A quick google got this:
I agreee with HD, I don't think any ATC systems use Mode-S ident to give code/callsign correlation on the displays. (The Mode 3A will soldier on for some time)
The Mode-S/ADS-B transponders does give a lot of possibilites, and I imagine SMR systems will be the first to make full use of it. (And my hung over brain thinks that they might use Mode-S in SMR systems some places allready
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