Method and apparatus for conducting device-to-device communication in wireless communication system

1. A method for performing, by a device-to-device (D2D) transmitting user equipment (UE), D2D communication in a wireless communication system, the method comprising:

transmitting, to a cluster head UE, a first message requesting allocation of radio resources to be used for the D2D communication;

receiving, from the cluster head UE, a second message including radio resource allocation information,

wherein the second message further includes scheduling information for each D2D UE that D2D UEs within a cluster use to monitor a specific signal, and

wherein the radio resource allocation information includes a time-frequency resource for the D2D transmitting UE to transmit data and a time-frequency resource for at least one D2D receiving UE to receive the data; and

transmitting the data in a radio resource area allocated by the second message,

wherein the data is transmitted to the cluster head UE and the at least one D2D receiving UE,

wherein the D2D transmitting UE, the cluster head UE, and the at least one D2D receiving UE are included in the cluster,

wherein a cluster size is changed according to a cell loading factor,

wherein, when the cell loading factor is larger than a threshold, the cluster size becomes small, and

wherein, when the cell loading factor is smaller than the threshold, the cluster size becomes large.

2. The method of claim 1 , wherein the D2D UEs include the D2D transmitting UE and the at least one D2D receiving UE.

3. The method of claim 1 , wherein the scheduling information includes a scheduling interval and an offset.

4. The method of claim 1 , wherein, when the cluster size becomes small, a transmission power of the D2D UEs within the cluster is set to a low value, and

wherein, when the cluster size becomes large, the transmission power of the D2D UEs within the cluster is set to a high value.

5. The method of claim 1 , further comprising:

relaying the second message to a specific D2D UE when the specific D2D UE among the at least one D2D receiving UE is located outside a network coverage supported by an evolved Node B (eNB).

6. A device-to-device (D2D) transmitting user equipment (UE) for performing D2D communication in a wireless communication system, the D2D transmitting UE comprising:

a transceiver; and

a processor functionally connected to the transceiver,

wherein the processor is configured to:

control the transceiver to transmit, to a cluster head UE, a first message requesting allocation of radio resources to be used for the D2D communication,

control the transceiver to receive, from the cluster head UE, a second message including radio resource allocation information,

wherein the second message further includes scheduling information for each D2D UE that D2D UEs within a cluster use to monitor a specific signal, and

wherein the radio resource allocation information includes a time-frequency resource for the D2D transmitting UE to transmit data and a time-frequency resource for at least one D2D receiving UE to receive the data, and

control the transceiver to transmit the data in a radio resource area allocated by the second message,

wherein the data is transmitted to the cluster head UE and the at least one D2D receiving UE,

wherein the D2D transmitting UE, the cluster head UE, and the at least one D2D receiving UE are included in the cluster,

wherein a cluster size is changed according to a cell loading factor,

wherein, when the cell loading factor is larger than a threshold, the cluster size becomes small, and

wherein, when the cell loading factor is smaller than the threshold, the cluster size becomes large.