LTE reselection counters

[dannthemann]

Hi,

I have UEs that suddenly change in idle state from a cell to another with poorer radio conditions.

So far, I can´t understant what's going on. The selection/reselection parameters are set as restrictive as possible, but this bizarre behaviour continues.

Any idea about LTE reselection counters?

Thx

[wolverine]

Is the source and target cell on the same LTE carrier?

[dannthemann]

No, they are in different ARFCNs.

I have configured both intra and inter freq blacklists, disabled HOs between them, but still there are users with fixed terminals complaining. And we can see that the problem is a cell change to a worse cell (no capacity issues neither).

Thx

[wolverine]

What are the reselection priorities configured on source and target EARFCNs? A UE will reselect to a cell with a higher priority even if radio conditions are worse.

[auto_art]

No, they are in different ARFCNs.


I have configured both intra and inter freq blacklists, disabled HOs between them, but still there are users with fixed terminals complaining. And we can see that the problem is a cell change to a worse cell (no capacity issues neither).

Thx

delete the inter freq. arfcns(SIB5) from config. action of this is UE will never scan any inter freq until current arfcn is out of service. this is what we configure. i could share you huawei and ZTE parameters if you need.

[tpkj]

delete the inter freq. arfcns(SIB5) from config. action of this is UE will never scan any inter freq until current arfcn is out of service. this is what we configure. i could share you huawei and ZTE parameters if you need.

Please, could you share?

[dannthemann]

Thanks for the comments.

I summarize what happens:

Huawei LTE-TDD eNB.
1 eNB with 4 cells: 2 cells in F1 and 2 cells in F2. All cells have different azimuths with no coverage overlapping.
Reselection priorities in each EARFCN are the same: 7 in CELLRESEL object.
Inter-freq cells included in a blacklist.
HO disabled via NOHOFLAG parameter.
No alarms in the eNB.
No mobility: fixed static UEs (CPEs).


Despite this, there are users (using fixed static terminals such as CPEs) changing from a good serving cell to a cosite inter-freq cell with poorer radio conditions. When this happens we start to receive complains from customers.

The movement from one cell to another is no via HOs as we can see from statistics.

But we don't know if this cell change is due to reselection (it shouldn't as we have blacklists) or due to other mechanism that we don't understand.

@auto_art, could you please share the parametrization you refer to? When you say "delete the inter freq. arfcns(SIB5) from config." do you mean to delete the inter-freq neighbour relationships?

Thx again!

[auto_art]

we suffered this problem, following is what we are doing. we are not actually restricting them now as restricting is something lead us to bad direction and made the situation worse. let me tell you why incase one cell is down CPE is would eventually to go to whatever cell it could see and will never come back to orignal cell as you have restricted to move.


what we are doing now is enabling the UE to scan interfreq also, when the CPE is in idle mode. i am pasting an email here which has those details. you may always reach me if you need further info. we dont have any handovers in our network too and it is huawei, LTE TDD. we have also tweaked our cellsimap settings since it is an only LTE network(no interworking) to make sleection reselction faster(reduced interval of sib5).

Please find a description of what was done to resolve the reselection problem:

1. we have made inter and intra freq threshold same in cellresel.
2. add interfreq. neighbours in cell list for each cell using "add eutraninternfreq" command i.e. if a cell has three interfreq. cells as neighbour, all those freq. should be present in eutraninternfreq. to make cpe freely select the best one.




testing outcome email:-

At the end of July , X & Y network agreed to the following changes to attempt to resolve the cell reselection problematic:

1) Specification of EUTRANINTERNFREQ with default Huawei settings. All cells were set to the same priority (Priority 7)

2) QQualMinCfgInd set to NOT_CFG in CELLRESEL

- Based on the current default Huawei settings, the CPE triggers Intra/ Inter frequency measurement based on both RSRP and RSRQ.
Intra-Freq trigger for Serving cell
RSRP < -70dBm
RSRQ < -13dB

Inter-Freq for Serving cell
RSRP < -108dBm
RSRQ < -14dB

By setting QQualMinCfgInd to NOT_CFG in CELLRESEL, the above thresholds will not be broadcast in SIB3 and the CPE will always search for the next best server based on RSRP (for both Intra and Inter frequency).

Both X & Y deployed inter frequency EARFCNs for all cells. The inter frequency EARFCNs deployed by X are attached. Y deployed sets of 6 inter frequency EARFCNs (block centers) for all cells.

Reselection Tests performed after the deployment were not conclusive and problems remained in the field during some installations.

Retesting with regard to the cell reselection issue was reinitiated in May 2015 at the offices with both X & Y modems connected to a X operator site (LRHQCE5058) and the problematic was present and repeatable. Y operator & Huawei participated in the tests and a Huawei service request was opened.

After much testing by Huawei & operators, the first part of the solution was found, that is setting the Inter-freq triggers to be identical to the Intra-freq triggers.

The command to change the reselection threshold:
MOD CELLRESEL: LocalCellId=xxx, SNonIntraSearchCfgInd=CFG, SNonIntraSearch=29;

With the change to the reselection threshold implemented on the test site, the Huawei R&D produced the analysis report attached. The conclusion was:

The B2268h ODU supports only 3 TDD inter-frequency carriers, but if the number of inter-frequency carriers is greater than 3 and all of them have the same reselection priority, the ODU only performs measurements for the first 3 carriers from the InterFreqList SIB5. This means that the ODU cannot perform measurements for the remaining carriers and cannot reselect to these carriers.

