3GPP TSG-RAN WG1 Meeting #121	R1-2503273
St Julian’s, Malta, May 19th – 23rd, 2025

Agenda Item:	9.12.2
Source:	Huawei, HiSilicon
Title:	Discussion on low band CA via switching
Document for:	Discussion and Decision

Conclusion
In summary, our proposals and observations are the following,
For switching from FDD carrier to SDL carrier, support Alt 2: NW configures whether the switching gap is at the FDD slot or SDL slot.
For the semi-static switching pattern, maximum 2 switches within 1 slot. 
Note: this does not violate the slot-level granularity of the switching pattern. 
Maximum time duration on one carrier should be considered in order to minimize its impacts on UE measurement/synchronization, which reply on SSB and CSI-RS receptions, and HARQ-ACK/NACK feedback on PUCCH.
For R19 low band switching, if a RACH procedure is triggered by a UE itself or by network signalling, the semi-static switching pattern, if configured, is temporarily suspended until the last DL reception or UL transmission involved in the RACH procedure is successfully done. 

3GPP TSG RAN WG1 Meeting #121			R1-2503331
St Julian’s, Malta, 19-23 May, 2025

Source:	ZTE Corporation, Sanechips
Title:	Discussion on low band carrier aggregation via switching
Agenda item:	9.12.2
Document for:	Discussion and Decision

Conclusion
In this contribution, we discuss the switching pattern design with following observations and proposals:
Proposal 1: The location of switching gap for switching from FDD carrier to SDL carrier should be configurable.
Proposal 2:  For the restriction of maximum X switch(es) within Y slot(s), X should be greater than 16 for Y=40.
Proposal 3:  There should be no other restrictions for switching pattern configuration.
Proposal 4:  There should only one TDM pattern for LB CA in Rel-19.
Proposal 5: There should be no specification impact for the switching gap duration.
Proposal 6: The additional processing time should not be needed for LB CA.
Proposal 7: It should be the NW implementation to avoid the collision, except for repetition or TBoMS, in which UE is expected to drop or postpone the corresponding reception and/or transmission.
Proposal 8: The same switching pattern should be applied to the dormant SCell and activated SCell.
Proposal 9: Introduce the following RRC parameters for low band carrier aggregation via switching.

3GPP TSG RAN WG1 #121                        		                                                    R1-2503384
St Julian’s, Malta, May 19th – 23rd, 2025

Source: 	vivo
Title:	Remaining issues on Low band carrier aggregation via switching
Agenda Item:	9.12.2
Document for:	Discussion and Decision

Conclusion
In this contribution, the following observations and proposals are summarized as follows: 
Proposal 1: For a SCell in a SDL carrier in R19 LB CA via switching, the PDCCH monitoring occasions should be configured in SDL carrier to support self-scheduling.
Proposal 2: When a switching pattern for LB CA via switching is configured, the SDL carrier cannot be configured with a dormant BWP.
Proposal 3: The configured time switching pattern shall guarantee that UE does not stay continuously on SDL carrier for longer than 15 slots.
Proposal 4: For the restriction of maximum X switch(es) within Y slot(s), at least support Y=5, X=1.
Proposal 5: UE is not expected to be scheduled uplink transmission in the switching gap duration of the last uplink slot before switching.
Proposal 6: Support alt1: switching gap is always assumed at the “switch from” carrier, i.e., FDD carrier.
Proposal 7：For Rel-19 low NR band carrier aggregation via switching, when NW configures a semi-static switching pattern to a UE, RAN1 does not support the UE to perform additional switching not following the semi-static switching pattern
Proposal 8: For DL/UL transmission on a serving cell, the symbols in invalid periods can be treated as the symbols semi-statically configured as TDD UL/DL symbols and similar UE behaviors can be defined.
Proposal 9: For low band carrier aggregation via switching, UE handles the overlapping among SPS PDSCHs after resolving overlapping with symbols in the slot indicated as invalid periods by semi-statically configured switching pattern including the switching gap.
Proposal 10: For periodic CSI-RS and semi-persistent CSI-RS on the serving cell configured in CSI report configuration in CSI-ReportConfig associated with the higher layer parameter reportQuantity comprising at least 'RI',
the UE is not expected to receive the periodic CSI-RS and semi-persistent CSI-RS during the invalid periods of the serving cell based on the configuration of switching pattern. 
The most recent CSI measurement occasion of semi-persistent CSI-RS resource or periodic CSI-RS resource on the serving cell occurs in valid time of the serving cell for CSI report configured by CSI-ReportConfig associated with the higher layer parameter reportQuantity comprising at least 'RI'.
the UE reports a CSI report only if receiving at least one CSI-RS transmission occasion of each periodic CSI-RS resource or semi-persistent CSI-RS resource on a serving cell in valid time of the serving cell, no later than CSI reference resource, and the UE drops the CSI report otherwise.

Proposal 11: If the higher layer parameter timeRestrictionForChannelMeasurements in CSI-ReportConfig is set to "Configured",
the UE shall derive the channel measurements for computing CSI reported in uplink slot n based on only the most recent, no later than the CSI reference resource, in cell DTX active time of a serving cell if cell DTX is activated, valid time of the carrier of the serving cell if a switching pattern for the serving cell, occasion of NZP CSI-RS associated with the CSI resource setting on the serving cell. 
the UE shall derive the interference measurements for computing the CSI value reported in uplink slot n based on the most recent, no later than the CSI reference resource, in cell DTX active time of a serving cell if cell DTX is activated, valid time of the carrier of the serving cell if a switching pattern for the serving cell, occasion of CSI-IM and/or NZP CSI-RS for interference measurement associated with the CSI resource setting on the serving cell. 
Proposal 12: For HARQ-ACK codebook generation of SPS PDSCHs, UE will not generate HARQ-ACK information for SPS PDSCH overlapping with symbols indicated as invalid periods of the serving cell based on semi-statically configured switching pattern including the switching gap.
Proposal 13: For type 1 HARQ-ACK codebook generation, a row of the TDRA table overlapping with the symbols in invalid periods of the serving cell is excluded when determining the set of occasions of candidate PDSCH receptions.
Proposal 14: During invalid periods of the serving cell, the UE configured with LB CA via switching is not expected to transmit the periodic SRS, or semi-persistent SRS for channel acquisition.
Proposal 15: UE performs UL multiplexing of PUCCH/PUSCH before considering limitations for UE transmission due to LB CA via switching.

