Safety and security increase for air traffic management through unnoticeable watermark aircraft identification tag transmitted with the VHF voice communication

Controller-pilot very high frequency (VHF) voice communication in air traffic control (ATC) relies on amplitude modulation by a carrier frequency of the transmitted analogue voice pattern. This technology is known for its poor voice quality and to be highly sensitive for any kind of noise on the transmission/reception path. On this party-line, pilots have to identify themselves with their call-sign. Human's imperfections in speaking and understanding added to the low channel quality may cause problems to identify without any ambiguity of an aircraft (AC) message without any ambiguity for the controller. The proposed aircraft identification tag (AIT) techniques aim at covering this security lag. The automatic insertion of the supplementary AIT in the transmitted voice communication secures and simplifies the association of a voice message to the specific AC. Supplementary safety increase may be achieved by the mental reinforcement of the audible stimulus (pilot's voice) with a simultaneous visual stimulus in form of e.g. highlighted AC track on the radar screen. Further security increase may be attended from the fact that fake AC VHF transmissions (e.g. jokers, terrorists, ...) becomes mode difficult or even may be impossible by special watermark coding. Simple airfield structures and oceanic high frequency (HF) communication could benefit from such a system, too. AIT technique, therefore, uses proven audio watermark techniques (e.g. used for intellectual property rights for audio CD and digital video). These watermarks are introduced in the voice signal such that, the watermarks are not noticeable. AC and ATC VHF-transceiver need no change. The technique is adapted to the reduced VHF channel spacing of 8.33 kHz. The prototype demonstrator shows very high robustness with a watermark datalink capacity of about 100 bits