Publications
Support vector machines using GMM supervectors for speaker verification
May 1, 2006
Journal Article
Published in:
IEEE Signal Process. Lett., Vol. 13, No. 5, May 2006, pp. 308-311.
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Summary
Gaussian mixture models (GMMs) have proven extremely successful for text-independent speaker recognition. The standard training method for GMMmodels is to use MAP adaptation of the means of the mixture components based on speech from a target speaker. Recent methods in compensation for speaker and channel variability have proposed the idea of stacking the means of the GMM model to form a GMM mean supervector. We examine the idea of using the GMM supervector in a support vector machine (SVM) classifier. We propose two new SVM kernels based on distance metrics between GMM models. We show that these SVM kernels produce excellent classification accuracy in a NIST speaker recognition evaluation task.
Summary
Gaussian mixture models (GMMs) have proven extremely successful for text-independent speaker recognition. The standard training method for GMMmodels is to use MAP adaptation of the means of the mixture components based on speech from a target speaker. Recent methods in compensation for speaker and channel variability have proposed the idea...
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Multifunction phased array radar pulse compression limits
April 25, 2006
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-327
Summary
An active phased array radar with distributed low-peak-power transmit modules requires pulse compression to provide high sensitivity and fine range resolution. A long transmitted pulse, however, has accompanying problems such as a near-range blind zone for the transmitting channel and a loss of other gate data (dead gates) in other channels for a multichannel system. In this report the trade-off between the benefits and costs of pulse compression (lengthening) for multifunction phased array radars (MPARs) are analyzed. Specific results are presented for a three-channel MPAR and a two-channel terminal-area MPAR (TMPAR) that have been proposed as replacement systems for current U.S. civil-sector aircraft anad weather surveillance radar systems. The recommended maximum compression ratio is 130 ofr the MPAR and 80 for the TMPAR. The results are independent of radar peak power and antenna gain, and represent upper bounds. Acutal pulse compression ratios that would be employed are likely to be somewhat less tha these values, based on fulfilling specific sensitivity and scan-time requirements with specific radar physical parameters.
Summary
An active phased array radar with distributed low-peak-power transmit modules requires pulse compression to provide high sensitivity and fine range resolution. A long transmitted pulse, however, has accompanying problems such as a near-range blind zone for the transmitting channel and a loss of other gate data (dead gates) in other...
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Support vector machines for speaker and language recognition
April 1, 2006
Journal Article
Published in:
Comput. Speech Lang., Vol. 20, No. 2-3, April/July 2006, pp. 210-229.
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Support vector machines (SVMs) have proven to be a powerful technique for pattern classification. SVMs map inputs into a high-dimensional space and then separate classes with a hyperplane. A critical aspect of using SVMs successfully is the design of the inner product, the kernel, induced by the high dimensional mapping. We consider the application of SVMs to speaker and language recognition. A key part of our approach is the use of a kernel that compares sequences of feature vectors and produces a measure of similarity. Our sequence kernel is based upon generalized linear discriminants. We show that this strategy has several important properties. First, the kernel uses an explicit expansion into SVM feature space - this property makes it possible to collapse all support vectors into a single model vector and have low computational complexity. Second, the SVM builds upon a simpler mean-squared error classifier to produce a more accurate system. Finally, the system is competitive and complimentary to other approaches, such as Gaussian mixture models (GMMs). We give results for the 2003 NIST speaker and language evaluations of the system and also show fusion with the traditional GMM approach.
Summary
Support vector machines (SVMs) have proven to be a powerful technique for pattern classification. SVMs map inputs into a high-dimensional space and then separate classes with a hyperplane. A critical aspect of using SVMs successfully is the design of the inner product, the kernel, induced by the high dimensional mapping...
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Afterpulsing in Geiger-mode avalanche photodiodes for 1.06um wavelength
March 27, 2006
Journal Article
Published in:
Appl. Phys. Lett., Vol. 88, No. 13, 27 March 2006, pp. 133503-1 - 133503-3.
