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Communications, IEEE Transactions on

Issue 8 • Date August 1978

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Displaying Results 1 - 25 of 34
  • [Front cover and table of contents]

    Publication Year: 1978 , Page(s): 0
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    Freely Available from IEEE
  • [Back cover]

    Publication Year: 1978 , Page(s): 0
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    Freely Available from IEEE
  • A Multipath Fading Channel Model for Terrestrial Digital Radio Systems

    Publication Year: 1978 , Page(s): 1247 - 1250
    Cited by:  Papers (33)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    The frequency transfer function of a multipath fading channel is examined in terms of its effects on digital radio signals. The transfer function is expanded into a power series about the channel center frequency and the coefficients are related to the multipath structure. It is then shown that, in the channelized common carrier bands below 15 GHz, the first two (complex) terms of the power series are usually sufficient for characterizing multipath effects. This demonstration is based on a mean-square error-of-fit measure which is applied to the multipath fading response and evaluated under some worst-case assumptions. View full abstract»

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  • Non-Coherent Pulse Detection with a Large Predetection Bandwidth

    Publication Year: 1978 , Page(s): 1297 - 1301
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    For a non-coherent detection circuit with a broad-band pre-detection filter and narrow-band post-detection-filter, equations are obtained for the probability of detection of a pulsed sinusoidal signal embedded in white noise. The equations can be used to calculate the detection probability directly from envelope form, noise power at the input of the circuit and the impulse response of the postdetection filter. The application of the equations is illustrated with reference to a sliding correlator acquisition circuit for PN-code generators. View full abstract»

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  • Bounds on the Number of Possible Distinct Networks

    Publication Year: 1978 , Page(s): 1315 - 1316
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    This note is concerned with the number of all distinct networks, also called connected graphs, or Cayley, or linear graphs that are possible for n given nodes. Since for any practical number of nodes an explicit enumeration appears difficult, if not impossible, we offer an improved lower bound that enables tight approximation for n reasonably large. View full abstract»

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  • Performance of Phase Comparison Sinusoidal Frequency Shift Keying

    Publication Year: 1978 , Page(s): 1250 - 1253
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    Some communication systems require the close packing of many signals into a fixed bandwidth while precluding an absolute phase reference at the receiver and time synchronization between the signals. This paper investigates the bit error performance in the presence of white Gaussian noise of PCSFSK, which has been found to be very bandwidth efficient under the above conditions; much more efficient than DQPSK. PCSFSK is found to perform slightly better than an upper bound on the performance of DQPSK for high signal-signal-to-noise ratios and somewhat worse for low signal-to-noise ratios, while allowing much closer packing of unsynchronized signals. View full abstract»

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  • Protocol Validation by Duologue-Matrix Analysis

    Publication Year: 1978 , Page(s): 1187 - 1194
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    A protocol is a set of rules which governs the interaction between processes. It is difficult to design protocols without errors because there are usually more interactions possible than anticipated. We are concerned with two-process protocols. A technique is described which identifies design errors in protocols. The technique is based on modeling a protocol as a pair of interacting graphs whereby interaction sequences are represented by path pairs (one path in each graph). The technique is currently limited to protocols that must revert to an initial or quiescent state after a finite number of interaction steps. The work represents a theory that can be automated on a digital computer. View full abstract»

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  • Differential Pulse Code Modulation of Stationary Gaussian Inputs

    Publication Year: 1978 , Page(s): 1137 - 1147
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    This paper is concerned with an exact analysis of DPCM systems with stationary Gaussian inputs. We consider a class of digital communication systems in which DPCM is included as a member. An integral equation for the joint probability of the input and the state of the system is derived first. Solution of the equation is sought in the form of a power series in the elements of the covariance matrix of the input that involves generalized Hermite functions. Then the integral equation is reduced to a set of algebraic equations for the coefficients in the series that are solved recursively. The steady-state distribution of the input and the state is thus found. We are interested particularly in the mean-squared error of the system as a function of step size, the sampling interval and the number of quantization levels. Numerical results are shown for the GaussMarkov input; the MSE is calculated in terms of system parameters and performance of DPCM and PCM is compared with reference to the theoretical bound. View full abstract»

