Apparatuses, systems, and methods for selecting channel access mechanisms in wireless communications, and particularly in 3GPP NR-U. For example, an appropriate listen-before talk (LBT) channel access category (Cat) may be defined for certain messages, such as certain DL and/or UL control messages and certain RACH messages. For other messages, an appropriate Cat may be signaled by the base station, e.g., in a DCI message or SIB. Mechanisms are provided for the base station to signal to the UE certain channel access profile parameters, such as an appropriate LBT Cat, CAPC, and/or CP extension. Mechanisms are also provided for adjustment of contention window duration.