8 Paging and SCCPCH selection and in FDD and 1.28 Mcps TDD the H-RNTI selection

25.3043GPPRelease 17TSUser Equipment (UE) procedures in idle mode and procedures for cell reselection in connected mode

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

8.1 Paging Channel selection

System information block type 5 (SIB 5) and System information block type 5bis (SIB 5bis)define common channels to be employed in Idle mode [4]. In a cell, a single or several PCHs may be established. Each Secondary Common Control Physical Channel (SCCPCH) indicated to the UE in system information may carry up to one PCH. Thus, for each defined PCH there is one uniquely associated PICH also indicated.

In case that more than a single PCH and associated PICH are defined in SIB 5 or SIB 5bis, the UE shall perform a selection according to the following rule:

– The UE shall select a SCCPCH from the ones listed in SIB 5 or SIB 5bis based on IMSI as follows:

"Index of selected SCCPCH" = IMSI mod K,

where K is equal to the number of listed SCCPCHs which carry a PCH (i.e. SCCPCHs carrying FACH only shall not be counted). These SCCPCHs shall be indexed in the order of their occurrence in SIB 5 or SIB 5bis from 0 to K-1.
For GSM-MAP, i.e. "IMSI (GSM-MAP)" is given as sequence of digits of type Integer(0..9), IMSI shall in the formula above be interpreted as a decimal integer number, where the first digit given in the sequence represents the highest order digit.
For DS-41, i.e. "IMSI (DS-41)" is given as octet string, IMSI shall in the formulae above correspond to the decoded decimal representation of the IMSI-S part included in the octet string (see TIA/EIA/IS-2000-5).

For example:

IMSI (GSM-MAP) = 12 (digit1=1, digit2=2)

In the calculations, this shall be interpreted as the decimal integer "12", not "1×16+2 = 18".

"Index of selected SCCPCH" identifies the selected SCCPCH with the PCH and the uniquely associated PICH to be used by the UE.

If the UE has no IMSI, for instance when making an emergency call without USIM, the UE shall use as default number IMSI = 0.

8.2 SCCPCH selection when entering Connected mode

If HS-DSCH operation in CELL_FACH state (FDD and 1.28 Mcps TDD) is not configured to the cell, when entering Connected mode from Idle mode by sending an RRC CONNECTION REQUEST message, the UE shall select the S-CCPCH which carries an FACH to be used for reception of the RRC CONNECTION SETUP message according to the following rule:

– the UE shall select an SCCPCH from the SCCPCHs listed in System Information Block type 5 (SIB 5) or System Information Block type 5bis (SIB 5bis) based on "Initial UE Identity" as follows:

"Index of selected SCCPCH" = "Initial UE Identity" mod K,

where K is equal to the number of listed SCCPCHs which carry a FACH (i.e. SCCPCHs carrying PCH only shall not be counted). These SCCPCHs shall be indexed from 0 to K-1 in the order of their occurrence in SIB 5 or SIB 5bis, and "Index of selected SCCPCH" identifies the selected SCCPCH. "Initial UE Identity" refers to the Information Element included by the UE into the RRC CONNECTION REQUEST message. In the above formula, the parameter "Initial UE Identity" shall be interpreted as follows, depending on the choice of UE-Id type of the respective IE:

For UE-Id type "IMSI (GSM-MAP)", i.e. the IE is given as sequence of digits of type Integer(0..9), "Initial UE Identity" shall be interpreted as an integer number, where the first digit given in the sequence represents the highest order digit.

For UE-Id types "TMSI and LAI (GSM-MAP)" or "P-TMSI and RAI (GSM-MAP)", only the TMSI or P-TMSI parts given as Bitstring(32) shall be used, and "Initial UE Identity" shall be interpreted as a binary representation of an integer number, where the first bit in the Bitstring represents the highest order bit.

For UE-Id type "IMEI", i.e. the IE is given as sequence of hexadecimal digits of type Integer(0..15), "Initial UE Identity" shall be interpreted as a hexadecimal representation of an integer number, where the first digit given in the sequence represents the highest order digit.

