Showing papers by "Mitre Corporation published in 1986"

On Tail Biting Convolutional Codes

Abstract: In this paper, we introduce generalized tail biting encoding as a means to ameliorate the rate deficiency caused by zero-tail convolutional encoding This technique provides an important link between quasi-cyclic block and convolutional codes Optimum and suboptimum decoding algorithms for these codes are described and their performance determined by analytical and simulation techniques

Using simulated annealing to solve routing and location problems

Abstract: In recent papers by Kirkpatrick et al., an analogy between the statistical mechanics of large multivariate physical systems and combinatorial optimization has been presented and used to develop a general strategy for solving discrete optimization problems. The method relies on probabilistically accepting intermediate increases in the objective function through a set of user-controlled parameters. It is argued that by taking such controlled uphill steps, from time to time, a high quality solution can eventually be found in a moderate amount of computer time. In this paper, we implement this idea, apply it to the traveling salesman problem and the p-median location problem, and test the approach extensively.

Application of guidelines for designing user interface software

Abstract: A survey was conducted of people who had received a report on guidelines for designing user interface software. Analysis of questionnaire responses indicates that respondents considered guidelines useful, that they have used guidelines in various stages of design, and that they plan to use guidelines again. However, respondents also reported significant problems in the practical application of guidelines. Respondents had difficulty locating relevant guidelines within the report, choosing which guidelines would actually be used, establishing priorities among the selected guidelines, and translating generally worded guidelines into specific design rules.

Standards versus guidelines for designing user interface software

Abstract: There are significant differences between designing hardware and software for the user interface to computer–based information systems. Formal standards may improve hardware design but may prove ineffective for aiding software design. Our present knowledge supports development of flexible design guidelines for user interface software, but does not justify imposition of standards. Effective application of guidelines will require a process of translation into system–specific design rules, and/or future incorporation into computer–based design algorithms.

Synchronized multiple access apparatus and method for a local area network

Abstract: The present access protocol for contention networks results in synchronous network operation. Each node determines the next transmission instant by counting from the beginning of the most recently received packet of information a time equal to that packet's labeled length minus the previously measured round trip propagation delay seen by the node. Subsequent instants will occur at intervals equal to the maximum propagation delay allowed on the network. Each time a subsequent packet is received, synchronization is rederived based on the packet. If no packets are received within predetermined slots, the network is considered to be in asynchronous mode, with transmissions allowed at any time following the next slot. The disclosed packet synchronized multiple access (PSMA) protocol improves the performance measures by which local area networks are evaluated.

Meteor Burst Communications: Bits per Burst Performance Bounds

Abstract: It is important for communications researchers and designers to understand the limitations of the media that they use. To enable a better understanding of meteor trails as a communications medium, classical received power equations were used to derive two performance bounds. These give the maximum number of bits that can be relayed during a single burst using 1)an optimum constant bit rate, and 2) a continuously varying bit rate. It was found that the second bound is about two to three times larger than the first. Examples are given to show how the maximum bits per burst varies as a function of great circle distance between terminals, wavelength, and trail electron line density, when the receiver uses an optimum constant bit rate. The first bound Was also used to estimate how the long-term bits per unit of time, or average bit rate, varies with changes in electron line density q when the meteor burst rate is considered.

Evaluation of an Opportunistic Replacement Policy for a 2-Unit System

Abstract: A probabilistic model represents a robust maintenance circumstance: a scheduled activity and a randomly-occurring activity with cost savings if they are combined. The activities are combined if the elapsed time for either activity exceeds a control limit, called a screen. The long-run rates of single and joint replacements are evaluated when the randomly-occurring activity is uniformly distributed.

Self-monitoring fiber optic link

Abstract: The self-monitoring link utilizes a GRIN lens/blazed grating combination to multiplex an optical time domain reflectometry (OTDR) signal with data signals on a fiber optic communication link. An initial average OTDR reference signature for the OTDR signal on the link is determined and is compared with a continuously determined average OTDR signature. The reference signature and the continuously determined signature are compared and a warning or alarm signal is generated when the continuously determined signature differs from the reference signature by a preselectable limit. A microprocessor is provided to adjust the preselectable limit in response to the communication link operational parameters.

