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Communications, IEEE Transactions on

Issue 7 • Date Jul 1988

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Displaying Results 1 - 17 of 17
  • Cycle slips in synchronizers subject to smooth narrow-band loop noise

    Publication Year: 1988 , Page(s): 867 - 874
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    The cycle slipping in synchronizers subject to smooth narrowband loop noise is discussed. Such loop noise is shown to occur in repeater chains and in ring local area networks. The average rate of cycle slips and of bursts of cycle slips is evaluated, and closely approximated by a very simple expression that clearly indicates the influence of the loop noise bandwidth and the phase-detector characteristic. A comparison to the case of white loop noise reveals that, for most phase-detector characteristics, the slip rate caused by smooth narrowband loop noise is larger by several orders of magnitude than for white loop noise View full abstract»

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  • Multipath propagation measurements on an overwater path in New Zealand

    Publication Year: 1988 , Page(s): 781 - 788
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The results are described of a 140 Mb/s, 16 QAM digital microwave radio field trial to characterize multipath fading on a 60-km overwater route in New Zealand. Propagation data have been collected from the path between September 1985 and September 1986, and include one fading season of the Southern Hemisphere. The authors specifically apply and extend work on multipath fading by W.D. Rummler and others (1979, 1981, 1986). To the spectral data collected from the trial, a Rummler-type model (echo delay 6.35 ns) has been fitted. Distributions for the parameters a, b, and fo ar observed to be similar to those presented by Rummler (1979) for the 26.4-mile Atlanta to Palmetto, Georgia path. Data which cannot be characterized well by the Rummler model include samples which show the evidence of a ray with equivalent long delay (⩾10 ns). This ray is either conjectured to be a sea reflection (however sea reflections are blocked at an Earth radius factor of k=4/3), or is indicative of the presence of more than one secondary ray View full abstract»

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  • Realization of IIR LDM digital filters

    Publication Year: 1988 , Page(s): 888 - 891
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    A method is presented of realizing an infinite impulse response (IIR) digital filter (DF) using linear delta modulation (LDM) as a simple analog/digital (A/D) converter. This method makes the realization of IIR digital filters much simpler than that of conventional ones because it does not require hardware multipliers or a pulse code modulation (PCM) A/D converter. Compared to the finite impulse response (FIR) LDMDF, this IIR LDMDF requires significantly less computation time View full abstract»

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  • Block-inversion-coded QAM systems

    Publication Year: 1988 , Page(s): 797 - 805
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    A novel block inversion code (BIC) which is both simple and effective in controlling low-frequency components of multilevel data signals is introduced, and its power spectrum is analyzed. The BIC's effect on the performance of QAM modems is studied, and an expression for the coded modem's symbol error rate is obtained. The code allows M-ary QAM system designs to incorporate unmodulated carrier-pilot insertion techniques using high-pass filters, for more robust, unambiguous carrier recovery and automatic gain control. The effect of BIC coding on the performance of a 256 QAM modem with carrier-pilot insertion using high-pass filters is investigated. It is found that, under some circumstances, BIC coding can significantly reduce the ill-effect of the high-pass filter on the modem's performance View full abstract»

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  • Analysis of a hybrid multiple access protocol with free access of new arrivals during conflict resolution

    Publication Year: 1988 , Page(s): 806 - 815
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    A hybrid multiple access protocol (HYMAP) was proposed by M. Rios and N.D. Georganas (1985), combining the best features of CSMA/CD and of a conflict-free protocol. Control is transferred from one protocol to the other according to state information sensed on the channel. The performance of HYMAP was evaluated by computer simulation. An exact analysis of this hybrid protocol is presented. Since HYMAP permits free access of new arrivals during collision resolution, the mean length of the conflict-free period is determined by solving a large system of linear equations. The basic mean performance measures (throughput, delay) can then be easily computed and compared to the performance of CSMA/CD View full abstract»

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  • Effects of solar transit in Ku-band VSAT systems

    Publication Year: 1988 , Page(s): 892 - 894
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    Behavior of networks of very small aperture satellite terminals (VSATs) operating at Ku band during the solar transit period, is compared to more traditional C or Ku-band satellite networks. Based on analyses and experiments, it is explained why solar transit outages are rarer in Ku-band VSAT systems than conventional satellite communications systems. In many cases, Ku-band VSAT systems will operate through periods of Sun transits without any significant increase in transmission error rates or incidences of link outages View full abstract»

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  • Routing with packet duplication and elimination in computer networks

    Publication Year: 1988 , Page(s): 860 - 866
    Cited by:  Papers (10)  |  Patents (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    Packet duplication is discussed as a means of increasing network reliability in an environment where packet loss exists. Several methods of routing the duplicates are presented, one of which-the st-numbering-is shown to have the combined advantage of using disjoint paths and more even utilization of network resources. An additional mechanism, deliberate packet elimination, is introduced as a means of controlling congestion that may result, in part, from the duplication. A comprehensive model is defined encompassing the process of packet duplication together with both forms of packet elimination. Within this model, a cost function based on average packet delay is defined. A quasi-static distributed algorithm is developed that is optimal, deadlock free, and loop free. Extension of the model to include packet retransmission is considered View full abstract»

