1. Field of the Invention
The present invention relates to a communication system and method for selecting an HPLMN (Home Public Land Mobile Network), and more particularly to a communication system and method capable of reducing power consumption when an MS (Mobile Station) searches for an HPLMN or higher-priority PLMN.
2. Description of the Related Art
Roaming is defined as a function of enabling an MS (Mobile Station) to receive a service outside of a predetermined area and to receive a service anywhere within a country as a single area. A PLMN (Public Land Mobile Network) is a public telecommunication network including the MS using telephony services from mobile communication carriers through the MS's roaming function, a BTS (Base Transceiver Subsystem), a subscriber location register and an MSC (Mobile Switching Center). An HPLMN (Home PLMN) is a PLMN used at a time when the MS selects another PLMN to receive a service from a corresponding service carrier.
In a second or third generation mobile communication service suggested by ETSI (European Telecommunications Standards Institute) or 3GPP (Third Generation Partnership Project), an MS is recommended to search for an HPLMN according to a set time period where the MS receives the service from a VPLMN (Visitor PLMN) rather than the HPLMN. Thus, the MS searches for the HPLMN using priority information when the MS selects the PLMN in an automatic mode or manual mode on the basis of the set time period stored in an SIM (Subscriber Identity Module).
However, where the MS receiving a service from the VPLMN automatically searches for a PLMN in the automatic mode, the MS located in the VPLMN must search for a higher-priority PLMN than an HPLMN or current PLMN on the basis of a set time period stored in the SIM irrespective of service conditions at a current location. That is, the MS located in the VPLMN must perform an operation of searching for another PLMN every “T” minutes. At this time, “T” as a value of a period used when the MS searches for the PLMN is a value arbitrarily set and fixed without considering service situations of the PLMN in which the MS is located.
Conventionally, the MS is in synchronization with a frequency not being monitored other than a currently monitored frequency in order to search for the PLMN. At this time, the MS detects system information contained in a synchronous frequency signal after the frequency synchronization and detects the PLMN's ID from the detected system information. While performing the above-described procedure, the MS consumes additional power. Moreover, where the MS does not utilize the service situations in the PLMN in which it is located and the set “T” value is smaller than an arbitrary reference value, the MS frequently performs a search operation for the PLMN on the basis of the set “T” value. Accordingly, there is a problem in that an available time of a charged battery for supplying the MS with power is greatly reduced.
Where the MS moves to an HPLMN or higher-priority PLMN during a search procedure for the PLMN, the power of the charged battery is consumed, but there is an advantage in that the MS can select a desired PLMN. However, where the MS is not located in the HPLMN or higher-priority PLMN, there are other problems in that the MS consumes unnecessary power and hence an available time of a charged battery is reduced.