Secondary usage of a frequency is discussed as a measure for alleviating future depletion of frequency resources. The secondary usage of a frequency means that part of or all the frequency channels preferentially allocated for a system is secondarily used by the other system. Typically, a system which is preferentially allocated with a frequency channel is called a primary system and a system which secondarily uses the frequency channel is called a secondary system.
A TV white space is an exemplary frequency channel whose secondary usage is discussed (see Non-Patent Literatures 1). The TV white space is a channel which is not used by a TV broadcast system depending on an area among frequency channels allocated for the TV broadcast system as a primary system. The TV white space is opened to a secondary system so that efficient utilization of the frequency resource is to be achieved. A standard for a physical layer (PHY) and a MAC layer for enabling the secondary usage of the TV white space can include IEEE802.22, IEEE802.11af and ECMA (European Computer Manufacturer Association)-392 (CogNea, see Non-Patent Literature 2 described later).
The secondary system is generally required to operate so as not to give a fatal interference to the primary system upon secondary usage of a frequency band. An important technique therefor is transmission power control. For example, Patent Literature 1 described later proposes therein a method in which a base station of a secondary system calculates a path loss therefrom to a reception device of a primary system and a discrete frequency width between frequency channels, and determines maximum transmission power for the secondary system based on the calculation result.