Showing papers by "Mitre Corporation published in 1992"

Radiometric detection of spread-spectrum signals in noise of uncertain power

Abstract: The standard analysis of the radiometric detectability of a spread-spectrum signal assumes a background of stationary, white Gaussian noise whose power spectral density can be measured very accurately. This assumption yields a fairly high probability of interception, even for signals of short duration. By explicitly considering the effect of uncertain knowledge of the noise power density, it is demonstrated that detection of these signals by a wideband radiometer can be considerably more difficult in practice than is indicated by the standard result. Worst-case performance bounds are provided as a function of input signal-to-noise ratio (SNR), time-bandwidth (TW) product and peak-to-peak noise uncertainty. The results are illustrated graphically for a number of situations of interest. It is also shown that asymptotically, as the TW product becomes large, the SNR required for detection becomes a function of noise uncertainty only and is independent of the detection parameters and the observation interval. >

Extended factored space-time processing for airborne radar systems

Abstract: Factored space-time processing has been proposed as a reasonable suboptimal solution to reduce ground clutter in an airborne radar system in order to lower the enormous computational complexity required in fully adaptive processing. An algorithm for mitigating loss in performance of the basic factored technique by extending the Doppler filter spatial weight set to include various degrees of adjacent Doppler coupling is described. The extended factored algorithm is developed, and performance results, vis-a-vis the optimal and basic factored approaches, are presented for both theoretical and measured airborne clutter scenarios. >

Objective image quality measure derived from digital image power spectra

Abstract: An objective image quality measure based on the digital image power spectrum of normally acquired arbitrary scenes is developed. This image quality measure, which does not require imaging either designed targets or a constant scene, utilizes the previously known invariance property for the power spectra of arbitrary scenes. The measure incorporates a representation of the human visual system, a novel approach to account for directional differences in perspective (scale) for obliquely acquired scenes, and a filter developed to account for imaging system noise as specifically evidenced in the image power spectra. The primary application is to assess the quality of digital images relevant to the image task of detection, recognition, and identification of man-made objects from softcopy displayed versions of visible spectral region digital aerial images. Experimental verification is presented demonstrating very good correlation (r=0.9) of this objective quality measure with visual quality assessments.

On the performance advantage of multitaper spectral analysis

Abstract: The performance advantage of multitaper spectral analysis is quantified relative to weighted overlapped segment averaging (WOSA). To make the comparison of these two nonparametric spectral estimators, theoretical performance measures are derived in terms of leakage, variance, and resolution. The methods are then compared by evaluating each measure in turn, while requiring the other two measures to be equal. The results show that multitaper analysis always performs better than WOSA. For example, given the same leakage and resolution, multitaper analysis can have three-quarters to one-half the variance of WOSA. Given the same resolution and variance, multitaper analysis can exhibit a 10-20-dB leakage advantage over WOSA. These and other results provide compelling evidence for greater use of multitaper analysis in situations for which a nonparametric spectral estimator is appropriate. >

Projecting software defects from analyzing Ada designs

Abstract: Models for projecting software defects from analyses of Ada designs are described. The research is motivated by the need for technology to analyze designs for their likely effect on software quality. The models predict defect density based on product and process characteristics. Product characteristics are extracted from a static analysis of Ada subsystems, focusing on context coupling, visibility, and the import-export of declarations. Process characteristics provide for effects of reuse level and extent of changes. Multivariate regression analyses were conducted with empirical data from industry/government-developed projects: 16 Ada subsystems totaling 149000 source lines of code. The resulting models explain 63-74% of the variation in defect density of the subsystems. Context coupling emerged as a consistently significant variable in the models. >

A resource allocation model for denial of service

Abstract: A denial-of-service protection base (DPB) is characterized as a resource monitor closely related to a TCB, supporting a waiting-time policy for benign processes. Resource monitor algorithms and policies can be stated in the context of a state-transition model of a resource allocation system. Probabilistic waiting-time policies are suggested in addition to the finite- and maximum-waiting-time policies. The model supports concurrency, multiprocessing and networking. A simple example of a DPB is given, as a feasibility and consistency check on the definitions. >

Apparatus and method for the detection of security violations in multilevel secure databases

Abstract: A tool for assisting an operator to detect security violations in a multilevel secure database. The database stores data classified at a plurality of security levels, where the different users of the database are cleared to different security levels and access the database through a multilevel secure database management system. Security constraints are represented in conceptual structures, rules, or frames, and operator communication with the constraint representation is provided by a user interface. An inference engine uses reasoning strategies on the security-constraint representations base to detect security violations in the database by inference.