3GPP TSG RAN WG1 #121 Meeting		             			R1-2503421
St Julian’s, Malta, May 19th – 23rd, 2025
Agenda item:	9.12.2
Source:	NEC
Title:	Discussion on low band carrier aggregation via switching 
Document for:	Discussion 

Conclusion
From the discussion, we discussed the issues to support low band carrier aggregation via switching and have the following proposals:
Proposal 1: Within switching gap from SDL to FDD in SDL slot, UE should be able to perform FDD UL transmissions from the first symbol of FDD UL slot after switching from SDL carrier to FDD carrier.
Proposal 2: For switching from FDD carrier to SDL carrier, select Alt 3 “Switching gap is always assumed at the SDL carrier”.
Proposal 3: Support activation of semi-static FDD/SDL switching pattern upon RRC configuration.
Proposal 4: Support dynamic activation of semi-static FDD/SDL switching pattern after RRC configuration.
Proposal 5: DCI may include an indicator to update to one of the Special Slot configurations.  
Proposal 6: DCI can support cross-carrier scheduling with SDL carrier indication.
Proposal 7: DCI which schedules SDL carrier from FDD carrier may support multi-slot and multi-carrier scheduling with common scheduling information.

3GPP TSG RAN WG1 #121	R1- 2503430
St Julian, Malta, 19 – 23 May 2025

Agenda item:		9.12.2
Source:	Nokia
Title:	Principles for low-band CA via switching
WI code:	NR_LBCA_Sw
Release:	Rel-19
Document for:		Discussion and Decision

Conclusion
In this contribution we provided the initial Nokia view on how to define the low band carrier aggregation via switching feature and make the following proposals:
The maximum switching frequency is 2 switches (one FDDSDL switch and one SDLFDD switch) over 4 slots, i.e. Restriction of maximum X=2 switch(es) within Y=4 slot(s).
For switching from FDD carrier to SDL carrier, Alt 1: Switching gap is always assumed at the “switch from” carrier, i.e., FDD carrier
The DL reception after the switch starts at symbol#0 of the slot
The UL transmission on the FDD uplink can start at symbol#0 of the FDD UL slot after the switch
Different switching gap lengths can be configured for the FDD  SDL switch and for the SDL  FDD switch.
PDSCH scheduling in FDD is managed by the PDCCH in FDD, while PDSCH scheduling in SDL is managed by the PDCCH in SDL.
PUSCH scheduling in FDD is managed by the PDCCH in FDD.
When the SDL carrier is deactivated, the FDD cell should resume ‘normal’ operations, i.e. not apply any switching, and be able to receive and transmit continuously on the FDD carrier.
When Cell DRX operates on the SDL carrier, the SDL carrier reception should be stopped completely and only reactivated based on traffic on the FDD carrier.
When Cell DTX is activated on the SDL carrier, the FDD cell should resume ‘normal’ operations, i.e. not apply any switching, and be able to receive and transmit continuously on the FDD carrier.

3GPP TSG RAN WG1 #121			R1-250XXXX
St Julian’s, Malta, May 19th – 23th, 2025
Agenda item:	9.12.2
Source: 	Spreadtrum, UNISOC
Title: 		Discussion on low band carrier aggregation via switching 
Document for:	Discussion and decision

Conclusion
In this contribution, we made the following observations and proposals.
For Rel-19 low NR band carrier aggregation via switching, support only one semi-static configuration of switching pattern to a UE based on UE-specific RRC configuration between PCell and SCell.
At most one switching from PCell to SCell exits in 5ms.
Contiguous slots of SCell cannot be exceed 8 slots in a period.
At least one SSB is available at the UE during every 160 ms for both of PCell and SCell if applicable
For switching from FDD carrier to SDL carrier, switching gap can locate at the “switch from” carrier, i.e., FDD carrier.
For the specification impact of UL TA, UE does not expect the UL dropping due to overlapping with the switching period.
The switching pattern for SDL SCell is not applied if SCell is in dormancy BWP
For Rel-19 low NR band carrier aggregation via switching, when NW configures the semi-static switching pattern to a UE, for Type-I HARQ-ACK codebook generation 
A row of the TDRA table is excluded from the determination of the set of occasions for candidate PDSCH receptions if the PDSCH associated with the row is not to be received by the UE due to LB-CA switching.
For Rel-19 low NR band carrier aggregation via switching, when NW configures the semi-static switching pattern to a UE, for HARQ-ACK codebook generation 
HARQ-ACK bit for a SPS PDSCH is not included in the HARQ-ACK codebook if the SPS PDSCH is not to be received by the UE due to LB-CA switching.
For Rel-19 low NR band carrier aggregation via switching, when NW configures a semi-static switching pattern to a UE, RAN1 does not consider the UE perform additional switching not following the semi-static switching pattern
FFS: whether and, if needed, how to support the only candidate exceptional scenario, i.e., CB RACH
For low band carrier aggregation via switching, semi-static pattern indicates UE to operate (receive or transmit) on only one serving cell.
The UE does not receive or transmit a semi-static signal/channel on a serving cell if the semi-static signal/channel overlaps with a non-operation period of the serving cell.
The UE does not expect to be scheduled with a transmission/reception on a serving cell by a DCI format and the transmission/reception overlaps with a non-operation period of the serving cell.

3GPP TSG RAN WG1 #121		R1-2503588
St. Julian’s, Malta, May 19th – 23rd, 2025
Agenda item:	9.12.2
Source:	Samsung
Title:	Discussion on low band carrier aggregation via switching
Document for:	Discussion and decision

Conclusion
The contribution discusses low band carrier aggregation via switching and the proposals and observations are summarized below.
Proposal 1: Regarding the restriction of maximum X switch(es) within Y slot(s), support Y = 40 and X = 8.
Observation 1: For low band carrier aggregation via switching, if the number of continuous slots on SCell is larger than 7, HARQ-ACK of a PDSCH reception in the last slot on PCell cannot be provided due to the K1 value restriction.
Proposal 2: For low band carrier aggregation via switching, the maximum of continuous slots on SCell is 7.
Observation 2: Alt 1 (Switching gap is always assumed at the “switch from” carrier, i.e., FDD carrier) would impact on UL transmissions on PCell as well as UCI multiplexing procedure.
Proposal 3: For switching from FDD carrier to SDL carrier, support Alt 3, i.e., Switching gap is always assumed at the SDL carrier.)

Proposal 4: For low band carrier aggregation via switching, 
The UE does not receive or transmit a semi-static signal/channel on a serving cell if the semi-static signal/channel overlaps with a non-operation period of the serving cell or the switching gap.
The UE does not expect to be scheduled with a transmission/reception on a serving cell by a DCI format and the transmission/reception overlaps with a non-operation period of the serving cell or the switching gap.
Proposal 5: For low band carrier aggregation via switching, additional processing time should be introduced for the following cases if carrier switching happens between a DL reception and a UL transmission,
a PDCCH reception schedules a PUSCH transmission
a PDCCH reception indicates SRS transmission
a RAR schedules a PUSCH transmission
a PUCCH transmission with HARQ-ACK for a PDSCH or PDCCH reception
Proposal 6: For low band carrier aggregation via switching, 
If a UE is provided with Type-1 HARQ-ACK codebook, and a candidate PDSCH reception on a serving cell overlaps with a non-operation period of the serving cell, the candidate PDSCH reception is excluded from the set of occasions for candidate PDSCH receptions.
If a SPS PDSCH reception on a serving cell overlaps with a non-operation period of the serving cell, the UE does not receive the SPS PDSCH and does not transmit HARQ-ACK for the SPS PDSCH reception.

