Note: Descriptions are shown in the official language in which they were submitted.
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AIRCRAFT LANDING SYSTEM USING RELATIVE GNSS
TECHNICAL FIELD
[0001] The present invention relates to the field of
aircraft landing systems, and in particular, to aircraft
landing systems when there is no known survey point for the
mobile base station.
BACKGROUND
[0002] GPS as a stand-alone system is known to have
several deficiencies that prevent it from enabling aircraft
precision approach.
[0003] Lack of positional accuracy and integrity. Sources
of error are known to be at least satellite clock alignment
error, ephemeris error, and error due to signal propagation
through the atmosphere. These errors can introduce several
meters of error in an aircraft's position. Uncertainty of
these errors contribute to the lack of system integrity,
which is required to enable precision approach. Such errors
must be corrected in real time to enable precision approach
where there is little or no visibility.
[0004] In the case where GPS experiences sudden system
accuracy corruption, GPS lacks the ability to immediately
detect such accuracy corruption and provide the immediate
alerts. For example, Instrument Landing Systems self-monitor
and will shut-down immediately if signal corruption is
detected. That is, they prevent Hazardously Misleading
Information from being transmitted to the aircraft in "real-
time". GPS as a stand-alone system has no such ability.for
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real-time self-monitoring that would enable aircraft
precision approach.
[0005] Since GPS alone is unable to provide the sufficient
accuracy and integrity to enable an aircraft to perform a
precision approach, it needs to be augmented. Several
augmentations are known at this time: Ground-Based
Augmentation System (GRAS) and Space-Based Augmentation
System (SBAS). The specific implementations in North America
are known as LAAS and WAAS respectively. These GPS
augmentation systems were developed to provide high accuracy
and high integrity system solutions that enable aircraft to
perform precision approaches. In all cases, these precision
approach solutions apply to known, pre-surveyed, final
approach segments to fixed terrain and provide sufficient
accuracy and integrity to enable the aircraft to perform a
precision approach.
[0006] The Ground-Based Augmentation System (GBAS) is an
all-weather aircraft landing system based on real-time
differential correction of a Global Positioning System (GPS)
signal; the Local Area Augmentation System (LAAS) is one
implementation of GBAS and GPS is one satellite constellation
forming the Global Navigation Satellite System (GNSS). A GBAS
ground station is installed at a known and fixed site and
transmits differential GPS (DGPS) corrections to be applied
to an aircraft. The ground GPS antenna location has been
surveyed and certified at a fixed site, and the corrections
are based on the surveyed and motionless antenna.
[0007] The data link between the LAAS ground station and
the LAAS avionics is called a Very High Frequency Data
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Broadcast (VDB) data link. The LAAS ground transmitter is
called a VDB transmitter and the LAAS avionics receiver is
called a VDB receiver. The final approach segment is a known
and surveyed approach. This final approach segment data is
transmitted on the VDB data link.
[00081 The Spaced-Based Augmentation System (SBAS) is an
all-weather aircraft navigation and landing system based on
real-time differential correction of a Global Positioning
System (GPS) signal; the Wide Area Augmentation System (WAAS)
is one implementation of SBAS. A network of SBAS ground
stations is installed at known and fixed sites and transmits
differential GPS (DGPS) corrections to be applied to an
aircraft. As in the case of GBAS, the final approach segment
is a known and surveyed approach. This final approach segment
data is stored in a database and is used when the approach is
selected by the pilot.
[00091 Within their coverage and applicability areas, both
SBAS and GBAS provide the capability for the corresponding
SBAS and/or GBAS receiver to accurately determine the
position/location of the aircraft with integrity. However,
when an aircraft must land in an area without a pre-surveyed
point, such as in a rescue operation on a mountain, or on a
mobile platform, such as a floating oil rig, or approach a
mobile platform, such as an airborne tanker for refueling, it
is no longer possible to use GRAS or SEAS since both systems
are based on the final approach being specified with respect
to known, previously surveyed, stationary earth-fixed point
from which integrity and differential corrections are
derived.
