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Communications, IEEE Transactions on

Issue 9 • Date September 1977

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  • [Front cover and table of contents]

    Publication Year: 1977 , Page(s): 0
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  • [Back cover]

    Publication Year: 1977 , Page(s): 0
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  • A Look at Crosstalk in Quadrature-Carrier Modulation Systems

    Publication Year: 1977 , Page(s): 884 - 892
    Cited by:  Papers (23)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    A method is presented for comparing the performance of different quadrature-carrier modulation techniques. It is based on the calculation of the mean-square crosstalk between adjacent digital communications channels. This method was used to determine the crosstalk of a number of constant envelope modulation schemes, including Staggered Quaternary Phase Shift Keying (SQPSK) and Minimum Shift Keying (MSK). The results, as have previous results, show the improved performance of MSK over SQPSK. By utilizing the general equation for mean-square crosstalk as a measure of performance, a search was made for constant envelope modulation methods with reduced crosstalk. A number of methods were found which have better mean-square crosstalk performance than MSK. Finally this paper presents a method for reducing degradation due to crosstalk by using mismatched windows in the standard correlation detector. An example of this technique for detection of MSK signals is analyzed. View full abstract»

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  • A Gaussian Sum Approach to Phase and Frequency Estimation

    Publication Year: 1977 , Page(s): 935 - 942
    Cited by:  Papers (11)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    In this paper, a theory of optimal nonlinear estimation from sampled data signals where the a posteriori probability densities are approximated by Gaussian sums is adapted for application to phase and frequency estimation in high noise. The nonlinear estimators (demodulators) require parallel processing of the received signal. In the limit as the number of parallel processors becomes infinite the FM demodulators become optimum in a minimum mean square error sense and the PM demodulators become optimum in some well defined sense. For the clearly suboptimal case of one processor, the demodulators can be readily simplified to the familiar phase-locked loop. On the other hand, for the intermediate case, significant extension of the phaselocked loop threshold is achieved where (say) six parallel processors are involved. View full abstract»

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  • Third Order Intermodulation Interference--Bounds and Interference-Free Channel Assignment

    Publication Year: 1977 , Page(s): 1041 - 1046
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    In this paper a relationship between difference triangles and third order intermodulation interference is demonstrated, and two applications of this relationship are developed. In the first application, the relationship allows us to find intermodulation-free channel assignments where such arrangements are possible. The second application concerns cases where this is not possible. In the second application, arguments connected with difference triangles are used to bound, from below, the total intermodulation interference and the maximum interference falling on any assigned channel for the optimum channel assignment. To determine the tightness of this bound, a random coding type argument is used to bound the total intermoduiation for the optimum channel assignment from above, and an upper bound on the maximum intermod is established using previously performed computer experiments. View full abstract»

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  • Applications of Ali-Silvey Distance Measures in the Design Generalized Quantizers for Binary Decision Systems

    Publication Year: 1977 , Page(s): 893 - 900
    Cited by:  Papers (73)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    The Ali-Silvey class of distance measures is applied to the problem of designing quantizers for use in binary detection systems. To find optimal solutions the notion of quantization must be generalized slightly, and necessary conditions are established for the selection of quantizer parameters in this context. Local, or small-signal, conditions are also derived and these are seen to agree with asymptotic results based on Pitman efficiency. As an example, four-level generalized quantization for detecting a constant signal in additive generalizedGaussian noise is investigated. View full abstract»

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  • A Maximum-Likelihood Sequence Estimator with Decision-Feedback Equalization

    Publication Year: 1977 , Page(s): 971 - 979
    Cited by:  Papers (66)  |  Patents (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (976 KB)  