3GPP TSG RAN WG1 #121                                                                                       R1-2503657
St Julian’s, Malta, May 19th – 23th, 2025

Agenda Item:	9.12.2
Source:	Lenovo
Title:	Discussion on carrier switching pattern for low band carrier aggregation via switching
Document for:	Discussion & Decision

Conclusion
In this contribution, we focus on the open issues for low band CA via switching and have below observations and proposals:
Observation 1: The carrier switching pattern should be designed to guarantee DL transmission occasions for SSBs and reference signals on one carrier different from those on another carrier to avoid losing the synchronization on two carriers.
Observation 2: The carrier switching pattern should be designed to avoid frequent switching as much as possible.
Observation 3: The carrier switching pattern should be designed to guarantee the HARQ-ACK feedback corresponding to PDSCHs on DL-only carrier can be transmitted on the paired carrier.
Observation 4: Rel-16 HARQ-ACK suspension and one-shot HARQ-ACK request can simplify the carrier switching pattern design to avoid frequent carrier switching for transmitting HARQ-ACK feedback for PDSCHs on Cell 2.

Proposal 1: For NR low band CA via switching, the semi-static carrier switching pattern can be designed to have maximum 2 switches within 10 slots (i.e., one radio frame) subject to UE capability.
Proposal 2: For NR low band CA via switching, for switching from FDD carrier to SDL carrier, if the time domain resource allocation of the ongoing DL transmission on the FDD carrier does not include the last symbol, or UE needs to monitor the search space from the first symbol of the SDL carrier, then the switching gap is located on the FDD carrier; otherwise, the switching gap is located on the SDL carrier.
Proposal 3: UE does not expect the case where the time domain resource allocation of the PDSCH transmission on the FDD carrier includes the last symbol and UE needs to monitor the search space from the first symbol of the SDL carrier.
Proposal 4: For Type-1 HARQ-ACK codebook, exclude candidate PDSCH reception occasions from a cell if UE switches to another cell. 
Proposal 5: For HARQ-ACK feedback timing, support more than 8 values in the K1 set with new values larger than 15. 

3GPP TSG RAN WG1 #121	R1-2503739
St Julian’s, Malta, May 19th – May 23rd, 2025

Agenda item:		9.12.2
Source:				Ofinno
Title:					Discussion on low-band CA with switching
Document for:		Discussion and Decision

Conclusion
This contribution has discussed the remaining issues related to the physical layer aspects of the low band carrier aggregation operation via semi-static switching pattern. The following are our proposals: 
Proposal 1: In terms of restriction, at least X = 1 and Y = 2 is supported. X = 1 and Y = M (5≥M≥2) can be considered. 
Proposal 2: Network ensures the semi-static switching pattern to satisfy a) maximum consecutive slots assigned to the SDL carrier 2 does not exceed 16 msec; b) at least one SMTC occasion per 40 msec is allocated to the FDD carrier 1 and SDL carrier 2 respectively.
Proposal 3: Alt 2 could be more flexible to handle different impact from Alt 1 or Alt 3. If we agree on Alt 2 or Alt 3, network ensures a slot has maximum one switching gap (e.g., by configuring a minimum number of two consecutive slots to SDL carrier). 
Proposal 4: During a switching gap, a UE is not required to either transmit or receive on the FDD carrier or receive on the SDL carrier. The UE drops a downlink channel/signal or uplink channel/signal if it overlaps with the switching gap. 
Proposal 5: RAN1 specification should specify the duration of the switching gap switching from SDL carrier to FDD carrier as the sum of Z1 symbols and UL TA, where Z1 is 1 or 2 symbols depending on the UE capability.
Proposal 6: Discussion related to the applicability of the semi-static switching pattern during the SCell deactivation is left for RAN4.
Proposal 7: The UE starts to apply the semi-static switching pattern at least one slot after transmitting a valid CSI report for the activated SCell (i.e. SDL carrier).
Proposal 8: When the SCell (SDL carrier) is put to dormant then the UE operates on PCell (FDD) carrier on both DL and UL without any switching to SCell (SDL carrier).
Proposal 9: Do not modify the existing UE procedure on Type-I HARQ-ACK codebook generation when the UE is configured with a semi-static switching pattern.
Proposal 10: For Rel-19 low NR band carrier aggregation via switching, the determination of the PDSCH processing time is further based on the switching time from Case 2 (with PDSCH reception) to Case 1 (with HARQ-ACK transmission).
Proposal 11: The UE configured with semi-static switching pattern drops the following reception and/or transmission of semi-statically configured reference signals and channels under the collision:
Periodic and semi-persistent CSI-RS
SSB
Periodic and semi-persistent SRS
Semi-static PDCCH
SPS-PDSCH
CG-PUSCH (Type-1/2)
SR on PUCCH
Proposal 12: For the UE configured with semi-static switching, the network can ensure that the SMTC duration of the SMTC of a serving cell (e.g., PCell) does not collide/overlap with the time slots of the other serving cell (e.g., SCell).
Proposal 13: The UE does not apply the semi-static switching pattern and stays on the PCell (FDD carrier) at least during there is on-going random access procedure on PCell.
Proposal 14: Additionally, 
For a RACH procedure triggered by a PDCCH order, the UE does not apply the semi-static switching pattern starting from a slot in which the UE has received the PDCCH order for the preamble transmission. 
For a contention-based RACH procedure, the UE starts to re-apply the semi-static switching pattern after a slot in which the UE transmits the PUCCH (containing an ACK) for a Msg 4 PDSCH. 
Proposal 15: Clarify the UE behavior on SDL carrier 2 (or FDD carrier 1) during the BWP switching on FDD carrier 1 (or SDL carrier2).

Proposal 16: Discuss CSI feedback, reference resource definition in consideration of the switching pattern.

3GPP TSG RAN WG1 #121                                         R1-2503780
St Julian’s, Malta, May 19th – 23rd, 2025

Source:         CATT
Title:            Discussion on low band carrier aggregation via switching
Agenda Item:    9.12.2
Document for:   Discussion and Decision

Conclusion
In this contribution, the potential spec impacts for LBCA are discussed. The proposals are summarized as follows:
Proposal 1: For restriction of maximum X switch(es) within Y slot(s), the following combinations can be considered 
{X =2, Y=10ms}
{X =3, or 4, Y=20ms}
{X =6, or 7,or 8, Y=40ms}
Proposal 2: For switching from FDD carrier to SDL carrier, the Alt 2 is preferred as follows
Alt 2: NW configures whether the switching gap is at the FDD carrier or SDL carrier
Proposal 3: For switching from SDL carrier to FDD carrier and the switching gap is located on SDL carrier, both SDL and FDD carrier shall omit the reception/transmission duration of the symbols of the switching gap.
Proposal 4: For switching from FDD carrier to SDL carrier and the switching gap is located on FDD carrier.
FDD carrier will omit reception duration of the symbols for switching gap.
FDD carrier will omit transmission following symbols at the end of last slot for FDD carrier transmission
 Max(0,. 
The GAP during is configured by RRC, The TA value can be configured by gNB to avoid ambiguity。
dur_OS is duration of one symbol for SCS=15KHz
Proposal 5: For switching from FDD carrier to SDL carrier and the switching gap is located on SDL carrier, both SDL and FDD carrier will omitted reception/transmission duration of the symbols for switching gap.
Proposal 6: For the UCIs other than the HARQ-ACK feedback, i.e. SR and CSI report, for the resource of PUCCH can be up to gNB configuration, ensuring that it falls within the period of case 1.
Proposal 7: When the UE is in case 2, it can suspend the switching pattern configuration and switch to case 1 to start sending preamble, and then resume the configuration until the random access procedure is completed.
Proposal 8: For the Type-1 HARQ-ACK codebook, the occasions for candidate PDSCH reception should be pruning based on the LBCA switching pattern for each of carrier.

