Method and apparatus for device-to-device communication in partial network environment

A first device for communication in a mobile communication system, the first device comprising:

• a transceiver configured to transmit and receive a signal;
• and
• at least one processor coupled with the transceiver and configured to:
• receive, from a base station, a first message including synchronization information and resource allocation information for a random access and a random access response,
• transmit, to a second device, a synchronization signal and a second message based on the first message, the second message including random access channel (RACH) resource allocation information for the random access, the RACH resource allocation information based on the resource allocation information for the random access,
• receive, from the second device, a third message for the random access based on the RACH resource allocation information, and
• transmit, to the second device, a fourth message for the random access response based on the resource allocation information for the random access response included in the first message, the fourth message including information on a timing advance (TA) determined based on the third message,
• wherein a synchronization for receiving signal of the second device is based on the synchronization signal, and a synchronization for transmitting signal of the second device is based on the information on the TA.

A second device for communication in a mobile communication system, the first second device comprising:

• a transceiver configured to transmit and receive a signal;
• and
• at least one processor coupled with the transceiver and configured to:
• receive, from a first device, a synchronization signal and a first message, wherein the synchronization signal is based on synchronization information received from a base station and the first message includes random access channel (RACH) resource allocation information for performing a random access, wherein the RACH resource allocation information is based on first resource allocation information for the random access, received from the base station,
• transmit, to the first device, a second message for the random access based on the RACH resource allocation information, and
• receive, from the first device, a third message for a random access response transmitted based on second resource allocation information which is for the random access response and received from the base station, the third message including information on a timing advance (TA) determined based on the second message,
• wherein a synchronization for receiving signal of the second device is based on the synchronization signal, and a synchronization for transmitting signal of the second device is based on the information on the TA.

A method for communication of a second device in a mobile communication system, the method comprising:

• receiving, from a first device, a synchronization signal and a first message, wherein the synchronization signal is based on synchronization information received from a base station and the first message includes random access channel (RACH) resource allocation information for performing a random access, wherein the RACH resource allocation information is based on first resource allocation information for the random access, received from the base station;
• transmitting, to the first device, a second message for the random access based on the RACH resource allocation information;
• and
• receiving, from the first device, a third message for a random access response transmitted based on second resource allocation information which is for the random access response and received from the base station, the third message including information on a timing advance (TA) determined based on the second message,
• wherein a synchronization for receiving signal of the second device is based on the synchronization signal, and a synchronization for transmitting signal of the second device is based on the information on the TA.