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Content for  TS 38.331  Word version:  18.0.0

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5.9  MBS Broadcastp. 427

5.9.1  Introductionp. 427

5.9.1.1  Generalp. 427

UE receiving or interested to receive MBS broadcast service(s) applies MBS broadcast procedures described in this clause as well as the MBS Interest Indication procedure as specified in clause 5.9.4.
MBS broadcast configuration information, except CFR configuration for MCCH/MTCH, is provided on MCCH logical channel. MCCH carries the MBSBroadcastConfiguration message which indicates the MBS broadcast sessions that are provided in the cell as well as the corresponding scheduling related information for these sessions. Optionally, the MBSBroadcastConfiguration message may also contain a list of neighbour cells providing the same broadcast MBS service(s) as provided in the current cell. The configuration information required by the UE to receive MCCH is provided in SIB1 and SIB20. Additionally, System Information may provide information related to service continuity of MBS broadcast in SIB21.
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5.9.1.2  MCCH schedulingp. 427

The MCCH information (i.e. information transmitted in messages sent over MCCH) is transmitted periodically, using a configurable repetition period and within a configured transmission window. MCCH transmissions (and the associated radio resources and MCS) are indicated via the PDCCH addressed to MCCH-RNTI. PDCCH monitoring occasion(s) for MCCH transmission are determined according to the common search space indicated by searchspaceMCCH. If searchspaceMCCH is set to zero, PDCCH monitoring occasions for MCCH message reception in the MCCH transmission window are the same as PDCCH monitoring occasions for SIB1 where the mapping between PDCCH monitoring occasions and SSBs is specified in TS 38.213. If searchspaceMCCH is not set to zero, PDCCH monitoring occasions for MCCH message are determined based on search space indicated by searchspaceMCCH. PDCCH monitoring occasions for MCCH message which are not overlapping with UL symbols (determined according to tdd-UL-DL-ConfigurationCommon) are sequentially numbered from one in the MCCH transmission window. The [x×N+K]th PDCCH monitoring occasion for MCCH message in MCCH transmission window corresponds to the Kth transmitted SSB, where x = 0, 1, ...X-1, K = 1, 2, …N, N is the number of actual transmitted SSBs determined according to ssb-PositionsInBurst in SIB1 and X is equal to CEIL(number of PDCCH monitoring occasions in MCCH transmission window/N). The actual transmitted SSBs are sequentially numbered from one in ascending order of their SSB indexes. The UE assumes that, in the MCCH transmission window, PDCCH for an MCCH message is transmitted in at least one PDCCH monitoring occasion corresponding to each transmitted SSB and thus the selection of SSB for the reception MCCH messages is up to UE implementation.
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5.9.1.3  MCCH information validity and notification of changesp. 428

Change of MCCH information only occurs at specific radio frames, i.e. the concept of a modification period is used. Within a modification period, the same MCCH information may be transmitted a number of times, as defined by its scheduling (which is based on a repetition period).
When the network changes (some of) the MCCH information, it notifies the UEs about the change starting from the beginning of the MCCH modification period via PDCCH which schedules the MCCH in every repetition in that modification period.
Upon receiving a change notification, a UE receiving or interested to receive MBS services transmitted using MBS broadcast acquires the new MCCH information starting from the same slot. The UE applies the previously acquired MCCH information until the UE acquires the new MCCH information. The notification is transmitted with a 2-bit bitmap, see clause 7.3.1.5.1 of TS 38.212. The MSB in the 2-bit bitmap, when set to '1', indicates the start of new MBS service(s). The LSB in the 2-bit bitmap, when set to '1', indicates modification of MCCH information other than the change caused by start of new MBS service(s), e.g. modification of a configuration of an on-going MBS session(s), MBS session(s) stop or neighbouring cell information modification.
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5.9.2  MCCH information acquisitionp. 428

5.9.2.1  Generalp. 428

Reproduction of 3GPP TS 38.331, Fig. 5.9.2.1-1: MCCH information acquisition
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The UE applies the MCCH information acquisition procedure to acquire the MBS broadcast configuration information broadcasted by the network. The procedure applies to MBS capable UEs interested to receive or that are receiving MBS broadcast services that are in RRC_IDLE, RRC_INACTIVE or RRC_CONNECTED with an active BWP with common search space configured by searchSpaceMCCH.

5.9.2.2  Initiationp. 428

A UE shall apply the MCCH information acquisition procedure upon becoming interested to receive MBS broadcast services. A UE interested to receive MBS broadcast services shall apply the MCCH information acquisition procedure upon entering the cell providing SIB20 (e.g. upon power on, following UE mobility), upon receiving SIB20 of an SCell via dedicated signalling and upon receiving a notification that the MCCH information has changed due to the start of new MBS service(s). A UE that is receiving data via broadcast MRB shall apply the MCCH information acquisition procedure upon receiving a notification that the MCCH information has changed due to MCCH information modification other than the change caused by the start of new MBS service(s).
Unless explicitly stated otherwise in the procedural specification, the MCCH information acquisition procedure overwrites any stored MCCH information, i.e. delta configuration is not applicable for MCCH information and the UE discontinues using a field if it is absent in MCCH information.
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5.9.2.3  MCCH information acquisition by the UEp. 429

An MBS capable UE interested to receive or receiving an MBS broadcast service shall:
1 >
if the procedure is triggered by an MCCH information change notification:
2 >
start acquiring the MBSBroadcastConfiguration message on MCCH in the concerned cell from the slot in which the change notification was received;
1 >
if the UE enters a cell providing SIB20; or
1 >
if the UE receives sCellSIB20:
2 >
acquire the MBSBroadcastConfiguration message on MCCH in the concerned cell at the next repetition period.

