Apparatus and method for controlling transmission power in wireless communication system

1. A method of controlling transmit power for a device-to-device (D2D) communication between user equipments (UEs), the method comprising:

determining, by a first UE, to transmit a D2D discovery channel for searching for a peer UE;

determining transmit power of the D2D discovery channel based on a pathloss estimate and a first parameter associated with a number of physical resource blocks (PRBs) for transmitting the D2D discovery channel;

transmitting, by the first UE, the D2D discovery channel based on the determined transmit power of the D2D discovery channel;

determining transmit power of a D2D data channel based on the pathloss estimate and a second parameter associated with a number of PRBs for transmitting the D2D data channel; and

transmitting the D2D data channel to the peer UE based on the determined transmit power of the D2D data channel,

wherein the number of PRBs for transmitting the D2D data channel is configured to have various sizes,

wherein the number of PRBs for transmitting the D2D discovery channel is fixed as 2, and

wherein the pathloss estimate is determined based on a link between an evolved NodeB (eNB) and the first UE.

2. The method of claim 1 , further comprising:

establishing a radio resource control (RRC) connection with the eNB; and

receiving, from the eNB, a radio resource allocation for the D2D communication.

3. The method of claim 1 , further comprising:

determining transmit power of a D2D scheduling assignment (SA) channel based on the pathloss estimate and a third parameter associated with a number of PRBs for transmitting the D2D SA channel; and

transmitting the D2D SA channel to the peer UE based on the determined transmit power of the D2D SA channel,

wherein the number of PRBs for transmitting the D2D SA channel is fixed as 1 or 2.

4. The method of claim 3 , wherein the third parameter is in proportion to the number of PRBs for transmitting the D2D SA channel.

5. The method of claim 3 , wherein at least one of the transmit power of the D2D discovery channel, the transmit power of the D2D SA channel, and the transmit power of the D2D data channel is configured to be determined further based on a compensation parameter for compensation of the pathloss estimate, the compensation parameter being configured to be received from the eNB.

6. The method of claim 5 , wherein at least one of the transmit power of the D2D discovery channel, the transmit power of the D2D SA channel, and the transmit power of the D2D data channel is configured to be determined further based on a UE specific power control value.

7. The method of claim 6 , wherein the UE specific power control value is differently set according to transmission types comprising a broadcasting transmission, a groupcasting transmission, and a unicasting transmission.

8. The method of claim 1 , wherein a maximum value of the transmit power of the D2D data channel is equal to a maximum value of a transmit power of a physical uplink shared channel (PUSCH).

9. The method of claim 1 , wherein the first parameter is in proportion to the number of PRBs for transmitting the D2D discovery channel, and the second parameter is in proportion to the number of PRBs for transmitting the D2D data channel.

10. A transmission (Tx) user equipment (UE) to control transmit power for a device-to-device (D2D) communication with a reception (Rx) UE, the Tx UE comprising:

a processor configured to determine to transmit a D2D discovery channel for searching for an Rx UE, determine transmit power of the D2D discovery channel based on a pathloss estimate and a first parameter associated with a number of physical resource blocks (PRBs) for transmitting the D2D discovery channel; and

a transceiver configured to transmit the D2D discovery channel based on the determined transmit power of the D2D discovery channel,

wherein the processor is further configured to determine transmit power of a D2D data channel based on the pathloss estimate and a second parameter associated with a number of PRBs for transmitting the D2D data channel,

wherein the transceiver is further configured to transmit the D2D data channel to the Rx UE based on the determined transmit power of the D2D data channel,

wherein the number of PRBs for transmitting the D2D data channel is configured to have various sizes,

wherein the number of PRBs for transmitting the D2D discovery channel is fixed as 2, and

wherein the pathloss estimate is determined based on a link between an evolved NodeB (eNB) and the Tx UE.

11. The Tx UE of claim 10 , wherein the transceiver establishes a radio resource control (RRC) connection with the eNB, and receives, from the eNB, a radio resource allocation for the D2D communication.

12. The Tx UE of claim 10 , wherein:

the processor is further configured to determine transmit power of a D2D scheduling assignment (SA) channel based on the pathloss estimate and a third parameter associated with a number of PRBs for transmitting the D2D SA channel; and

the transceiver is configured to transmit the D2D SA channel to the Rx UE based on the determined transmit power of the D2D SA channel; and

the number of PRBs for transmitting the D2D SA channel is fixed as 1 or 2.

13. The Tx UE of claim 12 , wherein the third parameter is in proportion to the number of PRBs for transmitting the D2D SA channel.

14. The Tx UE of claim 12 , wherein at least one of the transmit power of the D2D discovery channel, the transmit power of the D2D SA channel, and the transmit power of the D2D data channel is configured to be determined further based on a compensation parameter for compensation of the pathloss estimate, the compensation parameter being configured to be received from the eNB.

15. The Tx UE of claim 14 , wherein at least one of the transmit power of the D2D discovery channel, the transmit power of the D2D SA channel, and the transmit power of the D2D data channel is configured to be determined further based on a UE specific power control value.

16. The Tx UE of claim 15 , wherein the UE specific power control value is differently set according to transmission types comprising a broadcasting transmission, a groupcasting transmission, and a unicasting transmission.

17. The Tx UE of claim 10 , wherein the first parameter is in proportion to the number of PRBs for transmitting the D2D discovery channel, and the second parameter is in proportion to the number of PRBs for transmitting the D2D data channel.

18. The Tx UE of claim 10 , wherein a maximum value of the transmit power of the D2D data channel is equal to a maximum value of a transmit power of a physical uplink shared channel (PUSCH).

19. A transmission (Tx) user equipment (UE) to control transmit power for a device-to-device (D2D) communication with a reception (Rx) UE, the Tx UE comprising:

a processor configured to determine to transmit a D2D discovery channel for searching for an Rx UE, determine transmit power of the D2D discovery channel based on a pathloss estimate and a first parameter associated with a number of physical resource blocks (PRBs) for transmitting the D2D discovery channel; and

a transceiver configured to transmit the D2D discovery channel based on the determined transmit power of the D2D discovery channel,

wherein the processor is further configured to determine transmit power of a D2D scheduling assignment (SA) channel based on the pathloss estimate and a second parameter associated with a number of PRBs for transmitting the D2D SA channel, and to determine transmit power of a D2D data channel based on the pathloss estimate and a third parameter associated with a number of PRBs for transmitting the D2D data channel,

wherein the transceiver is further configured to transmit the D2D SA channel to the Rx UE based on the determined transmit power of the D2D SA channel, and to transmit the D2D data channel to the Rx UE based on the determined transmit power of the D2D data channel,

wherein the number of PRBs for transmitting the D2D data channel is configured to have various sizes,

wherein the number of PRBs for transmitting the D2D SA channel is fixed as 1,

wherein the number of PRBs for transmitting the D2D discovery channel is fixed as 2, and

wherein the pathloss estimate is determined based on a link between an evolved NodeB (eNB) and the Tx UE.