3GPP TSG RAN WG1 #121		      	R1-2504153
St Julian’s, Malta, May 19th – 23th, 2025

Agenda item:	9.12.2
Source: 	ETRI
Title: 	Discussion on low band carrier aggregation via switching
Document for:	Discussion/Decision

Conclusions
In this contribution, we provided our view on the semi-static pattern configuration and collision handling for the switching gap, and proposed the following.
Proposal 1: The switching gap for FDD to SDL transition can be configured at the switch-from carrier (i.e., FDD).
Proposal 2: Switching between FDD and SDL carriers may be configured to ensure that each carrier duration continues for a reasonable number of consecutive slots.
Proposal 3: Collisions between the switching gap and physical signals or channels can be avoided by the network through scheduling. The UE may drop a signal only if it overlaps with the switching gap and belongs to a predefined list of periodic or semi-static resources.

3GPP TSG RAN WG1 #121		R1-2504217
St Julian’s, Malta, May 19th – 23rd, 2025

Source:	OPPO
Title:	Discussion of low-band CA via switching
Agenda Item:	9.12.2
Document for:	Discussion and Decision

Conclusions
This contribution is concluded with the following proposals:
Proposal 1:  UE does not expect both of the following in switching pattern configuration. 
More than two switching within one frame; and
More than one switching within one subframe.
Proposal 2: For switching from FDD carrier to SDL carrier, NW configures whether the switching gap is on the FDD carrier or SDL carrier.
Proposal 3: UE does not expect to transmit and receive in switch-to carrier earlier than switching period after the starting of switching gap.
No further specification impact is introduced for the relation to TA.  
Proposal 4: RAN1 chooses from following for handling of collision between switching gap and physical channels/signals. 
Option-1: UE does not expect a physical channel/signal occasion to be overlapping with a switching gap. 
Option-2: UE cancels the transmission/reception for a physical channel/signal occasion that overlaps with a switching gap, where the physical channel/signal occasion is the outcome of legacy channel multiplexing/prioritization procedure.   
Observation 1: The overlapping between carrier unavailability duration and a channel/signal not involving in RACH procedure can be avoided by proper switching pattern configuration and channel/signal resource allocation.
Observation 2: There are two solutions to handle PRACH occasion in FDD-carrier unavailability duration.
Solution 1: PRACH occasion is invalid when FDD-carrier is indicated as unavailable carrier by switching pattern. In other words, UE transmits PRACH only when FDD carrier is indicated as available carrier by switching pattern.
Solution 2: PRACH occasion is still valid even when FDD-carrier is indicated as unavailable carrier by switching pattern. When UE needs to transmit PRACH, UE can autonomously switch to FDD carrier to transmit PRACH on PRACH occasion.
Proposal 5: For a RACH procedure on FDD carrier, 
Once a UE transmits PRACH, the UE stays on FDD carrier before the RACH procedure completes. 
After RACH procedure completes, the UE switches to SDL carrier at the next configured FDD-to-SDL switching gap. 
where the completion of the RACH procedure can refer to the ending of Msg-3 transmission or the ending of PUCCH transmission carrying HARQ-ACK of Msg-4, in both CFRA and CBRA.

3GPP TSG RAN WG1 #121			                 R1-2504255
St Julian’s, Malta, May 19th – 23th, 2025

Agenda Item:	9.12.2
Source: 	LG Electronics
Title: 	Discussion on low band CA operation via switching for Rel-19
Document for:	Discussion and decision

Conclusions
In this contribution, we discussed consideration points and potential issues on the low band CA operation via semi-static switching pattern in Rel-19, and the following proposals are provided:

Proposal #1: Consider X=1 and Y=1 on the restriction of maximum X switch(es) within Y slot(s).

Proposal #2: Consider K0 and K1 values on the restriction of configuring consecutive SDL slots.

Proposal #3: Support Alt 1 for the switching from FDD carrier to SDL carrier.
Alt 1: Switching gap is always assumed at the “switch from” carrier, i.e., FDD carrier

Proposal #4: Consider how to handle (or what is the UE behaviour in) the situation that the semi-static switching pattern activates Case 2 during essential DL signal/channel transmission (e.g. SSB, CSS, CSI-RS for RRM/RLM/BFR) on FDD carrier 1.

Proposal #5: Consider UE behaviour in the situation that the semi-static switching pattern activates Case 2 during periodic UL signal/channel transmission occasion/resource (e.g. RACH occasion, SR PUCCH, CG PUSCH, PUXCH repetition) on FDD carrier 1.
Discuss how to handle SR transmission counter/prohibit timer or available slot counting for PUSCH repetition on FDD carrier 1 during Case 2
Consider FDD carrier 1 with discontinuous UL slots as TDD carrier, and the UL occasions/ resources on FDD carrier 1 during Case 2 as invalid

Proposal #6: Consider to add the switching time from Case 2 (with PDSCH reception) to Case 1 (with HARQ-ACK transmission) in the determination of UE PDSCH processing time.

Proposal #7: Consider to exclude the slots invalid for PDSCH scheduling on carrier 1 (or 2) during Case 2 (or 1) in the construction of Type-1 HARQ-ACK codebook.

Proposal #8: Consider DAI signalling by DL DCI in case of Type-2 codebook for the CA of carrier 1 and 2 via switching where only one carrier can be scheduled at a time.

