Publications
Development of surveillance techniques for TCAS II
March 5, 1984
Conference Paper
Published in:
IEE Colloquium on Airborne Collision Avoidance, London, Uk, 5 March 1984, PP. 2/1-2/4.
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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 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.
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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Flight testing of TCAS II with subject pilots
March 5, 1984
Conference Paper
Published in:
IEEE Colloquium on Airborne Collision Avoidance, London, UK, 5 March 1984, pp. 3/1-3/4.
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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.
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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General aviation TCAS avionics (GATCAS)
February 27, 1984
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-115
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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.
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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Optimal searches for asteroids
January 1, 1984
Journal Article
Published in:
ICARUS, Vol. 57, No. 2, February 1984, pp. 259-266.
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Optimal searches for a fixed object are discussed and the rigorous analytical results of discrete search theory are presented. They show that the totally optimal, the uniformly optimal, the locally optimal, and the fastest searches are identical under not too restrictive assumptions. The mathematical formalism is illustrated by an Earth-approaching asteroid search and optimal searches for such objects are explicitly constructed. The approximation that Earth-approaching asteroids are fixed is equivalent to having a very high (>or=100 square degrees/hr) search rate. Generalizations to other types of astronomical search are briefly mentioned.
Summary
Optimal searches for a fixed object are discussed and the rigorous analytical results of discrete search theory are presented. They show that the totally optimal, the uniformly optimal, the locally optimal, and the fastest searches are identical under not too restrictive assumptions. The mathematical formalism is illustrated by an Earth-approaching...
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Experience with speech communication in packet networks
December 1, 1983
Journal Article
Published in:
IEEE J. Sel. Areas Commun., Vol. SAC-1, No. 6, December 1983, pp. 963-980.
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The integration of digital voice with data in a common packet-switched network system offers a number of potential benefits, including reduced systems cost through sharing of switching and transmission resources, flexible internetworking among systems utilizing different transmission media, and enhanced services for users requiring access to both voice and data communications. Issues which it has been necessary to address in order to realize these benefits include reconstitution of speech from packets arriving at nonuniform intervals, maximization of packet speech multiplexing efficiency, and determination of the implementation requirements for terminals and switching in a large-scale packet voice/data system. A series of packet speech systems experiments to address these issues has been conducted under the sponsorship of the Defense Advanced Research Projects Agency (DARPA). In the initial experiments on the ARPANET, the basic feasibility of speech communication on a store-and-forward packet network was demonstrated. Techniques were developed for reconstitution of speech from packets, and protocols were developed for call setup and for speech transport. Later speech experiments utilizing the Atlantic packet satellite network (SATNET) led to the development of techniques for efficient voice conferencing in a broadcast environment, and for internetting speech between a store-and-forward net (ARPANET) and a broadcast net (SATNET). Large-scale packet speech multiplexing experiments could not be carried out on ARPANET or SATNET where the network link capacities severely restrict the number of speech users that can be accommodated. However, experiments are currently being carried out using a wide-band satellite-based packet system designed to accommodate a sufficient number of simultaneous users to support realistic experiments in efficient statistical multiplexing. Key developments to date associated with the wide-band experiments have been 1) techniques for internetting via voice/data gateways from a variety of local access networks (packet cable, packet radio, and circuit-switched) to a long-haul broadcast satellite network and 2) compact implementations of packet voice terminals with full protocol and voice capabilities. Basic concepts and issues associated with packet speech systems are described. Requirements and techniques for speech processing, voice protocols, packetization and reconstitution, conferencing, and multiplexing are discussed in the context of a generic packet speech system configuration. Specific experimental configurations and key packet speech results on the ARPANET, SATNET, and wide-band system are reviewed.
Summary
The integration of digital voice with data in a common packet-switched network system offers a number of potential benefits, including reduced systems cost through sharing of switching and transmission resources, flexible internetworking among systems utilizing different transmission media, and enhanced services for users requiring access to both voice and data...
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Mode S surveillance netting
November 4, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-120
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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.
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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Frequency sampling of the short-time Fourier-transform magnitude for signal reconstruction
November 1, 1983
Journal Article
Published in:
J. Opt. Soc. Amer., Vol. 73, November 1983, pp. 1523- 1526.
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Unique recovery of a signal from the magnitude (modulus) of the Fourier transform has been of long-standing interest in image and optical processing in which Fourier-transform phase is lost or difficult to measure. We investigate an alternative problem of recovering a signal from the Fourier-transform magnitude of overlapping regions of the signal, i.e., from the short-time (or -space) Fourier-transform magnitude. Recently it was established that a discrete-time signal x (n) can be uniquely obtained under mild restrictions from its short-time Fourier-transform magnitude. In this paper we extend this result to the case when the short-time Fourier-transform magnitude is known at only one or two frequencies for each n. We also present a recursive algorithm for recovering a sequence from such samples and demonstrate the algorithm with an example.
Summary
Unique recovery of a signal from the magnitude (modulus) of the Fourier transform has been of long-standing interest in image and optical processing in which Fourier-transform phase is lost or difficult to measure. We investigate an alternative problem of recovering a signal from the Fourier-transform magnitude of overlapping regions of...
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The Experimental Integrated Switched Network - a system-level network test facility
October 31, 1983
Conference Paper
Published in:
Proc. 1983 IEEE Military Communications Conf., MILCOM, 31 October-2 November 1983.
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An Experimental Integrated Switched Network (EISN) has been developed to provide a system-level testbed for the evaluation of advanced communications networking techniques, including survivable network routing algorithms using a mix of transmission media, for application in the Defense Switched Network (DSN). EISN includes five CONUS sites linked by a wideband demand-assigned satellite channel and by dialed-up terrestrial trunks for alternate satellite/terrestrial routing experiments. Experiments to date have validated techniques for integration of circuit-switched terrestrial systems with the demand-assigned satellite system, and for the establishment of alternate routes over satellite and terrestrial paths. Currently, candidate routing algorithms for application in the DSN are being implemented and tested using external routing/controller processors attached to digital circuit switches at EISN sites. In addition, EISN is also being used to support data communication experiments using DoD standard data protocols in a combined satellite/terrestrial network environment. Work is ongoing both in system experiments and in testbed developments to include additional capabilities. This paper represents a description and status report on both the testbed and the experimental efforts.
Summary
An Experimental Integrated Switched Network (EISN) has been developed to provide a system-level testbed for the evaluation of advanced communications networking techniques, including survivable network routing algorithms using a mix of transmission media, for application in the Defense Switched Network (DSN). EISN includes five CONUS sites linked by a wideband...
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Airborne Intelligence Display (AID) phase I software description
October 24, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-123
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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.
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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Ground clutter cancellation for the NEXRAD system
October 19, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-122
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.
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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