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Communications, IEEE Transactions on

Issue 4 • Date April 1975

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Displaying Results 1 - 19 of 19
  • [Front cover and table of contents]

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  • [Back cover]

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  • Probability of Error in Pseudonoise (PN)-Modulated Spread Spectrum Binary Communication Systems

    Page(s): 467 - 472
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    The probability of error in a binary communication system using pseudonoise (PN) modulation to spread the transmitted spectrum is influenced by noise, bandlimiting, and synchronization errors. In this paper the average probability of error is determined, using a series expansion of the characteristic function of the intersymbol interference. It is shown that the effects of intersymbol interference are reduced by spreading and that local code synchronization errors become the dominant factor in the probability of error when the system bandwidth is large. View full abstract»

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  • Quantization Error in Predictive Coders

    Page(s): 423 - 429
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    Predictive coders have been suggested for use as analog data compression devices. Exact expressions for reconstructed signal error have been rare in the literature. In fact most results reported in the literature are based on the assumption of Gaussian statistics for prediction error. Predictive coding of first-order Gaussian Markov sequences are considered in this paper. A numerical iteration technique is used to solve for the prediction error statistics expressed as an infinite series in terms of Hermite polynomials. Several interesting properties of predictive coding are thereby demonstrated. First, prediction error is in fact close to Gaussian, even for the binary quantizer. Sencond, quantizer levels may be optimized at each iteration according to the calculated density. Finally, the existence of correlation between successive quantizer outputs is shown. Using the series solutions described above, performance in terms of meansquare reconstruction error versus bit rate can be shown to parallel the theoretical rate distortion function for the first-order Markov process by about 0.6 bits/sample at low bit rates. View full abstract»

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  • Bistable Behavior of ALOHA-Type Systems

    Page(s): 401 - 410
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    Packet switching has found widespread application in computer communications because of its ability to efficiently handle high ratios of peak-to-average data rate. Packet radio is the application of packet switching techniques to radio channels. The resultant multiple-access problem requires novel approaches. Such approaches have been developed by others and have primarily been analyzed in steady-state behavior. This paper demonstrates and analyzes an important aspect of the dynamic characteristics of packet radio, namely, that of bistable behavior. That is, the system possesses two statistically stable equilibrium points, one in a desirable low-delay region, and the other in an undesirable high-delay region. Since the stability is only statistical in nature, the system oscillates between these two points. Even if the resultant steady-state behavior is very poor, this dynamic analysis frequently shows that system performance will be acceptable. This is due to quiet periods (such as at night) which allow the system to recover. View full abstract»

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  • Multilevel Block Codes with DC-Constraint Property

    Page(s): 448 - 452
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    Multilevel fixed-length block codes which have a dcconstraint property are discussed, and the upper bounds of the transmission rates of such codes are described under the limitations of the running digital sums (RDS) of coded signal streams. Then stateindependent decodable codes whose transmission rates are equal to the upper bounds are presented for small values of word length. In these codes, four code words or less correspond to a source symbol. As an example, a 5-level code of length 4 whose RDS's do not exceed 4, whose transimission rate is equal to 2 bits per symbol, and from which good performance for bit timing, gain adjustment of repeaters, and word synchronization can be expected, is also described. View full abstract»

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  • Efficiency and Matching Tradeoffs for Inductively Loaded Short Antennas

    Page(s): 430 - 435
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    Efficiency and input resistance of short monopoles (or dipoles) may be significantly improved through use of a loading coil in series with the monopole wire. The piecewise sinusoidal moment method is used to analyze the loaded monopole. When loaded to resonance, the current rises from the feed value to a peak slightly beyond the load point with decay to zero at the end. Radiation resistance improvement factors as large as 5 have been calculated. The resonant loading reactance is shown to vary inversely with the antenna length for most lengths. Efficiency varies slowly with load point and peaks at roughly 0.4 from the feed, in contrast to earlier approximate theory that predicted higher efficiency for loads farther out toward the end. The curves allow a tradeoff between slightly reduced efficiency and larger input resistance (to allow easier matching) to be made. For this case, a 2/3 loading point may be a good compromise. The length for which efficiency is 50 percent is a useful design guide. This length varies slowly with Q and h/a and is in the range 0.06 to 0.09 λ. Thus shorter monopoles will have low efficiency. Bandwidth is improved due to loading coil losses at the expense of efficiency; lossless loading bandwidth is unchanged over the unloaded monopole as the radiation resistance and reactance slope increase commensurately. Extensive graphical data are presented. View full abstract»

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  • Error Correction in a Radio-Based Data Communications System

    Page(s): 458 - 462
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    This paper describes an interesting application of error correcting codes to improve the reliability of data transmission of a radio-based communication system. It shows how a low-cost system can be designed and constructed to bring significant improvements to the system's performance when a proper approach is taken to both select and implement the coding scheme. View full abstract»

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  • Measuring the Speed of Moving Objects from Television Signals

    Page(s): 474 - 478
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    Very simple techniques for estimating the speed of a moving object from a television signal are described. They assume that frame storage is available. One technique requires little more than two threshold circuits and two counters. The accuracy of one technique is better than ± 10 percent, quite sufficient to enable the measure to be used as a control signal for the efficient coding of television type signals. View full abstract»

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  • Improving Automatic Repeat-Request (ARQ) Performance on Satellite Channels Under High Error Rate Conditions

