U.S. patent application number 09/993922 was filed with the patent office on 2002-09-19 for satellite based collision avoidance system.
Invention is credited to Farmakis, Tom S., Routsong, Russell D..
Application Number | 20020133294 09/993922 |
Document ID | / |
Family ID | 23120820 |
Filed Date | 2002-09-19 |
United States Patent
Application |
20020133294 |
Kind Code |
A1 |
Farmakis, Tom S. ; et
al. |
September 19, 2002 |
Satellite based collision avoidance system
Abstract
This invention provides a method and apparatus to provide
coordinated evasive maneuver commands to aircraft to avoid
collisions. More specifically, the invention comprises a GPS system
to determined the location of aircraft, control logic to calculate
evasive maneuvers, display aircraft tracking information,
coordinate the evasive maneuver with the intruding aircraft, and
give a synthetic voice warning and command to the pilots.
Inventors: |
Farmakis, Tom S.;
(Sharpsburg, GA) ; Routsong, Russell D.;
(Peachtree City, GA) |
Correspondence
Address: |
Clifton W. Thompson
THORPE, NORTH & WESTERN, L.L.P.
P.O. Box 1219
Sandy
UT
84091-1219
US
|
Family ID: |
23120820 |
Appl. No.: |
09/993922 |
Filed: |
November 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09993922 |
Nov 6, 2001 |
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08291564 |
Aug 16, 1994 |
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6314366 |
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08291564 |
Aug 16, 1994 |
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08062406 |
May 14, 1993 |
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5351194 |
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08062406 |
May 14, 1993 |
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08275547 |
Jul 15, 1994 |
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Current U.S.
Class: |
701/301 |
Current CPC
Class: |
B60R 25/102 20130101;
G08G 1/205 20130101; G01S 2205/002 20130101; G01S 19/14 20130101;
G01S 5/0009 20130101; G08G 5/045 20130101; G01S 5/0072 20130101;
G08G 5/0013 20130101; G01S 2205/008 20130101; G01S 19/36 20130101;
G01S 19/51 20130101; G01S 19/07 20130101; G08G 5/0082 20130101;
B60W 2556/50 20200201; G01S 5/0027 20130101; G08G 9/00 20130101;
G01S 2205/005 20130101; G01S 19/23 20130101 |
Class at
Publication: |
701/301 |
International
Class: |
G06F 017/10 |
Claims
What is claimed is:
1. A method of vehicle collision avoidance using satellite
navigational signals and direct radio communication comprising the
steps of: determining a first vehicle position with a plurality of
satellite navigation signals; determining a second vehicle position
with a plurality of satellite navigation signals; encoding and
transmitting a direct radio messages that includes said first
vehicle identification and position; receiving and decoding a
direct radio message that includes said second vehicle
identification and position; determining by relative vehicle
positions and headings an evasive maneuver to keep said vehicles
separated a predetermined distance.
2. The method of claim 1 further comprising the steps of: encoding
and transmitting a direct radio message that includes said first
vehicle evasive maneuver;
3. The method of claim 2 further comprising the steps of: receiving
and decoding a direct radio message that includes said second
vehicle evasive maneuver.
4. The method of claim 1 further comprising the steps of:
displaying the relative position of said vehicles as a graphic
representation showing the relative bearing and distance on a
display unit. synthesizing an audio alert that informs the pilot of
said evasive maneuver.
5. The method of claim 1 wherein: said vehicle is an aircraft; said
satellite navigation signals are from earth based
pseudo-satellites; said evasive maneuver is a directive to change
the altitude of said vehicles.
6. The method of claim 1 wherein: said vehicle is a sea going
vessel; said satellite navigation signals are from earth based
pseudo-satellites said evasive is a directive to change the course
of said vehicle.
7. A method of vehicle collision avoidance using navigational
satellite signals and direct radio wave communication comprising
the steps of: determining a fixed position with a plurality of
navigational signals; encoding and transmitting a direct radio
message that includes said fixed position; receiving and decoding
said direct radio message; determining by vehicle position and
heading an evasive maneuver to direct said vehicle away from said
fixed position.
8. The method of claim 7 further comprising the steps of:
displaying the relative bearing and distance of said fixed position
on a display unit wherein: said fixed position marks a navigation
obstacle and navigation marker.
9. The method of claim wherein: said encoding and transmitting
direct radio message that includes said fixed position includes a
unique identification code and code representing the type of
navigational hazard; said vehicle position is determined from a
plurality of satellite navigation signals.
10. The method of claim 7 further comprising the steps of: encoding
and transmitting said evasive maneuver; receiving and decoding an
evasive maneuver confirmation signal.
11. An apparatus for vehicle collision avoidance with other like
equipped vehicles using satellite navigation signals and a direct
radio wave message comprising: a satellite receiver for receiving
satellite navigation signals; a control program to format the
direct radio wave message and determine an evasive maneuver; a
computer electrically connected to said satellite receiver for
processing signals from said satellite receiver and executing said
control program; a modem electrically connected to said computer
for transmitting and receiving the direct radio wave message from
the other like equipped vehicles; a transceiver electrically
connected to said modem to transmit and receive data.
12. The apparatus of claim further comprising: a display unit
electrically connected to said computer to display the relative
bearing and distance of the equipped vehicles; an audio interface
electrically connected to said computer to synthesize audio alarms;
a control unit electrically connected to said computer to program
and control the collision avoidance apparatus.
13. The apparatus of claim 12 wherein: said direct radio message is
a time division multiple access protocol message; said modem is
synchronized to said satellite receiver clock.
14. The apparatus of claim 11 wherein: said direct radio message is
a time division multiple access protocol message; said modem is
synchronized to said satellite receiver clock.
15. The apparatus of claim 11 wherein: said computer comprises: a
first microprocessor for satellite signal processing electrically
connected to a second microprocessor or for executing the control
program.
16. The apparatus of claim 15 further comprising: a third
microprocessor electrically connected between said second
microprocessor and said modem for executing the direct radio wave
communication protocol.
17. The apparatus of claim 11 wherein: said direct radio wave is a
skywave; and said satellite navigation signals are from ground
based pseudo-satellites.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of prior U.S.
patent application Ser. No. 08/291,564 filed Aug. 16, 1994; which
is a continuation-in-part of U.S. application Ser. No. 08/062,406
filed May 14, 1993 which is a continuation-in-part of U.S.
application Ser. No. 08/275,547 filed Jul. 15, 1994.
[0002] This application is a continuation-in-part of copending
application Ser. No. 08/062,406, filed May 14, 1993 and
incorporated herein by reference, and is a continuation-in-part of
copending application Ser. No. 08/275,547, filed Jul. 15, 1994.
BACKGROUND OF THE INVENTION
[0003] This invention relates generally to an automatic collision
avoidance control and alert system for tracking and directing
aircraft and other vehicles for collision avoidance. More
specifically, the invention is an improved collision avoidance
system for use in automatically alerting a pilot of a collision
threat and coordinating an evasive maneuver between aircraft. The
expected advantages of such a system is improved collision
avoidance, elimination of false collision alarms and an increased
target tracking capacity. The present invention is directed to such
an automatic vehicular-based system for automatically providing
collision avoidance.
[0004] Since the advent of aviation it has been desirable to avoid
aircraft collisions and near misses. Traditionally, pilots have
used a wholly manual method, i.e. visually identifying other
aircraft and flying to avoid a collision. Such a system is
susceptible to human error and is wholly unworkable in low
visibility conditions or within crowded airspace.
[0005] The use of a ground based air traffic control (ATC) system,
two-way voice radio communications and RADAR greatly enhance the
identification and control of aircraft to avoid collisions. Two-way
voice radio communication allows aircraft to communicate with one
another and the ATC operator to avoid potential conflicts. RADAR,
both on-board aircraft and at ground based ATC facilities provides
an operator intensive technique for avoiding aircraft collisions.
In the present ATC system the ATC operator coordinates the
location, altitude, and track of all aircraft within her assigned
control area by communicating with the aircraft over two-way voice
radio. Present ATC systems consist of a network of airport terminal
area and enroute surveillance radar systems. These systems consist
of both primary and secondary RADAR systems and computers that
display usable data for the control of air traffic in the national
and international airspace systems.
[0006] The basic ATC RADAR system consists of Primary RADAR and
secondary RADAR. Primary RADAR operates by transmitting a high
power, highly directional radio pulse at a known azimuth
(direction, in degrees from North) from a rotating antenna and
measures the time it takes to receive the reflected signal from an
object (aircraft) in space back to the point of transmission. This
time factor determines the range in nautical miles from the radar
site to the target. The direction of the target is determined by
the antenna azimuth from which the signal is received. The
limitations of using only this system result in the loss of targets
because of the difficulty in detecting weak reflected RADAR return
signals attenuated by atmospheric conditions and the difficulty in
operating a synchronized height finding radar.
[0007] Secondary RADAR known as the Air Traffic Control Radar
Beacon System (ATCRBS) utilizes cooperative equipment (a radio
receiver/transmitter or transponder) located in the target aircraft
to replace the conventional radar's passive reflected return signal
with an active reply signal. Like a conventional high power radar,
ground based secondary radar transmits a highly directional pulse
from a rotating antenna that is usually synchronized with the
primary radar antenna. The secondary radar pulse is called the
interrogating signal. The interrogating signal requires much less
power than conventional radar because secondary radar relies on an
active return signal from the target aircraft. In response to
receiving the interrogating signal the cooperative aircraft
transponder automatically transmits a distinctive reply signal back
to the secondary radar's antenna. The secondary radar measures the
time between the interrogating signal transmission and the
transponder reply signal and, like the reflected return in primary
radar, uses this time delay to determine the range of the target
aircraft. The direction of the target aircraft is determined by the
antenna azimuth from which the reply signal is received. The
secondary radar's cooperative transponder improves on the
conventional radar's passive reflective return by encoding
additional information in the transponder reply signal. The
additional information includes an aircraft identification number
and the aircraft pressure altitude. For example, Delta flight 195
to Dallas (Dal195) is requested by ground based ATC to squawk
"4142". In response, the aircraft pilot manually dials in "4142" at
the aircraft transponder control panel. The transponder control
logic can now encode the assigned four digit identification, e.g.