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  • A Comparison of Information Policies for Minimum Delay Routing Algorithms

    Publication Year: 1978 , Page(s): 1266 - 1271
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    The problem of routing in a computer networks is dealt with by separating the information problem and the control problem. Several classes of information policies are examined, and numerical comparisons are made of their performance, using representative values of network parameters. Routing based on the expected values of delay, rather than actual values of delay, is shown to be superior to the other algorithms considered. View full abstract»

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  • A New PLL Frequency Synthesis Structure

    Publication Year: 1978 , Page(s): 1195 - 1200
    Cited by:  Papers (4)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    In a PLL frequency synthesizer, the reference and VCO frequencies are divided down to their greatest common divisor frequency prior to phase comparison. We replace the dividers by a simplified form of digital frequency synthesizer, and examine the spectrum of the phase comparator outputs to show that the loop bandwidth can be dramatically increased, thereby improving the pull-in range and acquisition time. View full abstract»

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  • Noise Removal from Chrominance Components of a Color Television Signal

    Publication Year: 1978 , Page(s): 1318 - 1321
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    A solution to the problem of removing noise from the chrominance components of a color television signal is described. The inherent trade-off between noise removal and signal blurring is balanced adaptively using the luminance signal as a control for changing the characteristics of the chrominance filters. This adaptation is effective because: (1) in real pictures, most sharp changes of color are accompanied by sharp changes in luminance and, (2) sharp changes of luminance have a pronounced masking effect on the chrominance noise. Computer simulations show that a large amount of noise could be removed from the chrominance signals with no appreciable visible blurring. A simple filter, whose performance is close to the optimum, is proposed and a comparison with nonadaptive filters is made. View full abstract»

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  • On-Line Pseudo-Error Monitors for Digital Transmission Systems

    Publication Year: 1978 , Page(s): 1275 - 1282
    Cited by:  Papers (7)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    Pseudo-error detectors are devices which show great potential for the measurement of the bit error rate of an on-line digital communications link. They are implemented in the form of a second detector (in addition and in parallel to the traffic data bit detector) which is very perturbation-sensitive. They do not compromise the traffic handling capacity of the system. Four methods of generating the pseudo-error characteristic are described: i) shifted detection threshold; ii) intersymbol interference enhancement; iii) noise addition; iv) sampling phase offset. Practical considerations generally govern the choice of method. Experimental results of pseudo-error detector behavior in the presence of Gaussian noise show that stable characteristics can be achieved to estimate a wide range of bit error rate (BER's) in very modest time intervals. In addition, experimental results in a real complex environment consisting of a 1.544 Mbits/s T1 capacity digital link using QPSK modulation techniques, including both Gaussian and non-Gaussian perturbations, show pseudo-error detection to be reliable for the measurement of BER and for controlling channel switching. View full abstract»

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  • The Choice of the Desired Impulse Response in Combined Linear-Viterbi Algorithm Equalizers

    Publication Year: 1978 , Page(s): 1301 - 1307
    Cited by:  Papers (38)  |  Patents (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    Equalizer structures using the Viterbi Algorithm achieve at least order of magnitude performance improvement over linear equalizers on some intersymbol interference channels. Using a linear equalizer to shape the original channel impulse response to some shorter desired impulse response (DIR) is a technique which reduces the complexity of the Viterbi Algorithm equalizer. This paper looks at three techniques for choosing a DIR. These are choosing the DIR by truncation, minimum mean square error and matching the power spectrum to that of the original channel. Using effective signal to noise ratio as the figure of merit for comparison, results are given for one particular channel. View full abstract»

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  • Optimal Multistage Switching Networks

    Publication Year: 1978 , Page(s): 1282 - 1287
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    We consider the problem of determining the multistage network with the fewest crosspoints for given sizes of input and output terminal sets, traffic load, number of stages and blocking probability. In this paper, we present a solution for this problem when the sizes of the input and output terminal sets are greater than a certain value. View full abstract»

