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, the method comprising:

receiving, at a User Equipment (UE), a radio resource control (RRC) message transmitted from an evolved NodeB (eNB), the RRC message comprising power information for the UE, the power information comprising D2D maximum transmit power for a first D2D transmission through a first serving cell and maximum transmit power for an uplink transmission to the eNB through a second serving cell, wherein the uplink transmission to the eNB through the second serving cell comprises a Physical Uplink Shared Channel (PUSCH) transmission;

determining whether the first D2D transmission through the first serving cell and a second D2D transmission overlap in a subframe i, wherein the first D2D transmission is prioritized over the second D2D transmission;

determining, based on the priority of the first D2D transmission, the first D2D transmission in the subframe i;

determining whether the first D2D transmission through the first serving cell and the PUSCH transmission to the eNB through the second serving cell overlap in the subframe i;

based on allocation of transmit power of the overlapped PUSCH transmission to the eNB through the second serving cell in the subframe i, adjusting transmit power of the first D2D transmission through the first serving cell in the subframe i, wherein the adjusted transmit power of the first D2D transmission is greater than zero; and

performing the first D2D transmission through the first serving cell and the PUSCH transmission to the eNB through the second serving cell in the subframe i,

wherein the transmit power of the overlapped PUSCH transmission to the eNB through the second serving cell in the subframe i is prioritized over the transmit power of the first D2D transmission through the first serving cell in the subframe i.

2. The method of claim 1 , wherein the first D2D transmission through the first serving cell in the subframe i comprises at least one of:

a D2D discovery channel,

a D2D scheduling assignment (SA) channel, and

a D2D data channel.

3. The method of claim 2 , wherein the transmit power of the first D2D transmission through the first serving cell in the subframe i is adjusted such that the transmit power of the first D2D transmission through the first serving cell in the subframe i does not exceed remaining power being calculated by subtracting the transmit power of the overlapped PUSCH transmission to the eNB through the second serving cell in the subframe i from maximum transmit power configured for the UE.

4. The method of claim 1 , wherein the D2D maximum transmit power for the first D2D transmission through the first serving cell is determined based on a coverage of a D2D channel.

5. The method of claim 1 , further comprising:

adjusting transmit power of a D2D transmission through the first serving cell in a subframe j such that the transmit power of the D2D transmission through the first serving cell in the subframe j does not exceed remaining power being calculated by subtracting transmit power of a D2D transmission through a third serving cell in the subframe j from maximum transmit power configured for the UE.

6. The method of claim 5 , wherein the transmit power of the D2D transmission through the third serving cell in the subframe j is prioritized over the transmit power of the D2D transmission through the first serving cell in the subframe j.

7. The method of claim 1 , wherein the priority of the first D2D transmission is determined based on at least one of a D2D channel type and a D2D mode.

8. The method of claim 7 , wherein a D2D scheduling assignment (SA) channel in D2D Mode 1 transmission is prioritized over a D2D SA channel in D2D Mode 2 transmission or over a D2D data channel.

9. A user equipment (UE) to control transmit power for a device-to-device (D2D) communication, the UE comprising:

a transceiver to receive a radio resource control (RRC) message transmitted from an evolved NodeB (eNB), the RRC message comprising power information for the UE, the power information comprising D2D maximum transmit power for a first D2D transmission through a first serving cell and maximum transmit power for an uplink transmission to the eNB through a second serving cell, wherein the uplink transmission to the eNB through the second serving cell comprises a Physical Uplink Shared Channel (PUSCH) transmission; and

a processor configured to determine whether the first D2D transmission through the first serving cell and a second D2D transmission overlap in a subframe i, wherein the first D2D transmission is prioritized over the second D2D transmission,

wherein the processor determines, based on the priority of the first D2D transmission, the first D2D transmission in the subframe i,

wherein the processor determines whether the first D2D transmission through the first serving cell and the PUSCH transmission to the eNB through the second serving cell overlap in the subframe i,

wherein the processor adjusts transmit power of the first D2D transmission through the first serving cell in the subframe i based on allocation of transmit power of the overlapped PUSCH transmission to the eNB through the second serving cell in the subframe i, wherein the adjusted transmit power of the first D2D transmission is greater than zero,

wherein the transceiver performs the first D2D transmission through the first serving cell and the PUSCH transmission to the eNB through the second serving cell in the subframe i, and

wherein the transmit power of the overlapped PUSCH transmission to the eNB through the second serving cell in the subframe i is prioritized over the transmit power of the first D2D transmission through the first serving cell in the subframe i.

10. The UE of claim 9 , wherein the first D2D transmission through the first serving cell in the subframe i comprises at least one of:

a D2D discovery channel,

a D2D scheduling assignment (SA) channel, and

a D2D data channel.

11. The UE of claim 10 , wherein the processor adjusts the transmit power of the first D2D transmission through the first serving cell in the subframe i such that the transmit power of the first D2D transmission through the first serving cell in the subframe i does not exceed remaining power being calculated by subtracting the transmit power of the overlapped PUSCH transmission to the eNB through the second serving cell in the subframe i from maximum transmit power configured for the UE.

12. The UE of claim 9 , wherein the D2D maximum transmit power for the first D2D transmission through the first serving cell is determined based on a coverage of a D2D channel.

13. The UE of claim 9 , wherein the processor adjusts transmit power of a D2D transmission through the first serving cell in a subframe j such that the transmit power of the D2D transmission through the first serving cell in the subframe j does not exceed remaining power being calculated by subtracting transmit power of a D2D transmission through a third serving cell in the subframe j from maximum transmit power configured for the UE.

14. The UE of claim 13 , wherein the processor prioritizes the transmit power of the D2D transmission through the third serving cell in the subframe j over the transmit power of the D2D transmission through the first serving cell in the subframe j.

15. The UE of claim 9 , wherein the processor determines the priority of the first D2D transmission based on at least one of a D2D channel type and a D2D mode.

16. The UE of claim 15 , wherein the processor prioritizes a D2D scheduling assignment (SA) channel in D2D Mode 1 transmission over a D2D SA channel in D2D Mode 2 transmission or over a D2D data channel.