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Proceedings of the IEEE

Issue 6 • Date June 1979

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Displaying Results 1 - 25 of 28
  • [Front cover and table of contents]

    Page(s): c1
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    Freely Available from IEEE
  • Scanning the issue

    Page(s): 883
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  • Some physical constraints on the use of "Carrier-free" waveforms in radio-wave transmission systems

    Page(s): 884 - 890
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    Are there practical applications in radio-wave transmission of inherently broad-band "carrier-free" waveforms such as Walsh functions? We demonstrate in this paper that the band-limiting constraints of radiating systems limit mission of the low-frequency spectral components of such waveforms and severely restrict the radiation directivity that may be achieved in systems that employ them. We also find that dispersion in the propagating medium poses difficulties for the use of such waveforms, and we present an example that illustrates their impracticality in a case in which medium-related limits on coherence bandwidth are of concern. Considerations of capital cost, reliability, and maintenance militate against the use of these waveforms and in favor of conventional spread-spectrum modulation schemes where such service is required. Troublesome aspects of engineering analysis methods for systems employing such modulation schemes are also exposed, as are some practical and economic difficulties to be expected if they are to be introduced as co-users of the electromagnetic spectrum with conventional radio systems. View full abstract»

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  • Review of electromagnetic methods in nondestructive testing of wire ropes

    Page(s): 892 - 903
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    Wire ropes are used extensively in many life sustaining situations. Elevator and mine-hoist cables are two notable examples, but the support cable for aerial tramways, ski chairlifts and gondolas, helicopter and suspension cables we might also mention. In this review, we will deal mainly with wire ropes used in mine hoists, but the results are also relevant for testing support cables for ski lifts. There is an obvious need to perform tests of the integrity of such ropes without in any way impairing their function. Apart from careful visual examination and measurements of the external diameter, the nondestructive test methods available utilize electromagnetic fields, X-rays, or mechanical waves. Here, we will review progress in the electromagnetic methods. The early history of the subject will be described briefly, since this provides a remarkably good introduction to the working principles. We will then progress quickly to the current techniques and operating procedures. Next, we will summarize some of the basic papers that deal with the basic concepts and techniques for testing of cylindrical conductors by both electric and magnetic methods. At this juncture, we call our attention to the extensive related work on electromagnetic probing of geophysical targets such as ore bodies and other subsurface conductors. Finally, we turn to the various recent investigations, primarily of theoretical nature, that have been carried out; we include here only the most recent works. View full abstract»

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  • Digital interpolation beamforming for low-pass and bandpass signals

    Page(s): 904 - 919
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    Digital time-domain beamforming requires that samples of the sensor signals be available at a sufficient rate to realize accurate time delays for beam steering. For many applications, this input rate, which may be significantly higher than the Nyquist rate required for waveform reconstruction, places stringent requirements on A/D converter hardware and transmission cable bandwidth. Recently, a technique referred to as digital interpolation beamfonning was introduced which greatly relaxes the sampling requirement and provides substantial hardware savings through more flexible design options. In this approach, the sensor channels need only be sampled at a rate which satisfies aliasing requirements. The vernier beam-delay increments are then synthesized using digital interpolation which can be implemented at the beamformer input or output to minimize digital processing complexity. Previously, this concept was presented for the case of "low-pass" signals. This paper extends this work by examining the relationship between interpolation and beamforming for the important class of "bandpass" signals. Specifically, sampling methods are discussed whereby the original waveform can be reconstructed from samples taken at a rate consistent with the bandwidth of the bandpass signal. Beamformer implementations are presented which utilize these bandwidth-sampling techniques in conjunction with interpolation and which compute beam output points at the generally low rate dictated by the signal bandwidth. The interpolation beamformer achieves time-delay quantization (beam-steering accuracy) independent of both the input and output sampling rates. This approach generally requires less hardware than conventional procedures. Interpolation falter characteristics dictated by the bandwidth-sampling procedure are described and efficient methods of implementation employing nonrecursive digital bandpass and low-pass filters are presented. View full abstract»

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  • Target position estimation in radar and sonar, and generalized ambiguity analysis for maximum likelihood parameter estimation

    Page(s): 920 - 930
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    Target position estimation in radar and sonar means joint estimation of range and angle in the presence of noise and clutter. The global behavior of a maximum likelihood (ML) position estimator, and the clutter suppression capability of the system, can be written in terms of a range-angle ambiguity function. This function depends upon signal waveform and array configuration, i.e., upon both temporal and spatial characteristics of the system. Ambiguity and variance bound analysis indicates that system bandwidth can often be traded for array size, and direction-dependent signals can be used to obtain better angle resolution without increasing the size of the array. Wide-band direction-dependent signals (temporal diversity) can be traded for large real or synthetic arrays (spatial diversity). This tradeoff is apparently exploited by some animal echolocation systems. The above insights are obtained mostly from the properties of the range-angle ambiguity function. In general, an appropriate ambiguity function should be very useful for the design and evaluation of any ML parameter estimator. System identification methods and radio navigation systems, for example, can be optimized by minimizing the volume of a multiparameter ambiguity function. View full abstract»

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  • The processing of hexagonally sampled two-dimensional signals

    Page(s): 930 - 949
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    Two-dimensional signals are normally processed as rectangularly sampled arrays; i.e., they are periodically sampled in each of two orthogonal independent variables. Another form of periodic sampling, hexagonal sampling, offers substantial savings in machine storage and arithmetic computations for many signal processing operations. In this paper, methods for the processing of two-dimensional signals which have been sampled as two-dimensional hexagonal arrays are presented. Included are methods for signal representation, linear system implementation, frequency response calculation, DFT calculation, filter design, and filter implementation. These algorithms bear strong resemblances to the corresponding results for rectangular arrays; however, there are also many important differences. Some comparisons between the two methods for representing planar data will also be presented. View full abstract»

