INTEGRITY MONITORING OF DIFFERENTIAL SATELLITE POSITIONING SYSTEM SIGNALS

Methods for determining the integrity of pseudorange and pseudorange rate signals received from a plurality of M Satellite Positioning System satellites (SATPS, including GPS and GLONASS), numbered j=j1, j2, . . . , jM, at a reference SATPS station (RS), using pseudorange and pseudorange rate signals received from the same satellites at a signal integrity monitoring (SIM) station located near the reference station. Pseudorange correction values PRC(t;i;j).sub.RS and PRC(t;i;j).sub.SIM and pseudorange rate correction values PRRC(t;i;j).sub.RS and PRRC(t;i;j).sub.SIM for the signals received at the reference station (RS, number i) and at the SIM station are computed, and difference values DPRE(t;i;j)=PRC(t;i;j).sub.RS -PRC(t;i;j).sub.SIM and DRRE(t;i;j)=PRRC(t;i;j).sub.RS -PRRC(t;i;j).sub.SIM are computed from these correction values. If .vertline.DPRE(t;i;j).vertline..ltoreq.DPRE(i;j).sub.thr and .vertline.DPRRE(i;j).vertline..ltoreq.DPRRE(i;j).sub.thr, where DPRE(i;j).sub.thr and DPRRE(i;j).sub.thr are selected threshold values for a satellite (j), the pseudorange corrections and/or pseudorange rate corrections for that reference station are acceptable and can be used by a mobile station located near that reference station to differentially improve the accuracy of the location coordinates and/or the velocity coordinates for that mobile station. If at least one acceptable pair of difference values DPRE(t;i;j) and DPRRE(t;i;j) is found, for a particular satellite j, clock bias and frequency offset can be corrected using the SATPS signal received from that satellite at the SIM station. If at least two pairs of difference values DPRE(t;i;j) and DPRRE(t;i;j) are acceptable, for satellites j1 and j2, the accuracy of the clock bias and frequency offset parameters can be monitored using the SATPS signals received from that pair of satellites. If at least three pairs of difference values DPRE(t;i;j) and DPRRE(t;i;j) are acceptable (for three distinct satellites), the location coordinates and/or velocity coordinates can be corrected using the signals received from those satellites, if a precise SIM station clock is provided; otherwise, at least four acceptable pairs of difference values are required.