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Fundamentals of mode S parity coding

April 2, 1984
  |
Project Report
Author:
Jeffrey L. Gertz
Published in:
MIT Lincoln Laboratory Report ATC-117
Topic:
mode S data links
R&D area:
R&D group:

Summary

This report presents the details and basic theory of the coding scheme employed on Mode S uplink and downlink transmissions. Since ATCRBS interference is the main source of error for these signals, a cyclic burst detection code was chosen for Mode S. This code permits simple error detection at the transponder and more complex error correction at the sensor. The theory behind cyclic encoding and decoding as used for Mode S is presented first. Then, since polynomial multiplication and division are required for these processes, circuits for these operations are described. Finally, the last chapter describes the actual implementations specified for encoding and decoding in both the transponder and sensor.
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Summary

This report presents the details and basic theory of the coding scheme employed on Mode S uplink and downlink transmissions. Since ATCRBS interference is the main source of error for these signals, a cyclic burst detection code was chosen for Mode S. This code permits simple error detection at the...

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Fundamentals of mode S parity coding

A high stability TWTA for ground surveillance applications

March 13, 1984
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Conference Paper
Author:
C. E. Hayse
…
Published in:
Proc. 1984 IEEE Natl. Radar Conf., 13-14 March 1984, pp. 110-114.
Topic:
radar
R&D area:
R&D group:

Summary

A high stability, C-band transmitter capable of supporting -68 dBr subclutter visibility over a wide range of pulse widths and duty factors was developed for use in a multimode, battlefield surveillance radar. The transmitter was mode-switched between groups of 1/4, 20 and 65 microsecond radar pulses and long duration (100ms) FSK burst. A key feature was the use of a high speed, interpulse regulator to maintain proper TWT voltage and to limit ripple independent of waveform without the need for excessively large energy storage. Actual measured performance met the 100 mV cathode ripple specification without the use of PKF synchronization, independent of PKI, duty cycle and pulse width and was confirmed via direct evaluation of electrode voltages, serrodyne phase jitter and the radar pulsed-Doppler spectrum.
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Summary

A high stability, C-band transmitter capable of supporting -68 dBr subclutter visibility over a wide range of pulse widths and duty factors was developed for use in a multimode, battlefield surveillance radar. The transmitter was mode-switched between groups of 1/4, 20 and 65 microsecond radar pulses and long duration (100ms)...

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A high stability TWTA for ground surveillance applications

Development of surveillance techniques for TCAS II

March 5, 1984
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Conference Paper
Author:
William H. Harman III
Published in:
IEE Colloquium on Airborne Collision Avoidance, London, Uk, 5 March 1984, PP. 2/1-2/4.
Topic:
collision avoidance
R&D area:
R&D group:

Summary

In the development program of airborne collision avoidance, the equipment intended for installation on air carriers is designated TCAS 11 in the United States. A TCAS 11 installation my be thought of as consisting of two major subsystems: (1) air-to-air surveillance, and (2) control logic (including the logical tests that decide when another aircraft is dangerously close, algorithm that select an appropriate vertical resolution advisory, and a display of the advisory to the pilot). This paper focuses on the air-to-air surveillance subsystem. It identifies the disturbance phenomena that affect performance, presents a number of techniques that have been developed to overcome these difficulties, and presents performance measurements made through airborne testing. A TCAS II installation carries out surveillance in both Mode S and Mode C. The former is used for all Mode S aircraft, including other TCAS II aircraft. The latter is used for all other aircraft, provided they are equipped to reply in Mode C. This paper concentrates on surveillance in Mode C, which is by far the more demanding case.
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Summary

In the development program of airborne collision avoidance, the equipment intended for installation on air carriers is designated TCAS 11 in the United States. A TCAS 11 installation my be thought of as consisting of two major subsystems: (1) air-to-air surveillance, and (2) control logic (including the logical tests that...

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Development of surveillance techniques for TCAS II

Flight testing of TCAS II with subject pilots

March 5, 1984
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Conference Paper
Author:
John W. Andrews
Published in:
IEEE Colloquium on Airborne Collision Avoidance, London, UK, 5 March 1984, pp. 3/1-3/4.
Topic:
collision avoidance
R&D area:
R&D group:

Summary

All safety benefits to be derived from the Traffic Alert and Collision Avoidance System (TCAS) are dependent upon the aircraft crew understanding and reacting appropriately to the TCAS advisories. For this reason it is important to display the TCAS information so that it can be promptly and unambiguously understood by the crew. It is also important that the crew be able to integrate the TCAS advisory information with information from other sources so that TCAS becomes a compatible addition to pre-existing safety procedures and not a contending alternative. Because crew response to TCAS is strongly influenced by visual cues received from outside the cockpit, testing in actual flight has proven important. Under sponsorship of the Federal Aviation Agency (FAA), Lincoln Laboratory conducted a series of flight tests with an experimental TCAS II unit to investigate crew response issues.
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Summary

All safety benefits to be derived from the Traffic Alert and Collision Avoidance System (TCAS) are dependent upon the aircraft crew understanding and reacting appropriately to the TCAS advisories. For this reason it is important to display the TCAS information so that it can be promptly and unambiguously understood by...

