5 Synchronisation Counters and Parameters

25.4023GPPRelease 17Synchronisation in UTRAN Stage 2TS

This clause defines counters and parameters used in the different UTRAN synchronisation procedures.

BFN Node B Frame Number counter. This is the Node B common frame number counter. [FDD ‑BFN is optionally frequency-locked to a Network synchronisation reference].
Range: 0 .. 4095 frames.

RFN RNC Frame Number counter. This is the RNC node common frame number counter. RFN is optionally frequency-locked to a Network synchronisation reference.
Range: 0 .. 4095 frames.

SFN Cell System Frame Number counter. SFN is sent on BCH. SFN is used for paging groups and system information scheduling etc.
In FDD SFN = BFN adjusted with T_cell.
In TDD, if Inter Node B synchronisation port is used, SFN is locked to the BFN (i.e. SFN mod 256 = BFN mod 256).
Range: 0 .. 4095 frames.

CFN Connection Frame Number (counter). CFN is the frame counter used for the L2/transport channel synchronisation between UE and UTRAN. A CFN value is associated to each TBS and it is passed together with it through the MAC-L1 SAP. CFN provides a common frame reference (at L2) to be used e.g. for synchronised transport channel reconfiguration (see TS 25.423 [2] and TS 25.433 [3]).

The duration of the CFN cycle is longer than the maximum allowed transport delay between MAC and L1 (in UTRAN side, between SRNC and Node B, because the L1 functions that handle the transport channel synchronisation are in the Node B).
Range: 0 .. 255 frames. When used for PCH the range is 0 .. 4095 frames.

Frame Offset Frame Offset is a radio link specific L1 parameter used to map the CFN, used in the transport channel, into the SFN that defines the specific radio frame for the transmission on the air interface.

At the L1/L2 interaction, the mapping is performed as:

– SFN mod 256 = (CFN + Frame Offset) mod 256 (from L2 to L1) (5.1);

– CFN = (SFN – Frame Offset) mod 256 (from L1 to L2) (5.2).

The resolution of all three parameters is 1 frame. Frame Offset and CFN have the same range (0…255) and only the 8 least significant bits of the SFN are used. The operations above are modulo 256.

In the UTRAN, the Frame Offset parameter is calculated by the SRNC and provided to the Node B.

OFF The parameter OFF is calculated by the UE and reported to the UTRAN only when the UTRAN has requested the UE to send this parameter. In the neighbouring cell list, the UTRAN indicates for each cell if the Frame Offset is already known by the UTRAN or shall be measured and reported by the UE.

OFF has a resolution of 1 frame and a range of 0 .. 255.

Five different cases are discerned related to the determination of the OFF value by the UE:

1. The UE changes from common channel state to dedicated channel state: 1 RL.
In this case OFF is zero.

2. [FDD -The UE changes from common channel state to dedicated channel state: several RL’s.
OFF is in this case defined as being the difference between SFN of the candidate cells and the SFN of the camping cell. Again the UE sets OFF to zero for the cell to which the UE sends an UL RRC message (cell #1). For cells #2 to n, the UE sets OFF to the difference between the SFN of cell#2, n and the SFN of cell#1.
This could be seen as if a virtual dedicated physical channel (DPCH) already is aligned with cell #1].

3. The UE adds another RL or moves to another cell in dedicated channel state.
OFF is in this case defined as being the time difference between the CFN and the SFN of the cell in which the RL is to be added. In case this difference cannot be measured, a value as in [FDD – TS 25.215[13]] [TDD – TS 25.225 [14]] shall be reported instead.

4. The UE is coming from another RAN and goes to dedicated channel state: 1 RL.
This case is identical to case 1).

5. [FDD – The UE is coming from another RAN or another frequency in the same RAN and goes to dedicated channel state: several RL’s.
This case is identical to case 2], with one exception: OFF will not be zero for the cell to which the UE sends an UL RRC message (the measurement information will be received via the CN in this case) but for a reference cell selected by the UE. All other reported OFF values will be relative to the SFN of this selected reference cell].