    A decision-feedback equalizer (DFE) is proposed as a prefilter which limits the complexity of a maximum-likelihood sequence estimator (MLSE) implemented by the Viterbi algorithm (VA) for channels having a long impulse response. By imbedding a DFE into the structure of the MLSE, the overall impulse response of the system is truncated to a short duration. With this practical receiver, a compromise may be made between performance and complexity by properly choosing the duration of a desired impulse response. A technique is also developed to estimate the performance of the receiver numerically, taking into account the effect of incorrect decision feedback on the VA. Analysis and computer simulation over a single-pole channel show that the proposed scheme can reduce the complexity of the MLSE while retaining much of its performance advantages. View full abstract»

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  • On the Degradation of Hard-Limiting Systems by Sampling

    Publication Year: 1977 , Page(s): 1050 - 1052
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    Sampling performed in conjunction with hard-limiting of a narrow band signal in band-limited white Gaussian noise increases the loss in output signal-to-noise ratio over that incurred by hardlimiting the original time-continuous signal. The largest increase in noise is by a factor of \pi^{2}/8 in both the band-pass and the base-band cases, and occurs when the input signal-to-noise ratio is low and sampling is at Nyquist rate. Increase in the sampling rate gradually reduces the additional loss in both cases. View full abstract»

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  • Optimum Reception in an Impulsive Interference Environment--Part I: Coherent Detection

    Publication Year: 1977 , Page(s): 910 - 923
    Cited by:  Papers (146)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1360 KB)  

    Because communications systems are seldom significantly interfered with by classical white Gaussian noise, it is necessary to consider other, appropriate (and tractable) interference models, if realistic estimates of system performance are to be obtained for the general spectral-use environment. For this purpose, Middleton's recently developed canonical statistical-physical model of "impulsive" interference is applied to real-world communication channels. The principal features of this model are first summarized, including the statistical relations required for the solution of signal detection problems. [Excellent agreement of these model statistics with correspondingly measured statistics is also noted.] The model for narrow-band impulsive interference (Class A noise, a subset of the overall model) is next specifically applied to an important class of coherent signal detection problems. Algorithms for error probabilities in optimum detection are then obtained, along with performance bounds, for the same error probabilities. Since it is known that in order to gain significant improvement over current receivers, the number of (essentially) independent samples of the received interference waveform must be enlarged (i.e., large "processing gains"), the performance results here are given parametrically in the number of samples, or equivalently, in the time-bandwidth product. Performance of current suboptimum receivers is then obtained and compared to the optimum performance. It is shown that very substantial savings in signal power and/or spectrum space can usually be achieved by using the indicated optimal algorithms. Since physical realization of the completely optimum detection algorithms cannot, in general, be economically realized, the somewhat more conservative, corresponding locally optimum Bayes detection (LOBD) receivers are derived. In general, these LOBD structures require adaptive, highly non-linear filters, preceding the conventional correlation detector elements characteristic of optimum receivers for Gaussian interference. Performance for these non-linear, optimum threshold systems is then determined, specifically in Part I for coherent reception. View full abstract»

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  • A Simplified Analysis of Scan Times in an Asymmetrical Newhall Loop with Exhaustive Service

    Publication Year: 1977 , Page(s): 951 - 957
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    A Newhall loop with exhaustive service, infinite buffer storage, and non-identical terminals is analyzed. A simple and computationally efficient procedure is demonstrated for determining first and second moments of queue lengths and scan times. View full abstract»

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  • Phase Compensation Receivers for Optical Communication

    Publication Year: 1977 , Page(s): 900 - 909
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1008 KB)  

