Why there is an increased chance of VoLTE call drop while UE runs on Carrier Aggregation?


Why there is an increased chance of VoLTE call drop while UE runs on Carrier Aggregation?

One reason I can think of from UE perspective is UL power limitation.

Even if CA is mostly DL, it must still allocate some power for HARQ feedback etc which may limit VoLTE quality.

Thank you!

Recently we increased caUsageLimit (The value configures the number of SCell connections which can be in use for carrier aggregation). This resulted in increased sCell Cofigurations & Activations. CA Share of Traffic Increased but without any gain in CA Throughput. But at the same time we saw a sharp rise in VoLTE Drop Rate.

Now trying to come up with the solid justification regarding the impacts of CA on VoLTE.

What value have you set now for caUsageLimit?

Using Default value of 65535.

Try disabling UL CA if its enabled.

There is a feature for disabling CA during VoLTE call.

This might be the best course if its possible!

Yes there is a feature and it suppresses the sCell configurations during the VoLTE Call.
But I am not looking for a fix at the moment, rather an accurate reason.

Usage is negligible for CA in UL.

Like your spirit of finding reason for issue - that’s what good engineers should do :blush:

What is drop reason for VoLTE?

Do you get stats for UE PHR? Check those. My expectation is that more UEs are now getting UL power limited.

I will sure check the percentage of UL Power Limited UEs.
That much be increased if we assume it is wasting more power for HARQ feedbacks.

Usage means UL CA traffic right?

It will be less only.
But fact is that even though UL CA traffic is less, UL CA configured UEs can be high in number.
Once UL CA configured, all UL feedback scell goes through scell UL only.
And UE power gets divided in pcell an scell.
Hence possibility of call drop increases.

Drop reason for VoLTE?
Btw this may still lead you to same solution of disabling CA during VoLTE.

Drop reasons in Ericsson are mostly showing UE lost.
Again that much be attributed to week UL.

I agree with you.
CA be not be scheduled for UL but sCells may still be configured/activated.
Will try this out :+1:

Yes that sounds like power limitation.

Btw more CA also means higher interference on subcarriers.

If you haven’t seen any improvements in user experience or overall network capacity then it may worth reverting CA parameters.

Management likes to see more CA usage but if it’s not really helping then there is not much point keeping it on.

Exactly, operators just like to see more CA Usage in the charts even tough there are no visible gains.

Thanks for the insights :v:

Also, one of the second major reason for volte drop during CA is increase in number of RRC reconfiguration messages.
If UE is in very poor radio condition, scell release will happen.
Any signalling in poor RF field can lead to RRC dropb (herr volte drop).

Solution? Increase scell or release threshols to bit higher values.

Great, thanks!

May I know the name of the feature…?