UE transmitting on its max power but still data failing

Hi All Experts.

I have one concern regard to UL data transmission.

Assume UE reported power headroom 0, which means UE transmit on its max power 23 dBm.

Now let’s assume at gNB the signal (UL data packet) still failed and not successfully … typically on that case what will happen?

UE can’t increase more its power since it reached its maximum power, but still failure at cell side.

It shall be gNb detected RLF.

Are you sure?

I think maybe gNB decrease UL RBs on that case for getting more power?

In this case:

  1. UL scheduling would be with least MCS.
  2. UL RBs would be higher.
  3. In case of Voice, TTI budling kind of feature would be activted.
  4. In worst case, UE side RLF might get triggered. gNB side UL BLER, DTX might get experienced.

You may check slot level.
UE log for UL resource allocation (TBs, RB, MCS, HARQ RV, …), B883 would provide that info.
Or from gNB L1 log, you can the sane info.

It is exactly like you explained.

The only difference is that UL RBs would be less and less once UE reaches max tx power and RSRP degrades continuously.

Got it.

One concern regard to low MCS.

When MCS decreased then power headroom still zero reported, yes?

Since now we are only more robus but no power add…

No, PHR will be negative.


UL RBs would increase as long as power is available.

After that RBs can be reduced in order to maintain targer BLER.

Even in case when we decrease UL RBs so UE starts reporting negative PHR?

Yes, correct.

On that case when UL RBs decreased, PHR report negative?

Trying to understand when UE report negative PHR…

UE reports negative PHR when UE is at max TX power and the UE would have more data to send.

Got it!

So no positive PHR values reported?

Meaning if there is such cases?

There are positive PHR values reported.

Read LTE or 5G in Bullets about it.

UE report negative PHR mean UE can transmit over 23 dBm for a short time, right?

Power Headroom: Power headroom refers to the difference between the maximum transmit power of the UE and the actual power level it is currently using. It represents the UE’s capability to increase its transmit power without exceeding the limits.

Power Headroom = UE Max Transmission Power - PUSCH Power = Pmax -

Power Headroom is Positive in Value (+) = means still have some bandwidth and can
transmit more data if allowed.

Power Headroom is negative in value (-) = Already transmitting more power than allowed.

I got this from an article.
Hope this helps

Sorry… Still not getting you regard to negative PHR values.

For negative PHR values mean what?

It says already transmitting more than allowed… did you mean here more than 23 dBm?

PHR will be in dB not in dBm.

Negative PHR values means-> When UE is already transmitting with max power and and gNB still instructing UE to transmit with more power through power control command.

Negative PHR help to anlyse cell edge scenarios.