US 5,786,773 A · Local-area augmentation system for satellite navigation precision-approach system

Abstract

An aircraft local-area augmentation system that employs a differential global positioning system (GPS) to assist aircraft (102) landing is disclosed. One or more GPS ground stations (120), each including at least two GPS receivers (122) and a datalink transmitter (126), calculate and transmit GPS correction data to an aircraft (102). An aircraft (102) employs a GPS receiver (106) for receiving ranging signals (112) from GPS satellites (108), and a datalink receiver (116) for receiving GPS correction data and other information from a GPS ground station (120). The aircraft (102) further includes a data processor (110) for determining a global position of the aircraft (102) as a function of the aircraft GPS pseudorange data and the GPS correction data. The system minimizes the introduction of non-common errors by the use of double-differencing calculations using multiple combinations of satellite (108) and GPS ground station receiver (122). The system further comprises a method of transmitting a digital signature (626) from a GPS ground station (120) to an aircraft (102), in order to authenticate transmitted messages, thereby detecting spoofing. Messages transmitted from a GPS ground station (120) on a datalink (128) include an almanac message (930), providing data useful for locating other GPS ground stations (120), and a NOTAM message (940), providing satellite (108) status information. The airborne datalink receiver (116) includes an autonomous scanning mode that scans available datalink frequencies and time slots, searching for datalink signals (128). One or more optional pseudolite stations (130) employing a spread spectrum code sequence improve the accuracy and reliability of the system. The inclusion of an ILS glideslope frequency (952) in the datalink allows an airborne receiver to operate in a hybrid mode, combining a differential GPS determination of horizontal position with an ILS determination of altitude.

Claims37

Dependent claims

A landing assistance system to provide navigation information to an aircraft, said landing assistance system including:

(a) a plurality of satellites transmitting satellite signals containing satellite data sufficient to determine an approximate range between said aircraft and each satellite;
and
(b) at least one GPS ground station positioned at a fixed location on the ground, said GPS ground station including:
(i) a plurality of receivers operative for receiving said satellite signals and determining pseudoranges to said satellites, said plurality of receivers determining at least four pseudoranges, each pseudorange representing an approximate distance between one receiver and one satellite and having a corresponding error representing a deviation between said pseudorange corresponding to one receiver and one satellite and an actual distance between said one receiver and said one satellite associated with said pseudorange;
(ii) at least one data processor operative for determining differential correction information, said differential correction information determined by determining said error corresponding to each said pseudorange, each said error consisting of common mode errors and non-common mode errors, differentiating said common mode errors from said non-common mode errors, and filtering out pseudorange measurements having corresponding non-common mode errors that exceeds a threshold, said differentiation of said common mode errors from said non-common mode errors performed based on a comparison of said each error associated with said four pseudoranges;
and
(iii) a datalink transmitter operative for transmitting a datalink signal containing said differential correction information.

4 more elements

In a differential global positioning system comprising a plurality of satellites transmitting ranging signals, at least one GPS ground station having multiple receivers for receiving said ranging signals, at least one transmitter operative for transmitting datalink signals, and a data processor operative for determining differential correction information, said differential correction information determined by determining an error corresponding to each pseudorange, each said error consisting of common mode errors and non-common mode errors, an aircraft having a receiver operative for receiving said datalink signals, an improvement comprising filtering out pseudorange measurements having corresponding non-common mode errors that exceeds a threshold, differentiating the common mode errors from the non-common mode errors is based on a comparison of said each error associated with four pseudoranges, said comparison including determining a first difference by subtracting a first error from a second error, determining a second difference by subtracting a third error from a fourth error, and determining a double difference by subtracting said first difference from said second difference.

A method of automatically providing navigational assistance data including differential correction data, for use in a differential global positioning system employing multiple GPS satellites and at least one GPS ground station having multiple receivers, to an aircraft, the method comprising:

(a) receiving ranging signals from at least two GPS satellites, including a first GPS satellite and a second GPS satellite, said ranging signals received at a plurality of receivers, including a first receiver and a second receiver;
(b) determining, in accordance with said ranging signals, at least four unique pseudoranges between said GPS satellites and said receivers;
(c) determining, in accordance with said at least four pseudoranges and a known location of said receivers, an error corresponding to each of said pseudoranges, said error consisting of common mode errors and non-common mode errors;
(d) determining a first difference by subtracting a first error from a second error, determining a second difference by subtracting a third error from a fourth error, and determining a double difference by subtracting said first difference from said second difference, said double difference substantially consisting of non-common mode errors;
(e) combining a plurality of double differences in a manner such that the non-common mode errors associated with a particular combination of satellite and receiver are unevenly weighted in comparison with the non-common mode errors associated with different combinations of satellite and receiver;
(f) filtering out pseudoranges comprising non-common mode errors that vary from an expected value by a predetermined acceptable variation from said expected value;
(g) determining differential correction data based on pseudoranges that remain after said filtering out pseudoranges comprising said non-common mode errors that vary from said expected value by the predetermined acceptable variation from said expected value;
and
(h) transmitting a datalink signal containing said differential correction data.

6 more elements

Dependencies are inferred from the claim text.

Local-area augmentation system for satellite navigation precision-approach system

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Local-area augmentation system for satellite navigation precision-approach system

Life of this patent

Abstract

Claims37