11 MBMS related Transport Channel Synchronisation
25.4023GPPRelease 17Synchronisation in UTRAN Stage 2TS
11.1 General
Point-to-multipoint transmission is used to transfer MBMS specific control/user plane information between the network and several UEs in RRC Connected or Idle Mode. In p-t-m mode, FACH is used as a transport channel for MTCH and MCCH. S-CCPCH is used as a physical channel for FACH carrying MTCH or MCCH.
11.2 FDD MBMS related Transport Channel Synchronisation
For support of MBMS soft combining in the UE and operation in MBSFN mode, relative timing difference of MTCH transmissions from different cells respectively from different Node Bs has to be limited.
In the intra-Node B case, relative timing difference of MTCH transmissions is inherently controllable via S-CCPCH timing:
– S-CCPCH CFNs have a configured timing difference relative to the P-CCPCH of the cell (e.g. FDD SCCPCH Offset IE TS 25.433 [3])
– P-CCPCHs of all cells in a Node B are based on the BFN (and linked via T Cell IE TS 25.433 [3]).
For the inter-Node B case synchronisation of MTCH transmissions from different cells in different Node Bs may be achieved and maintained as follows:
1. RNC-Node B Node synchronisation (as described in chapter 6)
After carrying out this procedure, RNC is able to calculate BFN offsets assuming that the DL and UL propagation delay have the same value. Since, for every cell the relative timing of P-CCPCHs/SFNs is known to CRNC (as T Cell is known in CRNC) based on this measurement.
2. Calculations for Initial Uu-Timing Alignment of MTCH transmission on S-CCPCHs
Taking into account that transmission of a certain MTCH PDU has to start at CFNmodTTI=0, S-CCPCH timing offsets can be chosen in a way that the relative timing offset of the same MTCH PDU can be minimised. S-CCPCH timing offsets can be created by combining FDD SCCPCH Offset (roughly in the range of 0..10msec TS 25.433 [3]) and FDD S-CCPCH Frame Offset (10msec, 20msec or 40msec; 0msec in case IE not present TS 25.433 [3]) and will be associated with those S-CCPCHs carrying MTCH at the time of set up (i.e. at COMMON TRANSPORT CHANNEL SETUP REQUEST TS 25.433 [3]).
Initial Timing Alignment for MTCH Transmission is depicted in figure 24 below.
3. Maintenance of Uu-Timing Alignment of MTCH transmissions on S-CCPCHs
After S-CCPCHs have been established, Node_Bs timing difference may increase due to drifting Node B time reference (Node B clock). Increasing differences in relative timing may be detected by the RNC when periodically performing RNC-Node_B Node synchronisation measurements. In case time differences are growing unacceptably large, RNC may decide to either re-schedule the MTCH PDUs to the existing S-CCPCHs (granularity: 1TTI) or to delete and re-establish the corresponding S-CCPCHs (granularity: 256 chips when using FDD SCCPCH Offset TS 25.433 [3]).
Figure 24: Initial Timing Alignment for MTCH Transmission
(Example: MCCH and MTCH on separate S-CCPCH; 40msec TTI on MTCH)
11.3 TDD MBMS related Transport Channel Synchronisation
Soft combining of MBMS related transmissions in the UE and MBSFN delivery may be supported by those TDD Radio Interface Synchronisation schemes depicted in section 8.3.
11.4 Inter-Node B Synchronisation of MTCH Transmissions for IP Multicast
In case a transport bearer is used by several FACH channels with IP multicast option, the transport channel synchronisations of different FACHs respectively from different Node Bs shall be maintained as described in subclause 11.2 and 11.3. In addition, when Node B receives data frame from an IP multicast group, it shall consider the value of the CFN field in the data frame as MFN and calculate the radio frame in which the first data shall be transmitted on the concerned FACH according to:
CFN = (MFN – CFN Offset) mod 256,
where:
– CFN Offset is a FACH parameter indicated by RNC TS 25.433 [3].
When setting the value of CFN Offset for a FACH, the RNC shall take into account the timing difference of different S-CCPCHs so that relative timing difference of MTCH transmissions from different cells respectively from different Node Bs can meet the requirement of the MBMS combining method used (see Figure 25).
Figure 25: Inter-Node B Synchronisation of MTCH Transmissions for IP Multicast
(Example: 40msec TTI on MTCH)
NOTE: Please refer to section 7.2 for the detailed Timing Adjustment and Time of Arrival monitoring on Iub/Iur interfaces.
11.5 3.84Mcps TDD MBSFN IMB Transport Channel Synchronisation
High accuracy Transport Channel Synchronisation is achieved through Inter Node B Node Synchronisation (chapter 6.1.2.4), where the BFN is frequency-locked to a high accuracy Network synchronisation reference. The Transport Channel Synchronisation, as described for FDD in this document, is performed with frequency-locked BFN.
