A user equipment transmits a data packet using a selected signature in a time slot of a radio frame within a superframe of a random access channel. The superframe being time divided into radio frames. A base station identifies the selected signature, transmission time slot and transmission radio frame of the data packet. The base station determines an uplink scrambling code for the user equipment based on in part the identified signature, transmission time slot and transmission radio frame. The base station selectively transmits an acknowledgment message based on in part an availability of the determined uplink scrambling code. The user equipment receives the acknowledgment message and transmits a subsequent data packet using the determined uplink scrambling code.