Originally Posted by Ignitionnet

SCDMA is less efficient than ATDMA. 128QAM requires an insane upstream SNR, 64QAM is a challenge for operators to push to let alone another 3dB to cater to 128QAM and after overheads it doesn't actually provide anything more than 64QAM ATDMA.

SCDMA does indeed have a purpose, it is more resilient in the presence of burst noise that ATDMA, however horses for courses. If it were so evidently superior everyone would be doing it. They aren't.