Publications
Technical challenges of supporting interactive HPC
June 19, 2007
Conference Paper
Published in:
Ann. High Performance Computer Modernization Program Users Group Conf., 19-21 June 2007.
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Summary
Users' demand for interactive, on-demand access to a large pool of high performance computing (HPC) resources is increasing. The majority of users at Massachusetts Institute of Technology Lincoln Laboratory (MIT LL) are involved in the interactive development of sensor processing algorithms. This development often requires a large amount of computation due to the complexity of the algorithms being explored and/or the size of the data set being analyzed. These researchers also require rapid turnaround of their jobs because each iteration directly influences code changes made for the following iteration. Historically, batch queue systems have not been a good match for this kind of user. The Lincoln Laboratory Grid (LLGrid) system at MIT-LL is the largest dedicated interactive, on-demand HPC system in the world. While the system also accommodates some batch queue jobs, the vast majority of jobs submitted are interactive, on-demand jobs. Choosing between running a system with a batch queue or in an interactive, on-demand manner involves tradeoffs. This paper discusses the tradeoffs between operating a cluster as a batch system, an interactive, ondemand system, or a hybrid system. The LLGrid system has been operational for over three years, and now serves over 200 users from across Lincoln. The system has run over 100,000 interactive jobs. It has become an integral part of many researchers' algorithm development workflows. For instance, in batch queue systems, an individual user commonly can gain access to 25% of the processors in the system after the job has waited in the queue; in our experience with on-demand, interactive operation, individual users often can also gain access to 20-25% of the cluster processors. This paper will share a variety of the new data on our experiences with running an interactive, on-demand system that also provides some batch queue access. Keywords: grid computing, on-demand, interactive high performance computing, cluster computing, parallel MATLAB.
Summary
Users' demand for interactive, on-demand access to a large pool of high performance computing (HPC) resources is increasing. The majority of users at Massachusetts Institute of Technology Lincoln Laboratory (MIT LL) are involved in the interactive development of sensor processing algorithms. This development often requires a large amount of computation...
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Automatic language identification
June 15, 2007
Journal Article
Published in:
Wiley Encyclopedia of Electrical and Electronics Engineering, Vol. 2, pp. 104-9, 2007.
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Summary
Automatic language identification is the process by which the language of digitized spoken words is recognized by a computer. It is one of several processes in which information is extracted automatically from a speech signal.
Summary
Automatic language identification is the process by which the language of digitized spoken words is recognized by a computer. It is one of several processes in which information is extracted automatically from a speech signal.
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Integrated compensation network for low mutual coupling of planar microstrip antenna arrays
June 9, 2007
Conference Paper
Published in:
IEEE Antennas and Propagation Society Int. Symp., 2007 Digest, 9-15 June 2007, pp. 1273-6.
Summary
The unavoidable presence of mutual coupling of antenna elements in an array limits the ability to transmit and receive signals concurrently [1]. In the absence of mutual coupling, it is conceivable although still difficult to transmit and receive at the same frequency at the same time, i.e., FM-CW radars. The reflection from the antenna, leakage through the circulator, and any other possible deleterious paths from the high power amplifier to the low noise amplifier must be cancelled or compensated for in some manner to keep the receiver linear. With a single antenna the signal and noise paths are correlated and therefore cancellation of the signal inherently eliminates the noise. However, in an array environment the mutual coupling of antenna elements cause noise from neighboring high power amplifiers to couple into each channel's receiver. While the signal coupling is coherent, the noise is uncorrelated to a degree that depends on the amplifier gain and noise figure. The use of a low mutual coupling antenna array is a critical element in operating systems in this manner.
Summary
The unavoidable presence of mutual coupling of antenna elements in an array limits the ability to transmit and receive signals concurrently [1]. In the absence of mutual coupling, it is conceivable although still difficult to transmit and receive at the same frequency at the same time, i.e., FM-CW radars. The...
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Ultra-wideband step notch array using stripline feed
June 9, 2007
Conference Paper
Published in:
IEEE Antennas and Propagation Society Int. Symp., 2007 Digest, 9-15 June 2007, pp. 3361-4.
