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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

Adaptive noise cancellation in a fighter cockpit environment

March 19, 1984
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Conference Paper
Author:
William A. Harrison
…
Published in:
ICASSP'84, IEEE Int. Conf. on Acoustics, Speech and Signal Processing, 19-21 March 1984.
Topic:
speech
R&D area:
R&D group:

Summary

In this paper we discuss some preliminary results on using Widrow's Adaptive Noise Cancelling (ANC) algorithm to reduce the background noise present in a fighter pilot's speech. With a dominant noise source present and with the pilot wearing an oxygen facemask, we demonstrate that good (>10 dB) cancellation of the additive noise and little speech distortion can be achieved by having the reference microphone attached to the outside of the facemask and by updating the filter coefficients only during silence intervals.
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Summary

In this paper we discuss some preliminary results on using Widrow's Adaptive Noise Cancelling (ANC) algorithm to reduce the background noise present in a fighter pilot's speech. With a dominant noise source present and with the pilot wearing an oxygen facemask, we demonstrate that good (>10 dB) cancellation of the...

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Adaptive noise cancellation in a fighter cockpit environment

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)

Optimal searches for asteroids

January 1, 1984
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Journal Article
Author:
Laurence G. Taff
Published in:
ICARUS, Vol. 57, No. 2, February 1984, pp. 259-266.
Topic:
asteroids
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R&D group:

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 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.
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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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Optimal searches for asteroids

Experience with speech communication in packet networks

December 1, 1983
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Journal Article
Author:
Clifford J. Weinstein
…
Published in:
IEEE J. Sel. Areas Commun., Vol. SAC-1, No. 6, December 1983, pp. 963-980.
Topic:
signal processing
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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 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.
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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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Experience with speech communication in packet networks

Mode S surveillance netting

November 4, 1983
  |
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

Frequency sampling of the short-time Fourier-transform magnitude for signal reconstruction

November 1, 1983
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Journal Article
Author:
Jae S. Lim
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Published in:
J. Opt. Soc. Amer., Vol. 73, November 1983, pp. 1523- 1526.
Topic:
signal processing
R&D area:
R&D group:

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 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.
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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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Frequency sampling of the short-time Fourier-transform magnitude for signal reconstruction
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