Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2002-11-01
2004-11-30
Camby, Richard M. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S214000, C701S215000, C342S357490, C342S357490
Reexamination Certificate
active
06826476
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to satellite based positioning systems such as GPS and more specifically to the measurement and monitoring of the signals transmitted by differential satellite augmentation systems.
2. Description of Related Art
A satellite based positioning system is used to determine a position of a receiver and typically includes a plurality of satellites, the receiver, and one or more ground stations. Each of the satellites transmits a signal that contains a code and certain prescribed information useful to the receiver in determining its position.
The receiver synchronizes itself to the codes of at least four satellites and uses the information in the signals from these satellites in order to perform a triangulation-like procedure so as to determine its coordinates with respect to a reference, such as the center of the Earth and the GPS standard time. The receiver is not constrained to a specific location and, therefore, represents a variable position. The purpose of the satellite based positioning system is to make it possible for the receiver to determine its position regardless of the location of the receiver.
The accuracy of the position determined by the receiver is adversely affected by conditions that are common to all receivers in a given area. A ground station containing a receiver in a fixed location is used to monitor the signals transmitted by the satellites and determines corrections to the transmitted satellite signal. The ground station notifies the receiver of any necessary signal corrections to allow the receiver to make more accurate position calculations. This arrangement is referred to as differential positioning.
Since the mobile receiver completely relies on the corrections transmitted from the ground station as being correct, any condition that is inconsistent between the satellite measurements made at the mobile receiver and the ground station will cause a an undetected error in the mobile receiver. To protect the mobile receiver, the ground station monitors the signals transmitted by the satellites in order to detect faults within the satellites that would affect the mobile receiver. This function of detecting faults is referred to as providing integrity for the corrections that the ground station sends to the mobile receiver. For GPS, these faults include signal power, code signal deformation, code and carrier divergence, radio frequency interference, signal acceleration and erroneous ephemeris data.
The ground station system is also referred to as an augmentation system, since it augments both the accuracy and integrity of the original navigation satellite signals. There are two classes of augmentation systems: (1) Satellite Based Augmentation System (SBAS) that provides differential positioning across a wide area like the continental US, and (2) Ground Based Augmentation System (GBAS) that provides differential positioning to a smaller area, up to about 200 miles.
Satellite-Based Augmentation System (SBAS)
The known SBAS architecture used for wide-area coverage is shown in
FIGS. 1 and 2
. In the SBAS architecture
10
, a network of receivers
14
is used to collect satellite data
120
, and perform measurements
110
, from the navigational satellites
20
over a satellite to receiver communication path
214
and determine augmentation data
132
, which includes differential corrections, ionospheric delay errors, and accuracy of the navigation satellite signals at the receivers'
14
location.
This measurement data
110
is transferred from the receiver
14
to one or more master stations
12
via a receiver to master station communication path
232
. The master stations
12
are centralized data processing sites used to determine differential corrections and integrity of the augmentation
110
over the SBAS Area of Coverage
16
. The processed SBAS correction and integrity data
132
is then sent to an SBAS satellite
18
via a master station to satellite communication path
212
. This SBAS satellite
18
, that generally functions as a communications repeater, then broadcasts the correction and integrity data
132
via a satellite to SBAS user communication path
218
to any user
23
within the area of coverage
16
. This structure is illustrated in more detail in FIG.
2
.
Ground-Based Augmentation System (GBAS)
According to
FIG. 3
, the Ground Based Augmentation System (GBAS)
30
contains GBAS receivers
32
that measure navigation satellite data
120
provided by the satellite
20
via a satellite to GBAS receiver communication path
240
. These receivers
32
communicate satellite data and ranging measurements
150
to a GBAS processor
34
that determines the differential corrections and integrity of the satellite signals. The processor
34
communicates these corrections and integrity data
152
through a local area transmitter
36
to a GBAS user receiver
38
within the GBAS coverage area. Typically the area of coverage for a GBAS is 30 to 50 miles. This smaller coverage volume allows the GBAS to provide greater levels of accuracy and integrity than the SBAS.
The greater levels of accuracy and integrity lend the GBAS to precision airplane approach applications. Due to the strict integrity requirements of precision approach applications, current GBASs, such as those defined by the FAA in FAA Specification FAA-E-2937A (“FAA-E-2937A”), herein incorporated by reference, contain monitors for detecting the integrity of the satellite signal waveform as well as the integrity of the ranging measurement from the satellites. Use of these monitors and other requirements allow the accuracy, continuity and integrity of GBAS to be much greater than that of SBAS.
Known Solutions
Allowing for more complex operations like precision approach in the SBAS coverage volume requires a greater level of integrity and monitoring than is provided by current SBAS implementations. Two known solutions for addressing enhanced integrity on SBAS have been previously considered.
The first solution applies additional SBAS reference receivers
14
to provide additional sampling points within the coverage area
16
. The measurements from these additional receivers
14
develop a more detailed differential and ionospheric correction. Unfortunately, additional receivers
14
add cost for the receivers
14
and communication links
232
,
234
.
The second solution includes, in the SBAS receivers
14
, satellite signal monitors similar to that required per FAA-E-2937A. These monitors would increase the integrity of the measurements made by the receivers by monitoring for the types of anomalies defined in FAA-E-2937A. However, this solution also requires additional costs to update the numerous current receivers
14
that exist with these new monitors.
SUMMARY OF THE INVENTION
The present invention utilizes the resources of the GBAS station to supplement the measurement and integrity requirements of the of the SBAS station receivers. This is accomplished by an inventive rigorous communication link between the GBAS stations and the SBAS master station and the necessary processing, translation and storage of related information. The present invention also improves the functionality of the GBAS stations by exchanging data between the various GBAS stations on the communication link.
In its most rudimentary form, the GBAS passes raw measurements, corrections, integrity measurements, and integrity monitoring results to the SBAS station via this rigorous link. The SBAS station can utilize this data to produce corrections and monitoring consistent with the same level of rigor as the GBAS system and thereby increasing the SBAS stations integrity. This communication function and master station function mitigate the hazardous and misleading effects that can be caused on the SBAS user by the SBAS receiver. Thus the SBAS receiver can be can be developed to a lower level of certification or potentially completely removed.
Individual GBAS stations can use the data collected from other GBAS stations on the com
Ahlbrecht Mark A.
Hartman Randolph G.
Camby Richard M.
Honeywell International , Inc.
Schiff & Hardin LLP
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