Publications
Validation techniques for ADS-B surveillance data
October 27, 2002
Conference Paper
Published in:
21st DASC: Proc. of the Digital Avionics Systems Conf., Vol. 1, 27-31 October 2002, pp. 3.E.2-1 - 3.E.2-9.
Summary
Surveillance information forms the basis for providing traffic separation services by Air Traffic Control. The consequences of failures in the integrity and availability of surveillance data have been highlighted in near misses and more tragically, by midair collisions. Recognizing the importance and criticality of surveillance information, the U.S. Federal Aviation Administration (FAA) in common with most other Civil Aviation Authorities (CAAs) worldwide has implemented a surveillance architecture that emphasizes the independence of surveillance sources and the availability of crosschecks on all flight critical data. Automatic Dependent Surveillance Broadcast (ADS-B) changes this approach by combining the navigation and surveillance information into a single system element. ADS-B is a system within which individual aircraft distribute position estimates from onboard navigation equipment via a common communications channel. Any ADS-B receiver may then assemble a complete surveillance picture of nearby aircraft by listening to the common channel and combining the received surveillance reports with an onboard estimate of ownership position. This approach makes use of the increasing sophistication and affordability of navigation equipment (e.g. GPS-based avionics) to improve the accuracy and update rate of surveillance information. However, collapsing the surveillance and navigation systems into a common element increases the vulnerability of the system to erroneous information, both due to intentional and unintentional causes.
Summary
Surveillance information forms the basis for providing traffic separation services by Air Traffic Control. The consequences of failures in the integrity and availability of surveillance data have been highlighted in near misses and more tragically, by midair collisions. Recognizing the importance and criticality of surveillance information, the U.S. Federal Aviation...
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Analysis and comparison of separation measurement errors in single sensor and multiple radar mosiac display terminal environments
October 21, 2002
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-306
Summary
This paper presents an analyis to estimate and characterize the errors in the measured separation distance between aircraft that are displayed on a radar screen to a controller in a single sensor terminal environment compared to a multiple radar mosiac terminal environment. The error in measured or displayed separation is the difference between the true separation or distance between aircraft in the air and the separation displayed to a controller on a radar screen. In order to eliminate as many variables as possible and to concentrate specifically on the differences between displayed separation errors in the two environments, for the purposes of this analysis, only full operation Mode S secondary beacon surveillance characteristics are considered. A summary of the Mode S secondary radar error sources and characteristics used to model the resultant errors in measured separation between aircraft in single and multi-radar terminal environments is presented. The analysis for average separation errors show that the performance of radars in providing separation services degrades with range. The analysis also shows that when using independent radars in a mosiac display, separation errors will increase, on average, compared to the performance when providing separation with a single radar. The data presented in the section on average separation errors is summarized by plotting the standard deviation of the separation error as a function of range for the single radar case and for the independent mosiac display case. The sections on typical and specific errors in separation measurements illustrate that the separation measurement errors are highly dependent on the geometry of the aircraft and radars. Applying average results to specific geometries can lead to counter intuitive results is illustrated in an example case presented in analysis.
Summary
This paper presents an analyis to estimate and characterize the errors in the measured separation distance between aircraft that are displayed on a radar screen to a controller in a single sensor terminal environment compared to a multiple radar mosiac terminal environment. The error in measured or displayed separation is...
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The effect of identifying vulnerabilities and patching software on the utility of network intrusion detection
October 16, 2002
Conference Paper
Published in:
Proc. 5th Int. Symp. on Recent Advances in Intrusion Detection, RAID 2002, 16-18 October 2002, pp. 307-326.
R&D area:
R&D group:
Summary
Vulnerability scanning and installing software patches for known vulnerabilities greatly affects the utility of network-based intrusion detection systems that use signatures to detect system compromises. A detailed timeline analysis of important remote-to-local vulnerabilities demonstrates (1) vulnerabilities in widely-used server software are discovered infrequently (at most 6 times a year) and (2) Software patches to prevent vulnerabilities from being exploited are available before or simultaneously with signatures. Signature-based intrusion detection systems will thus never detect successful system compromises on small secure sites when patches are installed as soon as they are available. Network intrusion detection systems may detect successful system compromises on large sites where it is impractical to eliminate all known vulnerabilities. On such sites, information from vulnerability scanning can be used to prioritize the large numbers of extraneous alerts caused by failed attacks and normal background MIC. On one class B network with roughly 10 web servers, this approach successfully filtered out 95% of all remote-to-local alerts.
