Within a communication system that includes multiple communication channels, a low-power mode of operation and a higher-power mode of operation are provided. Each channel is allocated to one of several groups, based on criteria such as whether power is allocated to that channel in low power mode, and whether power was allocated to that channel in a previous high power mode. Initial power levels for each channel for each mode are approximated using an interpolation rule known to both the receive and the transmitter. The system switches between modes according to a PMD pre-defined schedule. When a new power mode begins, the receiver measures signal power received on each channel and then transmits corrective information sufficient to allow adaptation of power levels to achieve PMD pre-defined levels of received power.