Security for object-oriented database systems

Abstract: A design approach for a secure multilevel object-oriented database system is proposed by which a multilevel object-oriented system can be implemented on a conventional mandatory security kernel. Each object is assigned a single security level that applies to all its contents (variables and methods). The informal security policy model includes properties such as compatibility of security level assignments with the class hierarchy. After discussing the essential features of a general object system model, and then extending the object model to incorporate mandatory label-based security, it is shown how typical database security and integrity policies can be supported by this model, with special attention to inference problems and integrity constraints. The representation of integrity constraints and classification constraints are illustrated. >

Reducing air traffic delay in a space-time network

Abstract: The author describes a formulation of National Airspace System (NAS) traffic management problem as a multicommodity minimum cost flow problem over a network in space-time. It is a formulation of the multidestination delay minimization problem of managing traffic in the NAS. The model's potential for improving over present practice is described in terms of six assumptions of present practice. The space-time network model can address uncertainty in capacity values, restrictive airways capacities, and hubbing. The minimum cost flow formulation further assumes that attempted entries into the system are deterministic, not Poisson, and that actual entries are controllable. The formulation specifically allows dynamic capacities and possesses good potential for short execution time. >

A fast normal random number generator

Abstract: A method is presented for generating pseudorandom numbers with a normal distribution. The technique uses the ratio of uniform deviates method discovered by Kinderman and Monahan with an improved set of bounding curves. An optimized quadratic fit reduces the expected number of logarithm evaluations to 0.012 per normal deviate. The method gives a theoretically correct distribution and can be implemented in 15 lines of FORTRAN. Timing and source size comparisons are made with other methods for generating normal deviates. The proposed algorithm compares favorably with some of the better algorithms.

Visualization of fuzzy data using generalized animation

Abstract: In this paper, we present methods for visualization of fuzzy data based on the sensitivity of the human visual system to motion and dynamic changes and the ease with which electronic display devices can change their display. The methods presented include taking an otherwise static image and displaying in an animation loop either its segmented components or a series of blurred versions of the whole image. This approach was applied to seasurface temperature data and was found to be effective in showing fuzzy details embedded in the data and in drawing the viewer's attention. This approach and methods could play a significant role in the display of browse products for massive data and information systems.

On the interaction between plan recognition and intelligent interfaces

Abstract: Plan recognition is an active research area in automatic reasoning, as well as a promising approach to engineering interfaces that can exploit models of user's plans and goals. Much research in the field has focused on the development of plan recognition algorithms to support particular user/system interactions, such as found in naturally occurring dialogues. However, two questions have typically remained unexamined: 1) exactly what kind of interface tasks can knowledge of a user's plans be used to support across communication modalities, and 2) how can such tasks in turn constrain development of plan recognition algorithms? In this paper we present a concrete exploration of these issues. In particular, we provide an assessment of plan recognition, with respect to the use of plan recognition in enhancing user interfaces. We clarify how use of a user model containing plans makes interfaces more intelligent and interactive (by providing an intelligent assistant that supports such tasks as advice generation, task completion, context-sensitive responses, error detection and recovery). We then show how interface tasks in turn provide constraints that must be satisfied in order for any plan recognizer to construct and represent a plan in ways that efficiently support these tasks. Finally, we survey how interfaces are fundamentally limited by current plan recognition approaches, and use these limitations to identify and motivate current research. Our research is developed in the context of CHECS, a plan-based design interface.

