P-code enhanced method for processing encrypted GPS signals without knowledge of the encryption code

US6061390A · kind A · utility

Assignee

• CALIFORNIA INSTITUTE OF TECHNOLOGY · US

Inventors

• Thomas Meehan · Glendale, US
• Jess Brooks Thomas, Jr. · Tustin, US
• Lawrence E. Young · Tustin, US

Key dates

• Filing date: Sep 2, 1994
• Grant date: May 9, 2000
• Expiry date: Sep 2, 2014

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04L27/2332
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

In the preferred embodiment, an encrypted GPS signal is down-converted from RF to baseband to generate two quadrature components for each RF signal (L1 and L2). Separately and independently for each RF signal and each quadrature component, the four down-converted signals are counter-rotated with a respective model phase, correlated with a respective model P code, and then successively summed and dumped over presum intervals substantially coincident with chips of the respective encryption code. Without knowledge of the encryption-code signs, the effect of encryption-code sign flips is then substantially reduced by selected combinations of the resulting presums between associated quadrature components for each RF signal, separately and independently for the L1 and L2 signals. The resulting combined presums are then summed and dumped over longer intervals and further processed to extract amplitude, phase and delay for each RF signal. Precision of the resulting phase and delay values is approximately four times better than that obtained from straight cross-correlation of L1 and L2. This improved method provides the following options: separate and independent tracking of the L1-Y and L2…