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Communications, IEEE Transactions on

Issue 8 • Date August 1976

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Displaying Results 1 - 25 of 27
  • [Front cover and table of contents]

    Publication Year: 1976 , Page(s): 0
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    Freely Available from IEEE
  • Additions and Corrections to "New Convolution Codes--Parts I and II"

    Publication Year: 1976 , Page(s): 935
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  • Correction to "Present state and future of telecommunications in Turkey"

    Publication Year: 1976 , Page(s): 944
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    First Page of the Article
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  • [Back cover]

    Publication Year: 1976 , Page(s): 0
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  • The Spectral Density of a Sinusoid Phase Modulated by a Gaussian-Filtered Gaussian Process

    Publication Year: 1976 , Page(s): 935 - 938
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    A simple calculation is made for the power spectral density (psd) of a sinusoid phase modulated by a filtered Gaussian process. The premodulation filter has a Gaussian-shaped frequency response. Design curves are presented for the out-of-band interference, the in-band power, and the psd in terms of the premodulation filter's bandwidth and the rms modulation index. View full abstract»

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  • Packet Switching in Radio Channels: Part III--Polling and (Dynamic) Split-Channel Reservation Multiple Access

    Publication Year: 1976 , Page(s): 832 - 845
    Cited by:  Papers (59)  |  Patents (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1320 KB)  

    Here we continue the analytic study of packet switching in radio channels which we reported upon m our two previous papers [1], [2] Again we consider a population of terminals communicating with a central station over a packet-switched radio channel. The allocation of bandwidth among the contending terminals can be fixed [e.g., time-division multiple access (TDMA) or frequency-division multiple access (FDMA)], random [e.g., ALOHA or carrier sense multiple access (CSMA)] or centrally controlled (e.g., polling or reservation). In this paper we show that with a large population of bursty users, (as expected) random access is superior to both fixed assignment and polling. We also introduce and analyze a dynamic reservation technique which we call split-channel reservation multiple access (SRMA) which is interesting in that it is both simple and efficient over a large range of system parameters. View full abstract»

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  • An MSK Approach to Offset QASK

    Publication Year: 1976 , Page(s): 921 - 923
    Cited by:  Papers (4)
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    This paper demonstrates that an offset quadrature amplitude-shift-keyed (OQASK) signal can be represented as an ncomponent version of a minimum-shift-keyed (MSK) signal. For example, the signal set obtained by summing two MSK signals which are 6 dB different in power and are formed by continuous phase, frequency modulating the same oscillator with two independent binary antipodal data streams, is spectrally equivalent to an OQASK signal set composed of 16 signals in which the symbol pulse is a half-cycle sinusoid rather, than the conventional rectangular form. Such generalizations as the above allow for potentially simpler implementation of spectrally shaped OQASK. View full abstract»

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  • Partial Correlation Properties of Pseudonoise (PN) Codes in Noncoherent Synchronization/Detection Schemes

    Publication Year: 1976 , Page(s): 898 - 903
    Cited by:  Papers (13)
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    This concise paper considers the effect on the autocorrelation function of a pseudonoise (PN) code when the acquisition scheme only integrates coherently over part of the code and then noncoherently combines these results. The peak-to-null ratio of the effective PN autocorrelation function is shown to degrade to n^{-1/2} , where n is the number of PN symbols over which coherent integration takes place. View full abstract»

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  • A Simple Technique for Enhancing the Hypothesis Testing Capability of Devices Sensitive to Phase in the Presence of Narrow-Band Normal Noise

    Publication Year: 1976 , Page(s): 923 - 926
    Cited by:  Papers (2)
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    A new statistic is described for hypothesis testing on phase in the presence of narrow-band normal noise when the true phase, itself, is a nonuniformly distributed random variable. Comparisons are made with the more standard direct techniques. View full abstract»

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  • Second-Order Statistical Moments of a Surface Scatter Channel with Multiple Wave Direction and Dispersion

    Publication Year: 1976 , Page(s): 820 - 831
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1112 KB)  

