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Signal reconstruction from the short-time Fourier transform magnitude

May 2, 1982
  |
Conference Paper
Author:
Jae S. Lim
…
Published in:
IEEE-ASSP Int. Conf., 2 May 1982.
Topic:
signal processing
R&D area:
R&D group:

Summary

In this paper, a signal is shown to be uniquely represented by the magnitude of its short-time Fourier transform (STFT) under mild restrictions on the signal and the analysis window of the STFT. Furthermore, various algorithms are developed which reconstruct signal from appropriate samples of the STFT magnitude. Several of the algorithms can also be used to obtain signal estimates from the processed STFT magnitude, which generally does not have a valid short-time structure. These algorithms are successfully applied to the time-scale modification and noise reduction problems in speech processing. Finally, the results presented here have similar potential for other applications areas, including those with multidimensional signals.
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Summary

In this paper, a signal is shown to be uniquely represented by the magnitude of its short-time Fourier transform (STFT) under mild restrictions on the signal and the analysis window of the STFT. Furthermore, various algorithms are developed which reconstruct signal from appropriate samples of the STFT magnitude. Several of...

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Signal reconstruction from the short-time Fourier transform magnitude

L-Band DME multipath environment in the microwave landing system (MLS) approach and landing region

April 13, 1982
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Project Report
Author:
James E. Evans
Published in:
MIT Lincoln Laboratory Report ATC-116
Topic:
surveillance
R&D area:
R&D group:

Summary

The multipath environment in the approach and landing region represents an important factor in the optimization and ultimate performance of the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P). Various types of multipath are assessed in the context of the proposed DME/P implementation error characteristics to ascertain the principal challenges. It is shown (analytically and experimentally) that specular reflections from buildings represent a significant challenge, particularly at low altitudes (e.g., category II decision height and below) where terrain lobing can cause the effective multipath levels to exceed the effective direct signal level. However, the time delay discrimination capabilities of the proposed DME/P should effectively eliminate the bulk of such multipath. Limited S-band (3 GHz) measurements of diffuse reflections from nominally flat terrain indicated very low levels. However, specular reflections from bare, hilly terrain may present problems in some cases.
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Summary

The multipath environment in the approach and landing region represents an important factor in the optimization and ultimate performance of the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P). Various types of multipath are assessed in the context of the proposed DME/P implementation error characteristics to ascertain the principal...

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L-Band DME multipath environment in the microwave landing system (MLS) approach and landing region

En route weather data extraction from ATC radar systems

March 11, 1982
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Project Report
Author:
David Karp
Published in:
MIT Lincoln Laboratory Report ATC-113
Topic:
radar
R&D area:
R&D group:

Summary

This report describes the results of phase I of the En Route Radar Weather Program. The objective of this effort was to develop techniques for generating accurate en route weather reflectivity estimates in the presence of ground clutter. A candidate weather data extraction processor is proposed for use with either the ASR-MTD or ARSR-MTD radar systems. Principal features of the candidate processor include: (1) an antenna port (to permit use of an appropriate polarization), front end (with R^-2 STC) and quadrature video sampling subsystem which are separate from that used for aircraft surveillance. (2) use of a ground clutter map to select the form of clutter rejection to be used in each individual range-azimuth cell to estimate various weather reflectivity levels, and (3) spatial /temporal smoothing of the cell reflectivity estimates. The key elements of the suggested signal processing techniques were evaluated using data from MTD tests in Bedford, VA, Burlington, VT, and Atlantic City, NJ; however, the full system has not as yet received design validation/refinement and operational evaluation by ATC controllers. In particular, methods for identifying second trip weather echos should be addressed in the full system validation program.
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Summary

This report describes the results of phase I of the En Route Radar Weather Program. The objective of this effort was to develop techniques for generating accurate en route weather reflectivity estimates in the presence of ground clutter. A candidate weather data extraction processor is proposed for use with either...

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En route weather data extraction from ATC radar systems

Air-to-air mode S surveillance algorithms

February 8, 1982
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Project Report
Author:
Patricia H. Mann
Published in:
MIT Lincoln Laboratory Report ATC-111
Topic:
surveillance
R&D area:
R&D group:

Summary

Lincoln Laboratory is assisting the Federal Aviation Administration in developing a beacon-based airborne collision avoidance system known as the Traffic Alert and Collision Avoidance System (TCAS). The version of TCAS intended for air carrier use is called TCAS II. It provides traffic and resolution advisories and operates in the highest traffic densities predicted for the end of the century. TCAS II extends and replaces an earlier system known as BCAS (for Beacon Collision Avoidance System). Mode S surveillance algorithms form the basis for TCAS algorithms now under development at Lincoln Laboratory.
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Summary

Lincoln Laboratory is assisting the Federal Aviation Administration in developing a beacon-based airborne collision avoidance system known as the Traffic Alert and Collision Avoidance System (TCAS). The version of TCAS intended for air carrier use is called TCAS II. It provides traffic and resolution advisories and operates in the highest...

