Method and apparatus for determining position using global positioning satellites

• US 6,182,011 B1
• Filed: 08/10/1998
• Issued: 01/30/2001
• Est. Priority Date: 04/01/1996
• Status: Expired due to Fees

• Current Assignee: United States Administrator of National Aeronautics and Space Administration
• Original Assignee: United States Administrator of National Aeronautics and Space Administration
• Inventors: Ward, John L.
• Primary Examiner(s): Chin, Gary
• Application Number:
  US09/131,704
• Time in Patent Office: 904 Days
• Field of Search: 701/207, 701/213, 342/357.06, 342/357.09, 342/357.12, 375/208
• US Class Current: 701/213
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/52 Determining velocity
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station

Abstract

A global positioning satellite receiver having an antenna for receiving a L1 signal from a satellite. The L1 signal is processed by a preamplifer stage including a band pass filter and a low noise amplifier and output as a radio frequency (RF) signal. A mixer receives and de-spreads the RF signal in response to a pseudo-random noise code, i.e., Gold code, generated by an internal pseudo-random noise code generator. A microprocessor enters a code tracking loop, such that during the code tracking loop, it addresses the pseudo-random code generator to cause the pseudo-random code generator to sequentially output pseudo-random codes corresponding to satellite codes used to spread the L1 signal, until correlation occurs. When an output of the mixer is indicative of the occurrence of correlation between the RF signal and the generated pseudo-random codes, the microprocessor enters an operational state which slows the receiver code sequence to stay locked with the satellite cede sequence. The output of the mixer is provided to a detector which, in turn, controls certain routines of the microprocessor. The microprocessor will output pseudo range information according to an interrupt routine in response detection of correlation. The pseudo range information is to be telemetered to a ground station which determines the position of the global positioning satellite receiver.

Claims

1. A global positioning satellite receiver for generating pseudo-range data and pseudo-range rates for transmission to a ground station, said global positioning satellite receiver having an antenna and a preamplifier for receiving a L1 signal from a satellite and outputting the L1 signal as a radio frequency signal, said global positioning satellite receiver comprising:

a pseudo-random noise code generator for sequentially generating pseudo-random noise codes, corresponding to known satellite codes, in response to address signals received from microprocessor means;

a correlation mixer for de-spreading said radio frequency signal in response to said generated pseudo-random noise codes;

detecting means for detecting when an output of said correlation mixer is indicative of correlation between said radio frequency signal and said generated pseudo-random noise codes wherein said detecting means comprises;

means for down-converting an output of said correlation mixer to an intermediate frequency between direct current and a maximum Doppler shift plus harmonics of a generated frequency, wherein said generated frequency is generated due to a lack of 100% correlation,

lowpass filter means having a cutoff slightly higher than the generated frequency for filtering said intermediate frequency and producing a low-passed signal,

highpass filter means having a cutoff slightly lower than the generated frequency for filtering the low-passed signal and producing a high-passed signal,

a phase shifter for shifting the high-pissed signal in phase, producing an in-phase signal, and

an analog multiplexer with inputs of the in-phase signal and the high-passed signal which the multiplexer feeds into an analog to digital converter for sampling at a lower frequency than the generated frequency, said analog to digital converter producing a digitized signal which is fed into the microprocessor means;

said microprocessor means correlating the digitized signal with the lower frequency so as to indirectly measure a power of the high-passed signal, said power being related to a degree of correlation of an incoming pseudo-random noise code sequence and a pseudo-random noise code sequence of the generator;

a digital to analog converter for converting the digitized signal to an analog signal to be summed by summing means;

a carrier phase loop filter having a carrier phase output, said loop filter filtering said low-passed signal; and

said summing means summing the analog signal from the digital to analog converter and the carrier phase output.