[FDD – DOFF_FDD] The DOFF_FDD (FDD Default DPCH Offset value) is used to define Frame Offset and Chip Offset at first RL setup. The DOFF_FDD is used for both the DPCH and the F-DPCH. The resolution should be good enough to spread out load over Iub and load in Node B (based on certain load distributing algorithms). In addition it is used to spread out the location of Pilot Symbol in order to reduce the peak DL power since Pilot symbol is always transmitting at the fixed location within a slot (the largest number of chips for one symbol is 512 chips).

The SRNC sends a DOFF_FDD parameter to the UE when the new RL will make the UE change its state (from Cell_FACH state or other when coming from another RAN) to Cell_DCH state.

Resolution: 512 chips; Range: 0 .. 599 (< 80 ms).

[TDD – DOFF_TDD] The DOFF_TDD (TDD Default DPCH Offset value) is used to define Frame Offset at first RL setup, in order to spread out load over /Iur and load in Node B (based on certain load distributing algorithms).

The SRNC sends a DOFF_TDD parameter to the UE when the new RL will make the UE change its state (from Cell_FACH state or other when coming from another RAN) to the Cell_DCH state.

Resolution: 1 frame; Range: 0 .. 7 frames.

[FDD – Chip Offset] The Chip Offset is used as offset for the DL DPCH or the F-DPCH relative to the PCCPCH timing. The Chip Offset parameter has a resolution of 1 chip and a range of 0 .. 38399 (< 10 ms).

The Chip Offset parameter is calculated by the SRNC and provided to the Node B.

Frame Offset + Chip Offset (sent via NBAP) are in Node B rounded together to closest
256 chip boundary. The 256 chip boundary is used regardless of the used spreading factor, also when the spreading factor is 512. The rounded value (which is calculated in Node B) controls the DL DPCH air-interface timing or the F-DPCH air-interface timing.

The "Frame Offset + Chip Offset" 256 chip boundary rounding rules for Node B to consider for each DL DPCH and each F-DPCH are:

1. IF (Frame Offset x 38 400 + Chip Offset) modulo 256 [chips] = {1..127} THEN round (Frame Offset x 38 400 + Chip Offset) modulo 256 frames down to closest 256 chip boundary.

2. IF (Frame Offset x 38 400 + Chip Offset) modulo 256 [chips] = {128..255} THEN round (Frame Offset x 38 400 + Chip Offset) modulo 256 frames up to closest 256 chip boundary.

3. IF (Frame Offset x 38 400 + Chip Offset) modulo 256 [chips] = 0 THEN "Frame Offset x 38 400 + Chip Offset" is already on a 256 chip boundary.

[FDD – DPCH Frame Offset]

The DPCH Frame Offset is used as offset for the DL DPCH or the F-DPCH relative to the PCCPCH timing at both the Node B and the UE. The DPCH Frame Offset parameter has a resolution of 256 chips and a range of 0 .. 38144 chips (< 10 ms).

The DPCH Frame Offset is equivalent to Chip Offset rounded to the closest 256 chip boundary. It is calculated by the SRNC and sent to the UE by the SRNC for each radio link in the active set.

The DPCH Frame Offset controls the DL DPCH air-interface timing or the F-DPCH air-interface timing. It enables the DL DPCHs or the F-DPCH for radio links in the Active Set to be received at the UE at approximately the same time, which can then be soft combined during soft handover.

[FDD – S-CCPCH Frame Offset]

The S-CCPCH Frame Offset is used as offset for the S-CCPCH relative to the P-CCPCH timing of the same cell at the Node B. It may be applied to S-CCPCHs carrying MTCH. The purpose of S-CCPCH Frame Offset is enabling of soft combining of MBMS data at the UE, in particular for the case of long-lived MBMS sessions.

The S-CCPCH Frame Offset can take the values 0, 10, 20 or 40msecs.

[FDD –Tm] The reported Tm parameter has a resolution of 1 chip and a range of 0 .. 38399. The Tm shall always be sent by the UE.