A simplified stochastic model for the aeronautical mobile radio channel

Abstract: The aeronautical mobile radio channel is analyzed. A stochastic model for the channel is proposed in terms of the transmission coefficient. The power spectrum and the correlation functions are derived for cases of practical interest. The model is useful for predicting the error rate performance of digital modulation techniques. The results from a flight test showed the validity of the proposed model. >

The characterization of continuous, four-coefficient scaling functions and wavelets

Abstract: Four-coefficient dilation equations are examined and results converse to a theorem of Daubechies-Lagarias are given. These results complete the characterization of those four-coefficient dilation equations having a continuous solution. >

The representation of multimodal user interface dialogues using discourse pegs

Abstract: The three-tiered discourse representation defined in (Luperfoy, 1991) is applied to multimodal human-computer interface (HCI) dialogues. In the applied system the three tiers are (1) a linguistic analysis (morphological, syntactic, sentential semantic) of input and output communicative events including keyboard-entered command language atoms, NL strings, mouse clicks, output text strings, and output graphical events; (2) a discourse model representation containing one discourse object, called a peg, for each construct (each guise of an individual) under discussion; and (3) the knowledge base (KB) representation of the computer agent's 'belief' system which is used to support its interpretation procedures. I present evidence to justify the added complexity of this three-tiered system over standard two-tiered representations, based on (A) cognitive processes that must be supported for any non-idealized dialogue environment (e.g., the agents can discuss constructs not present in their current belief systems), including information decay, and the need for a distinction between understanding a discourse and believing the information content of a discourse; (B) linguistic phenomena, in particular, context-dependent NPs, which can be partially or totally anaphoric; and (C) observed requirements of three implemented HCI dialogue systems that have employed this three-tiered discourse representation.

Trusted products evaluation

Abstract: computer and communications technologies and trends toward standardization , interoperability, and connectivity pose a growing security threat to Automatic Data Processing (ADP) and te][ecommunications systems that process sensitive or classified information. The activation of a threat could result in: disclosure, modification, or destruction of' sensitive or classified information; modification to hardware or software; and/or nonavailability of the system services. ~F\" / / // / ,/ / /

Optically controlled remote by-pass switch

Abstract: An optical bypass switch for a fiber optic local area communications network (LAN) with a ring topology allows an optical signal carried on the ring to by pass a node, which includes terminal equipment and a stub cable, associated with the switch. In a non-bypass mode, the optical signal is transmitted to and from the associated terminal. The switch assembly is remote from its associated terminal and includes optical couplers and associated optical receivers and activity detectors to produce electrical signals indicative of an optical input to and output from the terminal. Logic circuitry analyzes these signals and produces an appropriate drive signal for a switch controller. The remote switch has a local power supply and is preferably located at the junction of the ring and an associated, purely dielectric stub cable. The terminal can include a dual path transceiver and bridging equipment to provide cross links between terminals in the event of a link failure to complement the node failure protection of the bypass switch.

A queueing system with two arrival streams and reserved servers with application to cellular telephone

Abstract: The authors consider a service system in which n servers render service to two classes of prioritized traffic, which arrive to the system according to independent Poisson processes. Newly arriving call requests are granted server access on a first-come-first-served (FCFS) basis as long as there are fewer than g servers occupied. If fewer than g servers are free at the arrival time of a lower priority customer, the higher priority call requests are granted immediate service unless all servers are busy, in which case the call is dropped. This model has been used to study the handoff problem in a cellular telephone system, but the analytic approach taken was very complicated. The authors present a simple, novel, alternative approach to solving for the equilibrium probabilities for the number of lower priority calls in the queue and other quantities of interest. They describe two additional alternative approaches based on Neuts' matrix analytic approach for checking results, and point out that while the results of all these approaches agree with each other, they differ from previously published results. Because these three approaches are essentially independent, it is conjectured that there are problems with the earlier numerical results. Further work has revealed that this is the case. >

Software metrics for object-oriented systems

Abstract: The application of software complexity metrics within the object-oriented paradigm is examined. Several factors affecting the complexity of an object are identified and discussed. Halstead's Software Science metrics and McCabe's Cyclomatic Complexity metric are extended to an object. A limit for the cyclomatic complexity of an object is suggested.

