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Communications, IEEE Transactions on

Issue 8 • Date August 1977

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Displaying Results 1 - 22 of 22
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Introduction: Special Issue on Spread Spectrum Communications

    Page(s): 745 - 747
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    Freely Available from IEEE
  • [Back cover]

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    Freely Available from IEEE
  • Spread Spectrum and Time Division Multiple Access Satellite Communications

    Page(s): 810 - 815
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    Although time division multiple access (TDMA) satellite communication provides the highest traffic capacity per satellite and offers efficient transmission of a wide variety of services, it suffers from network timing and ranging requirements and message security. On the other hand, spread spectrum multiple access (SSMA) satellite communication is suited for reliable random access and tactical transmission systems. Orthogonal functions such as Rademacher, Haar, and Walsh, or pseudonoise sequence coding of amplitude and phase of the analog message or code division of baseband signals, frequency and time hopping are among the several methods employed for spread spectrum communications. A combination of TDMA and SSMA can be used for asynchronous and reliable transmission of digital or analog signals. View full abstract»

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  • Low-Rate Convolutional Code Applications in Spread-Spectrum Communications

    Page(s): 815 - 822
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    Low-rate convolutional codes are useful as an interference mitigation technique in frequency-hopped spread-spectrum systems. In this paper we show how good low-rate convolutional codes can readily be constructed from higher-rate codes that are known to exhibit good performance. The performance of low-rate convolutional codes is established theoretically and through the use of computer simulation and hardware experimentation. Typical performance curves are shown for convolutional codes with rates between 1/64 and 1/2, both in additive white Gaussian noise and in burst interference. The impact of code rate, constraint length, burst length, interleaving and modulation on total system performance are discussed. View full abstract»

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  • Performance Criteria for Spread Spectrum Communications

    Page(s): 756 - 763
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    The criteria for antijam (AJ) and anti-intercept (AI) systems are described, in terms of the appropriate action taken by the jammer or interceptor. Avoiding pseudonoise (PN) sequences which can be partially or totally predicted is a foremost criteria, especially for AJ, and use of nonlinear feedforward logic (NFFL) with long-period linear maximal sequences appears attractive. A frequency-hopping (FH) system must anticipate a multitone jamming signal, and an error-control code is necessary. A novel method for generating a multitone signal using repeating maximal sequences is described. PN systems must anticipate a tone jammer, and now an errorcontrol code may be needed to assure that sporadic PN sequence correlation with the tone does not reduce the processing gain. Any AI system must anticipate that the interceptor may, if advantageous, integrate his decision energy over many communicator symbols (up to the message length). Now spreading both in frequency and in time may be valuable. Finally, the use of an automatic adaptive data rate is suggested to realize flexibly either AJ or AI objectives. View full abstract»

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  • Error Probability of Asynchronous Spread Spectrum Multiple Access Communication Systems

    Page(s): 803 - 809
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    Several approaches for the evaluation of upper and lower bounds on error probability of asynchronous spread spectrum multiple access communication systems are presented. These bounds are obtained by utilizing an isomorphism theorem in the theory of moment spaces. From this theorem, we generate closed, compact, and convex bodies, where one of the coordinates represents error probability, while the other coordinate represents a generalized moment of the multiple access interference random variable. Derivations for the second moment, fourth moment, single exponential moment, and multiple exponential moment are given in terms of the partial cross correlations of the codes used in the system. Error bounds based on the use of these moments are obtained. By using a sufficient number of terms in the multiple exponential moment, upper and lower error bounds can be made arbitrarily tight. In that case, the error probability equals the multiple exponential moment of the multiple access interference random variable. An example using partial cross correlations based on codes generated from Gold's method is presented. View full abstract»

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  • Implementing Spread Spectrum Technology in the Land Mobile Radio Services

    Page(s): 867 - 869
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    A spread spectrum technique is described which, when applied to the mobile radio cellular communication system, is seen to provide very substantial improvements over what can be achieved through the use of conventional modulation and spectrum accessing techniques. The expanded capabilities include an extremely large number of unique individual addresses probably sufficient for all foreseeable growth requirements as well as an improved geographic re-use capability, high simultaneous usage rate, and substantially improved spectral efficiency. View full abstract»

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  • Spread Spectrum Multiple Access Communications Experiment Through a Satellite

