Spectrum admission control

A primary user of a spectrum, such as a licensed user, has primary access authority to use of a spectrum. A plurality of secondary users of the spectrum, which may be unlicensed users, have secondary access authority to use of the spectrum. When the primary user wants to use the spectrum, the primary user sends a message that is propagated to all the secondary users in a geographic region that the primary user wants to use the spectrum. The message specifies the duration of time and the geographic region (location of use) where the primary user wants to use the spectrum. The secondary users in the location of use immediately stop using the spectrum for the duration of time specified in the message and then may resume use of the spectrum.