    Phase compensation receivers are investigated in the context of optical communication, with particular emphasis on low visibility channels. It is shown that phase compensation can be viewed as a reduction of the number of spatial modes in the signal field so that an improvement in communication performance can be realized by a receiver which exploits the spatial coherence of the compressed signal mode. The phase compensation receiver structure separates nicely into configurations for measuring the phase of the signal field across the aperture and the required processors to obtain the phase compensation control from the measurements. The optimum phase control, which is chosen to spatially concentrate the signal power in the focal plane, is shown to be the minimum-mean-squared-error estimate of the aperture field phase, when the estimation error is "small enough." The phase observation-estimator structures are placed in an idealized phase compensated receiver. Minimum signal power requirements for adequate phase estimation performance are established. Communication performance, in terms of the parameters that describe the low visibility channel, is examined for both compenstated and uncompensated receivers. Depending on the system used, and for phase coherence times in the tens of milliseconds, phase compensation is most appealing for signaling rates from the middle kilobit to low megabit per second range; the resulting improvement in communication performance made possible by phase compensation is as much as 40-60 dB in optical power relative to an uncompensated receiver. View full abstract»

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  • Adaptive Detection of Signals in Impulsive Noise Environments

    Publication Year: 1977 , Page(s): 1022 - 1027
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    A detector structure and an adaptive algorithm are proposed for the reception of signals in noise backgrounds possessing broad-tailed probability distributions typical of impulsive noise. The adaptive detector combines the best features of linear matched filtering and hard-limiting receiver structures resulting in a small-signal SNR performance which is an improvement over either of these detectors alone. Furthermore, the adaptive detector is relatively easy to implement and is shown to provide efficient and robust performance for a wide range of underlying noise distributions. View full abstract»

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  • The Use of a High Order Error Measure in Nonlinear Modulation

    Publication Year: 1977 , Page(s): 1016 - 1022
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    In this paper a high order error measure is used for the evaluation and design of nonlinear modulation schemes. This high order measure works as a deterrent against threshold effects, and through its use a simple, two-dimensional nonlinear modulation scheme is fully analyzed and efficiently designed. View full abstract»

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  • Codes for Combined Phase and Amplitude Modulated Signals in a Four-Dimensional Space

    Publication Year: 1977 , Page(s): 943 - 950
    Cited by:  Papers (17)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Data transmission with combined amplitude and phase modulation is considered with signal design carried out in a four-dimensional space of two amplitude and two phase variables. The energy for each signal is fixed. Quaternions are used to represent signal vectors and an algebra for quaternions is introduced which allows distance between signal vectors and equivalence between signal codes to be defined. It is also used to characterize the structure of codes. Code construction is based on regular four-dimensional polytopes and particular interest is focused on group codes with 8, 24, 48 and 120 elements. Two classes of phase modulated signals have interest as reference codes. Code evaluation is carried out by calculation of the distance distribution and the error probability assuming opitmum coherent detection. The group codes are found to be between 1.3 and 3.4 dB better than the best phase modulated codes. By using a suitable representation for a signal code it may be realized by using a few amplitude and several phase values. View full abstract»

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  • Optimum Reception in an Impulsive Interference Environment--Part II: Incoherent Reception

    Publication Year: 1977 , Page(s): 924 - 934
    Cited by:  Papers (58)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    In Part I, the relevant statistical properties of the recently developed statistical-physical model of generalized impulsive interference have been briefly reviewed (for sub Class A noise) and then applied specifically to optimum coherent detection. It is shown that by using optimum and (locally optimum) detection algorithms (canonically and explicitly derived), substantial savings in signal power and/or spectrum space can be achieved for operation in these highly nonGaussian interference environments. This paper (Part II) extends the preceding analysis to cover various important cases of incoherent reception. The same general model for narrow-band (Class A) impulsive interference and interference examples used in Part I are again employed here. In addition to providing both canonical LOBD structures and expressions for performance, this permits explicit quantitative comparisons between coherent and incoherent reception for common classes of specific digital signal waveforms. View full abstract»

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  • Improved Demodulation of Sampled FM Signals in High Noise