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[00101 Therefore, there is a need to adapt aircraft
landing systems such that they may be used on moving
platforms and/or on a fixed ground station without a
previously surveyed location, while providing the required
accuracy, and more importantly, the required integrity that
enables aircraft precision approach.
SUMMARY
[00111 The system described herein is based on Relative
GNSS (RGNSS), such that integrity is provided for the RGNSS
aircraft landing system. This includes airborne aircraft
rendezvous since the principles apply to both moving and
earth-fixed base stations. The mobile base station is
understood to be installed on a moving or ground-fixed
platform that the aircraft will either approach or land on.
Furthermore, the mobile base station will provide the
aircraft final approach segment or the data required to
construct it, among other data, to the aircraft.
[00121 In accordance with a first broad aspect, there is
provided an aircraft landing system comprising: at least two
mobile base station GNSS antennae at known fixed distances
for receiving signals from a GNSS satellite constellation; a
mobile base station module operatively connected to the at
least two mobile base station GNSS antennae and adapted to
receive GNSS signals from the at least two GNSS antennae,
extract measurement data therefrom, and determine relative
positions of the GNSS antennae for specifying an approach
path with respect to the relative positions of the mobile
base station GNSS antennae, the mobile base station module
also adapted to calculate a measured distance between the at
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least two mobile base station GNSS antennae using the
relative positions and compare the measured distance with the
known fixed distance to determine mobile base station
integrity; and a data transmitter for transmitting to an
aircraft mobile base station integrity data, approach path
data, and GNSS measurement data for at least one of the at
least two mobile base station GNSS antennae.
[0013] In one embodiment, the aircraft landing system also
comprises an air GNSS antenna for receiving signals from the
GNSS satellite constellation; an air data receiver for
receiving the mobile base station integrity data, the
approach path data, and the measurement data; and an air
module connected to the data receiver and to the air GNSS
antenna and adapted to extract and validate satellite data
from the GNSS satellite constellation signals, determine a
relative position of the air GNSS antenna to the at least one
of the at least two mobile base station antennae using the
extracted satellite data, the mobile base station measurement
data, and the mobile base station integrity data, and
determine approach guidance for the aircraft using the
relative position of the air GNSS antenna to the at least one
of the at least two mobile base station antennae and the
approach path data.
[00141 In accordance with a second broad aspect, there is
provided a method for confirming mobile base station
integrity in a relative GNSS aircraft landing system, the
method comprising: determining a relative position of a first
GNSS antenna fixed to the mobile base station with respect to
a second GNSS antenna also fixed to the mobile base station
by processing signals from a GNSS satellite constellation;
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calculating a distance between the first GNSS antenna and the
second GNSS antenna using the measured relative position;
comparing a calculated distance to a known fixed distance;
and confirming mobile base station integrity if the
calculated distance is within a predetermined threshold of
the known fixed distance.
