Publications
Polyphase nonlinear equalization of time-interleaved analog-to-digital converters
June 1, 2009
Journal Article
Published in:
IEEE J. Sel. Top. Sig. Process., Vol. 3, No. 3, June 2009, pp. 362-373.
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Summary
As the demand for higher data rates increases, commercial analog-to-digital converters (ADCs) are more commonly being implemented with multiple on-chip converters whose outputs are time-interleaved. The distortion generated by time-interleaved ADCs is now not only a function of the nonlinear behavior of the constituent circuitry, but also mismatches associated with interleaving multiple output streams. To mitigate distortion generated by time-interleaved ADCs, we have developed a polyphase NonLinear EQualizer (pNLEQ) which is capable of simultaneously mitigating distortion generated by both the on-chip circuitry and mismatches due to time interleaving. In this paper, we describe the pNLEQ architecture and present measurements of its performance.
Summary
As the demand for higher data rates increases, commercial analog-to-digital converters (ADCs) are more commonly being implemented with multiple on-chip converters whose outputs are time-interleaved. The distortion generated by time-interleaved ADCs is now not only a function of the nonlinear behavior of the constituent circuitry, but also mismatches associated with...
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A multi-frame, megahertz CCD imager
June 1, 2009
Journal Article
Published in:
IEEE Trans. Nuclear Sci., Vol. 56, No. 3, June 2009, pp. 1188-1192.
Summary
The Los Alamos National Laboratory's Dual Axis Radiographic Hydrodynamic Test Facility (DARHT) generates flash radiographs of explosive experiments using two linear induction electron accelerators situated at right angles. The DARHT second axis accelerator generates an 18-MeV, 2 kA, 2 sec electron beam which is converted or "chopped" into four individual pulses ranging from 20 to 100 nsec in length at 2 MHz frequency. The individual electron beam pulses are down-converted by a segmented lutetium oxyorthosilicate scintillator, creating four visible light flashes, to image explosively driven events. To record these events, a high efficiency, high speed, imager has been fabricated which is capable of framing rates of 2 MHz. This device utilizes a 512 512 pixel charge coupled device (CCD) with a 25 cm2 active area, and incorporates an electronic shutter technology designed for back-illuminated CCD's, making this the largest and fastest back-illuminated CCD in the world. Characterizing an imager capable of this frame rate presents unique challenges. High speed LED drivers and intense radioactive sources are needed to perform basic measurements.We investigate properties normally associated with single-frame CCDs such as read noise, gain, full-well capacity, detective quantum efficiency (DQE), sensitivity, and linearity. In addition, we investigate several properties associated with the imager's multi-frame operation such as transient frame response and frame-to-frame isolation while contrasting our measurement techniques and results with more conventional devices.
Summary
The Los Alamos National Laboratory's Dual Axis Radiographic Hydrodynamic Test Facility (DARHT) generates flash radiographs of explosive experiments using two linear induction electron accelerators situated at right angles. The DARHT second axis accelerator generates an 18-MeV, 2 kA, 2 sec electron beam which is converted or "chopped" into four individual...
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Advocate: a distributed architecture for speech-to-speech translation
June 1, 2009
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 18, No. 1, June 2009, pp. 54-65.
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Advocate is a set of communications application programming interfaces and service wrappers that serve as a framework for creating complex and scalable real-time software applications from component processing algorithms. Advocate can be used for a variety of distributed processing applications, but was initially designed to use existing speech processing and machine translation components in the rapid construction of large-scale speech-to-speech translation systems. Many such speech-to-speech translation applications require real-time processing, and Advocate provides this speed with low-latency communication between services.
Summary
Advocate is a set of communications application programming interfaces and service wrappers that serve as a framework for creating complex and scalable real-time software applications from component processing algorithms. Advocate can be used for a variety of distributed processing applications, but was initially designed to use existing speech processing and...
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Advocate: a distributed voice-oriented computing architecture
May 31, 2009
Conference Paper
Published in:
North American Chapter of the Association for Computational Linguistics - Human Language Technologies Conf. (NAACL HLT 2009), 31 May - 5 June 2009.
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Summary
Advocate is a lightweight and easy-to-use computing architecture that supports real-time, voice-oriented computing. It is designed to allow the combination of multiple speech and language processing components to create cohesive distributed applications. It is scalable, supporting local processing of all NLP/speech components when sufficient processing resources are available to one machine, or fully distributed/networked processing over an arbitrarily large compute structure when more compute resources are needed. Advocate is designed to operate in a large distributed test-bed in which an arbitrary number of NLP/speech services interface with an arbitrary number of Advocate clients applications. In this configuration, each Advocate client application employs automatic service discovery, calling them as required.
Summary
Advocate is a lightweight and easy-to-use computing architecture that supports real-time, voice-oriented computing. It is designed to allow the combination of multiple speech and language processing components to create cohesive distributed applications. It is scalable, supporting local processing of all NLP/speech components when sufficient processing resources are available to one...
