Hi All,
I would like to understand cell selection and cell reselection parameters & values in 5G.
Any comments from experts?
For which vendor and for SA or NSA ?
Below are the few parameters for NR SA Idle mode mobility Intra/Inter Cell selection and re-selction.
Major things here are SIBs.
SIB
Cell reselection procedure is used for intra NR SA Idle mode mobility.
Cell reselection identifies the cell that the UE should camp on. It is based on cell reselection criteria which involves measurements of the serving and neighboring cells.
SIB1 together with SIB2-5 are sent over the air so that the UE get proper parameters to do correct cell selection and reselection decisions.
• SIB1 defines the scheduling of other system information including periodicity.
• SIB2 contains cell re-selection information common for intra-frequency, inter-frequency and/ or inter-RAT cell re-selection.
• SIB4 contains information relevant only for inter-frequency cell re-selection.
• SIB5 contains information relevant only for inter-RAT cell re-selection.
Intra Frequency Cell Reselection
The measurement rule for Intra frequency cell reselection purpose is if the serving cell fulfils
Srxlev > SIntraSearchP and Squal > SIntraSearchQ, the UE may choose not to perform intra-frequency measurements. Otherwise, the UE shall perform intra-frequency measurements.
Where,
• Srxlev = Qrxlevmeas – (Qrxlevmin + Qrxlevminoffset) – Pcompensation - Qoffsettemp
• Squal = Qqualmeas – (Qqualmin + Qqualminoffset) - Qoffsettemp
Inter Frequency Cell Reselection
If the network is using more than one carrier frequency, the serving cell advertises the other carriers as part of SIB4. If another carrier is involved, the priority of the frequency compared to the serving frequency will be considered.
The UE shall perform measurement for a NR inter-frequency with an equal, higher or lower reselection priority than the reselection priority of the serving NR frequency under the following condition:
Srxlev < SnonIntraSearchP or Squal < SnonIntraSearchQ
Where,
• SnonIntraSearchP parameter is a threshold that the serving cell advertises as part of SIB2, s-NonIntraSearchP IE.
• SnonIntraSearchQ parameter is a threshold that the serving cell advertises as part of SIB2, s-NonIntraSearchQ IE.
Reselection to higher priority
The reselection to higher priority NR frequency than the serving is performed under the following conditions:
• The UE must have been camped on the serving cell for at least 1 second.
• The new cell fulfils Squal > ThreshX, HighQ condition during the time interval t-ReselectionNR when threshServingLowQ is already broadcast in SIB2.
• The new cell fulfils Srxlev > ThreshX, HighP condition during the time interval t-ReselectionNR when threshServingLowQ is not broadcast in SIB2.
Where,
• ThreshServing,LowQ and t-ReselectionNR advertise in SIB2.
• ThreshX, HighQ and ThreshX,HighP advertise in SIB4.
Reselection to lower priority
The reselection to lower priority NR frequency than the serving cell is performed when under the following conditions:
• The UE must have been camped on the serving cell for at least 1 second.
• The new cell fulfills Squal > ThreshX,LowQ condition during the time interval t-ReselectionNR when threshServingLowQ is already broadcast in SIB2 and Squal < ThreshServing,LowQ.
• The new cell fulfills Squal > ThreshX,LowP condition during the time interval t-ReselectionNR when threshServingLowQ is already broadcast in SIB2 and Srxlev < ThreshServing,LowP.
Where,
• ThreshServing,LowQ, ThreshServing,LowP, t-ReselectionNR advertise in SIB2.
• ThreshX,LowQ and ThreshX,LowP advertise in SIB4.
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Thanks!
In 5g started of SA mode 3.5 ghz and mm wave 26 ghz…its in testing phase only
Can I get CELL selection parameters value range and reselection for 5G?
Hi,
So what is significance in LTE for reselection new parameters introduced in 3gpp rel 9, i.e. snonintrasearchP and snonintrasearchQ?
Are these mandatory to configure over sites?
O snonintrasearch is enough for judgement of reselection toward inter Freq or inter rat layers having low or equal priority?
Normal reselection parameters (without rel 9) can be used.
P and Q parameters are introduced in rel 9 to enable reselection based on rsrp and rsrq respectively.
Refer to my article here for more details:
Ok so for RSRQ based reselection we need to use rel9 threshold:
- snonintrasearchq
- threshservinglowq part of sib3
- threshx high q and threshx low q
For RSRP based selection no need to use rel 9 parameter.
Yes correct. Generaly no one use RSRQ based reselction.
Not able to get usage of snonintrasearchp when we already have snonintrasearch present for evaluation of reselection.
It’s used in combination with Q parameters.
Pre rel9 parameters cannot be used with Q parameters.
Ok, you mean I can’t use snonintrasearchq without configuring snonintrasearchp, these are interlinked.
I think snonintrasearchq can be used independently.
q can be used independently.
But if you want to use both rsrp and rsrq, then you will have to enable p and q both.
Pre rel 9 and q combination won’t work.
Ok snonintrasearch and snonintrasearchq combination do not work, i.e. rsrp and rsrq based reselection do not work.
Yes. In this case only q will be configured to UE.
So conclusion.
We can use RSRQ based reselection independently, no linkage with other parameters.
For 3gpp rel 8 only RSRP based reselection there.
For 3gpp rel 9 there can be RSRP or RSRQ.
Prior to 3GPP rel 8 sNonIntraSearch could only be RSRP based.
In 3GPP rel 9, the standards split the above threshold into 2.
One is sNonIntraSearchP that is RSRP based and the second one is sNonIntraSearchQ which is RSRQ based.
So basically the UE can now make reselection decisions based on quality as well as signal strenght/pathloss.
You can still use the “old” sNonIntraSearch with rel9 and later UEs (backwards compatible).
So, P refers to RSRP and Q refers to RSRQ.
If RSRQ parameters are configured then both RSRP & RSRQ based measurement need to be satisfied.
Can we say that is a best practice to set sIntrasearch=sIntraSearchP in order to have equal conditions for 3gpp rel 8 and rel 9 UE?
Here are some steps to check in case of INTER VENDOR
- Incomplete Inter-Vendor Handoff: It’s possible the handoff process between Nokia LTE and the other vendor’s 5G SA isn’t fully configured. This could lead to the phone initiating reselection itself, bypassing the NRFIM/SIB24 process.
- Vendor Specific Behavior: Different vendors might have their own proprietary mechanisms for triggering reselection. This could explain why the phone reselects on its own in some cases.
- Network Misconfiguration: There might be a configuration issue on either the Nokia LTE or the other vendor’s 5G SA network that’s causing the unexpected reselection behavior.
Here’s what you can do:
- Check Vendor Documentation: Refer to the documentation for both Nokia and the other vendor to understand their specific inter-vendor handoff procedures and potential reselection triggers.
- Analyze Network Logs: Look for any error messages or unusual events in the network logs from both Nokia LTE and the 5G SA network around the time of these unexpected reselections.
- Contact Network Support: Reach out to the support teams of both Nokia and the other vendor to report the issue and see if they have any known solutions or workarounds.
Additional Tips:
- See if there are any firmware updates available for the Nokia LTE equipment or the user devices experiencing these reselection issues.
- Investigate if there are any ongoing network maintenance activities that might be impacting the handoff process.