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Air-to-air mode S surveillance algorithms

Classes of functions with explicit best uniform approximations

January 1, 1982
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Journal Article
Author:
Harold Z. Ollin
…
Published in:
J. Approx. Theory, Vol. 34, No. 3, 1982, pp. 264-276.
Topic:
algorithms
R&D area:
R&D group:

Summary

This paper concerns the construction of forms of the error function, en(x) = f(x)- p*n(x), where p*n is the best uniform polynomial approximation of degree n to a continuous function f on [-1, +l]. We show that it is always possible and, from the viewpoint of obtaining explicit results, expedient to write the error as en= a cos(n(Theta + phi), where x =cos Theta, |a|= En(f), the uniform norm of en(x), and the phase angle phi is a continuous function of Theta, depending on f and n. Our classes of explicit best approximations arise from a novel method of determining suitable phase angles in this representation of en(x).
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Summary

This paper concerns the construction of forms of the error function, en(x) = f(x)- p*n(x), where p*n is the best uniform polynomial approximation of degree n to a continuous function f on [-1, +l]. We show that it is always possible and, from the viewpoint of obtaining explicit results, expedient...

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Classes of functions with explicit best uniform approximations

Iterative techniques for minimum phase signal reconstruction from phase or magnitude

December 1, 1981
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Journal Article
Author:
Thomas F. Quatieri
…
Published in:
IEEE Trans. on Acoustics, Speech & Signal Processing, Vol. ASSP-29, No.6, Dec. 1981, pp.1187-1193.
Topic:
speech enhancement
R&D area:
R&D group:

Summary

In this paper, we develop iterative algorithms for reconstructing a minimum phase sequence from pthhea se or magnitude of its Fourier transform. These iterative solutions involve repeatedly imposing a causality constraint in the time domain and incorporating the known phase or magnitude function in the frequency domain. This approach is the basis of a new means of computing the Hilbert transform of the log-magnitude or phase of the Fourier transform of a minimum phase sequence which does not require phase unwrapping. Finally, we discuss the potential use of this iterative computation in determining samples of the unwrapped phase of a mixed phase sequence.
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Summary

In this paper, we develop iterative algorithms for reconstructing a minimum phase sequence from pthhea se or magnitude of its Fourier transform. These iterative solutions involve repeatedly imposing a causality constraint in the time domain and incorporating the known phase or magnitude function in the frequency domain. This approach is...

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Iterative techniques for minimum phase signal reconstruction from phase or magnitude

Moving Target Detector (Mod II) summary report

November 3, 1981
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Project Report
Author:
David Karp
…
Published in:
MIT Lincoln Laboratory Report ATC-95
Topic:
surveillance
R&D area:
R&D group:

Summary

Under FAA sponsorship, MIT/Lincoln Laboratory has developed a second generation, field operable Moving Target Detection System (MTD-II) which has been tested at operational FAA terminal and enroute radar sites, and serves as the basis for the ASR-9 MTD technical performance specifications. This summary report covers the period October, 1976 through September, 1979 in which design, development, field testing and system performance evaluation were carried out. Report No. FAA-RD-76-190, ATC-69, "Description and Performance Evaluation of the Moving Target Detector" dated 8 March 1977, serves as the technical foundation of this work. MTD-processing design modifications were effected to handle conditions of excessive ground clutter and moving ground traffic. The rationale for the modified algorithms is provided, and measured performance characteristics at several FAA field sites are discussed.
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Summary

Under FAA sponsorship, MIT/Lincoln Laboratory has developed a second generation, field operable Moving Target Detection System (MTD-II) which has been tested at operational FAA terminal and enroute radar sites, and serves as the basis for the ASR-9 MTD technical performance specifications. This summary report covers the period October, 1976 through...

