Showing papers in "Bell System Technical Journal in 1961"
TL;DR: In this paper, the authors apply the theory developed in the preceding paper to a number of questions about timelimited and bandlimited signals, and find the signals which do the best job of simultaneous time and frequency concentration.
Abstract: The theory developed in the preceding paper1 is applied to a number of questions about timelimited and bandlimited signals. In particular, if a finite-energy signal is given, the possible proportions of its energy in a finite time interval and a finite frequency band are found, as well as the signals which do the best job of simultaneous time and frequency concentration.
2,498 citations
TL;DR: In this paper, a theoretical investigation has been undertaken to study diffraction of electromagnetic waves in Fabry-Perot interferometers when they are used as resonators in optical masers.
Abstract: A theoretical investigation has been undertaken to study diffraction of electromagnetic waves in Fabry-Perot interferometers when they are used as resonators in optical masers. An electronic digital computer was programmed to compute the electromagnetic field across the mirrors of the interferometer where an initially launched wave is reflected back and forth between the mirrors. It was found that after many reflections a state is reached in which the relative field distribution does not vary from transit to transit and the amplitude of the field decays at an exponential rate. This steady-state field distribution is regarded as a normal mode of the interferometer. Many such normal modes are possible depending upon the initial wave distribution. The lowest-order mode, which has the lowest diffraction loss, has a high intensity at the middle of the mirror and rather low intensities at the edges. Therefore, the diffraction loss is much lower than would be predicted for a uniform plane wave. Curves for field distribution and diffraction loss are given for different mirror geometries and different modes. Since each mode has a characteristic loss and phase shift per transit, a uniform plane wave which can be resolved into many modes cannot, properly speaking, be resonated in an interferometer. In the usual optical interferometers, the resolution is too poor to resolve the individual mode resonances and the uniform plane wave distribution may be maintained approximately. However, in an oscillating maser, the lowest-order mode should dominate if the mirror spacing is correct for resonance. A confocal spherical system has also been investigated and the losses are shown to be orders of magnitude less than for plane mirrors.
1,420 citations
TL;DR: Theoretical questions concerning the possibilities of proving theorems by machines are considered in this article from the viewpoint that emphasizes the underlying logic, and a proof procedure for the predicate calculus is given that contains minor peculiar features.
Abstract: Theoretical questions concerning the possibilities of proving theorems by machines are considered here from the viewpoint that emphasizes the underlying logic. A proof procedure for the predicate calculus is given that contains a few minor peculiar features. A fairly extensive discussion of the decision problem is given, including a partial solution of the (x)(Ey)(z) satisfiability case, an alternative procedure for the (x)(y)(Ez) case, and a rather detailed treatment of Skolem's case. In connection with the (x)(Ey)(z) case, an amusing combinatorial problem is suggested in Section 4.1. Some simple mathematical examples are considered in Section VI. Editor's Note. This is in form the second and concluding part of this paper' Part I having appeared in another journal.1 However, an expansion of the author's original plan for Part II has made it a complete paper in its own right.
896 citations
TL;DR: Results indicate that the visual process involves a buffer storage which includes an erasure mechanism that is local in character and tends to erase stored information when new information is put in.
Abstract: Experiments are performed that demonstrate some of the functional properties of short-term storage in the visual system, its decay, readout and erasure. Results indicate that the visual process involves a buffer storage which includes an erasure mechanism that is local in character and tends to erase stored information when new information is put in. Storage time appears to be of the order of one-quarter second; storage capacity is more difficult to assess.
861 citations
TL;DR: In this article, a concave spherical resonator with two identical spherical reflectors, separated by any distance up to twice their common radius of curvature, is considered, and the diffraction losses are generally considerably lower for the curved surfaces than for the plane surfaces.
