Method for a radiotelephone to search for higher priority networks

Abstract

A method for a radiotelephone to search for a high priority, home, or home-equivalent public land mobile network (PLMN) includes a first step of camping the radiotelephone on a cell of visited PLMN. A next step includes uniquely identifying the cell. A next step includes searching for PLMNs with a higher priority than the visited PLMN. A next step includes storing a history of those frequencies found that are not of a higher priority PLMN for the uniquely identified cell. Any subsequent searches for frequencies of higher priority PLMNs performed while camped on that cell includes scanning for available frequencies except for those frequencies listed in the history for the uniquely identified cell in which the radiotelephone is camped.

What is claimed is:  
     
         1 . A method for a radiotelephone to search for higher priority public land mobile networks, each network having a plurality of cells for providing radiotelephone service to a radiotelephone within a corresponding geographic area, each cell having a radio communication coverage area established by fixed site base stations, and each base station operable to send messages to radiotelephones, the method comprising the steps of: 
 camping the radiotelephone on a cell of a visited public land mobile network;    uniquely identifying the cell;    searching for public land mobile networks with a higher priority than the visited public land mobile network; and    storing a history of those frequencies found during the scanning step that are not of a higher priority public land mobile network, the history being associated with the uniquely identified cell.    
     
     
         2 . The method of  claim 1 , further comprising the step of scanning for higher priority public land mobile networks in frequencies other than those frequencies listed in the history for the uniquely identified cell in which the radiotelephone is camped.  
     
     
         3 . The method of  claim 1 , wherein the storing step includes storing the PLMN IDs associated with each of the ARFCNs which were found to be not the home or higher priority PLMNs in the searching step.  
     
     
         4 . The method of  claim 1 , wherein the storing step includes storing an individual history of those frequencies found that are not of a higher priority public land mobile network for each of a plurality of cells of the visited public land mobile network.  
     
     
         5 . The method of  claim 1 , wherein the storing step includes adding any newly found frequencies that are not of a higher priority public land mobile network to any previously found frequencies of the history.  
     
     
         6 . The method of  claim 1 , wherein the history in the storing step is started anew at at least one of the group of: each time the radiotelephone is powered on and after a timeout period.  
     
     
         7 . The method of  claim 1 , further comprising the steps of: 
 periodically searching, at a slow rate so as not to consume much battery power, for higher priority public land mobile networks in all radio access technologies and frequencies supported by the radiotelephone; and    updating the history with any new frequencies found that are not of a higher priority public land mobile network.    
     
     
         8 . The method of  claim 1 , further comprising the steps of: 
 giving a list of public land mobile networks to the radiotelephone; and    erasing the history if there is a change in a stored preferred public land mobile network list.    
     
     
         9 . A method for a radiotelephone to search for higher priority public land mobile networks, each network having a plurality of cells for providing radiotelephone service to a radiotelephone within a corresponding geographic area, each cell having a radio communication coverage area established by fixed site base stations, and each base station operable to send messages to radiotelephones, the method comprising the steps of: 
 camping the radiotelephone on a cell of a visited public land mobile network;    giving a list of public land mobile networks to the radiotelephone;    uniquely identifying the cell;    searching for public land mobile networks with a higher priority than the visited public land mobile network;    storing a history of those frequencies found that are not of a higher priority public land mobile network for each of a plurality of cells of the visited public land mobile network, the history being associated with each uniquely identified cell; and    scanning for higher priority public land mobile networks except in those frequencies listed in the history for the uniquely identified cell in which the radiotelephone is camped.    
     
     
         10 . The method of  claim 9 , wherein the storing step includes storing the PLMN IDs associated with each of the ARFCNs which were found to be not the home or higher priority PLMNs in the searching step.  
     
     
         11 . The method of  claim 9 , wherein after the scanning step further comprising the step of adding any newly found frequencies that are not of a higher priority public land mobile network to any previously found frequencies of the history.  
     
     
         12 . The method of  claim 9 , wherein the history in the storing step is started anew at at least one of the group of: each time the radiotelephone is powered on and after a timeout period.  
     
     
         13 . The method of  claim 9 , further comprising the steps of: 
 periodically searching, at a slow rate so as not to consume much battery power, for higher priority public land mobile networks in all radio access technologies and frequencies supported by the radiotelephone; and    updating the history with any new frequencies found that are not of a higher priority public land mobile network.    
     
     
         14 . The method of  claim 9 , further comprising the step of erasing the history when there is a change in a stored preferred public land mobile network list.  
     
     
         15 . The method of  claim 9 , wherein the storing step includes storing the history in one or more of a non-volatile memory of the radio telephone and a subscriber identity module associated with the radiotelephone.  
     
     
         16 . A method for a radiotelephone to search for higher priority public land mobile networks, each network having a plurality of cells for providing radiotelephone service to a radiotelephone within a corresponding geographic area, each cell having a radio communication coverage area established by fixed site base stations, and each base station operable to send messages to radiotelephones, the method comprising the steps of: 
 camping the radiotelephone on a cell of a visited public land mobile network;    giving a list of public land mobile networks to the radiotelephone;    uniquely identifying the cell;    searching for public land mobile networks with a higher priority than the visited public land mobile network;    storing an individual history of those frequencies found that are not of a higher priority public land mobile network for each of a plurality of uniquely identified cells of the visited public land mobile network;    scanning for higher priority public land mobile networks except in those frequencies listed in the history for the uniquely identified cell in which the radiotelephone is camped; and    adding any newly found frequencies that are not of a higher priority public land mobile network to any previously found frequencies of the history.    
     
     
         17 . The method of  claim 16 , wherein the history in the storing step is started anew at at least one of the group of: each time the radiotelephone is powered on and after a timeout period.  
     
     
         18 . The method of  claim 16 , further comprising the steps of: 
 periodically searching, at a slow rate so as not to consume much battery power, for higher priority public land mobile networks in all radio access technologies and frequencies supported by the radiotelephone; and    updating the history with any new frequencies found that are not of a higher priority public land mobile network.    
     
     
         19 . The method of  claim 16 , further comprising the step of erasing the history when there is a change in a stored preferred public land mobile network list.  
     
     
         20 . The method of  claim 16 , wherein the storing step includes storing the PLMN IDs associated with each of the ARFCNs which were found to be not the home or higher priority PLMNs in the searching step.