCCH, DCCH
Temporary C-RNTI	Contention Resolution (when no valid C-RNTI is available)	DL-SCH	CCCH, DCCH
Temporary C-RNTI	Msg3 transmission	UL-SCH	CCCH, DCCH, DTCH
C-RNTI, MCS-C-RNTI	Dynamically scheduled unicast transmission	UL-SCH	DCCH, DTCH
C-RNTI	Dynamically scheduled unicast transmission	DL-SCH	CCCH, DCCH, DTCH
MCS-C-RNTI	Dynamically scheduled unicast transmission	DL-SCH	DCCH, DTCH
C-RNTI	Triggering of PDCCH ordered random access	N/A	N/A
CS-RNTI	Configured scheduled unicast transmission (activation, reactivation and retransmission)	DL-SCH, UL-SCH	DCCH, DTCH
CS-RNTI	Configured scheduled unicast transmission (deactivation)	N/A	N/A
TPC-PUCCH-RNTI	PUCCH power control	N/A	N/A
TPC-PUSCH-RNTI	PUSCH power control	N/A	N/A
TPC-SRS-RNTI	SRS trigger and power control	N/A	N/A
INT-RNTI	Indication pre-emption in DL	N/A	N/A
SFI-RNTI	Slot Format Indication on the given cell	N/A	N/A
SP-CSI-RNTI	Activation of Semi-persistent CSI reporting on PUSCH	N/A	N/A
CI-RNTI	Cancellation indication in UL	N/A	N/A
PS-RNTI	DCP to indicate whether to start drx-onDurationTimer for associated DRX cycle	N/A	N/A
SL-RNTI	Dynamically scheduled sidelink transmission	SL-SCH	SCCH, STCH
SLCS-RNTI	Configured scheduled sidelink transmission (activation, reactivation and retransmission)	SL-SCH	SCCH, STCH
SLCS-RNTI	Configured scheduled sidelink transmission (deactivation)	N/A	N/A
SL Semi-Persistent Scheduling V-RNTI (NOTE 2)	Semi-Persistently scheduled sidelink transmission for V2X sidelink communication (activation, reactivation and retransmission)	SL-SCH	STCH
SL Semi-Persistent Scheduling V-RNTI (NOTE 2)	Semi-Persistently scheduled sidelink transmission for V2X sidelink communication (deactivation)	N/A	N/A
AI-RNTI	Availability indication on the given cell	N/A	N/A
NOTE 1: The usage of MCS-C-RNTI is equivalent to that of C-RNTI in MAC procedures (except for the C-RNTI MAC CE). NOTE 2: The MAC entity uses SL Semi-Persistent Scheduling V-RNTI to control semi-persistently scheduled sidelink transmission on SL-SCH for V2X sidelink communication as specified in clause 5.14.1.1 of TS 36.321 [22].

專用RNTI中，RA-RNTI以及TC-RNTI，C-RNTI的確定

-RA-RNTI：

RA-RNTI = 1 + s_id + 14 × t_id + 14 × 80 × f_id + 14 × 80 × 8 × ul_carrier_id

<38.321, 5.1.3>

where s_id is the index of the first OFDM symbol of the PRACH occasion (0 ≤ s_id < 14), t_id is the index of the first slot of the PRACH occasion in a system frame (0 ≤ t_id < 80), where the subcarrier spacing to determine t_id is based on the value of μ specified in clause 5.3.2 in TS 38.211 [8], f_id is the index of the PRACH occasion in the frequency domain (0 ≤ f_id < 8), and ul_carrier_id is the UL carrier used for Random Access Preamble transmission (0 for NUL carrier, and 1 for SUL carrier).

- TC-RNTI:

UE由Msg2中獲得TC-RNTI，位于MAC RAR中，UE獲取到TC-RNTI后，用于發送Msg3和接收Msg4，

TS38.321，Figure 6.2.3-1: MAC RAR

-C- RNTI

UE接收到Msg4后，隨機接入競爭解決成功，則UE將TC-RNTI升級為C-RNTI，

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