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Communications, IEEE Transactions on

Issue 7 • Date July 1977

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Displaying Results 1 - 21 of 21
  • [Front cover and table of contents]

    Publication Year: 1977 , Page(s): 0
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    Freely Available from IEEE
  • Comments on "Design of Space Diversity Receiving and Transmitting Systems for Line-of-Sight Microwave Links"

    Publication Year: 1977 , Page(s): 744
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    First Page of the Article
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  • [Back cover]

    Publication Year: 1977 , Page(s): 0
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    Freely Available from IEEE
  • Quantization for Sequential Signal Detection

    Publication Year: 1977 , Page(s): 696 - 703
    Cited by:  Papers (6)
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    The quantization of the observed data for sequential signal detection is studied. The criteria used are the minimizations of the average sample number under the hypothesis, the average sample number under the alternative, and the maximum average sample number. Numerical results show that the performance is not very sensitive to different criteria. Using a sequential probability ratio test (SPRT), the performances of optimum quantizers are compared to systems with unquantized data. The asymptotic relative efficiencies of the quantizerSPRT's with respect to the SPRT for unquantized data are derived for symmetric noise densities. The relation between these asymptotic relative efficiencies and those of fixed-sample-size detectors is noted. View full abstract»

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  • Loop-Induced Magnetic Fields with Negligible Side-Lobes

    Publication Year: 1977 , Page(s): 723 - 727
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    In schools for the hard-of-hearing where adjacent classrooms are equipped with non-carrier induction loop systems, it is necessary to realize a geometric discrimination between the classroomfields. One approach to reaching the required 24 dB per meter rolloff at the boundaries is the orthogonal field principle reported first in 1965 by de Boer, Bosman and Joosten (ref. 2, 3, 4). In this paper a method is described and results are given for an heuristic development of this principle in the case of classrooms about 8 m in length with permissible roll-off ranges of 2 m. It is shown that it is also possible to discriminate in a vertical direction if a secondary field at the ceiling is used. The heuristic approach achieves very good results in this case and overcomes the mathematical difficulties arising when the field is calculated analytically. View full abstract»

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  • Sampling Rate Conversion for NTSC Color Television

    Publication Year: 1977 , Page(s): 707 - 712
    Cited by:  Papers (3)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    Techniques are investigated for conversion between different sampling rates for NTSC color television signals. It is concluded that sampling rate conversion between 3 times color subcarrier frequency and 4 times color subcarrier frequency using all digital processing is quite feasible, and that hardware requirements are not unreasonable. Also, accumulation of error due to cascaded sampling rate conversion can be avoided by use of appropriate finite-impulse-response digital filters. View full abstract»

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  • Self-Orthogonalizing Adaptive Equalization Algorithms

    Publication Year: 1977 , Page(s): 666 - 672
    Cited by:  Papers (60)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    A comparison is made of several self-orthogonalizing adjustment algorithms for linear tapped delay line equalizers. These adaptive algorithms accelerate the rate of convergence of the equalizer tap weights to those which minimize the output mean-squared error of a data transmission system. Accelerated convergence of the estimated gradient algorithm is effected by premultiplying the correction term in the algorithm by a matrix which is an estimate of the inverse of the channel correlation matrix. The various algorithms differ in the manner in which this estimate is sequentially computed. Depending on the degree of complexity available, the equalizer convergence time may be reduced more than an order of magnitude from that required by the simple gradient algorithm. View full abstract»

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  • Error Margin Estimating in Repeaters

    Publication Year: 1977 , Page(s): 727 - 730
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    In this paper a new method of estimating error margin in T carrier repeaters is proposed. This estimate is based on two sets of data: (a) measurements from a commonly used test wherein bipolar violations are inserted into the line at an audio rate, and (b) the crosstalk environment in which the repeater is operating. An audio component due to violations in the bipolar signal causes a shift in the eye pattern resulting in a change of repeater error rate. This in turn changes the regenerated audio signal power by an amount depending on the initial undisturbed error rate of the repeater. This then gives a basis for extrapolating the operating error rate of a repeater from a test measurement. This error rate combined with a knowledge of the cable crosstalk parameters and number of operating systems during the test, is then used to estimate the error margin or eye opening of the repeater, assuming a Gaussian distribution for the interference. A method of ranking repeaters in a repeatered line to indicate their relative margin is proposed wherein the effect of errors on the audio signal to an intermediate test repeater is taken into account. Results presented are quite general and valid at any line rate and repeater spacing, and hence applicable for different T -carriers such as T1, T1C, T2 , etc. View full abstract»

