Criteria for CQI step up and step down

4G LTE
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1

Hi for LTE link adaption I have one doubt:
For CQI step up and step down, what criteria to follow?
Is it ack correspond to step up and nack correspond to step down?

We have parameter dltargetblet set to 10%.
Does UE go for ack/nack criteria after 10% bler?
So after 10,% value only link adaption come in picture?

2

dltargetbler is criteria for step down, as you’ve already mentioned.

3

I need to check link adaption trigger before 10% or after 10% threshold.
As per my understanding till date, it’s after 10% but some expert informed me it is before 10%.

4

I thought link adaptation continously work to keep BLER below blertarget.
If BLER goes above 10%, eNB takes more serious measures.

5

Yes seems so, but I need more clarification and more experts opinion here…

6

Keep in mind that BLER depends on both PDCCH and PDSCH decoding.
One cannot go without the other.
We need good aggregation level for PDCCH and good MCS for PDSCH to keep a bler target rate for PDSCH.
Huawei for example has target bler on pdcch of 1.5% (adjustable parameter) that allows to change aggregation level for each UE to mantain this 1.5% bler.

7

Thanks @RFSpecialist. For PDCCH bler I think we don’t have option to change value for PDCCH agg level as per bler.

8

Which vendor do you have?
I am not sure, Ithink there is system constant for Ericsson part.
I didn’t deep dive in such hidden parameters or SCs since long time.

9

Nokia, any idea?

10

pdcchHarqTargetBler
MRBTS/LNBTS/LNCEL
Default Value is 1%

BLER target for PDCCH outer loop link adaptation in percent.
Defines target Block Error Ratio (BLER) of PDCCH and UL HARQ response for initial downlink transmissions for >PDCCH Outer Loop Link Adaptation in percents.
If PDCCH OLLA is additionally based on PUSCH TX/DTX detection, the parameter defines target Block Error Ratio (BLER) of PDCCH and PUSCH missed detection for initial uplink transmissions for PDCCH Outer Loop Link Adaptation in percents.

I hope it may help.

All the vendors provide this functionality, Ericsson has parameters available to adjust the PDCCH Target BLER via Enhanced PDCCH Link Adaptation Feature.
Through Huawei is more flexible in may aspects.