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Summary
We consider the phenomenon of afterpulsing in avalanche photodiodes (APDs) operating in gated and free-running Geiger mode. An operational model of afterpulsing and other noise characteristics of APDs predicts the noise behavior observed in the free-running mode. We also use gated-mode data to investigate possible sources of afterpulsing in these devices. For 30-um-diam, 1.06-um-wavelength InGaAsP/InP APDs operated at 290 K and 4 V overbias, we obtained a dominant trap lifetime of td=0.32 us, a trap energy of 0.11 eV, and a baseline dark count rate 245 kHz.
Summary
We consider the phenomenon of afterpulsing in avalanche photodiodes (APDs) operating in gated and free-running Geiger mode. An operational model of afterpulsing and other noise characteristics of APDs predicts the noise behavior observed in the free-running mode. We also use gated-mode data to investigate possible sources of afterpulsing in these...
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Exploiting nonacoustic sensors for speech encoding
March 1, 2006
Journal Article
Published in:
IEEE Trans. Audio, Speech and Language Process., Vol. 14, No. 2, March 2006, pp. 533-544.
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Summary
The intelligibility of speech transmitted through low-rate coders is severely degraded when high levels of acoustic noise are present in the acoustic environment. Recent advances in nonacoustic sensors, including microwave radar, skin vibration, and bone conduction sensors, provide the exciting possibility of both glottal excitation and, more generally, vocal tract measurements that are relatively immune to acoustic disturbances and can supplement the acoustic speech waveform. We are currently investigating methods of combining the output of these sensors for use in low-rate encoding according to their capability in representing specific speech characteristics in different frequency bands. Nonacoustic sensors have the ability to reveal certain speech attributes lost in the noisy acoustic signal; for example, low-energy consonant voice bars, nasality, and glottalized excitation. By fusing nonacoustic low-frequency and pitch content with acoustic-microphone content, we have achieved significant intelligibility performance gains using the DRT across a variety of environments over the government standard 2400-bps MELPe coder. By fusing quantized high-band 4-to-8-kHz speech, requiring only an additional 116 bps, we obtain further DRT performance gains by exploiting the ear's insensitivity to fine spectral detail in this frequency region.
Summary
The intelligibility of speech transmitted through low-rate coders is severely degraded when high levels of acoustic noise are present in the acoustic environment. Recent advances in nonacoustic sensors, including microwave radar, skin vibration, and bone conduction sensors, provide the exciting possibility of both glottal excitation and, more generally, vocal tract...
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Laser radar imager based on 3D integration of Geiger-mode avalanche photodiodes with two SOI timing circuit layers
February 6, 2006
Conference Paper
Published in:
ISSCC 2006, IEEE Int. Solid-State Circuits Conf., 6-9 February 2006.
Summary
We have developed focal-plane arrays and laser-radar (ladar) imaging systems based on Geiger-mode avalanche photodiodes (APDs) integrated with high-speed all-digital CMOS timing circuits. A Geiger-mode APD produces a digital pulse upon detection of a single photon. This pulse is used to stop a fast digital counter in the pixel circuit, thereby measuring photon arrival time. This "photon-to-digital conversion" yields quantum-limited sensitivity and noiseless readout, enabling high-performance ladar systems. Previously reported focal planes, based on bump bonding or epoxy bonding the APDs to foundry chips, had coarse (100um) pixel spacing and 0.5ns timing quantization.
Summary
We have developed focal-plane arrays and laser-radar (ladar) imaging systems based on Geiger-mode avalanche photodiodes (APDs) integrated with high-speed all-digital CMOS timing circuits. A Geiger-mode APD produces a digital pulse upon detection of a single photon. This pulse is used to stop a fast digital counter in the pixel circuit...
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An exploratory study of modeling enroute pilot convective storm flight deviation behavior
February 2, 2006
Conference Paper
Published in:
12th Conf. on Aviation Range and Aerospace Meteorology, 2 February 2006.
