Cellular terminal location using GPS signals in the cellular band

Abstract

Aspects of global positioning system (GPS) technology and cellular technology are combined in order to provide an effective and efficient position location system. In a first aspect of the invention, a cellular network is utilized to collect differential GPS error correction data, which is forwarded to a mobile terminal over the cellular network. The mobile terminal receives this data, along with GPS pseudoranges using a GPS receiver, and calculates its position using this information. According to a second aspect, when the requisite number of GPS satellites are not in view of the mobile terminal, then a GPS pseudosatellite signal, broadcast from a base station of the cellular network, is received by the mobile terminal and processed as a substitute for the missing GPS satellite signal. A third aspect involves calculating position using GPS when the requisite number of GPS satellites are in view of a GPS receiver, but when the requisite number of GPS satellites are not in view of the GPS receiver, then position is calculated using the cellular network infrastructure. When the requisite number of GPS satellites come back into view of the GPS receiver, then position is again calculated using GPS. A fourth aspect involves using cellular signals already being transmitted from base stations to terminals in a cellular network to calculate a round trip delay, from which a distance calculation between the base station and the terminal can be made. This distance calculation substitutes for a missing GPS satellite signal.

We claim:  
     
         1 . A position location system for determining a geographic position comprising: 
 a plurality of cellular network base stations positioned at predetermined locations; and    a communications network that communicates with said plurality of cellular network base stations,    wherein at least one of said plurality of cellular network base stations comprises a generator that generates a global positioning system pseudosatellite signal independent of receiving global positioning system satellite signals.    
     
     
         2 . The position location system of    claim 1   , wherein said generator comprises: 
 a global positioning system processor that generates a pseudo global positioning system data signal containing data representing a location of said one of said plurality of cellular network base stations,    a coarse acquisition code portion that generates a coarse acquisition encoding signal, and    a modulator connected to said global positioning system processor and to said coarse acquisition code portion,    wherein said modulator combines said pseudo global positioning system data signal and said coarse acquisition encoding signal to produce said global positioning system pseudosatellite signal.    
     
     
         3 . The position location system of    claim 2   , wherein said one of said plurality of cellular network base stations further comprises a converter connected to said modulator, wherein said converter converts said global positioning system pseudosatellite signal into a radio frequency signal having a frequency in a cellular frequency band.  
     
     
         4 . The position location system of    claim 3   , wherein said one of said plurality of cellular network base stations further comprises a level adjuster connected to said converter, wherein said level adjuster dynamically adjusts an amplitude level of said radio frequency signal to a predetermined level relative to transmitted cellular signals.  
     
     
         5 . The position location system of    claim 4   , wherein said one of said plurality of cellular network base stations further comprises: 
 a cellular radio that transmits said transmitted cellular signals, and    a combiner connected to said cellular radio and to said level adjuster,    wherein said combiner combines said cellular signals and said radio frequency signal into a combined cellular signal.    
     
     
         6 . The position location system of    claim 5   , wherein said one of said plurality of cellular network base stations transmits said combined cellular signal to a mobile terminal.  
     
     
         7 . The position location system of    claim 1   , further comprising a mobile terminal positioned in a transmitting vicinity of said one of said plurality of cellular network base stations, wherein said one of said plurality of cellular network base stations transmits said global positioning system pseudosatellite signal to said mobile terminal.  
     
     
         8 . The position location system of    claim 7   , wherein said mobile terminal comprises: 
 a cellular antenna that receives a radio frequency signal having a frequency in a cellular frequency band, said radio frequency signal containing differential error correction data;    a radio interface unit connected to said cellular antenna, wherein said radio interface unit converts said received radio frequency signal into an intermediate frequency signal;    a digital signal processor connected to said radio interface unit, wherein said digital signal processor converts said intermediate frequency signal into a data stream;    a central processor connected to said digital signal processor, wherein said central processor extracts said differential error correction data from said data stream; and    a differential global positioning system processor connected to said central processor,    wherein said central processor forwards said differential error correction data to said differential global positioning system processor.    
     
     
         9 . A position location system for determining a geographic position comprising: 
 a cellular antenna that receives a cellular signal having a frequency in a cellular frequency band, wherein said cellular signal contains global positioning system pseudosatellite data;    a first converter connected to said cellular antenna, wherein said first converter converts said received cellular signal into a first intermediate frequency signal having a first frequency;    a global positioning system receiver antenna that receives global positioning system satellite signals having frequencies in a satellite frequency band from a plurality of global positioning system satellites;    a second converter connected to said global positioning system receiver antenna, wherein said second converter converts said received global positioning system satellite signals into a second intermediate frequency signal having a second frequency, wherein said first frequency of said first intermediate frequency signal is substantially equal to said second frequency of said second intermediate frequency signal;    a selector connected to said first converter and to said second converter, wherein said selector selects one of said first intermediate frequency signal and said second intermediate frequency signal; and    a control processing unit connected to said selector, said control processing unit configured to utilize said first intermediate signal and said second intermediate signal when a requisite number of global positioning system satellites are not in view of the global positioning system receiver antenna, to calculate global positioning system pseudoranges.    
     
     
         10 . The position location system of    claim 9   , further comprising a mobile terminal that houses said cellular antenna, said first converter, said global positioning system receiver antenna, said second converter, said selector, and said control processing unit.  
     