Abstract: Multimode resonators of high quality factor will very likely play a significant role in the development of devices, such as the maser, which operate in the millimeter through optical wavelength range. It has been suggested that a plane-parallel Fabry-Perot interferometer could act as a suitable resonator. In this paper a resonator consisting of two identical concave spherical reflectors, separated by any distance up to twice their common radius of curvature, is considered. Mode patterns and diffraction losses for the low-loss modes of such a resonator are obtained analytically, using an approximate method which was suggested by W. D. Lewis. The results show that the diffraction losses are generally considerably lower for the curved surfaces than for the plane surfaces. Diffraction losses and mode volume are a minimum when the reflector spacing equals the common radius of curvature of the reflectors. For this case the resonator may be termed confocal. A further property of the concave spherical resonator is that the optical alignment is not extremely critical.
767 citations
TL;DR: In this article, an expression for calculating the average conductivity of a diffused layer in semiconductor material as a function of the surface concentration of the diffused impurity and the background impurity concentration is derived.
Abstract: In this paper an expression is derived for calculating the average conductivity of a diffused layer in semiconductor material as a function of the surface concentration of the diffused impurity and the background impurity concentration. Curves are presented depicting the relationship among these parameters for the case of germanium. Included are curves for both diffused impurity types for the complementary error function, gaussian, exponential and linear impurity distributions.
113 citations
TL;DR: In this paper, the authors describe the mechanical features of the horn-reflector antenna used for receiving signals reflected from the Project Echo balloon satellite and present in some detail the electrical characteristics (radiation patterns and gain) measured at a frequency of 2390 mc.
Abstract: This paper describes the mechanical features of the horn-reflector antenna used for receiving signals reflected from the Project Echo balloon satellite and presents in some detail the electrical characteristics (radiation patterns and gain) measured at a frequency of 2390 mc. Theoretically derived characteristics which agree very well with the measurements are also presented; details of the calculations are given in the appendices.
65 citations
TL;DR: A computer program known asBLODI, which accepts for an input a source program written in the BLODI language, is described, and the principles of the compiler are explained and applications are discussed.
Abstract: A computer program known as BLODI, which accepts for an input a source program written in the BLODI language, is described. The BLODI source language corresponds closely to an engineer's block diagram of a circuit and is easily learned, even by persons not familiar with computing machines. The input code consists essentially of designating the connectivity of a number of boxes drawn from an alphabet of about 30 types. These types include amplifiers, delay lines, counters, etc., which are familiar to designers of electronic circuits. The principles of the compiler are explained and applications are discussed.
59 citations
TL;DR: A general method is presented for applying error correction to synchronous binary digital systems to improve reliability, including the familiar scheme of triplication and “rote taking” as a special case.
Abstract: A general method is presented for applying error correction to synchronous binary digital systems to improve reliability. It includes the familiar scheme of triplication and “rote taking” as a special case. In principle, the method permits the system to operate continuously, even when a fault is present or maintenance is being performed. An efficient maintenance routine, including rapid repair of faults, is an essential adjunct to the scheme if the potentially large increase in reliability made possible by error correction is to be realized. The percentage redundancy needed to realize the scheme decreases as the complexity of the system to which it is applied increases, but may amount to triplication of equipment even for moderately large systems. The paper describes some error-correcting codes to implement the scheme, discusses error-correcting circuits in a general way, indicates how to estimate the redundancy, and presents a formula for determining the reliability improvement obtainable with a particular maintenance routine. In a companion paper,1 D. K. Ray-Chaudhuri develops a general theory of minimally redundant codes for this application.
59 citations
TL;DR: It is shown that for the case q = 2 these are the only alphabets (in the sense of equivalence) for which the bound is attained, and a method is given for constructing a class of alphABets which attain this bound.
