Abstract: A method for establishing a communication link of a first communication device includes: selecting a second communication device for establishing a communication link on a screen of the first communication device; transmitting a request for a communication link to the selected second communication device; receiving a communication link response from the second communication device; and establishing a communication link between the first communication device and the second communication device.

Abstract: The present invention provides a method for downlink packet scheduling for scheduling a real-time service and a non-real-time service. The method for downlink packet scheduling includes steps of: a) classifying inputted packets based on a type of packet and storing a maximum delay time information of the packets; b) determining a user urgency of the packets by using the maximum delay time information and a channel state by using an instantaneous channel state, an average channel state, or a ratio of the instantaneous channel state and the average channel state; c) determining a priority based on the user urgency and the channel state; and d) transmitting the packets according to the priority.