Publications
Integrated models of signal and background with application to speaker identification in noise
April 1, 1994
Journal Article
Published in:
IEEE Trans. Speech Audio Process., Vol. 2, No. 2, April 1994, pp. 245-257.
Topic:
R&D area:
Summary
This paper is concerned with the problem of robust parametric model estimation and classification in noisy acoustic environments. Characterization and modeling of the external noise sources in these environments is in itself an important issue in noise compensation. The techniques described here provide a mechanism for integrating parametric models of acoustic background with the signal model so that noise compensation is tightly coupled with signal model training and classification. Prior information about the acoustic background process is provided using a maximum likelihood parameter estimation procedure that integrates an a priori model of acoustic background with the signal model. An experimental study is presented in the paper on the application of this approach to text-independent speaker identification in noisy acoustic environments. Considerable improvement in speaker classification performance was obtained for classifying unlabeled sections of conversational speech utterances from a 16-speaker population under cross-environment training and testing conditions.
Summary
This paper is concerned with the problem of robust parametric model estimation and classification in noisy acoustic environments. Characterization and modeling of the external noise sources in these environments is in itself an important issue in noise compensation. The techniques described here provide a mechanism for integrating parametric models of...
READ MORE
Short-time signal representation by nonlinear difference equations
April 6, 1990
Conference Paper
Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech and Signal Processing, ICASSP, Vol. 3, Digital Signal Processing, 3-6 April 1990, pp. 1551-1554.
Topic:
R&D area:
Summary
The solution of a nonlinear difference equation can take on complicated deterministic behavior which appears to be random for certain values of the equation's coefficients. Due to the sensitivities to initial conditions of the output of such "chaotic" systems, it is difficult to duplicate the waveform structure by parameter analysis and waveform synthesis techniques. In this paper, methods are investigated for short-time analysis and synthesis of signals from a class of second-order difference equations with a cubic nonlinearity. In analysis, two methods are explored for estimating equation coefficients: (1) prediction error minimization (a linear estimation problem) and (2) waveform error minimization (a nonlinear estimation problem). In the latter case, which improves on the prediction error solution, an iterative analysis-by-synthesis method is derived which allows as free variables initial conditions, as well as equation coefficients. Parameter estimates from these techniques are used in sequential short-time synthesis procedures. Possible application to modeling "quasi-periodic" behavior in speech waveforms is discussed.
Summary
The solution of a nonlinear difference equation can take on complicated deterministic behavior which appears to be random for certain values of the equation's coefficients. Due to the sensitivities to initial conditions of the output of such "chaotic" systems, it is difficult to duplicate the waveform structure by parameter analysis...
READ MORE
The tradeoff between delay and TASI advantage in a packetized speech multiplexer
November 1, 1979
Journal Article
Published in:
IEEE Trans. on Commun., Vol. COM-27, No. 11, November 1979, pp. 1716-20.
Topic:
R&D area:
Summary
A packetized speech multiplexer differs from a circuit-switched TASI system in that the presence of a packet buffer allows a tradeoff where the TASI advantage can be increased at a cost in packet delay. This tradeoff is investigated via a simulation. Results are presented to show the relations between TASI advantage and delay, for both an average delay criterion and a maximum delay criterion. It is shown that, particularly for the case where small numbers of talkers are multiplexed, the packetized system offers significant improvements in TASI advantage over the conventional circuit-switched multiplexer, at modest costs in packet delay.
Summary
A packetized speech multiplexer differs from a circuit-switched TASI system in that the presence of a packet buffer allows a tradeoff where the TASI advantage can be increased at a cost in packet delay. This tradeoff is investigated via a simulation. Results are presented to show the relations between TASI...
READ MORE
New techniques applied to air-traffic control radars
June 1, 1974
Journal Article
Published in:
Proc. IEEE, Vol. 62, No. 6, June 1974, pp. 716-723.