".sub.4142", on the transponder reply signal. The aircraft's
transponder can also be connected to the aircraft's pressure
altimeter to enable the transponder control logic to encode the
aircraft pressure altitude on the transponder reply signal. The
aircraft transponder reply signal containing the encoded aircraft
identification and pressure altitude is processed by ground based
computers for display on the ATC operator's radar screen. The ATC
operators usually provide specific flight instructions to aircraft
to avoid flight conflicts and warn aircraft of other nearby
aircraft. In large aircraft, active on-board conventional nose
RADAR may also identify aircraft that are in front of the large
aircraft.
[0008] RADAR, however, has a number of disadvantages. Radar
systems, even secondary radar, provides limited range and accuracy
in the determination of the location and altitude of an aircraft.
The range of radar is inherently limited due to obstacles in the
line of sight of the radar, curvature of the earth, atmospheric
conditions, etc., and is subject to provide false readings or
ghosts. RADAR may also fail to provide sufficient target resolution
at the critical near collision phase where target aircraft are
close together. Radar coverage is not available in many areas of
the world, and is not available at all altitudes in the United
States.
[0009] The presently used and Federal Aviation Administration (FAA)
approved aircraft collision avoidance system is known as the
Traffic Alert and Collision Avoidance System (TCAS). The TCAS is an
airborne traffic alert and collision avoidance advisory system that
operates without support from ATC ground stations. TCAS detects the
presence of nearby intruder aircraft equipped with transponders
that reply to secondary radar interrogating signals. TCAS tracks
and continuously evaluates the threat potential of these aircraft
in relation to one's own aircraft, displays the nearby
transponder-equipped aircraft on a traffic advisory display, and
during threat situations provides traffic advisory alerts and
vertical maneuvering resolution advisories (RA) to assist the pilot
in avoiding mid-air collisions. A TCAS has a transmitter, a
transmit antenna, a transponder, one or two directional receiver
antennae, a control interface, display unit(s), and a
signal/control processor.
[0010] A TCAS determines the location of other aircraft by using
the cooperative secondary radar transponders located in other
aircraft. A TCAS transmitter asynchronously polls for other
aircraft with an active L-band interrogating signal, i.e. at the
same frequency as the ground based secondary radar interrogating
signal. The TCAS interrogating signal, however, is an
omni-directional signal whereas the ground based secondary radar
signal is highly directional. When a target aircraft's cooperative
transponder receives a TCAS interrogating signal the transponder
transmits a reply signal. By using RADAR timing principals, the
interrogating TCAS can measure the time between the interrogating
signal transmission and transponder reply to determine the
approximate range of the intruder aircraft. By using direction
finding antenna techniques, the interrogating TCAS determines the
relative direction of the transponder reply signal with a fixed
directional antenna array and the TCAS signal processor. The TCAS
omni-directional interrogating signal causes all secondary radar
cooperative transponders within receiving range to reply,
therefore, the TCAS signal processor uses a complex receiver input
blanking scheme to locate and distinguish the multiple reply
signals. For example, the TCAS interrogating signal is coordinated
with the TCAS signal processor to allow the TCAS signal processor
to create a variable width receiver blanking signal. The variable
width receiver blanking signal is used to progressively exclude
"closer" transponder reply signals. This allows the TCAS
interrogator signal and transponder reply signal processor to
receive transponder replies from progressively further away
aircraft.
[0011] The TCAS control logic uses the range, relative bearing, and
pressure altitude determined by the interrogating signal and
secondary radar transponder replies to track intruder aircraft. The
intruder track is displayed on the TCAS display. The TCAS display
is a VDU typically mounted on the aircraft front instrument panel.
TCAS tracking information, graphically depicting the relative
distance and relative bearing of intruder aircraft, greatly assists
a pilot in identifying and visually acquiring intruder aircraft.
The TCAS control logic also calculates the "tau" of the intruder
aircraft. "Tau" is the ratio of range to range-rate, and represents
the time to intercept for two aircraft on a collision course,
assuming un-accelerated relative motion. The TCAS compares the
"tau" with pre-determined collision threat parameters. If an
intruder aircraft falls within these parameters a TCAS declares the
intruder aircraft a threat. The pre-determined collision threat
parameters delineate the intruder aircraft "tau" into four threat
categories. In most categories the TCAS merely brings the intruder
status to the pilot's attention with an audible alert on the
aircraft intercom. In the highest category the TCAS creates an
evasive maneuver to vector both aircraft to increase the vertical
separation between the aircraft. For situations where one's own
TCAS equipped aircraft and another TCAS equipped aircraft are
declared collision threats to each other, the TCAS in each aircraft
in conjunction with their secondary radar transponder subsystem,
establish an air-to-air resolution advisory in both aircraft. The
resolution advisory is displayed on the TCAS display unit. The
resolution advisory is a directive to the pilots to either climb or
descend.
[0012] The TCAS system, however, suffers from a number of
disadvantages. First, the TCAS system issues numerous false alarms
and/or erroneous commands or instructions. Erroneous commands and
false alarms may increase the probability of collision by
erroneously instructing the aircraft to fly nearer the intruding
aircraft, or to descend when the aircraft is already at a minimal
altitude. Such false alarms and erroneous instructions are
prevalent during take-off and landing where the TCAS has particular
trouble discerning signals from the many nearby aircraft. Such
false alarms, in addition to distracting the pilot, can create
distrust in the entire TCAS system. This distrust can cause a pilot
to hesitate or ignore a valid evasive maneuver or resolution
advisory command because the pilot mistakenly believes the command
is just "another" TCAS false alarm. Another source of TCAS false
alarms is an overly simplistic collision prediction algorithm, i.e.
the "tau" calculation. The TCAS collision alert algorithm does not
account for whether an aircraft is proceeding on it's present
course or is leveling off at a predetermined altitude, i.e. it
assumes an un-accelerated aircraft track. Such problems are
reported by Dave Davis and Michael Sangiacomo in Jets in Jeopardy:
False Warnings from Midair Collision System have Led Airline Pilots
to Near Catastrophe, The Plain Dealer, Jul. 14, 1994, at 1A. The
Plain Dealer investigative reporters discovered that within the
span of a few months, TCAS false alarms nearly caused several
aircraft disasters. Furthermore, some pilots state that the TCAS is
so unreliable in crowded airspace that the TCAS does not work at
all under these conditions.
[0013] Second, TCAS requires an elaborate direction finding antenna
array and processing logic to find an intruder's relative
direction. Such a system is inherently susceptible to multipath
errors, noise clutter, and other spurious signals. Again, this can
create false alarms, false returns or phantom aircraft and
incorrect tracking displays.
[0014] Third, intruder pressure altitude information is only
transmitted from the TCAS transponder when the TCAS is connected to
a pressure altimeter. Thus, the existing TCAS system cannot detect
a collision danger with an aircraft that does not have a functional
pressure altimeter. Moreover, the pressure altimeter itself is
subject to the risk of human error. A pressure altimeter must be
periodically adjusted to compensate for local atmospheric
conditions and elevations. If the pilot does not make the proper
altimeter adjustment then the TCAS transponder will transmit
erroneous altitude information. The lack of altitude information or
incorrect altitude information seriously undermines the accuracy of
the TCAS system.
[0015] Fourth, the TCAS interrogator/transponder protocol requires
an elaborate antenna sidelobe suppression and receiver blanking
technique to block transponder replies from close aircraft and to
allow the system to poll aircraft further away. Such a system is
again susceptible to noise, signal clutter, other spurious signals
and multiple aircraft transponder within the same transponders
reply time frame.
[0016] ATC systems have been proposed that would use the global
positioning system (GPS) satellites. Such a propped system is
discussed in chapter 12 of Logsdon, The Navstar Global Positioning
System, Von Neistrand Reinhold (1992). In The Navstar Global
Positioning System, Logsdon discusses the proposed use of GPS
receivers on board aircraft, wherein the aircraft transmits its GPS
aircraft vector to air traffic controllers for display on the air
traffic controllers' screen. Logsdon also discusses another
proposed navigation system based on the proposed Geostar
satellites. In the Geostar system, when an aircraft needs to know
its location, interrogation pulses are transmitted from the
aircraft to three Geostar satellites, which immediately relay the
request to a centrally located computer on the ground. The ground
computer determines the location of the aircraft and relays the
location back to the aircraft using one of the satellites. The
Geostar system was described as also being able to relay short
telegram messages between two Geostar subscribers (aircraft) using
one of the satellites. This proposed Geostar navigation system
suffers from a number of drawbacks. For example, as with TCAS, each
aircraft does not provide its location, speed, heading to other
aircraft. Instead, in Geostar, aircraft must rely on the extensive
ground-based processing before the aircraft can obtain its own
position. Furthermore, the Geostar system provides no technique for
reducing collision of aircraft.
[0017] Other navigation aides are know to the art. In the 48
contiguous United States, most instrument navigating is done with
the aid of a VHF Omnidirectional Range (VOR) receiver for using the
VHF radio signals emitted by the ground based VOR transmitters.
Virtually all enroute navigation and many instrument approaches use
these signals, which are broadcast in the frequency range 108.0 to
119.0 Mhz. The VOR signal is a blinking omnidirectional pulse, and
has two parts: a reference phase signal and the variable phase
signal. It is transmitted in such a way that the phase between
these two signals is the same as the number of degrees the
receiving aircraft is from the VOR station. The VOR receives and
equipment uses the signals to determine the aircraft direction, or
course, from the VOR.
[0018] An additional navigation aide is known as Distance
Measurement Equipment (DME). DME uses two-way (interrogation and
reply) active spherical ranging to measure the slant range between
the aircraft and the DME transmitting station. Many pilots and
navigators vector airplanes from waypoint to waypoint using the
signals from VOR/DME, rather than traveling in a straight line. As
a result, aircraft are not traveling the shortest distance, causing
increased fuel usage and increased travel time. Also, routes along
the VOR/DME stations become heavily traveled resulting in increased
probability of mid-air collisions.
