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Selected Areas in Communications, IEEE Journal on

Issue 5 • Date September 1985

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Displaying Results 1 - 22 of 22
  • [Back cover]

    Publication Year: 1985 , Page(s): 0
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    Freely Available from IEEE
  • [Front cover and table of contents]

    Publication Year: 1985 , Page(s): 0
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    Freely Available from IEEE
  • Guest Editorial: Scanning the Issue

    Publication Year: 1985 , Page(s): 609 - 610
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    Freely Available from IEEE
  • Adaptive Spread-Spectrum Systems Using Least-Squares Lattice Algorithms

    Publication Year: 1985 , Page(s): 652 - 661
    Cited by:  Papers (14)
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    Practical communication systems must cope with many uncertainties in addition to determining the transmitted data, e.g., the direction, timing, and distortion of the desired signal, and the spectral and spatial distribution of the interference, all of which may change with time. This paper describes exact least-squares (LS) recursive lattice algorithms which resolve these uncertainties in a direct-sequence spread-spectrum digital communication system. The adaptive LS algorithm is recursive beth in order and time, and converges rapidly to the uncertain parameters. Time-discrete algorithms may be mechanized by a receiver containing integrate-and-dump circuits operating at the chip rate of the pseudonoise (PN) sequence, one in each in-phase and each quadrature channel of each sensor array element's output. Different configurations of optimal time-discrete receivers are presented and transformed into adaptive receivers by taking advantage of the spectral properties of the different kinds of LS filters. Simulation results are presented and some guide lines are given for the architecture of an adaptive direct-sequence spread-spectrum system. View full abstract»

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  • An Adaptive Digital Suppression Filter for Direct-Sequence Spread-Spectrum Communications

    Publication Year: 1985 , Page(s): 676 - 686
    Cited by:  Papers (33)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1007 KB)  

    This paper describes the structure of a digital implementation of the Widrow-Hoff LMS algorithm which uses a burst processing technique to obtain some hardware simplification. This adaptive system is used to suppress narrow-band interference in a direct-sequence spread-spectrum communication system. Several different narrow-band interferers are considered, and probability of error results are presented for all cases. While, in general, the results show significant improvement in performance when the LMS algorithm is used, certain disadvantages are also present and are discussed in this paper. View full abstract»

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  • A Physical Meteor-Burst Propagation Model and Some Significant Results for Communication System Design

    Publication Year: 1985 , Page(s): 745 - 755
    Cited by:  Papers (20)
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    This paper describes a meteor-burst communication model based on physical models and astronomical observations of meteor orbits and flux. It compares model results to experimental results and uses them to illuminate this complex propagation medium and to show how "hot spots" of meteor activity vary in position and relative importance with the fundamental meteor-burst link parameters. It also presents antenna and other meteor-burst link design considerations with emphasis on military systems. View full abstract»

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  • Comments on the Guest Editorial in "Undersea Lightwave Communications"

    Publication Year: 1985 , Page(s): 812
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    First Page of the Article
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  • Performance of Noncoherent Direct-Sequence Spread-Spectrum Multiple-Access Communications

    Publication Year: 1985 , Page(s): 687 - 694
    Cited by:  Papers (42)
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    The performance of noncoherent reception in direct-sequence spread-spectrum multiple-access communications systems is investigated for additive white Gaussian noise channels. Analytical and numerical results on the probability of error are presented for binary and M -ary frequency-shift-keying data modulation with noncoherent demodulation and differential-phase-shift-keying data modulation with differentiallycoherent demodulation. Both synchronous and asynchronous systems are analyzed. Systems which employ deterministic as well as random signature sequences are considered. The multiple access capability of noncoherent DS/SS systems is evaluated and compared to that of coherent DS/SS systems with the same parameters. The comparison shows that the loss in the performance of DS/SSMA systems due to noncoherent reception can be considerably larger than the loss incurred to noncoberent single-user systems operating in additive Gaussian noise. View full abstract»

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  • LPI Detection of Frequency-Hopping Signals Using Autocorrelation Techniques

