Hi All 5G Experts.
I have two scenarios which are confusing me…
Assume UE didn’t recieve RAR message on RAR RA window size. What will happen?
Second scenario:
Assume RAR message arrived, but UE decoded it unsuccesffuly (failure). What would happen on that case?
Check path loss…is it higher side.
Also check contention resolution timer value.
I mean what would happen?
Like on both cases RACH will be initialized from beginning or what?
There is msg1 retry, but i believe there is some timer for it.
If UE don’t receive the RAR within Ra-Window Time, it will consider RACH to be unsuccessful and will retry.
UE will initiate PRACH again in both cases.
In which case back off indicator will come into picture?
I think it’s case for PDN connectivity reject… back off timer.
No. It is to signal UE to transmit MSG1 after some time.
So in this both cases:
Back off indicator will apply or not if it is contention based?
I don’t think backoff timer will be sent.
Yes make sense.
With higher power of course and it will declare RLF if continously failed.
But assume UE didn’t decode successfully msg4.
So will it retry to message msg3 again or actually will do RACH from beginning msg1?
No backoff.
For UE MSG2 miss statement is simple.
Increase the power ~ Power ramping Step.
Based on PIRTP -PL(RSP-RSRP) = Initial RACH target power
Ramp up 
with 2/4 dB as per 36.331 value mentioned In sib-2 / LTE upto PMAX.
Backoffindicator will come in picture the when MAC scheduler or admission controller doesn’t have resources to provide.
Decisions rely on DU / MAC based PRB Utilizatioon or RRM based decision control.
Make sense thanks!
And regard to msg3 related.
Is there msg3 retx?
Like assume UE didn’t decode successfully msg4, so immediately will do rach msg1 again or retx for msg3 again?
Yes thanks!
I think that is back off timer for PDN case.
Msg3 Retx will be done.
If DCI Format 0_0 is scheduled and scrambled with TC-RNTI provided in RAR.
Is there parameter for how many retx msg3 attempts?
Not exactly sure about max value for msg3 retx.
Just a small clarification, DCI 0_0 is for the UL grants in fallback mode.
So are you refering to UE using this fallback mode to recalibrate MSG3 and sending it again?
It will be HARQ retx of msg3 using format 0_0.
I guess UE won’t recalibrate the msg3, rather retx with PUSCH resouces sent.