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Lithographically directed surface modification
May 26, 2009
Conference Paper
Published in:
J. Vacuum Sci. Technol. B, Microelectron. Process. Phenon., Vol. 27, No. 6, p. 3031-3037.
Summary
The directed assembly of polystyrene-block-poly(methyl methacrylate) films on a variety of photolytically nanopatterned siloxane-modified surfaces was investigated. The amount of siloxane removal is related to the exposure dose of a 157 nm laser. The modified surfaces were imaged using a 157 nm interference exposure system to lithographically define areas of different surface energies to direct the assembly of the diblock copolymer films. The analysis of the surface energy aerial image provided insights into the exposure doses required to result in defect-free films. While the slope of the surface energy aerial image was not found to be important by itself, in concert with the difference in high and low surface energy regions, as well as the maximum value of the low surface energy region, it provided insight into conditions needed to direct self-assembly of the block copolymer films. Preliminary investigations concerning the extension of this methodology to 193 nm showed that the polar surface energy of arylsiloxane-modified surfaces can also be affected by 193 nm exposure.
Summary
The directed assembly of polystyrene-block-poly(methyl methacrylate) films on a variety of photolytically nanopatterned siloxane-modified surfaces was investigated. The amount of siloxane removal is related to the exposure dose of a 157 nm laser. The modified surfaces were imaged using a 157 nm interference exposure system to lithographically define areas of...
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Wind-shear system cost benefit analysis update
May 13, 2009
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-341
Summary
A series of fatal commercial aviation accidents in the 1970s led to the development of systems and strategies to protect against wind shear. The Terminal Doppler Weather Radar (TDWR), Low Level Wind Shear Alert System (LLWAS), Weather Systems Processor (WSP) for Airport Surveillance Radars (ASR-9), pilot training and on-board wind shear detection equipment are all key protection components. While these systems have been highly effective, there are substantial costs associated with maintaining and operating ground-based systems. In addition, while over 85% of all major air carrier operations occur at airports protected by one of these ground-based wind-shear systems, the vast majority of smaller operations remain largely unprotected. This report assesses the technical and operational benefits of current and potential alternative ground-based systems as mitigations for the low-altitude wind-shear hazard. System performance and benefits for all of the current TDWR (46), ASR-9 WSP (35), and LLWAS (40) protected airports are examined, along with 40 currently unprotected airports. We considered in detail several alternatives and/or combinations for existing ground-based systems. These included the option to use data from current WSR-88D (or NEXRAD) and two potential future sensor deployments: (1) a commercially built pulsed-Doppler Lidar and (2) an X-band commercial Doppler weather radar. Wind-shear exposure estimates and simulation models for each wind shear protection component were developed for each site in order to accurately comare all alternatives. For the period 2010-2032, the current combination of wind-shear protection systems reduces teh $3.0 billion unprotected NAS overall wind-shear safety exposure to just $160 million over the entire study period. Overall, tehre were few alternatives that resulted in higher benefits than the TDWR, TDWR-LLWAS, and WSP configurations that currently exist at 81 airports. However, the cheaper operating costs of NEXRAD make it a potential alternative especially at LLWAS and non-wind-shear protected sites.
Summary
A series of fatal commercial aviation accidents in the 1970s led to the development of systems and strategies to protect against wind shear. The Terminal Doppler Weather Radar (TDWR), Low Level Wind Shear Alert System (LLWAS), Weather Systems Processor (WSP) for Airport Surveillance Radars (ASR-9), pilot training and on-board wind...
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Safety analysis of upgrading to TCAS Version 7.1 using the 2008 U.S. Correlated Encounter Model
May 11, 2009
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-349
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Summary
As a result of monitoring and modeling efforts by Eurocontrol and the FAA, two change proposals have been created to change the TCAS II V9.0 logic. The first, CP-112E, addresses the safety issues referred to as SA01. SA01 events have to do with the reversal logic contained in the TCAS algorithm, e.g., when TCAS reverses the sense of an RA from climb to descend. Typically, reversals occur to resolve deteriorating conditions during and encounter. V7.0 contained reversal logic based on certain assumptions and engineering judgment, but operational experience obtained since deployment has compelled a re-evaluation in areas of that logic, specifically having to do with late reversals. The second change proposal, CP-115, rectifies observed confusion surrounding the aural annunication AVSA during an RA by replacing it with the annunciation LOLO, and changing the TCAS V7.0 display and logic to appropriately support the change. Collectively, the changes to teh TCAS logic in both CP-112E and CP115 are referred to as TCAS II V7.1. Included in this document is a safety study that consideres V7.1 as a whole, and also the first safety study that uses teh U.S. correlated encounter model developed by Lincoln Laboratory for testing TCAS. Also included is a discussion of simulation capabilites developed at Lincoln Laboratory for evaluating CP-115 and for future analysis of TCAS in high density areas. Our study indicates that mroe risk lies in remaining with the current version of TCAS over upgrading to V7.1, and that no negative impact on safety in high density airspace occurs as a result of CP-115.