    Underwater acoustic communications channels involving surface reflection usually exhibit extensive time and frequency spreading. The phenomenon was studied in a recent paper [5] and the scattering function of the channel was obtained for large Rayleigh parameters using a Fresnel-corrected geometric optics model and a simple onedimensional surface correlation function. It was found that while extensive time spreading and Doppler were indeed predicted by this model, the Doppler shift and time delay were strongly correlated so that the scattering function had the form of a very narrow parabolic ridge. The problem considered in this paper is the extent to which this phenomenon persists when more realistic correlation-function models, dispersion, and small Rayleigh parameters are considered. It is found that the general form of the scattering function is not very much affected by fairly gross changes in the assumed surface statistics, and that substantial correlation between time delay and Doppler can be expected as long as the surface is not completely isotropic. The effect is also observed in a modified form with a small Rayleigh-parameter model, but since this model also features a strong coherent component it may be of less practical significance. View full abstract»

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  • Nearly Instantaneous Companding for Nonuniformly Quantized PCM

    Publication Year: 1976 , Page(s): 864 - 873
    Cited by:  Papers (9)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (952 KB)  

    The technique of nearly instantaneous companding (NIC) that we describe processes n -bit μ-law or A-law encoded pulse-code modulation (PCM) to a reduced bit rate. A block of N samples (typically N \cong 10 ) is searched for the sample having the largest magnitude, and each sample in the block is then reencoded to a nearly uniform quantization having ( n - 2 ) bits and an overload point at the top of the chord of the maximum sample. Since an encoding of this chord must be sent to the receiver along with the uniform reencoding, the resulting bit rate is f_{s}(n -2 + 3/N) bits/s where fsis the sampling rate. The algorithm can be viewed as an adaptive PCM algorithm that is compatible with the widely used μ-law and A -law companded PCM. Theoretical and empirical evidence is presented which indicates a performance slightly better than ( n - 1 ) bit companded PCM (the bit rate is close to that of ( n - 2 ) bit PCM). A feature which distinguishes NIC from most other bit-rate reduction techniques is a performance that is largely insensitive to the statistics of the input signal. View full abstract»

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  • Fractional Tap-Spacing Equalizer and Consequences for Clock Recovery in Data Modems

    Publication Year: 1976 , Page(s): 856 - 864
    Cited by:  Papers (146)  |  Patents (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    Adaptive equalizers are usually realized in the form of a transversal filter with variable tap gains and tap spacing equal to the symbol spacing T . The performance of these equalizers depends critically on the symbol-clock phase derived in the receiver, due to the clock-phase dependent aliasing of the spectral roll-off components, upon which the conventional equalizer has no influence. In this paper we study the possibility of overcoming this difficulty by making the tap spacing of the equalizer somewhat smaller than T (fractional tap spacing). It is shown that this leads to satisfactory performance of the equalizer for a broad continuous range of clock phases, without penalizing the speed of convergence. Furthermore, it allows the application of a simple clock recovery scheme which derives a phase control signal from the equalizer tap-gain values. View full abstract»

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  • Superconductive Coaxial Cable as a Communication Medium with Enormous Capacity

    Publication Year: 1976 , Page(s): 874 - 880
    Cited by:  Papers (5)
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    Superconductive coaxial cable has been investigated to survey its feasibility as a communication medium with enormous capacity. The measurements of the frequency and the temperature dependences of the attenuation of coaxial pairs show that dielectric loss is dominant at 4.2 K, but conductor loss increases and gets the attenuation sensitive to temperature as 5 K is exceeded at a few gigahertz. The effect of periodic impedance lrregularities, which is the greatest problem in the transmission characteristics, has been solved by the improvement of the manufacturing process based on spectral analysis of the dimensional variations of the materials, and it is suggested that superconductive coaxial line is applicable to wide-band communication. A thermal insulation pipe for the cable is manufactured and its insulation efficiency is measured. The feasibility of superconductive coaxial cable Will be increased not only by developing the refrigeration system, but also by applying superconductive materials with low surface resistance and critical temperatures higher than lead. View full abstract»

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  • Properties of the Eigenvectors of Persymmetric Matrices with Applications to Communication Theory

    Publication Year: 1976 , Page(s): 804 - 809
    Cited by:  Papers (39)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The matrices which are symmetric about both diagonals (persymmetric matrices) occur often in communication and information theory problems. There have been a number of problems whose solution involves the eigenvectors of persymmetric matrices. This paper summarizes a number of properties of the eigenvectors of persymmetric matrices and demonstrates how they can be applied to characterize and simplify the solution to a number of communication problems. View full abstract»

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  • Envelope Detector Performance for a Partially Coherent-Fading Sine Wave in Noise

