Abstract: In a GPS navigation satellite receiver, a pseudorange step detection method integrates the pseudorange rates to predict expected changes in the pseudoranges from one measurement to the next. The pseudorange rate is directly measured as the carrier Doppler shift. The pseudorange and pseudorange rate from a last measurement from each satellite and a pseudorange rate from a new measurement are used to estimate the expected pseudorange. Such estimate accounts for vehicle velocity and accelerations. The expected pseudorange is compared to a newly measured pseudorange. An impermissible pseudorange step is declared when the difference exceeds a variable threshold. Tests can be done on measurements taken up to ten seconds apart, e.g., using a threshold of five hundred meters. The maximum position dilution of precision is typically set at a value of twelve. Satellites that manifest a pseudorange step are thereafter excluded from participating in subsequent position solution activity.

Abstract: To reduce error introduced by the local oscillator in the velocity calculations, the receiver has two "tracking channels" and a microcomputer. With numbers required to, simultaneously, lock each of the "tracking channels" each to a respective satellite signal, the microcomputer employs a differential doppler technique to calculate the receiver velocity. The microcomputer calculates a number which represents the difference between the apparent doppler frequency shift of the carrier signal which is transmitted by the first "tracking channel" satellite and which is measured over a specific time period and the apparent doppler frequency shift of the carrier signal which is transmitted by the second "tracking channel" satellite and which is measured over substantially the same time period.

Abstract: Two receiver channels each driven by a common local oscillator signal are employed. The signal developed by the first receiver channel is used to drive in phase (I) and quadrature (Q) counters of a Castas-loop, which phase-locks to the signal. The signal developed by the second receiver channel is used to drive another pair of in phase (I) and quadrature (Q) counters, which develop signals from which heading information is calculated.