Radiant tubing can be used "almost" in any application as long as an accurate heat loss is performed. The heat loss will establish the correct amount of tubing to be used and the temperature that the system will operate at. There are numerous ways for an over concrete installation such as a lightweight concrete or Gypspan product, sleepers using aluminum heat transfer plates, pre-fabbed floor panels, etc.
You "must" ask your carpet supplier what the R-factor of the carpet and especially the padding because all carpets are not good for radiant.
Visit
www.radiantpanelassociation.org for some general do's and don'ts.
Designs for Comfortable & Efficient Heating & Cooling Systems