iRAT problem in UMTS 900

[itking]

Hi Experts,

We are deploying U900 as 4th carrier in our network, during KPIs acceptance stage we have serious problems with iRAT HO [U900 to G900 & vice versa], everything else including inter-frequency HO are OK. We've investigated but couldn't find any considerable solution. Vendor is Huawei, below are screenshot from last week


iRAT1.jpg
iRAT2.jpg

What options we can consider to overcome the issue, any specific parameter to modify?

[khurrambilal01]

You are talking about CS IRAT or PS IRAT?
Anyhow below are some ways how i improved this KPI:
1. Enable BSIC verify switch
2. Prioritize G1800 NBRs compared with G900 NBRs because most of G900 NBRs have worst quality after U900 due to reduction in number of frequencies
3. Relax thresholds for PS IRAT (Difficult to attempt and trigger Compressed mode)
4. For CS IRAT, make it easy to trigger because U900 carries alot of CS traffic while U900 is designed for PS preferably, This would increase number of CS attempts to G900/1800 and would improve IRAT SR.Chances of drop would reduce during IRAT
5. Increase target GSM cell search threshold to -95
6. Relieve CS/PS congestion in GSM cells otherwise you will face IRAT failures due to congestion on GSM part

[electron]

Hi,

Khurrambilal gave good comments but i would like to add something on it as well:

For number 5 : "Increase target GSM cell search threshold to -95 " it actually will increase number of attempt and putting UEs in bad radio condition it will actually degrade IRAT HO

For number 6:"Relieve CS/PS congestion in GSM cells otherwise you will face IRAT failures due to congestion on GSM part" in relation level investigation you might see is it related or no. Also proportionally failure with traffic rise will increase. Let's verify is it the case or no.


Cheers

You are talking about CS IRAT or PS IRAT?
Anyhow below are some ways how i improved this KPI:
1. Enable BSIC verify switch
2. Prioritize G1800 NBRs compared with G900 NBRs because most of G900 NBRs have worst quality after U900 due to reduction in number of frequencies
3. Relax thresholds for PS IRAT (Difficult to attempt and trigger Compressed mode)
4. For CS IRAT, make it easy to trigger because U900 carries alot of CS traffic while U900 is designed for PS preferably, This would increase number of CS attempts to G900/1800 and would improve IRAT SR.Chances of drop would reduce during IRAT
5. Increase target GSM cell search threshold to -95
6. Relieve CS/PS congestion in GSM cells otherwise you will face IRAT failures due to congestion on GSM part

[itking]

We have issue with both CS & PS but mainly we are working on CS right now..... Thanks for your comments...... will try and get back to you

[khurrambilal01]

Hi,

Khurrambilal gave good comments but i would like to add something on it as well:

For number 5 : "Increase target GSM cell search threshold to -95 " it actually will increase number of attempt and putting UEs in bad radio condition it will actually degrade IRAT HO

For number 6:"Relieve CS/PS congestion in GSM cells otherwise you will face IRAT failures due to congestion on GSM part" in relation level investigation you might see is it related or no. Also proportionally failure with traffic rise will increase. Let's verify is it the case or no.


Cheers

Actually the IRAT attempts is counted only when you find a good neighbor to attempts on if you don't find a good neighbor (>-95dBm) you will remain in compressed mode (-ve impact) but your IRAT failure will be saved because you will not handover the call to bad cell with bad Rx Level than -95dBm so probability of IRAT improvement will be there but yes compressed mode will be longer and chances of drop call too if the compressed mode 2D/2F was too relaxed (EcNo worse than -12/-14 etc)

[skysunmoon]

Try to optimization U900 neighbor and RF. Because of U900 have good coverage like GSM 900M, so don't let U900 get in compress mode too easy, if the U900 have good neighbor cell ,it's better do intra-frequency handover.
As the inter-RAT handover base on GSM Rx Level, so I don't think U900M prefer handover to DCS1800M.
Have a look at GSM KPI around the U900M, if you know GSM will easy to find does there have a BCCH or TCH interference on GSM 900M.
If it's really get problem on GSM 900M, optimization , or shift more traffic to DCS 1800M.

[electron]

Actually beside CPM bad influence by bad radio condition >-95 PROBABILITY of HO failure also will increase it is not about HO attempt.


Cheers

Actually the IRAT attempts is counted only when you find a good neighbor to attempts on if you don't find a good neighbor (>-95dBm) you will remain in compressed mode (-ve impact) but your IRAT failure will be saved because you will not handover the call to bad cell with bad Rx Level than -95dBm so probability of IRAT improvement will be there but yes compressed mode will be longer and chances of drop call too if the compressed mode 2D/2F was too relaxed (EcNo worse than -12/-14 etc)

[Shakeel_15]

hello,

i would like to add one point more here.

check the intersystem discrepancies between u900 and 2g as well. if the mistakes like CI, LAC etc are exists rectify them also.

BR

You are talking about CS IRAT or PS IRAT?
Anyhow below are some ways how i improved this KPI:
1. Enable BSIC verify switch
2. Prioritize G1800 NBRs compared with G900 NBRs because most of G900 NBRs have worst quality after U900 due to reduction in number of frequencies
3. Relax thresholds for PS IRAT (Difficult to attempt and trigger Compressed mode)
4. For CS IRAT, make it easy to trigger because U900 carries alot of CS traffic while U900 is designed for PS preferably, This would increase number of CS attempts to G900/1800 and would improve IRAT SR.Chances of drop would reduce during IRAT
5. Increase target GSM cell search threshold to -95
6. Relieve CS/PS congestion in GSM cells otherwise you will face IRAT failures due to congestion on GSM part

[khurrambilal01]

Try to optimization U900 neighbor and RF. Because of U900 have good coverage like GSM 900M, so don't let U900 get in compress mode too easy, if the U900 have good neighbor cell ,it's better do intra-frequency handover.
As the inter-RAT handover base on GSM Rx Level, so I don't think U900M prefer handover to DCS1800M.
Have a look at GSM KPI around the U900M, if you know GSM will easy to find does there have a BCCH or TCH interference on GSM 900M.
If it's really get problem on GSM 900M, optimization , or shift more traffic to DCS 1800M.

You can easily prioritize DCS1800 NBRs from U900 side in Huawei, there is a parameter to prioritize on neighbor level