Method and apparatus for determining modulation scheme for retransmission in a communication system

A method of determining a modulation scheme for a retransmission in a communication system using two modulation schemes, where at an initial transmission, information is modulated in the lower-order modulation scheme if a first MPR (Modulation order Product code Rate) is less than a first threshold, and in the higher-order modulation scheme if the first MPR is equal to or greater than the first threshold, the first MPR indicating a spectral efficiency for the initial transmission and being determined by an EP (Encoder Packet) size, the number of available Walsh codes, and the number of slots per sub-packet that are used for the initial transmission, the method comprising the steps of:

• calculating a second MPR indicating a spectral efficiency for the retransmission using an EP size, the number of available Walsh codes, and the number of slots per sub-packet that are used for the retransmission;
• selecting the lower-order modulation scheme if the second MPR is equal to or less than a second threshold greater than the first threshold;
• and
• selecting the higher-order modulation scheme if the second MPR is greater than the second threshold.

An apparatus for determining a modulation scheme for a retransmission in a communication system using at least three modulation schemes where information is modulated in one of the modulation schemes at an initial transmission, comprising:

• a plurality of modulators using different modulation schemes;
• a modulator selector for determining a modulation scheme for each transmission by an algorithm expressed as the following equation and outputting a modulator selection signal indicating the determined modulation scheme:
• 9 If 0 <MPRk ≦ THL, Select the lowest-order modualtion (8) scheme elseif THL < MPRk ≦ THH, if MPRe < THE, Select the medium-order modulation scheme else, Select the highest-order modualtion scheme else, Select the highest-order modualtion scheme
• where THL, THH, and THE are predetermined empirical thresholds, MPRk is a current spectral efficiency for a kth transmission, calculated using an EP (Encoder packet) size, the number of available Walsh codes, and the number of slots per sub-packet that are used for the kth transmission, and MPRe is a spectral efficiency reflecting modulation symbols transmitted before the current transmission of the same information;
• and
• a demultiplexer for outputting input data to a modulator selected according to the modulator selection signal.

An apparatus for determining a modulation scheme for a retransmission in a communication system where at an initial transmission, information is modulated in one of two available modulation schemes, comprising:

• a plurality of modulators using different modulation schemes;
• a modulator selector for determining a modulation scheme for each transmission by an algorithm expressed as the following equation and outputting a modulator selection signal indicating the determined modulation scheme:
• 10 If 0 < MPRk ≦ THM, Select the lower - order modulation scheme else, Select the higher - order modulation scheme
• where THM is a predetermined empirical threshold, MPRk is a current spectral efficiency for a kth transmission, calculated using an EP (Encoder packet) size, the number of available Walsh codes, and the number of slots per sub-packet that are used for the kth transmission;
• and
• a demultiplexer for outputting input data to a modulator selected according to the modulator selection signal.