Patent ID: 9668282
Date: 2017-05-30
CPC Classifications: H04W

Claim:
1. A method of controlling an uplink synchronization state of a user equipment in a mobile communication system by performing random access procedures, the method comprising: receiving, by the user equipment, a random access response including a time alignment command from a network during a first random access procedure; starting, by the user equipment, a time alignment timer for uplink time alignment when the time alignment command is received from the network; receiving, by the user equipment, a contention resolution message from the network to determine whether the first random access procedure is successful or not, wherein the user equipment considers itself in an asynchronous state and stops the time alignment timer when the user equipment determines that the first random access procedure is not successful based on the contention resolution message; and performing, by the user equipment, a second random access procedure when the user equipment obtains uplink data to be transmitted to the network after the time alignment timer has expired.