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In RACH how path loss effects selection of group A or group B preamble??

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In RACH how path loss effects selection of group A or group B preamble??
posted Apr 9 by Basavaraj Kamagond

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2 Answers

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Best answer

Path loss effects ue transmit power. Ue needs more tx power when it have more pathloss. As ue max tx power is fix so if enb gives less grant in case of more path loss then chances to reach enb will be more than if enb gives more grant for more pathloss ue.

answer Apr 20 by Veer Pal Singh Yadav
0 votes

Selection is based on:
if the pathloss is less than PCMAX,c (of the Serving Cell performing the RandomAccess Procedure) – preambleInitialReceivedTargetPower – deltaPreambleMsg3 – messagePowerOffsetGroupB, then:
- select the Random Access Preambles group B;
- else :
- select the Random Access Preambles group A.
PCMAX,c- maximum output power PCMAX,c of the serving cell.
preambleInitialReceivedTargetPower- taken from SIB2, Preamble initial received target power with values from -120 dBm to -90 dBm with step size of 2 dBm .
deltaPreambleMsg3 - power control related parameter .
messagePowerOffsetGroupB- Power offset for selecting preamble Group B (0, 5, 8, 10, 12, 15 or 18 dB).

answer Apr 13 by Mohit Mohan
Thank you, but my doubt is if pathloss < (some calculation) ,how they are deciding they need more grant ( group B )  else less grant( group A). How pathloss effects the grant size??
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+1 vote

UE will select preamble group based on the msg3 size and path loss, then if msg1 fails then pathloss is more so it should change the preamble group , because existing preamble group is having more path loss but UE selects same preamble group is mentioned in spec why?

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