    Publication Year: 1985 , Page(s): 714 - 726
    Cited by:  Papers (28)
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    Interception of frequency-hopping (FH) waveforms is commonly achieved by using a set of radiometers (energy detectors) that individually energy-detect subbands of the total spread bandwidth of the suspected transmission. In this paper, a scheme is analyzed which can improve the detection performance of FH waveforms in wide-band additive Gaussian noise (AWGN) using samples from the autocorrelation domain. It is shown that, under fairly general operational assumptions, an appreciable gain in decision signal-to-noise ratio (SNR) can be achieved over that of the radiometer. This gain is proportional to \gamma _{H}^{2} where \gamma _{H} is the hop SNR. The proposed algorithm, albeit inferior to the optimal likelihood-ratio test, has the advantage of reduced complexity. The overall approach has been motivated by the recent implementational feasibility of large time-bandwidth-product real-time correlators such as surface-acoustic wave devices (SAWD's). View full abstract»

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  • Design, Construction, and Test Results for Three Different Fiber Optic Tow Cables

    Publication Year: 1985 , Page(s): 801 - 811
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    The design, manufacture, and testing of three armored fiber optic tow cables is discussed. The motivation for these developments was the technical need to have low-loss high-bandwidth transmission lines, that function with negligible crosstalk and absence of ground loops, placed within the limited core space of the cable. General guidelines for avoiding serious microbending loss in this type of cable structure are reviewed, and different methods of implementing the design principles are demonstrated by way of discussions specific to the three electrooptic core designs that were manufactured. A discussion is given regarding some of the practical problems associated with manufacturing. For two of the cable designS, measurements of optical attenuation with a Tektronix model 150 optical time-domain reflectometer are presented for several stages of manufacture, and approximate changes in attenuation are given for a tension loading of 33kN. View full abstract»

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  • Survivable Timing Capability for a Worldwide Military Digital Communications Systems

    Publication Year: 1985 , Page(s): 792 - 800
    Cited by:  Papers (1)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (896 KB)  

    The evolving worldwide digital defense communications system (DCS) must be both more survivable and more responsive to the needs of its users than the analog system that it will replace. System timing problems not encountered in analog systems could prevent this. However, because of the availability of microprocessors, the survivability of system timing as a serious potential future problem for the DCS can be virtually eliminated; and it can be done economically. Important timing considerations for a wartime military digital communications system are discussed, and a description of a timing system that will economically satisfy survivability requirements is presented. View full abstract»

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  • Precorrelation Filter Design for Spread-Spectrum Code Tracking in Interference

    Publication Year: 1985 , Page(s): 662 - 675
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB)  

    Optimal design of a precorrelation filtering system for use in noncoberent direct-sequence code-tracking loops in the presence of colored noise is described, utilizing a linearized theory of loop operation. The design produces a bias-free loop with an odd S-curve, for which the rms tracking error is minimized. As a byproduct, one arm of the tracking loop provides an optimized signal for data-detection purposes. Widely applicable performance calculations, including rms tracking jitter, mean time to lose lock, and average detection signal-to-noise ratio, are given and illustrated, based on nonlinear models of loop operation. View full abstract»

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  • Low Probability of Intercept Performance Bounds for Spread-Spectrum Systems

    Publication Year: 1985 , Page(s): 706 - 713
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    An important application of spread-spectrum (SS) in military communication systems is that of making the signal difficult to intercept by unauthorized receivers. Error-correction coding techniques may be employed to reduce the required input signal-to-noise ratio at the receiver, allowing the system to operate at a lower power level, hence resulting in a lower probability of interception. In the absence of error-correction coding, a specified message bit rate, transmitted signal bandwidth, and required bit-error probability at the receiver will yield a required signal-to-noise ratio for each type of spread-spectrum system. When coding is employed, a specified decoder delay time implies a specified code complexity, and can be used to determine bounds on the required receiver signal-to-noise ratio. These performance bounds are evaluated as functions of the specified parameters. In addition, one may specify a burst interference environment in that the system must operate. Presented is the evaluation of the increase in the upper bound on signal-to-noise ratio as a result of the specification of a correctable single-burst time. This increase indicates an antiintercept /antijam tradeoff. View full abstract»