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  • Combination Sequences for Spread Spectrum Communications

    Publication Year: 1977 , Page(s): 691 - 696
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Certain communication systems which employ spread spectrum techniques as a means of supporting multiple users need very long codes to guard against the threat of intentional jamming, but cannot tolerate the lengthy acquisition time which long codes usually require. As a possible solution to this problem, the use of combination sequences has been suggested, and this paper presents some new results, both analytical and numerical, on this technique. View full abstract»

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  • Architecture and Construction of a Hardware Sequential Encoder for Speech

    Publication Year: 1977 , Page(s): 703 - 707
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Recent work has shown the usefulness of sequential or "tree" encoding of speech. We report on construction of a TTL hardware multi-path sequential encoder which uses the so-called M algorithm search procedure. The device attains a signal-to-noise ratio of about 20 dB at 16 kbits/s. Hardware peculiar to this type of encoder is discussed, including architecture of the search algorithm sorter, the squared error calculator, and the code generator. View full abstract»

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  • Robust Detectors for Signals in Non-Gaussian Noise

    Publication Year: 1977 , Page(s): 686 - 690
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    The robustness of suboptimal nonlinear detectors for known discrete-time signals in non-Gaussian noise is investigated. The measure of robustness used is the degradation of asymptotic relative efficiency (compared to a linear detector) from that achieved by an optimal nonlinear detector. The first order density of non-Gaussian noise is modeled as a mixture of a small variance Gaussian background noise pdf and a large variance impulsive pdf. View full abstract»

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  • Maximum Likelihood Sequence Estimation of Binary Sequences Transmitted Over Bandlimited Nonlinear Channels

    Publication Year: 1977 , Page(s): 633 - 643
    Cited by:  Papers (35)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    The problem of designing and evaluating the performance of a maximum likelihood sequence receiver for binary PSK transmission over bandlimited nonlinear channels is considered in this paper. The effects of intersymbol interference followed by AM/AM and AM/PM conversions are taken into account while optimizing the performance in the presence of white Gaussian noise. A new representation for the output of a bandpass nonlinearity is given when the input consists of a carrier signal modulated by a sum of binary overlapping pulses. The structure of a maximum likelihood sequence receiver for a bandlimited nonlinear channel is derived using this representation. The receiver uses a modified Viterbi algorithm to determine the most likely sequence of data symbols transmitted. An upperbound on the probability of symbol error for this receiver is obtained. Numerical results illustrating the applicability of the present work to optimizing the performance of a digital satellite communications link are also presented. View full abstract»

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  • Optimal Short Desired Impulse Response for Maximum Likelihood Sequence Estimation

    Publication Year: 1977 , Page(s): 735 - 738
    Cited by:  Papers (4)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    In Maximum Likelihood Sequence Estimation, the number of operations per symbol depends critically on the length of the Desired Impulse Response (DIR). In this paper it is shown that a short but complex DIR of length 2 may be sufficient to cope with most severe distortion impairments found in quadrature modulation systems, thus permitting MLSE data decoding at still manageable complexity. View full abstract»

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  • Systems Analysis and Design of a Fiber Optic VSB-FDM System for Video Trunking

    Publication Year: 1977 , Page(s): 680 - 686
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    The effect of repeater nonlinearities and noises on the transmission performance of a fiber optic VSB-FDM system for video trunking is analyzed. General design formulas are then given and used to derive a set of design requirements for fiber optic CATV systems. Finally, design results are presented for standard 5-, 12-, 21-, and 30channel CATV systems. View full abstract»

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  • The Effect of Carrier Phase Error on the Performance of a Duobinary Shaped QPSK Signal

    Publication Year: 1977 , Page(s): 738 - 744
    Cited by:  Papers (6)
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    An analysis is presented showing the effect of carrier phase error on the error-rate of a duobinary shaped, quaternary, phaseshift keying digital radio system. A simple upper bound on the probability of error as a function of phase error is derived and the results are compared to those obtained by computer simulation. The conclusion is reached that such a system exhibits approximately 1.0 dB degradation for a carrier phase error of 3° at an error-rate of 10-5and a 10 dB degradation at a phase error of 15°. View full abstract»

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  • Results on Discrete-Time, Decision-Directed Integrated Detection, Estimation, and Identification

    Publication Year: 1977 , Page(s): 715 - 723
    Cited by:  Papers (1)
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    New results are presented for symbol-by-symbol detection with decision-directed tracking of colored channel disturbances. Recursive sampled-data algorithms are shown for Maximum A Posteriori Probability of detection under colored additive and multiplicative Gaussian noises along with white Gaussian noise. Preliminary evaluation of the algorithms via Monte Carlo simulation shows good performance compared to standard white-noise only algorithms. View full abstract»