Abstract: A q-level alphabet is defined as a row vector space over a finite field with q elements. The letters of the alphabet are the rows of the vector space, each consisting of n symbols from the ground field. The weight of a letter is the number of nonzero symbols it contains. The minimum weight of the letters of the alphabet, excluding zero, is denoted by d. A relationship is established between the alphabet and a set of points S in a finite projective space. There is a many-one correspondence between the letters of the alphabet and the hyperplanes of the space. The weight of a letter is simply related to the incidence of the set S with the corresponding hyperplane. Two sets of points in a finite projective space are called equivalent if they are related by a collineation of the space. Two alphabets are called equivalent if there exists between them, as vector spaces, a weight-preserving semi-isomorphism. It is shown that these definitions mean the same thing and reduce to the usual definition when q = 2. An inequality is established between the dimension of the alphabet and the parameters d, q, n. This gives a lower bound for n in terms of the other parameters. It is shown that this bound cannot be achieved by alphabets with repeated columns. A method is given for constructing a class of alphabets which attain this bound. It is shown that for the case q = 2 these are the only alphabets (in the sense of equivalence) for which the bound is attained.
58 citations
TL;DR: In this article, general formulas for the electrical admittance of a piezoelectric crystal, in terms of its resonant frequencies and static and motional capacitances, are derived and applied to the investigation of the effect of electrode shape on the spectrum of resonances and the capacitance ratio of the crystal.
Abstract: In the present paper general formulas for the electrical admittance of a piezoelectric crystal, in terms of its resonant frequencies and static and motional capacitances, are derived and applied to the investigation of the effect of electrode shape on the spectrum of resonances and the capacitance ratio of the crystal. Particular attention is given in two cases of practical importance, namely, small piezoelectric coupling and thin crystal plates.
TL;DR: In this paper, the performance of various modulation and detection methods in the presence of phase distortion or equivalent envelope delay distortion was evaluated in different types of delay distortion, including linear and quadratic delay distortion.
Abstract: In pulse transmission systems, pulses modulated in various ways to carry information may be transmitted by amplitude, phase or frequency modulation of a carrier, and with each type of modulation various methods of detection are possible. An important consideration in many applications is the performance of various modulation and detection methods in the presence of phase distortion or equivalent envelope delay distortion, which may be appreciable in certain transmission facilities. The principal purpose of this presentation is a theoretical evaluation of transmission impairments resulting from certain representative types of delay distortion. These transmission impairments are reflected in the need for increased signal-to-noise ratio at the detector input to compensate for the effect of delay distortion. The performance in pulse transmission by various carrier modulation and detection methods can be formulated in terms of a basic function common to all, known as the carrier pulse transmission characteristic, which is related by a Fourier integral to the amplitude and phase characteristics of the channel. Numerical values are given here for the carrier pulse transmission characteristic with linear and quadratic delay distortion, together with the maximum transmission impairments caused by these fairly representative forms of delay distortion with various methods of carrier modulation and signal detection. These include amplitude modulation with envelope and with synchronous detection, two-phase and four-phase modulation with synchronous detection and with differential phase detection and binary frequency modulation.
TL;DR: In this article, measurements of sky noise temperature at a frequency of 6.0 kmc have been made for various conditions of absolute humidity and precipitation, and theoretical calculations of sky-noise temperature for typical dry and humid summer days are presented.
Abstract: Measurements of sky noise temperature at a frequency of 6.0 kmc have been made for various conditions of absolute humidity and precipitation. For an antenna beam position 5° above the horizon, the sky noise temperature was found to increase about 15°K from winter to summer due to the change in absolute humidity. During periods of rain, with the antenna beam pointed to the zenith, sky noise temperatures as high as 130°K have been observed, compared with the usual background value of 3° due to oxygen and water vapor. Theoretical calculations of sky noise temperature for typical dry and humid summer days are presented.
TL;DR: In this paper, a direct-reading ac bridge circuit was developed to measure semiconductor bulk and sheet resistivity, using a four-point (or other appropriate) probe, and the range of resistivity which can be measured is from 0.001 to 10,000 ohm-cm.
