These distribution systems differ mainly in the modulation schemes used and 
error correcting codes used, due to the different technical constraints. 
DVB-S (SHF) uses QPSK, 8PSK or 16-QAM. DVB-S2 uses QPSK, 8PSK, 16APSK or 
32APSK, at the broadcasters decision. QPSK and 8PSK are the only versions 
regularly used. DVB-C (VHF/UHF) uses QAM: 16-QAM, 32-QAM, 64-QAM, 128-QAM or 
256-QAM. Lastly, DVB-T (VHF/UHF) uses 16-QAM or 64-QAM (or QPSK) in 
combination with COFDM and can support hierarchical modulation.