Optimal book embeddings of the FFT, benes, and barrel shifter networks

Abstract: This paper gives 3-page book embeddings of three important interconnection networks: the FFT network, the Benes rearrangeable permutation network, and the barrel shifter network. Since all three networks are eventually nonplanar, they require three pages and the present embeddings are optimal. Also, the embeddings have pages of comparable widths.

Use of the Longley-Rice and Johnson-Gierhart Tropospheric Radio Propagation Programs:0.02-20 GHz

Abstract: The Longley-Rice and Johnson-Gierhart tropospheric propagation programs are particularly useful in predicting propagation losses for paths over irregular terrain commonly encountered in ground-to-ground, air-to-ground, and air-to-air military tactical scenarios. These programs use an empirical database to statistically weigh knife-edge diffraction losses with losses from multipath interference, smooth-spherical Earth diffraction, and troposcatter modes of propagation. The purpose of this paper is to provide perspective concerning the use of the two programs. Emphasis is placed upon the regions of applicability for the programs and on factors that must be considered in selecting and specifying the input parameters. Numerical results are given for various scenarios and ranges of input parameters.

Utilization of Atmospheric Transmission Losses for Interference-Resistant Communications

Abstract: Atmospheric absorption and scattering losses offer a means of protection against cochannel interference in RF communications links that operate above 18 GHz. By varying the operating frequency of such a link, the communicator can adjust the atmospheric attenuation of the signal and interference in order to improve link performance. If the effective length of the interference path exceeds that of the signal path, significant enhancement of the link's signal-to-interference-plus-noise ratio (SINR) can result. In many situations an optimal frequency exists at which the link SINR reaches a maximum value that substantially exceeds the values obtainable elsewhere in the available frequency band. This paper develops a technique for identifying the optimal operating frequency, and predicting the resultant SINR enhancement, on the basis of given equipment and environmental characteristics. The technique is applicable to the conceptual design of communications systems in the EHF and high SHF bands.

An algorithm for complex approximations in Z[e^{2{pi}i/8}] (Corresp.)

Abstract: An algorithm is described that approximates complex numbers by elements of the algebraic integers of Z[e^{2 \pi i / 8}] with integer coordinates of at most a prescribed size. The motivating application is to reduce the dynamic range requirements of residue number system implementations of the discrete Fourier transform. The closest points to zero of Z[e^{2 \pi i / 8}]_{M} gor any integer M are determined. A particular sequence of such points forms the basis of the algorithm. An example of 8 -bit Z[\omega]_{M} - approximations of the 128th roots of unity is considered. The algorithm yields M = 186; with scaling M is reduced to 18 .

Method and apparatus for measuring distance to an object

Abstract: The depth-gauging vision system includes illumination apparatus for projecting a preselected feature upon an object whose distance and orientation are to be determined. A camera is provided for generating an image of the feature reflected from the object. Processing apparatus is provided comparing the reflected image of the feature with the preselected feature itself to determine the distance to the object and its orientation.

Collision detection in a fiber optic local area network

Abstract: The fiber optic local area network includes an active star node including a plurality of optical receivers and transmitters. A logic element is interconnected with the output of each of the receivers in the node to detect simultaneous transmissions on the network. When simultaneous transmissions are detected, a collision signal is generated and this signal is transmitted by the node transmitters onto the network.

Low cost fiber optic network node

Abstract: The node includes plural optical receivers and transmitters. Each receiver and each transmitter of the node is connected to a user terminal by fiber optic cables. The output of each of the node receivers is electrically combined. Splitting logic is also included for splitting the electrical output of the receivers to serve as an input to the plural optical transmitters. The node may be used as an expansion mode or as a head-end unit. The optical receivers and transmitters have a low cost so that the overall node is approximately one fifth the cost of comparable nodes utilizing passive optical stars.

