Method and apparatus for a satellite payload and radiodetermination

Abstract

A satellite radiodetermination system comprises global navigation service (GNSS) satellites 2 such as GPS satellites, which generate GNSS ranging signals R n , geostationary satellites 6 which retransmit ranging signals R g generated at a navigation land earth station (NLES) 8 , including augmentation data A, and medium earth orbit (MEO) satellites 10 which generate ranging signals R m including regional augmentation data RA transmitted from a satellite access node (SAN) 14 . The regional augmentation data RA is supplied by regional augmentation systems 21 a , 21 b. A navigation receiver 11 receives the ranging signals R g , R m , R n and calculates ionospheric delay values for those ranging signals which are provided on dual frequencies. Using these ionospheric delay values, and optionally the regional augmentation data RA and the augmentation data A, the navigation receiver estimates ionospheric delay values for those ranging signals which are provided on single frequencies. The navigation receiver uses the ranging signals, corrected for ionospheric delay and errors indicated by the augmentation data A and regional augmentation data RA, to calculate position and time accurately.

1 . Satellite radiodetermination apparatus, comprising: 
 a radio receiver for receiving a multiple frequency ranging signal from a first satellite and a further ranging signal from a second satellite;    deriving means for deriving first ionospheric delay data from said multiple frequency ranging signal; and    estimating means for estimating second ionospheric delay data for the further ranging signal on the basis of said first ionospheric delay data.    
     
     
         2 . Apparatus as claimed in  claim 1 , further comprising data receiving means for receiving ionospheric data, said estimating means being operable to estimate the second ionospheric delay data additionally on the basis of said ionospheric data.  
     
     
         3 . Apparatus as claimed in  claim 2 , wherein said data receiving means is arranged to receive said ionospheric data from a satellite.  
     
     
         4 . Apparatus as claimed in  claim 2  or  3 , wherein said ionospheric data represents a plurality of ionospheric delay values corresponding to a plurality of spatially separated points.  
     
     
         5 . Apparatus as claimed in any preceding claim, wherein said estimating means includes modelling means for generating a model of spatial variation of ionospheric delay on the basis of said first ionospheric delay data, said estimating means being operable to estimate said second ionospheric delay data on the basis of said model.  
     
     
         6 . Apparatus as claimed in  claim 5  when dependent on  claim 2 , wherein said modelling means is operable to generate said model on the basis of said ionospheric data.  
     
     
         7 . Apparatus as claimed in  claim 5  or  claim 6 , wherein said model comprises a function which is variable in accordance with one or more parameters, said modelling means being arranged to calculate said one or more parameters such that said function is fitted to said first ionospheric delay data.  
     
     
         8 . Apparatus as claimed in  claim 7  when dependent on  claim 6 , wherein said modelling means is arranged to calculate said one or more parameters such that said function is additionally fitted to said ionospheric data.  
     
     
         9 . A method of satellite radiodetermination, comprising receiving a multiple frequency ranging signal from a first satellite; 
 receiving a further ranging signal from a second satellite, deriving first ionospheric delay data from said multiple frequency ranging signal; and    estimating second ionospheric delay data for the further ranging signal on the basis of said first ionospheric delay data.    
     
     
         10 . A satellite payload adapted for a satellite designed for a non-geostationary orbit, comprising: 
 a clock for generating a time signal;    a ranging signal generator for generating a ranging signal including timing data derived from said time signal;    relaying means for retransmitting data received by the satellite from a ground station; and    means for selectively activating and deactivating said relaying means independently of the activation of the ranging signal generator.    
     
     
         11 . A satellite payload adapted for a satellite designed for a non-geostationary orbit, comprising: 
 a clock for generating a time signal;    a ranging signal generator for generating a ranging signal including timing data derived from said time signal;    relaying means for retransmitting received data received by the satellite from a ground station;    means for detecting an absence of said received data; and    means for generating dummy data for transmission in response to detection of said absence.    
     
     
         12 . Apparatus for providing augmentation data for transmission by a satellite, comprising: 
 means for receiving the augmentation data;    means for providing position data relating to the position of the satellite;    determining means for determining whether the position data satisfies a predetermined criterion; and    means for selectively enabling output of said augmentation data for transmission to said satellite in response to the determining means.    
     
