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Discrete address beacon system (DABS) test plan for FY 1976

November 14, 1975
  |
Project Report
Author:
William H. Harman III
…
Published in:
MIT Lincoln Laboratory Report ATC-56
Topic:
surveillance
R&D area:
R&D group:

Summary

The major objectives of the continued DABS testing by Lincoln Laboratory are: (1) design validation and refinement, (2) performance assessment, and (3) the development of a data base of environmental characteristics. This document describes that portion of the test activities that will take place during FY 1976. Also included is a description of the special test facilities and teclmiques needed to collect and analyze the required data.
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Summary

The major objectives of the continued DABS testing by Lincoln Laboratory are: (1) design validation and refinement, (2) performance assessment, and (3) the development of a data base of environmental characteristics. This document describes that portion of the test activities that will take place during FY 1976. Also included is...

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Discrete address beacon system (DABS) test plan for FY 1976

Frequency scan antenna design for RPV radar sensors

October 22, 1975
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Project Report
Author:
Francis G. Willwerth
…
Published in:
MIT Lincoln Laboratory Report TT-5
Topic:
antennas
R&D area:
R&D group:

Summary

A small program to explore the feasibility of a frequency-scanned antenna as a low-cost, light-weight answer to the requirements of the mini- RPV radar system for the HCWLS program resulted in construction and study of a slotted-waveguide laboratory embodiment of the device. A general formulation of the relationships connecting design parameters was carried out and employed for guidance in selection of waveguide size, band center, and slot spacing. A 301 band from 14.8 to 20.3 GHz in empty WR-42 waveguide was selected. The beamwidth, sidelobe level, gain, attenuation, and efficiency were studied, including the effectiveness of tapered illumination and the occurrence of spurious cross-polarized radiation, as functions of the frequency-controlled scan direction. Some thought was given to alternatives such as aperiodic-array and subarray techniques as means of reducing the tunable bandwidth requirement, as well as stripline serpentine-waveguide designs, for possible future investigation. The work reported herein has shown that the frequency-scanned antenna will provide a low-cost implementation practical for some system applications. If the limitation, primarily in instantaneous signal bandwidth are acceptable in the applications pursued, further investigation of alternate designs is recommended.
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Summary

A small program to explore the feasibility of a frequency-scanned antenna as a low-cost, light-weight answer to the requirements of the mini- RPV radar system for the HCWLS program resulted in construction and study of a slotted-waveguide laboratory embodiment of the device. A general formulation of the relationships connecting design...

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Frequency scan antenna design for RPV radar sensors

A linear prediction vocoder with voice excitation

September 29, 1975
  |
Conference Paper
Author:
Clifford J. Weinstein
Published in:
Proc. EASCON, 29 September - 1 October 1975, pp. 30-a-30-g.
Topic:
speech processing
R&D area:
R&D group:

Summary

A speech bandwidth compression system, which employs voice excitation in conjunction with a Linear Predictive Coding (LPC) parameterization of the vocal tract filter, is described. To generate the excitation signal, the transmitted speech baseband is broadened at the receiver with a nonlinear distorter, and spectrally flattened by means of an adaptive inverse filter whose parameters are obtained through LPC analysis of the distorted baseband. The voice-excited linear prediction (VELP) system has been implemented in real time on the Fast Digital Processor at Lincoln Laboratory. A detailed description of an 8 kbps version of VELP is given. VELP offers promise as a good quality, medium rate speech compression system which, by avoiding the pitch problem, performs relatively well for telephone quality input speech.
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Summary

A speech bandwidth compression system, which employs voice excitation in conjunction with a Linear Predictive Coding (LPC) parameterization of the vocal tract filter, is described. To generate the excitation signal, the transmitted speech baseband is broadened at the receiver with a nonlinear distorter, and spectrally flattened by means of an...

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A linear prediction vocoder with voice excitation

Logan MLS multipath experiment

September 23, 1975
  |
Project Report
Author:
David A. Shnidman
Published in:
MIT Lincoln Laboratory Report ATC-55
Topic:
air traffic control
R&D area:
R&D group:

Summary

The National Plan for a Microwave Landing System (MLS) has specified a carrier frequency for the system in the vicinity of 5.1 GHz. At that frequency, no multipath data taken at a major civilian airport existed. The purpose of this experiment was to obtain such data at Logan International Airport in order to ascertain: 1) which objects are the major causes of measurable multipath reflections and their levels relative to the direct signal (MID level), 2) whether or not the reflections from these objects can be satisfactorily simulated by the Lincoln computer model and, if so, how complicated must that model be, and 3) if the characteristics of multipath provide a significant discriminant between the Doppler and scanning beam techniques. It was found in the experiment that regions where reflections were noted could be predicted from ray optics and diffraction. No measurable reflections were noted elsewhere. For the purpose of modeling for multipath, building surfaces could be characterized as a flat plate with a reflection coefficient determined by measurement if it were a complicated surface, or by the dielectric properties of the surface material, if a simple surface. The airplane reflection model was also found to agree well with measurements.
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Summary

The National Plan for a Microwave Landing System (MLS) has specified a carrier frequency for the system in the vicinity of 5.1 GHz. At that frequency, no multipath data taken at a major civilian airport existed. The purpose of this experiment was to obtain such data at Logan International Airport...