[0019] In addition, many aircraft employ so-called Instrument
Landing Systems (ILS) for performing precision landings. ILS
includes several VHF localizer transmitters that emit focused VHF
signals upwardly from the airport to provide horizontal guidance to
the aircraft and its autopilot systems. ILS also includes a UHF
glideslope transmitter that radiates a focused UHF signal that
angles downwardly across the runway to provide vertical guidance.
While ILS provides an effective technique for precision landings,
such ILS precision landings are not possible where the airport does
not include such localizer and glideslope transmitters.
SUMMARY OF THE INVENTION
[0020] Accordingly, to is an object of the present invention to
provide an improved automatic collision avoidance system based on
satellite navigation signals.
[0021] It is a further object of the present invention to provide
an improved automatic collision avoidance system based on the
global positioning system and a direct radio wave inter-aircraft
radio network synchronized with the GPS precision clock.
[0022] It is yet another object of the present invention to provide
an improved automatic collision avoidance system based on the
global positioning system that is backward compatible with existing
collision avoidance systems.
[0023] It is yet another object of the present invention to provide
an improved automatic collision avoidance system based on the
global positioning system, a direct radio wave multipoint network
synchronized with the GPS precision clock, and ground based
pseudo-satellites navigation enhancement signals.
[0024] It is yet another object of the present invention to provide
an automatic collision avoidance system based on the global
position system, a direct radio wave multipoint network
synchronized with the GPS precision clock, and communication with
fixed navigation obstructions equipped with a collision avoidance
beacon.
[0025] It is yet another object of the present invention to provide
an automatic collision avoidance system based on the global
positioning system, a direct radio wave multipoint network
synchronized with the GPS precision clock, and an interface with
the automatic navigation system or auto-pilot to control the
anti-collision maneuver without pilot intervention.
[0026] In accordance with the present invention, an improved
automatic collision avoidance system for guiding vehicles is
provided which includes a sensing system for receiving GPS signals,
an apparatus for translating the GPS signals to determine the GPS
location, GPS altitude and track, a transceiver system for
operating a multipoint direct radio wave protocol synchronized to
the GPS precision clock for transmitting the GPS position and
receiving other aircraft GPS positions, extrapolating the track of
all nearby aircraft and determining whether any aircraft pose a
collision threat, control logic to create evasive maneuvers to
separate aircraft that are within a predetermined collision track
tolerance, and establishing a data link between aircraft to
coordinate the evasive maneuver.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] A more complete appreciate the present invention and many of
the attendant advantages thereof will be readily obtained as the
invention becomes better understood by references to the following
detailed description when considered in connection with the
accompanying drawings.
[0028] FIG. 1 is a schematic diagram of an improved automatic
collision avoidance system in accordance with a preferred
embodiment of the present invention.
[0029] FIG. 2 is an overall functional block diagram of the
improved automatic collision avoidance system of FIG. 1.
[0030] FIG. 3 illustrates the relative display mode format for the
display unit of the improved automatic collision avoidance system
of FIGS. 1 and 2.
[0031] FIG. 4 illustrates the pseudo three dimensional display mode
format for the display unit of the improved automatic collision
avoidance system of FIGS. 1 and 2.
[0032] FIG. 5 illustrates the control panel for the control unit of
the improved automatic collision avoidance system of FIGS. 1 and
2.
[0033] FIG. 6 is a schematic diagram illustrating a set of steps to
operate the improved automatic collision avoidance system
illustrated in FIGS. 1 and 2.
[0034] FIG. 7 is a diagram illustrating the data message block used
to communicate between an improved automatic collision avoidance
system and another improved automatic collision avoidance
system.
[0035] FIG. 8 illustrates a sequence of steps which may be
performed to operate the multipoint direct radio protocol used in
the improved automatic collision avoidance system.
[0036] FIG. 9 illustrates a sequence of steps which may be
performed to operate the surveillance and tracking function to
operate the improved automatic collision avoidance system of FIGS.
1 and 2 by performing the steps of the function block shown in FIG.
6.
[0037] FIG. 10 illustrates a sequence of steps which may be
performed to operate the threat potential and evaluation function
to operate the improved automatic collision avoidance system of
FIGS. 1 and 2 by performing the steps of the function block shown
in FIG. 6.
[0038] FIG. 11 illustrates a sequence of steps which may be
performed by the traffic advisory display function to operate the
improved automatic collision avoidance system of FIGS. 1 and 2 by
performing the steps of the function block shown in FIG. 6.
[0039] FIG. 12 illustrates a sequence of steps which may be
performed by the evasive command generator function to operate the
improved automatic collision avoidance system of FIGS. 1 and 2 by
performing the steps of the function block shown in FIG. 6.
[0040] FIG. 13 is a schematic diagram of an automatic collision
avoidance system in accordance to a second seagoing vessel
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0041] Referring to the drawings in detail wherein like numerals
indicate like elements, FIG. 1 is a schematic diagram of an
improved automatic collision avoidance system in accordance with
the preferred embodiment of the present invention. The improved
automatic collision avoidance system is called the satellite
tracking alert resolution system (STARS). The STARS is a self
contained airborne collision avoidance system that does not require
any ground based support. The aircraft 8 is equipped with a STARS
10. An antenna 12 may be used to receive GPS signals from orbiting
GPS satellites a few of which are illustrated as 14, 16, 18, and
20. An optional antenna 22 may be used to receive pseudo-satellite
signals from ground based stations 24. Pseudo-satellite signals may
be used to increase the navigational accuracy of the STARS. The
STARS 10 processes the satellite navigational signals to determine
a GPS position and GPS altitude for the aircraft 8. A GPS position
is usually represented in the traditional navigational coordinate
system in hours, minutes, and seconds 26 from the prime meridian
and degrees from north or south of the equator on the so called
parallels 28. It is understood that any coordinate system can be
used to practice the present invention and is within the scope of
the present invention to convert between coordinate systems. The
STARS 10 sequentially determines the GPS position and GPS altitude
of the aircraft 8. The STARS 10 uses the sequential GPS positions
and GPS altitude to determine the track 39 of the aircraft 8. The
aircraft track 30 represents the velocity vector of the aircraft
8.
[0042] The STARS 10 transmits the aircraft 8 position and the
aircraft 8 track 30 on the STARS transceiver antenna 32 and
optional antenna 34. The STARS transmit power is calibrated with
the STARS receiver signal threshold to enable an effective range of
approximately 50 miles 36. It is understood that STARS 10 transmit
power and receiver signal thresholds can be adjusted to allow the
STARS to operate in a variety of range modes. Moreover, it is
understood that the antenna footprint 32 and 34 may be adjusted to
allow the STARS 10 to project the STARS transmit signal further,
e.g. 80 miles, in front of the aircraft 8 and increase receiver
sensitivity to targets in front of the aircraft 8.
[0043] An intruder aircraft 38 is equipped with a STARS identical
to the STARS 10 and antenna 32, 12, 22 and 34 of aircraft 8.
Likewise, the intruder aircraft 38 STARS also sequentially
determines aircraft 38 GPS position, GPS altitude and track 40. The
intruder aircraft 38 STARS is also transmitting the intruder
aircraft GPS position and track on the STARS transceiver. The
intruder aircraft 38 STARS transceiver transmit time is
synchronized to the aircraft 8 STARS 10 transceiver transmit time
with a time division multiple access protocol (TDMA), discussed in
detail below. The protocol may maintain synchronization with a
common timing source derived from the GPS precision clock. The GPS
precision clock is determined from the GPS satellite 14, 16, 18, 20
and pseudo-satellite 24 signals. It is understood that other
clocking means such as an internal crystal oscillator may be used
to synchronized the TDMA protocol.
[0044] The aircraft 8 STARS transceiver antenna 32 and optional
antenna 34 receives the transmit signal from intruder aircraft 38.
As described in substantive detail below, the aircraft 8 STARS
extrapolates the track of aircraft 8 and aircraft 38. It is
understood that STARS may extrapolate tracks from a plurality of
aircraft. It is also understood that the "tau" as known to the
collision avoidance art, i.e. range over range-rate, calculation is
within the scope of the present invention and may be used in place
of an extrapolated track. The aircraft 8 STARS 10 determines the
closest distance between the extrapolated track 44 of aircraft 8
and extrapolated track 42 of aircraft 38. The STARS compares the
closest distance between the extrapolated tracks to predetermined
safe distance and altitude parameters. Generally, the process of
determining the closest distance between the aircraft 8 and 38 is
an iterative process which is performed by a sequence of steps
programmed into a microcomputer. Consequently, the process of
extrapolating tracks, comparing the tracks and determining whether
the aircraft 8 will maintain a safe distance from all intruder
aircraft is continuously repeated as the aircraft 8 travels through
the air. The intruder aircraft 38 simultaneously and independently
performs an extrapolation of aircraft tracks 42 and 44, compares
the tracks, and determines whether the aircraft 38 will maintain a
safe distance from all intruder aircraft.
[0045] If aircraft 8 STARS 10 determines that the aircraft 8 will
pass by another aircraft, for example aircraft 38, with less than
the predetermined safe distance and attitude parameters, then the
STARS 10 will generate an evasive maneuver 48 for aircraft 8 to
increase the vertical distance between aircraft 8 and aircraft 38.
A preferred technique for calculating the evasive maneuver 48 is
discussed in substantive detail below but, in general the higher
aircraft will be directed to climb and the lower aircraft will be
directed to decsend. A data link is established, using the STARS
transceivers, between the aircraft 8 and 38 to coordinate the
evasive maneuver 48. The preferred data link technique is discussed
in substantive detail below but, generally, aircraft 38 receives
the aircraft 8 evasive maneuver and aircraft 38 generates an
opposite evasive maneuver 50. Aircraft 38 STARS transmits the
opposite evasive maneuver to aircraft 8 STARS 10. Upon receipt of
aircraft 38 STARS opposite evasive maneuver, aircraft 8 STARS 10 in
the preferred embodiment alerts and displays the evasive maneuver
48 to the aircraft 8 pilot. Aircraft 8 STARS 10 in the preferred
embodiment also transmits that the evasive maneuver is executing to
aircraft 38. Aircraft 38, upon receipt of the evasive maneuver
executing message alerts and displays evasive maneuver 50 to the
aircraft 38 pilot. As discussed in substantive detail below, the
STARS has numerous advisory and evasive maneuver commands to
resolve numerous possible scenarios between approaching aircraft.