3GPP TSG RAN WG1 #121                                                       R1-2504275
St Julian’s, Malta, May 19th – 23th, 2025
 
Agenda item:	9.12.2
Source: 	MediaTek Inc.
Title: 	Low band carrier aggregation via switching
Document for:	Discussion and decision

Conclusion 
We have the following observations in this contribution. 
Observation 1: In NR, CORESET duration can be configured only up to 3 OFDM symbols. And baseline UE capability supports PDCCH monitoring only in the first 3 OFDM symbols.
Observation 2: With 140us switching period and 10us transient period defined in RAN4, at least 2 PDCCH symbols will be jeopardized if switching gap is located at the switch-to carrier.
Observation 3: If switching gap is located at the “switch-to” carrier, the loss of PDCCH symbols cannot be recovered no matter how hard gNB tries by adjusting its configuration and/or changing its implementation.
Observation 4: PUCCH format 0 (short, 1~2 symbols) can serve as alternative to PUCCH format 1 for transmitting 1 or 2 UCI bits for SR and HARQ-ACK.
Observation 5: PUCCH formats 2 and 3 can serve as alternative to PUCCH format 4 for moderate UCI payload.
Observation 6: Durations of both PUCCH formats 1 and 4 are configurable from 4 to 14 symbols, and all NR UEs are mandatory to support different durations without capability signaling according to FG 4-1 in TR38.822.
Observation 7: With gNB’s proper configuration and implementation, legacy UEs on the FDD carrier will not be impacted due to the introduction of R19 LBCA.
Observation 8: SRS periods are often much larger than 1msec and NW should be able configure SRS in slots without switching for a bitmap based switching pattern.
Observation 9: Configuration of PUSCH TDRA is very flexible and ranges from 1 to 14 symbols. This TDRA configuration flexibility has been mandatorily supported by all NR UEs without capability signaling.
Observation 10: Shortening PUSCH to be less than 14 symbols is nothing new. This has been handled when UL Tx switching is supported.
Observation 11: It is not a typical configuration to place CSI-RS in the last two symbols in a slot.
Observation 12: Even if CSI-RS is placed in the last two symbols in a slot, it will not be impacted if there is no switching in the slot based on the configured switching pattern.
Observation 13: If Alt 2 (configurable by NW) is supported, both IODT progress and feature deployment will be delayed, if not infeasible.
Observation 14: Per RAN4 LS, SSB should be available at least every 160ms for UE to fulfill UL transmit timing requirements.
Observation 15: Some front-end components are shared for uplink transmission path and downlink reception path. Therefore, When SDL->FDD switch is performed, the transmission path for FDD uplink carrier is not ready before the RF retuning is complete.
We have the following proposals in this contribution. 
Proposal 1: If an issue can be resolved by gNB’s implementation and/or proper configuration, gNB should just do so. Its impact on RAN1 specifications and UE should be minimized.
Proposal 2: Optional UE features shall not be assumed or even mandated to support this feature, including cross-carrier scheduling, SSB-less SCell operation, etc.
Proposal 3: For switching from FDD carrier to SDL carrier, switching gap is always assumed at the “switch from” carrier, i.e., FDD carrier.
Proposal 4: SSB-based SCell operations is assumed as baseline for this WI.
Proposal 5: For an RRC-configured semi-static switching pattern, gNB shall guarantee SSB availability on both carriers at least once every X1 and X2 msec on the FDD carrier and SDL carrier, respectively, with X1 <=min(160, 2*SSB period on the FDD carrier) and X2<=min(160, 2*SSB period on the SDL carrier).
Proposal 6: In an RRC-configured semi-static switching pattern, the maximum number of switch(es) is X within Y slot(s) with (X, Y) = (8, 40) and (1, 1).
Proposal 7: Self-scheduling is assumed as baseline for this WI.
Proposal 8: UE is not expected to be scheduled or configured with UE-specific downlink resources overlapping with switching gaps.
Proposal 9: UE is not expected to be scheduled or configured with UE-specific uplink resources overlapping with switching periods.
Proposal 10: For a received PDSCH at slot n on either FDD or SDL carrier, UE expects to be configured a K1 value so that it is on the FDD carrier at slot n+K1 according to its configured switching pattern where K1 is configured according to existing UE capabilities reported by UE.
No new K1 values and HARQ process numbers are introduced for this feature.

Proposal 11: Once configured with a semi-static switching pattern, UE is in principle only expected to switch between the FDD carrier and the SDL carrier, according to the configured switching pattern. No additional switching is expected except for RACH procedure.
The base station shall not schedule or configure the UE in a way conflicting to the configured switching pattern.

Proposal 12: When RACH is triggered, UE discards the configured switching pattern and stays on the FDD carrier to complete RACH.
When RACH is completed, select one of the following for UE to continue switching between the two carriers
Alt 1: gNB reconfigures UE a switching pattern
Alt 2: UE autonomously resumes the applicability of its switching pattern.
FFS: detailed timeline to avoid ambiguity between gNB and UE

Proposal 13: For low-band carrier aggregation via switching, when there is at least a carrier switch between the received downlink PDCCH/PDSCH and the corresponding uplink transmission PUCCH/PUSCH/SRS,
introduce additional processing time for UE in the following cases: 
Case 1: A PUCCH transmission with HARQ-ACK for a PDSCH
Case 2: PDCCH reception schedules a PUSCH transmission
Case 3: A PDCCH reception indicates SRS transmission
The additional processing required for a UE is the switching period, 35us or 140us, indicated by the UE.  
UE does not expect to have more than one SDL->FDD switch or more than one FDD->SDL switch between the received downlink PDCCH/PDSCH and the corresponding uplink transmission (PUCCH/PUSCH/SRS).     

3GPP TSG RAN WG1 #121		             R1-2504347
St Julian’s, Malta, May 19th – 23rd, 2025

Agenda Item:	9.12.2
Source:	Apple
Title:	On low-band carrier aggregation via switching
Document for:	Discussion/Decision

Conclusion
In this contribution, we made the following observations/proposals on low-band carrier aggregation via switching:
Observation 1: With semi-static switching pattern, further restriction in terms of limiting the number of switching instances across multiple slots could be beneficial as network may not need to switch to different carrier on each slot

Observation 2: In Rel-19, since the switching is expected to be based on semi-static configuration of a pattern that triggers UE to switch between case 1 and case 2, therefore, in our view, network should be able to avoid other configurations that overlaps with the switching gap considering relaxed timeline


Proposal 1: Only a single switching pattern is configured to UE via UE specific RRC configuration
No further discussion/consideration on additional patterns, as the configuration is only applicable when SCell is activated, as per RAN4 agreement

Proposal 2: As a starting point, no more than 1 switching per slot should be considered 

Proposal 3: Further restriction in terms of number of switching per number of multiple slots can be supported, where candidates for different combinations could be based on UE capability

Proposal 4: For switching gap location in case of switching from FDD carrier to SDL carrier, adopt Alt 1, i.e. switching gap is always assumed at the “switch from” carrier, i.e., FDD carrier (same as for the case of switching from SDL carrier to FDD carrier)

Proposal 5: Network is not expected to allow misalignment/collision with switching pattern/switching gap, at least for cases other than PRACH occasions
However, if network may not avoid such misalignment/collision, the UE may simply ignore such collision and follow the semi-static switching pattern configuration

Proposal 6: For PRACH, adopt one of the three following approaches for special handling in case of misalignment/collision with semi-static switching pattern configuration and switching gap
Approach 1: Network avoids the collision
Approach 2 (if approach 1 is not feasible for network): concept of invalid PRACH occasions is extended to this feature such that whenever in a given slot PRACH transmission occasion(s) are triggered, but according to switching pattern, the slot is associated with SDL carrier, then in that case, PRACH occasion(s) are determined as invalid by the UE
Approach 3 (if approach 1 is not feasible for network and there is strong justification to keep PRACH occasion valid): If the PRACH transmission is triggered for the purpose of uplink timing synchronization, e.g. gNB triggers UE with CFRA, then additional switching is triggered by PRACH transmission where similar parameters/restrictions as configured with semi-static switching pattern are applied including:
Switching gap location
Switching gap duration
Switching instances restrictions
No Rx/Tx during switching gap

Proposal 7: For Rel-19 low NR band carrier aggregation via switching, when NW configures the semi-static switching pattern to a UE, for Type-I HARQ-ACK codebook generation, adopt one of the two following approaches: 
Approach 1: Network avoids the collision between PDSCH occasions and semi-static switching pattern/switching gap
Approach 2 (if approach 1 is not feasible for network): Row of the TDRA table is excluded from the determination of the set of occasions for candidate PDSCH receptions if the PDSCH associated with the row is not to be received by the UE due to LB-CA switching.

