A method of determining useable combinations of variables for transmitting a subpacket of an encoder packet in a communication system is disclosed. First, an arbitrary combination from a plurality of all combinations of transmission variables is selected based on a number of currently useable Walsh codes and channel environment. Next, an arbitrary MPR is determined based on a number of useable encoder packet bits, a number of useable slots, and the number of currently useable Walsh codes, all of which belong to the selected arbitrary combination transmission variables. Thereafter, a final MPR, which is the smallest one of MPR values of a MPR set that corresponds to the number of useable encoder packet bits and the number of useable slots, is determined, and a final number of Walsh codes is calculated based on the number of useable encoder packet bits, the number of useable slots, and the determined final MPR. Finally, one or more useable combinations of variables are determined based on the final number of Walsh codes.