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Communications, IEEE Transactions on

Issue 10 • Date Oct. 1993

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Displaying Results 1 - 18 of 18
  • Comments on "The effect of capture on performance of multichannel slotted ALOHA systems

    Page(s): 1433 - 1435
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (181 KB)  

    The commenters offer a counterexample to the results presented by W. Yue (see ibid., vol.39, no.6, p.818-22, June 1991) concerning the effect of capture on multichannel slotted ALOHA. A simplified deterministic capture is assumed by Yue. Numerical results show that the actual average throughput is much higher than that obtained by Yue for the same parameters.<> View full abstract»

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  • Topology control for multihop packet radio networks

    Page(s): 1474 - 1481
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    A distributed topology-control algorithm has been developed for each node in a packet radio network (PRN) to control its transmitting power and logical neighbors for a reliable high-throughput topology. The algorithm first constructs a planar triangulation from locations of all nodes as a starting topology. Then, the minimum angles of all triangles in the planar triangulation are maximized by means of edge switching to improve connectivity and throughput. The resulting triangulation at this stage, the Delaunay triangulation, can be determined locally at each node. The topology is modified by negotiating among neighbors to satisfy a design requirement on the nodal degree parameter. Simulations show that the final topology is degree-bounded, has a rather regular and uniform structure, and has throughput and reliability that are greater than that of a number of alternative topologies View full abstract»

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  • Maximum number of independent paths and radio connectivity

    Page(s): 1482 - 1494
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1012 KB)  

    Methods for determining the network reliability of a multihop packet radio network in the presence of hostile jammers are discussed. A new connectivity parameter called radio connectivity is defined as the maximum number of disjoint communication paths that are still usable between given nodes s and d after the jammer is on or, more generally, the minimum number of jammers needed to disconnect s and d. A lower bound on the radio connectivity is computed by studying the number of jamming independent paths. The time complexity of obtaining the radio connectivity is analyzed and shown to be NP-hard except for some special cases. Greedy heuristics for developing approximate answers for general networks are described. Euclidean networks, in which the nodes and links correspond to points and line segments in the Euclidean geometry and satisfy Euclid's four fundamental axioms, are also discussed. It is found that the maximum number of independent paths between a pair of source and destination nodes that can possibly exist is five. An extension in which there is a protected zone of known size around the sender and receiver is studied View full abstract»

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  • Performance analysis of a multiple-access ring network

    Page(s): 1494 - 1506
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1256 KB)  

    The authors model the delay-throughput performance of a class of multiple-access circuit-switched ring local area networks that allow multiple messages to be transferred concurrently on the ring. In particular, they model analytically the PLAYTHROUGH protocol under assumptions of uniform and symmetric traffic, infinite buffers, and a first-in, first-out (FIFO) queueing discipline at each station to predict message mean waiting times that adequately approximate waiting times observed through simulation. The queue is analyzed at an arbitrary station as a M/G/1 vacation system having a Bernoulli schedule with parameter p. Expressions for the vacation duration and p are derived in terms of service times and competing traffic intensities on PLAYTHROUGH rings. The vacation period is modeled as a series of subvacations because the server is allowed to take multiple subvacations when the queue is nonempty. Application of this modeling strategy is shown to provide good agreement between analytical predictions and simulation results. The performance of this class of networks is compared with that of token rings View full abstract»

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  • Sea surface scattering calculations in maritime satellite communications

    Page(s): 1525 - 1533
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    A method extending the Kirchhoff classical approach for mobile maritime satellite communications is presented. Carrier to specular and carrier to multipath ratios are evaluated from scattering by the rough sea surface calculations using the boundary perturbation method. They are compared with experimental results and with other experimental models. The results illustrate the limited effects of the wind speed and significant wave height, the important dependence on the elevation angle and the very large effects of the ship motions View full abstract»

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  • Design and analysis of a fast frequency-hopped DBPSK communication system. I. System description and hop timing tracking loop analysis

    Page(s): 1552 - 1564
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (860 KB)  

    Design and performance analyses of a fast frequency-hopped (FFH) spread spectrum communication system employing differential binary phase shift keying (DBPSK) modulation and differentially coherent demodulation are presented. The receiver utilizes a hop timing tracking loop to lock the hop clock. Through this tracking loop, the differentially coherent demodulation of an FFH signal is made possible. The authors present the system model of an FFH/DBPSK system. A digital, full-time early-late gate timing error estimator is investigated. The tracking loop is shown to be a Markov chain, and various performance characteristics of the tracking loop are studied View full abstract»