    Publication Year: 1976 , Page(s): 913 - 917
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    The performance of a matched filter square-law envelope detector is investigated for a new signal-in-noise model, that of a partially coherent-fading random-phase sine wave in additive zero-mean noise. This model is of interest when analyzing the effects of random amplitude and/or phase channels on narrow-band input signals. The amplitude and the phase of the sine wave are assumed to be independent random processes with known bandwidths. This paper obtains deflection-criteria detection-performance results for the envelope detector as a function of the bandwidths of the amplitude and phase of the signal process, the noise process, the observation time, and the second-moment statistics of the amplitude, phase, and noise processes. The results show quantitatively that the detection performance of the envelope detector is much more sensitive to loss of phase coherence than to loss of amplitude coherence. View full abstract»

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  • MSK and Offset QPSK Modulation

    Publication Year: 1976 , Page(s): 809 - 820
    Cited by:  Papers (125)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1152 KB)  

    Minimum shift keying (MSK) and offset keyed quadrature phase shift keying (OK-QPSK) modulation techniques are often proposed for use on nonlinear, severely band-limited communication channels because both techniques retain low sidelobe levels on such channels, while allowing efficient detection performance. A more detailed performance comparison of the two techniques on such channels is, therefore, of interest. In this paper a Markov process representation is developed which is applicable to either the MSK or OK-QPSK waveform. This representation is employed to illustrate the similarity between the modulation processes and to obtain the autocorrelations and power spectral densities of the two waveforms. This Markov process representation may be similarly employed with other modulation waveforms of the same class. The autocorrelations and power Spectral densities of MSK and offset QPSK provide initial insight to expected performance on band-limited channels. The results of a digital computer simulation are presented. The simulation compares the bit error rates (BER's) of MSK and offset QPSK on nonlinear, band-limited double-hop links such as encountered in satellite communications. The simmulation results are presented as E_{b}/N_{0} degradation with respect to ideal detection versus channel noise bandwidth. The error probability was used as a performance metric, and equal adjacent channel interference as a constraint. For the channels simulated, MSK is found to provide superior performance when the channel noise bandwidth exceeds about 1.1 times the binary data rate. For narrower bandwidths, offset QPSK provides superior performance. View full abstract»

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  • Analysis of FM Systems with Co-Channel Interference Using a Click Model

    Publication Year: 1976 , Page(s): 903 - 910
    Cited by:  Papers (3)
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    Rice's click model for ideal FM detection is applied to systems with co-channel interference. Output noise terms consist of a high signal-to-noise ratio (SNR) term due to noise alone, a term due to the desired signal beating with the interferer, and a term due to the clicks. Click rates are determined with and without modulation and it is shown that in the computation of noise due to clicks the interferer can be treated as a simple sinusoid [i.e., an unmodulated carrier] Plots are given for detected SNR versus carrier-to-noise (CNR) with signal-to-interferer ratio (SIR) and modulation index as parameters. The effect of signal suppression is analyzed and for the range of parameters used in this paper it is found to be negligible. View full abstract»

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  • A New Technique for Displaying Continuous Tone Images on a Bilevel Display

    Publication Year: 1976 , Page(s): 891 - 898
    Cited by:  Papers (11)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1176 KB)  

    A new technique for the display of continuous tone images on a bilevel graphical output device is described. This technique belongs to the general class of algorithms that convey intensity information by the spatial arrangement of lit and unlit cells which are in a one-to-one correspondence with the picture elements (PEL's) in the original image. Besides the rendition of a gray scale in the processed image, the new algorithm also incorporates edge emphasis to increase the legibility of textual information and other areas of high detail. A simple theory of the algorithm, derived from an intensity distribution function, is given, along with the details of an implementation and results obtained using the new technique. The technique is interesting as it requires a nonzero noise component in the image signal being processed in order to generate a gray scale. View full abstract»

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  • An Equivalent Linear Model for Marked and Filtered Doubly Stochastic Poisson Processes with Application to MMSE Linear Estimation for Synchronous m-ary Optical Data Signals

    Publication Year: 1976 , Page(s): 917 - 921
    Cited by:  Papers (8)
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    An equivalent linear model for minimum mean-squared error (MMSE) linear estimation of marked and filtered doubly stochastic Poisson processes is presented. The equivalence is employed to determine the structure of the MMSE noncausal steady-state linear receiver for synchronous m -ary optical data signals. View full abstract»

