Enhanced mode S is what you will find in the big iron. This transponder is integrated with the FMS and will include in its response various parameters of that FMS, including, but not limited to:
...
- GPS/INS derived position
Actually, position is not one of the EHS parameters. They are:
Magnetic Heading
Indicated Airspeed
Mach No
Vertical Rate
Roll Angle
Track Angle Rate (or True Airspeed)
True Track Angle
Groundspeed
Selected Altitude
Barometric Pressure Setting
That's because the parameters are sent as a supplement to Secondary Surveillance Radar, which knows where the aircraft is by traditional radar location.
But what's nice is that the format of the EHS response is essentially interoperable with an ADS-B response which does include position.
And as far as ADS-B is concerned: I think (but am not entirely sure) that ADS-B is simply the encoding mechanism for the parameters that are both required under Elementry mode S and Enhanced mode S. So both types of mode-S transponder will emit an ADS-B signal, but Elementry mode S will only use that to encode a few parameters, and that list does not include the GPS/INS derived position.
No, not quite. ADS-B is the idea that the data is
broadcast (that's the "-B") rather than waiting for an interrogation from ground radar. And of course if there's no ground radar involved, you need to add position to the broadcast. But the formats used are similar, so most EHS transponders can also do ADS-B. A bit more detail
here.