24. The system of claim 21 , wherein the determining whether the current working mode of the primary user has changed is responsive to a probe of the spectrum band.
21. A system comprising: a media access control (MAC) layer module configured for: receiving information about an expected use by a primary user of the spectrum band; classifying the expected use by the primary user into at least two working modes, the classifying responsive to the information about the expected use; and selecting one of the working modes as a current working mode of the primary user, the selecting responsive to the classifying and to a current access pattern of the primary user on the spectrum band; and a physical (PHY) layer module in communication with the MAC layer module, the PHY layer module configured for: sensing the spectrum band to determine the current access pattern of the primary user; scheduling transmissions on the spectrum band using a current schedule that is responsive to the current working mode of the primary user; determining whether the current working mode of the primary user has changed; if the current working mode of the primary user has changed, communicating the change to the MAC layer module, wherein the MAC layer module re-performs the selecting responsive to the communicating; and if the current working mode of the primary user has not changed, re-performing the scheduling and determining.