Method and apparatus for collecting subframes of satellite navigation data

Abstract

A method and apparatus for collecting subframes of navigation data of satellites are disclosed. In the method of the present invention, the subframe is divided into several sub-units, each sub-units includes one or more words. When a receiver receives a subframe with a subframe ID, the respective required sub-units of the subframe are checked. A dummy sub-unit is not necessary to be considered. Valid ones of the required sub-units are collected. If not all the required sub-units of the subframe have been collected, the absent sub-units are to be collected when the next subframe with the same subframe ID is received. Some protection schemes can be applied to raise the reliability of such sub-unit collection. Especially when the signal is weak or unstable, the present invention may significantly improve the TTFF (Time To First Fix) performance of the receiver.

1 . A method for receiving subframes of navigation data of a satellite, and said subframes including a plurality of sub-units, the method comprising steps of:
 receiving GNSS signals with subframes of navigation data;   checking if the sub-units of respective subframes are valid; and   collecting at least one required sub-units to obtain navigation data.   
     
     
         2 . The method of  claim 1 , wherein each sub-unit comprises one word. 
     
     
         3 . The method of  claim 1 , wherein each sub-unit comprises a plurality of words. 
     
     
         4 . The method of  claim 1 , further comprising a step of checking a sub-unit comprising a TLM (telemetry) word of a subframe after the receiving step, if the TLM is not valid, the subframe is discarded and no sub-units will be collected from the subframe. 
     
     
         5 . The method of  claim 1 , further comprising determining if all required subframes have been collected. 
     
     
         6 . The method of  claim 1 , further comprising determining if an update occurs in the navigation data, and abandoning old sub-units which have been collected when an update has occurred. 
     
     
         7 . The method of  claim 6 , wherein IOD (Issue of Data) information is checked to determine whether an update has occurred. 
     
     
         8 . The method of  claim 1 , wherein the checking step comprises firstly checking the sub-units comprising a TLM word and the sub-unit comprising a HOW word of the subframe, if both the TLM and HOW words are valid, then the other sub-units of the subframe are subjected to checking, otherwise the subframe is discarded and no sub-units will be collected from the subframe. 
     
     
         9 . The method of  claim 1 , wherein a sub-unit comprising reserved words is not considered as a required sub-unit. 
     
     
         10 . An apparatus for receiving subframes of navigation data of a satellite, and said subframes including a plurality of sub-units, the apparatus comprising:
 a decision device receiving the sub-units and check if the respective sub-units are valid; and   a subframe collecting database collecting at least one required sub-unit.   
     
     
         11 . The apparatus of  claim 10 , wherein the subframes subjected to sub-unit collection are transmitted together to update the navigation database after all required sub-units of these subframes are collected. 
     
     
         12 . The apparatus of  claim 10 , wherein a sub-unit comprising reserved words is not considered as a required sub-unit. 
     
     
         13 . The apparatus of  claim 10 , wherein the decision device checks if an update occurs in the navigation data, and indicate to abandon old sub-units which have been collected in the subframe collection database when an update has occurred. 
     
     
         14 . The apparatus of  claim 13 , wherein the decision device checks IOD (Issue of Data) information of the subframe to determine whether an update has occurred. 
     
     
         15 . The apparatus of  claim 10 , wherein the decision device discards and collects no sub-unit from a subframe if the sub-units comprising TLM and HOW words of the subframe are not valid. 
     
     
         16 . The apparatus of  claim 10 , wherein each sub-unit comprises one word. 
     
     
         17 . The apparatus of  claim 10 , wherein each sub-unit comprises a plurality of words. 
     
     
         18 . A method for receiving subframes of navigation data of a satellite, and said subframes including a plurality of sub-units, the method comprising steps of:
 receiving the sub-units;   checking if the respective sub-units are valid; and   collecting at least one required sub-units to obtain navigation data.