Abstract: A new direct-reading ac bridge circuit has been developed to measure semiconductor bulk and sheet resistivity, using a four-point (or other appropriate) probe. The range of resistivity which can be measured is from 0.001 to 10,000 ohm-cm. Resistivity is read directly from resistance decades and a ratio multiplier, eliminating voltmeter and ammeter errors — the final reading being the result of a bridge-balancing operation for each measurement. Stability and sensitivity provide better than 0.5 per cent electrical accuracy, with mechanical point spacing being the controlling limitation on the over-all accuracy of the measurement. The use of ac eliminates the influence of rectification, thermal, or contact potentials on the measurements, and also provides sensitivity more readily than with dc. The four-point probe and test specimen are the only nongrounded elements. An Appendix compiles four-point probe conversion factors for thin circular and rectangular slices of material. New tables are presented for slices having a continuous diffused skin all over, and thus also conducting across the back.
TL;DR: In this article, a model for telephone traffic in a loss system is considered: N trunks, calls arriving in a Poisson process and negative exponential holding times; calls which cannot be served at once are dismissed without retrials.
Abstract: Erlang's classical model for telephone traffic in a loss system is considered: N trunks, calls arriving in a Poisson process and negative exponential holding times; calls which cannot be served at once are dismissed without retrials. Let N (t) be the number of trunks in use at t. An explicit formula for the covariance R (·) of N (·) in terms of the characteristic values of the transition matrix of the Markov process N (·) is obtained. Also, R (·) is expressed purely in terms of constants and the “recovery” function, i.e. the transition probability Pr {N(t) = N|N(0) = N}; R (·) is accurately approximated by $R(0)e^{r_{1}^t}$ with r 1 the largest negative characteristic value, itself well approximated (underestimated) by − E{N (·)}/R(0). Exact and approximate formulas for sampling error in traffic measurement are deduced from these results.
TL;DR: In this paper, the authors discussed the minimum noise figure of parametric amplifiers under various conditions and showed that it is determined by a dynamic quality factor of the diode, which will be defined in this paper under the assumed model of a series resistance as the only parasitic element.
Abstract: The variable-capacitance diode is one of the most promising nonlinear elements for low-noise parametric amplifiers. In practice, however, these diodes have a small series resistance, and this limits the minimum obtainable noise figure; for the better diodes, the effect of the shunt conductance can be neglected. Taking the contribution of this series resistance into account, this paper discusses the minimum noise figure of parametric amplifiers under various conditions. It is shown that the minimum noise figures are basically determined by a dynamic quality factor of the diode, which will be defined in this paper, under the assumed model of a series resistance as the only parasitic element. Identical minimum noise figures are obtained for lower sideband amplifiers operated with optimum idler frequency, for those with the idler load at 0°K, and for the upper sideband up-converter. In terms of the over-all systems noise figure, however, the lower sideband amplifier is superior to the upper sideband up-converter, for here the gain is limited by the ratio of output to input frequency. Experimental values are given for the figure of merit of various diodes. Universal curves are also given which demonstrate noise behavior of the various systems as a function of the network parameters and component temperatures.
TL;DR: In this article, a constant-resistance filter capable of dividing a very wide band into two subbands is described, which can handle one octave in the millimeter region with only 1.5 db insertion loss for each subband.
Abstract: A constant-resistance filter capable of dividing a very wide band into two subbands is described. It can handle one octave in the millimeter region with only 1.5 db insertion loss for each subband. The splitting transition takes place in a very narrow band (160 mc). Two of its components are important devices: an elbow and a hybrid junction. Both are quasi-optical and work with TE 01 ° mode in 2 inch diameter waveguide.
TL;DR: In this article, the collection efficiency in solar cells is trealed by a new method in which all the effects of the solar spectrum and the absorption curve are contained in a single funetion readily obtained by numerical integration.
