8.5.15 CFN calculation
25.3313GPPProtocol specificationRadio Resource Control (RRC)Release 17TS
The DOFF used in the formulas in this clause concerns the value of IE "Default DPCH Offset Value" received in the message that instructs the UE to enter CELL_DCH state or to perform timing re-initialised hard handover.
Subclause 8.5.15.5 is used in FDD to initialise the CFN for MTCH and/or MSCH if the IE "MBMS Soft Combining Timing Offset" is included for an S-CCPCH in MBMS CURRENT CELL P-T-M RB INFORMATION or MBMS NEIGHBOURING CELL P-T-M RB INFORMATION, and if only MTCH and/or MSCH are on the S-CCPCH. Otherwise, subclauses 8.5.15.1 through 8.5.15.4 are used to intialise the CFN.
8.5.15.1 Initialisation for CELL_DCH state after state transition
When the UE receives any of the messages causing the UE to perform a state transition to CELL_DCH, the UE shall set the CFN in relation to the SFN of the first radio link listed in the IE "Downlink information per radio link list" included in that message according to the following formula:
– for FDD:
CFN = (SFN – (DOFF div 38400)) mod 256
where the formula gives the CFN of the downlink DPCH or F-DPCH frame which starts at the same time as or which starts during the PCCPCH frame with the given SFN. DOFF is determined according to subclause 8.6.6.14.
– for TDD:
CFN = (SFN – DOFF) mod 256.
8.5.15.2 Initialisation in CELL_DCH state at hard handover
When the UE is in CELL_DCH state and receives any of the messages causing the UE to perform a hard handover, the UE shall check the IE "Timing indication" in that message and:
1> if IE "Timing indication" has the value "initialise" (i.e. timing re-initialised hard handover):
2> read SFN on target cell identified by the first radio link listed in the IE "Downlink information per radio link list" included in that message;
2> set the CFN according to the following formula:
3> for FDD:
CFN = (SFN – (DOFF div 38400)) mod 256
where the formula gives the CFN of the downlink DPCH or F-DPCH frame which starts at the same time as or which starts during the PCCPCH frame with the given SFN.
3> for TDD:
CFN = (SFN – DOFF) mod 256.
1> if IE "Timing indication" has the value "maintain" (i.e. timing-maintained hard handover), the UE shall keep CFN with no change due to the hard handover, and only increase CFN (mod 256) by 1 every frame.
8.5.15.3 Initialisation for CELL_FACH
Unless the conditions of subclause 8.5.15.5 are met, when the UE performs cell selection, re-selection or changes to CELL_FACH state the UE shall set CFN for all common or shared channels according to:
CFN = SFN mod 256
where the formula gives the CFN of the downlink common or shared channel frame which starts at the same time as or which starts during the PCCPCH frame with the given SFN.
After the initialisation, the CFN in the UE is increased (mod 256) by 1 every frame.
8.5.15.4 Initialisation after intersystem handover to UTRAN
Upon inter RAT handover to UTRAN the UE shall, regardless of the value received within IE "Timing indication" (if received):
1> read SFN on target cell and set the CFN according to the following formula:
2> for FDD:
CFN = (SFN – (DOFF div 38400)) mod 256
where the formula gives the CFN of the downlink DPCH frame which starts at the same time as or which starts during the PCCPCH frame with the given SFN.
2> for TDD:
CFN = (SFN – DOFF) mod 256.
8.5.15.5 Initialisation for MTCH and/or MSCH carried on S-CCPCH that may be soft combined
For FDD, if the IE "MBMS Soft Combining Timing Offset" is included for an S-CCPCH in MBMS CURRENT CELL P-T-M RB INFORMATION or MBMS NEIGHBOURING CELL P-T-M RB INFORMATION, and if only MTCH and/or MSCH are on the S-CCPCH, the UE shall set CFN for the S-CCPCH according to:
CFN = (SFN (SCTO div 10ms)) mod 256
where the formula gives the CFN of the downlink S-CCPCH frame which starts at the same time as or which starts during the PCCPCH frame with the given SFN.
the SCTO used in the formula is the IE "MBMS Soft Combining Timing Offset".
After the initialisation, the CFN in the UE is increased (mod 256) by 1 every frame.