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Communications, IEEE Transactions on

Issue 4 • Date April 1989

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Displaying Results 1 - 16 of 16
  • Transmission performance analysis of a new class of line codes for optical fiber systems

    Page(s): 402 - 404
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (263 KB)  

    A family of mB(m+1)B binary, nonalphabetic, balanced line codes is presented that is suitable for high bit rate (>or=135 Mb/s) optical fiber transmission due to its relatively simple encoding and decoding rules. Here, B represents a block of m bits, where m is an odd number. The coding, decoding, and bit error rate (BER) performance of the codes are discussed. Statistical and spectral analysis for the specific case in which the number of bits, m, equals seven, is presented. This makes possible a detailed comparison of the proposed code with conventional 7B8B codes. View full abstract»

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  • A system for routing and capacity assignment in computer communication networks

    Page(s): 360 - 366
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    The combined problem of selecting a primary route for each communicating pair and a capacity value for each link in computer communication networks is considered. The network topology and traffic characteristics are given: a set of candidate routes and of candidate capacities for each link are also available. The goal is to obtain the least costly feasible design where the costs include both capacity and queuing components. Lagrangean relaxation and subgradient optimization techniques were used to obtain verifiable solutions to the problem. The method was tested on several topologies, and in all cases good feasible solutions, as well as tight lower bounds, were obtained. The model can be generalized to deal with different classes of customers, characterized by different priorities, message lengths, and/or delay requirements View full abstract»

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  • On the theory of importance sampling applied to the analysis of detection systems

    Page(s): 332 - 339
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (652 KB)  

    Detection systems are designed to operate with optimal or nearly optimal probability of a wrong decision. Analytical solutions of the performance of these systems have been very difficult to obtain. Monte Carlo simulations are often the most tractable method of estimating performance. However, in systems with small probability of error, this technique requires very large amounts of computer time. A technique known as importance sampling substantially reduces the number of simulation trials needed, for a given accuracy, over the standard Monte Carlo method. The theory and application of the importance sampling method in Monte Carlo simulation is considered in a signal detection context. A general method of applying this technique to the optimal detection problem is given. Results show that in cases examined, the gain is approximately proportional to the inverse of the error probability. Applications of the proposed method are not limited to optimum detection systems; analysis, leading to a measure of the gain in using this biasing scheme, shows that in all optimal systems considered, less than 100 trials is needed to achieve estimates with 45% confidence, even for extremely small error probabilities View full abstract»

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  • The analysis of a queue arising in overflow models

    Page(s): 367 - 372
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    A methodology is presented for analyzing a queuing submodel which frequently arises in the study of overflow models. In this submodel a finite capacity, multiserver queue with exponentially distributed service times, and arriving traffic consisting of a Poisson parcel and several overflow parcels, are assumed. By modeling the overflow parcels as interrupted Poisson processes, an exact queuing analysis is possible. The analysis yields the steady-state queue length distribution, and for each input parcel: (1) the steady-state queue length distribution at arrivals; (2) the probability that an arriving call is blocked (parcel blocking); and (3) the waiting time distribution of an arriving call, in addition to a complete characterization of the overflow due to each parcel View full abstract»

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  • Optical power requirements for detecting OOK and FSK signals corrupted by phase noise

    Page(s): 405 - 407
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    The decision of on-off keying (OOK) and frequency-shift keying (FSK) is considered for coherent lightwave communications in which the optical pulses are corrupted by the phase noise associated with nonzero laser linewidths. Heterodyne lightwave detection is assumed, followed by intermediate frequency filtering, envelope detection, and postdetection low-pass filtering. Using analytical results published previously, theoretical minimum values of the required average power are obtained in photons/bit, for achieving a bit error rate of 10-9. Numerical results are given as functions of laser linewidth-to-bit-rate ratio for OOK, binary FSK (or 2-FSK), and 8-FSK. It is shown that heterodyne detection for lightwave signals of this kind can be made highly robust to phase noise, in contrast to the case of binary phase-shift keying View full abstract»

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  • A limited sensing protocol for multiuser packet radio systems