Five different cases are discerned related to the determination of the Tm value by the UE:

1. The UE changes from common channel state to dedicated channel state: 1 RL.
In this case the Tm will be zero.

2. The UE changes from common channel state to dedicated channel state: several RL’s.
Tm is in this case defined as being the time difference between the received PCCPCH path of the source cell and the received PCCPCH paths of the other target cells. Again the UE sets Tm to zero for the cell to which the UE sends an UL RRC message (cell #1). For cells #2 to n, the UE sets Tm to the time difference of the PCCPCH reception timing of cell#2,n from the PCCPCH reception timing of cell#1.

3. The UE adds another RL in dedicated channel state (macro-diversity).
Tm is in this case defined as being the time difference between "T_UETX – T_o" and the earliest received PCCPCH path of the target cell. T_UETX is the time when the UE transmits an uplink DPCCH frame, hence "T_UETX – T_o" is the nominal arrival time for the first path of a received DPCH.

4. The UE is coming from another RAN and goes to dedicated channel state: 1 RL.
This case is identical to case 1.

5. The UE is coming from another RAN or another frequency in the same RAN and goes to dedicated channel state: several RL’s.
This case is identical to case 2, with one exception: Tm will not be zero for the cell to which the UE sends an UL RRC message (the measurement information will be received via the CN in this case) but for a reference cell selected by the UE. All other reported Tm values will be relative to the timing of the PCCPCH in this cell.

[FDD – T_cell] T_cell represents the Timing delay used for defining the start of SCH, CPICH and the DL Scrambling Code(s) in a cell relative BFN. The main purpose is to avoid having overlapping SCHs in different cells belonging to the same Node B. A SCH burst is
256 chips long. SFN in a cell is delayed T_cell relative BFN.

Resolution: 256 chips. Range: 0 .. 9 x 256 chips.

T1 RNC specific frame number (RFN) that indicates the time when RNC sends the DL NODE SYNCHRONISATION control frame through the SAP to the transport layer.

Resolution: 0.125 ms; Range: 0 .. 40959.875 ms.

T2 Node B specific frame number (BFN) that indicates the time when Node B receives the correspondent DL NODE SYNCHRONISATION control frame through the SAP from the transport layer.

Resolution: 0.125 ms; Range: 0 .. 40959.875 ms.

T3 Node B specific frame number (BFN) that indicates the time when Node B sends the UL NODE SYNCHRONISATION control frame through the SAP to the transport layer.

Resolution: 0.125 ms; Range: 0 .. 40959.875 ms.

T4 RNC specific frame number (RFN) that indicates the time when RNC receives the UL NODE SYNCHRONISATION control frame. Used in RNC locally. Not standardised over Iub.

TOAWS TOAWS (Time of Arrival Window Startpoint) is the window startpoint. DL DATA FRAMES are expected to be received after this window startpoint. TOAWS is defined with a positive value relative Time of Arrival Window Endpoint (TOAWE) (see Figure 10). A data frame arriving before TOAWS gives a TIMING ADJUSTMENT control frame response.
The resolution is 1 ms, the range is: {0 .. CFN length/2 –1 ms}.

TOAWE TOAWE (Time of Arrival Window Endpoint) is the window endpoint. DL DATA FRAMES are expected to be received before this window endpoint (see Figure 10). TOAWE is defined with a positive value relative Latest Time of Arrival (LTOA). A data frame arriving after TOAWE gives a TIMING ADJUSTMENT control frame response.
The resolution is 1 ms, the range is: {0 .. CFN length –1 ms}.

LTOA LTOA (Latest Time of Arrival) is the latest time instant a Node B can receive a data frame and still be able to process it. Data frames received after LTOA can not be processed (discarded). LTOA is defined internally in Node B to be a processing time before the data frame is sent in air-interface. The processing time (Tproc) could be vendor and service dependent.
LTOA is the reference for TOAWE (see Figure 14).

TOA TOA (Time of Arrival) is the time difference between the TOAWE and when a data frame is received. A positive TOA means that data frames are received before TOAWE, a negative TOA means that data frames are received after TOAWE. Data frames that are received after TOAWE but before LTOA are processed by Node B.
TOA has a resolution of 125 s. TOA is positive when data frames are received before TOAWE (see Figure 12).
The range is: {0 .. +CFN length/2 –125 s}.
TOA is negative when data frames are received after TOAWE.
The range is: {–125 s .. –CFN length/2}.