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Moving Target Detector (Mod II) summary report

A new asteroid observation and search technique

October 1, 1981
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Journal Article
Author:
Laurence G. Taff
Published in:
Publ. Astronom. Soc. Pacific, Vol. 93, No. 555, October 1981, pp. 658-660.
Topic:
asteroids
R&D area:
R&D group:

Summary

A prototype observatory was constructed near Socorro, New Mexico to search for and observe earth-approaching asteroids. Hardware modifications were made so that the discrimination of artificial satellites at an angular speed of 15 arcsec/sec can be used to observe minor planets at an angular speed of 0.01 arcsec/sec. Assuming no correlations between time of perigee passage and time of year, a recovery of 25 asteroids per year is expected.
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Summary

A prototype observatory was constructed near Socorro, New Mexico to search for and observe earth-approaching asteroids. Hardware modifications were made so that the discrimination of artificial satellites at an angular speed of 15 arcsec/sec can be used to observe minor planets at an angular speed of 0.01 arcsec/sec. Assuming no...

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A new asteroid observation and search technique

ATCRBS uplink environment measurements near Jacksonville, Florida

September 25, 1981
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Project Report
Author:
Ferenc Nagy Jr
Published in:
MIT Lincoln Laboratory Report ATC-94
Topic:
surveillance
R&D area:
R&D group:

Summary

Airborne measurements of the Air Traffic Control Radar Beacon System (ATCRBS) 1030 MHz uplink environment are described. Measurements were made using the AMF, a special purpose airborne sensor-recorder, during a 23 May 1979 flight in the greater Jacksonville, Florida area. The 2-way flight covered the 450 nm coastline between Fayetteville (NC) and Vero Beach (FL) first at 10,000 then at 25,000 feet. Data recorded at 61 locations have been analyzed to plot combined pulse, interrogation and suppression rates for all locations and individual rates, received powers and angles for 37 locations. Fifty-nine ground interrogators were detected and a list included serves as an all-interrogator/all-location (59 x 37) visibility matrix. PRI/PRF distributions of interrogations received are shown at three selected measurement locations. A pulse-by-pulse plot of over 50 Mode 4 interrogations shows their effect on a typical transponder. A "worst" location is examined for peak instantaneous interrogation rates capable of causing transponder reply-rate limiting (RRL), desensitization and track loss. Durations and periods of recurrence of "synchronous jamming" for 23 near-equal scan periods are computed. Probabilities of multiple mainbeam coincidences ("multi-PRF jamming") are also calculated. Airborne (AMF) and ground based (FAA En-Route) coverages are compared, and reported operational problems (target splits, lost tracks, poor coverage) are addressed.
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Summary

Airborne measurements of the Air Traffic Control Radar Beacon System (ATCRBS) 1030 MHz uplink environment are described. Measurements were made using the AMF, a special purpose airborne sensor-recorder, during a 23 May 1979 flight in the greater Jacksonville, Florida area. The 2-way flight covered the 450 nm coastline between Fayetteville...

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ATCRBS uplink environment measurements near Jacksonville, Florida

Results of L band multipath measurements at operational United States (U.S.) airports in support of the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P)

July 23, 1981
  |
Project Report
Author:
James E. Evans
…
Published in:
MIT Lincoln Laboratory Report ATC-109
Topic:
L-band
R&D area:
R&D group:

Summary

This report presents the results of a short duration L band multipath measurement program at five major U.S. airports (St. Louis, Tulsa, Wright Patterson Air Force Base, Philadelphia and Washington National) and one smaller airport (Quonset, RI) to better quantify the expected multipath environment for the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P). Specific objectives included: (1) Measurements of the principal multipath parameters (amplitude and time delay) with realistic aircraft/ground site locations at runways which had the major DME/multipath sources (large buildings) identified in previous analytical (simulation) studies. (2) Determination of whether significant DME/P multipath sources exist which had not been considered to date and (3) Comparison of the measured results with computer simulation results obtained with simplified airport models (such as have been used for DME/P system design to date). Particular emphasis was placed on the final approach region including the flare and rollout regions since these areas correspond to the most stringent DME/P accuracy requirements and, have not been utilized operationally with the current L band DME. All of the above objectives were achieved although in some cases the experimental data in the flare/rollout region was of poor quality due to low signal to noise ratio. The spatial region and time delay of specular multipath generally correlated well with expectations based on simple ray tracing. With the exception of Washington National, no significant (multipath to direct signal ratio (M/D >110 dB) multipath was encountered in operationally relevant areas which was not predicted. The quantitative predictions of the simple airport models agreed with the experimental data, although in some cases, (especially, near threshold) the measured M/D values were considerably higher than predictions.
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Summary

This report presents the results of a short duration L band multipath measurement program at five major U.S. airports (St. Louis, Tulsa, Wright Patterson Air Force Base, Philadelphia and Washington National) and one smaller airport (Quonset, RI) to better quantify the expected multipath environment for the Microwave Landing System (MLS)...

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Results of L band multipath measurements at operational United States (U.S.) airports in support of the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P)
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