    Page(s): 436 - 439
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    Large round trip delay associated with satellite channels reduces the throughput for automatic repeat-request (ARQ) system of error control rather drastically under high error rate conditians. Ground segments that usually accompany satellite circuits at both ends introduce bursts of errors, during which block error rates tend to be quite high, bringing down the throughput to very low values. In this paper, some schemes that modify the currently known variations of ARQ (Stop-and-Wait and continuous systems) are suggested with a view to obtaining higher throughput under high block error rate conditions. Specifically, the modified Go-Back- N system appears to be quite attractive, as it gives substantial improvement with little additional complexity in system implementation. View full abstract»

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  • Dynamic Response and Stability of Mutually Synchronized Systems

    Page(s): 443 - 448
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    One of the synchronized systems of large digital transmission networks is the mutually synchronized system called the equational timing system. This system is, however, complicated, and its dynamic responses are not obtained analytically for general configuration. This paper describes dynamic responses and stability conditions of mutually synchronized systems applying the equational timing system under less stringent restrictions compared with previous discussions. Similar results for the fundamental mutually synchronized system can be obtained easily. View full abstract»

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  • Computer Modeling of the Statistical Properties of Transionospheric Scintillation Channels

    Page(s): 462 - 467
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    This concise paper shows that a band-limited bivariatenormal time series is a useful model for the envelope of scintillating radio signals traversing the ionosphere. A software model is presented whose generated time series is compared to an actual block of scintillation data. A comparison of computer-generated and actual scintillation data shows that the fade-duration distribution of the simulated data fits that of the actual data closely through proper choice of model parameters. View full abstract»

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  • Packet Switching in a Multiaccess Broadcast Channel: Performance Evaluation

    Page(s): 410 - 423
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    In this paper, the rationale and some advantages for multiaccess broadcast packet communication using satellite and ground radio channels are discussed. A mathematical model is formulated for a "slotted ALOHA" random access system. Using this model, a theory is put forth which gives a coherent qualitative interpretation of the system stability behavior which leads to the definition of a stability measure. Quantitative estimates for the relative instability of unstable channels are obtained. Numerical results are shown illustrating the trading relations among channel stability, throughput, and delay. These results provide tools for the performance evaluation and design of an uncontrolled slotted ALOHA system. Adaptive channel control schemes are studied in a companion paper. View full abstract»

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  • Wide-Band Frequency-Shift Keyed Receiver Performance in the Presence of Intersymbol Interference

    Page(s): 453 - 458
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    The noncoherent binary frequency-shift keyed (FSK) receiver analyzed in this concise paper employs predetection filters with bandwidths much larger than the symbol rate. Wide-band predetection filtering is used in order to trade performance for simplicity and reduced costs. In this analysis bit-error rate (BER) degradation due to wide predetection filter bandwidths and intersymbol interference caused by postdetection filtering is determined. The postdetection filters considered are single-pole RC and two-pole Butterworth filters. The receiver performance using these filters is compared with the performance achieved when using integrate-and-dump postdetection filtering. Experimental and simulation results are presented which agree well with the analysis. View full abstract»

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  • Intersymbol Interference with Orthogonal Signaling

    Page(s): 472 - 474
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    The occurrence of both inter- and intrasymbol interference in a communications system utilizing orthogonal signals and memoryless correlation detection is described, and a system model is presented. A relationship between a bound on peak interference and time-bandwidth product for several well known orthogonal signal sets is reported. View full abstract»

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  • Binary Transversal Filters for PAM Pulse Generation with Correlative Coding

    Page(s): 483 - 486
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    High-speed pulse amplitude modulation (PAM) data transmission systems require carefully shaped pulses having small bandwidth, and various coding schemes are used to increase transmission efficiency via spectrum shaping. Traditional hardware for the generation of such pulses, whether coded or not, is both difficult to design and expensive to implement. The binary transversal filter (BTF) has recently been studied in this context, and shown to be a promising alternative to other methods. It is inherently a binary device, however, and some coding schemes require multilevel signal outputs. Simple methods are presented in this paper that permit the use of a BTF for generating pulses such as bipolar, partial response, etc. The additional hardware required when coding is used is shown to be trivial in most cases. View full abstract»

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  • An Automatic Protection System for Digital Lines

    Page(s): 478 - 482
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    An automatic transfer system provides a means of switching both ends of a working digital carrier span line automatically to a protection line when a failure occurs on a working line, without service interruption. Priority schemes enable one or two protection lines to serve any number of working lines. New design concepts expand the flexibility of automatic line transfer. Each digital span line may be protected separately and transferred independently. Interrogation and resetting on a span-by-span basis are also provided. All line transfers are signaled and the location of a failure anywhere in the system may be determined from a central location. Any span feeding lines originating or terminating within the system, or diverging at a remote office, may be protected by one or two protection lines. View full abstract»

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  • Quantizer Mismatch

    Page(s): 439 - 443
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    A simple upper bound is derived to the difference in performance obtained from applying a given quanfizer to two different sources. This provides a bound on the performance loss or mismatch resulting when applying a quantizer designed for one source to another. The bound is in terms of a generalization of the Vasershtein distance between the source random variables and does not depend on the particular quantizer chosen. In particular, if two sources are sufficiently close in this sense, then any quantizer results in nearly identical performance on either source. Implications for optimal performance bounds are discussed and examples are given. 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