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Uplink grant for UE while attempting random access procedure?

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I want to ask about the uplink grant for UE while attempting random access procedure. How the eNB decide the uplink grants of msg3? (Which subframe and which resource blocks). And the UE perform HARQ when transmitting and receiving the step 3 and step 4 messages. Some source said that, each step in HARQ is performed at 4 subframes intervals. If i get to the root of the problem, how many subframes ( or ms) does the random access procedure take?

posted Jul 23, 2016 by anonymous

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1 Answer

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Hi ,

Q 1 : Enb will decide the required grant based on your preamble transmission. there were spme size associated with the preamble index, so UE will select preamble based on its need.

Q2 : When UE perform HARQ process yes it will take 4ms to get the ACK/NACK, and one more 4ms to do newtx or retx .

Say examble RAR window is 8 Subframe(note : RAR window start 4 SF after rach subframe) and UE did rach in first subframe. ENB can send RAR within those 8 subframe. Say ENb send at 8th subframe (actually 12 subframe after RACH ( 8 + 4)), then UE will take 4 subframe to send uplink data (i.e msg 3 ) total 16 SF overed, then ENB will send contention resoultion message with in contention resoultion window timing, at the MAX 24 SF will take to finish rach process (only till msg3 transmission but actual rach procedure means till attach complete.).

answer Jul 25, 2016 by Jaganathan
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