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Logan MLS multipath experiment

DABS downlink coding

September 12, 1975
  |
Project Report
Author:
John T. Barrows
Published in:
MIT Lincoln Laboratory Report ATC-48
Topic:
surveillance
R&D area:
R&D group:

Summary

This report summarizes the encoding/decoding techniques incorporated into the DABS-downlink design. It has been determined that the binary cyclic code used for the uplink is applicable to the downlink interference environment, thus rendering considerable hardware simplification in the transponder. The downlink environment leads to a characterization as a burst erasure channel, which allows the code to be used to a burst correction capacity. This report concentrates on the error correction techniques including specific implementations. Evaluation of the performance of the code by simulation and/or bench test is presently being carried out and will be reported in a future document.
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Summary

This report summarizes the encoding/decoding techniques incorporated into the DABS-downlink design. It has been determined that the binary cyclic code used for the uplink is applicable to the downlink interference environment, thus rendering considerable hardware simplification in the transponder. The downlink environment leads to a characterization as a burst erasure...

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DABS downlink coding

DABS uplink coding

July 25, 1975
  |
Project Report
Author:
John T. Barrows
Published in:
MIT Lincoln Laboratory Report ATC-49
Topic:
surveillance
R&D area:
R&D group:

Summary

This report details the coding techniques incorporated into the DABS uplink design. Justification is given for the error control method selected in terms of the link characteristics and design constraints. Performance results, including extensive evaluation by simulation and bench test, are presented for the selected code. A binary shortened cyclic code having 24 redundant bits was selected. The overhead due to the code redundancy is minimized by a scheme in which the parity check bits are overlayed on the discrete address field in the encoded message. This code is shown to have the capability of protecting a DABS transponder from accepting an erroneous uplink message with an error probability of less than 10 to the -7 power in a severe interference environment. This same code will be used in the DABS downlink in a burst erasure correction mode. Results of the analysis of the downlink will appear in a separate report.
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Summary

This report details the coding techniques incorporated into the DABS uplink design. Justification is given for the error control method selected in terms of the link characteristics and design constraints. Performance results, including extensive evaluation by simulation and bench test, are presented for the selected code. A binary shortened cyclic...

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DABS uplink coding

Impact of obstacle shadows on monopulse azimuth estimate [project report]

July 17, 1975
  |
Project Report
Author:
Alex Spiridon
Published in:
MIT Lincoln Laboratory Report ATC-50
Topic:
surveillance
R&D area:
R&D group:

Summary

Obstacle shadows, within view of a sensor using monopulse azimuth estimate, cause an error in the azimuth estimate. This report discusses the azimuth error as a function of obstacle dimension and position, and the sensor antenna illumination.
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Summary

Obstacle shadows, within view of a sensor using monopulse azimuth estimate, cause an error in the azimuth estimate. This report discusses the azimuth error as a function of obstacle dimension and position, and the sensor antenna illumination.

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Impact of obstacle shadows on monopulse azimuth estimate [project report]

Plan for flight testing intermittent positive control

June 1, 1975
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Project Report
Author:
John W. Andrews
…
Published in:
MIT Lincoln Laboratory Report ATC-46
Topic:
air traffic control
R&D area:
R&D group:

Summary

Intermittent Positive Control is an automated aircraft collision avoidance system requiring the participation of the aircraft pilots involved. The operational interface between pilots and the IPC system is being evaluated in a series of live flight tests. The Lincoln Laboratory DABS Experimental Facility, augmented to include the IPC function, is the test bed for these evaluation flights. This document described the objectives and methods of the IPC flight testing being conducted by Lincoln Laboratory.
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Summary

Intermittent Positive Control is an automated aircraft collision avoidance system requiring the participation of the aircraft pilots involved. The operational interface between pilots and the IPC system is being evaluated in a series of live flight tests. The Lincoln Laboratory DABS Experimental Facility, augmented to include the IPC function, is...

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Plan for flight testing intermittent positive control

Model aircraft L-band beacon antenna pattern gain maps

May 16, 1975
  |
Project Report
Author:
Douglas W. Mayweather
Published in:
MIT Lincoln Laboratory Report ATC-44
Topic:
L-band
R&D area:
R&D group:

Summary

This document presents L-band antenna patterns for a variety of general aviation and air carrier aircraft; these pattern were based on scale-model measurements. The antenna patterns are described by aircraft-coordinate-referenced elevation vs azimuth gain-contour maps. This method of presentation conveniently displays the effects of aircraft configuration on antenna patterns and allows one to observe the changes in a pattern that result from a change in wheel, flap, or antenna location.
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Summary

This document presents L-band antenna patterns for a variety of general aviation and air carrier aircraft; these pattern were based on scale-model measurements. The antenna patterns are described by aircraft-coordinate-referenced elevation vs azimuth gain-contour maps. This method of presentation conveniently displays the effects of aircraft configuration on antenna patterns and...

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Model aircraft L-band beacon antenna pattern gain maps

Network management

May 16, 1975
  |
Project Report
Author:
Herman F. Vandevenne
Published in:
MIT Lincoln Laboratory Report ATC-45
Topic:
air traffic control
R&D area:
R&D group:

Summary

This report provides a discussion of the design of the DABS network management function. Network management is responsible for the interaction between the local sensor and the adjacent connected sensors. Based on a dynamic interpretation of the coverage map and the status of the network, network management determines (a) the coverage responsibility of the local sensor, (b) which other sensors are covering the same area, and (c) which of the sensors has principal data link responsibility. Interaction is effected through message exchange over ground communication links connecting the DABS sensors.
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Summary

This report provides a discussion of the design of the DABS network management function. Network management is responsible for the interaction between the local sensor and the adjacent connected sensors. Based on a dynamic interpretation of the coverage map and the status of the network, network management determines (a) the...

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Network management
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