[0015] In accordance with a third broad aspect, there is
provided a method for aircraft approach and landing using
relative GNSS positioning, the method comprising: determining
relative positions of at least two mobile base station GNSS
antennae provided at a known fixed distance; determining an
approach path relative to the at least two mobile base
station GNSS antennae; confirming mobile base station
integrity by comparing a measured distance between the
mobile base station GNSS antennae with the known fixed
distance; transmitting to an aircraft the mobile base station
integrity data, approach path data, and satellite measurement
data for one of the at least two mobile base station GNSS
antennae; receiving the mobile base station integrity data,
the approach path data, and the satellite measurement data at
the aircraft; determining a relative position with integrity
of an air GNSS antenna on the aircraft with respect to one of
the at least two mobile base station GNSS antennae using
combined satellite measurements from the air antenna and the
mobile base station antenna; and determining approach
guidance using the relative position of the air and mobile
base station GNSS antennae and the approach path data.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Further features and advantages of the present
invention will become apparent from the following detailed
description, taken in combination with the appended drawings,
in which:
[0017] Fig. 1 illustrates an aircraft landing system with
mobile base station and air portion, in accordance with one
embodiment;
[0018] Fig. 2 illustrates the aircraft landing system of
figure 1 with a mobile base station system closed loop check,
in accordance with one embodiment;
[0019] Fig. 3 illustrates an embodiment of the mobile base
station portion of the aircraft landing system of figure 1,
where the two GPS receiver antennae are provided on a single
landing system mobile base station unit;
[0020] Fig. 4 is a block diagram of a VDB transmitter, in
accordance with one embodiment;
[0021] Fig. 5 is a block diagram of a VDB receiver, in
accordance with one embodiment;
[0022] Fig. 6 is a block diagram of a landing system
mobile base station unit, in accordance with one embodiment;
[0023] Fig. 7 is a block diagram of a landing system air
unit, in accordance with one embodiment;
[0024] Fig. 8 is a block diagram of a mobile base station
computer, in accordance with one embodiment;
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[0025] Fig. 9 is a flowchart illustrating a method for
confirming mobile base station integrity in a relative GNSS
aircraft landing system, in accordance with one embodiment;
and
[0026] Fig. 10 is a flowchart illustrating a method for
aircraft approach and landing using relative GPS, in
accordance with one embodiment.
[0027] It will be noted that throughout the appended
drawings, like features are identified by like reference
numerals.
DETAILED DESCRIPTION
[0028] Figure 1 illustrates an exemplary embodiment of an
aircraft landing system 100, also referred to as Relative
GNSS (Global Navigation Satellite System) Aircraft Landing
System (RGLS). The system 100 consists of a mobile base
station portion 101 and an air portion 103. The mobile base
station portion 101 is found either on a mobile platform,
such as an oil rig or another type of platform on water, in
the air, or on fixed ground. The air portion 103 is provided
in any type of aircraft, such as a helicopter, a commercial
airplane, a cargo airplane, a recreational airplane, etc.
[0029] A mobile base station module 102 is provided as the
central part of the mobile base station portion 101. The
mobile base station module 102 is operatively connected to a
pair of mobile base station GPS antennae 112, 114 and adapted
to receive GPS signals, extract measurement data, and
determine the positions of the GPS antennae 112, 114 either
as absolute positions or relative to one another or both. The
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mobile base station module 102 is also adapted to calculate a
measured distance between the two mobile base station GPS
antennae 112, 114 using their respective absolute or relative
positions and compare the measured distance with a known and
fixed distance to determine mobile base station integrity.
[0030] In one embodiment, the mobile base station module
102 comprises a mobile base station computer 106. The mobile
base station computer 106 is responsible for data collecting,
processing, and distributing as will be explained in more
detail below. A first landing system mobile base station unit
108 is connected to the mobile base station computer 106 via
a wired or wireless connection. The landing system mobile
base station unit 108 is connected to a first GPS antenna
112. A second landing system mobile base station unit 110 is
also connected to the mobile base station computer 106, via a
wired or wireless connection. A second GPS antenna 114 is
connected to the second landing system mobile base station
unit 110.
[0031] GPS antenna 112 and GPS antenna 114 are provided at
a fixed distance. They both receive signals from a satellite
constellation 130 in order to quickly and accurately
determine the latitude, the longitude, and the altitude of
the point at their respective antenna sites. Alternatively,
the landing system units combine the information distributed
by the mobile base station computer with its own satellite
signal measurements to determine the relative position of the
mobile base station antennae in a manner similar to a landing
system air unit 124. The known distance between the two
antennae 112, 114 is compared with the calculated distance
between the two measured positions obtained individually via
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the satellites 130 or with the calculated distance obtained
from the measured relative position provided by one or both
landing system units. Mobile base station integrity is
therefore obtained when the calculated distance and the known
distance match within a pre-determined threshold. The
determination of integrity and/or determination of positions
may be done in the mobile base station computer 106 or in the
landing system mobile base station units 108, 110.