    Page(s): 853 - 856
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    The purpose of this paper is to demonstrate that spread spectrum performance characteristics under different conditions of limiting and audio channel SNR degradation with close separation of carrier frequencies are similar to that of sinusoidal signals. Experiments also show that simultaneous transmission of acceptable spread spectrum and TV signals are feasible. View full abstract»

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  • Software Implementation of a PN Spread Spectrum Receiver to Accommodate Dynamics

    Page(s): 832 - 840
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    To optimize the threshold of a pseudonoise (PN) spread spectrum modem for use over an aircraft/satellite communications link at SHF, the effects of Doppler must be taken into account. Reconstitution of carrier phase by a Costas loop to coherently demodulate the PSK data and also the delay-lock error voltage has typically been the practice in PN modems intended for ground applications. To accommodate the platform dynamics, the Costas loop must have a relatively wide bandwidth, and this implies a significant threshold degradation. An alternate implementation employs a noncoherent carrier tracking loop which maintains frequency lock rather than phase lock. Now, the delay-lock error voltage is noncoherently demodulated. For the airborne application, analysis and simulations show this implementation will extend the receiver's tracking threshold significantly (up to 6 dB) for the worst case dynamics profile. An experimental project was undertaken to modify an existing ground PN modem (AN/USC-28, ADM version) for flight test. A software implementation of the digital tracking algorithms was selected where a HP-2100A minicomputer controls carrier frequency and PN code phase via digital phase shifters. The Costas demodulator for extracting PSK data resides entirely in software, and is completely segregated from PN tracking. In laboratory testing of the receiver with simulated dynamics and in actual flight tests, the demonstrated performance was found to approach closely the goals established by the analyses and simulations. View full abstract»

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  • An Active RC Delay Line for Matched Filters Correlators

    Page(s): 856 - 861
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    For a matched filter correlator (MFC) required in a spread spectrum receiver, an active RC delay line has been developed and its performance evaluated. The building block of the delay line is a low pass type active RC filter with modifications to give desirable magnitude, phase and pulse response. An MFC processor for a bandwidth expansion of 15 in data communication application has been made using the RC delay lines and its experimental performance has been found to be close to the theoretical one. View full abstract»

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  • Acquisition of Pseudonoise Signals by Recursion-Aided Sequential Estimation

    Page(s): 784 - 794
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    An improved method of acquisition of pseudonoise signals (RARASE) is described and analyzed. This method is an outgrowth of the RASE method, rapid acquisition by sequential estimation. In the new method, the known recursion relation of the PN signal is used to determine if a short estimate of the state of the received PN signal is probably correct and if, consequently, an attempt should be made to track with that estimate. A high proportion of the incorrect initial state estimates can be discarded with relatively simple logic. Analyses are provided for a range of implementations from the simplest, a single 3-input modulo-2 gate, to multiple logic gates and for both a simple in-lock detector and a sequential detector. Significant improvement in acquisition time is shown for long PN signals and for the signal-to-noise range of -13 dB to +3 dB. Acquisition time reduction by a factor of 7.5 is calculated for a PN signal of length2^{15}-1bits compared to the sequential estimation (RASE) method using a simple in-lock detector. Reduction by factors of 1.5 to 3.5 is calculated using the sequential detector. View full abstract»

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  • The Spread Spectrum Concept

    Page(s): 748 - 755
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    This paper describes an idealized spread-spectrum communication system. The processing gain concept is developed as a measure of a well-designed system's robust performance against independent wide-sense stationary interference. Multipath and repeater jammer rejection, partial correlation problems, and security requirements are related to spread-spectrum code properties. View full abstract»

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  • Performance Evaluation for Phase-Coded Spread-Spectrum Multiple-Access Communication--Part II: Code Sequence Analysis

    Page(s): 800 - 803
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    An analysis of the code sequence parameters that are most important to the communication performance of an asynchronous phase-coded spread-spectrum multiple-access communication system is presented. Previously known bounds and computational techniques for such parameters are surveyed. Some new results on mean-square correlation are included. View full abstract»

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  • Optimum Design and Performance of Costas Recievers Containing Soft Bandpass Limiters

