A navigation processor for generating an H1 integrity protection level of a relative position of a user receiver relative to a reference receiver , comprising: an ephemeris monitor configured to generate, from a plurality of N differential global positioning system 'GPS' satellite measurements where N is at least five, an H1 integrity protection level from an N number of one satellite removed positions, wherein a one satellite removed position is derived by one of the differential GPS satellite measurements being removed from the plurality of N differential GPS satellite measurements; wherein the ephemeris monitor further comprises: a solution module configured to calculate a one satellite removed position by removing one differential measurement from one GPS satellite in a plurality of N GPS satellites (120-128) from the differential measurements of the plurality of N GPS satellites (120-128); a bias module configured to calculate a position bias between the one satellite removed positions and a N satellite position, where the N satellite position uses the differential measurements of the plurality of N GPS satellites (120-128); and an H1 protection level module configured to calculate an H1 integrity protection level for each of the one satellite removed positions using the position bias, and select a largest H1 integrity protection level from a group of H1 integrity protection levels representing the one satellite removed positions. an ephemeris monitor configured to generate, from a plurality of N differential global positioning system 'GPS' satellite measurements where N is at least five, an H1 integrity protection level from an N number of one satellite removed positions, wherein a one satellite removed position is derived by one of the differential GPS satellite measurements being removed from the plurality of N differential GPS satellite measurements; wherein the ephemeris monitor further comprises: a solution module configured to calculate a one satellite removed position by removing one differential measurement from one GPS satellite in a plurality of N GPS satellites (120-128) from the differential measurements of the plurality of N GPS satellites (120-128); a bias module configured to calculate a position bias between the one satellite removed positions and a N satellite position, where the N satellite position uses the differential measurements of the plurality of N GPS satellites (120-128); and an H1 protection level module configured to calculate an H1 integrity protection level for each of the one satellite removed positions using the position bias, and select a largest H1 integrity protection level from a group of H1 integrity protection levels representing the one satellite removed positions. a solution module configured to calculate a one satellite removed position by removing one differential measurement from one GPS satellite in a plurality of N GPS satellites (120-128) from the differential measurements of the plurality of N GPS satellites (120-128); a bias module configured to calculate a position bias between the one satellite removed positions and a N satellite position, where the N satellite position uses the differential measurements of the plurality of N GPS satellites (120-128); and an H1 protection level module configured to calculate an H1 integrity protection level for each of the one satellite removed positions using the position bias, and select a largest H1 integrity protection level from a group of H1 integrity protection levels representing the one satellite removed positions. <EOS>