Abstract: The collection efficiency in solar cells is trealed by a new method in which all the effects of the solar spectrum and the absorption curve are contained in a single funetion readily obtained by numerical integration. The method is illustrated by a detailed study of the effects of surface recombination, body recombination and junction depth in silicon cells. The method is also generalized to include built-in electric fields, and calc Illations are given for silicon. Sufficiently strong fields 10 improve the collection efficiency markedly can be produced in some compollnd semiconductors from a gradient in the energy gap. A disclLssion is given of the dependence of the collection efficiency on the absorption curve of the semiconductor. It is shown that silicon has a very favorable absorption curve in camparison with GaAs or InP. Finally, a treatment is given of the minority carrier collection in a two-Junction cell, and calculations arc presented for silicon. It is concluded that this structure may be important for cells with high energy gaps and short lifetimes.
TL;DR: In this paper, it is suggested that intramolecular crosslinks, occurring in a larger number in the single crystals, are responsible for this behavior, and the limitations of the conventional treatment of radiation effects are discussed and the possible significance of the present results for morphological problems is pointed out.
Abstract: Samples of Marlex 50 crystallized from dilute solution (yielding single crystals) and in the bulk form were irradiated by high-energy electrons and the solubilities compared. The single-crystal specimens remained fully soluble after a dose of 20 megarads, which rendered the bulk two-thirds to three-quarters insoluble. Since the initial free-radical concentration was identical and the chemical changes induced were not widely different in the two kinds of specimens, it is suggested that intramolecular crosslinks, occurring in a larger number in the single crystals, are responsible for this behavior. At high doses the same solubility limit is approached by both specimens, which is ascribed to the possibility of chain cutting becoming increasingly ineffective in the single crystal. In the light of these findings, the limitations of the conventional treatment of radiation effects are discussed and the possible significance of the present results for morphological problems is pointed out. A number of further effects are reported in connection with melting behavior and spin resonance spectra that are at variance with results in the literature.
TL;DR: Preliminary compositions indicate that exceedingly interesting music and useful psychological stimuli can be generated.
Abstract: A program for synthesizing music and psychological stimuli on a digital computer is described. The sound is produced by three operations: (a) A compiler generates the programs for a set of instruments. (b) These instruments are “played” by a sequencing program at the command of a sequence of “note” cards which contain information analogous to that given by conventional music notes. (c) The computer output, in the form of numbers on a digital magnetic tape, is converted to audible sound by a digital-to-analog converter, a desampling filter, and a loudspeaker. By virtue of the general nature of the compiling program a great variety of instruments may be produced, and the instrument programs are quite efficient in terms of computer time. The “note” cards are arranged to minimize the effort necessary to specify a composition. Preliminary compositions indicate that exceedingly interesting music and useful psychological stimuli can be generated.
TL;DR: The following basic theorem concerning active RC networks is proved in this paper : an arbitrary N × N matrix of real rational functions in the complex-frequency variable can be realized as the short-circuit admittance matrix of a transformerless active RC N-port network containing N real-coefficient controlled sources.
Abstract: The following basic theorem concerning active RC networks is proved: Theorem: An arbitrary N × N matrix of real rational functions in the complex-frequency variable (a) can be realized as the short-circuit admittance matrix of a transformerless active RC N-port network containing N real-coefficient controlled sources, and (b) cannot, in general, be realized as the short-circuit admittance matrix of an active RC network containing less than N controlled sources.
TL;DR: In this paper, it was shown that an arbitrary symmetric N × N matrix of real rational functions in the complex-frequency variable (a) can be realized as the immittance matrix of an N-port network containing only resistors, capacitors, inductors, ideal transformers, and negative-RC impedances if M < N.
