1. Way Forward on Alt. 2 vs. Alt
Way Forward on Alt. 2 vs. Alt. 3 for handling the EN-DC 1 Tx / 2 Tx UL issue
Sprint, AT&T

2. Single uplink granularity alternatives
Alt.1. spectrum holdings of a operator in a band
Alt.2. aggregated UE channel bandwidth configured by the network
Alt.3. transmission bandwidth

3. Scenario for comparing Alt.2 and Alt.3 (operator assumption)
Band DC_26A_n41A
Identified by RAN4 as a difficult band combination du to an IM3 into the Band 26 Rx
UE can indicate that it does not support 2 Tx in the difficult allocations of the band combination
Assume Band 41 UL/DL configuration 1 (~50% UL/DL duty cycle)
Band 26 operator/network allocation of / MHz
Band 41 operator/network allocation of MHz
With Alternative 2, the Band 26 channel bandwidth and the Band 41 channel bandwidth would also be labeled difficult because of an IM3 from MHz, so 2 TX would not be allowed. This would result in 100 MHz of uplink being unusable at the same time as the UE is transmitting on the Band 26 UL.
The UE could be scheduled to do 1 TX on Band 26 50% of the time and 1 Tx on Band 41 the other 50% of the time, wasting 50% of the Band 26 UL. This is a waste of valuable spectrum that has a much better link budget than the Band 41 spectrum.
Alternatively, more Tx time could be allocated for UL transmission on Band 26, causing 100 MHz of Band 41 to be wasted.
With Alternative 3, the scheduler can schedule the UE to transmit on MHz which would move the IM3 to MHz, outside of the Band 26 allocation. So the UE can transmit on the Band 41 and Band 26 uplink simultaneously, only sacrificing 5% of the Band 41 spectrum during the uplink time.
Alternative 3 has a clear, quantifiable advantage over Alternative 2.

4. RAN1 and RAN3 Mechanism for Scheduling Coordination (1/2)
Both in NR and LTE the scheduling grant is carried on PDCCH for ALL dynamic UL allocation on PUSCH. The DCI carrying the UL grant on PDCCH and the UL PUSCH transmission DO NOT happen in the same slot.
In the case of LTE there is a gap of 4 subframes. I.e. if the DCI with UL grant is carried in subframe N then the UL transmission happens in subframe N+4
In the case of NR we have a same timing relationship between the slot carrying the DCI with UL grant and the associated PUSCH
Observation 1: Both in the case of NR and LTE UL scheduling decision are made ATLEAST 4 msec ahead of the actual UL transmission.
Observation 2: Ideal backhaul (0msec) is not needed between the LTE eNB and the NR gNB and the system can tolerate a latency of 4msec for this dynamic shceudling coordination to ensure allocation are done in a manner to prevent IMD2 or IMD3 impact.

5. RAN1 and RAN3 Mechanism for Scheduling Coordination (2/2)
When 4 msec latency cannot be met there are additional RAN1 and RAN3 solution that can be used to coordinate the scheduling to prevent allocation that are impacted by IMD2 or IMD3
The LTE eNB and NR gNB can exchange scheduling restrictions between them on the X2 interface. This scheduling restriction is a TDM/FDM pattern which allows the scheduler in NR gNB and LTE eNB to avoid PRB allocation that are impacted by IMD 2 or IMD 3
The exchange of scheduling restriction has been defined in RAN3 X2 specs for other use cases such as LTE-NR co-existence. Also note that the exchange of this scheduling restriction information is on a PER UE basis.
Observation 3: In the case when the 4 msec latency cannot be met between LTE eNB and NR gNB the two can exchange scheduling restriction TDM/FDM pattern to avoid allocation that are impacted by IMD 2 or IMD 3.
Observation 4: RAN3 X2 specification support the exchange of shceudling pattern/restriction between LTE eNB and NR gNB for other use cases such a LTE-NR co-ex

6. Concerns with Operators who may assign bad band combinations
AT&T said operators will ensure that UEs are only allocated transmission bandwidths for good band combinations, in order to minimize/eliminate DL interference.
Oppo is concerned that some operators may not exercise due diligence and allocate UEs on difficult band combinations, which could result in unacceptable DL interference.
However, this is a concern that applies across the board, not just in this case.
For example, if an operator sets the hand-over threshold to a very low value, the hand-over may not occur in a timely fashion and the UE may remain camped on the old cell, resulting in bad call quality or even a dropped call.
Also, most operators across the globe will typically use equipment from the same set of infra-structure vendors that most other operators use, and hence they will get good engineering guidance that will alleviate these kinds of concerns.
In summary, device vendors should rest assured that it is very much in the interest of both operators and infra-structure vendors to ensure that that UEs are only allocated good band combinations, in order to minimize/eliminate DL interference, and hence increase the possibility of using 2 Tx UL, which will increase the performance of devices.

7. Way Forward
Agree that a scheduler will use Alt.3 for transmission bandwidth to avoid IMD issues, with restrictions on the 1Tx/2Tx reconfiguration time.
Confirm that impacts are limited to PCell