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  • Harmonic analysis of periodic discontinuous functions (new method). Part I—Exponential functions

    Page(s): 952 - 953
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    A new method to determine Fourier coefficients of periodic discontinuous exponential functions is presented. The advantage of the method is the substitution of algebraic addition to replace the integration operation in Fourier analysis. The method is applicable to every periodical exponential function that satisfies Dirichlet conditions. Application of the method is illustrated by example. View full abstract»

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  • Harmonic analysis of periodic discontinuous functions (new method). Part II—Polynomial functions

    Page(s): 953 - 954
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    A new method to determine Fourier coefficients of periodic discontinuous polynomial functions is presented. A method recently developed for exponential functions can be modified and applied to polynomial functions. Applications of the method is illustrated by example. View full abstract»

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  • An algorithm to compute large-change sensitivities of linear digital networks

    Page(s): 954 - 956
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    An algorithm to compute large-change sensitivities of linear digital networks to simultaneous changes in all the multiplier coefficients has been derived. The technique adopted in this correspondence is a generalization of the existing method for the case of an incremental change in one multiplier coefficient only. View full abstract»

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  • Adaptive signal processing using FIR and IIR filters

    Page(s): 957 - 958
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    A method is presented for designing optimal adaptive digital filters. The derivation is based upon filtering a desired signal which has been corrupted by a "noise" like signal so the least-square error between the filtered output and the desired output is minimized. The filter is contrasted with both the Levinson and Widrow filters. The greatest utility of the derived filters are in digital signal processing applications where real-time or stability are critical constraints. View full abstract»

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  • A design technique for transitional butterworth-Chebyshev filters

    Page(s): 958 - 960
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    For most of the given filter orders, the design technique reported recently [1] can generate neither a complete nor a gradual transition of filters between the Chebyshev and Butterworth extremes. An alternative design is proposed here without such difficulties. View full abstract»

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  • Perfectly linear ramp generation with lossy capacitor

    Page(s): 960 - 961
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    It is shown that a perfectly linear ramp voltage can be generated from a lossy capacitor using appropriate compensation current. View full abstract»

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  • On the active compensation of noninverting integrators

    Page(s): 961 - 963
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    A new active compensated balanced time constant (BTC) noninverting integrator is proposed. The compensation is achieved by using a voltage follower in the feedback path, and this result in an extremely high Q-factor, namely Q ≃ |A|3. It is also shown, that the use of a voltage follower with the Deboo noninverting integrator will only double its Q-factor. A novel method is proposed for active compensation of the Deboo integrator, which results in an extremely high Q-factor. View full abstract»

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  • A generalized active compensated noninverting VCVS with reduced phase error and wide bandwidth

    Page(s): 963 - 965
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    A general circuit for the active compensation of the op-amp noninverting VCVS is given. The circuit has the same topology as the Geiger maximally flat magnitude circuit [1]. The proposed design has the advantages of a smaller phase error and a larger bandwidth than the design in [1]. Moreover, it relaxes the restriction on the relizable dc gain obtained using the design in [1]. The proposed modified design includes the recently described, active compensated, voltage follower [2] as a special case. View full abstract»

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  • Beamshaping and polarization control properties of flexible hollow metallic rectangular pipes in the midinfrared

    Page(s): 965 - 966
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    Radiation patterns of midinfrared (MIF) lead-salt tunable diode lasers (TDL) after transmission through a flexible hollow rectangular metallic pipe are studied. Near 100 percent transmission efficiency and polarization control properties are observed, leading to possible TDL waveguide encapsulation as an MIF source assembly with well-defined far-field radiation pattern and polarization. View full abstract»

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  • GaAs MESFET demodulates gigabit signal rates from GaAlAs injection laser

    Page(s): 966 - 968
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    This letter describes the experimental results of an optical transmission link with modulation rates up to 4 GHz. The transmitter consists of an FET driven GaAlAs injection laser emitting at a 8500 Å wavelength. The receiver makes use of a GaAs MESFET chip which is compared with a standard silicon avalanche photodiode demodulator. View full abstract»

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  • Resolution of maximum entropy array processor

    Page(s): 968 - 969
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    An approximate expression for the resolution of the maximum entropy array processor is derived and compared with the resolution expression for the conventional linear array processor (beamformer). View full abstract»

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  • Moments, coefficients of skewness, and excess of hard-limited signals

    Page(s): 969 - 971
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    This paper summarizes the behaviors of some important statistical parameters, viz., the mean, variance, skewness, and excess, for hard-limited signals transmitted through the additive Gaussian channel. Computable dosed form expression of all moments is also given and numerical values of practical interest are provided. View full abstract»

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  • Image enhancement/coding systems using pseudorandom noise processing

    Page(s): 972 - 973
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    A new technique for image compression and/or enhancement is presented. The method comprises dividing the two-dimensional spectrum into low- and high-frequency components and digitizing the latter with a tapered, randomized quantizer. A version of the system in which the highs component is adaptively adjusted gives improved picture quality. View full abstract»

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  • Assembly language programming

    Page(s): 974 - 975
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    Freely Available from IEEE
  • Communication systems principles

    Page(s): 974
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    Freely Available from IEEE

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North Carolina State University