Abstract: Theorem: An arbitrary symmetric N × N matrix of real rational functions in the complex-frequency variable (a) can be realized as the immittance matrix of an N-port network containing only resistors, capacitors, and N negative-RC impedances, and (b) cannot, in general, be realized as the immittance matrix of an N-port network containing resistors, capacitors, inductors, ideal transformers, and M negative-RC impedances if M < N. The necessary and sufficient conditions for the immittance-matrix realization of transformerless networks of capacitors, self-inductors, resistors, and negative resistors follow as a special case of the theorem. In addition, an earlier result is extended by presenting a procedure for the realization of an arbitrary N × N short-circuit admittance matrix as an unbalanced transformerless active RC network requiring no more than N controlled sources. The passive RC structure has the interesting property that it can always be realized as a (3 N + 1)-terminal network of two-terminal impedances with common reference node and no internal nodes. The active subnetwork can always be realized with N negative-impedance converters.
TL;DR: In this paper, a field investigation and supplemental laboratory surge tests indicate that, in well-shielded underground cable pairs, electrical surges do not exceed approximately 90 volts peak, and that transistorized apparatus capable of withstanding such surge amplitudes need no further protection.
Abstract: The problem of protecting apparatus against lightning surges from connected transmission facilities has become more complex with the use of solid state devices in apparatus design. Consideration of the protection requirements for such apparatus has indicated that existing information concerning the incidence and characteristics of lightning surges is insufficient to develop optimum protection measures. A recently completed field investigation provides additional information in this specific area. The results of this field investigation and supplemental laboratory surge tests indicate that, in well-shielded underground cable pairs, electrical surges do not exceed approximately 90 volts peak, and that transistorized apparatus capable of withstanding such surge amplitudes needs no further protection. In aerial and buried cable, however, transistorized apparatus requires protection up to the full sparkover potential of 3-mil protector gaps, i.e., to about 600 volts peak. A firm basis for testing and evaluating transistorized apparatus from the lightning surge voltage standpoint is presented.
TL;DR: A method of performing recursive least squares data smoothing is described in which optimum (or arbitrary) weights can be assigned to the observations, and the usual restriction of a constant data interval can be removed without affecting the optimum weighting or recursive features.
Abstract: A method of performing recursive least squares data smoothing is described in which optimum (or arbitrary) weights can be assigned to the observations. The usual restriction of a constant data interval can be removed without affecting the optimum weighting or recursive features. The method also provides an instantaneous (i.e. real time) estimate of the statistical accuracy in the smoothed coordinates for a set of arbitrary data intervals. Optimum gate sizes for arbitrary predictions can be determined. These features greatly increase the flexibility of recursive least squares data smoothing, and several applications are discussed.
TL;DR: In this article, a TE 01 ° hybrid junction that operates similarly to the Riblet short-slot hybrid is described, but because the modes involved are circular-electric, the hybrid can be telescopically mounted, allowing for adjustment to almost any power division.
Abstract: A TE 01 ° hybrid junction that operates similarly to the Riblet short-slot hybrid is described, but because the modes involved are circular-electric, the hybrid can be telescopically mounted, allowing for adjustment to almost any power division. The experimental results show that, centered at 55.6 kmc, the frequency range is larger than 20 per cent. Adjusted for equal power division, the balance is better than 0.5 db and the unwanted reflections in the driven and balanced (isolation) arms are at least 23 db below the input signal. Using the hybrid together with band-reflection, band-transmission or high-pass filters, it is possible to build low-loss channel-dropping filters. In particular, the use of simple cutoff waveguides permits the design of filters with almost rectangular transfer characteristics.
TL;DR: In this paper, a program has been set up for automatically finding the complex roots by iterative approximation starting from the known roots at infinite jacket conductivity, the characteristic equation is solved for all practical values of wall impedance of the jacket and all modes of interest.
