What can be reasons for High HO latency apart from RF coverage issue affecting VoLTE mute call?
Assuming there are no PCI confusions since SON is in place.
Scheduling delay, mostly in congested network.
SON is one reason. It tunes the CIO to delay the handover for a better success rate.
CIOs are tunned with + and - to avid HO too early and too late and to improve Ho success rate.
So SON does not care of muted calls.
I have seen CIOs up to 6 dB values.
He is talking about HO Latency.
It means time difference between HO command (RRC Reconf) up Reconf complete.
So make sure your SON acts normally if activated.
From parameter or counter perspective what can I check?
Checking SON config is not an option since it is not network wide issue.
Are you asking about late HO triggered or late HO executed?
Check counters for HO too early or too late.
Ericsson has those counters in 4G.
Hmm… Let me see.
Too early is when handover happens too early and there is RLF on target cell immediately after HO.
Too late is when handover happens too late and there is RLF on source cell.
Cell individual offset tuning required to improve late and early HO ratio.
For Nokia refer RSlte031 report.
Per neighbour relations can be check to monitor ratio.
Yes so for example you have too early like 457 samples per hour and too late you have just 43 samples per hour than you definitely need to delay the handover.
This is from counters perspective.
Son can also help but results are not good.
From QoS perspective the right approach woudl be to reduce overlap between those 2 neighbors.
VoLTE will be muted either way.
Because cells overlap too much.
For NR we are using PDCP sn size 18 bits which is configured at eNB end and transfer to sGNB during sGNB addition request.
Does sn size depends on UE capability as well?
Too early HO maybe: UE moving very fast, UE report target cell is better, after HO procedure complete and UE HO to new cell, but at that time, signal of target cell already changed, not good as the time UE report -> RLF on target cell.
Too late the same.
UE must support SN 18bits. If not, enb/gnb SN > UE SN, maybe pdcp/rlc packet loss
Thank you guys for the inputs
Dear, for Handover delay and call Dragging issue check Time to Trigger changes from 640ms to 320ms.