    Publication Year: 1977 , Page(s): 1052 - 1054
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Simulation results are presented which are very convincing in favor of FM demodulators driven by in-phase and quadraturephase signals. Application of the extended Kalman filtering algorithms to the appropriate signal model directly yields demodulators in which the error covariance equations are uncoupled from the state estimate equations. These demodulators perform a little better than others derived using different nonlinear filtering techniques and the necessary approximations to achieve "decoupling." More significantly, these demodulators using in-phase and quadrature-phase sampled signals are readily augmented to achieve demodulation with delay by the application of fixed-lag smoothing algorithms. Simulations highlight the attractive trade-offs between demodulation complexity and performance results for this class of demodulator. View full abstract»

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  • A Worst-Case Crosstatk Comparison Among Several Modulation Schemes

    Publication Year: 1977 , Page(s): 1032 - 1037
    Cited by:  Papers (15)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    The effects of worst-case crosstalk (from a time-domain point of view) on unsynchronized frequency division multiplexed (FDM) constant envelope modulations are considered assuming coherent hard-decision receivers and no filtering for bandwidth constraint. Continuous-phase frequency shift keying (FSK) is found to be superior to various forms of phase shift keying (PSK). View full abstract»

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  • Buffer Sharing in Computer-Communication Network Nodes

    Publication Year: 1977 , Page(s): 958 - 970
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1048 KB)  

    This paper discusses a technique of sharing extra storage buffers among a number of nodes (for example concentrators) or among a number of output lines in a single node (for example, in a message switching center). Buffer sharing can be used to reduce the probability that a message is blocked, while at the same time buffer storage cells can be conserved. In addition, buffer sharing reduces sensitivity to variations in traffic. Although the improvement increases as the size and complexity of the buffer sharing system increases, significant improvement is possible even for relatively simple systems. In modeling these systems, a precise model would use data unit storage. However, a simpler model using message storage is easier to analyze. A linear relationship can be used for converting message storage into data unit storage. View full abstract»

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  • Binomial Switching Networks for Concentration and Distribution

    Publication Year: 1977 , Page(s): 873 - 883
    Cited by:  Papers (22)  |  Patents (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1232 KB)  

    In this paper a new class of switching networks is presented for concentration and distribution interconnection assignments between disjoint sets of input and output terminals. These networks are called binomial switching networks because of their structural association with the binomial distribution. Binomial networks are uniform in that all connecting paths are of equal length and are such that cycles or iterations through stages of the network are not permitted, and binomial networks are rearrangeable in that implementing an additional path through the network for a new connection can require the rearranging of existing paths. It is shown that an upper bound on the number of such rearrangements is closely related to the number of stages in the network. A sparse crossbar switch construction of the binomial switching network is presented which contains crossbar switches in which it is not possible to connect each switch input to each switch output. Finally, the number of crosspoints needed for such networks for sufficiently large numbers of input and output terminals is seen to be less than the classical, benchmark alternatives for both concentration and distribution assignments. View full abstract»

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  • Incohernet Adaptive Reception of Signal with Unknown Envelope

    Publication Year: 1977 , Page(s): 1009 - 1016
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    This paper deals with the design of adaptive algorithms for reception of a narrowband signal with an unknown envelope in a noisy channel (Gaussian noise). We here consider a system (with a "real teacher") which learns from the samples classified by this self-learning system (decision directed adaptive receiver). By using those samples which are accepted as learning samples, the parameters of the unknown envelope are estimated. The envelope's parameters appear in the form of coefficients of the generalized Fourier series expansion of the signal (with respect to eigenfunctions of appropriate integral equation). It is possible to utilize any orthonormal set with respect to the interval (0, T) under the usual assumption, that the complex autocovariance function is R(\tau ) = N\delta (\tau ) (i.e., that the noise bandwidth is much greater than both 1/T and the signal bandwidth and N is the unilateral spectral density of the noise in the neighborhood of the signal spectrum). We present expressions that enable the upper bound estimates of the error probability to be found for the derived algorithms. The results obtained for the binary detection are readily generalized to the case of an M -ary signal. View full abstract»

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  • A Technique for Estimating the Minimum Number of Frequencies Required for Urban Mobile Radio Communication

