Digital system for codeless phase measurement
First Claim
1. In a method for determining baseline vectors from information contained in the L1 and L2 signals from a plurality of G.P.S. transmitters of the type wherein said transmissions are detected by receivers located at each end of said baseline and said transmitters are identified by comparing the measured phase of said received transmissions with predicted values thereof whereby a priori knowledge of the singal modulating codes is not required, the improvement comprising measuring the phases of said signals by the steps of:
- (a) mixing said L2 signals with a local oscillator to provide an intermediate frequency signal; and
(b) clocking a counter with said local oscillator; and
(c) starting said counter with a signal that is synchronized with and whose frequency is a fraction of said local oscillator;
then(d) stopping said counter with said intermediate frequency signal; and
then(e) discarding the most significant bit of said count.
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Accused Products
Abstract
A codeless digital method and apparatus for obtaining measured phase from a plurality of L2 signal transmissions. An intermediate frequency signal is derived by mixing the L2 transmissions with a local oscillator. That signal is hardlimited and employed to terminate the count of a divide-by-32 counter that is clocked by the local oscillator signal and initiated by a signal in synchronization therewith whose frequency is a fraction of the local oscillator. The state of the counter is applied to a four bit latch. The state of the latch, which effectively discards the most significant bit of the count, provides the measured phase of the L2 transmissions from which position can be obtained by reference to the satellite phase and delta range values derived therefrom.
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Citations
14 Claims
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1. In a method for determining baseline vectors from information contained in the L1 and L2 signals from a plurality of G.P.S. transmitters of the type wherein said transmissions are detected by receivers located at each end of said baseline and said transmitters are identified by comparing the measured phase of said received transmissions with predicted values thereof whereby a priori knowledge of the singal modulating codes is not required, the improvement comprising measuring the phases of said signals by the steps of:
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(a) mixing said L2 signals with a local oscillator to provide an intermediate frequency signal; and (b) clocking a counter with said local oscillator; and (c) starting said counter with a signal that is synchronized with and whose frequency is a fraction of said local oscillator;
then(d) stopping said counter with said intermediate frequency signal; and
then(e) discarding the most significant bit of said count. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. Apparatus for codeless digital measurement of the phase of a code-modulated signal of the spread spectrum type comprising, in combination:
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(a) means for mixing said signals with a local oscillator to provide an intermediate frequency signal; (b) a counter, said counter being clocked by said local oscillator; (c) means for dividing the frequency of said local oscillator to produce a third signal that is synchronized with said local oscillator and having a frequency that is a fraction of that of said local oscillator; (d) said third signal being applied to said counter whereby the counter is initiated to begin counting in response to said third signal; and (e) means for discarding the most significant bit of the count of said counter. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification