The presence of the non-television transmission within a channel is used
to indicate that secondary non-licensed usage of the channel is
permitted. Specifically, if secondary users incorporate the means to
identify the unique modulation signature of the secondary user, decoding
of a beacon signal may not be necessary. With the above in mind, a radio
will be prevented from transmitting within a frequency band when no
transmission within the licensed spectrum is currently taking place; the
licensee is currently transmitting on the spectrum (e.g., television
transmissions are taking place utilizing the spectrum, or the radio
cannot sense the presence of a data channel (beacon).