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A new approach to achieving high-performance power amplifier linearization

April 17, 2007
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Conference Paper
Author:
Joel I. Goodman
…
Published in:
IEEE Radar Conf., 17-20 April 2007. doi: 10.1109/RADAR.2007.374329
Topic:
signal processing
R&D area:
R&D group:

Summary

Digital baseband predistortion (DBP) is not particularly well suited to linearizing wideband power amplifiers (PAs); this is due to the exorbitant price paid in computational complexity. One of the underlying reasons for the computational complexity of DBP is the inherent inefficiency of using a sufficiently deep memory and a high enough polynomial order to span the multidimensional signal space needed to mitigate PA-induced nonlinear distortion. Therefore we have developed a new mathematical method to efficiently search for and localize those regions in the multidimensional signal space that enable us to invert PA nonlinearities with a significant reduction in computational complexity. Using a wideband code division multiple access (CDMA) signal we demonstrate and compare the PA linearization performance and computational complexity of our algorithm to that of conventional DBP techniques using measured results.
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Summary

Digital baseband predistortion (DBP) is not particularly well suited to linearizing wideband power amplifiers (PAs); this is due to the exorbitant price paid in computational complexity. One of the underlying reasons for the computational complexity of DBP is the inherent inefficiency of using a sufficiently deep memory and a high...

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A new approach to achieving high-performance power amplifier linearization

Language recognition with word lattices and support vector machines

April 15, 2007
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Conference Paper
Author:
William M. Campbell
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Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech, and Signal Processing, ICASSP, 15-20 April 2007, Vol. IV, pp. 989-992.
Topic:
language recognition
R&D area:
R&D group:

Summary

Language recognition is typically performed with methods that exploit phonotactics--a phone recognition language modeling (PRLM) system. A PRLM system converts speech to a lattice of phones and then scores a language model. A standard extension to this scheme is to use multiple parallel phone recognizers (PPRLM). In this paper, we modify this approach in two distinct ways. First, we replace the phone tokenizer by a powerful speech-to-text system. Second, we use a discriminative support vector machine for language modeling. Our goals are twofold. First, we explore the ability of a single speech-to-text system to distinguish multiple languages. Second, we fuse the new system with an SVM PRLM system to see if it complements current approaches. Experiments on the 2005 NIST language recognition corpus show the new word system accomplishes these goals and has significant potential for language recognition.
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Summary

Language recognition is typically performed with methods that exploit phonotactics--a phone recognition language modeling (PRLM) system. A PRLM system converts speech to a lattice of phones and then scores a language model. A standard extension to this scheme is to use multiple parallel phone recognizers (PPRLM). In this paper, we...

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Language recognition with word lattices and support vector machines

An evaluation of audio-visual person recognition on the XM2VTS corpus using the Lausanne protocols

April 1, 2007
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Conference Paper
Author:
Kevin Brady
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Published in:
Proc. 32nd IEEE Int. Conf. on Acoustics, Speech, and Signal Processing, ICASSP, April 2007, pp. IV-237 - 240.
Topic:
speaker recognition
R&D area:
R&D group:

Summary

A multimodal person recognition architecture has been developed for the purpose of improving overall recognition performance and for addressing channel-specific performance shortfalls. This multimodal architecture includes the fusion of a face recognition system with the MIT/LLGMM/UBM speaker recognition architecture. This architecture exploits the complementary and redundant nature of the face and speech modalities. The resulting multimodal architecture has been evaluated on theXM2VTS corpus using the Lausanne open set verification protocols, and demonstrates excellent recognition performance. The multimodal architecture also exhibits strong recognition performance gains over the performance of the individual modalities.
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Summary

A multimodal person recognition architecture has been developed for the purpose of improving overall recognition performance and for addressing channel-specific performance shortfalls. This multimodal architecture includes the fusion of a face recognition system with the MIT/LLGMM/UBM speaker recognition architecture. This architecture exploits the complementary and redundant nature of the face...

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An evaluation of audio-visual person recognition on the XM2VTS corpus using the Lausanne protocols

Robust speaker recognition with cross-channel data: MIT-LL results on the 2006 NIST SRE auxiliary microphone task

April 1, 2007
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Conference Paper
Author:
Douglas E. Sturim
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Published in:
Proc. 32nd IEEE Int. Conf. on Acoustics, Speech, and Signal Processing, ICASSP, April 2007, pp. IV-49 - IV-52.
Topic:
speaker recognition
R&D area:
R&D group:

Summary

One particularly difficult challenge for cross-channel speaker verification is the auxiliary microphone task introduced in the 2005 and 2006 NIST Speaker Recognition Evaluations, where training uses telephone speech and verification uses speech from multiple auxiliary microphones. This paper presents two approaches to compensate for the effects of auxiliary microphones on the speech signal. The first compensation method mitigates session effects through Latent Factor Analysis (LFA) and Nuisance Attribute Projection (NAP). The second approach operates directly on the recorded signal with noise reduction techniques. Results are presented that show a reduction in the performance gap between telephone and auxiliary microphone data.
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Summary

One particularly difficult challenge for cross-channel speaker verification is the auxiliary microphone task introduced in the 2005 and 2006 NIST Speaker Recognition Evaluations, where training uses telephone speech and verification uses speech from multiple auxiliary microphones. This paper presents two approaches to compensate for the effects of auxiliary microphones on...