Additionally, the communication process between different STARS may
include information concerning aircraft identification, status,
telemetry from instrumentation, and altitude window information.
The altitude window is an altitude set at the STARS control panel
by the pilot that indicates the altitude at which the pilot will
level off. As discussed more fully below, this information in
general may be used to calculate appropriate evasive commands for
the aircraft. Thus, the STARS altitude window feature may be used
to extrapolate aircraft tracks that are much more accurate than a
track extrapolated with a function that assumes all aircraft will
remain unaccelerated.
[0046] FIG. 2 is an overall functional block diagram of the STARS
system of FIG. 1. The STARS 10 comprises GPS antenna 12, optional
GPS antenna 22, GPS receiver 56, GPS processor 58, modem 60,
transceiver 62, transceiver antenna 32, optional transceiver
antenna 34, STARS computer 66, control unit 68, storage unit 70,
input and output interface 72, display unit 74, and audio interface
76. The STARS computer 66 comprises a microprocessor or
microcomputer based system having a microprocessor, read only
memory (ROM), random access memory (RAM), and input/output ports
(I/O ports). It is understood that STARS computer 66 may also
comprise any additional circuitry, such as A/D and D/A converters,
combinational logic circuitry, latching circuitry, etc., that may
be necessary for the operation and interconnection of STARS
computer 66 with respect to the components of the STARS 10. All of
the above-described components of STARS computer 66 may be located
on an individual semiconductor chip. The STARS 10 may also be
located on an individual or plurality of custom VLSI chips. The
antenna 12 may be an antenna mounted to the top of the aircraft to
receive GPS signals from orbiting satellites. Antenna 22 is an
optional antenna mounted to the bottom of the aircraft to receive
ground based pseudo-satellite signals. Pseudo-satellite signals can
be used to increase the positional and altitude accuracy of the
STARS 10 during an airport approach or when the aircraft is flying
below dense cloud cover. The GPS receiver 56 is used to determine
the aircraft's position (longitude, latitude and altitude). Other
types of satellite receivers, such as receivers for receiving
signals from the Soviet Glonass satellites, may be used. As well
understood by those skilled in the art, each GPS satellite
transmits binary pulse trains, copies of which are created in the
GPS receiver electronics. The GPS receiver antenna detects the
signals (binary pulse trains) transmitted from GPS satellites,
amplifies the received signals, and inputs them into two tracking
loops that lock onto the carrier waves. The GPS pulse train is
adjusted in the tracking loop until it is brought into
correspondence with the satellite pulse train. When correspondence
is achieved, the GPS receiver resident processor can determine
signal travel time based on the pulse adjustment. The GPS receiver
resident processor then may determine the pseudo-range (distance
from the GPS receiver to each satellite) based on the signal travel
time (plus or minus clock bias error) multiplied times signal
travel time; (pseudo-range=C.times.delta T). The GPS receiver 56
may then determine its location using four pseudo-ranges, solving
four simultaneous equations having four unknowns, as well known to
those skilled in the art. The GPS processor 58 may be resident in
the GPS receiver or separate. The GPS processor 58 automatically
determines the user's current position (longitude, latitude and
altitude) tracking and speed.
[0047] The GPS receiver 56 should be a multi-channel receiver for
receiving positioning signals from a plurality of GPS satellites. A
number of GPS receivers are commercially available from such
companies as Sony Corporation, Motorola, Rockwell International
(the Navcore V GPS receiver), and others. One such commercially
available GPS receiver is the Nav 1000 GPS receiver manufactured by
Magellan Systems Corporation. The data output by GPS receiver 56 is
input to the GPS processor 58.
[0048] The GPS processor 58 performs the calculations necessary to
determine the aircraft track, speed, and acceleration, and
precision GPS time. The precision GPS time can be found by
determining the clock bias error as one of the four unknowns in the
standard four equation GPS navigation solution. It is well known in
the art how to determine an highly accurate clock from the GPS
signals. In the preferred embodiment the STARS 10 uses the absolute
time synchronization mode. With absolute time synchronization a
special time synchronization is derived from a GPS satellite.
Absolute time synchronization can achieve accuracy's of about 100
nanoseconds. GPS synchronized time is used to synchronize the modem
60 with other aircraft STARS. It is understood to those skilled in
the microprocessor controller arts that the GPS processor functions
may be incorporated into a single faster microprocessor to form an
integrated STARS computer/GPS signal processor 66 and 58. Such a
high speed microcomputer or digital signal processor is the
TMS320C40 or TMS320C50 available from Texas Instruments
Incorporated.
[0049] The modem and data transfer protocol provide communications
between STARS. The modem 60 uses a suitable data transmission
modulation technique such as frequency shift keying (FSK), pulse
position modulation, or quadrature phase shift keying (QPSK) for
use with a multiple Access protocol. The modulation may be
synchronized with GPS precision time. In the preferred embodiment
the STARS 10 will transmit and receive on the L-band TCAS
interrogator frequency. The multiple access protocol of the
preferred embodiment is the time division multiple access protocol
(TDMA). TDMA is run by a sequence of computer instructions on the
STARS computer 66. The protocol may also execute on its own
microprocessor and interface to the STARS processor 66 as a
microprocessor peripheral device. The TDMA protocol works by
dividing a radio frequency into a fixed number of time slots. For
example, a frequency could be divided into 100 time slots where
each slot is 1/100 of a second. Since the preferred L-band TCAS
frequency is very high, approximately 1 Ghz or 1,000,000,000 cycles
per second, a time slot of 1/100 of a second has a theoretical
transmission rate of 1 million bits per second. In practice,
however, TDMA throughput is some what less than the theoretical
limit because of protocol overhead and synchronization time. The
preferred STARS TDMA implementation, discussed in substantive
detail below, automatically assigns each STARS within a limited
direct radio range a TDMA slot. Each STARS transmits on its
assigned slot and receives signals from other STARS on all the
other TDMA slots. It is understood that other multiple access
protocols such as collision detection retransmission, spread
spectrum techniques and code division multiple access are within
the scope of the present invention. The STARS TDMA message has a
general broadcast mode and a specific broadcast or data link mode.
In the general broadcast mode the STARS 10 transmits on the
appropriate TDMA slot a message that all other STARS receivers
within the broadcast range will receive and process. In the
specific or data link broadcast mode the STARS transmits, on the
appropriate time slot, a message with a specific aircraft
identification number encoded in the TDMA message. All other STARS
receivers within the broadcast range receive and process the data
link message. If the message encoded aircraft identification
matches a STARS aircraft identification then the STARS whose
aircraft identification matches the message processes the message
as a specific data link message.
[0050] The display unit 74 may be a CRT or other suitable display
such as gas plasma, LCD, or active matrix LCD. In the preferred
embodiment the display will fit into the standard aircraft
instrument hole and can be mounted in the front aircraft instrument
panel. Preferably the STARS 10 electronics are located in a
separate housing but it is with the scope of the present invention
to house the STARS electronics in the display unit 74.
[0051] The storage unit 70 is a non-volatile computer memory such
as flash memory available from Intel Corporation and Texas
Instruments Incorporated or volatile RAM with battery back up. The
storage unit 70 may also contain the permanent program memory for
the STARS program. The STARS program may be fixed in ROM memory or
flash memory. The storage unit 70 may also contain a mass storage
device such as a PCI card, floppy disk, or hard disk to store
database information. The STARS 10 storage unit 70 may contain a
worldwide Jeppesen data base which includes the coordinates of all
airports with runways over 1000 feet in length, including airport
elevations, VHF, VOR's, and NBD's, and an expanded database,
including information, such as airport VHF communication
frequencies, fuel availability, instrument landing system (ILS)
details, DMEs, and intersections.
[0052] The audio interface 76 contains a digital to analog
converter and is connected to the aircraft audio intercom system
78. The audio interface 76 is used to synthesize speech to notify
the aircraft pilot of the STARS alarm status or if necessary the
STARS evasive maneuver. A suitable voice synthesizing
coder/de-coder digital to analog chip is the TSP53C30 available
from Texas Instruments. It is, understood that there are a wide
variety of D/A chips and digital storage formats available and that
these formats and D/A techniques are within the scope of the
present invention. In the preferred embodiment the STARS 10 audio
alarms may be stored in pulse code modulation or linear predictive
coding format. The audio interface 76 is used by STARS 10 to
produce audio alarms, synthetic voice alarms and synthetic voice
commands into the cockpit via the aircraft intercom system 78.
[0053] The peripheral input and output (I/O) control unit 72
contains the circuits necessary, e.g. parallel and serial digital
circuits, A/D converters and switch sensors, to interface the STARS
10 to auxiliary aircraft systems and controls. It is understood
that the I/O control unit 72 may be a separate set of integrated
circuits or may be combined as a subsystem to a custom VLSI STARS
computer 66. The peripheral equipment interface to the STARS 10 may
be an open and close switch, a parallel or serial digital interface
from another on-board system, or an analog signal from an aircraft
sensor. For example, one such external control interface is to a
switch for detecting whether the landing gear is up or down,
aanother is from an internal high gravity force shock detector. Yet
another is from a switch that detects whether the aircraft door or
cargo hatch is open. In addition, aircraft subsystems and
instrumentation such as data from the ground proximity and wind
shear systems, the on-board maintenance computer, the radio
altimeter, the roll gyro synchro, the pitch gyro synchro, the
magnetic heading synchro, the barometric pressure altitude, the
flight recorder, and the autopilot may be connected to the STARS 10
at the I/O control unit 73. It is understood that some aircraft
subsystems such as the roll gyro, pitch gyro, and magnetic heading
gyro may use either an analog or digital interface signal and that
the A/D conversion necessary to interface the STARS 10 to these
systems is within the scope of the present invention. It is
understood that other aircraft systems may be connected to the
STARS 10 and that the STARS 10 TDMA transceiver system 62 may
transfer and process data from these other aircraft systems.