[0032] Also present in the mobile base station portion 101
of the system 100 is a data transmitter 116 used to transmit
data to the air portion 103 of the system 100. In one
embodiment, data received by the data transmitter 116 from
the mobile base station computer 106 is modulated such that
it may be sent via Radio Frequency (RF) signals, using an RF
antenna 118. In one embodiment, the data transmitter is a
Very High Frequency (VHF) Data Broadcast (VDB) unit that
transmits in the VHF band between 108HZ-118Hz using a format
compatible with the LAAS VBD ICD RTCA/DO-246C.
[0033] The air portion 103 of the system 100 comprises a
data receiver 120 equipped with an RF antenna 122 for
receiving the signals sent by the data transmitter 116. Once
received, the signals are demodulated by the data receiver
120 and sent to an air module 104, which comprises a landing
system air unit 124. In one embodiment, a LAAS VBD receiver
serves as the data receiver. The air module 104 is connected
to a GPS antenna 126 that receives signals from a satellite
constellation 130 to determine the latitude, longitude, and
altitude of the aircraft. A relative position of the aircraft
is determined using the data received from the satellite
constellation 130 and the information from the data receiver
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120. In one embodiment, a landing system unit 124 extracts
the appropriate information from the received data and sends
it to various aircraft equipment.
[0034] As in the case of the Mobile Base Station, airborne
integrity may be derived in a manner identical to the Mobile
Base Station Module 101. This can be done by installing at
least two GPS antennae 126 on the aircraft and measuring the
distances between these GPS antennae 126, and providing this
information to the landing system air unit 124. The
methodology for determining airborne integrity would be
identical to the mobile base station module 101.
[0035] The satellite measurement data of the antenna on
the aircraft 122 and of the antennae 112, 114 on the mobile
base station are used in a relative manner to allow the
aircraft to land on the mobile platform. Conceptually, one
GPS antenna 112 on the mobile base station is used as the
approach landing point (or end point) on the mobile base
station. The other GPS antenna 114 on the mobile base station
is used to define an approach vector from GPS antenna 112 to
GPS antenna 114. This approach vector may be used to define
approach path azimuth, approach path elevation, or both, and
an approach landing point and direct the aircraft in its
approach. In practice, the approach path is constructed
relative to this vector, translated and rotated as
appropriate to the geography of the area. Several such
relative approach paths can be so constructed to allow
landing under various conditions such as different wind speed
and direction. When multiple approach paths are transmitted,
the pilot selects the appropriate path in the air module.
Alternatively, the air module can construct the path based on
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raw approach data from the base station and pilot input of
relevant data such as wind speed.
[00361 Figure 2 illustrates another embodiment of the
aircraft landing system 100, whereby a mobile base station
system closed loop check is provided. In this embodiment, a
replica of the data receiver 120 with its RF antenna 122 and
the landing system air unit 124 with its GPS antenna 126 is
also provided on the mobile base station in order to confirm
the data sent by the mobile base station portion 101 to the
air portion 103. As RF antenna 118 sends out its modulated
signal, it will be received by the RF antenna 122 on the
aircraft as well as antenna 122 on the mobile base station.
The modulated data will be demodulated by the data receiver
120 on the mobile base station in the same way that it is
demodulated in the air, and it will be transmitted to the
landing system air unit 124 on the mobile base station. This
air unit will validate the data and can transmit to the
mobile base station computer 106 statistics on the received
data like the number and type of messages received and any
message decoding errors. This will allow the mobile base
station computer to report on the health of the data
transmission and shut off the transmission as required. In
another embodiment (not illustrated), the data will return to
the mobile base station computer 106 directly from the data
receiver 120 on the mobile base station and it can be
compared with the original sent data to confirm that the data
received by the aircraft is indeed the intended data.
