LTE: How source eNodeB get to know when it has to trigger handover required message towards MME ?

Question

I have basic handover related query. How source eNodeB get to know when it has to trigger handover required message ? I mean to ask, how a source eNodeB come to know the threshold values of RSRP or RSRQ or both (related to target eNodeB) , required to do a successful handover towards eNodeB ? Is it due to network planning ?

Comments

I think HO can be triggered on any of the following 2 event reports from UE.
1) Event A5 (PCell becomes worse than threshold1 and neighbour becomes better than threshold2)
2) Event B2 (PCell becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2)

The threshold values need to be derived from trial & error in field testing. The values can be fixed based on these points
1) the cell coverage we want
2) HO must go through smoothly without call drop
3) interference (if interference is high, we need lower values for threshold to trigger HO early)
4) speed at which UE is moving(here HO execution shall be fast & call should not drop)

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Thanks for sharing the information. I still have some query.  As you mentioned "The threshold values need to be derived from trial & error in field testing" , How it works for SON where no human intervention required ? With respect to 4th point, speed at which UE is moving (How eNodeB come to know about the speed of an UE ? )

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I think SON does REM scan and finds out neighboring cells(frequency, PSC, CellId etc), not thresholds. UEs will be few meters away from HNB/NodeB so HNB/NodeB can't measure power at UEs location. So HNB/NodeB sends measurement control message to UE & UE shall measure neighboring cells' power & report(may be events) to HNB/NodeB. The HNB/NodeB shall take a call to handover based on reports.

The threshold values are sent in Measurement control message along with neighbor cell list, events list measurement type, measurement quantity etc. Proper values shall be provided in config files or through OAM.

We need not measure UE's speed. What I meant was we need to take care of how the end user move with UE(in cars or by walk). Call should not drop while handover signalling. Thresholds should be set accordingly.

Note: Above comments are based on 3G n/w, may be applicable to LTE as well.

-Shivanand Gavalkar