The following examples pertain to further aspects. Example 1 is an access point (AP) device for controlling spectrum usage of a hierarchical communication system, in which a spectrum reserved for an Incumbent is usable by at least one user equipment (UE) for transmission when the spectrum is not required by the Incumbent, the AP device comprising a processor configured to: enforce the at least one UE into a mode protecting use of the spectrum by the Incumbent based on a spectrum request indication from the Incumbent; and enable transmission of the at least one UE using the spectrum reserved for the Incumbent based on a spectrum availability indication from the Incumbent.
In Example 2, the subject matter of Example 1 can optionally include: a network interface with a controller of the hierarchical communication system, in particular a Spectrum Access System (SAS) controller or a Licensed Shared Access (LSA) system controller, wherein the processor is configured to receive the spectrum request indication and/or the spectrum availability indication via the network interface.
In Example 3, the subject matter of Example 2 can optionally include that the processor is configured to: receive a message requesting vacating of the reserved spectrum from the controller of the hierarchical communication system upon a spectrum request indication from the Incumbent; and receive a message making the reserved spectrum available for transmission of the at least one UE from the controller of the hierarchical communication system upon a spectrum availability indication from the Incumbent.