For UE-Id type "IMSI (DS-41)", i.e. the IE is given as octet string, "Initial UE Identity" shall correspond to the decoded decimal representation of the IMSI-S part included in the octet string (see TIA/EIA/IS-2000-5).

For UE-Id types "ESN (DS-41)" or "TMSI (DS-41)", i.e. the IE is given as Bitstring(32), "Initial UE Identity" shall be interpreted as a binary representation of an integer number, where the first bit in the Bitstring represents the highest order bit.

For UE-Id type "IMSI and ESN (DS-41)" only the ESN part shall be used as "Initial UE Identity", as defined above.

8.2b H-RNTI selection when entering Connected mode (FDD and 1.28 Mcps TDD)

If HS-DSCH operation in CELL_FACH state is configured to the cell in System Information Block type 5 (SIB 5) or System Information Block type 5bis, when entering Connected mode from Idle mode by sending an RRC CONNECTION REQUEST message, the UE shall start listening to the HS-SCCH indicated in System Information Block type 5 (SIB 5) or in System Information Block type 5bis (SIB 5bis).

The detection of HS-SCCH is based on Common H-RNTI listed in System Information Block type 5 (SIB 5) or System Information Block type 5bis (SIB 5bis). The UE shall select the Common H-RNTI to be used for reception of the RRC CONNECTION SETUP message according to the following rule:

– the UE shall select a Common H-RNTI from the Common H-RNTIs listed in System Information Block type 5 (SIB 5) or System Information Block type 5bis (SIB 5bis) based on "Initial UE Identity" as follows:

"Index of selected Common H-RNTI" = "Initial UE Identity" mod K,

– where K is equal to the number of listed Common H-RNTI. These Common H-RNTIs shall be indexed from 0 to K-1 in the order of their occurrence in SIB 5 or SIB 5bis, and "Index of selected Common H-RNTI" identifies the selected Common H-RNTI. "Initial UE Identity" refers to the Information Element included by the UE into the RRC CONNECTION REQUEST message. In the above formula, the parameter "Initial UE Identity" shall be interpreted as follows, depending on the choice of UE-Id type of the respective IE:

For UE-Id type "IMSI and ESN (DS-41)" only the ESN part shall be used as "Initial UE Identity", as defined above.

After detecting the HS-SCCH with Common H-RNTI, the UE start reception of the corresponding HS-PDSCH(s) TTI.

8.3 Discontinuous Reception for Paging

The UE may use Discontinuous Reception (DRX) in idle mode in order to reduce power consumption. When DRX is used the UE needs only to monitor one Page Indicator, PI, (see definition in [7] and [8]) in one Paging Occasion per DRX cycle.

The DRX cycle length shall be MAX(2^k, PBP) frames, where k is an integer and PBP is the Paging Block Periodicity. PBP is only applicable for TDD and is equal to the PICH repetition period that is broadcast in system information. For FDD, PBP=1.

The UE may be attached to different CN domains with different CN domain specific DRX cycle lengths. The UE shall store each CN domain specific DRX cycle length for each CN domain the UE is attached to and use the shortest of those DRX cycle lengths. The CS CN specific DRX cycle length coefficient shall be updated locally in the UE using information given in system information. On the other hand, the PS CN specific DRX cycle length coefficient shall be updated after the negotiation between the UE and PS CN by NAS procedure. If no specific value "k" is negotiated in NAS procedure, the UE and PS CN shall use the DRX cycle length given for PS CN domain in system information.

The DRX cycle lengths to use for UTRAN connected mode is the shortest of the following:

– UTRAN DRX cycle length;

– any of the stored CN domain specific DRX cycle length for the CN domains the UE is only attached to with no signalling connection established.