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  • A Generalization of Minimum-Shift-Keying (MSK)-Type Signaling Based Upon Input Data Symbol Pulse Shaping

    Publication Year: 1976 , Page(s): 845 - 856
    Cited by:  Papers (61)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    In recent years, minimum-shift-keying (MSK) has gained increasing popularity as a modulation technique because of its desirable spectral properties. Quite often, the spectral concentration provided by MSK is not sufficient to meet requirements on out-of-band energy spillover. In these situations, one might apply additional input pulse shaping m such a way as to still maintain constant envelope signals. The properties of such MSK-type signals are the subject of this paper. Specific examples are included as illustrations of the theory both for the binary and M -ary cases. View full abstract»

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  • Routing in Packet-Switching Broadcast Radio Networks

    Publication Year: 1976 , Page(s): 926 - 930
    Cited by:  Papers (18)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    Packet-switching broadcast radio networks are receiving considerable attention as a feasible solution for applications involving fast network deployment requirements, inaccessible physical environments, and mobile communication devices. Such networks also offer economic alternatives to traditional multiplexing schemes for local distribution. Most of the published papers relating to packet-switching broadcast radio networks address the case in which all communication devices are within an effective transmission range of the destination receiver, thus forming a single-hop network in which no packet routing is involved. In this paper, we address multihop networks. The problems encountered in packet transportation are identified and strategies to resolve these are proposed. View full abstract»

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  • Design of Chaff and Chaff-Supported Communication Systems

    Publication Year: 1976 , Page(s): 785 - 803
    Cited by:  Papers (1)
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    The use of chaff for establishing communications of limited duration between nonadjacent troposcatter stations is investigated. The optimum location for the release of chaff is determined theoretically considering the path geometry, the antenna elevation and directivity, and the weather and atmospheric effects. Amplitude, polarization, and fading characteristics of the signal energy scattered by chaff are calculated and the type and weight of chaff required to provide a given signal-to-noise ratio ( S/N ) is estimated. Experiments which were conducted to check the validity of the theoretical calculation are then described. Finally, a practical scheme for overpassing troposcatter stations and for communications between mobile users which are not in line of sight is considered. View full abstract»

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  • On a Closed Form Expression for Phase-Locked Loop Pull-In Range

    Publication Year: 1976 , Page(s): 910 - 913
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    A closed form expression is derived for the pull-in range of second-order phase-locked loops (PLL's) with sinusoidal phase detectors. Pull-in range, normalized with respect to gain G , is expressed as a function of the damping factor \zeta and normalized natural frequency β of the linearized loop model. Results are presented for various values of β and \zeta and compared with earlier results. View full abstract»

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  • Linear Delta Modulation Quantizing Noise Characteristics

    Publication Year: 1976 , Page(s): 940 - 943
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    A formula for signal-to-quantizing noise ratio (SNR) in delta modulation systems is obtained by modifying an existing result for DPCM systems. Computer simulation is used to examine the behavior of the terms in the modified SNR formula. View full abstract»

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  • A Multidigit Adaptive Delta Modulation (ADM) System

    Publication Year: 1976 , Page(s): 931 - 935
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    A multidigit adaptive delta modulation (ADM) system has been proposed where the error signal, between the input and the approximated signal produced by ADM coder, is coded in an auxiliary encoder. The error in the auxiliary coder is processed by another ADM and so on. The bit rate of each of these coders is f_{r}/N where fris the overall transmission rate and N is the number of coders used. The bit streams are interleaved for transmission and at the receiver they are separated and decoded, and these signals are added and filtered. It is shown that for a given transmission rate, each coder operates at a basic sampling rate of frBsuch that N_{opt} = f_{r}/f_{rB} gives the optimum number of coders to be used for maximum signal-to-noise ratio (SNR). A bound is derived for the maximum SNR of such a system and is compared with the bounds derived for other predictive coders. The experimental results of a two-digit ADM are presented. An average SNR of 30 dB is obtained with a dynamic range of 32 dB at fr= 32 kbits/s for band-limited noise signals. The SNR increases with the sampling rate at 15 dB/octave, as against 9 dB for a single-digit ADM. The frequency response is good and the variation of SNR with the message frequency of the delta coding system has been improved. The effect of channel errors has also been studied and the performance of the system is found satisfactory. 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.

 

 

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Editor-in-Chief
Robert Schober
University of British Columbia