3GPP TSG RAN WG1 #121			R1-2504348
St Julian’s, Malta, May 19th – 23th, 2025

Agenda Item:	9.12.2

Source:	Moderator (Apple)
Title:	FL summary #1 of Low band carrier aggregation via switching
Document for:	Discussion/Decision

Conclusion 2-1
For RRC configuration of semi-static switching pattern in Rel-19 low NR band carrier aggregation via switching, there is no consensus to introduce any SCell dormancy enhancement.
The same switching pattern should be applied regardless whether SCell is dormant or not.
 Collision handling
 Collision with switching gap
In the previous RAN1#120bis meeting, the following agreement was made with the highlight part for down-selection 

[Closed][R1] Proposal 3-1
For Rel-19 low NR band carrier aggregation via switching,  during a switching gap, a UE is not expected to either transmit or receive on the FDD carrier or receive on the SDL carrier, except the first UL slot corresponding to the first DL slot after SDL switching to FDD.

SDL to FDD switch

FDD to SDL switch

 Collision with RACH operation
In terms of the need for the UE to perform switching in addition to the RRC configured semi-static switching pattern, based on the discussion in the last RAN1 meeting, only possible exception is RACH procedure. 
[Closed][R1] Proposal 3-2
For Rel-19 low NR band carrier aggregation via switching, when NW configures a semi-static switching pattern to a UE, the UE is not expected to perform additional switching not following the semi-static switching pattern, except the only candidate exceptional scenario, i.e., PRACH transmission 
Regarding PRACH transmission, downselect one of the following 
Alt 1: Does not support UE to perform additional switching due to PRACH transmission
For a UE in RRC_CONNECTED, if a PRACH occasion occurs in a slot for which the switching pattern indicates the SDL carrier, the UE shall not transmit PRACH. 
Alt 1.1: The definition of valid PRACH occasions in current specifications is not changed.
Alt 1.2: The corresponding PRACH occasion is considered as invalid 
Alt 2: UE performs additional switching for PRACH transmission
UE resumes the semi-statically configured switching pattern after the RACH procedure completes
FFS: how to define that the RACH procedure completes 

 Other Collisions
Below is the summary of the proposals based on the contributions

[Closed][R1] Question 3-1

 LS to RAN4 and RAN2
[Open][R1] Question 4-1

 Others
If you have other issues that you believe that need to be discussed, please provide those issues in the following table 
[Open][R1] Question 5-1

(Closed Discussion) Low band carrier aggregation via switching

Summary of contribution 
R1-2503273 Huawei, HiSilicon
R1-2503331 ZTE
R1-2503384 vivo
R1-2503421 NEC
R1-2503430 Nokia
R1-2503532 Spreadtrum
R1-2503588 Samsung
R1-2503657 Lenovo
R1-2503739 Ofinno
R1-2503780 CATT
R1-2504153 ETRI
R1-2504217 OPPO
R1-2504255 LG 
R1-2504275 MediaTek
R1-2504347 Apple
R1-2504416 Qualcomm 
R1-2504440 Ericsson
R1-2504520 DOCOMO
R1-2504606 Google 
R1-2504304 Apple

3GPP TSG RAN WG1 #121			R1-2504349
St Julian’s, Malta, May 19th – 23th, 2025

Agenda Item:	9.12.2

Source:	Moderator (Apple)
Title:	FL summary #2 of Low band carrier aggregation via switching
Document for:	Discussion/Decision

Conclusion 2-1
For RRC configuration of semi-static switching pattern in Rel-19 low NR band carrier aggregation via switching, there is no consensus to introduce any SCell dormancy enhancement.
The same switching pattern should be applied regardless whether SCell is dormant or not.
 Collision handling
 Collision with switching gap
In the previous RAN1#120bis meeting, the following agreement was made with the highlight part for down-selection 

[Closed][R1] Proposal 3-1
For Rel-19 low NR band carrier aggregation via switching,  during a switching gap, a UE is not expected to either transmit or receive on the FDD carrier or receive on the SDL carrier, except the first UL slot corresponding to the first DL slot after SDL switching to FDD.

SDL to FDD switch

FDD to SDL switch

 Collision with RACH operation
In terms of the need for the UE to perform switching in addition to the RRC configured semi-static switching pattern, based on the discussion in the last RAN1 meeting, only possible exception is RACH procedure. 
[Closed][R1] Proposal 3-2
For Rel-19 low NR band carrier aggregation via switching, when NW configures a semi-static switching pattern to a UE, the UE is not expected to perform additional switching not following the semi-static switching pattern, except the only candidate exceptional scenario, i.e., PRACH transmission 
Regarding PRACH transmission, downselect one of the following 
Alt 1: Does not support UE to perform additional switching due to PRACH transmission
For a UE in RRC_CONNECTED, if a PRACH occasion occurs in a slot for which the switching pattern indicates the SDL carrier, the UE shall not transmit PRACH. 
Alt 1.1: The definition of valid PRACH occasions in current specifications is not changed.
Alt 1.2: The corresponding PRACH occasion is considered as invalid 
Alt 2: UE performs additional switching for PRACH transmission
UE resumes the semi-statically configured switching pattern after the RACH procedure completes
FFS: how to define that the RACH procedure completes 

 Other Collisions
Below is the summary of the proposals based on the contributions

[Closed][R1] Question 3-1

Summary of contribution 
R1-2503273 Huawei, HiSilicon
R1-2503331 ZTE
R1-2503384 vivo
R1-2503421 NEC
R1-2503430 Nokia
R1-2503532 Spreadtrum
R1-2503588 Samsung
R1-2503657 Lenovo
R1-2503739 Ofinno
R1-2503780 CATT
R1-2504153 ETRI
R1-2504217 OPPO
R1-2504255 LG 
R1-2504275 MediaTek
R1-2504347 Apple
R1-2504416 Qualcomm 
R1-2504440 Ericsson
R1-2504520 DOCOMO
R1-2504606 Google 
R1-2504304 Apple

3GPP TSG RAN WG1 #121			R1-2504350
St Julian’s, Malta, May 19th – 23th, 2025

Agenda Item:	9.12.2

Source:	Moderator (Apple)
Title:	FL summary #3 of Low band carrier aggregation via switching
Document for:	Discussion/Decision

Conclusion 2-1
For RRC configuration of semi-static switching pattern in Rel-19 low NR band carrier aggregation via switching, there is no consensus to introduce any SCell dormancy enhancement.
The same switching pattern should be applied regardless whether SCell is dormant or not.
 Collision handling
 Collision with switching gap
In the previous RAN1#120bis meeting, the following agreement was made with the highlight part for down-selection 

[Closed][R1] Proposal 3-1
For Rel-19 low NR band carrier aggregation via switching,  during a switching gap, a UE is not expected to either transmit or receive on the FDD carrier or receive on the SDL carrier, except the first UL slot corresponding to the first DL slot after SDL switching to FDD.