Summary
Electronically scanned array (ESA) antennas capable of efficiently radiating over an octave of bandwidth provide system designs with more flexibility in multiple mode operation. Communication and radar bands occupy different frequency allocations and the growing research in Ultra-Wideband (UWB) communications make the use of a single ESA to cover these frequencies an area of interest. Array antennas constructed of tapered-slot antennas and TEM horns have been investigated and shown to operate successfully over an octave bandwidth. These antennas use vertical feeds which make them optimal for brick architectures, but less than desirable for tile architectures. Conventional notch antennas require a feed extending vertically away from the notch antenna which makes a flat 2-D connection between antennas difficult. In this work an Ultra-Wideband Step Notch Array (UWSNA) was designed for ESA applications. The array operates over a 6-12 GHz range using a flat, tile-based 2-D feed network making this array optimal for conformal applications with a minimum of vertical distance. Simulation results and measurements on a small prototype demonstrate the concept.
Summary
Electronically scanned array (ESA) antennas capable of efficiently radiating over an octave of bandwidth provide system designs with more flexibility in multiple mode operation. Communication and radar bands occupy different frequency allocations and the growing research in Ultra-Wideband (UWB) communications make the use of a single ESA to cover these...
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Design of overlapped subarrays using an RFIC beamformer
June 9, 2007
Conference Paper
Published in:
IEEE Antennas and Propagation Society Int. Symp., 2007 Digest, 9-15 June 2007, pp. 1791-4.
Summary
Electronically scanned arrays require a minimum number of controls, Nmin, given by the number of orthogonal beams that fill a prescribed scan sector. Most practical antenna arrays require considerably more than Nmin control elements, but overlapped subarray architectures can approach this theoretical limit. Figure 1 shows a block diagram of an overlapped subarray architecture. The overlapped subarray network produces a flattopped sector pattern with low sidelobes that suppress grating lobes outside of the main beam of the subarray pattern. Each radiating element of the array is connected to multiple subarrays, creating an overlapping geometry. It is possible to scan one beam, or a fixed set of contiguous beams, over the main sector of the subarray with a set of Nmin phase shifters. Alternatively, digital receivers can be connected to the Nmin subarrays and multiple simultaneous beams can be formed digitally. Digital subarray architectures using a combination of element level phase shifters and subarray level receivers makes it possible to scan multiple beam clusters over all space. The conventional approach to the design and manufacturing of the overlapped subarray network shown in Figure 1 is challenging and costly due to the complexity of the microwave network. However, the design of the overlapped subarray beamformer using Radio Frequency Integrated Circuits (RFIC) represents a novel approach for implementing an efficient trade-off between the agility and capability of fully digital arrays and the cost effectiveness of analog arrays.
Summary
Electronically scanned arrays require a minimum number of controls, Nmin, given by the number of orthogonal beams that fill a prescribed scan sector. Most practical antenna arrays require considerably more than Nmin control elements, but overlapped subarray architectures can approach this theoretical limit. Figure 1 shows a block diagram of...
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A component model approach for the RCS validation of an electrically large open-ended cylindrical cavity
June 9, 2007
Conference Paper
Published in:
IEEE Antennas and Propagation Society Int. Symp., 2007 Digest, 9-15 June 2007, pp. 2275-2278.
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Summary
A novel RCS component prediction model approach to producing both fast and accurate scattering from an electrically large open-ended cylindrical cavity (circular cross section) is presented. The component model is a hybrid approach which easily permits individual scattering mechanisms to be coherently combined to produce a high fidelity signature. For this problem, the component model included scattering produced from the interior of the cavity calculated via the waveguide modal approach combined with the scattering produced from the cavity's finite thick rim opening (i.e., annulus) computed via the Method of Moments (MoM) and finally combined with the cavity's external base ring edge diffraction computed via PTD. Narrowband and wideband signature analysis for the circular cylindrical cavity configuration are presented to validate the component prediction model with static range measurements, and another prediction result computed using MoM for X- band frequencies and linear polarization. Excellent agreement is achieved among the data sets: measurement and prediction (component and MoM model).
Summary
A novel RCS component prediction model approach to producing both fast and accurate scattering from an electrically large open-ended cylindrical cavity (circular cross section) is presented. The component model is a hybrid approach which easily permits individual scattering mechanisms to be coherently combined to produce a high fidelity signature. For...
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Orthogonal transfer arrays for wide-field adaptive imaging
June 7, 2007
Conference Paper
Published in:
Proc. 2007 Int. Image Sensor Workshop, 7-10 June 2007.
