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

Question

How ENB decides size of GroupA , GroupB and contention free preambles. based on what basis ENB decides this information?

Answer 1

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 2

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).

Comments

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??