Mobile communication system and user terminal

1. A method for performing D2D (Device-to-Device) communication comprising:

broadcasting, from a base station, system information block message, the system information block message including first control information indicating a first frequency band;

receiving, by a first user terminal being in coverage of the base station, the first control information from the base station;

performing, by the first user terminal, D2D communication on the basis of the received first control information;

broadcasting, from the first user terminal, the first control information indicating the first frequency band to be used for the D2D communication, and second control information, using a first time radio resource, in response to:

receiving, by the first user terminal, the first control information from the base station; and

a reception level of a signal received by the first user terminal from the base station satisfying a predetermined condition, wherein

the second control information indicates that the first user terminal is in the coverage;

receiving, by a second user terminal being out of coverage of the base station, the first control information and the second control information from the first user terminal,

selecting, by the second user terminal, a second time radio resource different from the first time radio resource, for transmitting, by the second user terminal, third control information and fourth control information; and

transmitting, by the second user terminal, using the second time radio resource, the third control information and the fourth control information, wherein

the third control information is determined by the second user terminal based on the first control information,

the second user terminal transmits the third control information and the fourth control information in response to receiving, by the second user terminal, the first control information and the second control information from the first user terminal,

the third control information indicates a second frequency band to be used for the D2D communication, and

the fourth control information indicates that the second user terminal is out of the coverage; and

performing, by the second user terminal, D2D communication on the basis of the first control information and the second control information received from the first user terminal.

2. A user terminal supporting D2D (Device-to-Device) communication, comprising:

a processor and a memory coupled to the processor, the processor configured to:

receive, when the user terminal is in coverage of a base station, first control information from the base station;

perform D2D communication on the basis of the received first control information;

broadcast the first control information indicating a frequency band to be used for the D2D communication, along with second control information indicating that the user terminal is in the coverage, using a first time radio resource, in response to:

receiving, by the user terminal, the first control information from the base station; and

a reception level of a signal received by the user terminal from the base station satisfying a predetermined condition, wherein

the first control information and the second control information transmitted by the user terminal are received by another user terminal being out of coverage of the base station,

the another user terminal performs D2D communication on the basis of the first control information and the second control information received from the user terminal, and

the another user terminal selects a second time radio resource different from the first time radio resource used by the user terminal, and transmits third control information and fourth control information using the second time radio resource, wherein

the another user terminal transmits the third control information and the fourth control information in response to receiving the first control information and the second control information from the user terminal,

the third control information is determined by the another user terminal based on the first control information,

the third control information indicates a second frequency band to be used for the D2D communication, and

the fourth control information indicates that the another user terminal is out of the coverage.

3. A user terminal supporting D2D (Device-to-Device) communication, comprising:

a processor and a memory coupled to the processor, the processor configured to:

receive fourth control information and second control information from another user terminal when the user terminal is out of coverage, the fourth control information and the second control information being transmitted by the another user terminal using a first time radio resource;

select a second time radio resource different from the first time radio resource, for transmitting, by the user terminal, first control information determined based on the second control information, and third control information; and

transmit, using the second time radio resource, the first control information and the third control information, in response to:

receiving, by the user terminal, the fourth control information and the second control information from the another user terminal, wherein

the first control information indicates a first frequency band to be used for the D2D communication,

the second control information indicates a second frequency band to be used for the D2D communication,

the third control information indicates that the user terminal is out of the coverage, and

the fourth control information indicates that the another user terminal is in the coverage, and

perform D2D communication on the basis of the fourth control information and the second control information received from the another user terminal.