XM Satellite Radio recently applied for a U.S. Patent for transmitting the digital satellite radio signal over HD Radio. One of the inherit problems with the current FM modulator method is that while XM takes all this effort to broadcast digitally up to the satellites, and back down to the receivers, it then gets converted to an analog signal when transmitted over FM. It works great because FM radios are readily available, but at the cost of sound quality.

This new patent application would preserve the digital signal, but utilizing HD Radio. Instead of transmitting to traditional FM, XM will send the satellite radio signal over an IBOC (in-band over carrier) digital audio broadcast. The patent application further extends the capabilities of the Digital FM Modulator by allowing other mediums like MP3, CD or other alternatives to be re-transmitted onto an HD Radio.

You have to love the irony behind XM taking advantage of HD Radio for its own use.

[XM's Digital FM Modulator Patent Application] (PDF)