Method and apparatus for processing satellite positioning system signals

Abstract

Method and apparatus for processing a satellite positioning system (SPS) signal is described. In one example, a timing reference related to a SPS time of day is obtained from a wireless communication signal received by a mobile receiver. A bias in a local clock of the mobile receiver with respect to a frame timing of a repeating code broadcast by the satellite is compensated for in response to the timing reference. An expected code delay window is obtained for the SPS signal at the mobile receiver. The SPS signal is correlated with a reference code within the expected code delay window. In another example, an expected code delay window is obtained at the mobile receiver. The mobile receiver selects a sampling resolution in response to a size of the expected code delay window. The SPS signal is sampled at the selected sampling resolution and then correlated with a reference code.

1 . A method of processing a satellite positioning system signal received by a mobile receiver from a satellite, comprising:
 obtaining a timing reference related to a satellite positioning system time of day from a wireless communication signal received at said mobile receiver;   compensating for a bias in a local clock of said mobile receiver with respect to a frame timing of a repeating code broadcast by said satellite in response to said timing reference;   obtaining an expected code delay window for said satellite positioning system signal at said mobile receiver; and   correlating said satellite positioning system signal with a reference code within said expected code delay window.   
     
     
         2 . The method of  claim 1 , wherein said step of obtaining said expected code delay window comprises:
 receiving acquisition assistance data from a server in communication with the mobile receiver; and   deriving said expected code delay window in response to said acquisition assistance data.   
     
     
         3 . The method of  claim 1 , wherein further comprising:
 determining a delay between said mobile receiver and a base station in communication with said mobile receiver;   adjusting said timing reference in response to said delay.   
     
     
         4 . The method of  claim 2 , wherein said assistance data comprises expected pseudorange data and said expected code delay window is generated using said expected pseudorange data. 
     
     
         5 . The method of  claim 1 , wherein said step of obtaining said expected code delay window comprises:
 obtaining satellite trajectory data at said mobile receiver;   obtaining an estimated location of said mobile receiver; and   computing said code delay window in response to said satellite trajectory data and said estimated location.   
     
     
         6 . The method of  claim 5 , wherein said satellite trajectory data comprises ephemeris. 
     
     
         7 . The method of  claim 5 , wherein said satellite trajectory data comprises almanac data. 
     
     
         8 . The method of  claim 5 , wherein said satellite trajectory data is received from a server in communication with said mobile receiver. 
     
     
         9 . The method of  claim 1 , wherein said expected code delay window spans only a portion of said repeating code. 
     
     
         10 . The method of  claim 1 , further comprising:
 selecting a sampling resolution in response to said expected code delay window; and   sampling said satellite positioning system signal at said selected sampling resolution prior to correlation step.   
     
     
         11 . The method of  claim 1 , further comprising:
 repeating said steps of obtaining an expected code delay window and correlating for at least one additional satellite positioning system signal received by said mobile receiver from a respective at least one additional satellite.   
     
     
         12 . The method of  claim 1 , further comprising:
 computing a pseudorange from said mobile receiver to said satellite in response to results of said correlation.   
     
     
         13 . The method of  claim 1 , wherein said step of compensating comprises:
 comparing said timing reference with a timing of said local clock to estimate said bias.   
     
     
         14 . The method of  claim 1 , wherein said step of compensating comprises:
 synchronizing a timing of said local clock to said timing reference.   
     
     
         15 . A method of processing a satellite positioning system signal received by a mobile receiver from a satellite, comprising:
 obtaining an expected code delay window at said mobile receiver;   selecting a sampling resolution in response to a size of said expected code delay window;   sampling said satellite positioning system signal at said selected sampling resolution; and   correlating said sampled satellite positioning system signal with a reference code.   
     
     
         16 . The method of  claim 15 , wherein said step of selecting a sampling resolution comprises:
 selecting a first sampling resolution in response to said size failing a threshold; and   selecting a second sampling resolution in response to said size satisfying said threshold.   
     
     
         17 . The method of  claim 16 , wherein said second sampling resolution is higher than said first sampling resolution. 
     
     
         18 . The method of  claim 15 , further comprising:
 obtaining a timing reference related to a satellite positioning system time-of-day from a time synchronization signal broadcast by a base station in communication with said mobile receiver; and   compensating for a bias in a local clock of said mobile receiver with respect to a frame timing of a repeating code broadcast by said satellite in response to said timing reference.   
     
     
         19 . The method of  claim 18 , further comprising:
 obtaining acquisition assistance data; and   deriving said expected code delay window in response to said acquisition assistance data.   
     
     
         20 . The method of  claim 19 , wherein said sampled satellite positioning system signal is correlated within said expected code delay window.