What is the typical value for IBLER in PDSCH?

5G NR
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22

We tried many times this trial, but we lag in term of throughput.

Yes👍

23

InitDlTargetIbler - CellQciPara:

  • A larger value of this parameter results in a higher selected MCS index and a higher probability of retransmissions. If the spectral efficiency gains brought by the MCS index increase are more significant than the performance loss caused by the retransmission rate increase, the downlink traffic volume increases. Otherwise, the downlink traffic volume decreases.
  • A smaller value of this parameter results in the opposite effects.
24

When we change ibler threshold from 10 to 15%, higher MCS samples marginally increased.
Because target bler is set comparatively higher.
With MCS increase both MAC and RLC tput marginally increased.
No effect of call drop, etc as expected.

(These are field trial result)

25

Prefered set this parameter not too large.

26

MCS increased I don’t think MAC layer throughput, phy throughput may inceased.
But due to retransmisison may increased, so actual user throughput is not sure to increased.
As you see from parameter description: If the spectral efficiency gains brought by the MCS index increase are more significant than the performance loss caused by the retransmission rate increase, the downlink traffic volume increases.
As you know, MAC throughput formula include TBS & BLER.

27

I think downlink traffic volume increase doesn’t mean thp increase, it may cause utilization increase.
Other user may get impact.

29

My 2c:

  • Increasing initialBLER may or may not result in gains, it all depends on the scheduler.
  • If the eNB/gNB scheduler is conservative in terms of MCS/PRB allocation, as we saw for some vendors in the LTE old days, once you increase the i-BLER you may actually improve the throughput.
  • As someone stated before, although i-BLER may change, it is likely the r-BLER continues the same, what may change is the amount of HARQ retransmissions required to converge, which means, lower throughput.

In a way, you must test and observe. 10% is what the LTE and NR system was “designed” to operate, but the eNB/gNB schedulers may be more or less accurate to allocate resources to meet this target.

1 Like
30

Increasing IBLER Value will decrease DL UserTHPT. Because you are sustaining your call for longer period by increasing retransmission of HARQ value. This means your MCS as low level & not at high. 10% is optimised value in many vendors
KIndly correct if I am wrong.
The same should for NR & 4G both. Because it has to be of same concept.

31

You can check below parameter
NRDUCELLPDSCH.DlTargetIbler: Ibler adjustment target value: Indicates the target value of initial transmission bit error convergence in outer-loop adjustment. The recommended value is 10%.

32

What threshold we should use of iBLER ?

33

Normally it is 10%.

34

Is user experience affected if its around 15%?

35

For good radio conditions, it should be low.
For poor radio conditions, it can be kept a little high to avoid retransmissions.

36

No, for poor RF it should be low bler as it will be lead to high retransmission and drops.
Normally its 10 percent.

37

It increases throughput, but drop can also increase.

38

Hi @parkarnadeem86, I don’t think that’s correct.
Please re-examine.

39

My understanding it’s correct.
In poor RF high bler is there already.
Check CQI table with retx, you will get the answers.

In good RF if low retx is there then we increase bler for throughout.
We don’t want drops in poor RF increase.

40

So, BLER alone cannot be taken as any performance metric?
From OSS KPIs what combination can be used?

41

Yes sure bler is just one part.
Depends on number of things .

42

If you keep low BLER in poor rf, it will definitely drop and ask for retransmission, isn’t it?
It cannot demodulate the data.