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Robust speaker recognition with cross-channel data: MIT-LL results on the 2006 NIST SRE auxiliary microphone task

Multisensor dynamic waveform fusion

April 1, 2007
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Conference Paper
Author:
Alan V. McCree
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Published in:
Proc. 32nd Int. Conf. on Acoustics, Speech, and Signal Processing, ICASSP, April 2007, pp. IV-577 - IV-580.
Topic:
speech enhancement
R&D area:
R&D group:

Summary

Speech communication is significantly more difficult in severe acoustic background noise environments, especially when low-rate speech coders are used. Non-acoustic sensors, such as radar sensors, vibrometers, and bone-conduction microphones, offer significant potential in these situations. We extend previous work on fixed waveform fusion from multiple sensors to an optimal dynamic waveform fusion algorithm that minimizes both additive noise and signal distortion in the estimated speech signal. We show that a minimum mean squared error (MMSE) waveform matching criterion results in a generalized multichannel Wiener filter, and that this filter will simultaneously perform waveform fusion, noise suppression, and crosschannel noise cancellation. Formal intelligibility and quality testing demonstrate significant improvement from this approach.
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Summary

Speech communication is significantly more difficult in severe acoustic background noise environments, especially when low-rate speech coders are used. Non-acoustic sensors, such as radar sensors, vibrometers, and bone-conduction microphones, offer significant potential in these situations. We extend previous work on fixed waveform fusion from multiple sensors to an optimal dynamic...

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Multisensor dynamic waveform fusion

The MIT-LL/IBM 2006 speaker recognition system: high-performance reduced-complexity recognition

April 1, 2007
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Conference Paper
Author:
William M. Campbell
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Published in:
Proc. 32nd IEEE Int. Conf. on Acoustics, Speech, and Signal Processing, ICASSP, April 2007, pp. IV-217 - IV-220.
Topic:
speaker recognition
R&D area:
R&D group:

Summary

Many powerful methods for speaker recognition have been introduced in recent years--high-level features, novel classifiers, and channel compensation methods. A common arena for evaluating these methods has been the NIST speaker recognition evaluation (SRE). In the NIST SRE from 2002-2005, a popular approach was to fuse multiple systems based upon cepstral features and different linguistic tiers of high-level features. With enough enrollment data, this approach produced dramatic error rate reductions and showed conceptually that better performance was attainable. A drawback in this approach is that many high-level systems were being run independently requiring significant computational complexity and resources. In 2006, MIT Lincoln Laboratory focused on a new system architecture which emphasized reduced complexity. This system was a carefully selected mixture of high-level techniques, new classifier methods, and novel channel compensation techniques. This new system has excellent accuracy and has substantially reduced complexity. The performance and computational aspects of the system are detailed on a NIST 2006 SRE task.
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Summary

Many powerful methods for speaker recognition have been introduced in recent years--high-level features, novel classifiers, and channel compensation methods. A common arena for evaluating these methods has been the NIST speaker recognition evaluation (SRE). In the NIST SRE from 2002-2005, a popular approach was to fuse multiple systems based upon...

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The MIT-LL/IBM 2006 speaker recognition system: high-performance reduced-complexity recognition

Triage framework for resource conservation in a speaker identification system

April 1, 2007
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Conference Paper
Author:
Arvind Jairam
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Published in:
Proc. 32nd IEEE Int. Conf. on Acoustics, Speech, and Signal Processing, ICASSP, April 2007, pp. IV-69 - IV-72.
Topic:
speaker recognition
R&D area:
R&D group:

Summary

We present a novel framework for triaging (prioritizing and discarding) data to conserve resources for a speaker identification (SID) system. Our work is motivated by applications that require a SID system to process an overwhelming volume of audio data. We design a triage filter whose goal is to conserve recognizer resources while preserving relevant content. We propose triage methods that use signal quality assessment tools, a scaled-down version of the main recognizer itself, and a fusion of these measures. We define a new precision-based measure of effectiveness for our triage framework. Our experimental results with the 35-speaker tactical SID corpus bear out the validity of our approach.
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Summary

We present a novel framework for triaging (prioritizing and discarding) data to conserve resources for a speaker identification (SID) system. Our work is motivated by applications that require a SID system to process an overwhelming volume of audio data. We design a triage filter whose goal is to conserve recognizer...

