Method for saving power in a user terminal after synchronization loss in broadband wireless access communication system

1. A method for reducing power consumption of a user terminal in a broadband wireless access communication system including the user terminal and a base station when synchronization between the user terminal and a base station is disrupted, the method comprising the steps of:

calculating a first error rate (E) based on first channel state information included in a signal transmitted from the base station;

comparing the first error rate (E) with a first threshold value;

determining that the synchronization is disrupted and maintaining a transmission-off mode for a predetermined period of time if the first error rate (E) is greater than the first threshold value;

maintaining a reception-on mode during a period of time set for a reception mode after the transmission-off mode is performed;

receiving from the base station second channel state information during the reception-on mode;

calculating a second error rate (E 1 ) based on the second channel state information;

comparing the second error rate (E 1 ) with a second threshold value; and

determining that the synchronization based on reestablished and maintaining the transmission mode in a transmission-on mode if the second error rate (E 1 ) is less than the second threshold value.

2. The method as claimed in claim 1 , further comprising the steps of:

a) determining that the synchronization continues to be disrupted and maintaining the transmission-off mode during a period of time if the second error rate (E 1 ) is equal to or greater than the second threshold value;

b) maintaining the reception-on mode during a period of time after performing the transmission-off mode;

c) receiving from the base station third channel state information during the reception-on mode to calculate a third error rate (E 2 );

d) comparing the third error rate (E 2 ) with the second threshold value; and

e) determining that the synchronization has been reestablished and entering the transmission-on mode during a period of time if the third error rate (E 2 ) is less than the second threshold value; and

referring to step a) if the third error rate (E 2 ) is equal to or greater than the second threshold value.

3. The method as claimed in claim 2 , wherein the channel state information is included in a downlink frame prefix.

4. The method as claimed in claim 1 , wherein the first threshold value is a 30% error rate.

5. The method as claimed in claim 1 , wherein the second threshold value is a 25% error rate.

6. The method as claimed in claim 1 , wherein the broadband wireless access communication system is operating under the IEEE 802.16e standard in which a time division duplex (TDD) method is utilized.