1. Field of the Invention
The present invention relates generally to a time synchronization method and system, and in particular, to a time synchronization method of a mobile station based on an asynchronous scheme and a system using the same.
2. Description of the Related Art
Global System for Mobile communication (GSM) is a digital mobile communication system widely used in Europe and other areas. The GSM digital mobile communication system is a type of Time Division Multiple Access (TDMA) communication system and is one of three most popular digital mobile communication technologies which include TDMA and a Code Division Multiple Access (CDMA) mobile communication systems. In the GSM communication system, data is digitalized, compressed and transmitted with other user data through a single channel, and each data is transmitted in a unique time band. The GSM communication system can operate in both a 900 MHz and a 1800 MHz communication band. Wideband CDMA (WCDMA) is an asynchronous mobile communication system using the CDMA communication system based on the GSM communication system and a General Packet Radio Services (GPRS) communication system.
Among the above described communication systems, the WCDMA scheme is a communication scheme that can be commonly used throughout the world. Moreover, because a user can use the same mobile station throughout the world, it is necessary to change the mobile station's time information according to each time zone in each country or province. However, unlike the CDMA communication system in which synchronization is set using time, for a mobile station based on the GSM or WCDMA communication systems, time must be manually set unless a relevant network gives time information to the mobile station.
Each typical asynchronous scheme mobile station is equipped with a real time clock (RTC) chip and uses time information provided by the RTC chip. That is, each mobile station displays time by counting the time using a self-operating clock. Though such a clock performs the same function as a typical watch, if a user moves to an area in which time is changed, the user typically has to change the time of the mobile station to match the local time of the area.
Thus, when an asynchronous scheme mobile station moves to an area in which time has changed, if the mobile station cannot get a local time, the time will be counted in a state of having a time difference. Even if the mobile station user can determine a local time, if a user manually sets the time of the mobile station, the user cannot set the exact time to the second.
However, since a method of obtaining time information is not implemented in mobile stations based on asynchronous schemes, there is no easy way to depend upon information transmitted from networks. A communication protocol of providing a message representing time information exists, but in reality, this function is not implemented in the networks. Thus, since it is desirable that a mobile station's an internal clock be reset when a local time changes, it is desirable that a user check a local time at a current location and manually reset an existing time to the local time.
As described above, in the prior art, if a local time at a location where a user uses a mobile station is changed, the user should manually reset an internal clock of the mobile station to the changed local time. For example, if the entire area of a country is included in a single time zone, an additional time change is not required once time has been set. However, in European countries using asynchronous schemes such as GSM and WCDMA, since a plurality of countries are adjacent to each other, if a user moves from a country to another country, a case where a current time should be changed to a local time may frequently occur. Accordingly, since a user using a mobile station using an asynchronous scheme should manually change an internal time of the mobile station, time accuracy is lowered, and it is difficult to obtain reliable time information when compared to a mobile station of a synchronous scheme such as CDMA.
As described above, for a mobile station based on a conventional asynchronous scheme, when a user moves to an area having a standard time which is different than an internal time of the mobile station, the user is inconvenienced by having to manually change the internal time to the standard time (local time) of the area. In addition, according to time setting by an RTC chip equipped in a mobile station based on a conventional asynchronous scheme, since a user manually sets the time, an exact standard time cannot be set. In asynchronous schemes, a technology of exactly setting an internal time of a mobile station by itself by obtaining reliable time information from the outside through communication has not been implemented.