Some limitations on the effectiveness of airborne adaptive radar

Abstract: It is shown that internal clutter motion, aircraft crabbing, scattering from near-field obstacles, and channel mismatch can limit the effectiveness of space-time processing in eliminating airborne clutter. An analytical expression is developed to show how each of these effects produces a deterioration in the signal-to-clutter-plus-noise ratio achievable. By studying the spectral decomposition of the covariance matrix, it is found that the effects of both internal clutter motion and crabbing can either be compensated by artificially adding noise or by processing more pulses. A near-field obstacle produces a spread of the clutter into all of sine azimuth-Doppler space. It is shown that the space-time processor attempts to compensate for this effect by placing a near-field null on the obstacle. Thus, adding more elements is much more effective in eliminating this effect than is processing more pulses. Channel mismatch can be alleviated by controlling the dispersive errors more tightly and by increasing the number of receive elements. >

Receiver autonomous integrity monitoring (RAIM) capability for sole-means GPS navigation in the oceanic phase of flight

Abstract: Receiver autonomous integrity monitoring (RAIM), a GPS integrity monitoring scheme that uses redundant ranging signals to detect a satellite malfunction that results in a large range error, involves two functions: detection of the presence of a malfunctioning satellite and identification of which satellite (or satellites) is malfunctioning. An analysis is presented of GPS RAIM capability for sole-means navigation in the oceanic phase of flight, where the position protection limit requirement for the integrity function is not as stringent as for nonprecision approaches, and yet both detection and identification function may be required if GPS is to be used as a sole-means system. For this purpose, a detection and identification algorithm is developed which takes advantage of the fact that for the oceanic phase of flight, a much larger position error is acceptable than for the nonprecision approach phase of flight. The performance of this algorithm and an algorithm proposed previously by others is estimated via simulation and compared. On the basis of the results, recommendations are made on how RAIM may be used if GPS is to be coupled with an inertial system to provide a sole-means capability in the oceanic phase of flight. >

Performance and fault modeling with VHDL

Abstract: Describes how VHDL can be used across the system design process, from specification to the development of maintenance strategies. The contributors provide advanced techniques, and detail how these can be adapted to improve the system development process, reducing time and cost.

Maximum possible gain for an arbitrary ideal antenna with specified quality factor

Abstract: Analytical and universally applicable numerical results are obtained for the maximum possible gain achievable by an ideal antenna for which the size and quality factor are specified. >

Sequencing formally defined reactions for robotic activity: integrating RAPS and GAPPS

Abstract: Construction of robots which operate in unstructured environments has of late produced a number of approaches for transforming sensor readings into activity in the world. Most of these approaches provide no formal semantics for discussing the way in which the internal state of the robot maps to the desired state of the world. We have been investigating the use of the GAPPS programming language as a mechanism for defining robotic reactions. This work has resulted in the creation of reactive modules which mediate between discrete statements about world states to achieve or maintain and the required continuous activity. While relatively complex goals have been achieved with this approach, the syntax and semantics of the GAPPS language is inappropriate for complicated dynamically changing goals. As a result, we have begun investigating the use of Reactive Action Packages (RAPs) as a mechanism for sequencing the activation of GAPPS-based reactive skills. The motivation for using RAPs is twofold. First, the syntax and semantics of the RAPs language integrates smoothly with a traditional non-linear planning system, allowing the construction and execution of plans for increasingly complex tasks. Second, GAPPS-based reactions fulfill a missing component of a RAPs-based controller system, namely the transformation of discrete RAP primitives (e.g., (maintain grasp ?thing)) into continuous physical activity. This paper presents the approach we are taking and discusses some of the issues involved in integrating these two systems.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Virtual private network call processing in the intelligent network

Abstract: The author explains the main features of the virtual private network (VPN) and proposes and defines a new integrated service control point call processing design model for the intelligent network. The model allows multiple application services to be executed simultaneously and provides real-time behavior. The features and capabilities of this model of call processing are addressed, and it is applied to the VPN application services. >

