Innovative Watermark Technique for ATC Voice Communication

Which controller has never experienced difficulty understanding the callsign in a pilot’s voice communication or in locating an aircraft on the display?

Small amounts of digital information, such as the aircraft callsign, can be added inaudibly to voice communications using a technique called watermarking. This data can then be used to highlight the transmitting aircraft on the controller’s display. This would make the controller’s identification of the transmitting aircraft faster and more reliable which has a clear safety benefit. The same technique can be used to add a digital signature to a voice message to ensure authenticity.

Click on the following image to see and hear a Powerpoint animation which illustrates the concept.

Watermark data is hidden in the voice spectrum and is unnoticeable for human beings. A demonstrator system, called Aircraft Identification Tag (AIT), has been developed within the Innovation Business Area and has shown very high performance and robustness. AIT uses proven mass-market technologies and does not require modification of existing aircraft VHF equipment. The AIT concept was realised in collaboration with the Signal Processing and Speech Communication Laboratory of the Graz University of Technology (Austria) and the firm Frequentis, Innovations Graz (Austria) which realised the demonstrator. A paper on AIT was presented at the 22nd Digital Avionics System Conference (DASC) in Indianapolis in October.

Paper watermarks are nearly as old as paper itself and were originally used to prove the authenticity of a document. Today, digital watermarks are used for the protection of intellectual property rights of digital data such as music or pictures. AIT’s innovation is to adapt the watermark technique to the special needs of an ATC voice channel using signal processing. For more details refer to the AIT Powerpoint presentation at DASC or contact horst.hering@eurocontrol.int.