B1 only triggering on delta between LTE and NR

5G NR
1

Hey there,
I have a network where we are struggling to get certain phone models to switch to the NR carrier in an NSA deployment.

What I have already tried: (all events set as RSRP)

  1. lower B1 to always trigger (NR good)
  2. raise A2 to always trigger (LTE bad)
  3. raise A1 to never trigger (LTE good)
  4. raise S-measure to always trigger (always measure)

Doing this allows everything to function correctly. I can see A2 events trigger and A1 events aren’t stopping B1 events.

Issue is, certain phones seem to still not trigger B1. For example, iPhones will connect to the NR carrier anywhere no matter the signal condition. But Pixels will only connect if the NR SINR > LTE SINR by around 15-20 dB. In the case with the Pixel, this has happened at higher and lower power levels but that SINR gap seems to always be needed, and when the gap does exist the Pixels switch to NR reliably. RSRP does not seem to predict the handovers.

Now, this is NSA. So SIB24 shouldn’t impact this and isn’t set. Is there anything else I can do to change this behavior? And why would it be phone model specific?

Ideas:

  1. maybe B1 events need to be RSRQ based, and by not sending a RSRQ B1 the Pixel is using some other rule.
  2. the Pixel has some rule beyond B1 setting that prevents it from happening?
  3. I feel like this should be modifiable, but maybe the network sends additional rules in higher layer messages?