A reactive robot system for find and fetch tasks in an outdoor environment

Abstract: This paper describes the results of using a reactive control software architecture for a mobile robot retrieval task in an outdoor environment. The software architecture draws from the ideas of universal plans and subsumption's layered control, producing reaction plans that exploit low-level competences as operators. The retrieval task requires the robot to locate and navigate to a donor agent, receive an object from the donor, and return. The implementation employs the concept of navigation templates (NaTs) to construct and update an obstacle space from which navigation plans are developed and continually revised. Selective perception is employed among an infrared beacon detector which determines the bearing to the donor, a real-time stereo vision system which obtains the range, and ultrasonic sensors which monitor for obstacles en route. The perception routines achieve a robust, controlled switching among sensor modes as defined by the reaction plan of the robot. In demonstration runs in an outdoor parking lot, the robot located the donor object while avoiding obstacles and executed the retrieval task among a variety of moving and stationary objects, including moving cars, without stopping its traversal motion. The architecture was previously reported to be effective for simple navigation and pick and place tasks using ultrasonics. Thus, the results reported herein indicate that the architecture will scale well to more complex tasks using a variety of sensors.

Methotrexate-induced developmental toxicity in rabbits is ameliorated by 1-(p-tosyl)-3,4,4-trimethylimidazolidine, a functional analog for tetrahydrofolate-mediated one-carbon transfer.

Abstract: Dihydrofolate reductase reduces folic acid to tetrahydrofolate as a prerequisite to one-carbon metabolism, which is required for normal embryonic de novo DNA synthesis. The developmental toxicity of methotrexate (MTX) has been attributed to MTX's ability to inhibit the activity of dihydrofolate reductase and thereby indirectly suppress one-carbon metabolism. The compound 1-(p-tosyl)-3,4,4-trimethylimidazolidine (TTI), which is structurally unrelated to folate, reestablishes one-carbon metabolism by the biomimetic transfer of single carbon units. Whether the developmental toxicity of MTX is indeed caused via suppressed one-carbon metabolism was tested in New Zealand white rabbits following concurrent maternal treatment with MTX and TTI. TTI reduced MTX developmental toxicity judged by increased mean fetal body weights, decreased percentage of malformed fetuses, and reduced incidences of major malformations. Two doses of TTI (90 mg/kg, each) at 1 hr prior to and 1 hr after MTX also reduced the developmental toxicity, but was no more effective than the single-injection regimen. Treatment with TTI alone caused no developmental toxicity. Histologically, MTX caused enlarged intercellular spaces in limb bud mesenchyme that began at 6-8 hr and increased in size until 16 hr. Mesenchymal nuclei appeared basophilic, with angular contours. Pretreatment with TTI delayed MTX-induced histological changes until 20-24 hr after MTX in 36-50% of embryos and completely protected the remainder. The sequence of MTX-induced changes was not altered among affected embryos, although the severity of the lesions did not appear as great. Saline-only or TTI-only treatments caused no alterations in limb buds. These data are consistent with the concept that impaired one-carbon metabolism is indeed the fundamental process underlying MTX developmental toxicity.

Optical interconnects for high speed backplanes using spectral slicing

Abstract: An n-channel optical interconnect is suitable for use as a high speed, low latency interconnect at a backplane of a parallel processing computer. The interconnect uses spectral slicing to address the output of the processor to one or more other processors. Each processor has an optical receiver and n optical sources that each produce the same spectrum. The light output of the sources is directed to a wavelength division multiplexer (WDM) that produces an optical output signal in one or more portions of the spectrum. A selected portion is produced by energizing a selected one of the n optical sources. Each portion is associated with a single addressee processor. A passive star coupler combines all of the outputs of all of the WDM's. A wavelength division demultiplexer (WDDM) separates this composite signal back into the spectral portions. Electronic gating logic enables the appropriate source or sources at each transmitting processor. Control logic monitors transmissions from the star coupler to prevent collisions.

Maneuver option manager: automated simplification of complex air traffic control problems

Abstract: Maneuver option manager (MOM) is part of an air traffic control automation project, sponsored by the Federal Aviation Administration (FAA), in which the computer for the first time assumes responsibility for separation assurance between en route aircraft. MOM's purpose is to detect and simplify certain complex air traffic control problems, identified here as sets of interrelated potential pairwise separation problems. MOM determines which of six types of maneuver options is available (free of possible separation problems) for each aircraft. MOM simplifies a complex problem by protecting (for future use) an available maneuver option for one or more of the involved aircraft. Routinely, a single maneuver option resolves multiple pairwise problems. MOM's actions cause complex problems to be iteratively broken down into independent, smaller, and less complex problems. >