A CDMA data transmission system and method for periodically allocating channels to subscriber units, wherein prior to the beginning of any period all active subscriber units are identified that are in communication with the transmitter and for which there are data, exceeding a given minimal quantity, stored in a buffer. For each active subscriber unit one or more priority factors are calculated as a function of associated power levels; and on the basis of the priority factors, at least one channel is allocated to a corresponding active subscriber unit. The channel allocation is repeated in respect of any active subscriber units to which no channels have yet been allocated, subject to an availability of unallocated channels and subject to a limitation of maximum transmitter power.