    Page(s): 822 - 831
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    This paper investigates several key questions concerning the mechanization and design of a Costas receiver for reconstruction of a carrier from a suppressed carrier signal. For baseband NRZ encoded data symbols and a soft bandpass limiter preceding the loop, several design issues which are considered herein and which affect acquisition and tracking performance are: (1) The choice of an IF bandwidth. (2) The optimum choice of the Costas arm filter bandwidths as well as the spectral roll-off characteristics. (3) The optimum choice of loop bandwidth to data rate ratio for a given signal-to-noise ratio. (4) The signal suppression factor and the combined limiter-squaring loss. (5) The variations in loop bandwidth and damping with signal level. (6) The choice of the limiter transfer characteristic. (7) Performance degradation due to the presence of a limiter. Various new results in system design are presented and typical numerical results are given and graphically demonstrated in SNR regions of practical interest. The theory is applicable to the design of carrier reconstruction loops required in the implementation of spread spectrum communication receivers. View full abstract»

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  • Spread Spectrum Performance Analysis in Arbitrary Interference

    Page(s): 848 - 853
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    An important application of spread spectrum modulation is to Provide interference immune communications. Generally, the approach to system performance analysis will assume a host of various interference situations with the hope the results give wide applicability, while, based on the concept and properties of pseudo-random spreading waveforms, it is possible to rid the analysis of artificial or restricting interference assumptions and obtain completely general performance bounds. View full abstract»

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  • Acquisition Time Performance of PN Spread-Spectrum Systems

    Page(s): 778 - 784
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    This paper develops the mean and variance of the time to acquire for single dwell time PN-type spread-spectrum systems. A model is specified, and then exact results are obtained by use of the generating function for the acquisition process. The paper is somewhat tutorial in that the analysis technique is developed in a logical step-to-step manner for the Markov chain model and can be readily used on other models. The effects of Doppler and other imperfections of the original model are discussed. Finally the results of the double dwell time system are presented and the appropriate modifications for Doppler effect are given. View full abstract»

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  • Performance Evaluation for Phase-Coded Spread-Spectrum Multiple-Access Communication--Part I: System Analysis

    Page(s): 795 - 799
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    An analysis of an asynchronous phase-coded spread-spectrum multiple-access communication system is presented. The results of this analysis reveal which code parameters have the greatest impact on communication performance and provide analytical tools for use in preliminary system design. Emphasis is placed on average performance rather than worst-case performance and on code parameters which can be computed easily. View full abstract»

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  • Computer-Aided Spread Spectrum Signal Design

    Page(s): 861 - 867
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    The calculations required in the formulation of surface acoustic wave device signals have been removed from the design process into a large-scale digital computer. The designer is left to trade off application-critical signal characteristics while the computer presents the alternatives and controls fabrication of the interdigital transducers. View full abstract»

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  • Spread Spectrum Receiver Using Surface Acoustic Wave Technology

    Page(s): 841 - 847
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    In this paper, various potential implementations of spread spectrum systems using surface acoustic wave (SAW) devices are discussed and experimental results for a phase-shift keyed (PSK) signal embedded in unwanted interference is presented. An overview of acoustic surface wave technology as it applies to signal processing in spread spectrum communication systems is presented. The ability to implement most of the basic elements of such systems using SAW devices is discussed, with emphasis on the space charge coupled convolver and Fourier transformer. SAW implementation of a fairly general block diagram applicable to a variety of signal and interference situations is described, and the relative advantages of SAW technology with respect to other technologies such as charge coupled devices is discussed. View full abstract»

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  • A Unified Analysis of Pseudonoise Synchronization by Envelope Correlation

    Page(s): 770 - 778
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    The problem of acquiring and maintaining synchronization of a pseudonoise code, particularly at low signal-to-noise ratios, is analyzed to determine the mean time to acquisition and the mean time to lose lock. An analysis procedure is developed which explicitly considers the search/lock strategy and the transition from search to lock. A practical example is included to demonstrate the technique. View full abstract»

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  • Optimization of Coded Spread Spectrum System Performance

    Page(s): 763 - 770
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    Error correction coding techniques significantly improve performance of spread spectrum communication systems in environments containing jamming, multipath, and unregulated multiple access. This paper investigates the optimization of spread spectrum system performance for time-varying unknown interference. Noncoherent frequency hopping (FH) spread spectrum modulation, and hybrid FH-PN incorporating a direct sequence PN modulation on each hopped frequency are studied. For FH or FH-PN, the data modulations considered are differential phase-shift-keying (DPSK), differential quadriphase-quadriphase-shift-keying (DQPSK), and multiple-frequency-multiple-frequency-shift-keying (MFSK). Both block and convolutional error correction coding techniques are studied as a means of improving the spread spectrum performance. View full abstract»

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Aims & Scope

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

 

 

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia