Importance

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Abstract

A Global Positioning System (GPS) commercial receiver is provided with a digital processor that can utilize to advantage P-code modulated L1 and L2 satellite signals which have been modulated with an unknown security code. Integration of the L1 and L2 signals, after demodulation by locally generated carrier and P-code signals, is repetitively accomplished over a duration that is estimated to be the period of the modulation code. The C/A-code L1 signal, which is not modulated with the unknown security code, is also used in locking the locally generated carrier and P-code generators in phase with the received L1 and L2 satellite signals. An interpolative technique is used for adjusting the phase of the locally generated carriers and code in increments much smaller than the period clock sources. Those locked phases can then be utilized to determine position, distance, time, etc., as is done in GPS receivers not utilizing the anti-spoofed signals but with increased accuracy and resolution. A novel structure of the GPS receiver radio frequency and intermediate frequency sections, having a specific combination of demodulating frequencies, is also disclosed.

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First Claim