Method and apparatus of searching for operator network in a multi-radio access technology environment

An apparatus of searching for an operator network in a multi-Radio Access Technology (RAT) environment, the apparatus comprising:

• a controller to calculate a length of a sleep interval to perform background Public Land Mobile Network (PLMN) searching, and to control background PLMN searching during the sleep interval by comparing the length of the sleep interval with a predetermined reference parameter;
• and
• a receiver to perform, if the length of the sleep interval is larger than the reference parameter, background PLMN searching in a passive RAT during the sleep interval, and to perform, if the length of the sleep interval is equal to or smaller than the reference parameter, background PLMN searching in an active RAT during the sleep interval.

A method of searching for an operator network in a multi-Radio Access Technology (RAT) environment, the method comprising:

• calculating a length of a sleep interval during which background Public Land Mobile Network (PLMN) searching is performed;
• and
• determining whether to perform background PLMN searching in a passive RAT or background PLMN searching in an active RAT based on the length of the sleep interval.