    Page(s): 353 - 359
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    A protocol for a multiuser packet radio communication channel is proposed. The basic functions of this protocol are determined by a modified stack-type limited sensing collision resolution algorithm. The protocol is a hybrid of a pure random-access scheme and a reservation scheme. A message consists of a number of packets that are capable of revealing the current activity of the channel. The performance of the system is investigated in terms of throughput and average message delay and analytical results are provided View full abstract»

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  • Enhancement of one-dimensional variable-length DPCM images corrupted by transmission errors

    Page(s): 373 - 379
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    Methods are presented for enhancing one-dimensional variable-length differential pulse-code modulation (VLDPCM) images corrupted by transmission errors, are presented. The proposed methods take advantage of the VLDPCM code's high sensitivity to errors. Two methods are described. The first involves no increase of transmitted bit rate and consists of processing the corrupted image. The second method involves the transmission of additional information to enable an almost exact reconstruction of the original image. The amount of added redundancy can be reduced at the cost of performing more computations. In a simulation, the authors used less than 7% redundancy. Both methods achieve significant improvements which are demonstrated by the simulation results. The simulation results include original, corrupted, and enhanced images as well as the signal-to-noise ratio (SNR) versus bit-error rate (BER) curve. For BER 10-3, the SNR (signal-to-noise ratio) gains for the first and second methods are greater than 17 and 44 dB, respectively View full abstract»

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  • Simulation performance of optimal and suboptimal nonsynchronized receivers

    Page(s): 407 - 411
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    Two optimal receivers, along with their approximations derived for the optical on-off keying channel, are briefly described. These receivers make symbol decisions in the absence of synchronization. The various approximations to the optimal rules are derived. Computer simulations are presented that compare the performance of suboptimal receivers to that of jointly optimal receivers, as well as to receivers utilizing a separate synchronizer. It is observed that one of the approximations, which is rather simple to implement, performs as well as the significantly more complicated receiver that utilizes a separate, optimal, synchronizer. Further computer simulations show that the suboptimal receivers are quite robust to nonperfect knowledge of the received signal power View full abstract»

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  • Two-tier DPCM codec for videoconferencing

    Page(s): 380 - 386
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    A two-tier differential pulse-code modulation (DPCM) codec for videoconference applications is described that utilizes the so-called masking effect of motion. In this approach, an image is separated into high-frequency and low-frequency components. The low-frequency signal is processed by an adaptive spatiotemporal DPCM codec. A motion indicator derived from the low-frequency signal is used to control the corresponding block of high-frequency component pixels. The system is aimed at adaptively removing the high-frequency component of an image in those areas which contain motion. Since less information is needed to be sent, the data rate is lower. Since the missing high-frequency information occurs only in moving areas, the human eyes are less likely to notice. In this way, the data rate is lowered without unduly giving up on the subjective image quality. Simulation results have shown that the amount of visible degradation in image quality is small while the reduction in data rate is substantial View full abstract»

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  • An adaptive algorithm for the compression of computer data

    Page(s): 317 - 324
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (780 KB)  

    A scheme for compressing computer data by treating them as sequences of bytes is described. For each individual sequence to be compressed, a source model of predetermined complexity is built adaptively starting from a memoryless model. An alphabet reduction technique which permits handling of each bit within a byte separately is introduced. Variable-order Markov contexts are generated for each bit within a byte by a process of selective context splitting. The selection of a context for splitting is based on the context's probability as well as the bit entropy under the context. Estimation of bit statistics under the different contexts is made adaptively and encoding is accomplished by an arithmetic code. The scheme allows the complexity of the source model, and thereby the compression performance, to be altered easily. Experiments on typical computer files show that the present scheme, at a moderate complexity level, often outperforms some of the existing schemes View full abstract»

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  • A general analysis of bit error probability for reference-based BPSK mobile data transmission

    Page(s): 398 - 402
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    Unified analysis of the performance of binary phase shift keying (BPSK) under static and mobile operating conditions is presented for the case in which a separate reference tone is used for channel sounding and subsequent `coherent' data detection. It is shown that under both Rician and Rayleigh fading conditions, the use of a reference can eliminate the irreducible error rate phenomenon, with minimal sacrifice in bit error rate performance over an ideal BPSK system View full abstract»

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  • Soft-decision decoding applied to the generalized type-II hybrid ARQ scheme