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  • Coherent Hybrid DS-SFH Spread-Spectrum Multiple-Access Communications

    Publication Year: 1985 , Page(s): 695 - 705
    Cited by:  Papers (36)  |  Patents (4)
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    The performance of synchronous and asynchronous hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access communications over additive white Gaussian noise channels is examined. Systems employing binary or quaternary phase-shift-keying modulation with coherent demodulation are investigated. Both deterministic and random signature sequences and frequency-hopping patterns are considered and several possible assignments for them are discussed. It is shown that the multiple-access capability of hybrid spread-spectrum is superior to that of pure frequency-hopped spread-spectrum, and inferior to that of pure direct-sequence spread-spectrum for systems with identical bandwidth expansion which employ the same data modulation and demodulation scheme and random hopping patterns and signature sequences. View full abstract»

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  • FH/MFSK Performance in Multitone Jamming

    Publication Year: 1985 , Page(s): 627 - 643
    Cited by:  Papers (26)
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    The performance of frequency-hopped (FH) M -ary frequency-shift keyed (MFSK) signals in partial-band noise has been extensively analyzed in the open literature. This paper extends the previous research to the usually more effective class of multitone jamming. Specifically, this paper will 1) categorize several different multitone jamming strategies; 2) analyze the performance of FH/MFSK signaling, both uncoded and with diversity, assuming a noncoherent energy-detection metric with linear combining and perfect jamming-state side information, in the presence of worst-case interference for each of these multitone categories; 3) compare the effectiveness of the various multitone jamming techniques, and contrast the results with the partial-band noise jamming case. View full abstract»

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  • Propagation of Wide-Band Signals at VHF/UHF

    Publication Year: 1985 , Page(s): 756 - 766
    Cited by:  Papers (2)
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    The experimental jam-resistant secure voice communications (JRSVC) system developed by M.I.T. Lincoln Laboratory was used to conduct a series of VHF/UHF (225-400 MHz) propagation measurements, representative of a veriety of tactical communications situations, both ground to ground and ground to low-flying aircraft. Results are unusual in two regards: they were made with the receiver in motion, covering many contiguous propagation paths, and the JRSVC system, by frequency-hopping over almost an octave and averaging the results, largely eliminated the effects of frequency-selective (multipath) fading that generally dominate VHF/UHF propagation measurements. View full abstract»

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  • Coding and Modulation Techniques for Frequency-Hopped Spread-Spectrum Communications Over a Pulse-Burst Jammed Rayleigh Fading Channel

    Publication Year: 1985 , Page(s): 644 - 651
    Cited by:  Papers (9)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    In this paper, the results of comparing the performance of various forward error correction techniques and several modulation formats when used over a nonselective Rayleigh fading channel in the presence of a pulse-burst jammer are presented. Both binary and nonbinary codes are considered, as well as concatenated codes consisting of either a block or a convolutional inner code and a Reed-Solomon outer code. Finally, the use of side information to allow the decoding of both erasures and errors is also analyzed. View full abstract»

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  • Strategies for FH/MFSK Signaling with Diversity in Worst-Case Partial-Band Noise

    Publication Year: 1985 , Page(s): 622 - 626
    Cited by:  Papers (3)
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    Optimum diversity and worst-case partial-band noise jamming conditions have been derived for noncoherent energy detection of frequency-hopped (FH) M -ary frequency-shift keyed (MFSK) signals using a soft-chip decision suboptimum linear combining metric with perfect jamming-state side information. However, the assumption implicit in previous publications is that the error rate is first maximized over the jammer's partial-band duty factor for arbitrary diversity, and the result is then minimized over the amount of diversity. This paper shows that if the order of optimization is reversed, different conditions and performance are produced; that is, the previous solution is not a saddlepoint. This introduces some game-theoretic considerations for the communicator and the jammer, the risks and advantages of which are explored. View full abstract»

