A communication system for a power line is described. A transmission system of the communication system divides the time axis into a number of time slots synchronized such that one time slot can start about a zero crossing of the power line signal. These time slots may be referred to as channels. Data may initially be modulated into at least one of these time slots over a first transmission period according to a modulation scheme. The time slots and/or modulation scheme used in subsequent transmission periods may be adjusted depending on transmission feedback relating to prior modulated data.