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Communications, IEEE Transactions on

Issue 3 • Date March 1985

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Displaying Results 1 - 23 of 23
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • [Back cover]

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    Freely Available from IEEE
  • Comparison Between the Performance of QPSK, SQPSK, QPR, and SQPR Systems Over Microwave LOS Channels

    Page(s): 291 - 296
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    This paper studies the effectiveness of adaptive equalizers used with QPSK, SQPSK, QPR, and SQPR modems over frequency selective microwave LOS channels. A power series model is employed to represent the channel model, giving special attention to the channels with a null in the passband. The effect of staggering the symbols on the performance of modems with and without an adaptive equalizer is provided. With a deep null in the passband of the channel, the performance of QPR modems is slightly worse than SQPR modems, while QPSK systems significantly outperform SQPSK systems. The general conclusion that a decision feedback equalizer is required for a robust performance by each modem is reached. View full abstract»

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  • Local Network Area Size Optimization

    Page(s): 199 - 202
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    A foundation for economically optimizing the size of a local network area, defined as an area comprising a transit switch and a number of local switches homing on it, is obtained by introducing the concept of an "intra-area traffic ratio." The local network area radius is found to be optimal when the gradient of the intra-area traffic ratio relative to the area radius equals the ratio of the junction cost per kilometer to the cost per circuit for trunks going out of the area. An empirical formula for determining this intra-area traffic ratio is given. View full abstract»

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  • Statistics of Impulsive Noise Crosstalk in Digital Line Systems on Multipair Cable

    Page(s): 259 - 270
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    Crosstalk theory is applied to the prediction of error rates in digital line systems due to analog telephony signaling events on adjacent pairs in the same cable. Measurements of the margin against impulsive noise at a given probability of error have been performed, and these show reasonable agreement with predictions based on crosstalk theory. For a simple switching event, the regenerator NEXT impulsive noise figure for the near-end crosstalk path is defined. Measurements of the mean and variance of near-end crosstalk attenuation are then used to calculate the maximum exchange section loss (from central office to first line regenerator) which satisfies a suggested error performance criterion. View full abstract»

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  • The Effect of Channel Coding on the Efficiency of Cellular Mobile Radio Systems

    Page(s): 288 - 291
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    Error correcting codes have two opposite effects on the efficiency of cellular mobile-radio systems. Although they increase the bandwidth per channel, the codes also make signals more robust and thereby reduce the required distance between users of the same frequency band. This paper reports a mathematical study of the interactions of these two effects in determining the efficiencies of a large number of sourcecode and channel-code combinations. Within a statistical performance objective (baseband SNR \geq 11 dB for 90 percent of the users), the most efficient scheme in this study has an embedded differential pulse code modulation (DPCM) source code and a rate 1/2 channel code that protects 2 bits of each 4 bit DPCM code word. Based on a conservative model of cellular transmission, we estimate that the bandwidth efficiency is 3 users/cell/MHz of system bandwidth. By contrast, there are only 1.2 users/cell/MHz with uncoded transmission and 4.5 users/cell/MHz with a rather complicated variable-rate scheme. We also observe that the embedded source code, originally devised for variable-rate operation, has a higher baseband SNR than conventional DPCM in certain fixed-rate environments. View full abstract»

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  • Application of the Volterra Functional Expansion in the Detection of Nonlinear Functions of Gaussian Processes

    Page(s): 276 - 279
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    Detection of a memoryless nonlinear functional of a Gaussian process in additive Gaussian white noise is considered. The Volterra functional expansion for the likelihood ratio, and two examples of calculating the kernels are presented. It is shown that kernels up to third order can be obtained for a hard-limited Gaussian process and for the absolute value of a Gaussian process. For the case of hard limiting, the kernels are nonlinear functions of the autocorrelation of the Gaussian process. For the absolute value case, the kernels are nonlinear functions of the kernel derived for the linear problem. A Monte Carlo simulation of receiver performance is presented for the case of detection of the absolute value of a first-order Butterworth process in additive Gaussian white noise. The suboptimal detector is obtained by truncating the log likelihood ratio to second order. View full abstract»

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  • On the Performance of Three Suboptimum Detection Schemes for Binary Signaling

    Page(s): 241 - 245
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    The penalties incurred in using the sample-and-sum, weighted partial decision, and binary Partial decision detectors are analyzed. Even though these schemes are inferior to the digital matched filter detector, they could be used in systems with more modest computational capabilities. Analytic expressions are obtained for the losses when the number of samples M is large. Examples are also given which indicate how these losses vary with M . View full abstract»

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  • Error Performance of Binary NCFSK in the Presence of Multiple Tone Interference and System Noise

    Page(s): 203 - 209
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    This paper presents a general solution to the problem of calculating the error performance of binary NCFSK systems in the presence of multiple tone interference and system noise. The development uses the concepts of circularly symmetric signals and expresses the results in terms of a Bessel integral. This integral is then evaluated using a rapidly converging Fourier-Bessel series. The error in this approximation to the integral is controlled by two parameters which may be adjusted so that the desired accuracy is attained. It is determined that, in the useful probability-of-error range and when the total tone power is constrained, the error rate increases for an increase in the number of interfering tones. In addition, for equal amplitude tones, the performance is independent of the distribution of the tones within the channel. The technique used is also applicable to other detection problems where the threshold is a random variable. View full abstract»