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  • The Analyses of Uncoded Performances for Certain ECCM Receiver Design Strategies for Multihops/Symbol FH/MFSK Waveforms

    Publication Year: 1985 , Page(s): 611 - 621
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    Frequency-hopping (FH) M -ary FSK (MFSK) spread-spectrum modulation is an effective choice for an electronic counter-countermeasures (ECCM) system. When the power efficient MFSK ( M > 2 ) baseband orthogonal waveform is transmitted with L -fold diversity under constrained symbol energy, the resultant multiple ( L ) hops/symbol FH/ MFSK becomes a most viable low probability of intercept (LPI) waveform. In this paper, analyses are presented for the uncoded performance of such a waveform for two types of square-law nonlinear combining soft-decision receiver strategies under the assumption of worst-case partial-band noise jamming (countermeasures). The receivers employ, prior to combining, nonlinear weighting strategies of 1) adaptive gain control and 2) soft limiting (clipping) of the detector output of each channel of the dehopped waveform. The primary focus is on exact analytical results and, as such, the system's thermal noise is not neglected in the analyses. Numerical results of the error rates are graphically displayed as a function of signal-to-jamming power ratio with L and M as parameters under assumed values of signal-to-noise ratio. It is shown that. a diversity gain for error-rate improvement is realized for the nonlinear diversity combining receiver strategies. No attempt is made in this paper to compare the diversity performance to any error-control coding schemes. View full abstract»

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  • Data Link Communications in Tactical Air Command and Control Systems

    Publication Year: 1985 , Page(s): 779 - 791
    Cited by:  Papers (1)  |  Patents (2)
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    Data links in tactical air command and control systems (ACCS's) connect the computers of command and control units to one another and to weapon systems to enable rapid exchanges of real-time tactical information. This paper, presents an overview description of the current and future ACCS data link architecture used by the Services and NATO. This architecture currently consists of various tactical digital information link (TADIL) standards and NATO link standards. In the near future, the Joint Tactical Information Distribution System (JTIDS) will be a major component of the architecture. While the architecture of the far future is speculative, a description of some concepts being considered, such as the role of the International Standards Organization (ISO) reference model, is presented. View full abstract»

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  • Stochastic Effects in Adaptive Null-Steering Antenna Array Performance

    Publication Year: 1985 , Page(s): 767 - 778
    Cited by:  Papers (3)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1112 KB)  

    A new average equation for the adaptive weights which takes into account the effects of statistical weight fluctuations has been developed. Past researchers have derived results by using an approximate average equation for the weights obtained under the assumption that the weights vary much more slowly than the input process. The weights are then treated as constants for averaging. The new method employs a two-variable perturbation analysis which uses as a small parameter the ratio of the loop bandwidth to the input process bandwidth. The analysis yields a significant correction term for the directivity pattern in interference nulls. This correction term is the result of stochastic weight fluctuations which are usually ignored in most analyses. Comparison of these results to those found by past researchers is given and the results of a computer simulation substantiate the analysis. View full abstract»

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  • Detection Performance Considerations for Direct-Sequence and Time-Hopping LPI Waveforms

    Publication Year: 1985 , Page(s): 727 - 744
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1592 KB)  

    The implementation and performance of wide-band detectors for direct-sequence and time-hopping spread-spectrum waveforms in the presence of additive white Gaussian noise are considered in this paper. Of interest here is the performance penalty incurred when going from optimal to suboptimal detector structures. In both cases, performance is quantified by appropriately defined distance measures and is ultimately compared to that of the simplest hypothesis-discriminating device, namely, the energy detector (radiometer). View full abstract»

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Aims & Scope

IEEE Journal on Selected Areas in Communications focuses on all telecommunications, including telephone, telegraphy, facsimile, and point-to-point television, by electromagnetic propagation.

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Meet Our Editors

Editor-in-Chief
Muriel Médard
MIT