In Initial UL sync up of UEⁱ with ENB (after decoding and obtaining all info present in SIB2 -- DL sync) , when will UE Tx RACH preamble
1) where --he knows by BW and frequency offset of PRACH

but as UL timing is not synchronized, when it will transmit ...or is it that it transmits anytime and ENB decodes it (due to awesome properties of ZC prime sequence)

My precise question is though he knows the resource config (time domain resource opportunity pattern for PRACH in UL) , how he wil know that is the time that RACH slot has come etc ....