In the 3GPP (3rd Generation Partnership Project) which is a standardization project, standardization of EUTRA (Evolved Universal Terrestrial Radio Access) is performed, in which high-speed communication is realized by adopting an OFDM (Orthogonal Frequency-Division Multiplexing) communication scheme and flexible scheduling with a predetermined frequency and time unit called a resource block. The EUTRA is also referred to as LTE (Long Term Evolution) in some cases.
Moreover, in the 3GPP, LTE Advanced (also referred to as LTE-A) that achieves higher-speed data transmission and has an upward compatibility with the LTE has been studied.
In the LTE Advanced, a technique by which direct communication is performed from an apparatus (a terminal apparatus) to an apparatus (a terminal apparatus) has been studied. The direct communication from an apparatus to an apparatus is referred to as D2D (Device to Device) or device-to-device communication. Note that, D2D which is standardized in the 3GPP is particularly referred to as LTE-D2D or LTE-Direct as well. Moreover, D2D is simply referred to as services between proximal terminal apparatuses (Proximity based Services: ProSe) in some cases.
In order to realize various kinds of services related to ProSe by using the D2D, a method for discovery of a proximal terminal apparatus, a method for enabling direct communication between terminal apparatuses, and the like have been studied in the 3GPP (NPL 1).
Furthermore, for example, in a case where D2D is used for public safety such as police radio or disaster prevention radio, required is a system by which switching is performed to a mode in which a terminal apparatus autonomously selects a radio resource for the D2D communication and the communication between terminal apparatuses is thereby continued even in a state where a signal from a base station apparatus is unable to be received. Conditions for the switching of a communication scheme (mode) of D2D are described in NPL 2.