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Summary
The optimization of traffic flows in highly congested airspace with rapidly varying convective weather is an extremely complex problem. Aviation weather systems such as the Corridor Integrated Weather System (CIWS) provide weather products and forecasts that aid en route traffic managers in making tactical routing decisions in convective weather, but traffic managers need automated decision support systems that integrate flight information, trajectory models and convective weather products to assist in developing and executing convective weather mitigation plans. A key element of an integrated ATM/wx decision support system is the ability to predict automatically when pilots in en route airspace will choose to deviate around convective weather and how far they will deviate from their planned path. The FAA Aeronautical Information Manual suggests that pilots avoid thunderstorms characterized by intense radar echo in en route airspace by at least 20 nautical miles (40 km). However, a recent study (Rhoda, et. al., 2002) of pilot behavior in both terminal and en route airspace near Memphis, TN suggested that pilots fly over high reflectivity cells in en route airspace and penetrate lower cells whose reflectivity is less than VIP level 3. Recent operational experience with CIWS supports the Rhoda findings (Robinson, et. al., 2004). This study presents initial results of research to develop a quantitative model that would predict when a pilot will deviate around convective weather in en route airspace. It also presents statistics that characterize hazard avoidance distances and weather penetrations. The results are based on the analysis of more than 800 flight trajectories through two Air Traffic Control (ATC) en route super-sectors (geographical regions that include several adjacent ATC en route sectors) on five days in the summer of 2003. One supersector from the Indianapolis Air Route Traffic Control Center (ZID ARTCC) encompassed southern Indiana, southwestern Ohio and northern Kentucky (ZID); the other, located in the Cleveland ARTCC (ZOB), included northern Ohio, along the southern shore of Lake Erie (ZOB). The weather encountered along the flight trajectories was characterized by the CIWS high-resolution precipitation (VIL) and radar echo tops mosaic (Klingle-Wilson and Evans, 2005) and NLDN lightning products. Flight trajectories were taken from the Enhanced Traffic Management System (ETMS).
Summary
The optimization of traffic flows in highly congested airspace with rapidly varying convective weather is an extremely complex problem. Aviation weather systems such as the Corridor Integrated Weather System (CIWS) provide weather products and forecasts that aid en route traffic managers in making tactical routing decisions in convective weather, but...
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A "demand pull" approach to short term forecast development and testing
January 30, 2006
Conference Paper
Published in:
86th AMS Annual Mtg., 1st Symp. on Policy Research, January 2006.
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We discuss two specific short term aviation weather forecasts - convection and ceiling - to illustrate the issues that arise in thinking about the overall decision support system, key users, and training needed to generate benefits. We also consider reducing weather-related fatal accidents. Second, what is the preexisting "baseline" of aviation forecasts/decision processes that already exists to address the user needs? In most cases, there are already various weather information sources that can be viewed as providing a short term forecast (e.g., a Center Weather Service Unit (CWSU) meteorologist, persistence, or animation loops of the past weather). How well do we understand how the "baseline" forecast and the associated user decision support system operate? How will the new forecast and its decision support compare? What are the training implications if the new forecast is rather different than the "baseline"? Third, how will we measure the change in system performance? For example, if the new forecast claims to help reduce delays and/or accidents, how will one address differences in the weather between the "before" and "after" time periods? How will one determine whether the new forecast is in fact the key factor, if there was a change? The paper concludes with some suggestions for development and testing of new aviation forecasts to improve safety and reduce delays.
Summary
We discuss two specific short term aviation weather forecasts - convection and ceiling - to illustrate the issues that arise in thinking about the overall decision support system, key users, and training needed to generate benefits. We also consider reducing weather-related fatal accidents. Second, what is the preexisting "baseline" of...
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Upgrade and technology transfer of the San Francisco Marine Stratus Forecast system to the National Weather Service
January 30, 2006
Conference Paper
Published in:
86th AMS Annual Mtg., 1st Symp. on Policy Research, January 2006.