[00371 Figure 3 illustrates only the mobile base station
portion 101 of the system 100. In the embodiment illustrated,
a single landing system mobile base station unit 302 is
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provided in the mobile base station module 102, with GPS
antenna 112 and GPS antenna 114 provided thereon separated by
a fixed distance. The mobile base station computer 106 is the
central processing unit for the measurements provided by the
landing system mobile base station unit 302, the external
sensors 304, and any operator input to produce the data for
the data transmitter 116. As stated above, the calculations
based on received data may be performed either in the landing
system mobile base station unit 302 or in the mobile base
station computer 106.
[0038] In another alternative embodiment, the mobile base
station module 102 may consist of only a single integrated
unit (not shown) adapted to perform all of the functions of
the mobile base station computer 106 and the landing system
mobile base station unit 302, or of two landing system mobile
base station units 108, 110 as illustrated in figure 1, with
all of the functions and capabilities of the mobile base
station computer 106 integrated in one or both of the landing
system mobile base station units 108, 110.
(0039] Figure 4 is a block diagram illustrating an
embodiment of the data transmitter 116. In one embodiment,
data transmitter 116 is a basic coder/modulator which can
convert digital data into an analog (modulated-wave) signal
suitable for RF transmission. A digital signal 402 is
received from the mobile base station computer 106 and a data
modulator 404 converts the signal 402 into a modulated analog
signal 406. The analog signal 406 is sent to transmitter 408
for transmission via the RF antenna 118.
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[0040] Various types of data may be provided in the
digital signal 402 to be sent to the aircraft. In addition to
the mobile base station integrity data, the mobile base
station satellite measurement data, and the approach path
data, other types of data such as weather data (for example
the wind direction and speed, and current visibility),
platform orientation (roll, pitch, yaw), multiple approach
paths, platform outline and salient features (heliport
location, main obstructions), magnetic variation, and mobile
base station operator messages may also be embedded in the
data. The sensors 304 illustrated in figure 3 can be a source
of this additional digital data. An interface to the mobile
base station computer like a keyboard can also be provided
for operator messages.
[0041] Figure 5 is block diagram of the data receiver 120
found in the air portion 103 of the system 100. Similarly to
the data transmitter 116, a basic demodulator/decoder adapted
for data demodulation may be used. An RF signal 504 is
received by a receiver 502 via RF antenna 122 and sent to a
data demodulator 506. A digital signal 508, i.e. a series of
decoded bits matching digital signal 402 is output from the
data receiver 120.
[0042] Figure 6 is a block diagram illustrating an
exemplary embodiment of landing system mobile base station
unit 108. A GPS antenna 112 receives an RF signal from the
satellite constellation 130 via receiver 602. This signal is
sent to a data extraction module 604, where measurement data
such as pseudo-ranges, carrier cycles, ephemeris, and
satellite position, is extracted therefrom. The extracted
data is sent to a position determination module 606, whereby
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the position of antenna 112 is calculated and sent to the
mobile base station computer 106 along with the satellite
measurement data. In an alternative embodiment, extracted
data is sent directly to the mobile base station computer 106
and position determination is performed therein.
[0043] In one embodiment, the landing system air unit 124
is a GPS Landing System Sensor Unit (GLSSU) per ARINC
characteristic 743B augmented to perform the relative
positioning function. The landing system air unit 124 may be
designed to meet all requirements applicable to airborne
equipment such as TSO-C145c Beta-3, TSO-C146c Delta-4, and
TSO-C161a. As such, it would be designed to meet FAA
certification FAR Part-25, RTCA/DO-178B Level B and RTCA/DO-
254 Level B requirements, RTCA/DO-160E environmental
requirements.
[0044] Landing system mobile base station units 108 and/or
110 may be a replica of the landing system air unit 124 or it
may have alternative and/or additional features and
capabilities. Replicating the air unit 124 within the mobile
base station module 102 provides a convenient way for one
mobile base station module 102 to receive data from the
second mobile base station air unit 124 via the mobile base
station computer 106 in order to compute the relative
position of the two mobile base station GPS antennae. In such
an embodiment, the mobile base station computer need only
compare this relative position to the fixed distance between
these antennae in order to confirm mobile base station module
integrity, as described above.