Annex A (informative):
Change history
|
TSG # |
TSG Doc. |
CR |
Rev |
Subject/Comment |
New |
|---|---|---|---|---|---|
|
11 |
RP-010164 |
14 |
Approved at TSG RAN #11 |
4.0.0 |
|
|
11 |
RP-010166 |
16, 17 |
Approved at TSG RAN #11 |
4.0.0 |
|
|
12 |
RP-010371 |
019,020,024 |
Approved at TSG RAN #12 |
4.1.0 |
|
|
12 |
RP-010390 |
021.022 |
Approved at TSG RAN #12 |
4.1.0 |
|
|
13 |
RP-010576 |
027 |
Notation of Time Instances |
4.2.0 |
|
|
13 |
RP-010705 |
025 |
1 |
Correction of the Frequency Accuracy in the Frequency Acquisition Phase |
4.2.0 |
|
14 |
RP-010869 |
028 |
Text amendments for TDD Node B synchronisation |
4.3.0 |
|
|
14 |
RP-010846 |
030 |
2 |
Correction to CFN Calculation for UE |
4.3.0 |
|
15 |
RP-020163 |
034 |
Clarification on the DPCH frame offset |
4.4.0 |
|
|
15 |
RP-020191 |
032 |
Node B Synchronisation for 1.28Mcps TDD |
5.0.0 |
|
|
16 |
RP-020400 |
037 |
Reference corrections |
5.1.0 |
|
|
20 |
RP-030318 |
039 |
Removal of the Frequency Acquisition for Late-Entrant Cells for 1.28Mcps TDD |
5.2.0 |
|
|
22 |
RP-030684 |
042 |
1 |
Removal of the ambiguity about the activation time |
5.3.0 |
|
22 |
– |
– |
– |
Introduction of Release 6 specification |
6.0.0 |
|
26 |
RP-040437 |
045 |
3 |
MBMS related changes |
6.1.0 |
|
27 |
RP-050056 |
046 |
– |
Introduction of Fractional DPCH |
6.2.0 |
|
28 |
RP-050222 |
048 |
– |
Feature clean-up: Removal of DSCH (FDD mode) |
6.3.0 |
|
28 |
RP-050228 |
050 |
1 |
Synchronisation for MBMS p-t-m Transmissions from Multiple Cells (Simulcast) |
6.3.0 |
|
31 |
RP-060073 |
051 |
1 |
Introduction of 7.68Mcps TDD option |
7.0.0 |
|
33 |
RP-060499 |
053 |
– |
Correction of CFN for MBMS |
7.1.0 |
|
34 |
RP-060702 |
055 |
– |
Adding a new formula for Frame Offset and Chip Offset calculation |
7.2.0 |
|
34 |
RP-060837 |
056 |
1 |
Consistency of Specification Notations |
7.2.0 |
|
36 |
RP-070335 |
58 |
– |
Introduction of MBMS SFN (TDD) |
7.3.0 |
|
36 |
RP-070333 |
59 |
– |
Introduction of MBMS SFN (FDD) |
7.3.0 |
|
36 |
RP-070336 |
61 |
– |
Introduction of MBMS LCR TDD physical layer enhancements |
7.3.0 |
|
37 |
RP-070568 |
63 |
1 |
Introduction of GANSS (Galileo and Additional Navigation Satellite Systems) |
7.4.0 |
|
37 |
RP-070629 |
64 |
Timing Advance Corrections for 3.84/7.68 Mcps TDD EDCH |
7.4.0 |
|
|
38 |
RP-070846 |
65 |
2 |
The Improvement of Iub Efficiency for MBMS in IP RAN |
7.5.0 |
|
38 |
RP-070840 |
67 |
Further corrections on Enhanced Cell_FACH |
7.5.0 |
|
|
41 |
RP-080575 |
74 |
– |
Enable node synchronization is supported by the user plane protocols for HS-DSCH |
7.6.0 |
|
42 |
RP-081120 |
0076 |
1 |
Support for 3.84 Mcps MBSFN IMB operation |
8.0.0 |
|
44 |
RP-090633 |
0077 |
Correction of Transport Channel Synchronisation contradiction |
8.1.0 |
|
|
12/2009 |
Created version 9.0.0 based on version 8.1.0 |
9.0.0 |
|||
|
SP-49 |
SP-100629 |
Clarification on the use of References (TS 21.801 CR#0030) |
9.0.1 |
||
|
03/2011 |
Created version 10.0.0 based on version 9.0.1 |
10.0.0 |
|||
|
06/2011 |
RP-110686 |
0079 |
Correction related to the References and clean-up of 25.402 |
10.1.0 |
|
|
09/2012 |
Update to Rel-11 version (MCC) |
11.0.0 |
|||
|
09/2014 |
– |
– |
Update to Rel-12 version (MCC) |
12.0.0 |
|
|
12/2014 |
RP-142093 |
0080 |
1 |
Rapporteur Review |
12.1.0 |
|
12/2015 |
– |
– |
Update to Rel-13 version (MCC) |
13.0.0 |
|
Change history |
|||||||
|
Date |
Meeting |
TDoc |
CR |
Rev |
Cat |
Subject/Comment |
New version |
|
2017-03 |
SA#75 |
Promotion to Release 14 without technical change |
14.0.0 |
||||
|
2018-06 |
SA#80 |
– |
– |
– |
– |
Promotion to Release 15 without technical change |
15.0.0 |
|
2020-07 |
SA#88-e |
– |
– |
– |
– |
Update to Rel-16 version (MCC) |
16.0.0 |
|
2022-03 |
SA#95-e |
Promotion to Release 17 without technical change |
17.0.0 |
||||
|
2022-06 |
RAN#96 |
RP-221148 |
0081 |
1 |
D |
Inclusive language review for TS 25.402 |
17.1.0 |