Method for selecting of sidelink grant for a D2D UE in a D2D communication system and device therefor

1. A method for transmitting sidelink data by a User Equipment (UE) in a wireless communication system, the method comprising:

determining whether resource pool information for selecting a sidelink grant is configured by a base station;

determining whether more sidelink data is available in a Sidelink Traffic Channel (STCH) than can be transmitted in a current Sidelink Control (SC) period;

selecting resources for the sidelink grant from the resource pool information based on the resource pool information for selecting the sidelink grant being configured by the base station, and more sidelink data being available in the STCH than can be transmitted in the current SC period; and

transmitting the sidelink data to another UE through the resources,

wherein the sidelink grant is for a next SC period after the current SC period,

wherein the sidelink grant is considered to be a configured sidelink grant occurring in time intervals starting at a beginning of a first available SC period which starts at least N time intervals after a time interval in which the sidelink grant is selected, and

wherein N is a positive integer.

2. The method according to claim 1 , further comprising:

clearing the sidelink grant at an end of the next SC period.

3. The method according to claim 1 , wherein the UE is a Device-to-Device UE in Mode 2.

4. A User Equipment (UE) transmitting sidelink data in a wireless communication system, the UE comprising:

a transceiver; and

a processor configured to:

determine whether resource pool information for selecting a sidelink grant is configured by a base station;

determine whether more sidelink data is available in a Sidelink Traffic Channel (STCH) than can be transmitted in a current Sidelink Control (SC) period;

select resources for the sidelink grant from the resource pool information based on the resource pool information for selecting the sidelink grant being configured by the base station, and more sidelink data being available in the STCH than can be transmitted in the current SC period; and

transmit the sidelink data to another UE through the resources,

wherein the sidelink grant is for a next SC period after the current SC period,

wherein the sidelink grant is considered to be a configured sidelink grant occurring in time intervals starting at a beginning of a first available SC period which starts at least N time intervals after a time interval in which the sidelink grant is selected, and

wherein N is a positive integer.

5. The UE according to claim 4 , wherein the processor is further configured to:

clear the sidelink grant at an end of the next SC period.

6. The UE according to claim 4 , wherein the UE is a Device-to-Device UE in Mode 2.