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Communications, IEEE Transactions on

Issue 4 • Date Apr 1988

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Displaying Results 1 - 19 of 19
  • Detection of coded modulation signals on linear, severely distorted channels using decision-feedback noise prediction with interleaving

    Page(s): 401 - 409
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    On linear bandlimited Gaussian noise channels with sufficiently high SNR, channel capacity can be approached by combining powerful coded modulation schemes designed for Nyquist channels with the equalization power of decision-feedback equalization (DFE). However, this combination may not be realized in a straightforward manner, since, in general, DFE requires delay-free decisions for feedback, and in a coded system such decisions are not sufficiently reliable. A technique is proposed that combines periodic interleaving with noise-predictive DFE, so that delayed reliable decisions can be used for feedback. When sufficient delay in the interleavers can be tolerated, this technique can attain the DFE performance. On severely distorted channels, modest delays can be sufficient to obtain respectable gains over linear equalization View full abstract»

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  • Interpolative vector quantization of color images

    Page(s): 465 - 470
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    Interpolative vector quantization has been devised to alleviate the visible block structure of coded images plus the sensitive codebook problems produced by a simple vector quantizer. In addition, the problem of selecting color components for color picture vector quantization is discussed. Computer simulations demonstrate the success of this coding technique for color image compression at approximately 0.3 b/pel. Some background information on vector quantization is provided View full abstract»

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  • Synchronization over fading dispersive channels

    Page(s): 499 - 505
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    An investigation is reported of an acquisition system for digital communication over fading dispersive channels that is optimum in the maximum-likelihood sense. A performance measure for the synchronizer in the acquisition mode is defined. Upper and lower bounds on the performance measure are derived. The effective bounds on parameters, such as signal-to-noise ratio, pulse width and modulation, number of pulses, spread of the channel, and the size of the resolution cell, on the performance of the synchronizer is investigated View full abstract»

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  • Refinements to the theory of error rates for narrow-band digital FM

    Page(s): 509 - 513
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    The bit-error-rate performance of narrowband digital FM with limiter-discriminator detection is considered for the cases of integrate and dump postdetection filtering with partial-bit integration, and sample-and-hold bit detection at the discriminator output. Error rate curves are presented for Gaussian, six-element Butterworth, and two-stage synchronously tuned IF filters. The calculations illustrate just how much more Eb/N0 is required as the partial-bit integration time goes from 100% down to the limiting case of sample and hold. The results show that it is important to have a well-designed IF filter especially if the entire bit time is not available for detection View full abstract»

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  • On Poisson contention resolution problem with feedback based on conflict intensity

    Page(s): 513 - 516
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    Communication over a random multiple-access, time-slotted, packet-switched, collision-type, broadcast channel with feedback is considered under a Poisson infinite-user model. The feedback generated by the channel provides some information about the intensity of conflicts. Two conflict-resolution algorithms are discussed for the above channel; they achieve throughputs of 0.334 and 0.369, respectively. The modification technique used to arrive at the second algorithm is emphasized. It is pointed out that the modification technique could be helpful in improving the performance of the conflict-resolution algorithms operating under other types of feedback View full abstract»

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  • PN code synchronization effects on narrow-band interference rejection in a direct-sequence spread-spectrum receiver

    Page(s): 420 - 429
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (820 KB)  

    The impact of imperfect synchronization on the performance of prediction-error interference rejection filters in noncoherent direct-sequence (DS) spread-spectrum communications is considered. Bit-error-rate analysis (BER) analysis (BER) of binary DPSK (differential phase-shift keying) data modulation used in conjunction with direct-sequence spread-spectrum is used as a performance measure. A first-order noncoherent delay-lock loop is used for the pseudonoise (PN) code tracking. Conditional BER results for the DS/DPSK systems for fixed values of the code tracking error are obtained. The average BER of the system is then evaluated by averaging the conditional BER expressions over the probability density function of the code tracking error. Results include the effects of both a single fading tone and a narrowband Gaussian interferer on the overall system performance. Interferer offset frequency is considered in determining the code tracking loop noise as well as the receiver BER View full abstract»

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  • Rate-compatible punctured convolutional codes (RCPC codes) and their applications