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  • Carrier-to-Intermodulation Performance of Multiple FM/FDM Carriers Through a GaA1As Hetrojunction Laser Diode

    Page(s): 246 - 248
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    The simple nonlinear rate equations are used to predict the carrier-to-intermodulation performance of laser diodes excited by an arbitrary number of equal-amplitude, equally spaced FM carriers. The special case of relatively small input carrier amplitudes and slowly varying angle modulations is considered and closed-form approximations are obtained. View full abstract»

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  • An Analysis of a Point-to-Multipoint Channel Using a Go-Back-N Error Control Protocol

    Page(s): 282 - 285
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    This paper contains a performance analysis of an error control protocol operating in a point-to-multipoint environment. This protocol, called broadcast go-back- N [BGB( N )], is a generalization of the standard go-back- N point-to-point protocol. Expressions for the message throughput and expected message delay are obtained. Numerical results are provided for a satellite communications system. View full abstract»

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  • Specification and Verification of Switching Software

    Page(s): 193 - 198
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    This paper describes specification and verification technology for software development. This technology consists of 1) a Specification description language called LAN-S, 2) a compiler to generate data for specification verification, and 3) a specification analysis algorithm (analyzer). A switching system and terminals are regarded as state transition machines in this technology. From specifications described in LAN-S, input data for the specification analyzer are generated. The analyzer incorporates a concept of the reduced reachability tree (RRtree), which can solve the "state space explosion" encountered in the ordinary teachability tree analysis. Using some subprocedure libraries, the switching software specification in LAN-S is transformed into an executable control program for a system with "process based software architecture." When applied to software development for a model switching system SPICE, the analyzer produced a reachability tree smaller than the one produced via the ordinary reachability tree analysis by 99.95 percent, and proved to be applicable to practical systems analysis. View full abstract»

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  • Capacity Estimation of Cyclic Queues

    Page(s): 279 - 282
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    In many data communication and telephone switching systems, one processor must perform more than one type of task. In some systems it is advantageous to place the different tasks in different queues and have the processor serve the queues in a cyclic manner. Moreover, the system design often imposes a (finite or infinite) limit on the number of entries that may be served per cycle from any given queue; this limit typically varies from queue to queue. This paper will derive the capacity estimation of such systems. We consider systems which, in addition to serving n queues cyclically, must execute maintenance (or other low-priority jobs) without severely disrupting the queues' performance. For two alternative methods of scheduling the maintenance, we compute steady state values of i) the average cycle time, ii) the average number of entries of each queue served per cycle, iii) the average time spent at each queue per cycle, iv) the average amount of elapsed time necessary to complete a given amount of maintenance execution real time, and v) if the arrival rate to queue i,\lambda _{i} , is proportional to N , the number of customers in the system, i.e., \lambda _{i} = N\alpha _{i} , then we a) compute the value of N which saturates the system and b) predict which queue will first become saturated as N is increased towards this value. View full abstract»

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  • SQAM: A New Superposed QAM Modem Technique

    Page(s): 296 - 300
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    A spectral and power efficient modulation techniquesuperposed quadrature amplitude modulation (SQAM-is introduced. In SQAM, the premodulation baseband signal is a double-interval ( 2T_{s} ) raised-cosine pulse superposed with weighted single-interval (Ts) raisedcosine pulses. Our results indicate that SQAM has spectral advantages over OQPSK, QBL, and MSK, and better P(e) performance than MSK, IJF-OQPSK (or SQORC), and TFM. View full abstract»

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  • Performance of Block Cosine Image Coding with Adaptive Quantization

    Page(s): 210 - 217
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    Quantizers for block transform image coding systems are typically designed under the assumption of Gaussian statistics for the transform coefficients. While convincing arguments can be provided in support of this approach, empirical evidence is presented demonstrating that, except possibly for the dc term, wide departures from Gaussian behavior can be expected for real-world imagery at typical block sizes. In this paper we describe the performance of a block cosine image coding system with an adaptive quantizer matched to the statistics of the transform coefficients. The adaptive quantizer is based upon a recently developed algorithm which employs a training sequence in the design procedure. At encoding rates of approximately 1 bit/pixel and above, this approach results in significant improvement in reconstructed image quality compared to fixed quantization schemes designed under the Gaussian assumption. For rates much below 1 bit/pixel the relative improvement is negligible. View full abstract»

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  • Exact Results for Nonsymmetric Token Ring Systems