SDL to FDD switch

FDD to SDL switch


[Closed][R2] Proposal 3-1
For Rel-19 low NR band carrier aggregation via switching,  during a switching gap, a UE is not expected to be scheduled/configured by network to either transmit or receive on the FDD carrier or receive on the SDL carrier, except the first UL slot corresponding to the first DL slot after SDL switching to FDD.


 Collision with RACH operation
In terms of the need for the UE to perform switching in addition to the RRC configured semi-static switching pattern, based on the discussion in the last RAN1 meeting, only possible exception is RACH procedure. 
[Closed][R1] Proposal 3-2
For Rel-19 low NR band carrier aggregation via switching, when NW configures a semi-static switching pattern to a UE, the UE is not expected to perform additional switching not following the semi-static switching pattern, except the only candidate exceptional scenario, i.e., PRACH transmission 
Regarding PRACH transmission, downselect one of the following 
Alt 1: Does not support UE to perform additional switching due to PRACH transmission
For a UE in RRC_CONNECTED, if a PRACH occasion occurs in a slot for which the switching pattern indicates the SDL carrier, the UE shall not transmit PRACH. 
Alt 1.1: The definition of valid PRACH occasions in current specifications is not changed.
Alt 1.2: The corresponding PRACH occasion is considered as invalid 
Alt 2: UE performs additional switching for PRACH transmission
UE resumes the semi-statically configured switching pattern after the RACH procedure completes
FFS: how to define that the RACH procedure completes 

[Closed][R1] Discussion on RACH operation 
Based on the feedback in round 1, likely there is no consensus to support RACH enhancement for LB CA via switching. If you see a strong need of RACH enhancement, i.e., UE to perform additional switch, please provide more concrete design as least cover the following 
Which RACH procedure, i.e., 2-step, 4-step, CBRA, CFRA, PDCCH-order, etc. 
Which part of RACH procedure, i.e., Msg1, Msg2, Msg3, Msg4, MsgA, MsgB, etc. 
How to handle the beginning of the additional switch, i.e., switching gap location 
How to handle the end of the additional switch, i.e., after Msg 3, after Msg 4, after HARQ-ACK of Msg 4, how to handle retransmission, etc.
Other issues 

 Other Collisions
Below is the summary of the proposals based on the contributions

[Closed][R1] Question 3-1

[Closed][R2] Discussion on the handling of other collision cases 
Can we consider the solution reusing the legacy TDD collision handling, as in current TS38.213 quoted below
If not, please provide a complete solution as much as possible that can be specified 


For Rel-19 low NR band carrier aggregation via switching, and for a transmission/reception overlapping with (in) a slot indicated as ‘0’ on SDL carrier or a slot indicated as ‘1’ on FDD carrier by the bitmap or switching gap, reuse the collision handling rules for a transmission/reception overlapping with semi-static DL/UL symbols for unpaired spectrum
For a transmission overlapping, even partially, with the set of symbols of the slot indicated as SDL carrier [or switching gap], the UE does not transmit PUSCH, PUCCH, PRACH, or SRS
For a reception on FDD carrier overlapping, even partially, with the set of symbols of the slot indicated as SDL carrier [or switching gap], the UE does not receive PDCCH, PDSCH, or CSI-RS
For a reception on SDL carrier overlapping, even partially, with the set of symbols of the slot indicated as FDD carrier [or switching gap], the UE does not receive PDCCH, PDSCH, or CSI-RS 

LS to RAN4 and RAN2
[Closed][R1] Question 4-1

 Others
If you have other issues that you believe that need to be discussed, please provide those issues in the following table 
[Closed][R1] Question 5-1


Summary of contribution 
R1-2503273 Huawei, HiSilicon
R1-2503331 ZTE
R1-2503384 vivo
R1-2503421 NEC
R1-2503430 Nokia
R1-2503532 Spreadtrum
R1-2503588 Samsung
R1-2503657 Lenovo
R1-2503739 Ofinno
R1-2503780 CATT
R1-2504153 ETRI
R1-2504217 OPPO
R1-2504255 LG 
R1-2504275 MediaTek
R1-2504347 Apple
R1-2504416 Qualcomm 
R1-2504440 Ericsson
R1-2504520 DOCOMO
R1-2504606 Google 
R1-2504304 Apple

3GPP TSG RAN WG1 Meeting #121    	            R1-2504416
St Julian’s, Malta, May 19th – 23st, 2025

Source:	Qualcomm Incorporated
Title:	Low band carrier aggregation via switching
Agenda Item:	9.12.2
Document for: 	Discussion and Decision

Conclusion
In this contribution we have following proposals.

Proposal 1:
For Rel-19 low NR band carrier aggregation via switching, for the duration of the switching gap configured by RRC, NW ensures that the switching gap is enough to also cover the DL receive timing difference between the FDD carrier and SDL carrier
The maximum downlink receive timing difference between the FDD carrier and SDL carrier is up to RAN4

Proposal 2:
For switching from FDD carrier to SDL carrier, adopt Alt.2
Alt 2: NW configures whether the switching gap is at the FDD carrier or SDL carrier

Proposal 3:
For RRC configuration of semi-static switching pattern in Rel-19 low NR band carrier aggregation via switching, consider following restrictions:
Maximum 8 switches within 40 slots of the P = 40ms periodicity
At most 1 switch per consecutive 4 slots

Proposal 4:
UE does not expect a conflict between the semi-statically configured switching pattern (including switching periods) and semi-static DL/UL configured by dedicated RRC or dynamic DL/UL scheduled/triggered by unicast DCI
UE prioritizes the semi-statically configured switching pattern over SSB/PRACH
It is up to RAN4 whether to specify special cases such as RLF or BFD where the UE does not follow the switching pattern to transmit PRACH on the FDD carrier 

Proposal 5:
For switch from FDD carrier to SDL carrier, availability of UL symbols on the FDD carrier is determined by semi-static switching pattern/gap based on DL timing assuming UL TA = 0 and remains unchanged regardless of the UL TA.