5.9.2.4  Actions upon reception of the MBSBroadcastConfiguration messagep. 429

No UE requirements related to the contents of the MBSBroadcastConfiguration message apply other than those specified elsewhere e.g. within the corresponding field descriptions.

5.9.3  Broadcast MRB configurationp. 429

5.9.3.1  Generalp. 429

The broadcast MRB configuration procedure is used by the UE to configure PDCP, RLC, MAC and the physical layer upon starting and/or stopping to receive a broadcast MRB transmitted on MTCH, or upon modification of a configuration of a broadcast MRB received by the UE. The procedure applies to MBS capable UEs that are interested to receive or that are receiving an MBS broadcast service that are in RRC_IDLE, RRC_INACTIVE or RRC_CONNECTED with an active BWP with common search space configured by searchSpaceMTCH or searchSpaceMCCH.
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5.9.3.2  Initiationp. 429

The UE applies the broadcast MRB establishment procedure to start receiving an MBS session of an MBS broadcast service it is interested in. The procedure may be initiated e.g. upon start of the MBS session, upon entering a cell providing an MBS broadcast service the UE is interested in, upon becoming interested in the ongoing MBS broadcast service, upon removal of the UE capability limitations inhibiting reception of the ongoing MBS broadcast service UE is interested in.
The UE applies the broadcast MRB release procedure to stop receiving a session of an MBS broadcast service. The procedure may be initiated e.g. upon stop of the MBS session, upon leaving the cell broadcasting the MBS service the UE is interested in, upon losing interest in the MBS service, when capability limitations start inhibiting reception of the concerned service.
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5.9.3.3  Broadcast MRB establishmentp. 429

Upon a broadcast MRB establishment, the UE shall:
1 >
establish a PDCP entity and an RLC entity in accordance with MRB-InfoBroadcast for this broadcast MRB included in the MBSBroadcastConfiguration message and the configuration specified in clause 9.1.1.7;
1 >
configure the MAC layer in accordance with the mtch-SchedulingInfo (if included);
1 >
configure the physical layer in accordance with the mbs-SessionInfoList, searchSpaceMTCH, and pdsch-ConfigMTCH, applicable for the broadcast MRB;
1 >
if an SDAP entity with the received mbs-SessionId does not exist:
2 >
establish an SDAP entity as specified in clause 5.1.1 of TS 37.324;
2 >
indicate the establishment of the user plane resources for the mbs-SessionId to upper layers;
1 >
receive DL-SCH on the cell where the MBSBroadcastConfiguration message was received for the established broadcast MRB using g-RNTI and mtch-SchedulingInfo (if included) in this message for this MBS broadcast service.
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5.9.3.4  Broadcast MRB releasep. 430

Upon broadcast MRB release for MBS broadcast service, the UE shall:
1 >
release the PDCP entity, RLC entity as well as the related MAC and physical layer configuration;
1 >
if the SDAP entity associated with the corresponding mbs-SessionId has no associated MRB:
2 >
release the SDAP entity, as specified in clause 5.1.2 of TS 37.324;
2 >
indicate the release of the user plane resources for the mbs-SessionId to upper layers.
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5.9.4  MBS Interest Indicationp. 430

5.9.4.1  Generalp. 430

Reproduction of 3GPP TS 38.331, Fig. 5.9.4.1-1: MBS Interest Indication
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The purpose of this procedure is to inform the network that the UE in RRC_CONNECTED is receiving or is interested to receive MBS broadcast service(s) and to inform the network about the priority of MBS broadcast versus unicast and multicast MRB reception. MBS Interest Indication can only be sent after AS security activation.

