In Adaptive Coding and Modulation (ACM), the receiver sends feedback to the transmitter, which indicates the transmission quality. However, there are two other methods that work without feedback: Constant
Coding and Modulation (CCM) and Variable Coding and Modulation (VCM). In the VCM method, the transmission parameters are dynamically adapted to the
depending on the priority of
the input data. The VCM method is used in Standard Definition Television (SDTV) and is much more robust than the services of HDTV.