Proposal 6:
Type-1 HARQ-ACK codebook is generated as if no semi-static switching pattern/gap is configured
I.e., no RAN1 spec impact on Type-1 HARQ-ACK codebook generation

Proposal 7:
RAN1 to discuss potential impact on UE processing timeline after overall UE procedures for low-band CA via switching is clear.
UE processing timeline extension would be necessary at least if a UE is required to switch based on a DCI scheduling DL reception or UL transmission

3GPP TSG RAN WG1 #121			R1-2504440
St Julian’s, Malta, May 16th – 23rd, 2025

Agenda Item:	9.12.2
Source:	Ericsson
Title:	Low band carrier aggregation through switching 
Document for:	Discussion, Decision
1	

Conclusion
In the previous sections we made the following observations: 
Observation 1	For switching from the SDL to the FDD carrier, there is no need to specify any UL dropping rules to handle overlap of the switching gap with the UL transmission on the FDD carrier since the network ensures that the switching gap is configured large enough to cover at least the switching period and timing advance.
Based on the discussion in the previous sections we propose the following:
Proposal 1	Do not specify the maximum number of switches X within a time period Y
Proposal 2	If it is needed to specify the maximum number of switches X within a time period Y, then support Y = 40 (equal to the 40 ms pattern period) and support X to be no less than X = 10.
Proposal 3	Do not specify other restrictions on the switching pattern.
Proposal 4	For switching from FDD carrier to SDL carrier, the switching gap is always assumed to be on the “switch from” carrier, i.e., FDD carrier (Alt-1 in the RAN1#120bis agreement).
Proposal 5	For switching from FDD carrier to SDL carrier, the switching gap ends at the end of the slot on the FDD carrier. Note: as previously agreed, the timing reference for configuration of the switching gap is based on the downlink timing of the PCell.
Proposal 6	For switching from the FDD to the SDL carrier, the UE omits UL transmission on the FDD carrier in the symbol(s) that overlap the switching gap. FFS: whether or not a similar omission rule is needed for DL reception on the FDD carrier.
Proposal 7	For a UE in CONNECTED mode when the SDL SCell is in activated state, if a PRACH occasion occurs in a slot for which the switching pattern indicates the SDL carrier, the UE shall not transmit PRACH. Note: this does not imply that the definition of valid PRACH occasions in current specifications is changed.
Proposal 8	For lowband carrier aggregation via switching, when the UE is configured with a semi-static switching pattern, the UE shall not perform additional switching that violates the configured switching pattern.
 

3GPP TSG RAN WG1 #121			R1-2504520
St Julian's, Malta, 19 - 23 May, 2025

Source:	NTT DOCOMO, INC.
Title:	Discussion on Low band carrier aggregation via switching
Agenda Item:	9.12.2
Document for: 	Discussion and Decision

Conclusion
In this contribution, we discussed on remaining RAN1 issues on low NR band carrier aggregation via switching. We provided following proposals:
Proposal 1: For semi-static switching pattern, the restriction based on Y-X equals to 3 or 4 should be considered.
Proposal 2: For the semi-static switching pattern, the restriction of maximum 8 consecutive SDL slots should be considered.
Proposal 3: UE does not expect that semi-static switching pattern covers no SSB reception occasion/slot for a carrier.
If SSB reception occasion/slot on FDD carrier and that on SDL carrier are not collided, all SSB reception occasions/slots on each carrier should be ensured.
If SSB reception occasion/slot on FDD carrier and that on SDL carrier are fully collided, SSB reception occasions/slots on two carriers should be alternately ensured.
If subset of SSB reception occasions/slots on one carrier are collided with SSB reception occasions/slots on another carrier, SSB reception occasions/slots on carrier having longer periodicity should be ensured as well as non-collided SSB reception occasions/slots on another carrier.
Proposal 4: For switching from FDD carrier to SDL carrier, down-selection should be done from following solutions.
Alt 1: Switching gap is always assumed at the “switch from” carrier, i.e., FDD carrier.
Alt 2: NW configures whether the switching gap is at the FDD carrier or SDL carrier.
Proposal 5: UE does not expect to be scheduled to transmit or receive signal/channel on unavailable resource according to the semi-static switching pattern.
Proposal 6: The collision between part of occasions for configured transmission/reception or scheduled transmission/reception on multiple occasions and unavailable resource according to the semi-static switching pattern should be allowed, and only transmission/reception on the occasion colliding with unavailable re-source should be dropped.
Proposal 7: When NW configures a semi-static switching pattern to a UE, the only candidate scenario for further discussion that requires UE to perform additional switching not following the semi-static switching pattern is RACH.
Proposal 8: RAN1 does not need to discuss SCell activation/deactivation related aspects for LBCA unless triggered by RAN4.
Proposal 9: UE is expected to follow the configured switching pattern even when SCell is dormant.

3GPP TSG RAN WG1 #121                                                  R1- 2504606
St Julian’s, Malta, May 19th – 23th, 2025


Source: Google
Title:	On Low band carrier aggregation via switching
Document for: Discussion and Decision

Conclusion
In this contribution, we have presented several proposals to specify the support of low band carrier aggregation. We made the following proposals: 

For the location of the switching gap,  support Alt 2 with a network-configurable switching gap:
Alt 2: NW configures whether the switching gap is at the FDD carrier or SDL carrier
 For the selection of the values X and Y, a sliding window within any continuous number Y of slots (which could span across the pattern periodicities) can be specified, the number of carrier switches in the continuous window of Y slots must not exceed X.
A condition X < Y/T can be defined. This means the number of switches X in any window Y must be less than Y divided by the threshold T. T can be viewed as the minimum number of slots between the switches. T is reported as a UE capability
The UE can perform or the network can trigger the UE to perform carrier switching outside the semi-static carrier switching pattern to initiate or respond to specific high-priority procedures. The set of procedures and conditions for such UE deviation needs further study (e.g., RACH initiation on PCell, handover command, RLF, LTM, …).
When a Beam Failure Recovery (BFR) procedure or a handover procedure is initiated while the UE is active on PCell, the UE shall disregard any imminent switch to an SCell as per a configured semi-static carrier switching pattern and shall remain on PCell to complete the ongoing BFR or handover procedure.
When an RRC-configured measurement gap overlaps with a switching gap associated with the semi-static carrier switching pattern, the UE shall prioritize the measurement gap (i.e., performing measurements). Upon completion of the measurement gap, the UE shall resume adherence to the semi-static carrier switching pattern.
When a UE is configured with both DRX and a semi-static carrier switching pattern, the switching pattern shall only be considered during DRX Active Time. 
The UE is not expected to do carrier switches during DRX Inactive Time.
If a switching gap, as defined by a semi-static carrier switching pattern, is scheduled to coincide with the expiry of drx-OnDurationTimer or drx-InactivityTimer (thus aligning with the transition to DRX Inactive Time), the UE shall prioritize entering DRX Inactive Time. The scheduled carrier switch shall be deferred, and the UE shall determine the appropriate carrier based on the state of the semi-static switching pattern upon starting the next DRX Active Time.
The UE is not expected to receive or transmit during the switching gap. Any configured/scheduled transmission/reception during switching gap is considered as error case.