What are the reasons to Random Access Failures in 5G?

5G NR
1

Hello Experts.
What are the reasons to Random Access Failures?
5GNR MAC RACH Attempt - FAILURE_MSG2_RA_TIMER_EXP

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UE didn’t get msg2.

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Looks like UE did not receive msg2 .
But this is what UE thinks .
But there can also be other issues:

  • gNB might not have received RACH at all from UE - need to check gNB logs for RACH.
  • PDCCH blocking at gNB if Cell is Loaded.
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RACH attempt initiate in low RSRP , MSG1 is not received by gNB, then in the UE MSG2 timer expire. After 10 attempts, RACH procedure is aborted.

check 5G coverage or increase reambleTransMax to 20

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1- gnb may already send Msg2-RAR but UE can not receive it. Pls check coverage.
2- gnv may not send Msg2-RAR to UE. Maybe, lack of sxheduling resource such as CCE, Pdsch. Pls check coreset RB number, CCE ul/dl ratio,…

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This kind of problem can appear due to misconfiguration, excessive load or software/firmware problem at the Base Station (BS)