Patent ID: 6182011
Filing Date: 2001-01-30
Classification: G01S

Abstract:
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, andan 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; andsaid summing means summing the analog signal from the digital to analog converter and the carrier phase output.