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Summary
The local airspace surrounding the San Francisco International Airport (SFO) is prone to regular occurrences of low ceiling conditions from May through October due to the intrusion of marine stratus along the Pacific coast. The low cloud conditions prohibit dual parallel landings of aircraft to the airport's closely spaced parallel runways, thus effectively reducing the arrival capacity by a factor of two. The behavior of marine stratus evolves on a daily cycle, filling the San Francisco Bay region overnight, and dissipating during the morning. Often the low ceiling conditions persist throughout the morning hours and interfere with the high rate of air traffic scheduled into SFO from mid-morning to early afternoon. The result is a substantial number of delayed flights into the airport and a negative impact on the National Air Space (NAS). Air traffic managers face a continual challenge of anticipating available operating capacity so that the demand of incoming planes can be metered to match the availability of arrival slots.
Summary
The local airspace surrounding the San Francisco International Airport (SFO) is prone to regular occurrences of low ceiling conditions from May through October due to the intrusion of marine stratus along the Pacific coast. The low cloud conditions prohibit dual parallel landings of aircraft to the airport's closely spaced parallel...
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A characterization of NWP ceiling and visibility forecasts for the terminal airspace
January 29, 2006
Conference Paper
Published in:
86th AMS Annual Meeting, 1st Symp. on Policy Research, 2006.
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Summary
The Federal Aviation Administration (FAA) is sponsoring a Terminal Ceiling and Visibility (C&V) initiative to provide automated C&V guidance to the air traffic managers for both tactical (0-2 hour) and strategic (3-12 hour) decision making. To meet these requirements, particularly in the strategic time frame, it will most likely be necessary for the C&V system to incorporate guidance from an explicit numerical weather prediction (NWP) model. If NWP forecasts are found to be suitable for this application, they will be used as the backbone of the terminal C&V forecast system. More details on the terminal area C&V forecast product development for the FAA can be found in Allan et al. (2004). Before these NWP forecast products can be used, it is necessary to first characterize their accuracy relative to operational air traffic control (ATC) requirements. This makes it possible to exploit observed strengths, avoid weaknesses, and facilitate a better utilization of NWP forecast products. This study provides an assessment tailored specifically to address the terminal C&V application. Consequently, the results represent forecast performance for relatively small geographic locations that for practical purposes can be considered point forecasts. It is our intention to answer four questions with this preliminary analysis: 1. How accurate are the NWP forecasts relative to the observational truth and a human generated forecast? 2. For the terminals of interest to this study (i.e. New York City Airports), are there any advantages to utilizing a non-hydrostatic mesoscale model run at horizontal resolutions of 3 km or less? 3. Do the NWP models exhibit forecast skill for non-traditional forecast metrics such as trends in C&V parameters and timings of threshold crossings associated with the onset and clearing of low ceiling and visibility conditions? 4. Are there obvious situations/conditions during which the NWP forecasts have more/less skill? In addition to a report on the NWP terminal ceiling and visibility forecast accuracy, we provide preliminary recommendations on the direction we feel this line of research should pursue, and where we see opportunities to utilize NWP forecasts in an automated terminal C&V decision guidance system. An ancillary goal of this study is to assemble the analysis software infrastructure required to quantitatively evaluate numerical forecast accuracy. We envision using these tools to develop and test modifications to the translation algorithms and techniques that will be necessary to integrate the NWP forecasts into the C&V guidance system. They will be instrumental in reducing the time required to make engineering turns during the upcoming development and implementation stages of this research.
Summary
The Federal Aviation Administration (FAA) is sponsoring a Terminal Ceiling and Visibility (C&V) initiative to provide automated C&V guidance to the air traffic managers for both tactical (0-2 hour) and strategic (3-12 hour) decision making. To meet these requirements, particularly in the strategic time frame, it will most likely be...
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