The InterFreqList S1B5 for cell LRHQCE5058-1Q1 was reduced to 3 including the EARFCNs of the 3 cells of site LRHQCE5058-1 and then reselection process occurred and the appropriate cell was selected.

The 2nd part of the solution is setting the InterFreqList to 3 carriers per cell, including the EARFCNs of the cell’s site.

In summary,
1. Set the Inter-freq triggers to be identical to the Intra-freq triggers for each cell.
2. Set the InterFreqList SIB5 to 3 carriers per cell, including the EARFCNs of the cell’s site. Do not include the Intra-freq in the list.

Sample worksheets with the InterFreqList per cell are include:


Cell ID
EARFCN
ULEARFCNCFGIND
CELLRESELPRIORITYCFGIND
SPEEDDEPENDSPCFGIND
MEASBANDWIDTH
PMAXCFGIND
QQUALMINCFGIND
Site_Name
Abrev site

ID?
Earfcn?
abrev site
Cell ID
intra EARFCN


ADD EUTRANINTERNFREQ:LOCALCELLID=1
DLEARFCN=42715
ULEARFCNCFGIND=NOT_CFG
CELLRESELPRIORITYCFGIND=NOT_CFG
SPEEDDEPENDSPCFGIND=NOT_CFG
MEASBANDWIDTH=MBW100
PMAXCFGIND=NOT_CFG
QQUALMINCFGIND=NOT_CFG
{LBHNTD0148-1}
D0148

1
42715






Or


Cell ID
EARFCN
ULEARFCNCFGIND
CELLRESELPRIORITYCFGIND
CellReselPriority
SPEEDDEPENDSPCFGIND
MEASBANDWIDTH
PMAXCFGIND
QQUALMINCFGIND
Site_Name
Abrev site

ID?
Inter Earfcn
abrev cell
Intra EARFCN- Bell lic
Intra EARFCN- Inuk lic


ADD EUTRANINTERNFREQ:LOCALCELLID=11
DLEARFCN=43715
ULEARFCNCFGIND=NOT_CFG
CELLRESELPRIORITYCFGIND=CFG
CellReselPriority=7
SPEEDDEPENDSPCFGIND=NOT_CFG
MEASBANDWIDTH=MBW100
PMAXCFGIND=NOT_CFG
QQUALMINCFGIND=NOT_CFG
{LBHONT0021-1}
T0021

11
43715
T0021-1Q2
42715
42965


ADD EUTRANINTERNFREQ:LOCALCELLID=11
DLEARFCN=43215
ULEARFCNCFGIND=NOT_CFG
CELLRESELPRIORITYCFGIND=CFG
CellReselPriority=7
SPEEDDEPENDSPCFGIND=NOT_CFG
MEASBANDWIDTH=MBW100
PMAXCFGIND=NOT_CFG
QQUALMINCFGIND=NOT_CFG
{LBHONT0021-1}
T0021

11
43215





ADD EUTRANINTERNFREQ:LOCALCELLID=11
DLEARFCN=43965
ULEARFCNCFGIND=NOT_CFG
CELLRESELPRIORITYCFGIND=CFG
CellReselPriority=7
SPEEDDEPENDSPCFGIND=NOT_CFG
MEASBANDWIDTH=MBW100
PMAXCFGIND=NOT_CFG
QQUALMINCFGIND=NOT_CFG
{LBHONT0021-1}
T0021

11
43965






I hope that this is helpful.






our SIB settings
Display CellSiMap
-----------------
Local cell ID = 0
SIB mapping SI algorithm switch = True
SIB2 period = 8 radio frames
SIB3 period = 16 radio frames
SIB4 period = 16 radio frames
SIB5 period = 16 radio frames
SIB6 period = 512 radio frames
SIB7 period = 512 radio frames
SIB8 period = 512 radio frames
SIB10 period = 512 radio frames
SIB11 period = 512 radio frames
ETWS PN message duration time(s) = 6
ETWS SN message overlap policy = DISCARD
ETWS PN message overlap policy = DISCARD
SIB12 period = 32 radio frames
Effective code rate for SI transmission = 27
(Number of results = 1)

[dannthemann]

Hi auto_art, thanks for your help.

We have only 2 EARFCNs in this LTE-TDD network (band 42).

If I correctly understand your explanation, a trial should be:


Set SINTRASEARCH and SNONINTRASEARCH parameters into CELLRESEL object to the same value (29).
Set inter-freq neighbours in EUTRANINTERNFREQ: we already have cells with F1 asigned to inter freq F2 and vice versa. I think I don't understand the worksehets you attach (perhaps I can`t see them properly). Please, have a look to my screenshot following showing our current configuration for EUTRANINTERNFREQ:


40407

The EARFCNs of the local cells are:
LOCALCELLID 1 -> F2 (42890)
LOCALCELLID 2 -> F2 (42890)
LOCALCELLID 3 -> F1 (41890)
LOCALCELLID 4 -> F1 (41890)

Thanks again!

[auto_art]

yeah i try changing the cell reselection for inter freq. and observe it. rest looks good.

[rimeka]

Another possibility is call reestablishment. Ue can move to blacklisted neighbor after RLF.
having trace result for this case is better.