Ericsson MINI-LINK 6351 Technical Description page 10

Technical Description
Figure 3 Principles of Adaptive Coding and Modulation
When using only Adaptive Modulation, the steps in Figure 3 only differ in
terms of modulation. When using ACM, the steps can differ in both coding and
modulation, which increases the number of possible steps.
In order to handle channel variations, the channel conditions are continuously
monitored on the Rx side by measurement of Signal to Noise and Interference
Ratio (SNIR). When the receiver, based on this data, detects that channel
conditions imply a change to the next higher or lower ACM profile, a message
is sent to the transmitter on the other side requesting a higher or lower ACM
profile. Upon receipt of such request the transmitter starts transmitting with the
new ACM profile. Each direction is independent. At demodulation the receiver
follows the ACM profile as a slave.
The ACM profile can also be configured with the maximum ACM profile equal to
the minimum ACM profile, and thereby achieving a mode comparable to static
mode, where the ACM profile remains unchanged.
Hitless ACM is compatible with Automatic Transmit Power Control (ATPC),
which is working in a closed loop only in the highest configured ACM profile. In
lower ACM profiles the output power is set as high as possible.
Note: Hitless ACM requires a license.
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