Device and method for forming a set of cells for time difference measurements and for measuring time differences for locating a user of a mobile terminal

Abstract

A method and device are provided, for locating a user of a mobile terminal, for forming a set of cells for time difference measurements for a mobile terminal camped on a first cell of a cellular network and being in idle mode, the method including the steps of: receiving a first set of cell identifiers of neighboring cells for the first cell, with each of the neighboring cells sending a radio signal on synchronization channels; and measuring the received signal strength for cells having identifiers which are included in the first set, with a number N of cells having a signal strength exceeding a predefined threshold constituting a set of available cells; wherein the improvement includes the steps of: reading the synchronization channels for the set of available cells, thereby measuring time differences for the set of available cells; and selecting a second set from the set of available cells using a predefined selection rule, the second set including M<N cells, thus forming a new set of cells for time difference measurements.

1 . A method for locating a user of a mobile terminal, the method comprising the steps of: 
 providing that the mobile terminal be camped on a first cell of a cellular network and is in idle mode;    receiving, at the mobile terminal, a first set of cell identifiers respectively associated with neighboring cells of the first cell, with each of the neighboring cells sending a radio signal;    measuring, at the mobile terminal, received signal strengths of the neighboring cells having identifiers which are included in the first set of cell identifiers, with a number N of cells having a signal strength exceeding a predefined threshold constituting a set of available cells;    reading, at the mobile terminal, a synchronization channel for the set of available cells, thereby measuring time differences for the set of available cells;    selecting, at the mobile terminal, a second set of cells from the set of available cells using a predefined selection rule, the second set of cells including M<N cells, wherein the predefined selection rule causes a non-selection of a cell having a same cell identity as another cell in the set of available cells if it is probable that the cell which is not selected and the another cell belong to one sectorized base station;    reading, at the mobile terminal, a synchronization channel for the second set of cells, thereby measuring time differences for the second set of cells; and    using the time difference measurements to obtain the location of the user.    
   
   
       2 . A method for locating a user of a mobile terminal as claimed in  claim 1 , wherein locationing is performed on the cellular network side in response to a transfer of the time difference measurements.  
   
   
       3 . A method for locating a user of a mobile terminal as claimed in  claim 2 , wherein the transfer is performed in response to a call which is one of originated by the user and terminated to the user.  
   
   
       4 . A method for locating a user of a mobile terminal as claimed in  claim 3 , wherein the call is an emergency service call.  
   
   
       5 . A mobile terminal, comprising: 
 parts for receiving a first set of cell identifiers respectively associated with neighboring cells of a first cell of a cellular network on which the mobile terminal is camped, the mobile terminal being in idle mode, with each of the neighboring cells sending a radio signal;    parts for measuring received signal strengths of the neighboring cells having identifiers which are included in the first set of cell identifiers, with a number N of cells having a signal strength exceeding a predefined threshold constituting a set of available cells;    parts for reading a synchronization channel for the set of available cells, thereby measuring time differences for the set of available cells;    parts for selecting a second set of cells from the set of available cells using a predefined selection rule, the second set of cells including M<N cells, wherein the predefined selection rule causes a non-selection of a cell having a same cell identity as another cell in the set of available cells if it is probable that the cell which is not selected and the another cell belong to one sectorized base station;    parts for reading a synchronization channel for the second set of cells, thereby measuring time differences for the second set of cells; and    parts for using the time difference measurements to obtain a location of the user.    
   
   
       6 . A mobile terminal as claimed in  claim 5 , wherein the mobile terminal is a GSM terminal.