The Residue Number System For VLSI Signal Processing

Abstract: A new VLSI design method is developed for digital signal processors based on residue number systems and linear systolic arrays. The method breaks large processors into a set of small parallel processors that are interconnected only at the input and the output. Each of the parallel processors is a linear systolic array made up of a set of nearest-neighbor-connected, minimally complex, identical cells. The method has been illustrated by the design of a digital finite impulse response (FIR) filter which is projected for single chip VLSI implementation in 1.25 μm technology to have more than 5 x 1012 gate-Hz/cm2 throughput rate. A proof-of-concept filter has been implemented in 4 micron nMOS by 23 custom chips, each of approximately 20,000 transistor complexity. The filter has a combination of characteristics difficult to achieve with other design techniques--128 fully programmable taps and 136 dB dynamic range--yet it contains only 150,000 gates and has 5 MHz throughput. A fault-tolerant version of the filter provides the error-correction capability of triplication and voting, but it requires a redundancy of only 40%--one-third that required by triplication. In general, an RNS filter with N parallel processing channels can be provided with the fault tolerance of triplication and voting with one-Nth as much redundant hardware. By choosing a systolic architecture that computes outputs in parallel, an amount of fault tolerance can be provided that equals the use of triplication and voting at every stage of the filter.

The NASA Space Shuttle???A Vehicle for University/ Industry Educational Interaction

Abstract: In December of 1982 Worcester Polytechnic Institute, with the cooperation and support of the MITRE Corporation, initiated a program to propose, select, design, and develop experiments to be flown onboard a NASA Space Shuttle. The educational objectives of this program, based on the experiences of the students, and the cooperative objectives based on the experiences of the faculty and staff of the two institutions, are presented. All of the proposed experiments are being developed by undergraduates with the advisorship of WPI faculty. MITRE engineers and scientists are supporting the projects through detailed development advice, design reviews, and program management advice. Overall, the program will require four years of effort, involving between 30 and 50 students and approximately a dozen WPI faculty and MITRE professional staff each year. The administrative structure designed to coordinate this program, the logistics of interactions between WPI, MITRE, and NASA, and the program schedule are presented in detail.

A systolic discrete Fourier transform using residue number systems over the ring of Gaussian integers

Abstract: A VLSI implementation of a bit-serial systolic architecture for a DFT processor has been developed which performs residue number system (RNS) processing over the ring of Gaussian integers. An architecture for a 128-point DFT using the chirp z-transform algorithm is described, and its use in an R2FFT architecture to obtain a 16,384-point transform is illustrated. Based on three custom-designed chips, the processor is capable of transforming data at a continuous 2 MHz rate. The use of RNS techniques and systolic arrays provides two dimensions of parallelism, resulting in hardware of low complexity and high speed. The overall system has great flexibility in dynamic range, and can be used in many signal processing applications.

Effective earth radius for refraction of radio waves at altitudes above 1 km

Abstract: Atmospheric refractivity gradients are responsible for the bending of radio and microwave propagation paths such that the electromagnetic line-of-sight deviates from the geometrical line-of-sight. Such refraction effects must be accounted for when the performance of airborne surveillance radar systems is modeled. For propagation paths within 1 km of the earth's surface, the effective earth radius model is normally valid and commonly used. In the present work, a ray trace method for determination of propagation paths in a semi-empirical, stratified atmosphere is described. Results obtained from the ray trace model are employed to show that the effective earth radius method (EERM) can be used for approximate determinations of grazing angle, ground range and slant range for higher altitude paths. Effective earth radius scale factors are given as functions of transmitter altitude for selected values of surface refractivity.

A random network model of message transmission

Abstract: A model for message transmission through a network with unreliable nodes and links is presented; the assumptions are that nodes and links operate independently with probabilities α and β respectively. The following performance measures are derived: the probability of reaching k nodes by transmission m, the probability an arbitrary operable node is reached on the mth transmission, and the probability that d transmissions are required to reach all operable nodes. The algorithms are illustrated with a five-node example network; some performance measures are shown graphically for a range of parameter values. This work was sponsored by the Electronic Systems Division of the United States Air Force Systems Command.

