Publications
Technical Assessment of Satellites for CONUS Air Traffic Control, Volume III - Satellite-To-Aircraft Techniques
February 19, 1974
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-26,III
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Summary
A number of satellite system techniques have been suggested as candidates to provide ATC surveillance, communication, and/or navigation service over CONUS. All techniques perform postion determination by multilateration using a constellation of satellites. They can be categorized as follows: 1) Coordinated Aircraft-to-Satellite Techniques (CAST), 2) Random Access Aircraft-to-Satellite Techniques (RAST), and 3) Satellite-to-Aircraft Techniques (SAT). A technical assessment is made of the various techniques with no one particular technique emerging as superior; several feasible alternatives are identified. The assessment indicates that satellite bases techniques for CONUS ATC can be developed without relying on high risk technology. This three-volume report is a technical assessment of all three techniques. The present volume examines satellite-to-aircraft techniques (SAT). The remaining two volumes treat CAST and RAST. The assessment has shown that workable systems could be configured using any one of the three techniques without reliance on high risk technology. No one technique has emerged as superior. Rather several viable alternatives have been identified. All techniques appear to require more costly avionics than today's ground-based system.
Summary
A number of satellite system techniques have been suggested as candidates to provide ATC surveillance, communication, and/or navigation service over CONUS. All techniques perform postion determination by multilateration using a constellation of satellites. They can be categorized as follows: 1) Coordinated Aircraft-to-Satellite Techniques (CAST), 2) Random Access Aircraft-to-Satellite Techniques (RAST)...
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A system for acoustic-phonetic analysis of continuous speech
February 15, 1974
Conference Paper
Published in:
Proc. IEEE Symp. on Speech Recognition, 15-19 April 1974, pp. 54-67.
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Summary
A system for acoustic-phonetic analysis of continuous speech is being developed to serve as part of an automatic speech understanding system. The acoustic system accepts the speech waveform as an input and produces as output a string of phoneme-like units referred to as acoustic phonetic elements (APEL'S). This paper should be considered as a progress report, since the system is still under active development. The initial phase of the acoustic analysis consists of signal processing and parameter extraction, and includes spectrum analysis via linear prediction, computation of a number of parameters of the spectrum, and fundamental frequency extraction. This is followed by a preliminary segmentation of the speech into a few broad acoustic categories and formant tracking during vowel-like segments. The next phase consists of more detailed segmentation and classification intended to meet the needs of subsequent linguistic analysis. The preliminary segmentation and segment classification yield the following categories: vowel-like sound; volume dip within vowel-like sound; fricative-like sound; stop consonants, including silence or voice bar, and associated burst. These categories are produced by a deviation tree based upon energy measurements in selected frequency bands, derivatives and ratios of these measurements, a voicing detector, and a few editing rules. The more detailed classification algorithms include: 1) detection and identification of some diphthongs, semivowels, and nasals, through analysis of formant motions, positions, and amplitudes; 2) a vowel identifier, which determines three ranked choices for each vowel based on a comparison of the formant positions in the detected vowel segment to stored formant positions in a speaker-normalized vowel table; 3) a fricative identifier, which employs measurement of relative spectral energies in several bands to group the fricative segments into phoneme-like categories; 4) stop consonant classification based on the properties of the plosive burst. The above algorithms have been tested on a substantial corpus of continuous speech data. Performance results, as well as detailed descriptions of the algorithms are given.
Summary
A system for acoustic-phonetic analysis of continuous speech is being developed to serve as part of an automatic speech understanding system. The acoustic system accepts the speech waveform as an input and produces as output a string of phoneme-like units referred to as acoustic phonetic elements (APEL'S). This paper should...
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Report on DABS/ATCRBS Field Testing Program
February 13, 1974
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-31
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Summary
The purpose of this field test program was to verify laboratory measurements of the effect of DABS uplink signal formats on ATCRBS transponders. The DABS interrogations tested were: (i) a combined ATCRBS Mode A/DABS All-Call consisting of a standard Mode A interragation with an additional pulse following the P(3) pulse; (ii) a DABS uplink message transmission consisting of a P(1)-P(2) pulse pair followed by 25 microseconds of 4 megabit per second DPSK data modulation. The timing aspects of these waveforms were selected on the basis of a previous series of laboratory bench tests made in a small cross-section of the ATCRBS transponder population. The results of these field measurements performed on a larger cross-section of field operational ATCRBS transponders agree with the results of the bench testing program: The recommended DABS uplink transmissions result in an effective combined ATCRBS/DABS All-Call mode and minimum triggering of ATCRBS transponders by DABS message transmissions.