    Publication Year: 1977 , Page(s): 1054 - 1056
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    In this correspondence paper a technique for estimating the minimum number of frequencies required for Urban Mobile Radio Communication is presented. The technique is algebraic in origin and can be implemented as a computer algorithm. View full abstract»

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  • Analysis of Radio Frequency Transmission in a Semicircular Mine Tunnel Containing Two Axial Conductors

    Publication Year: 1977 , Page(s): 1046 - 1050
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    We present an analysis of the propagation in a uniform tunnel of semicircular cross section that contains two axial conductors. In particular, we show that, even if one of these conductors has high ohmic loss, one of the two propagating modes has relatively low attenuation. This corresponds to the situation where an unloaded dedicated wire is used to improve radio frequency communication in a mine tunnel that contains a heavily loaded trolley wire. View full abstract»

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  • An Analysis of Jitter Accumulation in a Chain of PLL Timing Recovery Circuits

    Publication Year: 1977 , Page(s): 1027 - 1032
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    This paper analyzes the timing jitter accumulation which is produced in a chain of regenerative repeaters when a second-order phase-locked loop (PLL) is used as a timing filter. In a PLL timing recovery circuit, the growth of timing jitter varies with the value of damping factor \zeta . In this paper, therefore, approximate equations of timing jitter accumulation are given with respect to a case in which \zeta is sufficiently large, and the timing jitter is calculated with a digital computer for various values of \zeta . It is shown that, when \zeta is sufficiently large, results similar to those for first order loops or single tuned circuits are obtained, i.e., the meansquare random jitter is almost proportional to the square root of the number of repeaters, and the mean-square systematic jitter is almost proportional to the number of repeaters. When \zeta is small the meansquare jitter increases exponentially as the number of repeaters is increased. This paper also describes the optimum value of \zeta , considering both the jitter accumulation and the transient response of the PLL, by using the number of repeaters N as a parameter. As a result, it is postulated that the optimum value of \zeta is 5 to 8 when N is 100, and 15 to 18 when N is 1,000. View full abstract»

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  • A Fast Computational Algorithm for the Discrete Cosine Transform

    Publication Year: 1977 , Page(s): 1004 - 1009
    Cited by:  Papers (415)  |  Patents (53)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    A Fast Discrete Cosine Transform algorithm has been developed which provides a factor of six improvement in computational complexity when compared to conventional Discrete Cosine Transform algorithms using the Fast Fourier Transform. The algorithm is derived in the form of matrices and illustrated by a signal-flow graph, which may be readily translated to hardware or software implementations. View full abstract»

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  • An Experimental 560 Mbits/s Repeater with Integrated Circuits

    Publication Year: 1977 , Page(s): 995 - 1004
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1176 KB)  

    The bandwidth penalty of digital systems is very obvious in the case of transmission over coaxial cables because of the exponential increse of cable attenuation with square root of frequency. From capacity point of view, it is only at very high information rates (> 500 Mbit/s typically) that a digital system might be competitive with an analog system, because the disadvantage of noise accumulation in an analog system ultimately cancels the bandwidth penalty of the digital system. In addition, it is, however, difficult to realize common functions, such as amplification, equalization, regeneration, clock extraction, etc. with electronic components having a frequency range comparable to the frequency range of the information signal, which extends from zero frequency to the microwave range. Besides, the complexity of a regenerative repeater should be kept to a minimum for reliability reasons. It is shown in the paper that with present-day technology a 560 Mbit/s repeater can be constructed, operating in sections of 1.5 km coaxial cable (2.6/9.5 mm). Also, we demonstrate that new technologies exist which may lead to repeaters with a high degree of monolithic integration, even at such a speed, which is important from the reliability viewpoint. The constructed and described repeater is characterized by unconventional and economic design of amplifier/equalizer and clock extractor and by monolithically integrated decision circuits. 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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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia