Methods utilized in mobile device for handling situations when time alignment timer expires, and mobile device thereof

1. A method utilized in a mobile device, the method comprising:

starting a time alignment timer when receiving a time alignment message transmitted by a base station, wherein the time alignment timer is used for determining whether the mobile device is synchronized with the base station on uplink timing, and the time alignment message is utilized to update timing advance for the mobile device;

ignoring at least a first control message, which comprises a downlink grant and at least one associated data message or comprises an uplink grant, sent from the base station by a communication unit and transmitted via a physical downlink control channel (PDCCH), by discarding the first control message after the time alignment timer expires without receiving the at least one associated data message or without transmitting data to the base station according to the uplink grant; and

starting a random access procedure for obtaining uplink synchronization by transmitting a random access preamble to the base station, once a buffer status report is triggered to update a buffer status of the mobile device for the base station for precise uplink scheduling after the time alignment timer has expired or once the mobile device receives a second control message via the PDCCH comprising downlink data arrival information sent by the base station after the time alignment timer has expired.

2. The method of claim 1 , wherein the step of ignoring the first control message sent from the base station comprises:

discarding the first control message after the time alignment timer of the mobile device has expired.

3. A mobile device, comprising:

a communication unit, for communicating with a base station;

a control unit, for controlling the communication unit; and

a time alignment timer, for determining whether the mobile device is synchronized with the base station on uplink timing;

wherein the control unit starts the time alignment timer when the communication unit receives a time alignment message transmitted by the base station, the time alignment message is utilized to update timing advance for the mobile device; and

the communication unit ignores at least a first control message, which comprises a downlink grant and at least one associated data message or comprises an uplink grant, sent from the base station to the mobile device and transmitted via a physical downlink control channel (PDCCH), by discarding the first control message after the time alignment timer expires without receiving the at least one associated data message or without transmitting data to the base station according to the uplink grant;

the control unit controls the communication unit to start a random access procedure for obtaining uplink synchronization by transmitting a random access preamble to the base station, once a buffer status report is triggered to update a buffer status of the mobile device for the base station for precise uplink scheduling after the time alignment timer has expired or once the communication unit receives a second control message via the PDCCH comprising downlink data arrival information sent by the base station after the time alignment timer has expired.

4. The mobile device of claim 3 , wherein the communication unit discards the first control message after the time alignment timer of the mobile device has expired.