5.9.4.2  Initiationp. 430

An MBS capable UE in RRC_CONNECTED may initiate the procedure in several cases including upon successful connection establishment/resume, upon entering or leaving the broadcast service area, upon MBS broadcast session start or stop, upon change of interest, upon change of priority between MBS broadcast reception and unicast/multicast reception, upon change to a PCell providing SIB21 (i.e. where the SIB1 scheduling information contains SIB21), upon receiving SIB20 of an SCell via dedicated signalling, upon handover, and upon RRC connection re-establishment, upon change to a PCell providing nonServingCellMII in SIB1, upon starting or stopping reception of MBS broadcast service on a non-serving cell, upon change of CFR information or subcarrier spacing for MBS broadcast reception on a non-serving cell. If the UE does not have the CFR information and subcarrier spacing for MBS broadcast reception on a non-serving cell at the time it sends the MBS Interest Indication, the UE sends an MBS Interest Indication after it has acquired those information from the non-serving cell.
Upon initiating the procedure, the UE shall:
1 >
if SIB21 is provided by the PCell; or
1 >
if nonServingCellMII is provided in SIB1 by the PCell:
2 >
ensure having a valid version of SIB21 for the PCell, if present;
2 >
if the UE did not transmit MBS Interest Indication since last entering RRC_CONNECTED state; or
2 >
if since the last time the UE transmitted an MBS Interest Indication, the UE connected to a PCell not providing SIB21:
3 >
if the set of MBS broadcast frequencies of interest, determined in accordance with clause 5.9.4.3, is not empty:
4 >
set the contents of MBS Interest Indication according to clause 5.9.4.5 and initiate transmission of the MBSInterestIndication message;
2 >
else:
3 >
if the set of MBS broadcast frequencies of interest, determined in accordance with clause 5.9.4.3, is different from mbs-FreqList included in the last transmission of the MBS Interest Indication; or
3 >
if the set of MBS broadcast frequencies of interest for MBS broadcast reception on non-serving cell, determined in accordance with clause 5.9.4.3, is different from the list of MBS broadcast frequencies of interest for MBS broadcast reception on non-serving cell included in the last transmission of the MBS Interest Indication; or
3 >
if any of the subcarrier spacing and the CFR information for MBS broadcast reception on non-serving cell has changed since the last transmission of the MBS Interest Indication; or
3 >
if the subcarrier spacing and the CFR information for MBS broadcast reception on non-serving cell have been acquired from the non-serving cell which were not reported in the previous MBS Interest Indication; or
3 >
if the prioritisation of reception of all indicated MBS broadcast frequencies compared to reception of any of the established unicast bearers and multicast MRBs has changed since the last transmission of the MBS Interest Indication:
4 >
set the contents of MBS Interest Indication according to clause 5.9.4.5 and initiate transmission of the MBSInterestIndication message;
3 >
else if SIB20 is provided for the PCell or for the SCell:
4 >
if since the last time the UE transmitted the MBS Interest Indication, the UE connected to a PCell not providing SIB20 and the UE was not provided with SIB20 for an SCell; or
4 >
if the set of MBS broadcast services of interest determined in accordance with clause 5.9.4.4 is different from mbs-ServiceList included in the last transmission of the MBS Interest Indication:
5 >
set the contents of MBS Interest Indication according to clause 5.9.4.5 and initiate the transmission of MBSInterestIndication message.
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5.9.4.3  MBS frequencies of interest determinationp. 431

The UE shall:
1 >
consider a frequency to be part of the MBS frequencies of interest if the following conditions are met:
2 >
at least one MBS session the UE is receiving or interested to receive via a broadcast MRB is ongoing or about to start; and
2 >
for at least one of these MBS sessions, SIB21 acquired from the PCell or a non-serving cell includes mapping between the concerned frequency and one or more MBS FSAIs indicated in the USD for this session, or for at least one of these MBS sessions, the concerned frequency is not included in SIB21 but is indicated in the USD for this session; and
2 >
the supportedBandCombinationList the UE included in UE-NR-Capability contains at least one band combination including the concerned MBS frequency.
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5.9.4.4  MBS services of interest determinationp. 432

The UE shall:
1 >
consider an MBS service to be part of the MBS services of interest if the following conditions are met:
2 >
the UE is receiving or interested to receive this service via a broadcast MRB; and
2 >
the session of this service is ongoing or about to start; and
2 >
one or more MBS FSAIs in the USD for this service is included in SIB21 acquired from the PCell for a frequency belonging to the set of MBS frequencies of interest, determined according to clause 5.9.4.3 or SIB21 acquired from the PCell does not provide the frequency mapping for the concerned service but that frequency is included in the USD of this service.
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5.9.4.5  Setting of the contents of MBS Interest Indicationp. 432

The UE shall set the contents of the MBS Interest Indication as follows:
1 >
if the UE has a valid version of SIB21 for the PCell; and
1 >
if the set of MBS frequencies of interest, determined in accordance with clause 5.9.4.3, is not empty:
2 >
include mbs-FreqList and set it to include the MBS frequencies of interest sorted by decreasing order of interest, using the absoluteFrequencySSB for serving frequency, if applicable, and the ARFCN-ValueNR(s) as included in SIB21 or in USD (for neighbouring frequencies);
2 >
include mbs-Priority if the UE prioritises reception of all indicated MBS frequencies above reception of any of the unicast bearers and multicast MRBs;
2 >
if SIB20 is provided for the PCell or for the SCell:
3 >
include mbs-ServiceList and set it to indicate the set of MBS services of interest sorted by decreasing order of interest determined in accordance with clause 5.9.4.4.
1 >
if nonServingCellMII is included in SIB1 for the PCell; and
1 >
if the set of MBS frequencies for MBS broadcast reception on non-serving cell, determined in accordance with clause 5.9.4.3, is not empty:
2 >
include freqInfoMBS;
2 >
if the UE has acquired cfr-InfoMBS and subcarrierSpacing for MBS broadcast reception on the non-serving cell:
3 >
include cfr-InfoMBS and subcarrierSpacing;
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