A communication protocol for use in a mobile cellular communication system using time division duplex establishes a communication channel between a user station (e.g., a handset) and a base station in a time slot by assigning a first time segment within the time slot for a user station transmission and assigning a second time segment within the time slot for a base station transmission. The protocol also provides for virtual time slots wherein a time segment assigned for periodic transmission from the base station to a given user station may be non-contiguous with respect to the time segment assigned for periodic transmissions from the user station to the base station.