Here is a bit of it. You can read the entire concept if you follow the link and form your own opinion.
" The transition from analog to digital technology could be made in any number of ways--the possible architectures for a new band plan are as infinite as the engineering imagination. The most popular transition model in use around the world today is the Eureka 147. In this model, an existing radio station receives a new swath of spectrum from which to broadcast its digital signal. Over time, the station's analog signal is terminated and new stations are allowed to use the vacated bandwidth. This model has been proven effective in efficiently allocating new and existing audio space.
The U.S. implementation model before the Federal Communications Commission, however, is quite different. Called the In-Band-On-Channel plan, it allows existing stations to use the space on and around their current analog channel to broadcast the digital signal. For example, a station broadcasting at 97.9 would use the space between it and the stations next to it on the dial for its digital broadcasting. When its analog signal is eventually terminated, the entire swath of bandwidth would belong to that station. "
http://oldsite.prometheusradio.org/artdigital.shtml
