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The effects of microphones and facemasks on LPC vocoder performance

March 1, 1981
  |
Conference Paper
Author:
Elliot Singer
Published in:
Proc. of IEEE Int. Conf. on Acoustics, Speech & Signal Processing, 30 March - 1 April 1981.
Topic:
speech
R&D area:

Summary

The effects of oxygen facemasks and noise cancelling microphones on LPC vocoder performance were analyzed and evaluated. Likely sources of potential vocoder performance degradation included the non-ideal frequency response characteristics of the microphone and the possible presence of additional resonances in the speech waveform due to the addition of the facemask cavity. Examination of vowel spectra revealed that spurious resonances do not occur in the vocoder frequency band for speech generated using the facemask and microphone. Also observed was a vowel-dependent reduction in the bandwidths of the upper formants, a result which can be predicted from acoustic theory. Finally, it is shown that the low frequency emphasis associated with small enclosures is not relevant when using a pressure gradient (noise cancelling) microphone. Diagnostic Rhyme Tests involving three subjects indicated that the presence of the oxygen facemask and noise cancelling microphone did not result in a significant increase in the LPC vocoder processing loss.
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Summary

The effects of oxygen facemasks and noise cancelling microphones on LPC vocoder performance were analyzed and evaluated. Likely sources of potential vocoder performance degradation included the non-ideal frequency response characteristics of the microphone and the possible presence of additional resonances in the speech waveform due to the addition of the...

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The effects of microphones and facemasks on LPC vocoder performance

Radar Beacon Transponder (RBX) functional description

February 18, 1981
  |
Project Report
Author:
Ronald G. Sandholm
Published in:
MIT Lincoln Laboratory Report ATC-104
Topic:
surveillance
R&D area:
R&D group:

Summary

The Radar Beacon Transponder (RBX) is a ground-based transponder used to control the threat-detection sensitivity level of BCAS aircraft operating in high density terminal airspace. THe RBX is also used to deliver displayed resolution advisories from BCAS to the ATC facility. The normal DABS interrogation waveforms and message formats are used for communication between the RBX and BCAS aircraft. The appropriate BCAS sensitivity level is selected by comparing the BCAS aircraft position with an internally stored sensitivity level map of the surrounding airspace volume. This document provides a functional description of the RBX and shows that reliable performance is achievable in the presence of interference from ATCRBS and BCAS air-to-air interrogations.
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Summary

The Radar Beacon Transponder (RBX) is a ground-based transponder used to control the threat-detection sensitivity level of BCAS aircraft operating in high density terminal airspace. THe RBX is also used to deliver displayed resolution advisories from BCAS to the ATC facility. The normal DABS interrogation waveforms and message formats are...

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Radar Beacon Transponder (RBX) functional description

Electronic flight rules: an alternative separation assurance concept

December 31, 1980
  |
Project Report
Author:
John W. Andrews
…
Published in:
MIT Lincoln Laboratory Report ATC-93
Topic:
air traffic control
R&D area:
R&D group:

Summary

This report presents results of a study of alternative concepts for tactically separating aircraft in low altitude en route airspace. It describes a concept designated Electronic Flight Rules (EFR) which allows aircraft to fly under instrument meteorological conditions in a manner that retains most of the freedom and flexibility of VFR flight. Feasibility considerations, potential benefits, applicable technologies, and alternative system configurations are evaluated.
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Summary

This report presents results of a study of alternative concepts for tactically separating aircraft in low altitude en route airspace. It describes a concept designated Electronic Flight Rules (EFR) which allows aircraft to fly under instrument meteorological conditions in a manner that retains most of the freedom and flexibility of...

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Electronic flight rules: an alternative separation assurance concept

Active Beacon Collision Avoidance System (BCAS) functional overview

December 17, 1980
  |
Project Report
Author:
Jerry D. Welch
…
Published in:
MIT Lincoln Laboratory Report ATC-102
Topic:
collision avoidance
R&D area:
R&D group:

Summary

The Active Beacon Collision Avoidance System (BCAS) is a beacon-based airborne collision avoidance system that provides for cooperative threat resolution between BCAS and conflicting aircraft and coordination with the ground ATC control function through the DABS data link. All beacon-equipped aircraft in the vicinity of the BCAS are detected. ATCRBS-equipped aircraft are interrogated using a special Mode C interrogation. DABS aircraft are initially detected passively. Those aircraft that represent a possible threat are discretely interrogated to maintain a range/altitude track. This document provides a functional overview of BCAS including operational features, a description of the avionics package, and examples of surveillance data obtained with experimental BCAS equipment. The results show that reliable surveillance performance is achieved in low and medium density airspace.
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Summary

The Active Beacon Collision Avoidance System (BCAS) is a beacon-based airborne collision avoidance system that provides for cooperative threat resolution between BCAS and conflicting aircraft and coordination with the ground ATC control function through the DABS data link. All beacon-equipped aircraft in the vicinity of the BCAS are detected. ATCRBS-equipped...