[0054] The STARS computer 66 is a single or multiple microprocessor
or microcomputer based system used to execute the STARS
programming. As stated above, in the preferred embodiment the STARS
processor may be a TMS320C40 or TMS320C50 general purpose digital
signal processor available from Texas Instruments Incorporated. The
STARS 10 program is understood to have a
multitasking/multiprocessor embodiment as well as a linear program
embodiment within the scope of the invention. A
multitasking/multiprocessor environment uses a plurality of
microprocessors executing computer instructions in parallel with
one another. For example, the STARS computer 66 may have a
microprocessor for executing the instructions for the TDMA
protocol, another microprocessor for executing the instructions for
GPS signal processing, and another microprocessor for overall
system control that communicates with the TDMA and GPS
microprocessors. Thus, the several processors each execute their
own particular sequence of instructions (programs) simultaneously,
i.e. multitasked. The multiple programs executing on the TDMA and
GPS microprocessors may also execute on a single fast
microprocessor if the single microprocessor is fast enough to
switch between the TDMA and GPS programs to give the two programs
the same execution speed as the dual microprocessor configuration,
e.g. a multitasked and single processor embodiment. Likewise, all
the processing functions TDMA, GPS and control processing may be
performed on a single microprocessor if the single microprocessor
is fast enough to give all of the processes a sufficient execution
speed. In a multitasking environment the multiple processes are
executing simultaneously and communicate between processes as if
the process are executing independently of one another.
Multitasking can be accomplished on a multiprocessor configuration
or on a single fast microprocessor. A linear embodiment of the
STARS 10 program is also within the scope of the present invention.
A linear embodiment of the STARS program is a sequence of
instructions that performs all of the necessary STARS processes in
a one sequential loop. In the linear embodiment each task, e.g. the
TDMA, GPS and control processes, are executed in fast sequence one
after another.
[0055] It is understood that aircraft power is operably connected
to the STARS system 10. This includes normal aircraft power at 115
VAC 400 Hz and +28 VDC and emergency aircraft back-up power from
the aircraft batteries. Internal STARS battery power may be used
for long term variable storage and for emergency beacon power.
[0056] FIG. 3 shows the display 74 in the relative bearing mode 80.
The relative bearing mode 80 displays the relative bearing of
intruder aircraft within the STARS 10 tacking range. The relative
bearing mode 80 is calibrated with concentric circles 82
representing the range in nautical miles to the intruders
representation 84. It is understood that the calibrated marking 86
may change depending on the STARS range mode, discussed below.
Intruders that are beyond the calibrated range display are
represented in the relative bearing mode 80 as intruders at the
very edge of the display 88. The display 74 is preferably a color
display capable of sufficiently high resolution to display aircraft
in a relative bearing mode 80 as shown in FIG. 3.
[0057] FIG. 4 shows the three dimensional altitude and bearing mode
90 on the display unit 74. The three dimensional mode 90 shows the
three dimensional track for one's own aircraft representation 92
and intruder aircraft representations 94. The vertical index 96 is
calibrated with in feet to show the aircraft altitude. The
horizontal index 98 is calibrated to show the range in nautical
miles.
[0058] FIG. 5 shows the STARS 10 control unit 68. The control unit
68 is the user interface for the STARS 10. In the preferred
embodiment the control unit 68 is mounted in the aircraft front
instrument panel just below the display unit 74. The control unit
68 physical dimensions in the preferred embodiment allows the
control unit 68 to fit into a standard aircraft instrument hole.
The control unit comprises: alpha-numeric display 100; control
knobs 102; buttons 104; control knob 106; and numeric display 108.
The knob 106 selects the altitude window that is displayed in
numeric display 108.
[0059] The altitude window data is used when a STARS extrapolates
the track of the host aircraft and any intruder aircraft. Thus, the
altitude window information may be used to create more accurate
predictions of aircraft tracks. More accurate aircraft: track
predictions will reduce the number of false collision alarms
created by more simplistic track prediction methods such as the
TCAS "tau" calculation. The altitude window is the pilot's intended
level off amplitude. For example, if an aircraft pilot is taking
off from an airport and the pilot intends to maintain a standard
climb rate and level off at 12,000 feet then the pilot may select
with knob 106 the level off altitude, e.g. 12,000 feet. The STARS
10 transmits the altitude window data in the regular STARS 10 TDMA
transmission discussed below.
[0060] FIG. 6 illustrates the STARS 10 control program sequence.
The STARS 10 control program sequence is a continues loop
comprising the following steps: STARS initialization 110, read GPS
receiver queue 112, read I/O queue and control switches 113,
transmit information 114, read receiver queue 116, surveillance and
tracking function 118, threat evaluation function 120, display and
alert function 112; determination of whether an evasive command is
required 124; calculation of an evasive command 126; establishing a
data link 128; and issuing the evasive command 130. The
initialization step 110 contains the sequence of steps necessary to
initialize the STARS 10. The initialization step 110 includes
placing the STARS processor 66, internal registers, I/O units 72,
GPS receiver processor 58, display unit 74, and control unit 68 to
a known predetermined initialization state. The initialization step
110, in addition, executes a power on self test routine to test the
STARS 10, peripheral I/O connections 72, the CPS receiver 56, and
GPS processor 58, modem 60, and transceiver 62. If the STARS 10
passes the built in test routine the initialization step 110 allows
the control program sequence to advance to step 112. If the STARS
10 fails the built in test then the initialization step 110 causes
a diagnostic code that describes which STARS 10 component failed to
be displayed on the STARS alpha numeric display 100 and halts
further control program execution.
[0061] The read GPS receiver queue step 112 in the preferred
embodiment may check a processor register for information from the
GPS receiver subsystem. The information from the GPS receiver
subsystem, i.e. the CPS receiver 56 and GPS processor 58, is the
aircraft position, altitude, and track in digital data form is
automatically sent to the STARS computer 66. In the preferred
embodiment the STARS GPS receiver subsystem executes the GPS
program sequence separate and apart from the STARS control program.
Thus, the receiver queue is a set of data storage registers
contained in the STARS computer 66 interface to the STARS GPS
processor 58. The receiver queue latches the information from the
GPS processor 58 and serves as a data buffer between the GPS
processor 58 and the STARS computer 66. The STARS control process
at the read receiver queue step 112 moves the data from the
receiver queue to an internal STARS computer 66 data storage
register. This empties the receiver queue data registers and
readies the data registers for new information. The STARS control
process can manipulate and use the aircraft position, altitude, and
track data as necessary to perform the STARS 10 functions in the
STARS computer 66 internal registers. The use and manipulation of
the positional and tracking data are described in substantive
detail below.
[0062] The STARS control program advances to the read I/O queue and
control switches step 113. The STARS computer 66 checks the status
of the I/O control unit 72 for data. It is understood that
temporary data storage and I/O status registers are used in the
STARS computer 66 to connect to the I/O control unit 72. The
temporary data storage and I/O registers buffer data and facilitate
communications between the STARS processor 66 and the I/O control
unit 72. The I/O status register may indicate which data registers
contains new and valid data. For example, if the STARS 10 is
connected to another aircraft system such as the radio altimeter,
the radio altimeter is connected to the STARS with the I/O control
unit 72. The I/O control unit 72 latches the digital data from the
radio altimeter into an I/O storage register. The I/O unit then
sets a bit in the I/O status register to indicate that digital data
from the radio altimeter has been received. When the STARS control
process reaches the step 113, the control process reads and decodes
the I/O status word. The decoded status word indicates whether data
is present from the radio altimeter. The control process may move
the data from the I/O control unit 72 data register to an internal
storage register or to the storage unit 70. The STARS control
process 113 may set or clear the I/O status word to represent that
the data has been moved from the I/O control 72 storage register
and that the storage register is now free to receive more data.
Thus, the I/O control unit 72 data and I/O status registers serve
as buffers between the fast execution of the STARS control program
and relatively slow speed of STARS 10 I/O communications. Likewise,
the STARS computer 66, at step 113, scans the control unit 68
switches.
[0063] The STARS control program now advances to the transmit
information step 114. In the preferred embodiment, the transmit
information step 114 comprises the sequence of instructions
necessary to format a STARS 10 TDMA message and transfer the
message to the STARS transmitter system 132. The STARS transmitter
system comprises the modem 60 and transceiver 62. The STARS message
comprises a block of digital data with the following encoded data
fields: a synchronizing pattern; the sending aircraft
identification; the receiving aircraft identification; a control
word; longitude data; latitude data; altitude data; velocity x;
velocity y; velocity z; altitude window; user programmable
telemetry; a status message; and a cyclic redundancy check (CRC)
field. The construction of the STARS message block is discussed in
substantive detail below.
[0064] The STARS control program now advances to read the receiver
queue 116. The read receiver queue step 116 in the preferred
embodiment may check a processor register for information from the
transceiver 62 and modem 60. The information from the transceiver
62 and modem 60 is STARS message blocks from other STARS equipped
vehicles in receiving range. As discussed in substantive detail
below, the transceiver 62 and modem 60 executes the tasks necessary
to receive and transmit messages with other STARS separate and
apart from the STARS control program. Thus, the transceiver queue
is a set of data storage registers contained in the STARS computer
66 interface to the STARS modem 60. The transceiver queue latches
the information from the modem 60 and serves as a data buffer
between the modem 60 and the STARS computer 66. The STARS control
process at the read receiver queue step 116 moves the data from the
receiver queue to an internal STARS computer 66 data storage
register. This empties the receiver queue data registers and
readies the data registers for new information. The STARS control
process can manipulate and use the messages from other STARS as
necessary to perform the STARS 10 functions in the STARS computer
66 internal registers.