    Page(s): 389 - 400
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    The concept of punctured convolutional codes is extended by punctuating a low-rate 1/N code periodically with period P to obtain a family of codes with rate P/(P+l), where l can be varied between 1 and (N-1)P. A rate-compatibility restriction on the puncturing tables ensures that all code bits of high rate codes are used by the lower-rate codes. This allows transmission of incremental redundancy in ARQ/FEC (automatic repeat request/forward error correction) schemes and continuous rate variation to change from low to high error protection within a data frame. Families of RCPC codes with rates between 8/9 and 1/4 are given for memories M from 3 to 6 (8 to 64 trellis states) together with the relevant distance spectra. These codes are almost as good as the best known general convolutional codes of the respective rates. It is shown that the same Viterbi decoder can be used for all RCPC codes of the same M. the application of RCPC codes to hybrid ARQ/FEC schemes is discussed for Gaussian and Rayleigh fading channels using channel-state information to optimise throughput View full abstract»

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  • Automatic decision threshold level control (ADTLC) in direct-sequence spread-spectrum systems based on matched filtering

    Page(s): 519 - 527
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    An automatic decision threshold level control (ADTLC) algorithm for direct-sequence spread-spectrum systems is described and analyzed. Two parameters of interest, probability of false alarm Pa and probability of correct signal detection Pd, are controlled simultaneously. As an example, the implementation of the algorithm in several practical direct-sequence spread-spectrum receivers is discussed. A considerable advantage of this algorithm compared to the classical approach (constant false alarm probability control) to the problem is demonstrated View full abstract»

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  • A new algorithm for performance analysis of communication systems

    Page(s): 516 - 519
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    An algorithm is proposed for generating in order the most likely states of a probabilistic system, thus allowing a more-rapid procedure than previously available for analyzing the performance of communication networks with stochastically failing components. The algorithm improves the algorithm reported by Y. F. Lam and V.O.K. Li (ibid., vol.COM-34, no.5, p.496-7, May 1986), in terms of both storage requirements and execution efficiency View full abstract»

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  • A comparison between CCITT Recommendation X.25 and international standards 8208 and 7776

    Page(s): 492 - 498
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    CCITT Recommendation X.25 defines the interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) operating in packet mode over a dedicated circuit. As such, X.25 views the interface from the perspective of the DCE and is written specifically for a DTE/DCE interface between host and network. ISO (International Organization for Standardization) standards 7776 and 8208 are the ISO versions of the X.25 link and packet levels, respectively, but have a wider scope than X.25 in also describing a DTE/DTE interface. Furthermore, ISO 8208 provides guidelines for connecting a private data network to a public data network using X.25 procedures. An overview of the technical difference between X.25 and the two ISO standards is presented View full abstract»

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  • Locating concentrators for primary and secondary coverage in a computer communications network

    Page(s): 450 - 458
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    A model is developed that assigns primary and secondary (backup) concentrator coverage to each terminal site. The objective is to minimize communications costs as well as costs for setting up and operating the concentrators subject to capacity constraints. A relaxation of the problem is studied, and an effective solution procedure that makes the use of this relaxation is developed. Experimental results over a wide range of problem structures show that this solution procedure is very effective. It is also found to be significantly faster than a state-of-the-art commercial integer programming package View full abstract»

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  • Matched chirp modulation: detection and performance in dispersive communication channels

    Page(s): 506 - 509
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    Matched chirp modulation (MCM) is an improved version of chirp modulation (CM) in which the frequency sweep rate is matched to the dispersion parameters of the communication channel. It is an attractive constant-envelope digital modulation technique for adaptive transmission over dispersive communication channels. The performance of the optimum noncoherent (NC) and partially coherent (PC) receivers for MCM is analyzed and evaluated. In particular, the optimum value of the time-bandwidth product is evaluated, and the probability of error is calculated for the optimum NC and PC receivers View full abstract»

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  • A graphical methodology for simulating communication networks

    Page(s): 459 - 464
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    A novel approach for simulating communication networks is discussed and illustrated with two examples of a token-passing network. The method is based on a graphical representation of the network consisting of three components: topology, nodes, and protocols. The topology and nodes are drawn to a network specification. The protocols are drawn by using Petri nets with some extended features. A simulation model can be automatically generated from this representation. Results of the simulation are compared to those of an analytical model, showing excellent agreement View full abstract»

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  • Error-correcting codes and nonlinear diversity combining against worst case partial-band noise jamming of frequency-hopping MFSK systems

