A method of performing a location update. The method according to one embodiment includes receiving, by a mobile station, information related to a first paging group and a second paging group assigned for the mobile station, from at least one base station; starting, by the mobile station, a timer when the mobile station leaves the first paging group but stays within the second paging group; determining, by the mobile station, whether the mobile station is within the first paging group or the second paging group, before an expiration of the timer; and performing, by the mobile station, a location update before the expiration of the timer if the mobile station is determined to be not within the first paging group and the second paging group.