Abstract: Helix waveguide, composed of closely wound insulated copper wire covered with an absorptive or reactive jacket, transmits circular electric waves with low loss Mechanical imperfections, such as curvature and deformation, cause coupling between the circular electric waves and unwanted modes and degrade the transmission In designing a helix waveguide for a particular application, a jacket must be found that minimizes the transmission degradation Unwanted mode characteristics and their coupling coefficients must be known; these quantities are given by the roots of a transcendental equation involving complex Bessel functions A program has been set up for automatically finding the complex roots by iterative approximation Starting from the known roots at infinite jacket conductivity, the characteristic equation is solved for all practical values of wall impedance of the jacket and all modes of interest The representation of the mode characteristics as a function of wall impedance leads to a definite designation of modes in heterogeneous waveguide The TE pn modes of helix waveguide with n ≠ 1 can have only a limited attenuation These limits determine the design of mode filters Manufacturing imperfections increase the average TE 01 loss independently of the wall impedance Random curvature with large correlation distance is produced by laying tolerances, but its contribution to the average loss is minimized in a helix waveguide with very large wall impedance
TL;DR: In this paper, an approximate solution for small deformations, mode conversion and circular electric wave loss were found in a uniformly deformed helix waveguide, which is nearly independent of the wall impedance which the helix jacket presents to the waveguide interior.
Abstract: Small uniform deformations of the cross section of helix waveguide perturb the circular electric waves slightly. From these perturbations the added circular electric wave loss is found in a uniformly deformed helix waveguide. For a nonuniformly deformed helix waveguide Maxwell's equations are converted into generalized telegraphist's equations. By an approximate solution for small deformations, mode conversion and circular electric wave loss are found. Random imperfections with small correlation distance cause an average circular electric wave loss that is nearly independent of the wall impedance which the helix jacket presents to the waveguide interior. It is therefore nearly the same as in metallic waveguide. Near 50 kmc, the rms value of elliptical diameter differences should not be more than 0.0015 inch in order that on the average not more than 10 per cent of TE 01 loss in a perfect 2-inch inside diameter copper pipe is added to the TE 01 loss in a helix waveguide of the same inside diameter.
TL;DR: In this paper, the FM receiving demodulators used in the Echo experiment were described in terms of negative feedback applied to the local oscillator to reduce the FM modulation index in the receiver intermediate frequency amplifiers.
Abstract: The FM receiving demodulators used in the Echo experiment are described in this paper. These receivers have negative feedback applied to the local oscillator to reduce the FM modulation index in the receiver intermediate frequency amplifiers. This technique results in a threshold performance which is superior to that of a conventional FM receiver.
TL;DR: In this paper, the authors describe the general organization and operation of the Holmdel station, and discuss the results of the Project Echo experiments that took place between the launching of the balloon March 1, 1961.
Abstract: On August 12, 1960, a 100-foot-diameter spherical balloon was placed in orbit around the earth by the National Aeronautics and Space Administration. The objective was to demonstrate the feasibility of long distance communication by means of reflection of microwaves from a satellite. It was intended that a two-way coast-to-coast voice circuit be established between the Jet Propulsion Laboratories facility at Goldstone, California, and a station provided for this purpose by Bell Telephone Laboratories at Holmdel, New Jersey. Similar tests were also planned with the Naval Research Laboratory and other stations. Construction of the Holmdel station was begun early in 1959. This paper describes the general organization and operation of the station, and discusses the results of the Project Echo experiments that took place between the launching of the balloon March 1, 1961. Successful voice communication wvas achieved a number of times using a variety oj modulation methods, including frequency modulation with feedback, amplitude modulation, single-sideband modulation, and narrow-band phase modulation. Careful measurements were also made of the loss in the transmission path.
TL;DR: The delay distribution for last-come first-served service and a single server with constant service time is derived and it is shown that the identity persists for a group of fully accessible servers, each with exponential distribution of service times.
Abstract: For Poisson input to a single server, it is shown that the stationary delay distribution function for last-come first-served service is equal to the distribution function for the busy period (the interval of time during which the server is continuously busy) only for exponential distribution of service time. A similar argument shows that the identity persists for a group of fully accessible servers, each with exponential distribution of service times — a result which has been a curiosity for some time. Finally, the delay distribution for last-come first-served service and a single server with constant service time is derived.