For TDD, and for FDD in IDLE mode as well as in RRC Connected mode, if HS-DSCH operation in CELL_PCH and URA_PCH state is not configured to the cell, or for 1.28 Mcps TDD if both HS-DSCH operation in CELL_PCH and URA_PCH state and legacy PCH are configured to the cell but no dedicated H-RNTI is allocated to the UE, the UE shall use the IMSI, the number of available SCCPCH which carry a PCH (K) as derived according to subclause 8.1,the Cell System Frame Number (SFN), Np (for FDD, Np is the number of page indicators within a frame; for TDD, Np is the number of page indicators within a paging block), Frame offset (For FDD, Frame offset = 0; for TDD, PICH frame offset values are given in system information), PBP and the DRX cycle length to determine the Paging Occasions.

For FDD, if HS-DSCH operation in CELL_PCH and URA_PCH state is configured to the cell, the UE in RRC Conneced mode shall use the IMSI, the number of indexed PICH for HSDPA supported paging (K) as derived from System Information Block Type 5 or System Information Block Type 5bis, the Cell System Frame Number (SFN), Np (Np is the number of page indicators within a frame), Frame offset (Frame offset = 0), PBP and the DRX cycle length to determine the Paging Occasions.

For 1.28 Mcps TDD, if HS-DSCH operation in CELL_PCH and URA_PCH state is configured to the cell and no legacy PCH is configured in the cell, or if both HS-DSCH operation in CELL_PCH and URA_PCH state and legacy PCH are configured to the cell and the dedicated H-RNTI is allocated to the UE, the UE in RRC Conneced mode shall use the IMSI, the number of indexed PICH for HSDPA supported paging (K) as derived from System Information Block Type 5 or System Information Block Type 5bis, the Cell System Frame Number (SFN), Np (Np is the number of page indicators within a frame), Frame offset, PBP and the DRX cycle length to determine the Paging Occasions.

In FDD the UE shall monitor its paging indicator in the PICH frame with SFN given by the Paging Occasion

In TDD the UE shall monitor its paging indicator in the paging block given by the Paging Occasion. The Paging Occasion gives the SFN of the first frame of the paging block.

The value of the Paging Occasion is determined as follows:

Paging Occasion= {(IMSI div K) mod (DRX cycle length div PBP)} * PBP + n * DRX cycle length + Frame Offset

Where n = 0,1,2… as long as SFN is below its maximum value.

The actual Page Indicator within a Paging Occasion that the UE shall read is similarly determined based on IMSI.

The Page Indicator to use is calculated by using the following formula:

PI = DRX Index mod Np

where DRX Index = IMSI div 8192

In FDD mode, Np = (18,36,72,144) is the number of Page Indicators per frame, and is given in IE "Number of PI per frame", part of system information in FDD mode. In TDD mode, Np is the number of Page Indicators per paging block and is calculated by the Paging Indicator Length L_PI,the Burst Type (long or short midamble for 3.84/7.68 Mcps TDD) and the PICH repetition length, which are given in system information.

If the UE has no IMSI, for instance when making an emergency call without USIM, the UE shall use as default numbers, IMSI = 0 and DRX cycle length = 256 (2.56 s), in the formulas above.

For FDD, see [7] for details about the timing between a PICH frame and when the paging message is transmitted on the PCH in the associated S-CCPCH frame.

In TDD mode, in case of PCCH mapping on PCH, the Paging Message Receiving Occasion is calculated using the following formula:

Paging Message Receiving Occasion = Paging Occasion + N_PICH + N_GAP + {(DRX Index mod Np) mod N_PCH } *2

For 1.28 Mcps TDD, in case of PCCH on HS-DSCH, the Paging Message Receiving Occasion is calculated using the following formula:

Paging Message Receiving Occasion = Paging Occasion + N_PICH + N_GAP + {(DRX Index mod Np) mod N_HS-PCH } *m

Where N_HS-PCHis the number of Paging sub-channels for PCCH on HS-DSCH and m is the length of each sub-channel in Radio Frame. The timing of PICH and Paging Message on HS-DSCH as well as the transmission pattern of PCCH on HS-DSCH is defined in [8].