Summary
The purpose of this field test program was to verify laboratory measurements of the effect of DABS uplink signal formats on ATCRBS transponders. The DABS interrogations tested were: (i) a combined ATCRBS Mode A/DABS All-Call consisting of a standard Mode A interragation with an additional pulse following the P(3) pulse...
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The effect of phase error on the DPSK receiver performance
February 4, 1974
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-32
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Several methods of realizing a DPSK receiver use a delay line. Temperature variations cause changes in the delay which, in turn, cause errors in the phase differences between the reference and information signals. The effect of these errors on the performance of an optimum DPSK receiver is studied in this report.
Summary
Several methods of realizing a DPSK receiver use a delay line. Temperature variations cause changes in the delay which, in turn, cause errors in the phase differences between the reference and information signals. The effect of these errors on the performance of an optimum DPSK receiver is studied in this...
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Technical Assessment of Satellites for CONUS Air Traffic Control, Executive Summary
January 31, 1974
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-26
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Summary
A number of satellite system techniques have been suggested as candidates to provide ATC surveillance, communication, and/or navigation service over CONUS. All techniques perform postion determination by multilateration using a constellation of satellites. They can be categorized as follows: 1) Coordinated Aircraft-to-Satellite Techniques (CAST), 2) Random Access Aircraft-to-Satellite Techniques (RAST), and 3) Satellite-to-Aircraft Techniques (SAT). A technical assessment is made of the various techniques with no one particular technique emerging as superior; several feasible alternatives are identified. The assessment indicates that satellite bases techniques for CONUS ATC can be developed without relying on high risk technology. This volume summarizes the results of a technical assessment of all three techniques. The detailed assessment is presented in companion volumes. The assessment has shown that workable systems could be configured using any one of the three techniques without reliance on high risk technology. No one technique has emerged as superior. Rather several viable alternatives have been identified. All techniques appear to require more costly avionics than today's ground-based system.
Summary
A number of satellite system techniques have been suggested as candidates to provide ATC surveillance, communication, and/or navigation service over CONUS. All techniques perform postion determination by multilateration using a constellation of satellites. They can be categorized as follows: 1) Coordinated Aircraft-to-Satellite Techniques (CAST), 2) Random Access Aircraft-to-Satellite Techniques (RAST)...
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Technical Assessment of Satellites for CONUS Air Traffic Control, Volume I - Coordinated Aircraft-To-Satellite Techniques
January 31, 1974
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-26,I
Topic:
R&D area:
Summary
A number of satellite system techniques have been suggested as candidates to provide ATC surveillance, communication, and/or navigation service over CONUS. All techniques perform postion determination by multilateration using a constellation of satellites. They can be categorized as follows: 1) Coordinated Aircraft-to-Satellite Techniques (CAST), 2) Random Access Aircraft-to-Satellite Techniques (RAST), and 3) Satellite-to-Aircraft Techniques (SAT). A technical assessment is made of the various techniques with no one particular technique emerging as superior; several feasible alternatives are identified. The assessment indicates that satellite bases techniques for CONUS ATC can be developed without relying on high risk technology. This volume deals with CAST, RAST and SAT are treated in companion volumes. A system employing CAST could operate by having each aircraft transmit only in response to interrogation from a satellite. The position of the aircraft is then obtained by multilateration using the arrival times of its response at coordinating the interrogations, mutual interference between different response can be avoided. The critical technical aspects of CAST are explored with special emphasis on signaling formats, avionics, the satellite antenna and susceptibility to jamming.
Summary
A number of satellite system techniques have been suggested as candidates to provide ATC surveillance, communication, and/or navigation service over CONUS. All techniques perform postion determination by multilateration using a constellation of satellites. They can be categorized as follows: 1) Coordinated Aircraft-to-Satellite Techniques (CAST), 2) Random Access Aircraft-to-Satellite Techniques (RAST)...
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Morphology of ionospheric scintillation
January 30, 1974
Conference Paper
Published in:
Proc. AIAA 12th Aerospace Sciences Mtg., 30 January - 1 February 1974, pp. 1-16.
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Small scale ionospheric irregularities in the F-region can cause fluctuations in the amplitude, phase, and angle of arrival of VHF. UHF, and SHF signals traversing the ionosphere. Under some conditions, the power level fluctuations or scintillations at VHF and UHF may become severe with 12 dB signal level increases and fades in excess of 30 dB being observed. Current information about the probabilities of occurrence of severe fades is derived from a number of experiments using either radio star or satellite borne sources. The measurements are generally of signal level only and have been used to calculate scintillation indices to characterize scintillation intensity. An examination of the global distribution of scintillation indices show that scintillations are of importance to communication system performance primarily in the auroral and polar regions and at night near the geomagnetic equator.
