Why UE selects same preamble group after MSG1 failure ?

Question

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?

Answer 1

UE selects one of the 64 available RACH preambles in Msg1.Msg1 transmission time is 1 ms, in case of msg1 fails it means random access preamble fails & it do the msg1 re transmission within the selected group A or B to simplify the random access procedure.
This group was chosen in Msg1 first transmission.
Sequence is like:
According to root sequence number, cyclic shift and preamble formats , UE generates the preamble sequence.
Select preamble in group A/B randomly according to the MSG3 size and pathloss information, then send the preamble on PRACH.
In case of Msg1 fails, it does the re transmission in same group as many available RACH preambles in same group.