    Page(s): 223 - 231
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    This paper derives exact results for a token ring system with exhaustive or gated service. There are N nodes on the ring and control is passed sequentially from one to the next. Messages with random lengths arrive at each node and are placed on the ring when the control arrives at that node. Exhaustive service means that the queue at a node is empty before the token is released and gated means that only those messages in the queue at the arrival of the token are served at that cycle. Generating function recursions for the terminal service time (the total sojourn time of a token at a node) and, from this, joint cycle and intervisit times are derived. Using known results relating the marginal generating functions of the waiting time and the cycle and intervisit time, it is shown that the N mean waiting times at the nodes require the solution of N(N - 1) and N2equations for the exhaustive and gated cases, respectively. The arrival processes are assumed to be Poisson with different rates and the service processes are general and different at each node. In addition the token overhead is allowed to have an arbitrary but independent distribution at each node. Explicit, simply programmed equations are given. It is shown, arguing from the form of the equations, that there is a conservation law in effect in this system. If the nodal mean waiting times are weighted by the relative intensity, defined here as the intensity weighted mean, then the sum takes on a particularly simple form and is independent of the placement of the nodes on the ring. When the service means at each node are equal, this quantity is just the system mean waiting time. View full abstract»

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  • Robust Quantization of ε-Contaminated Data

    Page(s): 218 - 222
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    The problem of robust quantization of data with uncertain statistical properties is considered. Uncertainty in the statistics of the data is modeled by assuming that the data have a probability density function of the ε-contaminated form, and a minimax approach to robust design is adopted. An approximation is developed for the asymptotic worst-case distortion (over the ε-contaminated class) produced by an arbitrary companded quantizer, and the quantizer design which minimizes this worst-case distortion is derived. The robustness of the resulting design is verified numerically for the particular problem of quantizing ε-contaminated Gaussian data. View full abstract»

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  • A Use of Double Integration in Sigma Delta Modulation

    Page(s): 249 - 258
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    Sigma delta modulation is viewed as a technique that employs integration and feedback to move quantization noise out of baseband. This technique may be iterated by placing feedback loop around feedback loop, but when three or more loops are used the circuit can latch into undesirable overloading modes. In the desired mode, a simple linear theory gives a good description of the modulation even when the quantization has only two levels. A modulator that employs double integration and two-level quantization is easy to implement and is tolerant of parameter variation. At sampling rates of 1 MHz it provides resolution equivalent to 16 bit PCM for voiceband signals. Digital filters that are suitable for converting the modulation to PCM are also described. View full abstract»

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  • An ARQ Scheme with Memory and Soft Error Detectors

    Page(s): 285 - 288
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    This paper describes a technique for increasing the efficiency of an ARQ communication system utilizing error detection codes. In this technique the blocks containing errors are not discarded at the receiver, as in the conventional ARQ systems. Such blocks are retained in order to make use of the information contained in them. A reliability value is associated to each demodulated symbol; this reliability value is updated every time a new retransmission is made, even if the vector received is in error. The process of updating the symbols often eliminates automatically the errors introduced by the channel. The results obtained by means of a simulation show that this method offers a considerable reduction in the average number of retransmissions, in comparison with conventional ARQ systems. View full abstract»

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  • Multidestination Protocols for Satellite Broadcast Channels

    Page(s): 232 - 240
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    Two retransmission procedures, the go-back- N (GBN) scheme and the selective repeat (SR) scheme, have been analyzed for data transfer from one transmitter to many receivers. We consider transfer of error-controlled bulk data over a satellite broadcast channel. Two retransmission strategies, the dynamic retransmission group reduction (DRGR) technique and the fixed retransmission group (FRG) technique, are proposed. We study the GBN and SR schemes for both strategies. Analytic expressions are derived for the throughput performance of the GBN scheme and of the SR scheme with infinite resources, while discrete event simulation is used to estimate the throughput of the selective repeat scheme with finite resources. Only the SR scheme using the DRGR technique provides acceptable performance for high-speed bulk data transfer. For the DRGR technique, the throughput falls logarithmically with an increase in the number of receivers. In contrast, the throughput for the FRG technique falls exponentially with an increase in the number of receivers. View full abstract»

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  • Bounds and Approximations for Rapid Evaluation of Coherent MPSK Error Probabilities

    Page(s): 271 - 273
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    The error probability for MPSK detection is expressed here as a sum of a familiar upper-bound approximation and a correction term which is well suited for numerical integration. An asymptotic expansion of the correction term is derived, from which simple and extremely tight upper and lower bounds are obtained. Relative errors in using these bounds and approximations of them are graphed for cases of practical interest. View full abstract»

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  • Direct-Detection Optical Communication with Color Coded Pulse Position Modulation Signaling

    Page(s): 273 - 276
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    The performance characteristics of a direct-detection optical communication system, in which a laser transmitter sends short optical pulses of selected nonoverlapping center frequencies, are analyzed. It is shown that this signaling scheme can be used in conjunction with ReedSolomon coding to obtain high data rate, reliable communication under conditions of optimal energy efficiency. View full abstract»

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  • A Nonlinear Device to Suppress Strong Interfering Signals with Arbitrary Angle Modulation in Spread-Spectrum Receivers

    Page(s): 300 - 302
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    A device which can be used to suppress strong constantenvelope interfering signals at the input of spread-spectrum receivers is described and analyzed. Unlike similar circuits known from literature, this device is not restricted to the suppression of narrow-band jamming signals; it can also cope with broad-band interfering signals bearing any kind of angle modulation. The theoretical results are confirmed by measurements. 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