adaptive coding and modulation (ACM)
Various radio technologies use optimization techniques to transmit as much data as possible over a radio channel. However, if the radio technical conditions are impaired, then the error rate increases.
Against this background, unicasts and broadcasts adapt their coding and modulation to the actual transmission quality. When the transmission channel is unimpaired, a more efficient coding scheme is used than when transmission is impaired. An example of this is DVB-S2, in which the reception quality is transmitted from the receiver to the transmitter via a return channel and ensures that the modulation scheme is adapted. This process is called Adaptive Coding and Modulation ( ACM). The ACM method is also used for dynamic modulation switching in microwave directional radio and prevents transmission impairments in poor weather conditions.
Constant Coding and Modulation( CCM) and Variable Coding and Modulation( VCM) are other control methods for coding and modulation, but they do not use return channels.