Patent ID: 7298319

Claim:
A method of determining a position estimate based on an updated Kalman filter, comprising: receiving a first measurement L 1 based on a first signal with wavelength λ 1 and frequency f 1 ; receiving a second measurement L 2 based on a second signal with wavelength λ 2 and frequency f 2 ; selecting a model α of distance dependent and distance independent errors in the first and second measurements, wherein the model α is selected from α=λ 1 /λ 2 , α=λ 2 /λ 1 , and α=1; based on the model α, calculating a double differenced variance matrix: D ⁡ ( L 1 , L 2 ) =  D 11 0 0 D _ 22  ; wherein D 11 = 2 ⁢ R L2 2 ⁢  W 1 + W ref W ref … W ref W ref W ref W 2 + W ref … W ref W ref ⋮ ⋮ ⋰ ⋮ ⋮ W ref W ref … W n - 2 + W ref W ref W ref W ref … W ref W n - 1 + W ref  ; wherein D _ 22 = ⁢ ( R L2 2 + α 2 ⁢ R L1 2 - 2 ⁢ α ⁢ ⁢ R L1 , L2 ) ⁢ ⁢  ⁢ W 1 + W ref W ref … W ref W ref W ref W 2 + W ref … W ref W ref ⋮ ⋮ ⋰ ⋮ ⋮ W ref W ref … W n - 2 + W ref W ref W ref W ref … W ref W n - 1 + W ref  ; wherein R L1 = ( 1 λ 1 2 ⁡ [ R non - dist , L1 2 + ( R ion 2 + R trop 2 + R orb 2 ) · B 2 ] ) 1 2 ; wherein R L2 = ( 1 λ 2 2 ⁡ [ R non - dist , L2 2 + ( R ion 2 + R trop 2 + R orb 2 ) · B 2 ] ) 1 2 ; wherein R L1 , L2 = 1 λ 1 ⁢ λ 2 ⁢ ( R ion 2 + R trop 2 + R orb 2 ) · ( f 1 4 f 2 4 ⁢ R ion 2 + R trop 2 + R orb 2 ) · B 2 ; wherein R non-dist,L1 is a non-distance dependant measurement error for the L 1 measurement; wherein R non-dist,L2 is a non-distance dependant measurement error for the L 2 measurement; wherein R ion is measurement error due to ionospheric delay; wherein R trop is measurement error due to tropospheric delay; wherein R orb is measurement error due to orbit bias; wherein each W is: W n =1.0+7.5e −E/15 ; wherein n is a satellite ordinal of a plurality of satellites; wherein W ref corresponds to a reference satellite of the plurality of satellites; wherein E is the elevation angle of each satellite of the plurality of satellites; updating a Kalman filter with the calculated variance matrix; and determining a present position estimate based on the updated Kalman filter.