Method for a space-efficient gps receiver

Abstract

In a Global Positioning System (GPS) receiver, rather than storing both GPS satellite ephemeredes and almanacs to the GPS receiver's on-chip non-volatile memory, storing into the non-volatile memory only the more recent ephemeris or almanac data for each satellite. When an ephemeris expires, the parameters in the ephemeris are converted into corresponding parameters of an almanac. The ephemeris or almanac is used to determine whether a given satellite is visible to the GPS receiver. A method of the present invention allows efficient use of the memory space in the non-volatile memory. A study by the inventors shows that differences in positions and velocities of satellites estimated using aged ephemeris and almanac data associated with the same week number are insignificant.

1 . In a GPS receiver, a method for storing satellite orbital parameters, comprising:
 receiving an ephemeris and almanac data of a satellite;   comparing the week number and reference time associated with the ephemeris with the week number and reference time associated with the almanac data; and   based on the comparison, selecting the more recent one of the ephemeris and the almanac data to be stored in a non-volatile memory of the GPS receiver.   
   
   
       2 . A method as in  claim 1 , further comprising, when the GPS receiver is power up, retrieving from the non-volatile memory of the GPS receiver the stored almanac data or ephemeris to compile a list of visible satellites. 
   
   
       3 . A method as in  claim 1  wherein, for each satellite, only the more recent one of the ephemeris and the almanac data is stored in the non-volatile memory. 
   
   
       4 . A method as in  claim 1 , wherein the non-volatile memory comprises a random access memory element. 
   
   
       5 . A method as in  claim 1  further comprising computing a position or a velocity of the satellite using the more recent one of the almanac data and the ephemeris. 
   
   
       6 . A method as in  claim 5 , further comprising determining whether or not the satellite is visible to the GPS receiver based on the computing. 
   
   
       7 . A method as in  claim 1  wherein when only an ephemeris but not almanac data is available for the GPS receiver to compute a position or a velocity of a satellite, the GPS receiver computes the position or velocity of the satellite using the ephemeris.