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Active Beacon Collision Avoidance System (BCAS) functional overview

Active BCAS: design and validation of the surveillance subsystem

December 17, 1980
  |
Project Report
Author:
William H. Harman III
…
Published in:
MIT Lincoln Laboratory Report ATC-103
Topic:
collision avoidance
R&D area:
R&D group:

Summary

Lincoln Laboratory, under FAA sponsorship, is developing an Active Beacon Collision Avoidance System (BCAS), concentrating primarily on the air-to-air surveillance subsystem. The surveillance functions required are to detect the presence of nearby aircraft (whether they are equipped with ATCRBS transponders or DABS transponders), and then generate a surveillance track on each aircraft, issuing range and altitude reports once per second. The development effort consisted of airborne measurements complemented by simulation studies and analyses. The basic effects of ground-bounce multipath, interference, and power fading were assessed by air-to-air measurements. In other measurements, the BCAS interrogation and reply signal formats were transmitted between aircraft, and the results recorded for later playback and computer processing using the BCAS surveillance algorithms. This is a flexible means of experimentation which allows many of the design parameters to be changed as the effects are noted. In the most recent phase of the program, Lincoln designed and built realtime BCAS Experimental Units (BE Us), flight tested them, and then delivered them to the FAA for more extensive flight testing. In one of these flight tests, a BEU-equipped Boeing 727 flew to New York, Atlanta, and other major terminal areas in the eastern U.S. An analysis of BEU performance during this "Eastern Tour" is given in this report.
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Summary

Lincoln Laboratory, under FAA sponsorship, is developing an Active Beacon Collision Avoidance System (BCAS), concentrating primarily on the air-to-air surveillance subsystem. The surveillance functions required are to detect the presence of nearby aircraft (whether they are equipped with ATCRBS transponders or DABS transponders), and then generate a surveillance track on...

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Active BCAS: design and validation of the surveillance subsystem

Registration errors in a netted air surveillance system

September 2, 1980
  |
Technical Report
Author:
William L. Fischer
…
Published in:
MIT Lincoln Laboratory Report TN-1980-40
Topic:
radar
R&D area:
R&D group:

Summary

Today's tactical military air surveillance radars generally operate in a stand-alone configuration. The many performance improvements that result when data from multiple radars of this type are merged have made such netted operations an attractive goal for many years. A major obstacle to achieving this goal has traditionally been the difficulty associated with the registration of multisensor data, the expression of the data in a common coordinate system free from errors due to site uncertainty, antenna orientation, and improper alignment. This report presents the results of a modest effort to develop a self-registration procedure by which multiple radar sensors operating in consort each calculate the errors In their data by comparing it with data from the remainder of the system and then uses the information to upgrade performance. The technique has been tested with experimental data and appears quite capable of improving system performance, measured in terms of residual inter-site bias errors, by almost a factor of one hundred.
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Summary

Today's tactical military air surveillance radars generally operate in a stand-alone configuration. The many performance improvements that result when data from multiple radars of this type are merged have made such netted operations an attractive goal for many years. A major obstacle to achieving this goal has traditionally been the...

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Registration errors in a netted air surveillance system

Voice communication in integrated digital voice and data networks

September 1, 1980
  |
Journal Article
Author:
Theodore Bially
…
Published in:
IEEE Trans. Commun., Vol. COM-28, No. 9, September 1980, pp. 1478-90.
Topic:
signal processing
R&D area:
R&D group:

Summary

Voice communication networks have traditionally been designed to provide either analog signal paths or fixed-rate synchronous digital connections between individual subscribers. These designs were aimed at accommodating the "streamlike" character of speech, which has traditionally been considered to flow from source to destination at a more or less constant rate. By way of contrast, interactive and computer-to-computer data transactions tend to be "bursty" in nature, and this has given rise to the development of packet-switching methods for data communications. The dichotomous nature of these two major traffic classes and the apparent conflict between the types of network services they require has resulted in the deployment of separate military communications facilities for voice and data. A challenge in the design of future systems is to achieve overall economy and flexibility in the allocation of resources via the efficient integration of both traffic types in common network facilities. This paper summarizes a number of advanced concepts for switching and flow control of combined voice and data traffic in integrated environments. Performance characteristics are described based on analysis results and computer simulation studies for both multilink terrestrial and broadcast satellite network topologies.
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Summary

Voice communication networks have traditionally been designed to provide either analog signal paths or fixed-rate synchronous digital connections between individual subscribers. These designs were aimed at accommodating the "streamlike" character of speech, which has traditionally been considered to flow from source to destination at a more or less constant rate...