Summary
Vulnerability scanning and installing software patches for known vulnerabilities greatly affects the utility of network-based intrusion detection systems that use signatures to detect system compromises. A detailed timeline analysis of important remote-to-local vulnerabilities demonstrates (1) vulnerabilities in widely-used server software are discovered infrequently (at most 6 times a year) and...
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Investigation of the physical and practical limits of dense-only phase shift lithography for circuit feature definition
October 1, 2002
Journal Article
Published in:
J. Microlith., Microfab., Microsyst., Vol. 1, No. 3, October 2002, pp. 243-252.
Topic:
R&D area:
Summary
The rise of low- k1 optical lithography in integrated circuit manufacturing has introduced new questions concerning the physical and practical limits of particular subwavelength resolution-enhanced imaging approaches. For a given application, trade-offs between mask complexity, design cycle time, process latitude and process throughput must be well understood. It has recently been shown that a dense-only phase shifting mask (PSM) approach can be applied to technology nodes approaching the physical limits of strong PSM with no proximity effects. Such an approach offers the benefits of reduced mask complexity and design cycle time, at the expense of decreased process throughput and limited design flexibility. In particular, dense-only methods offer k1,0.3, thus enabling 90 nm node lithography with high-numerical aperture 248 nm exposure systems. We present the results of experiments, simulations, and analysis designed to explore the trade-offs inherent in dense-only phase shift lithography. Gate and contact patterns corresponding to various fully scaled circuits are presented, and the relationship between process complexity and design latitude is discussed. Particular attention is given to approaches for obtaining gate features in both the horizontal and vertical orientation. Since semiconductor investment is dependent on cost amortization, the applicability of these methods is also considered in terms of production volume.
Summary
The rise of low- k1 optical lithography in integrated circuit manufacturing has introduced new questions concerning the physical and practical limits of particular subwavelength resolution-enhanced imaging approaches. For a given application, trade-offs between mask complexity, design cycle time, process latitude and process throughput must be well understood. It has recently...
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An analysis of the impacts of wake vortex restrictions at LGA
September 16, 2002
Project Report
Published in:
Project Report ATC-305, MIT Lincoln Laboratory
Summary
Wake vortex restrictions at New York's La Guardia airport cause a significant reduction in capacity when aircraft land on runway 22 and depart on runway 31. This report presents an analysis of the annual delay cost at LGA associated with the wake vortex restrictions. We find that the delay due to these restrictions exceeds 4000 hours annually, and that these restrictions cause a significant workload increase to controllers at both La Guardia and the New York TRACON. If traffic levels were to increase 10% from their February 2001 levels, the corresponding increase in delay due to the wake vortex restrictions would rise from 30 hours a day to over 400 hours a day in this runway configuration. It is also found that for a meaningful increase in passenger capacity in this runway configuration to be as demand grows, restrictions must be reduced from their current levels. If the percentage of heavy/757's doubled at LGA, there would be no increase in passenger capacity while daily delays in this runway configuration due to current wake vortex separation standards would increase by 250 hours.
Summary
Wake vortex restrictions at New York's La Guardia airport cause a significant reduction in capacity when aircraft land on runway 22 and depart on runway 31. This report presents an analysis of the annual delay cost at LGA associated with the wake vortex restrictions. We find that the delay due...
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2-D processing of speech with application to pitch estimation
September 16, 2002
Conference Paper
Published in:
7th Int. Conf. on Spoken Language Processing, ICSLP 2002, 16-20 September 2002.
Topic:
R&D area:
Summary
In this paper, we introduce a new approach to two-dimensional (2-D) processing of the one-dimensional (1-D) speech signal in the time-frequency plane. Specifically, we obtain the shortspace 2-D Fourier transform magnitude of a narrowband spectrogram of the signal and show that this 2-D transformation maps harmonically-related signal components to a concentrated entity in the new 2-D plane. We refer to this series of operations as the "grating compression transform" (GCT), consistent with sine-wave grating patterns in the spectrogram reduced to smeared impulses. The GCT forms the basis of a speech pitch estimator that uses the radial distance to the largest peak in the GCT plane. Using an average magnitude difference between pitch-contour estimates, the GCT-based pitch estimator is shown to compare favorably to a sine-wave-based pitch estimator for all-voiced speech in additive white noise. An extension to a basis for two-speaker pitch estimation is also proposed.
Summary
In this paper, we introduce a new approach to two-dimensional (2-D) processing of the one-dimensional (1-D) speech signal in the time-frequency plane. Specifically, we obtain the shortspace 2-D Fourier transform magnitude of a narrowband spectrogram of the signal and show that this 2-D transformation maps harmonically-related signal components to a...