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  • A Subscriber Carrier System Based Upon Frame Addressing System

    Publication Year: 1978 , Page(s): 1287 - 1295
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    A new channel assignment scheme called a frame addressing system is proposed in this paper to realize an efficient telephone subscriber carrier system by means of PCM loop having a simplified switching capability at each subscriber. In the frame addressing system, a speech signal time slot is assigned by sending a bit for each subscriber at the beginning of each transmission frame. This results in an improvement of efficiency by a TASI-like effect in addition to efficiency by switching. The principle and an example of a practical circuit are described. Characteristics of the system are analyzed and a design example is described. View full abstract»

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  • A Polarization Control System for Satellite Communications with Multiple Uplinks

    Publication Year: 1978 , Page(s): 1201 - 1211
    Cited by:  Papers (3)  |  Patents (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    Several groups have designed polarization control systems to solve the rain-crosspolarization problem in satellite communications. However, the multiple-uplink problem still exists, i.e., one system cannot receive signals from different uplink stations with different rain conditions simultaneously. In order to solve this problem, a new scheme is developed in this paper based on the assumption that an obtainable correlation exists between the uplink and downlink crosspolarizations and the concept that uplink and downlink can be compensated separately. The currently designed systems can be used directly in this scheme; only the addition of similar devices is necessary. The feasibility is checked by a practical example, and satisfactory performance is observed. View full abstract»

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  • Tracking Performance of Unbalanced QPSK Demodulators: Part I-Biphase Costas Loop with Passive Arm Filters

    Publication Year: 1978 , Page(s): 1147 - 1156
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Unbalanced quadriphase-shift-keying (QPSK) is an attractive means for transmitting two digital data streams which in general have different average powers, data rates, and data formats. Previous analyses of the tracking performance of Costas loop demodulators of unbalanced QPSK have accounted only for the filtering effect produced by the loop's two arm filters on the equivalent additive noise perturbing the loop. When the bandwidth of these filters is selected on the order of the data rate, as is typical of optimum Costas loop design, the filtering degradations of the data modulations themselves and the crossmodulation noise produced by their multiplication in the loop often cannot be neglected. The purpose of this paper is to incorporate these additional filtering effects into the analysis. Many of the results obtained herein are in the form of closed-form expressions which can easily be evaluated numerically for design and performance prediction purposes. View full abstract»

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  • A First-Order Markov Model for Understanding Delta Modulation Noise Spectra

    Publication Year: 1978 , Page(s): 1316 - 1318
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    A first-order Markov process is used to model the sequence of quantization noise samples in delta modulation. An autocorrelation parameter C in the Markov model controls the shape of the noise spectrum, and as C decreases from 1 to 0 and then to -1, the spectrum changes from a low-pass to a flat, and then to a high-pass characteristic. One can also use the Markov model to predict the so-called out-of-band noise rejection that is obtained when delta modulation is performed with an oversampled input, and the resulting quantization noise is lowpass filtered to the input band. The noise rejection G is a function of C as well as an oversampling factor F and an interesting asymptotic result is that G=frac{1-C}{1+C} \dot F if F \gg frac{1+C}{1-C} \dot frac{\pi}{2} . Delta modulation literature has noted the importance of the special G values, F and 2F . These correspond to autocorrelation values of 0 and -1/3. View full abstract»

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  • Performance of SSB-PM Suboptimum and Optimum Demodulators

    Publication Year: 1978 , Page(s): 1232 - 1239
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    Suboptimum SSB-PM envelope and phase detectors are considered and their performances above threshold are evaluated and compared. The results show a slight superiority of the phase SSB-PM over the envelope SSB-PM demodulator. Both detectors show poor performance for high index modulation. A lower bound on the MMSE of an optimum SSB-PM demodulator is computed and it is shown to be slightly higher than the corresponding bound for PM for small index modulation and that it deteriorates (becomes much larger) for high index modulation. View full abstract»

