Method of measuring time difference, and radio system

Abstract

The invention relates to a method of measuring a time difference and a radio system employing the method, the radio system comprising base stations, terminals, time difference units and a time difference centre. A real time difference RTD of the base station is formed on the basis of measurements carried out by the time difference units by means of an observed time difference OTD and a geometrical time difference GTD in the time difference centre as a function of time, in which case the moment of occurrence of the real time difference RTD measured is connected to the real time difference RTD of the base station.

1 . A method of measuring a time difference, the method being used in a radio system comprising at least two base stations ( 100  to  104 ) and a terminal ( 114 ,  116 ), in which radio system an observed time difference OTD of the base stations ( 100  to  104 ) is measured and a geometrical time difference GTD is calculated, characterized in that the real time difference RTD of the base stations ( 100  to  104 ) is formed by means of the observed time difference OTD and the geometrical time difference GTD as a function of time by connecting the moment of occurrence of the measured real time difference RTD to the real time difference RTD of the base stations ( 100  to  104 ).  
     
     
         2 . A method as claimed in  claim 1 , characterized in that the real time difference RTD is utilized in the location of the terminal ( 114 ,  116 ) in a manner such that the subscriber terminal ( 114 ,  116 ) measures the observed time difference OTD of the base stations ( 100  to  104 ), and the real time difference RTD corresponding thereto in time is subtracted from the OTD.  
     
     
         3 . A method as claimed in  claim 1 , characterized in that the radio system comprises at least a time difference unit ( 106  to  110 ) and a time difference centre ( 112 ) from which the time difference unit ( 106  to  110 ) measures the observed time difference OTD and transmits information on the observed time difference OTD to the time difference centre ( 112 ) which forms the real time difference RTD of the base station ( 100  to  104 ) by means of the observed time difference and the geometrical time difference GTD as a function of time, and the time difference centre ( 112 ) interpolates and extrapolates by means of the real time differences RTD the behaviour of the measured real time difference RTD of the base station ( 100  to  110 ) at times other than the moment of occurrence.  
     
     
         4 . A method as claimed in  claim 3 , characterized in that the time difference unit ( 106  to  110 ) comprises a clock ( 120 ) by means of which the time difference unit ( 106  to  110 ) measures the real time difference RTD of the base station ( 100  to  104 ) and by which the moment of occurrence of the real time difference RTD is determined.  
     
     
         5 . A method as claimed in  claim 3 , characterized in that the time difference centre ( 112 ) filters and averages the measured real time differences RTD in a predetermined time window.  
     
     
         6 . A method as claimed in  claim 1 , characterized in that the real time difference RTD of the base station ( 100  to  104 ) is measured in accordance with the rate at which the average value of the real time difference RTD changes.  
     
     
         7 . A method as claimed in  claim 2 , characterized in that in the GSM radio system the time difference centre ( 112 ) transmits information on the real time difference RTD measured, information on the moment of occurrence of the real time difference RTD and/or information on the location of the terminal ( 114 ,  116 ) in a short message.  
     
     
         8 . A method as claimed in  claim 1 , characterized in that in the radio system, transmission is carried out in frames and in timing frame numbers are used by means of which the moment of occurrence of the real time differences RTD of the base stations ( 100  to  104 ) is determined.  
     
     
         9 . A method as claimed in  claim 1 , characterized in that in the radio system, information is transmitted on a control channel, by means of which the time difference unit ( 106  to  110 ) measures the real time difference RTD and by which the moment of occurrence of the real time difference RTD is determined.  
     
     
         10 . A method as claimed in  claim 1 , characterized in that the real time difference RTD is measured regularly.  
     
     
         11 . A method as claimed in  claim 2 , characterized in that in when the terminal ( 114  to  116 ) is located, the real time difference RTD of the base stations ( 100  to  104 ), which has the closest moment of occurrence, is used.  
     
     
         12 . A radio system comprising at least two base stations ( 100  to  104 ) and a terminal ( 114 ,  116 ), a time difference unit ( 106  to  110 ) arranged to measure an observed time difference OTD of the base station ( 100  to  104 ), and a time difference centre ( 112 ) whereto the time difference unit ( 106  to  104 ) is arranged to transmit its measuring information, and which radio system has information available on geometrical time differences GTD of the base stations ( 100  to  104 ), characterized in that the time difference centre ( 112 ) is arranged to form a real time difference RTD of the base stations ( 100  to  104 ) as a function of time by utilizing the observed time difference OTD and the geometrical time difference GTD calculated in a manner such that the time difference centre ( 112 ) is arranged to connect the moment of occurrence of the real time difference RTD to the real time difference RTD.  
     
     
         13 . A radio system as claimed in  claim 12 , characterized in that the radio system comprises a location system of the terminal ( 114 ,  116 ) and the location system is arranged to utilize the real time difference RTD of the base stations ( 100  to  104 ) in a manner such that the terminal ( 114 ,  116 ) is arranged to measure the observed time difference OTD of the base stations ( 100  to  104 ), and the location system is arranged to subtract the real time difference RTD from the observed time difference OTD so as to form the geometrical time difference GTD of the terminal ( 114 ,  116 ) and determine the location of the terminal ( 114 ,  116 ).  
     
     
         14 . A radio system as claimed in  claim 12 , characterized in that the time difference unit ( 106  to  110 ) comprises a clock ( 120 ) by means of which the time difference unit ( 106  to  110 ) is arranged to measure the real time difference RTD.  
     
     
         15 . A radio system as claimed in  claim 12 , characterized in that the time difference centre ( 112 ) is arranged to interpolate and extrapolate by means of the measured real time differences RTD the behaviour of the real time difference RTD of the base stations ( 100  to  104 ) at times other than the moment of occurrence.  
     
     
         16 . A radio system as claimed in  claim 12 , characterized in that the radio system is arranged to use frame numbers by means of which the time difference unit ( 106  to  110 ) is arranged to time stamp the measurement of the real time difference RTD.  
     
     
         17 . A radio system as claimed in  claim 12 , characterized in that the radio system is arranged to transmit time information on a control channel and the time difference unit ( 106  to  110 ) is arranged to time stamp the measurement of the real time difference RTD by means of the time information.  
     
     
         18 . A radio system as claimed in  claim 12 , characterized in that the time difference centre ( 112 ) is arranged to measure the real time difference RTD regularly.  
     
     
         19 . A radio system as claimed in  claim 12 , characterized in that the time difference centre ( 112 ) is arranged to filter and average the measured real time differences RTD in a predetermined time window.  
     
     
         20 . A radio system as claimed in  claim 12 , characterized in that the time difference centre ( 112 ) is arranged to measure the real time difference RTD of the base station ( 100  to  104 ) in accordance with the rate at which the average value of the real time difference RTD changes.  
     
     
         21 . A radio system as claimed in  claim 13 , characterized in that the radio system is a GSM radio system in which short messages are transmitted and the time difference centre ( 112 ) is arranged to transmit a short message which comprises the real time difference RTD measured, the measurement time associated with the time difference and/or the location of the terminal ( 114 ,  116 ).  
     
     
         22 . A radio system as claimed in  claim 13 , characterized in that the location system of the terminal ( 114 ,  116 ) is arranged to use the real time difference of the base station ( 100  to  104 ) that is closest in time.