A method and apparatus is disclosed for increasing calling capacity in a carrier using enhanced Terrestrial Trunk Radio (TETRA) protocols. The method includes transmitting, by a base station to at least one mobile station, a permission signal for an assigned timeslot on a carrier, wherein each timeslot is divided into at least two sub-slots. The method also includes configuring a control signal that is associated with each of the plurality of timeslots. Specific fields in the control signal are associated with each sub-slot on each of the plurality of timeslots. The method further includes providing usage markers through the control signal. Usage markers values are divided into ranges, each range used to identify a timeslot or a sub-slot assignment on the carrier. The base station sends a time advance value to the mobile station to indicate when transmission from the mobile station is to begin.