Summary
As a result of monitoring and modeling efforts by Eurocontrol and the FAA, two change proposals have been created to change the TCAS II V9.0 logic. The first, CP-112E, addresses the safety issues referred to as SA01. SA01 events have to do with the reversal logic contained in the TCAS...
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Design and development of the TFDM information management architecture
April 30, 2009
Conference Paper
Published in:
Integrated Communication, Navigation and Surveillance Conf., ICNS, 13-15 May 2009.
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The Tower Flight Data Manager (TFDM) is a new terminal automation platform that will provide an integrated tower-user display suite including an extended electronic flight strip or "flight data management" (FDM) display. The integrated information exchange and processing environment established by TFDM will support a suite of automation-assisted user support tools collectively designated as the Arrival/Departure Management Tool or A/DMT. A/DMT will develop and manage an integrated plan for arrival, scheduled (and to the extent possible) non-scheduled departure operations at the airport, based on 4D-trajectory assignments. A primary concern of A/DMT is the efficient use of the runway complex to meet service demand from both arrivals and departures. In addition, A/DMT seeks to reduce fuel usage and engine emissions on the airport surface, to permit more efficient use of gates and holding areas, and to enhance the safety of surface operations. We first put forth a strategy for developing a scalable TFDM-A/DMT Information Management Architecture (TIMA) employing standard information exchange models, services and data formats. This architecture will be consistent with evolving System Wide Information Management (SWIM) technologies and data standards, and will support efficient insertion of processing algorithms (e.g. surface trajectory management algorithms) developed by the research community and/or industry. Next, we describe TIMA . While TIMA makes use of Service-Oriented Architecture (SOA) principles, it is primarily an information-oriented architecture; we discuss why this architectural style is necessary for TFDM, and how it is also beneficial for SWIM. We conclude with a description of a general model for managing temporal aspects of information within TFDM. TIMA needs to support not only real-time operations, but post-facto analysis as well. A major difficulty in conducting analyses involving different data sources is time synchronization of data. We describe a method for associating temporal information with data sources in a data-agnostic manner, so that data can be retrieved from a variety of sources in a uniform manner.
Summary
The Tower Flight Data Manager (TFDM) is a new terminal automation platform that will provide an integrated tower-user display suite including an extended electronic flight strip or "flight data management" (FDM) display. The integrated information exchange and processing environment established by TFDM will support a suite of automation-assisted user support...
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Evaluation of TCAS II Version 7.1 using the FAA Fast-Time Encounter Generator model [volume 1]
April 29, 2009
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-346,I
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This report documents the Lincoln Laboratory evaluation of the Traffic Alert and Collision Avoidance System II (TCAS II) logic version 7.1. TCAS II is an airborne collision avoidance system required since 30 December 1993 by the FAA on all air carrier aircraft with more than 30 passenger seats operating in the U.S. airspace. Version 7.1 was created to correct two potential safety problems in earlier versions. The first change focuses on the sense reversal logic. The second change focuses on avoiding "wrong way" responses to Vertical Speed Limit or "Adjust Vertical Speed, Adjust" RAs. Lincoln Laboratory evaluated the logic by examining more than eight million simulated pairwise encounters, derived from actual tracks recorded in U.S. airspace. The main goals of the evaluation were: (1) to study the performance of the revised sense reversal logic for encounters where one pilot ignores the TCAS advisory; (2) to determine if the revised sense reversal logic has an adverse impact on encounters where both pilots follow the TCAS advisories; (3) to determine if the change from "Adjust Vertical Speed, Adjust" advisories to "Level Off, Level Off" advisories provides a safety benefit for TCAS. Three sets of encounters were examined in order to fulfill these goals: encounters where both aircraft are TCAS-equipped and both pilots follow the advisories; encounters where both aircraft are TCAS-equipped and one pilot does not follow the advisory; and encounters where only one aircraft is TCAS-equipped. A detailed analysis followed by a summary is provided for each set of encounters. An overall summary is given at the end of the report.
Summary
This report documents the Lincoln Laboratory evaluation of the Traffic Alert and Collision Avoidance System II (TCAS II) logic version 7.1. TCAS II is an airborne collision avoidance system required since 30 December 1993 by the FAA on all air carrier aircraft with more than 30 passenger seats operating in...
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Evaluation of TCAS II Version 7.1 using the FAA Fast-Time Encounter Generator model : appendix [volume 2]
April 29, 2009
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-346,II
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Summary
Appendix to Project Report ATC-346, Evaluation of TCAS II Version 7.1 Using the Fast-Time Encounter Generator Model, Volume 1.
Summary
Appendix to Project Report ATC-346, Evaluation of TCAS II Version 7.1 Using the Fast-Time Encounter Generator Model, Volume 1.
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