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Voice communication in integrated digital voice and data networks

The DABS data link airborne intelligent display operator's manual

September 1, 1980
  |
Project Report
Author:
James C. Anderson
…
Published in:
MIT Lincoln Laboratory Report ATC-100
Topic:
air traffic control
R&D area:
R&D group:

Summary

The Federal Aviation Administration is currently evaluating the Discrete Address Beacon System (DABS) which will provide increased air traffic safety in current and future air traffic conditions. In addition to improved surveillance accuracy and reliability, DABS provides a two-way data link between the DABS sensor and all DABS transponder equipped aircraft in view. A DABS data link avionics system, called the Airborne Intelligent Display (AID), was developed by M.I.T. Lincoln Laboratory for the purpose of evaluating and demonstrating initial and future data link applications. The microprocessor-based AID system communicates with the DABS ground sensor through the DABS transponder onboard the aircraft. Data link information included in uplink interrogations to the transponder is decoded in the airborne microprocessor and then made available to the pilot on a high visibility cathode ray tube display. The purpose of this report is to describe the operation and use of the AID.
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Summary

The Federal Aviation Administration is currently evaluating the Discrete Address Beacon System (DABS) which will provide increased air traffic safety in current and future air traffic conditions. In addition to improved surveillance accuracy and reliability, DABS provides a two-way data link between the DABS sensor and all DABS transponder equipped...

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The DABS data link airborne intelligent display operator's manual

Convergence of iterative nonexpansive signal reconstruction algorithms

August 1, 1980
  |
Journal Article
Author:
Victor T. Tom
…
Published in:
IEEE Trans. Acoust. Speech Signal Process., Vol. ASSP-29, No. 5, October 1981, pp. 1052-1059.
Topic:
signal processing
R&D area:
R&D group:

Summary

Iterative algorithms for signal reconstruction from partial time- and frequency-domain knowledge have proven useful in a number of application areas. In this paper, a general convergence proof, applicable to a general class of such iterative reconstruction algorithms, is presented. The proof relies on the concept of a nonexpansive mapping in both the time and frequency domains. Two examples studied in detail are time-limited extrapolation (equivalently, band-limited extrapolation) and phase-only signal reconstruction. The proof of convergence for the phase-only iteration is a new result obtained by this method of proof. The generality of the approach allows the incorporation of nonlinear constraints such as time- (or space-) domain positivity or minimum and maximum value constraints. Finally, the underrelaxed form of these iterations is also shown to converge even when the solution is not guaranteed to be unique.
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Summary

Iterative algorithms for signal reconstruction from partial time- and frequency-domain knowledge have proven useful in a number of application areas. In this paper, a general convergence proof, applicable to a general class of such iterative reconstruction algorithms, is presented. The proof relies on the concept of a nonexpansive mapping in...

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Convergence of iterative nonexpansive signal reconstruction algorithms

Format for DABS data link applications

July 30, 1980
  |
Project Report
Author:
John L. Leeper
…
Published in:
MIT Lincoln Laboratory Report ATC-96
Topic:
surveillance
R&D area:
R&D group:

Summary

The purpose of this paper is to describe formats developed for transmitting aviation-related messages over the Discrete Address Beacon System (DABS) data link. Initial data link applications include: (1) Minimum Safe Altitude Warning (MSAW) alerts (Terminal Area) (2) Takeoff Clearance Confirmation (3) Altitude Assignment Clearance Confirmation (Enroute) (4) Weather Reports (a) Surface Observations (b) Terminal Forecasts (c) Pilot Reports (d) Winds Aloft (e) Hazardous Weather Advisories (f) Digitized Weather Radar Maps (5) Enhanced terminal Information Service (ETIS) (6) Downlink of Airborne Measurements. The formats described in this paper cover the DABS communications formats for uplink messages from the DABS sensor to the airborne data link system, and the downlink messages from the aircraft. Downlink messages include pilot requests for routine weather information and ETIS service, pilot acknowledgements for uplink tactical messages, and airborne measurements.
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Summary

The purpose of this paper is to describe formats developed for transmitting aviation-related messages over the Discrete Address Beacon System (DABS) data link. Initial data link applications include: (1) Minimum Safe Altitude Warning (MSAW) alerts (Terminal Area) (2) Takeoff Clearance Confirmation (3) Altitude Assignment Clearance Confirmation (Enroute) (4) Weather Reports...

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Format for DABS data link applications
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