Global positioning system receiver with improved radio frequency and digital processing

In a global position electronic receiver having a radio frequency section connected to receive a radio frequency signal from an antenna and deliver an intermediate frequency signal to an input of a digital processor that derives therefrom information of the relative phase of said received radio frequency signal, an improved relative phase measuring portion of said digital processor:

• a phase-locked loop circuit connected to receive and lock upon said intermediate frequency signal, said phase lock loop circuit including a multibit counter whose most significant bit is utilized in the phase locked loop, said counter being characterized by shifting its output an amount of phase in response to an input pulse developed as part of said phase locked loop in order to keep said loop locked onto said intermediate frequency signal, counter
• means connected to the output of said for periodically latching all bits of its output in response to a periodic clock signal, thereby to obtain a base measurement of relative phase of the intermediate frequency signal,
• means receiving and counter phase shifting pulses for periodically determining the average number of said pulses over a fixed period of time, thereby to provide an incremental phase measurement, and
• means receiving both the base phase measurement and the incremental phase measurement for summing said measurements, thereby to obtain the relative phase of said received radio frequency signal.

A method of determining the relative phase of a plurality of L-band radio frequency signals having unique modulation and originating in a plurality of global positioning system satellites, comprising the steps of:

• receiving said plurality of radio frequency signals and reducing them by a common radio frequency down-converting system to a plurality of intermediate frequency signals,
• digitally identifying each of said plurality of intermediate frequency signals by their unique modulation,
• simultaneously locking a separate phase locked loop electronic circuit onto each of said plurality of signals,
• simultaneously determining a base relative phase of each of said plurality of intermediate frequency signals,
• determining separately for each of said plurality of intermediate signals from a quantity that responds to their relative phase an incremental relative phase having a higher degree of resolution than the base relative phase determinations, and
• arithmetically combining the base and incremental phase values for each of the intermediate frequency signals, whereby the relative phase of each of the radio frequency signal is determined.

A method of determining the relative phase of a plurality of L-band radio frequency signals having unique modulation and originating in a plurality of global positioning system satellites, comprising the steps of:

• receiving said plurality of radio frequency signals,
• mixing said plurality of radio frequency signals with a local oscillator frequency of substantially 1372f.sub.0, where f.sub.0 =1.023 MHz., thereby to reduce the frequency of the radio frequency signals,
• mixing said reduced frequency signals with a local oscillator frequency of substantially 171.5f.sub.0, thereby to obtain a plurality of intermediate frequency signals,
• digitally identifying each of said plurality of intermediate frequency signals by their unique modulation.
• simultaneously locking a separate phase locked loop electronic circuit onto each of said plurality of signals,
• simultaneously determining a base relative phase of each of said plurality of intermediate frequency signals,
• determining separately for each of said plurality of intermediate signals from a quantity that responds to their relative phase an incremental relative phase having a higher degree of resolution than the base relative phase determinations, and
• arithmetically combining the base and incremental phase values for each of the intermediate frequency signals, whereby the relative phase of each of the radio frequency signals is determined.

In the global position electronic receiver having a radio frequency section connected to receive a radio frequency signal from an antenna and deliver an intermediate frequency signal to an input of a digital processor that derives therefrom information of the relative phase of said received radio frequency signal, an improved relative phase measuring portion of said digital processor comprising:

• means for generating a clock signal of a given period;
• means responsive to said clock generating means for determining a base measurement of the relative phase of said intermediate frequency signal to an accuracy of the period of said clock signal;
• means responsive to said base measurement means and said clock means for determining an incremental phase measurement over a series of clock periods with an accuracy that is better than that of said base measurement;
• and
• means responsive to said base and incremental phase measurement means for summing said base and incremental phases, thereby deriving a very accurate relative phase measurement.