What would be common causes of SCG Failure ?

It may have different causes depending on the type of DC type (ENDC, NEDC, NRDC etc). For now, the tips for ENDC mode is described in this wikik.

NSA(ENDC) mode

If you encounter a SCG Failure Information during the 5G NR bearer addition, this might come from one of the following reasons:

1. The RRC Connection Reconfiguration is not triggered by UE NR B1 measurement report .
2. The bandwidth of 5G NR cell is not supported

How to overcome such issue  ?

NR B1 measurement report

- We've seen that several devices send a SCG Failure Information after the RRC Connection Reconfiguration/complete (with the 5G bearer addition) if the 5G NR cell has not been reported first by the UE. - To overcome this issue, it's recommended to trigger the NR bearer addition upon the measurement report NR B1 reception. To do that , add the measurement configuration in the enb.cfg file under the lte cell_default: field :

Example

/* measurement configuration */ meas_config_desc: { a1_report_type: "rsrp", a1_rsrp: -70, a1_hysteresis: 10, a1_time_to_trigger: 320, a2_report_type: "rsrp", a2_rsrp: -110, a2_hysteresis: 0, a2_time_to_trigger: 640, a3_report_type: "rsrp", a3_offset: 6, a3_hysteresis: 0, a3_time_to_trigger: 256, rsrp_filter_coeff: 3, nr_b1_report_type: "rsrp", nr_b1_rsrp: -119, nr_b1_hysteresis: 10, nr_b1_time_to_trigger: 480, nr_rsrp_filter_coeff: 3 }, meas_gap_config: "gp0", /* DRB configuration */ drb_config: "drb.cfg", },

NR cell bandwidth not supported

If the UE doesn't support the 5G NR cell bandwidth, it may accept the RRC Connection Reconfiguration and answer with the RRC Connection Reconfiguration Complete but send a SCG Failure Information just after.

To verify that bandwidth is supported , you can check the bitmap in the UE capabilities (UE Capability Information message) :

For FR1, the bits starting from the leading / leftmost bit indicate 5, 10, 15, 20, 25, 30, 40, 50, 60 and 80MHz

Example 0000001111 means 40, 50, 60 and 80MHz supported .