Method of despreading GPS spread spectrum signals

Abstract

A method of despreading a GPS spread spectrum signal received at a mobile unit MS1 with assistance from a base station BS1 is disclosed comprising the steps of (a) receiving and despreading GPS signals at the base station and deriving GPS signal information therefrom; (b) estimating the location of the mobile unit; (c) modifying the GPS signal information so as reflect the GPS signal characteristics as would be observed at the estimated location of the mobile unit; (d) transmitting the GPS signal information from the base station to the mobile unit; (e) generating replica signals containing PRN codes corresponding to those of the GPS signal using the modified GPS signal information; and (f) performing a correlation of the GPS signal and the replica signals in order to acquire the GPS signal.

1 . A method of despreading a GPS spread spectrum signal received at a mobile unit with assistance from a base station comprising the steps of: 
 (a) receiving and despreading GPS signals at the base station and deriving GPS signal information therefrom;    (b) estimating the location of the mobile unit;    (c) modifying the GPS signal information so as reflect the GPS signal characteristics as would be observed at the estimated location of the mobile unit;    (d) transmitting the GPS signal information from the base station to the mobile unit;    (e) generating replica signals containing PRN codes corresponding to those of the GPS signal using the modified GPS signal information; and    (f) performing a correlation of the GPS signal and the replica signals in order to acquire the GPS signal.    
     
     
         2 . A method according to  claim 1  wherein step (c) is done before step (d).  
     
     
         3 . A method according to  claim 2  wherein the initial estimate of the location of the mobile unit is determined in the mobile unit and transmitted to the base station.  
     
     
         4 . A method according to any of the preceding claims wherein the GPS signal information comprises Doppler information.  
     
     
         5 . A method according to any of the preceding claims wherein the GPS signal information comprises code phase information.  
     
     
         6 . A method of providing base station assistance to a mobile unit for despreading GPS spread spectrum signals received at the mobile unit substantially as hereinbefore described with reference to the accompanying drawings.  
     
     
         7 . The combination of a base station and a mobile unit for despreading a GPS spread spectrum signal received at a mobile unit with assistance from a base station by a method according to any preceding claims.  
     
     
         8 . The combination of a base station and a mobile unit for despreading a GPS spread spectrum signal received at a mobile unit with assistance from a base station; wherein the base station comprises a GPS receiver for receiving and despreading GPS signals at the base station and deriving GPS signal information therefrom, a processor arranged to modify the GPS signal information so as reflect the GPS signal characteristics as would be observed at an estimated location of the mobile unit; and a transmitter for transmitting the modified GPS signal information from the base station to the mobile unit; and wherein the mobile unit comprising a GPS receiver for receiving the GPS signal, a communications receiver for receiving GPS signal information from a base station; and a processor arranged to generate replica signals containing PRN codes corresponding to those of the GPS signal using the modified GPS signal information and perform a correlation of the GPS signal and the replica signals in order to acquire the GPS signal.  
     
     
         9 . The combination of a base station and a mobile unit for despreading a GPS spread spectrum signal received at a mobile unit with assistance from a base station; wherein the base station comprises a GPS receiver for receiving and despreading GPS signals at the base station and deriving GPS signal information therefrom, and a transmitter for transmitting the modified GPS signal information from the base station to the mobile unit; and wherein the mobile unit comprising a GPS receiver for receiving the GPS signal; a communications receiver for receiving GPS signal information from a base station; and a processor arranged to modify the GPS signal information so as reflect the GPS signal characteristics as would be observed at an estimated location of the mobile unit, generate replica signals containing PRN codes corresponding to those of the GPS signal using the modified GPS signal information and perform a correlation of the GPS signal and the replica signals in order to acquire the GPS signal  
     
     
         10 . The combination of a base station and a mobile unit for despreading a GPS spread spectrum signal received at a mobile unit with assistance from a base station substantially as hereinbefore described with reference to the accompanying drawings.  
     
     
         11 . A base station for providing assistance to a mobile unit for despreading GPS spread spectrum signals received at the mobile unit comprising a GPS receiver for receiving and despreading GPS signals at the base station and deriving GPS signal information therefrom, a processor arranged to modify the GPS signal information so as reflect the GPS signal characteristics as would be observed at an estimated location of the mobile unit; and a transmitter for transmitting the modified GPS signal information from the base station to the mobile unit.  
     
     
         12 . A base station for providing assistance to a mobile unit for despreading GPS spread spectrum signals received at the mobile unit substantially as hereinbefore described with reference to the accompanying drawings.  
     
     
         13 . A mobile unit for despreading a received GPS spread spectrum signal with assistance from a base station comprising a GPS receiver for receiving the GPS signal; a communications receiver for receiving GPS signal information from a base station; and a processor arranged to modify the GPS signal information so as reflect the GPS signal characteristics as would be observed at an estimated location of the mobile unit, generate replica signals containing PRN codes corresponding to those of the GPS signal using the modified GPS signal information and perform a correlation of the GPS signal and the replica signals in order to acquire the GPS signal  
     
     
         14 . A mobile unit for despreading a received GPS spread spectrum signal with assistance from a base station substantially as hereinbefore described with reference to the accompanying drawings.