Digital Signatures for the Analogue Radio

The air/ground voice communication between air traffic controller and aircraft does not provide any means of automatic speaker identification and is therefore susceptible to call sign confusion and originator ambiguity. In the near future the analogue VHF radio will not disappear from avionic communications. With an add-on to the analogue radio it is possible to automatically detect the originator of a voice message. Watermarking allows the embedding of an identification into the voice signal. The tag is ideally not audible to the human listener, but is for an electronic system clearly detectable. Requirements on the system are driven by functionality and deployment constraints. The reviewed in-band modem system is in our opinion not fully compatible to the legacy radio infrastructure. The spread spectrum watermarking approach shows room for improvements in functionality and capacity. With informed embedding and known host state algorithms a new trend in watermarking promises large capacity increases.