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Triage framework for resource conservation in a speaker identification system

PMatlab: parallel Matlab library for signal processing applications

April 1, 2007
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Conference Paper
Author:
Nadya T. Bliss
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Published in:
ICASSP, 32nd IEEE Int. Conf. on Acoustics Speech and Signal Processing, April 2007, pp. IV-1189 - IV-1192.
Topic:
high performance computing
R&D area:
R&D group:

Summary

MATLAB is one of the most commonly used languages for scientific computing with approximately one million users worldwide. At MIT Lincoln Laboratory, MATLAB is used by technical staff to develop sensor processing algorithms. MATLAB'S popularity is based on availability of high-level abstractions leading to reduced code development time. Due to the compute intensive nature of scientific computing, these applications often require long running times and would benefit greatly from increased performance offered by parallel computing. pMatlab implements partitioned global address space (PGAS) support via standard operator overloading techniques. The core data structures in pMatlab are distributed arrays and maps, which simplify parallel programming by removing the need for explicit message passing. This paper presents the pMaltab design and results for the HPC Challenge benchmark suite. Additionally, two case studies of pMatlab use are described.
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Summary

MATLAB is one of the most commonly used languages for scientific computing with approximately one million users worldwide. At MIT Lincoln Laboratory, MATLAB is used by technical staff to develop sensor processing algorithms. MATLAB'S popularity is based on availability of high-level abstractions leading to reduced code development time. Due to...

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PMatlab: parallel Matlab library for signal processing applications

Coverage maximization using dynamic taint tracing

March 28, 2007
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Technical Report
Author:
Timothy R. Leek
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Published in:
MIT Lincoln Laboratory Report TR-1112
Topic:
cyber security
R&D area:
R&D group:

Summary

We present COMET, a system that automatically assembles a test suite for a C program to improve line coverage, and give initial results for a prototype implementation. COMET works dynamically, running the program under a variety of instrumentations in a feedback loop that adds new inputs to an initial corpus with each iteration. One instrumentation in particular is crucial to the success of this approach: dynamic taint tracing. Inputs are labeled as tainted at the byte level and all read/write pairs in the program are augmented to track the flow of taint between memory objects. This allows COMET to determine from which bytes of which inputs the variables in conditions derive, thereby dramatically narrowing the search over inputs necessary to expose new code. On a test set of 13 example program, COMET improves upon the level of coverage reached in random testing by an average of 23% relative, takes only about twice the time, and requires a tiny fraction of the number of inputs to do so.
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Summary

We present COMET, a system that automatically assembles a test suite for a C program to improve line coverage, and give initial results for a prototype implementation. COMET works dynamically, running the program under a variety of instrumentations in a feedback loop that adds new inputs to an initial corpus...

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Coverage maximization using dynamic taint tracing

Analysis of operational alternatives to the Terminal Doppler Weather Radar (TDWR)

February 26, 2007
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Project Report
Author:
Mark E. Weber
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Published in:
MIT Lincoln Laboratory Report ATC-332
Topic:
wind shear
R&D area:
R&D group:

Summary

Possible alternatives to the Terminal Doppler Weather Radar (TDWR) are assessed. We consider both the low altitude wind shear detection service provided by TDWR and its role in reducing weather-related airport delays through its input to the Integrated Terminal Weather System (ITWS). Airborne predictive wind shear (PWS) radars do not provide the broad area situational awareness needed to proactively reroute aircraft away from the affected runways. We considered in detail the alternative of using the ASR-9 Weather Systems Processor (WSP) and NEXRAD in lieu of TDWR. An objective metric for wind shear detection capability was calculated for each of these radars at all TDWR equipped airports. TDWR was uniformly superior by this metric, and at a number of the airports, the ASR-9/NEXRAD alternative scored so low as to raise questions whether it would be operationally acceptable. To assess airport weather delay reduction impact, we compared the accuracy of the high-benefit ITWS "Terminal Winds" product with and without TDWR input. Removal of the TDWR data would have increased the mean estimate error by a factor of 3 near the surface.
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Summary

Possible alternatives to the Terminal Doppler Weather Radar (TDWR) are assessed. We consider both the low altitude wind shear detection service provided by TDWR and its role in reducing weather-related airport delays through its input to the Integrated Terminal Weather System (ITWS). Airborne predictive wind shear (PWS) radars do not...

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Analysis of operational alternatives to the Terminal Doppler Weather Radar (TDWR)
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