Software Reporting Metrics

Abstract: A set of software development indicators has been prepared by the ESD/MITRE Software Center for use by program managers at the Air Force Electronic Systems Division (ESD) These metrics can be used to help track the progress of software development by providing better visibility into the development process This paper describes the metrics and a strategy for their application and reporting

Low data rate communications link

Abstract: The data link includes a phase noise compensator to eliminate phase noise resulting from microwave frequency sources on a communications satellite. In addition, Fourier analyzers are utilized to determine the frequency of received signals having low carrier-to-noise density. The combination of the phase noise compensator and the Fourier analyzers permits data rates on the order of 50 to 400 bits per second to provide economically attractive communication links with aircraft over ocean areas.

Defense Data Network an Overview

Abstract: The paper provides the genesis of the Defense Data Network (DDN), its scope and implementation strategy. This is followed by a description of the DDN today in terms of its hardware elements, protocols, architecture and topology. The paper concludes with a discussion of the planned and projected improvements needed for the evolution of the DDN in the 1980s and its maturation in the 1990s.

CSMA/CD LANs with overload detection and protection

Abstract: Classic Markovian models for CSMA/CD LANs are modified to handle a finite number of stations with dissimilar arrival rates among the stations. Simple rules are derived for overload detection and protection of a CSMA/CD LAN. It is demonstrated that a station can correctly determine the total network load and decide whether the medium is currently overloaded or not. A fair share algorithm is suggested for every station in a CSMA/CD LAN to protect the medium from being overloaded. With proper overload protection, it is shown that the expected penalty due to collisions for each successful transmission is geometrically distributed. In conclusion, this analysis shows that the performance of CSMA/CD LANs is significantly better than predicted by simpler models and it can be improved by a simple modification to the standard CSMA/CD protocol.

Differences in the in vivo and in vitro Effects of the Carbamate Insecticide, Carbaryl on rat Hepatic Monooxygenases

Abstract: The effects of one of the most widely used insecticides, carbaryl, on the hepatic cytochrome P-450—dependent monooxygenases were determined. Addition of carbaryl to liver microsomes from untreated or phenobarbital (PB)-pretreated rats resulted in a weak Type I binding spectrum. A much stronger spectral Type I interaction was observed when microsomes from 3-methylcholanthrene(3—MC)-treated rats were used. In vitro, carbaryl caused marked inhibition of ethylmorphine and benzphetamine N-demethylases, benzo(a)pyrene hydro-xylase, 7-ethoxycoumarin and 7-ethoxyresorufin 0-deethylases in liver microsomes. Kinetic studies demonstrated that carbaryl was a competitive inhibitor of ethylmorphine N-demethylase activity. Daily administration of carbaryl for 4 days by gavage or intra-peritoneally resulted in no significant alterations in hepatic cytochrome P-450 levels, ethylmorphine N-demethylase or benzo(a)-pyrene hydroxylase activities. The lack of effect of carbaryl in vivo may be due to the rapid metabolis...

Dissemination of COSTAR: promises and realities

Abstract: COmputer-STored Ambulatory Record (COSTAR) is an automated medical record, fiscal management and reporting system, developed in the mid-1970s for use in ambulatory care settings. Its flexibility, full functionality, low cost, and transportability held great promise for wide system dissemination in the 1980s. Reportedly, over 150 health organizations have installed COSTAR worldwide. In reality, this number represents a small fraction of the potential market. Several factors are listed below as contributing to the slower than expected dissemination. Of major importance may be that COSTAR--written in the MUMPS language--could not be installed on IBM hardware. Recently, however, third-party software houses announced MUMPS operating systems that allow COSTAR to run in a multiuser environment on the IBM PC/AT. Developments in the microcomputer field that may impact on the dissemination of COSTAR are described in this paper in addition to early experiences at MITRE with COSTAR on the IBM PC/AT.

The CURRY chip

Abstract: The CURRY chip is • ¢ombintor reduction machine in VLSI. Normal order evaluation is implemented using a pointer reversal scheme that stores the stack in the celia representing the function. Program eval- uation maps an input stream to an output stream, Methods used to write elable programs for the chip are given, along with experience gained using super combinators.