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Approaches to language identification using Gaussian mixture models and shifted delta cepstral features
September 16, 2002
Conference Paper
Published in:
Proc. Int. Conf. on Spoken Language Processing, INTERSPEECH, 16-20 September 2002, pp. 33-36, 82-92.
Topic:
R&D area:
Summary
Published results indicate that automatic language identification (LID) systems that rely on multiple-language phone recognition and n-gram language modeling produce the best performance in formal LID evaluations. By contrast, Gaussian mixture model (GMM) systems, which measure acoustic characteristics, are far more efficient computationally but have tended to provide inferior levels of performance. This paper describes two GMM-based approaches to language identification that use shifted delta cepstra (SDC) feature vectors to achieve LID performance comparable to that of the best phone-based systems. The approaches include both acoustic scoring and a recently developed GMM tokenization system that is based on a variation of phonetic recognition and language modeling. System performance is evaluated on both the CallFriend and OGI corpora.
Summary
Published results indicate that automatic language identification (LID) systems that rely on multiple-language phone recognition and n-gram language modeling produce the best performance in formal LID evaluations. By contrast, Gaussian mixture model (GMM) systems, which measure acoustic characteristics, are far more efficient computationally but have tended to provide inferior levels...
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An analysis of the impacts of wake vortex restrictions at LGA
September 16, 2002
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-305
Summary
Wake vortex restrictions at New York's La Guardia airport cause a significant reduction in capacity when aircraft land on runway 22 and depart on runway 31. This report presents an analysis of the annual delay cost at LGA associated with the wake vortex restrictions. We find that the delay due to these restrictions exceeds 4000 hours annually, and that these restrictions cause a significant workload increase to controllers at both La Guardia and the New York TRACON. If traffic levels were to increase 10% from their February 2001 levels, the corresponding increase in delay due to the wake vortex restrictions would rise from 30 hours a day to over 400 hours a day in this runway configuration. It is also found that for a meaningful increase in passenger capacity in this runway configuration to be as demand grows, restrictions must be reduced from their current levels. If the percentage of heavy/757's doubled at LGA, there would be no increase in passenger capacity while daily delays in this runway configuration due to current wake vortex separation standards would increase by 250 hours.
Summary
Wake vortex restrictions at New York's La Guardia airport cause a significant reduction in capacity when aircraft land on runway 22 and depart on runway 31. This report presents an analysis of the annual delay cost at LGA associated with the wake vortex restrictions. We find that the delay due...
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CSKETCH image processing library
August 21, 2002
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-283
Topic:
R&D area:
R&D group:
Summary
The CSKETCH image processing library is a collection of C++ classes and global functions which comprise a development environment for meteorological algorithms. The library is best thought of as a 'tool-kit' which contains many standard mathematical and signal processing functions often employed in the analysis of weather radar data. A tutorial-style introduction to the library is given, complete with many examples of class and global function usage. Included is an in-depth look at the main class of the library, the SKArray class, which is a templatized and encapsulated class for storing numerical data arrays of one, two, or three dimensions. Following the tutorial is a complete reference for the library which describes all publicly-available class data members and class member functions, as well as all global functions included in the library.
Summary
The CSKETCH image processing library is a collection of C++ classes and global functions which comprise a development environment for meteorological algorithms. The library is best thought of as a 'tool-kit' which contains many standard mathematical and signal processing functions often employed in the analysis of weather radar data. A...
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Improving the high altitude performance of tail-controlled endoatmospheric missiles
August 5, 2002
Journal Article
Published in:
AIAA Guidance, Navigation, and Control Conf., 5-8 August 2002.
Summary
It is demonstrated that at high altitude the performance of a tail-controlled aerodynamic missile can degrade because of the existence of low frequency right-half plane zeroes in the airframe transfer function when either proportional navigation or optimal guidance is used. A new guidance law that accounts for the airframe zeroes is developed numerically and shown to have superior performance to existing guidance laws at the higher altitudes. Although no closed-form solution for the guidance law is presented, the resultant numerical values for the control gains of the guidance law can easily be stored as a multidimensional table in existing on-board flight control computers. Two methodologies for computing the guidance law control gains are presented.
Summary
It is demonstrated that at high altitude the performance of a tail-controlled aerodynamic missile can degrade because of the existence of low frequency right-half plane zeroes in the airframe transfer function when either proportional navigation or optimal guidance is used. A new guidance law that accounts for the airframe zeroes...
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