     
         11 . The position location system of    claim 10   , further comprising: 
 a plurality of cellular network base stations positioned at predetermined locations; and    a communications network that communicates with said plurality of cellular network base stations,    wherein at least one of said plurality of cellular network base stations comprises a generator that generates said cellular signal containing said global positioning system pseudosatellite data, and    wherein said one of said plurality of cellular network base stations transmits said cellular signal to said mobile terminal.    
     
     
         12 . The position location system of    claim 9   , wherein said cellular signal further contains differential error correction data, and wherein said control processing unit is further configured to correct said global positioning system pseudoranges using said differential error correction data, to obtain corrected global positioning system ranges.  
     
     
         13 . The position location system of    claim 9   , further comprising an amplitude controller connected to said first converter, wherein said amplitude controller adjusts an amplitude of said first intermediate frequency signal before said first intermediate frequency signal is forwarded to said selector.  
     
     
         14 . A method for determining a geographic position of a mobile terminal comprising the steps of: 
 receiving global positioning system satellite signals having frequencies in a satellite frequency band at the mobile terminal from a plurality of global positioning system satellites that are in view of the mobile terminal;    converting said global positioning system satellite signals into a first intermediate frequency signal;    receiving a cellular signal having a frequency in a cellular frequency band at the mobile terminal, wherein said cellular signal contains global positioning system pseudosatellite data;    converting said cellular signal into a second intermediate frequency signal; and    calculating the geographic position using both said first intermediate frequency signal and said second intermediate frequency signal when a requisite number of global positioning system satellites are not in view of the mobile terminal.    
     
     
         15 . The method of    claim 14   , further comprising the step of transmitting said cellular signal from a cellular network base station to the mobile terminal.  
     
     
         16 . The method of    claim 15   , further comprising the step of generating said cellular signal in the cellular network base station, 
 wherein said generating step comprising the steps of 
 generating a pseudo global positioning system data signal containing data representing a location of the cellular network base station,  
 generating a coarse acquisition encoding signal,  
 combining said pseudo global positioning system data signal and said coarse acquisition encoding signal into a pseudosatellite signal, and  
 converting said pseudosatellite signal to produce at least a part of said cellular signal.  
   
     
     
         17 . A method for determining a geographic position of a mobile terminal comprising the steps of: 
 receiving global positioning system satellite signals having frequencies in a satellite frequency band at the mobile terminal from a plurality of global positioning system satellites that are in view of the mobile terminal;    receiving a cellular signal having a frequency in a cellular frequency band at the mobile terminal,    calculating a cellular distance measurement representing a distance between the mobile terminal and a cellular network base station using said cellular signal;    calculating the position of the mobile terminal using said received global positioning system signals when a requisite number of global positioning system satellites are in view of the mobile terminal; and    calculating the position of the mobile terminal using said received global positioning system signals and the cellular distance measurement when the requisite number of global positioning system satellites are not in view of the mobile terminal.    
     
     
         18 . The method of    claim 17   , wherein said received cellular signal is a code division multiple access cellular signal.  
     
     
         19 . The method of    claim 17   , wherein said received cellular signal is a time division multiple access cellular signal.  
     
     
         20 . The method of    claim 17   , wherein said step of calculating the cellular distance measurement utilizes a round trip delay measurement.  
     
     
         21 . The method of    claim 17   , wherein said step of calculating the cellular distance measurement utilizes a plurality of time difference of arrival measurements.  
     
     
         22 . A method for determining a geographic position of a mobile terminal comprising the steps of: 
 receiving global positioning system satellite signals having frequencies in a satellite frequency band at the mobile terminal from a plurality of global positioning system satellites that are in view of the mobile terminal;    receiving a cellular signal having a frequency in a cellular frequency band at the mobile terminal,    calculating a cellular distance measurement representing a distance between the mobile terminal and a cellular network base station using said cellular signal;    correcting said cellular distance measurement using a cellular correction term, to obtain a corrected cellular distance measurement;    calculating the position of the mobile terminal using said received global positioning system signals when a requisite number of global positioning system satellites are in view of the mobile terminal; and    calculating the position of the mobile terminal using said received global positioning system signals and said corrected cellular distance measurement when the requisite number of global positioning system satellites are not in view of the mobile terminal.    
     
     
         23 . The method of    claim 22   , wherein said cellular correction term is a round trip delay correction term that is calculated by the steps comprising: 
 determining an expected round trip delay between the mobile terminal, whose position is determined using reference global positioning satellites, and said cellular network base station, whose position is known;    determining an actual round trip delay between the mobile terminal and said cellular network base station;    calculating a difference between said expected round trip delay and said actual round trip delay; and    storing the calculated difference as said round trip delay correction term.    
     
     
         24 . The method of    claim 22   , wherein said received cellular signal is a code division multiple access cellular signal.  
     
     
         25 . The method of    claim 22   , wherein said received cellular signal is a time division multiple access cellular signal.  
     
     
         26 . The method of    claim 22   , wherein said cellular correction term is a time difference of arrival correction term that is calculated by the steps comprising: 
 determining an expected time difference of arrival between the mobile terminal, whose position is determined using reference global positioning satellites, and said cellular network base station, whose position is known;    determining an actual time difference of arrival between the mobile terminal and said cellular network base station;    calculating a difference between said expected time difference of arrival and said actual time difference of arrival; and    storing the calculated difference as said time difference of arrival correction term.