Method and apparatus for determining gnss time for a gnss receiver without accurate time information

Abstract

A method and an apparatus for determining a Global Navigation Satellite System (GNSS) time for a GNSS receiver are provided. The method includes storing ephemeris information into a non-volatile memory, and utilizing the ephemeris information to determine a GNSS time without referring a real time clock (RTC). The apparatus includes a storage module and a processing module coupled to the storage module. The storage module is utilized for storing data. The stored data in the storage module is non-volatile. The processing module stores ephemeris information into the storage module and utilizes the ephemeris information to determine a GNSS time without referring a real time clock (RTC).

1 . A method for determining a Global Navigation Satellite System (GNSS) time for a GNSS receiver, comprising:
 storing ephemeris information into a non-volatile memory before powering down the GNSS receiver; and   utilizing the ephemeris information to determine a GNSS time without referring to a real time clock (RTC) when resuming the GNSS receiver.   
     
     
         2 . The method of  claim 1 , wherein the step of utilizing the ephemeris information to determine the GNSS time further comprises:
 after a power-on or restart, determining the GNSS time without referencing any RTC.   
     
     
         3 . The method of  claim 1 , further comprising:
 storing at least one timestamp with optional position information into the non-volatile memory; and   after a power-on or restart, tracking GNSS satellites to decode a new value of Time Of Week (TOW), deriving an old value of TOW from the timestamp, and making a guess of a new value of Week Number (WN) according to the new value of TOW and the old value of TOW when the new value of WN is not decoded.   
     
     
         4 . The method of  claim 3 , wherein the step of making the guess of the new value of WN further comprises:
 when the new value of WN is not decoded, making the guess of the new value of WN according to a comparison result between the new value of TOW and the old value of TOW.   
     
     
         5 . The method of  claim 4 , wherein the step of making the guess of the new value of WN further comprises:
 when the new value of TOW is greater than the old value of TOW, determining the new value of WN to be substantially the same as an old value of WN from the timestamp; otherwise, determining the new value of WN to be substantially equal to the old value of WN plus one.   
     
     
         6 . The method of  claim 3 , further comprising:
 determining whether the ephemeris information is expired; and   when the ephemeris information is not expired, trying to calculate a fix according to the new value of TOW and the new value of WN.   
     
     
         7 . An apparatus for determining a Global Navigation Satellite System (GNSS) time for a GNSS receiver, comprising:
 a storage module for storing data, wherein the stored data in the storage module is non-volatile;   a processing module, coupled to the storage module, for storing ephemeris information into the storage module before powering down the GNSS receiver, and utilizing the ephemeris information to determine a GNSS time without referring a real time clock (RTC) when resuming the GNSS receiver.   
     
     
         8 . The apparatus of  claim 7 , wherein the storage module comprises a non-volatile memory for storing the ephemeris information. 
     
     
         9 . The apparatus of  claim 7 , wherein the apparatus comprises the GNSS receiver. 
     
     
         10 . The apparatus of  claim 7 , wherein the apparatus is a circuit positioned within the GNSS receiver. 
     
     
         11 . The apparatus of  claim 7 , the processing module further stores position information with at least one timestamp into the storage module; and after a power-on or restart, the processing module tracks GNSS satellites to decode a new value of Time Of Week (TOW), derives an old value of TOW from the timestamp, and makes a guess of a new value of Week Number (WN) according to the new value of TOW and the old value of TOW when the new value of WN is not decoded. 
     
     
         12 . The apparatus of  claim 11 , wherein when the new value of WN is not decoded, the processing module makes a guess of the new value of WN according to a comparison result between the new value of TOW and the old value of TOW. 
     
     
         13 . The apparatus of  claim 12 , wherein when the new value of TOW is greater than the old value of TOW, the processing module determines the new value of WN to be substantially the same as an old value of WN from the timestamp; otherwise, the processing module determines the new value of WN to be substantially equal to the old value of WN plus one. 
     
     
         14 . The apparatus of  claim 11 , wherein the processing module determines whether the ephemeris information is expired; and when the ephemeris information is not expired, the processing module tries to calculate a fix according to the new value of TOW and the new value of WN.