[0065] The surveillance and tracking function 118, discussed in
substantive detail below, processes the data blocks received in
step 116. This includes determining the range of any intruder
aircraft, determining the relative bearing, determining the
relative altitude, calculating the closing rate, deciding whether
the intruder should be put into the tracking mode, and calculating
an estimate miss distance.
[0066] The threat evaluation function 120, discussed in substantive
detail below, divides all intruder aircraft into a threat
classification. The threat classifications are non-threat,
proximity, traffic advisory, and resolution advisory threat.
[0067] The display and alert function 122, discussed in substantive
detail below, generates the display of the intruder aircraft for
the display unit 74 and generates the pre-programmed audio alerts
with the audio interface 76.
[0068] The determination whether an evasive command is required at
step 124 is based on a list of pre-determined parameters discussed
in substantive detail below. Generally, the altitude of the
aircraft and the calculated miss distance will determine whether
the STARS will issue an evasive command.
[0069] The calculation of an evasive command 126, discussed in
substantive detail below, generally depends on which aircraft is at
the higher altitude and aircraft performance factors.
[0070] The establishment of a data link 126, discussed in
substantive detail below, is used to coordinate evasive maneuvers
between aircraft. The coordination of evasive maneuvers assures
that aircraft on a collision course will increase their separation
by the execution of a coordinated evasive maneuver.
[0071] The issuance of the evasive command 130, discussed in
greater detail below, is the alert and display of the evasive
maneuver to the pilot. The evasive command issues after the
coordination of the evasive command 128.
[0072] FIG. 7 illustrates the STARS data message block sent and
received by the STARS control program shown in FIG. 6. The STARS
data block comprises a synchronizing pattern 140, a sending
aircraft identification 142, a receiving aircraft identification
144, a control word 146, longitude data 148, latitude data 150,
altitude data 152, velocity X 154, velocity Y 156, velocity Z 158,
altitude window 160, telemetry 162, a message 164 and a CRC
character 166. The synchronizing pattern 140 is a predetermined
synchronization pattern that indicates the start of STARS data
block. The synchronization pattern is the same for all STARS data
blocks, therefore, when a STARS transceiver recognizes the
synchronization pattern it synchronizes the receiver queue with the
start of the STARS message. The aircraft ID field 142 is a digital
word that encodes the full aircraft registration number of the
transmitter STARS aircraft. Block 142, in addition, contains
encoded information about the aircraft model. For example,
N1234567B727 represents the registration number of an aircraft,
e.g. N1234567, and that the aircraft is a Boeing 727, e.g. B727.
The aircraft ID receiving field 144 is the registration number for
a targeted intruder aircraft. This field 144 is used to designate
whether the data block is a general STARS location beacon message
or a STARS data link message. The data link message is used to
coordinate resolution advisory commands between aircraft. The data
link block contains information for communication between two
particular aircraft, whereas, a general STARS beacon message is
directed to all aircraft and ground sites within receiving range.
The control word 146 is used in conjunction with the aircraft
receiving ID 144 to coordinate the data link and resolution
advisory. The control word 146 also identifies whether the STARS
message is a general poll, data link, or an ATC message. The
control word 146 can also be used to prioritize a message or encode
emergency indications. The longitude data field 148 is data that
represents the GPS longitude of the aircraft. The latitude data
field 150 is data that represents the GPS latitude of the aircraft.
The altitude data field 152 is data that represents the GPS
altitude of the aircraft. It is important to note that the
longitude, latitude, and altitude data is from the GPS receiver
system and not from a solely internal aircraft reference such as
the inertial navigation system (INS) or a pressure altimeter. A GPS
commercial grade receiver may have resolution errors in it's
positioning calculations. These resolution errors, however, are
inherent in the GPS methodology and therefore are common to all
commercial grade GPS receivers operating in the same geographic
area. Since all STARS GPS receivers have the same commercial grade
resolution error, when the position and tracking information are
used to calculate relative distance between aircraft the resolution
error cancels. This makes the STARS 10 local GPS beacon method of
the present invention extremely accurate at determining the
relative location and altitude of intruder aircraft. The velocity X
154, velocity Y 156, and velocity Z 158 data fields together
represent the velocity vector of the aircraft. The velocity vector
is calculated by continuously measuring the distance between GPS
positions divided by the time the aircraft took to cover the
distance. The altitude window 160 represents the "fly to" altitude
of the aircraft. The altitude window 160 data is input from the
STARS control panel 68. As pointed out earlier, a source of
numerous false alarms in present anti-collision systems arises from
a condition where one aircraft is taking off and climbing and
another aircraft is descending. The alarm is false because the
climbing aircraft may level out at a predetermined altitude and,
therefore, present no collision danger. The present invention
overcomes this limitation by allowing the pilot to designate in
advance the predetermined level off altitude on the STARS control
panel 68. A STARS transmits this information in the altitude window
field 160. STARS processors use the altitude window 160 information
to determine the extrapolated trajectory of aircraft and whether a
resolution advisory should be generated. The telemetry field 162
represents data that encodes selected aircraft telemetry. For
example, whether the landing gear up or down may be encoded in this
field. It is within the scope of the present invention to send and
receive other instrumentation or other aircraft system data within
the telemetry data field. The message field 164 represents data
that encodes messages and is otherwise reserved as a maintenance
channel and for future use. It is understood that a data block
(CRC) 166 can be included with the data block transmission. A CRC
check field assures, to a high degree of probability, that the data
block is received without bit errors. Thus, data blocks with bad
CRC fields can be rejected as blocks having bit error(s). It is
also within the scope of the present invention that data coding,
such as, forward error correction (FEC) and other noise immunity
techniques can be employed to improve the effective signal to noise
ratio of the STARS signal. For example, the Reed-Solomon FEC
algorithm can be used to make a more robust data sequence.
[0073] FIG. 8 illustrates the TDMA protocol sequence. The STARS 10
at power on and when placed into active beacon mode will initialize
the transmission protocol 166 by setting data registers and
protocol procedures to a predetermined initial state. In the
preferred embodiment, the TDMA protocol is used to synchronize
STARS beacon and data link signals. It is understood to those in
the art, however, that other suitable multiple access protocols are
within the scope of the present invention. The TDMA protocol
initially scans the beacon frequency for open time slots 168. After
listening for six TDMA cycles 170 the protocol identifies a time
slot that has been open for six consecutive cycles 172. The TDMA
protocol seizes the time slot by transmitting a data block shown in
FIG. 7 to the modem 60 at the precise time slot. It is understood
that a FEC coder/decoder maybe inserted at this point. The modem 60
modulates the beacon frequency carrier for the transceiver 62 to
broadcast through the beacon antenna 32. The TDMA protocol will
continue to beacon the data block at it's seized TDMA slot for a
randomized number from three to nine TDMA cycles 180. It is
understood that the carrier frequency should be sufficiently high
to support multiple TDMA time slots. In the preferred embodiment
the STARS 10 transmits on the TCAS L-Band interrogator SHF radio
frequency, however, a laser, infrared, UHF or VHF carrier is within
the scope of the invention. When the transmission cycle is compete
180, the TDMA protocol listens for whether its seized TDMA slot is
clear 182. If the slot is clear the protocol keeps the slot and
returns to the beacon mode 176. If the slot is not clear the TDMA
protocol returns to the scan mode 168 and begins to scan for
another free slot. Thus, the TDMA protocol synchronizes into the
TDMA slot by finding a clear TDMA channel and transmitting it's
data block in that slot. During transmission the transceiver 62
blanks the receiver input to prevent receiver overload. When the
TDMA protocol and transceiver 62 stops transmission on the seized
time slot it immediately returns to the listen mode to receive
beacons from other STARS systems. When the TDMA protocol decodes a
beacon on another slot it places the received data block into the
receiver queue 116. It is understood that the transmission time
slot is relatively small when compared to the total number of
available slots. Thus, the receiver queue 116 is understood to be
large enough to acccomodate a plurality of incoming messages. It is
also understood that the TDMA protocol requires precise timing to
obtain the maximum number of time slots available at any given
frequency and burst size. The GPS precision clock provides an
excellent source of precision timing signals to maintain a single
timing source for all STARS within a given geographic area and thus
maximize the TDMA synchronization between STARS.
[0074] FIG. 9 illustrates the sequence of instructions required to
execute the surveillance and tracking function shown in FIG. 6. The
surveillance and tracking function 118 comprises the sequence of
instruction necessary to: determine the range to all aircraft in
the STARS receiving range 186, determine the relative bearing to
all intruders 188, determine the relative altitude of intruders
190, calculate aircraft closing rates 192, determine whether the
aircraft should be placed into the track mode 194; calculate the
relative position 198, calculate the altitude closing rate 200, and
estimate the miss distance 202. The surveillance and tracking
function 118 function first determines the range 186 of intruding
aircraft. Range is determined by calculating the length of the
vector between the intruder aircraft position and altitude and
one's own aircraft position and altitude. The function next
calculates the relative bearing 188 of the intruder aircraft. The
relative bearing is calculated by determining the angle of the
intruder aircraft relative to the baseline zero degree angle
directly ahead of one's own aircraft. This calculation is performed
by determining the X and Y displacement from one's own location to
the intruder aircraft. The displacement is adjusted for the display
units 74 distance calibration 86 and is used to display the
intruder aircraft in the relative display mode 80. The function 118
next calculates the relative altitude between one's own aircraft
and an intruder aircraft at step 190. The relative altitude 190 may
be calculated by using the Z component of the vector distance
between one's own aircraft and the intruder aircraft. The function
118 next calculates the closing rate of the intruder aircraft at
step 192. The closing rate is determined by subtracting the
velocity vector of one's own aircraft from the intruder aircraft.