Summary
Small scale ionospheric irregularities in the F-region can cause fluctuations in the amplitude, phase, and angle of arrival of VHF. UHF, and SHF signals traversing the ionosphere. Under some conditions, the power level fluctuations or scintillations at VHF and UHF may become severe with 12 dB signal level increases and...
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Effects of airborne transponder antenna lobe switching on en route (PCD) and terminal (BDAS) beacon reply processing
January 29, 1974
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-18
Summary
The comparative performances of switching top and bottom transponder antennas versus the bottom antenna alone, in target detection by ARTS III and by PCD, were investigated in order to determine which of the two antenna configurations is preferable. A variety of military aircraft participated, performing climbouts, orbits, straight and level segments, and descents, in order to expose a wide range of aspect angles to the interrogator. Data were collected at Washington, D.C., utilizing the ATCBI at Andrews Air Force Base, and at NAFEC, utilizing the Elwood site. The frequency of occurrence of lost targets, particularly of consecutive lost targets, was found to vary considerably from one aircraft type to another. Analysis of the reduced data provides a reasonable basis, however, for concluding that, to maximize average probability of detection, the bottom antenna is better in the terminal area but switching antennas are better for En Route application. To minimize long sequences of misses which cause track loss on turns, the switching antenna appears more favorable in both flight regimes. The data also suggest that a higher probability of detection can be obtained in both environments, without incurring serious penalties, by reducing the leading edge detection thresholds.
Summary
The comparative performances of switching top and bottom transponder antennas versus the bottom antenna alone, in target detection by ARTS III and by PCD, were investigated in order to determine which of the two antenna configurations is preferable. A variety of military aircraft participated, performing climbouts, orbits, straight and level...
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Effects of ATCRBS P2 pulses on DABS reliability
January 28, 1974
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-20
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Summary
An analytical study is performed to determine the effects of ATCRBS P2 pulses as interference to DABS uplink transmissions. These effects constitute a major component of all uplink error-producing mechanisms that are anticipated to occur in DABS operation. The study is fomulated in a way that includes effects of both receiver noise and P2 pulse interference, where the interference can be received from any of a number of different transmitters at different distances from the receiving aircraft. The model includes the randomness associated with whether or not a particular DABS signal is overlapped by any interference pulse, and also the conditional randomness of error production given that an overlap does occur. In fact, a major portion of the study is the determination of the conditional error probability given the occurrence of an overlap with stated signal-to-interference ratio and stated signal-to-noise ratio. The results are given as the probability of a "miss," where a "miss" is the event that at least one of the bits in the DABS data block is demodulated in error. The study is carried out for both DPSK and PAM which are the two modulation options being considered in the DABS design. Results are given both as general formulas and as evaluations of these fomulas in various specific cases. In these evaluations, the interference environment is based on ATCRBS interrogator locations, transmitter powers, and repetition frequencies as listed in ECAC's IFF Master File. The numerical results are presented graphically to display the dependence on signal level, noise level, and geographical location between Boston and Washington, D.C. A concept referred to as "effective interference tolerance" is introduced, and numerical evaluations are presented to indicate the accuracy of this concept.
Summary
An analytical study is performed to determine the effects of ATCRBS P2 pulses as interference to DABS uplink transmissions. These effects constitute a major component of all uplink error-producing mechanisms that are anticipated to occur in DABS operation. The study is fomulated in a way that includes effects of both...
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Digital signal processor for air traffic control radars
January 1, 1974
Conference Paper
Published in:
Northeast Electronics Research and Engineering Meeting, NEREM, 28-31 October 1974.
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At a previous NEREM Meeting [1] and in a subsequent paper [2], we described the general philosophy and particular ideas which can be used to overcome the problems associated with achieving good radar detection performance in the presence of various types of clutter; ground clutter (including second-time-around returns ), weather clutter and angels (bird flocks). Recently, a digital signal processor called an MTD (Moving Target Detector) has been designed and built for application to an S-band ASR (Airport Surveillance Radar). This paper describes the MTD and presents some preliminary test results. The MTD is a special purpose hard-wired digital signal processor which is capable of processing a full 360 coverage in 1/16 nmi steps out to a nominal range of 48 nmi. The MTD was designed to provide digital radar output to an automated air traffic control system.
Summary
At a previous NEREM Meeting [1] and in a subsequent paper [2], we described the general philosophy and particular ideas which can be used to overcome the problems associated with achieving good radar detection performance in the presence of various types of clutter; ground clutter (including second-time-around returns ), weather...
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