How WiMAX System Change the Modulation Techniques?

WiMAX system adjust or change the modulation used based on the radio link quality/signal strength; in other words based on SNR:

1. When the quality of radio link is very good, the highest modulation scheme (the most complex) is used, which translates into greater bandwidth capacity to the system.
2. In contras, when the signal quality is degrade, the system will shift to a lower order of modulation scheme in order to retain the connection quality instead of the data bandwidth.
   

for example:

1. 22 dB of SNR = 64QAM modulation is used.
   
2. 16 db of SNR = 16QAM modulation is used.
3. 9dB of SNR = QPSK modulation is used.
4. 6dB of SNR = BPSK modulation is used.