A responder authenticity determination system, comprising: a responder that sends a response signal in response to a received signal; an interrogation signal generator that generates an interrogation signal having a random waveform; a transceiver that sends the generated interrogation signal to the responder,...http://www.google.co.uk/patents/US7961077?utm_source=gb-gplus-sharePatent US7961077 - Authenticity determination system of responder, identification system, and interrogation unit