Thus, aircraft velocity vectors that are pointed at each other will
have an additive velocity effect. While two velocity vectors
pointed in the same direction will have a set off effect on the
closing rate. The function 118 next determines whether the intruder
aircraft should be put into the track mode at step 194. This
determination is made by comparing the aircraft altitude, bearing,
and closure rate to predetermined parameters. In the preferred
embodiment the predetermined parameters are whether the intruder is
within 80 miles of one's own aircraft. If the intruder aircraft
falls within the predetermined parameters the intruder aircraft is
put into track mode and the function proceeds to step 198. If the
intruder aircraft falls outside of the predetermined track
thresholds at step 194 then the function 118 returns to the main
loop 196. If the intruder is put into track mode then the function
118 calculates the relative position of the intruder aircraft at
step 198. The relative position of an intruder aircraft is the X
and Y vector displacement between the intruder aircraft and one's
own aircraft. The function 118 then calculates the altitude closing
rate at step 200. The altitude closing rate is the value of the Z
component of the difference between one's own aircraft velocity
vector and the intruders velocity vector. The function 118 next
estimates the miss distance between an intruder aircraft and one's
own aircraft at step 202. This may be performed by step 202:
extrapolating the trajectory of the intruder aircraft from the
intruder aircraft position, velocity vector, and altitude window
data; extrapolating one's own aircraft trajectory from one's own
position, velocity vector, and altitude window data; and using the
extrapolated trajectories to determine the closest distance between
the two aircraft trajectories by iteratively calculating the
distance from a point on one's own track to each point on the
intruders track. The surveillance and tracking function 118 then
returns at step 204 to the STARS control program shown in FIG. 6.
The STARS control program then calls the threat evaluation function
120.
[0075] Turning now to FIG. 10, data calculated in the surveillance
and tracking function 118 is passed to the threat evaluation
function 120. Depending on the altitude, position, closure rates,
and velocity vector and the STARS sensitivity mode, discussed
below, the threat potential and evaluation function 120 categorizes
at step 206 intruder aircraft as either a resolution advisory
threat 208, a traffic advisory 210, proximity 212, or a non-threat
214. If it is determined that the intruder aircraft is a non-threat
214 then the system returns from the function at step 216. If it is
determined that the intruder is outside the traffic advisory
parameters but within the predetermined proximity parameters then
the intruder is classified as a proximity threat 212. The function
212 flags the intruder aircraft for a proximity alert on the
display. If the intruder aircraft is within the traffic advisory
parameters but outside the resolution advisory parameters then the
function 210 will flag the intruder aircraft for a traffic advisory
display. If the intruder aircraft is within the resolution advisory
parameters then the intruder aircraft is flagged as a resolution
advisory. The categorized intruder aircraft are then passed to the
display and alert routine 122. It is understood that all intruder
aircraft are tracked simultaneously and that the data may be stored
in an array of data organized by the intruder aircraft
identification number (ID).
[0076] FIG. 11 illustrates the sequence of steps necessary to
perform the display and alert function 122 shown in FIG. 6. The
display and alert function 122 comprises the following steps:
create a resolution advisory (RA) tracking display 226; create a
traffic alert (TA) tracking display 228; create a tracking display
for proximity alerts 230; create a tracking display for non-threats
232; create an audio alert for a resolution advisory 236; create an
audio alert for a traffic advisory 234; create a display for an
"evasive maneuver" 242; create a display for "traffic" 244; create
a display to highlight an RA target 246; and create a, display to
highlight a TA target 248. The display and alert function 122 uses
the classification from the threat evaluation function 120 to
divide intruder aircraft records into the resolution advisory 218;
traffic advisory 220, proximity alert 222, or non-threat 224
categories. If the intruder aircraft is classified as an resolution
advisory 218 the function 122 creates an RA tracking display 226,
creates and audio alert 236, creates a display to display "evasive
maneuver" 242 and displays the intruder target as a highlighted
icon 246. The function to create an RA tracking display 226 reads
the intruder aircraft ID, range, altitude, and time to point of
contact (TPOC) from the intruder aircraft data record. Function 226
formats and sends this data to the STARS display unit 74. The audio
alert function 236 creates a synthetic voice stating "alert, alert
. . . " and sends this information to the STARS audio interface 76.
The function 242 creates and an "evasive maneuver" display for the
STARS display unit 74. The "evasive maneuver" display appears as
flashing text across the bottom of the STARS display 74 and
indicates that an evasive maneuver is imminent. The display target
highlight function 246 displays the intruder aircraft
representation on the display unit 74 as bright and flashing. If
the intruder aircraft is classified as a traffic advisory 220 the
display and alert function 122 executes the following steps: create
a TA tracking display 228, create and audio alert 234, create a
display "traffic" 244, and display a target highlight 248. The
create TA tracking display 228 function reads the intruder aircraft
ID, range, altitude, and TPOC from the intruder aircraft data
record. The function 228 formats and sends this data to the STARS
display unit 74. The traffic advisory creates a synthetic voice
audio alert to announce "traffic, traffic, . . . " over the
aircraft intercom system. The audio alert 234 function sends the
synthetic voice commands to the audio interface 76. The display
function 244 creates a "traffic" display at the bottom of the STARS
display unit 74. If the intruder aircraft is classified as a
proximity alert 222 function 230 creates a tracking display. The
function 230 creates a tracking display of the intruder aircraft
for display on the STARS display unit 74. The display is a dot that
represents the relative bearing and distance to the intruder
aircraft. If the display and alert function 122 classifies the
intruder aircraft as a non-threat 224 then the function creates a
tracking display for a non-threat aircraft at step 232. The
tracking display 232 step creates a dot that represents the
intruder aircraft at the edge of the STARS display unit 74. The dot
represents the relative bearing to the intruder aircraft and that
the intruder aircraft is outside the display unit 74 calibrated
display range. The function 122 returns to the control program
illustrated in FIG. 6 at step 250.
[0077] FIG. 12 illustrates the steps necessary to calculate an
evasive command as shown in FIG. 6 step 126. The calculate evasive
command function 126 comprises the following: determining if the
intruder aircraft is higher 254, reading the altitude window
information 256, determining aircraft performance data 258;
calculating aircraft altitude 260, and determining an evasive
maneuver for one's own aircraft 262. The calculate evasive command
function 126 calculates an initial evasive command by determining
which aircraft is at a higher GPS altitude at step 254. The
calculate evasive command function at step 254 tentatively
determines that the higher aircraft will be issued the climb
command and the lower aircraft will coordinate with a descend
command. The function 126 then retrieves the altitude window
information at step 256, the aircraft performance data at step 258
and the aircraft altitude at step 260 from the STARS 10 memory and
storage unit 70. The function 126 determines at step 262 using
these factors and a set of predetermined parameters whether the
initial evasive maneuver calculated in step 254 is permissible. If
the initial evasive maneuver calculated at step 254 is permissible
the evasive command function 126 returns with the initial evasive
maneuver at step 264. If the function at step 262 determines that
the initial evasive maneuver calculated at step 254 is
impermissible then step 262 determines a permissible evasive
maneuver. It is understood that the evasive maneuver generator will
generate an evasive command that requires the least radical
maneuver. For example, if two aircraft are at the same altitude but
one aircraft is descending, the evasive command will allow the
descending aircraft to keep descending and order the possibly lower
aircraft to climb. The function 126 then returns with the
permissible evasive maneuver calculated at step 262 at step
264.
[0078] Turning back to FIG. 6 the calculate evasive command
function 126, shown in detail at FIG. 12, returns with an evasive
command. The STARS control process shown in FIG. 6 advances to the
establish data link step 128. The data link step 128 sends the
evasive command generated for one's own aircraft to the intruder
aircraft. This is accomplished by formatting a standard STARS data
block, shown in FIG. 7, with the intruder aircraft ID in the
receiving aircraft data field 144. More specifically, the establish
data link function 128 builds a TDMA transmit block as follows:
one's own aircraft ID is encoded in field 142; the receiver
aircraft ID field 144 is programmed with the intruder aircraft ID,
the control word 146 is encoded with a pattern that indicates an
initial evasive maneuver data link command, fields 148, 150, and
152 are encoded with the respective longitude, latitude, and
altitude data of one's own aircraft; the velocity vector fields
154, 156 and 158 are encoded with data that represents the evasive
maneuver velocity vector calculated at step 126. This message is
sent by the STARS control program to the STARS modem 60 for
transmission by the transceiver 62.
[0079] STARS within receiving range receive the TDMA data link
message sent at step 128. Receiving STARS, e.g. intruders, scan the
receiving aircraft ID field 144 to determine if the message has a
receiving aircraft ID 144 that matches it's own unique aircraft ID.
If the IDs match, the STARS decodes the control word 146 and the
evasive maneuver velocity vector encoded in fields 148, 150, and
152. The receiving STARS then creates an evasive maneuver that is
opposite to the other aircraft's altitude change. For example, if
one's own aircraft originally generates an evasive maneuver to
climb then the opposite evasive maneuver generated by an intruder
aircraft would be to descend. The receiving STARS builds a TDMA
data reply block as follows: The sending aircraft ID field 142 is
encoded with the intruder aircraft's ID; the receiver aircraft ID
field 144 is programmed with the aircraft sending ID field decoded
from the received data link block 142; the control word 146 is
encoded with a pattern that represents an evasive maneuver data
link acknowledgment; fields 148, 150, and 152 are encoded with the
positional data; field 154, 156 and 158 are encoded with data that
represents an evasive maneuver velocity vector. The receiving STARS
transmits this "acknowledgment" message.
[0080] The originating STARS receives the acknowledgment message
and the opposite evasive maneuver from the receiving STARS, e.g.
the intruder STARS. When the evasive maneuver originating aircraft
receives the data link acknowledgment with an opposite maneuver the
originating aircraft at step 128 creates and formats the evasive
maneuver for display on the STARS display unit 74. The originating
STARS also creates the appropriate audio message with the audio
interface unit 76. A contrary maneuver from the intruder indicates
that the evasive command was rejected and the data link originating
aircraft should display an opposite maneuver. Appropriate evasive
maneuver synthetic voice commands and corresponding display are as
follows:
[0081] "CLIMB" "CLIMB", "DESCEND" "DESCEND"
[0082] "STOP CLIMB", "STOP CLIMB"
[0083] "STOP DESCENT", "STOP DESCENT"
[0084] "DO NOT CLIMB", "DO NOT CLIMB"
[0085] "DO NOT DESCEND", "DO NOT DESCEND"
[0086] If the STARS command is a reversal of a preceding command
then the STARS uses a special reversal command notice. Reversal
evasive commands can be generated in high traffic areas were
repetitive evasive maneuvers are required between multiple aircraft
to assure safe distance. Generally, reversal commands are created
that could require the executing aircraft to sustain approximately
+/-0.35 G. When a reversal vertical maneuver is required, one of
the following appropriate evasive commands will be issued.