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Flight testing of TCAS II with subject pilots

General aviation TCAS avionics (GATCAS)

February 27, 1984
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Project Report
Author:
Randal L. Briggs
…
Published in:
MIT Lincoln Laboratory Report ATC-115
Topic:
collision avoidance
R&D area:
R&D group:

Summary

Experimental Traffic Alert and Collision Avoidance System (TCAS) avionics developed for the FAA at MIT Lincoln Laboratory are described. The objective of the program under which this equipment was developed was to assess the feasibility of providing a small, low-cost unit for general aviation usage. The experimental general aviation TCAS (GATCAS) avionics incorporates a new system architecture using a microprogrammed sequencer, a 16-bit microprocessor and a low-power, solid state sransmitter appropriate to the class of aircraft expected to employ GATCAS. The general aviatio unit is designed to operate below 10,000 feet in densities of up to 0.02 aircraft/nmi^2, and to provide a pilot warning time (TAUR) of 25 seconds. Assuming a track acquisition time of 10 seconds and a maximum closing speed of 300 knots, the required theoretical range of GATCAS is 3.4 nmi. The report includes (as an appendix) a cost analysis for general aviation TCAS avionics.
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Summary

Experimental Traffic Alert and Collision Avoidance System (TCAS) avionics developed for the FAA at MIT Lincoln Laboratory are described. The objective of the program under which this equipment was developed was to assess the feasibility of providing a small, low-cost unit for general aviation usage. The experimental general aviation TCAS...

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General aviation TCAS avionics (GATCAS)

Mode S surveillance netting

November 4, 1983
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Project Report
Author:
Jeffrey L. Gertz
Published in:
MIT Lincoln Laboratory Report ATC-120
Topic:
mode S data links
R&D area:
R&D group:

Summary

The surveillance performance of a single Mode S Sensor is degraded by several factors, including: poor crossrange accuracy at long range, diffraction-induced azimuth errors, missing of incomplete reports, and extraneous reports. The surveillance netting project reported here sought to overcome these difficulties by employing information from a secondary (and perhaps also a tertiary) sensor. The project was performed to determine what auxiliary information is most useful, how this information could be used for maximum effect, when help should be sought from other sensors, what form this inter-sensor communication should take, and where the netting algorithms should be implemented. It was also planned to include the construction of a real-time netting demonstration system to exercise and test the concepts developed. The central issue in this project was the approach to be used for multi-sensor azimuth determination. In particular, a new form of incremental bilateration, employing a flat earth model, is shown to be both accurate and bias-resistant. Altitude estimation methods and multi-sensor tracker design are also addressed, with new algorithms developed in each case. Finally, the deisgn of the netting subsystem for a Mode S sensor is presented.
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Summary

The surveillance performance of a single Mode S Sensor is degraded by several factors, including: poor crossrange accuracy at long range, diffraction-induced azimuth errors, missing of incomplete reports, and extraneous reports. The surveillance netting project reported here sought to overcome these difficulties by employing information from a secondary (and perhaps...

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Mode S surveillance netting

Airborne Intelligence Display (AID) phase I software description

October 24, 1983
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Project Report
Author:
Ann C. Drumm
…
Published in:
MIT Lincoln Laboratory Report ATC-123
Topic:
collision avoidance
R&D area:
R&D group:

Summary

The Airborne Intelligent Display is a microprocessor-based display capable of serving as a cockpit data terminal in a variety of FAA developmental applications. A prototype of this display was developed by Lincoln Laboratory during 1979-1980 in order to evaluate and demonstrate the use of the data link between Mode S ground sensor and Mode S transponder-equipped aircraft. The AID served as a data link interface allowing the pilot to see, respond to, and initiate communications from a ground sensor. Later, when Lincoln began testing the Traffic Alert and Collision Avoidance System (TCAS), the AID became the TCAS display device, showing position estimates for TCAS-tracked aircraft. More recently, a redesign effort, focused principally on software, was begun to extend the AID design so that it could be more quickly adapted to a variety of FAA developmental programs. This document describes the redesigned Airborne Intelligent Display, with special emphasis on software design.
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Summary

The Airborne Intelligent Display is a microprocessor-based display capable of serving as a cockpit data terminal in a variety of FAA developmental applications. A prototype of this display was developed by Lincoln Laboratory during 1979-1980 in order to evaluate and demonstrate the use of the data link between Mode S...

