A method is performed by user equipment (UE) for communicating on a secondary cell (SCell) with fast activation or deactivation. The method includes receiving, from a serving cell, a medium access control (MAC) control element (CE) including a plurality of bits, wherein individual bits of the plurality of bits each indicate whether respective secondary cells (SCells) of a fifth generation (5G) wireless cellular network are activated or deactivated. The method includes based on a numerology of the serving cell, determining an activation delay time for one or more activated SCells indicated by the plurality of bits of the MAC CE. The method includes communicating using the one or more activated SCells based on the determined activation delay time.