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  • Throughput analysis of tandem-type go-back-N ARQ scheme for satellite communications

    Page(s): 1517 - 1524
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    The tandem-type go-back-N (GBN) scheme has been proposed for satellite communications to reduce the long roundtrip delay using the onboard processing of satellites. The author considers the exact analysis of the throughput performance of this scheme and its application to a broadcast communications system such as a point-to-multipoint file transfer system. First, the throughput expression for the point-to-point tandem-type GBN scheme is derived. Second, applying the results of this point-to-point tandem-type GBN scheme to a broadcast (point-to-multipoint) communications system, the relationship of the number of receiving stations to the link bit error rate and the roundtrip propagation delay is shown View full abstract»

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  • Maximally smooth image recovery in transform coding

    Page(s): 1544 - 1551
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    The authors consider the reconstruction of images from partial coefficients in block transform coders and its application to packet loss recovery in image transmission over asynchronous transfer mode (ATM) networks. The proposed algorithm uses the smoothness property of common image signals and produces a maximally smooth image among all those with the same coefficients and boundary conditions. It recovers each damaged block by minimizing the intersample variation within the block and across the block boundary. The optimal solution is achievable through two linear transformations, where the transform matrices depend on the loss pattern and can be calculated in advance. The reconstruction of contiguously damaged blocks is accomplished iteratively using the previous solution as the boundary conditions in each new step. This technique is applicable to any unitary block-transform and is effective for recovering the DC and low-frequency coefficients. When applied to still image coders using the discrete cosine transform (DCT), high quality images are reconstructed in the absence of many DC and low-frequency coefficients over spatially adjacent blocks. When the damaged blocks are isolated by block interleaving, satisfactory results have been obtained even when all the coefficients are missing View full abstract»

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  • Coded modulation with unequal error protection

    Page(s): 1439 - 1449
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (924 KB)  

    It is always desirable to maintain communications in difficult situations, even though fewer messages can get across. The author has developed such capabilities for one-way broadcast media, such as the envisioned terrestrial broadcasting of digital high-definition television signals. In this television broadcasting, the data from video source encoders are not equally important. It is desirable that the important data be recovered by each receiver even under poor receiving conditions. Two approaches for providing such unequal error protection to different classes of data are presented. Power-efficient and bandwidth-efficient coded modulation is used in both approaches. The first approach is based on novel signal constellations with nonuniformly spaced signal points. The second uses time division multiplexing of different conventional coded modulation schemes. Both approaches can provide error protection for the important data to an extent that can hardly be achieved using conventional coded modulation with equal error protection. For modest amounts of important data, the first approach has, additionally, the potential of providing immunity from impulse noise through simple bit or signal-point interleaving View full abstract»

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  • A simple and effective precoding scheme for noise whitening on intersymbol interference channels

    Page(s): 1460 - 1463
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    A precoding scheme for noise whitening on intersymbol interference (ISI) channels is presented. This scheme is compatible with trellis-coded modulation and, unlike Tomlinson precoding, allows constellation shaping. It can be used with almost any shaping scheme, including the optimal SVQ shaping, as opposed to trellis precoding, which can only be used with trellis shaping. The implementation complexity of this scheme is minimal-only three times that of the noise prediction filter, hence effective noise whitening can be achieved by using a high-order predictor View full abstract»

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  • An algorithmic approach to the optimization of importance sampling parameters in digital communication system simulation

    Page(s): 1464 - 1473
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    Importance sampling is recognized as a potentially powerful method for reducing simulation runtimes when estimating the bit error rate (BER) of communications systems using Monte Carlo simulation. Analytically, minimizing the variance of the importance sampling (IS) estimator with respect to the biasing parameters has typically yielded solutions for systems for which the BER could be found analytically. A technique for finding an asymptotically optimal set of biasing parameter values, in the sense that as the resolution of the search and the number of runs used both approach infinity, the algorithm converges to the true optimum, is proposed. The algorithm determines the amount of biasing that minimizes a statistical measure of the variance of the BER estimate and exploits a theoretically justifiable relationship, for small sample sizes, between the BER estimate and the amount of biasing. The translation biasing scheme is considered, although the algorithm is applicable to other parametric IS techniques. Only mild assumptions are required of the noise distribution and system. Experimentally, improvement factors ranging from two to eight orders of magnitude are obtained for a number of distributions for both linear and nonlinear systems with memory View full abstract»

