Satellite-based positioning system improvement

Abstract

A method, device and system for determining a receiver location using weak signal satellite transmissions. The invention involves a sequence of exchanges between an aiding source and a receiver that serve to provide aiding information to the receiver so that the receiver's location may be determined in the presence of weak satellite transmissions. With the aiding information, the novel receiver detects, acquires and tracks weak satellite signals and computes position solutions from calculated pseudo ranges despite the inability to extract time synchronization date f, 'n the weak satellite signals. The invention includes as features, methods and apparatus for the calibration of a local oscillator, the cancellation of cross correlations, a Doppler location scheme, an ensemble averaging scheme, the calculation of almanac aiding from a table of orbit coefficients, absolute time determination, and a modified search engine.

1 . An SPS system for identifying the location of a receiver in the presence of satellite signal attenuation comprising: a plurality of orbital satellites sending synchronized encoded signals on a carrier frequency wherein said encoded signals have repeated epochs containing synchronization data; a receiver for detecting, acquiring, tracking a set of the encoded signals and simultaneously determining the code phases of said set with respect to said epochs; an aiding source to transmit information to the SPS system, and; a processor executing an algorithm for computing an initial approximate location from measured satellite Doppler differences. 
     
     
         2 . The SPS system for identifying the location of a receiver in the presence of satellite signal attenuation of  claim 1  wherein the receiver has a local oscillator and the algorithm executed by the processor has no dependence on a current local oscillator offset. 
     
     
         3 . A method for identifying the location of a receiver in the presence of satellite signal attenuation of  claim 1  wherein an SPS system executes a Doppler positioning algorithm comprising the steps of applying space vehicle (SV) clock corrections to both the satellite time of transmit and the satellite Doppler frequency for each input observation made by the GPS receiver. calculating satellite positions at the corrected satellite time of transmit estimating the receiver location, iterating through the following steps until a residual error in receiver location is below a predetermined criteria, determining an estimate of the satellite range-rate. correcting the current estimate of the user position. 
     
     
         4 - 5 . (canceled) 
     
     
         6 . A method of calibrating a local oscillator of an SPS receiver comprising the steps of
 performing acquisition searches;   counting local oscillator cycles and fractions thereof over a period determined by a number of signal framing intervals,   calculating a calibration offset; and   correcting the oscillator frequency based upon said calculated calibration offset.   
     
     
         7 . The method of calibrating a local oscillator of an SPS receiver of  claim 6 , wherein the calibration offset is used to correct the oscillator frequency so as to minimize the offset. 
     
     
         8 . An SPS system for identifying the location of a receiver in the presence of satellite signal attenuation comprising: a plurality of orbital satellites sending synchronized encoded signals on a carrier frequency wherein said encoded signals have repeated epochs containing synchronization data; a receiver for detecting, acquiring, tracking a set of the encoded signals and simultaneously determining the code phases of said set with respect to said epochs; an aiding source to transmit information to the SPS system, a canceler for reducing the amplitude of strong signals wherein the canceler is integrated into a correlator. 
     
     
         9 . The SPS system for identifying the location of a receiver of  claim 8 , wherein a canceling finger is provided for each channel for which canceling is to be performed and said canceling finger takes one input from the code generator input to a prompt finger of a channel tracking a jamming signal and a second input from a code generator input of the finger for which cancellation is to be performed. 
     
     
         10 . The SPS system for identifying the location of a receiver of  claim 8  wherein the cancellation is performed at a point where the signal is represented by approximately 10 bits. 
     
     
         11 - 18 . (canceled) 
     
     
         19 . An SPS system for identifying the location of a receiver in the presence of satellite signal attenuation comprising: a plurality of orbital satellites sending synchronized encoded signals on a carrier frequency wherein said encoded signals have repeated epochs containing synchronization data; a receiver for detecting, acquiring, tracking a set of the encoded signals and