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[0045] Figure 7 is a block diagram illustrating an
exemplary embodiment of landing system air unit 124.
Similarly to landing system mobile base station unit 108, an
RF signal is received from the satellite constellation 130
via GPS antenna 126 to receiver 702. The received signal is
sent to data extraction module 704 and extracted data is then
sent on to position determination module 706, which also
receives the decoded data from the data receiver 120. The
position determination module 706 applies an integrity
algorithm to the received satellite signals, computes the
relative position of the airborne antenna with respect to the
mobile base station antenna and provides guidance along the
specified approach path. The integrity algorithm may be
augmented by the same type of RGNSS integrity computation as
used in the mobile base station using the known distances
between the airborne antennae 126. As indicated above, the
decoded data may contain various types of information, such
as mobile base station operator messages, weather data, etc.
This additional data is processed into a format appropriate
for use by other aircraft equipment.
[0046] Figure 8 is a diagram illustrating an exemplary
embodiment for the mobile base station computer 106. Various
types of data, such as sensor data, operator inputs, mobile
base station unit data, etc, may be received by the mobile
base station computer 106 and stored in a memory 802. A
processor 804 can access the memory 802 to retrieve the
stored data. A plurality of applications 806a, 806b, 806n are
running on the processor 804. One application may be used to
establish mobile base station integrity, as described above.
This application uses the measured relative positions of
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antenna 112 and antenna 114 as input, as well as the known
fixed distance between antenna 112 and antenna 114. A
statistical threshold may be used to determine whether there
is integrity or not. Another application of the mobile base
station computer 106 may be used to package platform
orientation data in order to send it to the aircraft. Yet
another application may be used to construct the approach
path (with operator assistance as needed) at the desired
location with respect to the position of GPS antenna 112 to
ensure that the aircraft properly aligns itself during
landing. Various other applications will be readily
understood by the person skilled in the art. Data to be sent
to the data receiver 120 may be retrieved from memory 802.
[0047] Figure 9 is a flowchart illustrating a method for
confirming mobile base station integrity, in accordance with
one embodiment. In the first steps 902, 904, measured
positions of a first GPS antenna and a second GPS antenna are
determined. The two GPS antennae are at a known fixed
distance from each other. Determining their measured
positions may be done using any of the embodiments described
above, such as receiving satellite signals, extracting data
from the signals, and calculating the respective positions of
the GPS antennae. The positions may be calculated using
various information, such as pseudo-range and/or carrier
cycle measurements of the signal, ephemeris, satellite
location, etc.
[0048] In a following step 906, a distance between the
first GPS antenna and the second GPS antenna is calculated.
This distance is calculated using the two measured positions
previously determined. As described previously, another
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embodiment (not illustrated) directly determines the relative
position of the two antennae from the combination of
satellite measurements from both GPS antennae; this relative
position is then used to compute the distance between the two
antennae. The calculated distance is then compared with the
known fixed distance 908. Mobile base station integrity is
confirmed when the calculated distance and the known fixed
distances are within a predetermined threshold value of each
other 910.
[0049] This method may be used to confirm mobile base
station integrity in the case of a mobile platform, such as
an oil rig, or in an area where no pre-surveyed point can be
used. Mobile base station integrity data may be transmitted
to an aircraft indicating whether or not mobile base station
integrity is confirmed and also providing satellite specific
integrity information. The integrity data can be sent with
other data typically transmitted to an aircraft, such as the
pseudo-range measurements to the GPS satellites, weather
data, approach path, platform orientation, etc.
[0050] Persons skilled in the art will recognize that the
satellite measurements will normally be taken simultaneously
within each GPS antenna on the mobile base station 112, 114
and in the air 122 but that the measurement time for each
antenna may be different. Some advantage may be gained by
making measurements simultaneous between mobile base station
antennae especially in a moving platform but such a
measurement method is optional.