Summary
The orthogonal transfer array (OTA) is a novel charge-coupled device (CCD) imager based on the orthogonal-transfer CCD (OTCCD). The OTCCD, in turn, is a device capable of charge transfer in all directions and has been developed for adaptive imaging in ground-based astronomy. By using a bright guide star as a beacon, the OTCCD can correct for wavefront tilt due to atmospheric effects as well as compensation for telescope shake, which in turn enhances the resolution and SNR. However, for wide field-of-view imaging the atmospheric wavefront distortions decorrelate over distances more than a few 10's of arcmin and hence an array of independently driven OTCCDs is required. To resolve this issue we developed the OTA, which consists of a two-dimensional array of OTCCDs combined with addressing and control logic to enable independent clocking of each OTCCD. This device enables spatially varying electronic tip-tilt correction and was developed for the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) program at the University of Hawaii Institute for Astronomy (UH/IfA)
Summary
The orthogonal transfer array (OTA) is a novel charge-coupled device (CCD) imager based on the orthogonal-transfer CCD (OTCCD). The OTCCD, in turn, is a device capable of charge transfer in all directions and has been developed for adaptive imaging in ground-based astronomy. By using a bright guide star as a...
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Guidance material for Mode S-specific protocol application avionics
June 4, 2007
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-334
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Summary
This ATC report presents guidance material for the use of "Ground-Initiated Comm. B" (GICB) register set contained in a Mode S transponder. The guidance material is intended to provide assistance for implementers of Mode S avionics installations. A common summary of the requirements and specifications for Mode S GICB transponder register data link applications is developed. While this ATC report focuses primarily on the "Elementary Surveillance" (ELS), "Enhanced Surveillance" (EHS), and "Automatic Dependent Surveillance-Broadcast" (ADS-B) applications, guidance information is also provided for general transponder configuration and architecture of other Mode S functions employing the GICB register set. Although the information contained in this ATC report is drawn from a number of approved national and international standards, it is not intended to replace or supersede those standards documents. In the event of a conflict or contradiction between this ATC report and any approved standards (see references 1 through 6), the approved standard takes precedence and the reader is encouraged to contact the authors of this document. Reference 4 is the most-recent and complete specification for the Mode S register contents. For ease of reference, the relevant Mode S register images have been duplicated in Appendix A of this report.
Summary
This ATC report presents guidance material for the use of "Ground-Initiated Comm. B" (GICB) register set contained in a Mode S transponder. The guidance material is intended to provide assistance for implementers of Mode S avionics installations. A common summary of the requirements and specifications for Mode S GICB transponder...
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A 16mW 8Mbps fractional-n FSK modulator at 15.8-18.9GHz
June 3, 2007
Conference Paper
Published in:
2007 IEEE Radio Frequency Integrated Circuits Symp., 3-5 June 2007, pp. 533-536.
Summary
Indirect modulation of fractional-N synthesizers is an energy-efficient architecture capable of moderate data rates, and is well-suited for use in sensor networks or WLAN. Although the architecture is used primarily at low RF frequencies, the capability for fractional- N synthesizers at Ku-band and above currently exist in available silicon technology. Recent demonstrations at 10- 25GHz show promising results, although power consumption at this higher frequency remains high for small batterypowered devices. This work implements a fully-integrated fractional-N synthesizer optimized for power efficient modulation at 15.8 to 18.9GHz with an 80MHz reference. Binary and 4-ary FSK modulation of up to 8Mbps is achieved while consuming 16mW in IBM 0.18um SiGe BiCMOS.
Summary
Indirect modulation of fractional-N synthesizers is an energy-efficient architecture capable of moderate data rates, and is well-suited for use in sensor networks or WLAN. Although the architecture is used primarily at low RF frequencies, the capability for fractional- N synthesizers at Ku-band and above currently exist in available silicon technology...
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A sub-10mW 2Mbps BFSK transceiver at 1.35 to 1.75GHz.
June 3, 2007
Conference Paper
Published in:
2007 IEEE Radio Frequency Integrated Circuits Symp., 3-5 June 2007, pp. 97-100.
Summary
This work presents the design and measurement of a 2Mbps BFSK transceiver at 1.35 to 1.75GHz for use in wireless sensor node applications. The receiver is a direct conversion architecture and has a sensitivity of -74dBm at 2Mbps and consumes 8.0mW. The transmitter generates orthogonal BFSK modulation through the use of digital pre-emphasis of the synthesizer frequency control word and consumes 9.7mW including the power amplifier. The transmitter delivers >3dBm of output power for a total transmitter power efficiency of 23% and a transmitter FOM of 4.85nJ/bit at 2Mbps.
Summary
This work presents the design and measurement of a 2Mbps BFSK transceiver at 1.35 to 1.75GHz for use in wireless sensor node applications. The receiver is a direct conversion architecture and has a sensitivity of -74dBm at 2Mbps and consumes 8.0mW. The transmitter generates orthogonal BFSK modulation through the use...
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