Q. LTE Throughput have been degraded once 5G-NR DC configured?
A. In NSA deployment, 5G Secondary node addition have been configured during normal LTE-ERAB_Setup progress in RRC_Connection_Reconfiguartion once UE_Capability information include UE-MRDC-Capability , SupportedBandListNR-r15 IEs.
5G Secondary node addition means UE that camped on LTE will enter MR GAP configured via RRC_Connection_Reconfiguartion to measure 5G-NR Cell and triggering B1 event as shown below.
Problem here is that for UEs that did not locate in 5G-NR coverage will continuous config LTE GAP pattern forever as not suitable 5G NR coverage can get to report event B1. This behavior will degrade LTE user throughput around 25% as shown below.
Note that for UE that support 5G inter-system measurements without Measurement Gaps have no effect on LTE throughput degradation. But not all UEs may support this , many UEs would be unable to complete 5G measurements if Measurement Gaps are disabled.
- Design LTE cell edge coverage to align with 5G-NR Scell-addition coverage as possible.
- Specify timer to allocate measurement gaps only for the first 3Sec of a RRC connection then end MeasureGap after 3Sec expiration.
- Define how long the B1 measurements are going to be active, and if deactivated, how long it will take to reactivate the B1-NR measurements.