    Page(s): 471 - 478
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    Error probability analyses are performed for a coded M-ary frequency-shift keying system (MFSK) using L hops per M-ary word frequency-hopping spread-spectrum waveforms transmitted over a partial-band Gaussian noise jamming channel. The bit error probabilities are obtained for a square-law adaptive gain control receiver with forward-error-control coding under conditions of worst-case partial-band noise jamming. Both thermal noise and jamming noise are included in the analyses. Performance curves are obtained for both block codes and convolutional codes with both binary and M-ary channel modulations. The results show that thermal noise cannot be neglected in the analysis if correct determinations of the optimum order of diversity and the worst-case jamming fraction are to be obtained. It is shown that the combination of nonlinear combining, M -ary modulation, and forward-error-control coding is effective against worst-case partial-band noise jamming View full abstract»

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  • Multiple trellis coded modulation (MTCM)

    Page(s): 410 - 419
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    The authors demonstrate a trellis coded modulation technique referred to as multiple trellis coded modulation (MTCM) wherein more than one channel symbol per trellis branch is transmitted. They have found simple two-state trellis codes for symmetric MPSK multiple phase-shift keying and AM modulations that can achieve 3-dB gain over uncoded modulation at very high signal-to-noise ratios without bandwidth expansion or reduction in information bit rate. The gain of these codes with respect to previously reported two-state trellis codes is between 1 and 2 dB at very high signal-to-noise ratios, depending on the number of bits per Hertz transmitted. These gains are achieved for those of the equivalent conventional trellis codes with the same number of states in the trellis diagram. The authors note that additional computations per branch are needed for the multiple trellis coding scheme. The concept can be extended to a higher number of states and other types of modulations View full abstract»

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  • On the performance effects of station locations and access protocol parameters in Ethernet networks

    Page(s): 441 - 449
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    A simulation study is presented in several distributions of stations on a linear-bus Ethernet. Aggregate performance is shown to depend on the distribution of stations. Individual station performance varies with the location of the station. Unbalanced distributions can lead to large performance differences between individual stations, with isolated stations achieving relatively poor performance compared to the average. The effects of access protocol parameters such as the number of buffers per station and the retransmission algorithm are examined. A modification of the standard retransmission algorithm is presented that enables a higher throughput to be achieved at high load. The results are compared to the predictions of theoretical models, and the applicability of the models to finite-population Ethernets is examined View full abstract»

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  • Channel allocation protocols in frequency-time controlled high speed networks

    Page(s): 430 - 440
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    In conventional high-speed systems, the high ratio between the end-to-end propagation delay and the message transmission time severely restricts the system performance. Thus, the increase in channel bandwidth may be accompanied by only a marginal increase in actual system capacity. A combined frequency-time division-based control of the high-speed channel that significantly reduces this problem is proposed. The design of protocols subject to the unique channel control penalties of the resulting multichannel system is considered. The allocation of channels on a demand assignment basis is hindered in the multichannel configuration by the time penalty involved in locating an idle channel and by practical limitations on the transmit/receive multichannels mode interface. A new class of fixed allocation protocols is introduced in which the channel access is obtained without the aforementioned penalties. The protocols build on the allocation of source and destination oriented transmission rights, taking into account the implementation aspects of multichannel networks. It is shown that this class of protocols covers the whole range of random-access to fixed-channel-access control policies. An analytic approach for a uniform analytic treatment is introduced, showing the potential for a significant improvement in the system capacity and the average message delay View full abstract»

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  • Accurate method for analysis of a packet-speech multiplexer with limited delay

    Page(s): 479 - 483
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    In a packet-speech multiplexer with limited delay, packets arriving once the queue has reached a certain limit are either discarded, or if embedded encoding has been used, shortened. The uniform arrival and service model, which assumes that the information flow in and out of the multiplexer is uniform rather than in discrete packets, is used to analyze such a multiplexer. The equilibrium queue distribution is described by a set of differential equations that can be solved, together with a set of boundary equations describing the queue behavior at its limits, to yield equilibrium distributions of delay and packet loss. Comparisons to simulations using data collected from real conversations show that the packet loss can be determined accurately if the delay limit is less than 400 ms and more than half the packet length View full abstract»

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  • The rearrangement process in a two-stage broadcast switching network

    Page(s): 484 - 491
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    The rearrangement process in the two-stage broadcast switching network presented by F.K. Hwang and G.W. Richards (ibid., vol.COM-33, no.10, p.1025-1035, Oct. 1985) is considered. By defining a certain function it is possible to calculate an upper bound on the number of connections to be moved during a rearrangement. When each inlet channel appears twice, the maximum number of connections to be moved is found. For a special class of inlet assignment patterns in the case of which each inlet channel appears three times, the maximum number of connections to be moved is also found. In the general case, an upper bound is given when the number of outlets at each second-stage switch is kept below a certain bound 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