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  • Performance evaluation of input and output queueing techniques in ATM switching systems

    Page(s): 1565 - 1575
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (836 KB)  

    Modeling alternatives for a fast packet switching system are analyzed. A nonblocking switch fabric that runs at the same speed as the input/output links is considered. The performance of the considered approaches are derived by theoretical analysis and computer simulations. Performance comparison between input queueing approaches with different selection policies are presented. Novel input and output queueing techniques are also proposed. In particular it is shown that, depending on the implementation, the input queueing approach studied in this paper achieves the same performance as the optimum (output) queueing alternative, without resorting to a faster packet switch fabric View full abstract»

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  • Analysis of a direct-sequence spread-spectrum cellular radio system

    Page(s): 1507 - 1517
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    The uplink and downlink performance of a digital cellular radio system that uses direct sequence code division multiple access is evaluated. Approximate expressions are derived for the area averaged bit error probability while accounting for the effects of path loss, log-normal shadowing, multipath-fading, multiple-access interference, and background noise. Three differentially coherent receivers are considered: a multipath rejection receiver, a RAKE receiver with predetection selective diversity combining, and a RAKE receiver with postdetection equal gain combining. The RAKE receivers are shown to improve the performance significantly, except when the channel consists of a single faded path. Error correction coding is also shown to substantially improve the performance, except for slowly fading channels View full abstract»

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  • Adaptive DCT coding of video signals

    Page(s): 1534 - 1543
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A coefficient-by-coefficient adaptive discrete cosine transform (DCT) is investigated. The interframe DCT has been known to possess an adverse effect in that it generates mosquito and blocking noise. By analyzing DCT for the intraframe and the interframe video signals, a new adaptive intra/interframe DCT is developed. Cases without and with the movement-compensation are discussed separately. Through simulations, it is shown that a substantial improvement gain (1.0-5.0 dBp-p or 0.2-2.0 dBp-p, respectively) can be obtained by the new adaptive method. The improvement is brought about by the reduction of the blocking noise conventionally generated by the coarse quantization of the higher order interframe DCT coefficients. By calculating the improvement bound, a further possibility is discussed View full abstract»

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  • A simple exact method for generating continuous phase modulated signals

    Page(s): 1429 - 1432
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    A new, relatively simple architecture for generating continuous phase modulation (CPM) signals is presented. It can produce arbitrary frequency pulses for binary full-response signals with arbitrary modulation indexes. It can also produce partial-response signals or M -ary signals with reasonable accuracy. The method filters and then hard limits the switched and summed outputs of a 90° hybrid View full abstract»

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  • A phase modulator with variable maximum phase deviation

    Page(s): 1425 - 1428
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    A phase modulator, constructed with three Armstrong modulators, is presented. In this modulator, the maximum phase deviation can be extended up to π without frequency multiplication. Numerical results of the signal distortion are given for several values of the maximum phase deviation and compared to other Armstrong type phase modulators View full abstract»

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  • Interpolative BTC image coding with vector quantization

    Page(s): 1436 - 1438
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    The authors suggest two interpolative block truncation coding (BTC) image coding schemes with vector quantization and median filters as the interpolator. The first scheme is based on quincunx subsampling and the second one on every-other-row-and-every-other-column subsampling. It is shown that the schemes yield a significant reduction in bit rate at only a small performance degradation and, in general, better channel error resisting capabilities, as compared to the absolute moment BTC. The methods are further demonstrated to outperform the corresponding BTC schemes with pure vector quantization at the same bit rate and require minimal computations for the interpolation View full abstract»

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  • Multifrequency trellis coding with low delay for fading channels

    Page(s): 1450 - 1459
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    An L-frequency trellis coding scheme designed for fading channels that provides diversity up to order L is described. L-frequency coding is advantageous over channel coding schemes that achieve implicit time-diversity through trellis coding in conjunction with time-interleaving because it requires negligible end-to-end delay. The authors derive an upper-bound for the probability of symbol error of the L-frequency code. Based on this upper-bound, they then deduce the design criteria for optimum L-frequency codes. A numerical approximation to this upper-bound and the design of a two-state and two four-state, two-frequency codes are presented. Through simulations, it was found that relative to the traditional dual frequency diversity approach, the two-state and four-state codes achieve 3- and 4-dB coding gains, respectively. This energy efficiency gain can be translated into a spectral efficiency gain. A brief discussion on the difference in code design techniques for the Gaussian channel and the fading channel is also presented 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