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  • Concepts of System Balance

    Publication Year: 1978 , Page(s): 1220 - 1231
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (992 KB)  

    A conceptual framework is proposed for characterizing those electrical interactions between the power system and telephone system which contribute to low-frequency interference. This framework describes the interference source, the susceptibility of telephone plant, and their interactions, utilizing generally applicable concepts of system balance. In particular, the concept of an overall Interference Quality Factor (IQF) has been introduced in terms of a Power System Balance Factor, a Telephone System Balance Factor, and an Effective Coupling Factor. Hence, a rigorous numerical comparison of various interference environments may be possible, allowing for problem areas in the overall power-telephone system to be identified, and costeffective mitigative engineering considerations to be implemented in the system design. View full abstract»

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  • A Novel Approach for Finding the Spectrum of Periodically Modulated FM Carriers

    Publication Year: 1978 , Page(s): 1309 - 1315
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    A new technique for finding the frequency spectrum of a carrier frequency modulated by a periodic signal is presented. The technique is based on the frequency modulation (FM) equation due to Hess, which in the frequency domain is a double convolution equation. The technique reduces the FM spectrum problem to the solution of a set of linear equations in which the FM side-band amplitudes are the unknowns. The results obtained through this new technique can, in most cases, be obtained by other means. However, the technique is simple and as a result its implementation on a standard computer is both simple and fast. Furthermore, it is especially suitable when the modulating signal is in the form of a Fourier series with a large number of terms or requires a large number of terms to approximate it. Numerical results obtained using the technique for a large number of complex modulating signals are presented. View full abstract»

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  • Estimating Year-to-Year Variability of Rainfall for Microwave Applications

    Publication Year: 1978 , Page(s): 1321 - 1324
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1160 KB)  

    Recent progress is reported for extensions of the RiceHolmberg rainfall-prediction model. This extension provides for the year-to-year variation expected for rainfall and is required to permit any useful comparison of predicted with observed rainfall (or predicted with observed microwave attenuation due to rainfall). The results are illustrated for Europe. View full abstract»

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  • An Adaptive Technique for Local Distribution

    Publication Year: 1978 , Page(s): 1178 - 1186
    Cited by:  Papers (61)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    A critical component of computer communications networks is local distribution, i.e., techniques for connecting geographically dispersed users to a central facility. A drawback to conventional polling techniques for local distribution is excessive overhead. Thus, in systems with many lightly loaded terminals, message delay is more a function of the time required to poll all terminals than of traffic from competing sources. A technique for reducing overhead is presented together with the results of analysis and simulation. The technique identifies terminals having messages by a process of elimination starting with a poll of groups of terminals. Further, the technique is adaptive in that the sizes of groups to be polled are chosen according to the probability of a terminal having a message. The object of the adaptivity is to minimize the average time required to examine all terminals. The results of analysis and simulation show considerable reduction in this average for systems with many lightly loaded terminals. Moreover, the adaptive feature insures that there is no penalty for heavy loading. With reduced overhead there is a reduction in the average delay of messages. View full abstract»

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  • A Recursive Method Based on Case Analysis for Computing Network Terminal Reliability

    Publication Year: 1978 , Page(s): 1166 - 1177
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (968 KB)  

    In this paper a unified treatment is provided of the methods for computing terminal reliability based on recursive case analysis. The possible choices in case enumeration are discussed, and a rationale is given to support a particular policy. Simplification and decomposition techniques are also examined, and some experimental results are described, obtained with a computer program, which is a good compromise between efficiency and simplicity. View full abstract»

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  • Quantizing Characteristics for Signals Having Laplacian Amplitude Probability Density Function

    Publication Year: 1978 , Page(s): 1295 - 1297
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    The optimum (minimum mean-squared-error criterion) and optimum uniform quantizer characteristics for signals characterized by the Laplacian amplitude probability density function are given in tabular form. These results correct and extend previously published results. 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