Hi there,
You can send pulses down any power line by injecting the line with the pulses
using a carrier frequency and then at the receive end reconstruct with a
detector. This is similar to how radio works. Your transmitter sends the
signal, your receiver detector changes the info back to its regular form.
The only trick is you have to use a frequency that is much higher than the
line frequency so that you can easily filter out the line and keep the signal,
which is very much smaller than the line amplitude.
You might also have to use special transmit codes that keep the average
dc level to zero.
For example, say you use a carrier of 200kHz. You would couple this to the
line with a high pass filter. At the receive end, you would have a filter that
has a center frequency of 200kHz, which would filter out everything but
the 200kHz carrier. You would then use a detector to detect the modulated
control pulses and then a microcontroller to convert them back into the
required one's and zero's for the logic.