     
         13 . A method of providing augmentation data for transmission by a satellite, comprising: 
 providing position data relating to the position of the satellite;    determining whether the position data satisfies a predetermined criterion; and    selectively enabling output of said augmentation data for transmission to a satellite in response to the result of said determining step.    
     
     
         14 . Satellite radiodetermination apparatus, comprising: 
 means for receiving a plurality of ranging signals from a corresponding plurality of satellites; and    means for receiving ionospheric delay data, the apparatus being arranged to perform radiodetermination on the basis of said plurality of ranging signals and selectively on the basis of said ionospheric delay data in response to authorization data provided at said apparatus.    
     
     
         15 . Apparatus as claimed in  claim 14 , further including means for receiving differential correction data which is substantially independent of ionospheric delay, wherein said apparatus is arranged to perform radiodetermination additionally on the basis of said differential correction data.  
     
     
         16 . Apparatus as claimed in  claim 14  or claim is, wherein said ionospheric delay data is encrypted, and said apparatus includes decryption means for decrypting said ionospheric delay data in response to said authorization data.  
     
     
         17 . Apparatus as claimed in any one of  claims 14  to  16 , including input means for inputting said authorization data.  
     
     
         18 . Apparatus for providing augmentation data for transmission via a satellite, comprising: 
 means for receiving said augmentation data which includes unencrypted ionospheric delay data and unencrypted differential correction data which is substantially independent of ionospheric delay;    means for encrypting said ionospheric delay data; and    means for outputting said encrypted ionospheric delay data and said unencrypted differential correction data for transmission via said satellite.    
     
     
         19 . A method of providing ionospheric delay data and differential correction data which is substantially independent of ionospheric delay for transmission via a satellite, comprising: 
 receiving said ionospheric delay data and said differential correction data in an unencrypted form;    encrypting said ionospheric delay data; and    outputting said encrypted ionospheric delay data and said unencrypted differential correction data for transmission via said satellite.    
     
     
         20 . Satellite radiodetermination apparatus, comprising: 
 means for receiving a plurality of ranging signals from a corresponding plurality of satellites;    means for receiving ionospheric delay data; and    means for receiving residual error data relating to residual errors in said ionospheric delay data, said satellite radiodetermination apparatus being arranged to perform radiodetermination on the basis of said plurality of ranging signals, said ionospheric delay data and said residual error data.    
     
     
         21 . Apparatus as claimed in  claim 20 , wherein said residual error information includes error bound information relating to the error bounds of said ionospheric delay information.  
     
     
         25 . Apparatus for determining residual errors in a satellite radiodetermination system, comprising: 
 means for receiving a plurality of ranging signals from a plurality of satellites;    means for receiving ionospheric delay data and differential correction data relating to errors in said ranging signals which are independent of ionospheric delay;    calculating means for calculating a position or time on the basis of said ranging signals corrected on the basis of said differential correction data and said ionospheric delay data; and    error calculating means for calculating errors in said ionospheric delay data on the basis of the difference between said calculated position or time and a predetermined reference position or time.    
     
     
         23 . Apparatus as claimed in claim  22 , wherein said means for receiving said ranging signals comprises a dispersed plurality of receiving stations, said calculating means being arranged to calculate a plurality of positions corresponding respectively to said receiving stations, and said error calculating means being arranged to calculate said errors on the basis of the respective differences between said calculated positions and predetermined positions corresponding to said receiving stations.  
     
     
         24 . A satellite radiodetermination receiver including apparatus as claimed in any one of  claims 1  to  8 ,  14  to  17 ,  20  and  21 .  
     
     
         25 . A terrestrial station including apparatus as claimed in any one of claims  12 ,  18 ,  22  or  23 .  
     
     
         26 . A satellite including a satellite payload as claimed in  claim 10  or  11 .  
     
     
         27 . A satellite radiodetermination system including a plurality of satellite radiodetermination receivers as claimed in  claim 24  and at least one terrestrial station as claimed in  claim 25.