    Page(s): 393 - 396
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    A generalized hybrid automatic-repeat-request (GH-ARQ) scheme using hard-decision decoding and variable depth (redundancy) for adaptive error control in digital communications systems has recently been proposed by S.D. Morgera and H. Krishna (see Digital Signal Processing over Finite Fields: Applications to Communications and Algebraic Coding Theories. New York: Academic, 1988). An important feature of the GH-ARQ scheme is that variable depth and, consequently, variable minimum distance, is possible with a single encoder/decoder configuration. The present authors use binary PSK signaling, an additive white Gaussian noise (AWGN) channel, and several relevant code parameter choices in computer simulations to illustrate the improvement in throughput efficiency when soft-decision decoding is used in the GH-ARQ method. From the computational complexity standpoint, the use of GH-ARQ soft-decision decoding is feasible, since the code lengths used are relatively short. Comparison of simulation results is also made to the soft-decision ARQ scheme of G. Benelli (see ibid., vol.COM-33, p.285-8, Mar. 1985) View full abstract»

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  • On the self-noise in QASK decision-feedback carrier tracking loops

    Page(s): 387 - 392
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    Quadrature amplitude-shift keying (QASK) is often used for transmitting two digital data streams in bandwidth-constrained communication systems. Previous analyses of the tracking performance of a decision-feedback carrier tracking loop, which can be used to provide a carrier reference for a QASK signal set, have neglected the effects of the self-noise in the derivation of the loop resonance. The authors incorporate the effects of the self-noise will only result in a conservative assessment of the system's performance, contrary to what might be expected. All results obtained are in closed form and can easily be evaluated numerically for performance prediction purposes View full abstract»

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  • Troposcatter link performance in the presence of two jammers

    Page(s): 325 - 331
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    Performance predictions of a Rayleigh fading channel are calculated for a troposcatter radio in the presence of two line-of-sight (LOS) jammers. The receiver incorporates dual main antennas and a sidelobe canceller. The countermeasure approach used is array processing. A communications approach is taken, with the goal of deriving an analytic expression for the bit error rate, in terms of the signal-to-noise ratio. After deriving the general solution, an approximation is introduced and proposed as an alternative measure of performance. It is insensitive to the fine-grain structure of the problem geometry, and it contains a minimal number of parameters, namely, the various signal energies reaching the receiver View full abstract»

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  • Dynamic range and other fundamentals of the complex Bessel function series approximation model for memoryless nonlinear devices

    Page(s): 397 - 398
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    An explanation is given of the application of the complex Bessel function series approximation model of the memoryless amplitude and phase characteristics of nonlinear devices. Confusion had arisen because of the choice of a value of a parameter in the approximating expression. The practice had been to choose this simply as though it was just an arbitrary constant which scales the input, or as an optimizing parameter in the effort to get a best fit of the approximation to the measured data. By examining the derivation of the particular approximation, a determining and important link between this parameter and the desired operating dynamic range of the nonlinear characteristic being approximated is shown. How values for this parameter are calculated in terms of input overdrive relative to device saturation is also shown. In examining the origin of the approximating expressions, an alternative and simpler derivation to that given by J.C. Fuenzalida et al. (1973) is presented that is based on the work of M.J. Eric et al. (1972) View full abstract»

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  • A new approximation to the symbol error probability for coded modulation schemes with maximum likelihood sequence detection

    Page(s): 340 - 352
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1028 KB)  

    The power efficiency of coded modulation schemes in additive white Gaussian noise depends on the signal space distribution of their most common error events. Symbol error probability calculation allowing for the pairwise interaction of these error events is discussed. Two optimality criteria are considered for detectors. The first minimizes the probability of symbol error for each symbol decision. This is called the symbol-to-symbol detector. The second (which is superior) is the maximum likelihood sequence detector (MLSD). A lower bound for the symbol-to-symbol detector and an approximation to the MLSD symbol error probability are described. The theoretical performance difference between these two detectors is given. The results are more accurate than minimum squared Euclidean distance predictions, especially at low and intermediate signal-to-noise ratios. The MLSD symbol error probability approximation is obtained for considerably less cost than computer simulation and gives more insight into the signal space structure of the scheme being analyzed. Numerical results are presented for a continuous phase modulation (CPM) example 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