A method of a user equipment (UE) in a wireless communication system supporting a shared spectrum channel access is provided. The method comprises: receiving, from a base station (BS), a set of higher layer parameters including a subcarrier spacing of a physical random access channel (PRACH) preamble, a logical root index (ilog) for the PRACH preamble, and an index (zeroCorrelationZoneConfg); determining a sequence length (LRA) for the PRACH preamble based on the subcarrier spacing of the PRACH preamble; determining a physical root index (iphy) for the PRACH preamble based on the logical root index (ilog); determining a cyclic shift (NCS) for the PRACH preamble based on the index (zeroCorrelationZoneConfg); generating the PRACH preamble based on the determined sequence length LRA, the determined physical root index iphy, and the determined cyclic shift NCS; and transmitting, to the base station (BS) over the shared spectrum channel, the PRACH preamble.