Method and device for determining protection levels for satellite navigation systems
A method and apparatus for determining protection levels in a satellite navigation system includes the following steps: (1) determining an integrity risk at the alert limit for a plurality of application situations—for example, starting from approaches in category I (Category I precision approach) up to the operation “oceanic enroute;” (2) determining an interval of the alert limits between the largest set of alert limits which produces too high an integrity risk, and the smallest set of alert limits which produces an acceptable integrity risk; and (3) carrying out an interval nesting for the interval of the alert limits that was determined in the previous step, the integrity risk between the horizontal and the vertical being divided in the same way as it is obtained from the relationship between these integrity risks in the largest set of alert limits.
1. A method for determining protection levels in a satellite navigation system, which method comprises:
determining, with a device for receiving signals of the satellite navigation system, an integrity risk at an alert limit for a plurality of application situations;
determining, with said device, alert limit intervals between horizontal and vertical alert limits producing an excessive integrity risk that exceeds a specified integrity risk and horizontal and vertical alert limits producing an acceptable integrity risk that does not exceed said specified integrity risk;
carrying out, with said device, interval nesting sequences for the alert limit intervals determined by (a) determining horizontal integrity risks at centers of horizontal intervals and changing ends of the horizontal intervals until the horizontal interval size is no larger than a selected percentage of a lower horizontal alert limit, and (b) determining vertical integrity risks at centers of vertical intervals and changing ends of the vertical intervals until the vertical interval size is no larger than a selected percentage of a lower vertical alert limit;
setting, with said device, a horizontal protection level to an upper end of the horizontal interval having said horizontal interval size; and
setting, with said device, a vertical protection level to an upper end of the vertical interval having said vertical interval size.
2. A device for determining protection levels in a satellite navigation system, which device comprises:
a receiver that receives satellite navigation system signals; and
a processor for:
determining from said satellite navigation system signals an integrity risk at an alert limit for a plurality of application situations;
determining alert limit intervals between horizontal and vertical alert limits producing an excessive integrity risk that exceeds a specified integrity risk and horizontal and vertical alert limits producing an acceptable integrity risk that does not exceed said specified integrity risk;
carrying out interval nesting sequences for the alert limit intervals determined by (a) determining horizontal integrity risks at centers of horizontal intervals and changing ends of the horizontal intervals until the horizontal interval size is no larger than a selected percentage of a lower horizontal alert limit, and (b) determining vertical integrity risks at centers of vertical intervals and changing ends of the vertical intervals until the vertical interval size is no larger than a selected percentage of a lower vertical alert limit;
setting a horizontal protection level to an upper end of the horizontal interval having said horizontal interval size; and
setting a vertical protection level to an upper end of the vertical interval having said vertical interval size.
3. The method as defined by claim 1 , wherein said selected percentage of the lower horizontal alert limit is one percent of said lower horizontal alert limit.
4. The method as defined by claim 1 , wherein said selected percentage of the lower vertical alert limit is one percent of said lower vertical alert limit.
5. The device as defined by claim 2 , wherein said selected percentage of the lower horizontal alert limit is one percent of said lower horizontal alert limit.
6. The device as defined by claim 2 , wherein said selected percentage of the lower vertical alert limit is one percent of said lower vertical alert limit.