Sperry Marine Inc.

Fred W Phillips

Gregory Schluge

Edmund S Zavada

Dhanvant H Goradia

Kelly L Mahoney

Christopher G Ranson

Van E Hanson

A squaring loop for a GPS receiver locks to a carrier that is bi-phase modulated with a PRN acquisition code and a data message. The receive signal is down converted and hard limited and phase measurements are made between the rising edges of a local clock and every edge of the hard limited carrier. Phase measurements made with respect to extraneous or missing transitions resulting from the data bits that would result in phase locking instability are removed by a phase evaluation comparison. Phase measurements that are outside of limits determined in accordance with the noise characteristics of the channel are excluded thereby removing measurements that would cause the instability. The phase measurements outside the limits are resonably attributable to data bit transitions rather than to noise.

Spread spectrum squaring loop with invalid phase measurement rejection

A Long Loop GPS receiver converts the pseudo random noise code bi-phase modulated input signal to a first IF frequency. The first IF is correlated against a duplicate of the pseudo random noise code that modulates the input signal. The correlator output is converted to a last IF having a frequency of one-half the pseudo random noise code sequence repetition rate. Local oscillator leakage into the receiver input is spread in spectrum by the correlator into spectral lines that do not lie on the received signal. A bandpass filter in the last IF removes the leakage spectral lines. A hard limiter converts the last IF to digital format. A digital phase detector adjusts the local oscillator to lock the local oscillator signal to the receive signal. The correlator pseudo random noise code signal is clocked by the local oscillator.

Spread spectrum long loop receiver

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Afton, VA, United States of America

Fred W Phillips