Top 5G Interview Question: 5G RACH Process

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Top 5G Interview Question: 5G RACH Process
In 5G, The RACH Process (Random Access) is very important especially in case of NSA since a 5G RACH failure in NSA results in a 5G Call Drop. In this session, we go through UE logs to understand various RACH Information Elements (IE) while explaining how UE decodes those IEs to find the RACH configuration and location.
The session also explains the basic RACH Issues that are observed in the networks along with potential troubleshooting and optimization actions.
Reference: 3GPP 38.211
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[@OurTechPlanet]

For 5G topics discussed in 5G Job Interviews, check out the complete playlist below :)
🌐5G Interview Topics
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[@KAMLESHYADAV-vw8dj]

Hi i m from India 🇮🇳 I m working in Ericsson Global I think this is best channel for me for telecom knowledge and also best for interview questions thanks a lot brother keep it I solute your hard work

[@OurTechPlanet]

Thanks Kamlesh, you just made my day! :)

[@KAMLESHYADAV-vw8dj]

@@OurTechPlanet I will try to make videos like you in Hindi so that we are transfer knowledge to max people because of in India English Language is the barrier for most people that belongs to village

[@farhanejaz9911]

Salute to you Sir for such wonderful videos

[@OurTechPlanet]

Thanks a lot :)

[@dreambigwithomkara9787]

Its very helpful information...authentic and simple.....

[@OurTechPlanet]

Thanks a lot. Kindly do help us share the word :)

[@rajeshkarra]

Hi Ali, This was the simplest explanation with high precision. Can you please make a detailed video on RACH planning too.
Thank You.

[@OurTechPlanet]

Thanks. RACH Planning is a topic that has been in my list for some time. Will work on it soon.

[@saaz345]

HI Ali Khalid,Amazing explaination ,I must say you are my mentor as your way of explaination is fantastic and really help to get Network insights.
my question is regarding MSG4 failure especially in SA configuration.what are the possible reason of MSG4 failure.and tips to mitigate it?
upon successfull reception of MSG3 by GNB ,I belief MSG4 is the acknowledgement from the GNB to UE for the RACH complete.
so if UE fail to recieve the MSG4 it will restart the rach process again?

[@OurTechPlanet]

Yes, MSG4 failure would normally happen when UE is unable to decode the PDCCH or the PDSCH. One possible reason could be if MSG4 uses a more aggressive PDCCH aggregation layer than that could reduce the PDCCH's robustness. But in any case, it would need some UE side logs to verify the real reason.

[@saaz345]

@@OurTechPlanet Thanks Ali

[@ShivamPandey-km6rv]

The excellent way of explanation...

[@OurTechPlanet]

Thanks a lot :)

[@andrewl3939]

How does ssb-perRACH-OccasionAndCB-PreamblesPerSSB and msg1-FDM factor in?

[@anuragchakra]

Thanks nice clear explanation

[@OurTechPlanet]

Glad it was helpful!

[@ihteshamullah3131]

Thanks a lot for this Great work .Sir...

[@OurTechPlanet]

You are welcome! :)

[@nitsr6053]

very nice video

[@OurTechPlanet]

Thanks

[@MrGmksamy]

Hi, is it mandatory that LTE anchor and NSA cell should be configured with same RACH format to have proper sync ?

[@OurTechPlanet]

No, LTE anchor and 5G NSA Cell have no such constraint to have similar RACH format from sync perspective. Although it is good to have similar cell radius.

[@georgioskarouzos7418]

All the preambles that a ue generates in a cell, with root sequence index and zero correlation zone have the same format. Is it correct? Thank you

[@OurTechPlanet]

Yes, within the cell, the format should be same.

[@hitendramalik3093]

Hello Bro.One small question please.If Max RETX defined 4 or anyvalue it means that in every re TX UE will Increase Power or It will try with same power for ReTX number and when it failed than at end UE will increase power

[@OurTechPlanet]

UE will increase power on every retransmission by the step size

[@request_scudling]

Thanks for share, i think that the number of MSG2 is not always equal to MSG1 because there are some cases where the MSG2 is not sended ( MSG1 out of coverage , UE Cell radius bigger than configured cell radius ) or RAR window expired or MSG1 discarded because the number of MSG3 retransmission expired (in this case the MSG1 is counted but the MSG2 not sent)

[@OurTechPlanet]

Yes, correct.

[@georgioskarouzos7418]

Very helpful! Is Msg3 retransmitted in case that cannot be decoded by gNB or UE initiates new Rach procedure ? Thank you

[@OurTechPlanet]

Yes, MSG3 can be retransmitted.

[@sankarthangaraj1]

Thanks a lot bro.if msg 3 fail due to dtx means what could be the possible actions to improve RACH

[@OurTechPlanet]

MSG3 DTX is the one of the most common problems but also one of the issues which can be caused by many different scenarios. So, mostly, it would need further troubleshooting. The main causes would be low MSG3 power, UEs in bad coverage, RACH planning conflicts, UEs too far away beyond the cell range.

[@m.karthikeyan6482]

Hi..thanks for your effort🎉🎉 Really helpful for my career 🤝...do you know any contact about protocol testing course?..if means please give me .. thanks.

[@OurTechPlanet]

Thanks! Let me check around for any good courses.

[@hamidrezasaneh-px4nw]

Hi, thanks for your good training. Please share slides.

[@OurTechPlanet]

Unfortunately, we do not share the slides. Thanks for understanding.