Method and apparatus for selecting a relay user equipment

1. A method for a User Equipment (UE) to select a Relay UE in a cellular communication system, the method comprising:

transmitting, to a plurality of Relay UEs, a first signal including an amount of data to send;

receiving, from the plurality of Relay UEs, a plurality of second signals, each second signal including (a score of a respective Relay UE, a number N of Remote UEs attempting to access to the respective Relay UE) pair; and

selecting one of the plurality of Relay UEs based on the received (score, N) pairs,

wherein the score of respective Rely UE is determined based on at least (i) the amount of data to send, and (ii) a power availability in the respective Rely UE.

2. The method of claim 1 , wherein the first signal further includes a residual power of the UE, and the score of the respective Relay UE is determined further based on the residual power of the UE.

3. The method of claim 1 , wherein a Relay UE with a highest score is selected from the plurality of Relay UEs, and if there are plural Relay UEs with the highest score, a Relay UE with a lowest N is selected from the plural Relay UEs with the highest score.

4. The method of claim 1 , wherein a Relay UE with a highest preference is selected from the plurality of Relay UEs, and the preference is determined based on a value of score/N.

5. The method of claim 1 , wherein if the data to send is an urgent data, the one of the plurality of Relay UEs is selected primarily based on the number N, and if the data to send is a non-urgent data, the one of the plurality of Relay UEs is selected primarily based on the score.

6. The method of claim 5 , wherein the urgent data include data of a real-time application, and the non-urgent data include data of a non-real-time application.

7. A User Equipment (UE) configured to select a Relay UE in a wireless communication system, the UE comprising:

a radio frequency (RF) unit; and

a processor, wherein the processor is configured to:

transmit, to a plurality of Relay UEs, a first signal including an amount of data to send,

receive, from the plurality of Relay UEs, a plurality of second signals, each second signal including (a score of a respective Relay UE, a number N of Remote UEs attempting to access to the respective Relay UE) pair, and

select one of the plurality of Relay UEs based on the received (score, N) pairs,

wherein the score of respective Rely UE is determined based on at least (i) the amount of data to send, and (ii) a power availability in the respective Rely UE.

8. The UE of claim 7 , wherein the first signal further includes a residual power of the UE, and the score of the respective Relay UE is determined further based on the residual power of the UE.

9. The UE of claim 7 , wherein a Relay UE with a highest score is selected from the plurality of Relay UEs, and if there are plural Relay UEs with the highest score, a Relay UE with a lowest N is selected from the plural Relay UEs with the highest score.

10. The UE of claim 7 , wherein a Relay UE with a highest preference is selected from the plurality of Relay UEs, and the preference is determined based on a value of score/N.

11. The UE of claim 7 , wherein if the data to send is an urgent data, the one of the plurality of Relay UEs is selected primarily based on the number N, and if the data to send is a non-urgent data, the one of the plurality of Relay UEs is selected primarily based on the score.

12. The UE of claim 11 , wherein the urgent data include data of a real-time application, and the non-urgent data include data of a non-real-time application.