[0087] "CLIMB NOW", "CLIMB NOW"
[0088] "DESCEND NOW", "DESCEND NOW"
[0089] The STARS evasive command generator 126 operates in
different modes for different altitudes. Lower layers have less
sensitive RA and TA threshold levels to prevent unnecessary
advisories in higher traffic density areas. These parameters can be
delineated, however, it is understood that these parameters are
subject to FAA regulatory approval and frequent changes are within
the scope of the present invention. The sensitivity modes are:
[0090] Sensitivity Level 1:
[0091] Own aircraft is below 500 feet above programmed/selected
reference altitude (P/S/REF/ALT). In this mode only TAs are
generated and RAs are inhibited. A TA is generated if (1) the STARS
calculates that at the current closing rate a safe miss distance of
1200 feet in relative GPS altitude between one's own aircraft and
intruder aircraft will be violated in 20 seconds or less or (2) if
the STARS determines that separation between one's own aircraft and
intruder aircraft is less than 1200 feet in GPS Altitude.
[0092] Sensitivity Level 2
[0093] Own aircraft is between 500 feet above P/S/REF/ALT and 2500
feet above P/S/REF/ALT, in this mode TAs and RAs will be generated.
A TA is generated if the STARS calculates that (1) at the current
closing rate a safe miss distance of 1200 feet in relative CPS
altitude between one's own aircraft and intruder aircraft will be
violated in 35 seconds, (2) separation between one's own aircraft
and intruder aircraft is less than 1200 feet in GPS altitude and
less than 0.35 NM (2128 feet) in range. A RA is generated if the
STARS calculates that (1) at the current rate of closure a safe
miss distance between one's own aircraft and intruder aircraft will
be violated in 20 seconds or less, and (2) the extrapolated
aircraft tracks have a miss distance between 400 and 700 feet. A
corrective (RA) evasive command will be generated if (1) the
extrapolated aircraft tracks determine an aircraft miss distance is
less than 400 feet and (2) separation between one's own aircraft
and intruder aircraft is less than 750 feet in altitude and less
than 0.35 NM (2128) in range.
[0094] Sensitive Level 3
[0095] Own aircraft altitude is above 2500 feet P/S//REF/ALT and
below 10,000 feet above P/S/REF/ALT. In this mode TAs and RAs will
be generated. A TA is generated if the STARS calculates that (1) at
the current closing rate a safe miss distance of 1200 feet in
relative GPS altitude between one's own aircraft and intruder
aircraft will be violated in 40 seconds, (2) separation between
one's own aircraft and intruder aircraft is less than 1200 feet in
altitude and less than 0.55 NM (3344 feet) in range. A RA is
generated if the STARS calculates that at the current closure rate
a safe miss distance between one's own aircraft and intruder
aircraft will be violated in 25 seconds. A preventative RA evasive
command will be generated if the extrapolated miss distance is
between 400 and 700 feet. A corrective (RA) evasive command will be
generated if (1) the extrapolated miss distance is less than 400
feet or (2) separation between own aircraft and intruder aircraft
is less than 750 feet in altitude and less than 0.55 NM (3344 feet)
in range.
[0096] Sensitive Level 4
[0097] Own aircraft altitude is above 10,000 feet P/S/REF/ALT and
below 20,000 feet above P/S/REF/ALT. In this mode TAs and RAs will
be generated. A TA is generated if the STARS calculates that (1) at
the current closing rate a safe miss distance of 1200 feet in
relative GPS altitude between one's own aircraft and intruder
aircraft will be violated in 45 seconds or (2) separation between
one's own aircraft and intruder aircraft is less than 1200 feet in
altitude and less than 0.8 NM (4864 feet) in range. A RA is
generated if the STARS calculates that (1) at the current closure
rate a safe miss distance between own aircraft and intruder
aircraft will be violated in 30 seconds. A preventative RA evasive
command will be generated if miss distance is between 500 and 750
feet. A corrective (RA) evasive command will be generated if (1)
the miss distance is less than 500 feet, or (2) extrapolated
separation between one's own aircraft and intruder aircraft is less
than 750 feet in altitude and less than 0.8 NM (4864 feet) in
range.
[0098] Sensitive Level 5
[0099] Own aircraft altitude is above 20,000 feet P/S/REF/ALT and
below 30,000 feet above P/S/REF/ALT. In this mode both TAs and RAs
will be generated. A TA is generated is the STARS calculates that
(1) at the current closing rate a safe miss distance of 1200 feet
in relative GPS altitude between own aircraft and intruder aircraft
will be violated in 45 second or (2) separation between own
aircraft and intruder aircraft is less than 1200 feet in altitude
and less than 1.10 NM (6688 feet.) in range. A RA is generated is
the STARS calculates that at the current closure rate a safe miss
distance between one's own aircraft and intruder aircraft will be
violated in 35 seconds. A preventative RA evasive command will be
generated if miss distance is between 640 and 850 feet. A
corrective (RA) evasive command will be generated if (1) the miss
distance is less than 640 feet or (2) the extrapolated separation
between one's own aircraft and intruder aircraft is less than 1200
feet in altitude and less than 1.10 NM (6688 feet) in range.
[0100] Sensitive Level 6
[0101] Own aircraft altitude is above 30,000 feet P/S/REF/ALT. In
this mode both TAs and RAs will be generated. A TA is generated is
the STARS calculates that (1) at the current closing rate a safe
miss distance of 1200 feet in relative GPS altitude between own
aircraft and intruder aircraft will be violated in 45 seconds or
(2) separation between one's own aircraft and intruder aircraft is
less than 1200 feet in altitude and less than 1.10 NM (6688 feet)
in range. A RA is generated is the STARS calculates that at the
current closure rate a safe miss distance between own aircraft and
intruder aircraft will be violated in 35 seconds. A preventative RA
evasive command will be generated if the extrapolated miss distance
is between 740 and 950 feet. A corrective (RA) evasive command will
be generated if (1) the miss distance is less than 740 feet or (2)
separation between one's own aircraft and intruder aircraft is less
than 1200 feet in altitude and less than 1.10 NM (6688 feet) in
range.
[0102] FIG. 13 shows a second embodiment of the present invention
wherein the disclosed STARS apparatus and method could be deployed
as a ship anti-collision system. The Ship Satellite Tracking Alert
Resolution System (SSTARS) 266, is a self contained shipboard
traffic alert and collision avoidance system that utilizes the same
methods and apparatus as the STARS 10 but with several changes to
adapt the STARS operation to ships.
[0103] As well know to the art, large sea going vessels such as
supertankers and container ships require a substantial distance to
stop or change course. For example, a fully laden supertanker may
require several miles to stop. Therefore, it is critical that large
vessels coordinate their movements with other vessels in the area
while maintaining a safe distance from navigational hazards such as
reefs and sand bars. Typically the coordination of ships is
conducted by two way voice radio communication with the harbor
master. However, as shown in the EXXON Valdez disaster this system
is an inadequate collision avoidance method especially in remote
areas.
[0104] The SSTARS 266 may use the same hardware configuration as
the STARS 10. The SSTARS 266 has a three GPS receiver
configuration. In the three receiver configuration the receiver
antennae are separated by a predetermined distance, for example,
one forward 272, one mid-ship 270, and one aft 268. Since the
distance between the receiver antennae is known the SSTARS 266 can
constantly check whether the receivers are functional by verifying
that the reported distance between the receiver antennae remains a
constant predetermined distance. Should a receiver report a distant
that does not correspond to the other two then that receiver can be
disabled. Therefore, the three receiver configuration may be used
to continuously check GPS receiver operation.
[0105] The SSTARS 266 receives satellite navigational signals on
receiver antennae 272, 270, and 268. The SSTARS 266 compares the
positions from the receivers to the predetermined distance between
the receiver antennae. The SSTARS 266 formats a message as
illustrated in FIG. 7. The SSTARS 266 message is the same as the
STARS 10 with additional information encoded in the message section
164. The additional information encodes the ship's length height,
tonnage, lading, turn rate, and draw. This information is used by
the SSTARS evasive maneuver generator program to generate
navigational evasive maneuvers to keep ships separated. Generally,
a lighter tonnage ship in the SSTARS embodiment will be given the
more aggressive evasive command while a large vessel is given a
more minor course correction. The SSTARS embodiment also equips
fixed navigational hazards such as reefs, shoals, and sand bars
with a SSTARS 266 type apparatus. It is understood that the SSTARS
storage device contains geographic maps. A standard SSTARS can be
used to track molecular navigational hazards such as icebergs. The
SSTARS fixed navigational embodiment may be preprogrammed with a
fixed position, i.e. a fixed navigational hazard does not need to
continuously update and track its own movements since it is fixed.
The fixed embodiment also offers the advantage of allowing the
collision avoidance system to avoid collisions with temporary or
newly occurring navigational hazards such as newly formed sand bars
that are not on navigational maps.
[0106] The fixed embodiment, in addition, may allow the SSTARS to
correlate an internal topographical SSTARS database (a Map) with a
known fixed SSTARS beacon signal. The SSTARS 266 database may
contain information concerning ports, port master frequencies,
topographical maps of the water ways, water hazards, and seasonal
information. The SSTARS transceiver system operates primarily with
frequencies for line of sight distance operation i.e. in the UHF,
VHF, or SHF frequency range. For example, the line of sight
limitation for a ship with a 200 feet tall transmit antenna and
another ship with a 200 feet receiving antenna is approximately 40
miles. However, it is without the scope of the invention that the
SSTARS nay use HF frequencies and sky-wave propagation to give the
SSTARS a long range mode.
[0107] Thus, the SSTARS can act like a radio warning lighthouse to
alert passing ships of dangerous waters.
* * * * *