US Patent 7283594 Impedance modulation signaling

Signalling between transmitting means and receiving means wherein signals from the transmitting means are subjected by the receiving means to deliberate reflections and resulting signals are transmitted back as meaningful at the transmitting means, different deliberate reflections having effects on said resulting signals that have different meanings at said transmitting means. Two-way signalling involves first signalling in one direction by sending signals with certainty of deliberate reflection thus resulting signals for return related to the signals sent according to the nature of the deliberate reflection and second signalling in the other direction by varying the nature of the deliberate reflection.