[0051] Figure 10 is a flowchart of a method for aircraft
approach and landing using relative GPS. The first step
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consists in determining mobile base station positions
(absolute and/or relative) of the two mobile base station GPS
antennae that are provided at a known fixed distance 1002.
Once this information is obtained, mobile base station
integrity is confirmed by comparing the measured distance
between the two GPS antennae to the known fixed distance
1004. The mobile base station satellite measurement data, the
approach path data, and the mobile base station integrity
data are transmitted to an aircraft 1006. This information is
received at the aircraft 1008. A GPS antenna on the aircraft
is used to receive the signals from the satellite
constellation, apply an integrity algorithm, possibly apply
the same type of integrity algorithm employed in the mobile
base station, and determine its relative position to the
mobile base station antenna 1010. Approach guidance is
determined using this relative position and the relative
approach path received from the mobile base station 1012 in a
manner that cancels any common mode errors in the satellite
measurements to the air and mobile base station antennae.
[00521 RGLS is based on relative GNSS positioning
(guidance to the mobile base station antenna regardless of
motion or location of the mobile base station), not
differential GPS (DGPS). No mobile base station position pre-
survey is required and corrections per se are not
transmitted. Actual mobile base station satellite
measurements and a relative approach path definition are
transmitted in support of relative GNSS positioning. This
avoids significant certification and installation issues. In
addition, weather data such as wind speed, wind direction,
and visibility data may be transmitted from the mobile base
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station to the aircraft. Platform attitude and orientation,
as well any operator message may also be transmitted from the
mobile base station.
[0053] The embodiments described above consist of only two
GPS antennae 112, 114 connected to landing system mobile base
station units 108, 110. This represents a minimum
configuration and is used as an example for its simplicity.
Further advantages may be derived from multiple GPS antennae
with respect to determining mobile base station integrity and
approach path definition. The basic concept for determining
mobile base station integrity in a timely fashion is the use
of two mobile base station antennae at a fixed known relative
position from one another. This known relative position can
be limited to only the distance between the two antennae or
include two or three-dimensional offset. There is no
requirement for the absolute position of these antennae to be
provided to the mobile base station by means of a survey or
any other process that the mobile base station cannot perform
on its own.
[0054] With respect to the air portion 103 of the system
100, the RGLS function may be enabled within WAAS/LAAS
equipment. The same data receivers as those used in LAAS may
be used to enable the RGLS function as well. With respect to
the mobile base station portion 101 of the system 100, Flight
Management System (FMS) hardware may be used as the mobile
base station computer 106.
[0055] In one embodiment, landing system air unit 124 is
designed to operate using LAAS and/or, WAAS (Wide Area
Augmentation System) infrastructure and may be selectively
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set for LAAS, WAAS, or RGLS. The single unit may be used as a
primary means of navigation.
[0056] The embodiments described above discuss the use of
GPS satellites however the same principles apply to the use
of SBAS or Galileo satellites or any other satellite system
that provide signals for safety of life aircraft operations
generally known as Global Navigation Satellite Systems
(GNSS). Nothing herein should be interpreted to limit this
invention to the sole use of the GPS satellite constellation
or even require the use of any particular satellite
constellation or combination thereof.
[0057] While illustrated in the block diagrams as groups
of discrete components communicating with each other via
distinct data signal connections, it will be understood by
those skilled in the art that the embodiments are provided by
a combination of hardware and software components, with some
components being implemented by a given function or operation
of a hardware or software system, and many of the data paths
illustrated being implemented by data communication within a
computer application or operating system. The structure
illustrated is thus provided for efficiency of teaching the
present preferred embodiment.
[0058] It should be noted that the present invention can
be carried out as a method, can be embodied in a system, a
computer readable medium or an electrical or electro-magnetic
signal. The embodiments of the invention described above are
intended to be exemplary only. The scope of the invention is
therefore intended to be limited solely by the scope of the
appended claims.
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