Method and apparatus for deriving pseudo range from earth-orbiting satellites

A method for deriving pseudo range from a user to a signal transmitting satellite that transmits a radio frequency signal having a first component at a given frequency and a second component at a frequency higher than the given frequency, the method comprising the steps of:

• intercepting the signal from the satellite at the position of the user;
• recovering the first and second components from the intercepted signal;
• measuring the phase of the first component;
• determining a coarse range value from the satellite to the position of the user to an accuracy better than a wavelength of the first component;
• processing the coarse range value and the measured phase of the first component to resolve the ambiguity of the measured phase as a representation of a first pseudo range value, the frequency of the first component being sufficiently high that the first pseudo range value is accurate to better than a wavelength of the second component;
• measuring the phase of the second component;
• and
• processing the first pseudo range value as a coarse range value and the measured phase of the second component to resolve the ambiguity of the measured phase as a representation of a second pseudo range value.

A method of deriving pseudo range from a user to a plurality of signal transmitting satellites that transmit radio frequency signals having a component at a given frequency, the method comprising the steps of:

• intercepting the signals from the satellites at the position of the user;
• recovering components from the intercepted signal, Doppler shifted according to the position of the transmitting satellites;
• Fourier transforming the recovered components in phase and phase quadrature to separate the components from the different satellites;
• comparing the in phase and quadrature phase Fourier transforms to derive phase measurements of the components;
• determining a coarse range value from one of the satellites to the position of the user to an accuracy better than a wavelength of the given frequency;
• and
• processing the coarse range value and the phase measurements to resolve the ambiguity of the measured phase values as representation of the pseudo range from the satellite to the position of the user.