Summary
During the past two years a program has been carried out to show how new techniques can greatly improve the performance of radars used for air-traffic control. A survey of problems associated with presently used radars was undertaken. This survey indicates that primary radar in an automated air-traffic control system can be made significantly more effective by the use of new techniques. The radar's handling of extraneous reflections (clutter) is critical to its performance. Three types of interfering clutter were found to predominate: ground clutter, weather clutter, and angels. Angels are generally accepted to be radar returns from flocks of birds. In addition, second-time-around clutter is often troublesome. For each type of clutter, all known remedies for improving the signal-to-clutter ratio were studied and radar systems were configured using appropriate sets of remedies. Some specific solutions incorporated in the resulting radar systems are: a) the use of linear large dynamic range, near-optimum digital signal processors to filter signals from clutter, b) the use of electronically step-scanned antennas to improve the correlation of aircraft and clutter returns from pulse to pulse, c) the use of multiple PRF's instead of staggered PRF's together with coherent transmitters to keep second-time-around clutter returns well correlated while still overcoming blind speeds, d) the use of a fine grained ground clutter map to give superclutter visibility on tangential targets, and e) the use of lower operating frequencies to greatly reduce weather and angel returns. Two demonstration radar systems have been implemented, an S-band radar using a mechanically rotating antenna and a UHF radar using an electronically step-scanned cylindrical antenna. Experimental results are described.
Summary
During the past two years a program has been carried out to show how new techniques can greatly improve the performance of radars used for air-traffic control. A survey of problems associated with presently used radars was undertaken. This survey indicates that primary radar in an automated air-traffic control system...
READ MORE
Concepts for improvement of airport surveillance radars
February 26, 1973
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-14
Summary
This report reviews the performance of operational ASR's, discusses each type of clutter with which the target must compete, examines presently employed methods of overcoming clutter and several state-of-the-art techniques which have not found their way into the ASR's for one reason or another. It concludes by describing two radars, one at S-band and one at UHF, which are believed to come closest to fulfilling ASR requirements in advanced ARTS facilities. The major improvements in performance will be derived from the use of linear optimum signal processing. Further gains will be achieved through the use of adaptive thresholds. STC will combat bird clutter. The radar will incorporate proper shaping of the antenna pattern so that aircraft off the peak of the antenna elevation beam will not be at a disadvantage compared to moving clutter at the peak. The recommended radar concepts also include radial velocity determination by Doppler measurement. This should prove of value in maintaining target tracks and in discrimination against ground vehicles.
Summary
This report reviews the performance of operational ASR's, discusses each type of clutter with which the target must compete, examines presently employed methods of overcoming clutter and several state-of-the-art techniques which have not found their way into the ASR's for one reason or another. It concludes by describing two radars...
READ MORE
A theory of multiple antenna AMTI radar
April 8, 1971
Technical Report
Published in:
MIT Lincoln Laboratory Report TN-1971-21
Topic:
R&D area:
Summary
This note presents a detailed mathematical analysis of a multiple-antenna AMTI radar system capable of detecting moving targets over a significantly wider velocity range than is achievable with a single-antenna system. The general system configuration and signaling strategy is defined, and relationships among system and signaling parameters are investigated. A deterministic model for the target return and a statistical model for the clutter and noise returns are obtained, and an optimum processor for target detection is derived. A performance measure applicable to a large class of processors, including the optimum processor, is defined and some of its analytical properties investigated. It is shown that an easily implementable sub-optimum processor, based on two-dimensional spectral analysis, performs nearly as well as the optimum processor. The resolution and ambiguity properties of this sub-optimum processor are studied and a detailed numerical investigation of system performance is presented, including a study of how performance varies with basic system parameters such as the number of antennas.
Summary
This note presents a detailed mathematical analysis of a multiple-antenna AMTI radar system capable of detecting moving targets over a significantly wider velocity range than is achievable with a single-antenna system. The general system configuration and signaling strategy is defined, and relationships among system and signaling parameters are investigated. A...
READ MORE