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  • A Statistical Model for Urban Radio Propogation

    Publication Year: 1977 , Page(s): 673 - 680
    Cited by:  Papers (374)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    A statistical model, based on extensive experimental data, was established to characterize the urban radio propagation medium in various urban environments. Describing the medium by a linear filter, the peaks of the multipath response were analyzed statistically concerning the distribution of the path strength and the path arrival time. The statistical properties of these quantities depend on the modulation delay time. The resulting model can be used for simulation experiments in order to avoid costly hardware tests of ad hoc systems. View full abstract»

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  • An Approximate Analysis of Delay for Fixed and Variable Length Packets in an Unslotted ALOHA Channel

    Publication Year: 1977 , Page(s): 644 - 654
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    In this paper we compute the mean delay for an unslotted ALOHA random access channel for both fixed and variable length packets. The analysis is based on the concept of a user cycle and obtains steady state results. When the channel is "stable", the results seem quite accurate. The input parameters to the model are the number of users, the mean think time, and mean retransmission time. The model yields total traffic, throughput and delay but only the latter is emphasized here. Because of the steady state nature of the analysis, no information is obtained on stability. The results are verified by simulation. View full abstract»

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  • A Passband Data-Driven Echo Canceller for Full-Duplex Transmission on Two-Wire Circuits

    Publication Year: 1977 , Page(s): 654 - 666
    Cited by:  Papers (47)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2104 KB)  

    A digitally-implemented echo canceller operating at a rate greater than twice the highest passband frequency is proposed for fullduplex data transmission on a two-wire circuit. Located at each end of the communication circuit, the cancellers operate independently of the local receivers and do not require synchronization of the two data stations. Economies in storage and A/D conversion, in comparison with voice-type cancellers described in the literature, are achieved by accepting data symbols as reference input instead of samples of the transmitted line signal. Convergence of transversal filter tap weights is demonstrated under a mean-squared error criterion, and use of the real passband error rather than the complex analytic error is found to lead to the same residual error at the expense of a doubled convergence time. An operational protocol and adaptation algorithm are proposed which make possible both rapid start-up and slower adaptation during double talking. Provision is made for limiting the number and location of active taps on the transversal filter to those actually necessary for replicating the echo channel, resulting in two transversal filter sections of moderate length separated by a bulk delay. Results from a computer simulation of the proposed canceller are offered to demonstrate that convergence of mean-squared tap-weight error follows the predicted exponential characteristic, that the length of the bulk delay can be determined from a single channel sounding under typical channel noise conditions, and that the use of an averaged-gradient algorithm will allow the canceller to adapt, although slowly, to a change in the echo channel during full-duplex operation. View full abstract»

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  • Statistical Analyses of Digital Phase-Locked Loops with Time Delay

    Publication Year: 1977 , Page(s): 731 - 735
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    In this correspondence, first it is pointed out that introducing time delay of one sampling interval in digital phase-locked loop considerably eases restriction on operating times of digital circuits in the loop. Then statistical analyses are performed for first- and secondorder loops with time delay of one sampling interval in order to see the effect of the time delay on their performances. Approximate analytic expressions are obtained for the steady-state phase error probability density and phase error variance, and their validity is confirmed by numerical analysis. Increase in the phase error variance due to the introduction of the time delay is found to be of tolerable order for sufficiently high input SNR, and thus the delayed sampling scheme proposed here is considered to be effective in easing the restriction on the operating times of the digital circuits in the loop. View full abstract»

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  • Simultaneous Phase Tracking and Detection in Data Transmission Over Noisy Dispersive Channels

    Publication Year: 1977 , Page(s): 712 - 715
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    A new technique, related to the Viterbi algorithm for simultaneous phase jitter tracking and data detection of signals transmitted over the dispersive channel with Gaussian noise is proposed. This technique produces a reliable phase estimate and avoids the poor receiver performance which occurs with Viterbi decoding in the presence of phase jitter due to the use of a phase estimate derived from unreliable preliminary decisions. The effectiveness of this approach is demonstrated through computer simulation of the voiceband channel. It was found that for the case of a typical meeting the combined requirements of C2 and D1 conditioning and signaled at 14,400 bits/s, no errors were experienced in a computer simulation run of 2000 symbols compared to a previous run with a less sophisticated phase tracking algorithm which experienced 17 errors in 2000 symbols. 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