Publications
Nonlinear equalization for RF receivers
June 26, 2006
Conference Paper
Published in:
Proc. Conf. on High Performance Computer Modernization Program, 26-29 June 2006, pp. 303-307.
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This paper describes the need for High Performance Computing (HPC) to facilitate the development and implementation of a nonlinear equalizer that is capable of mitigating and/or eliminating nonlinear distortion to extend the dynamic range of radar front-end receivers decades beyond the analog state-of-the-art. The search space for the optimal nonlinear equalization (NLEQ) solution is computationally intractable using only a single desktop computer. However, we have been able to leverage a combination of an efficient greedy search with the high performance computing technologies of LLGrid and MatlabMPI to construct an NLEQ architecture that is capable of extending the dynamic range of Radar front-end receivers by over 25dB.
Summary
This paper describes the need for High Performance Computing (HPC) to facilitate the development and implementation of a nonlinear equalizer that is capable of mitigating and/or eliminating nonlinear distortion to extend the dynamic range of radar front-end receivers decades beyond the analog state-of-the-art. The search space for the optimal nonlinear...
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Ultra-linear superwideband chirp generator using digital compensation
June 11, 2006
Conference Paper
Published in:
IEEE MTT-S Int. Microwave Symp., 11-16 June 2006, pp. 403-406.
Summary
A novel digital compensation technique is applied to linearize the frequency generation of a superwideband chirp. Ultra-linear, low-noise swept local oscillators (SLO) are critical to the two-tone dynamic range performance of compressive receivers. The proposed technique enables full software control of the chirp linearity, slope, and offset to allow automated real-time calibration and testing, including automatic compensation for temperature variation. This approach combines recently available commercial high-speed digital, mixed-signal, and analog integrated circuits along with microwave components to create a 15.5-24 GHz chirp over 60 nsec with
Summary
A novel digital compensation technique is applied to linearize the frequency generation of a superwideband chirp. Ultra-linear, low-noise swept local oscillators (SLO) are critical to the two-tone dynamic range performance of compressive receivers. The proposed technique enables full software control of the chirp linearity, slope, and offset to allow automated...
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Advances in operational weather radar technology
June 1, 2006
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 16, No. 1, June 2006, pp. 9-30.
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The U.S. aviation system makes extensive use of national operational Doppler weather radar networks. These are critical for the detection and forecasting of thunderstorms and other hazardous weather phenomena, and they provide dense, continuously updated measurements of precipitation and wind fields as inputs to high-resolution numerical weather prediction models. This article describes recent Lincoln Laboratory activities that significantly enhance the operational effectiveness of the nation's Doppler weather radar networks. An open radar controller and digital signal processor has been developed for the Terminal Doppler Weather Radar (TDWR), which provides safety-critical low-altitude wind-shear warnings at large airports. This processor utilizes a small computer cluster architecture and standards-based software to realize high throughput and expansion capability. Innovative signal processing algorithms enabled by the new processor significantly improve the quality of the precipitation and wind measurements provided by TDWR. In a parallel effort, the Laboratory is working with engineers in the National Weather Service to augment the national NEXRAD Doppler weather radar network's algorithm suite. Laboratory staff develop and test enhancements directed at the aviation weather problem. Then they provide plug-and-play software to the NEXRAD second-level engineering support organization. This effort has substantially improved the operational value of NEXRAD data for the aviation system. Finally, we discuss nascent efforts to define a future multifunction radar network using an active-array architecture, which could realize the capabilities of today's multiple weather and air traffic control radar networks.
Summary
The U.S. aviation system makes extensive use of national operational Doppler weather radar networks. These are critical for the detection and forecasting of thunderstorms and other hazardous weather phenomena, and they provide dense, continuously updated measurements of precipitation and wind fields as inputs to high-resolution numerical weather prediction models. This...
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Advanced aviation weather forecasts
June 1, 2006
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 16, No. 1, June 2006, pp. 31-58.
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The U.S. air transportation system faces a continuously growing gap between the demand for air transportation and the capacity to meet that demand. Two key obstacles to bridging this gap are traffic delays due to en route severe-weather conditions and airport weather conditions. Lincoln Laboratory has been addressing these traffic delays and related safety problems under the Federal Aviation Administration's (FAA) Aviation Weather Research Program. Our research efforts involve real-time prototype forecast systems that provide immediate benefits to the FAA by allowing traffic managers to safely reduce delay. The prototypes also show the way toward bringing innovative applied meteorological research to future FAA operational capabilities. This article describes the recent major accomplishments of the Convective Weather and the Terminal Ceiling and Visibility Product Development Teams, both of which are led by scientists at Lincoln Laboratory.
Summary
The U.S. air transportation system faces a continuously growing gap between the demand for air transportation and the capacity to meet that demand. Two key obstacles to bridging this gap are traffic delays due to en route severe-weather conditions and airport weather conditions. Lincoln Laboratory has been addressing these traffic...
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Corridor Integrated Weather System
June 1, 2006
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 16, No. 1, June 2006, pp. 59-80.
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Flight delays are now a major problem in the U.S. National Airspace System. A significant fraction of these delays are caused by reductions in en route capacity due to severe convective weather. The Corridor Integrated Weather System (CIWS) is a fully automated weather analysis and forecasting system designed to support the development and execution of convective weather impact mitigation plans for congested en route airspace. The CIWS combines data from dozens of weather radars with satellite data, surface observations, and numerical weather models to dramatically improve the accuracy and timeliness of the storm severity information and to provide state-of-the-art, accurate, automated, high-resolution, animated three-dimensional forecasts of storms (including explicit detection of storm growth and decay). Real-time observations of the Federal Aviation Administration (FAA) decision making process during convective weather at Air Route Traffic Control Centers in the Midwest and Northeast have shown that the CIWS enables the FAA users to achieve more efficient tactical use of the airspace, reduce traffic manager workload, and significantly reduce delays. A real-time data-fusion architecture to assist in national deployment of CIWS is under development, and the CIWS products are being used in integrated air traffic management decision support systems.
Summary
Flight delays are now a major problem in the U.S. National Airspace System. A significant fraction of these delays are caused by reductions in en route capacity due to severe convective weather. The Corridor Integrated Weather System (CIWS) is a fully automated weather analysis and forecasting system designed to support...
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Integrating advanced weather forecast technologies into air traffic management decision support
June 1, 2006
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 16, No. 1, June 2006, pp. 81-96.
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Explicit integration of aviation weather forecasts with the National Airspace System (NAS) structure is needed to improve the development and execution of operationally effective weather impact mitigation plans and has become increasingly important due to NAS congestion and associated increases in delay. This article considers several contemporary weather-air traffic management (ATM) integration applications: the use of probabilistic forecasts of visibility at San Francisco, the Route Availability Planning Tool to facilitate departures from the New York airports during thunderstorms, the estimation of en route capacity in convective weather, and the application of mixed-integer optimization techniques to air traffic management when the en route and terminal capacities are varying with time because of convective weather impacts. Our operational experience at San Francisco and New York coupled with very promising initial results of traffic flow optimizations suggests that weather-ATM integrated systems warrant significant research and development investment. However, they will need to be refined through rapid prototyping at facilities with supportive operational users.
Summary
Explicit integration of aviation weather forecasts with the National Airspace System (NAS) structure is needed to improve the development and execution of operationally effective weather impact mitigation plans and has become increasingly important due to NAS congestion and associated increases in delay. This article considers several contemporary weather-air traffic management...
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Operational evaluation of runway status lights
June 1, 2006
Journal Article
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Lincoln Laboratory Journal, Vol. 16, No. 1, June 2006, pp. 123-146.
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To maintain safe separation of aircraft on the airport surface, air traffic controllers issue verbal clearances to pilots to sequence aircraft arrivals, departures, and runway crossings. Although controllers and pilots work together successfully most of the time, mistakes do occasionally happen, causing several hundred runway incursions a year and, less frequently, near misses and collisions in the United States. With this rate of incursions, it is imperative to have an independent warning system as a backup to the current system. Runway status lights, a system of automated, surveillance-driven stoplights, have been designed to provide this backup function. The lights are installed at runway-taxiway intersections and at departure points along the runways. They provide a clear signal to pilots crossing or departing from a runway, warning them of potential conflicts with traffic already on the runway. Existing FAA-installed radar surveillance is coupled with Lincoln Laboratory-developed algorithms to generate the light commands. To be compatible with operations at the busiest airports, the algorithms must drive the lights such that during normal operations pilots will almost never encounter a red light when it is safe to cross or depart from a runway. A minimal error rate must be maintained even in the face of inevitable imperfections in the surveillance system used to drive the safety logic. A prototype runway status light system has been designed at Lincoln Laboratory and installed at the Dallas/Fort Worth International Airport, where Laboratory personnel have worked with the FAA to complete an operational evaluation of the system, demonstrating the feasibility of runway status lights in the challenging, complex environment of one of the world's busiest airports.
Summary
To maintain safe separation of aircraft on the airport surface, air traffic controllers issue verbal clearances to pilots to sequence aircraft arrivals, departures, and runway crossings. Although controllers and pilots work together successfully most of the time, mistakes do occasionally happen, causing several hundred runway incursions a year and, less...
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Surveillance accuracy requirements in support of separation services
June 1, 2006
Journal Article
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Lincoln Laboratory Journal, Vol. 16, No. 1, June 2006, pp. 97-122.
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The Federal Aviation Administration is modernizing the Air Traffic Control system to improve flight efficiency, to increase airspace capacity, to reduce flight delays, and to control operating costs as the demand for air travel continues to grow. Promising new surveillance technologies such as Automatic Dependent Surveillance Broadcast and multisensor track fusion offer the potential to augment the ground-based surveillance and controller-display systems by providing more timely and complete information about aircraft. The resulting improvement in surveillance accuracy may potentially allow the expanded use of the minimum safe-separation distance between aircraft. However, these new technologies cannot be introduced with today's radar-separation standards, because they assume surveillance will be provided only through radar technology. In this article, we review the background of aircraft surveillance and the establishment of radar separation standards. The required surveillance accuracy to safely support aircraft separation with National Airspace System technologies is then derived from currently widely used surveillance systems. We end with flight test validation of the derived results, which can be used to evaluate new technologies.
Summary
The Federal Aviation Administration is modernizing the Air Traffic Control system to improve flight efficiency, to increase airspace capacity, to reduce flight delays, and to control operating costs as the demand for air travel continues to grow. Promising new surveillance technologies such as Automatic Dependent Surveillance Broadcast and multisensor track...
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The mixer and transcript reading corpora: resources for multilingual, crosschannel speaker recognition research
May 24, 2006
Conference Paper
Published in:
Proc. Int. Conf. on Language Resources and Evaluation, LREC, 24-26 May 2006, pp. 117-20.
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This paper describes the planning and creation of the Mixer and Transcript Reading corpora, their properties and yields, and reports on the lessons learned during their development.
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This paper describes the planning and creation of the Mixer and Transcript Reading corpora, their properties and yields, and reports on the lessons learned during their development.
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A scalable phonetic vocoder framework using joint predictive vector quantization of MELP parameters
May 14, 2006
Conference Paper
Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech and Signal Processing, Speech and Language Processing, ICASSP, 14-19 May 2006, pp. 705-708.
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We present the framework for a Scalable Phonetic Vocoder (SPV) capable of operating at bit rates from 300 - 1100 bps. The underlying system uses an HMM-based phonetic speech recognizer to estimate the parameters for MELP speech synthesis. We extend this baseline technique in three ways. First, we introduce the concept of predictive time evolution to generate a smoother path for the synthesizer parameters, and show that it improves speech quality. Then, since the output speech from the phonetic vocoder is still limited by such low bit rates, we propose a scalable system where the accuracy of the MELP parameters is increased by vector quantizing the error signal between the true and phonetic-estimated MELP parameters. Finally, we apply an extremely flexible technique for exploiting correlations in these parameters over time, which we call Joint Predictive Vector Quantization (JPVQ).We show that significant quality improvement can be attained by adding as few as 400 bps to the baseline phonetic vocoder using JPVQ. The resulting SPV system provides a flexible platform for adjusting the phonetic vocoder bit rate and speech quality.
Summary
We present the framework for a Scalable Phonetic Vocoder (SPV) capable of operating at bit rates from 300 - 1100 bps. The underlying system uses an HMM-based phonetic speech recognizer to estimate the parameters for MELP speech synthesis. We extend this baseline technique in three ways. First, we introduce the...
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