The value N_PICH is the number of frames for PICH transmission and is equal to the PICH repetition length given in system information. The value N_GAP is the number of frames between the last frame carrying PICH for this Paging Occasion and the first frame carrying paging messages for this Paging Occasion. The value N_PCH is the number of Paging Groups. N_PCH and N_GAP are given in system information.

For GSM-MAP, i.e. "IMSI (GSM-MAP)" is given as sequence of digits of type Integer(0..9), IMSI shall in the formulae above be interpreted as a decimal integer number, where the first digit given in the sequence represents the highest order digit.

For DS-41, i.e. "IMSI (DS-41)" is given as octet string, IMSI shall in the formulae above correspond to the decoded decimal representation of the IMSI-S part included in the octet string (see TIA/EIA/IS-2000-5).

For example:

IMSI (GSM-MAP) = 12 (digit1=1, digit2=2)

In the calculations, this shall be interpreted as the decimal integer "12", not "1×16+2 = 18".

8.4 Discontinuous Reception for MBMS

The UE may use discontinuous reception (DRX) on MBMS channels (MCCH, MSCH, MTCH) to reduce power consumption while subscribed to MBMS services.

8.4.1 Discontinuous Reception for MCCH

The UE may operate DRX on the MCCH either by monitoring the MICH to determine when it needs to receive the MCCH or by using the MODIFIED SERVICES INFORMATION message on the MCCH to determine that it does not need to acquire the remainder of the MCCH information.

The timing of the MCCH information transmission and the need to receive the MCCH are described in detail in [4].

8.4.1.1 Discontinuous Reception via MICH

When the UE operates DRX on the MCCH through monitoring the MICH, the UE needs to monitor one Notification Indicator (NI), as defined in [7], [8], for each MBMS service it is subscribed to. For each service, a corresponding NI will be set continuously through the entire length of the modification period preceding a change in the associated MCCH information. The modification period should be long enough that a UE that only receives the MICH during its paging occasions can still reliably detect a notification.

For each service, the 16 bit Notification Indicator to use is calculated as a function of the TMGI:

, where G = 2¹⁶.

A UE with one or more activated MBMS services may monitor the MICH. The exact timing with which the UE reads the MICH within a given modification period is left to the UE implementation, with the proviso that the UE needs to be able to detect notifications reliably for its activated MBMS service(s).

The TMGI is structured as follows [16]:

8	7	6	5	4	3	2	1
Temporary Mobile Group Identity IEI								Octet 1
Length of Temporary Mobile Group Identity contents								Octet 2
MBMS Service ID								Octet 3 Octet 4
								Octet 5
MCC digit 2				MCC digit 1				Octet 6
MNC digit 3				MCC digit 3				Octet 7
MNC digit 2				MNC digit 1				Octet 8

NOTE: The MBMS Service identity, which is signalled in [4] (see subclause 10.3.9a.8), concerns a signalling optimisation of the TMGI.

For the calculation of the NI, the TMGI shall be interpreted as a binary representation of an integer number, represented by the bitstring formed by the exclusive OR operation of the MBMS Service ID (octets 3 to 5 of the TMGI) and the PLMN identity (octets 6 to 8 of the TMGI) with the first/ leftmost/ most significant bit corresponding with b8 of the first octet.

8.4.1.2 Discontinuous Reception via MODIFIED SERVICES INFORMATION

If the UE receives the MODIFIED SERVICES INFORMATION message on the MCCH and determines from its contents that no service whose information the UE needs to acquire has been modified, the UE may refrain from receiving the MCCH for the remainder of the modification period.

8.4.2 Discontinuous Reception for MTCH

If the UE operates DRX on the MTCH, the UE shall receive the MSCH as described in [4] to obtain scheduling information for the MTCH.

The reception intervals for MBMS services are given by the IE "Service transmissions list" in the MBMS SCHEDULING INFORMATION message on the MSCH.