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Airborne Intelligence Display (AID) phase I software description

Ground clutter cancellation for the NEXRAD system

October 19, 1983
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Project Report
Author:
James E. Evans
Published in:
MIT Lincoln Laboratory Report ATC-122
Topic:
radar
R&D area:
R&D group:

Summary

Returns from the ground and associated obstacles surroudning a NEXRAD weather radar (i.e., ground clutter) will contaminate the estimates of weather echo spectral features (e.g., reflectivity, mean velocity, and spectral width). The ground clutter returns are particularly large at low elevation angles and close range (e.g., within 40 km). Additionally, the pulse repetition frequency (PRF) values necessary to obtain the desired weather Doppler features result in ground clutter contamination at ranges that are multiples of the unambiguous range interval (e.g., 115-175 km for a typical NEXRAD). Fortunately, the groung clutter power spectrum is localized around zero velocity so that one can reduce its effect by appropriate Doppler signal processing. Automatic reduction of clutter contamination is essential if NEXRAD is to achieve the desired automatic weather product generation capability. The results of an analytical/experimental study oreinted toward development of a clutter cancellation specification and assiciated quality assurance tests for the NEXRAD system are described.
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Summary

Returns from the ground and associated obstacles surroudning a NEXRAD weather radar (i.e., ground clutter) will contaminate the estimates of weather echo spectral features (e.g., reflectivity, mean velocity, and spectral width). The ground clutter returns are particularly large at low elevation angles and close range (e.g., within 40 km). Additionally...

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Ground clutter cancellation for the NEXRAD system

A traffic alert and collision avoidance system for general aviation

October 1, 1983
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Conference Paper
Author:
Vincent A. Orlando
…
Published in:
IEEE/AIAA 5th Digital Avionics Systems Conf., Seattle, WA, 31 October - 3 November 1983, pp. 20.
Topic:
air traffic control
R&D area:
R&D group:

Summary

One component of the Federal Aviation Administration approach to independent aircraft separation assurance is known as the Traffic Alert and Collision Avoidance System I (TCAS I), which employs passive or active techniques for the detection of nearby transponder-equipped aircraft. This paper gives the results of a study conducted by Lincoln Laboratory of simple techniques for the passive and active detection of transponders. Filter criteria that may be used to restrict passive detections to potentially threatening aircraft are described and evaluated. These techniques and criteria were used in a candidate passive detector whose performance was evaluated in flight against targets of opportunity. A candidate low-power active interrogator was also evaluated through link calculations and airborne measurements. The results indicate that a low-power active interrogator can provide more reliable detection of nearby aircraft and a lower false alert rate than any of the simple passive techniques considered. The active technique generates insignificant levels of interference and, unlike a passive system, also provides protection in regions where there are no ground interrogators.
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Summary

One component of the Federal Aviation Administration approach to independent aircraft separation assurance is known as the Traffic Alert and Collision Avoidance System I (TCAS I), which employs passive or active techniques for the detection of nearby transponder-equipped aircraft. This paper gives the results of a study conducted by Lincoln...

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A traffic alert and collision avoidance system for general aviation

An experimental GPS navigation receiver for general aviation: design and measured performance

September 27, 1983
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Project Report
Author:
Steven D. Campbell
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Published in:
MIT Lincoln Laboratory Report ATC-121
Topic:
GPS
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R&D group:

Summary

This report describes work performed by MIT Lincoln Laboratory between 1 October 1979 and 1 March 1983, to evaluate the use of the Global Positioning System (GPS) for low-cost civil air navigation. The report describes a GPS Test and Evaluation System developed jointly by MIT Lincoln Laboratory, Stanford Telecommunications, Inc., and Intermetrics, Inc., using techniques that could lead to low-cost commercial avionics. System performance results obtained in the laboratory and during flight tests are provided which demonstrate compliance with current and future navigation accuracy requirements for enroute, terminal, and non-precision flight paths. The report also includes functional specifications for a low-cost GPS navigation system for civil aircraft. The GPS Test and Evaluation system design was based on two important features: 1) automatic tracking of all visible satellites (rather than a minimum set of four) and 2) a dual-channel GPS C/A code receiver. Tracking all visible satellites allows the system to maintain continuous navigation when a satellite sets or is momentarily masked during aircraft maneuvers. The dual-channel receiver dedicates one channel to pseudo-range measurements, and the other channel to acquiring new satellites as they become visible. These two features, validated by flight test, allow the system to provide continuous navigation updates during critical aircraft maneuvers, such as non-precision approaches, and during satellite constellation changes.
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Summary

This report describes work performed by MIT Lincoln Laboratory between 1 October 1979 and 1 March 1983, to evaluate the use of the Global Positioning System (GPS) for low-cost civil air navigation. The report describes a GPS Test and Evaluation System developed jointly by MIT Lincoln Laboratory, Stanford Telecommunications, Inc...

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An experimental GPS navigation receiver for general aviation: design and measured performance
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