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  • Sequential decoding with ARQ and code combining: a robust hybrid FEC/ARQ system

    Publication Year: 1988 , Page(s): 773 - 780
    Cited by:  Papers (43)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    Sequential decoding with ARQ (automatic-repeat-request) and code combining under the timeout condition is considered. That is, whenever the decoding time of a given packet exceeds some predetermined duration, decoding is stopped and retransmission of the packet is requested. However, the unsuccessful packets are not discarded, but are combined with their retransmitted copies. It is shown that the use of code combining allows sequential decoding to operate efficiently even when the coding rate R exceeds the computational cutoff rate R comp. Furthermore, an analysis of the selective-repeat ARQ scheme shows that the use of code combining yields a significant throughput even at very high channel error rates, thus making the system very robust under severe degradations of the channel View full abstract»

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  • Bit error probability calculations for convolutional codes with short constraint lengths on very noisy channels

    Publication Year: 1988 , Page(s): 885 - 888
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    A technique for estimating convolutional code performance on very noisy channels is considered. Specifically, the performance of short constraint length codes operating near the channel cutoff rate is estimated. Decoding convolutional codes with a sliding window decoder (SWD) are considered. This decoder is an optimal (maximum likelihood) symbol decoder as the window size grows toward infinity, while the Viterbi decoder is the maximum-likelihood sequence estimator. The difference in the decoded BERs (bit error rates) between the two decoders is very small and approaches zero asymptotically as the channel BER decreases. Therefore, an estimate on the decoded BER for the SWD can also be used as an estimate of the decoded BER for Viterbi decoding View full abstract»

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  • Adaptive harmonic noise cancellation with an application to distribution power line communications

    Publication Year: 1988 , Page(s): 875 - 884
    Cited by:  Papers (10)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    Adaptive LMS (least mean squares) filter are applied to cancel harmonic noise. Simulations were done using actual noise recorded at a distribution power substation. Two implementation methods are discussed. Using the characteristic properties of the noise, a constrained filter is proposed which greatly reduces computation without reducing its effectiveness. It is shown that both constrained and unconstrained adaptive noise cancellation filters can be used effectively. For either case, significant improvement in the error rate is obtained View full abstract»

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  • Selective fading on LOS microwave links: classical and spread-spectrum measurement techniques

    Publication Year: 1988 , Page(s): 789 - 796
    Cited by:  Papers (5)  |  Patents (101)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    A survey is presented of techniques for measuring selective fading on line-of-sight (LOS) microwave links, particularly over a wide band. Classical pulse methods, including pulse compression, as well as the much used frequency-sweep approach are covered. Methods utilizing both frequency-hopping and direct-sequence spread-spectrum transmissions are also discussed. An analysis of this latter method (used by the US National Bureau of Standards and by the authors) is included and a relationship is established between the true channel transmittance and that estimated by this approach. The advantages and disadvantages of the various schemes are outlined with the aim of assisting an experimenter in the choice of technique in a given experimental context View full abstract»

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  • Dynamic bandwidth allocation on a slotted ring with integrated services

    Publication Year: 1988 , Page(s): 826 - 833
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    The authors discuss what they consider the fundamental issue of bandwidth allocation on an integrated local area network. An approach is introduced for dynamic bandwidth allocation which is based on traffic prediction concepts. It is especially well suited for real-time services such as video and voice. Using a control model two allocation schemes are proposed: the first is based on an analytical model of the traffic flow; the second is a simpler version that can be easily implemented on very high-speed systems. The results of simulation studies indicate a marked improvement in performance. The presented approach is especially effective when used in systems with large transmission path latencies as the network performance does not deteriorate with increasing latency. This is very useful if the network is to be used as a metropolitan area network View full abstract»

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  • Performance models of statistical multiplexing in packet video communications

    Publication Year: 1988 , Page(s): 834 - 844
    Cited by:  Papers (460)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1052 KB)  

    Models and results are presented that assess the performance of statistical multiplexing of independent video sources. Presented results indicate that the probability of buffering (or delaying) video data beyond an acceptable limit drops dramatically as the number of multiplexed sources increases beyond one. This demonstrates that statistical or asynchronous time-division multiplexing (TDM) can efficiently absorb temporal variations of the bit rate of individual sources without the significant variations in reception quality exhibited by multimode videocoders for synchronous TDM or circuit-switched transmission. Two source models are presented. The first model is an autoregressive continuous-state, discrete-time Markov process, which was used to generate source data in simulation experiments. The second model is a discrete-state, continuous-time Markov process that was used in deriving a fluid-flow queuing analysis. The presented study shows that both models generated consistent numerical results in terms of queuing performance View full abstract»

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  • Window flow control on a trunked byte-stream virtual circuit

    Publication Year: 1988 , Page(s): 816 - 825
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (764 KB)  

    The throughput versus window-size behavior of the sliding window protocol is studied on a trunked byte-stream virtual circuit. For the case studied, the node service discipline is processor sharing, background traffic is Poisson with exponentially distributed message lengths, propagation times are a significant fraction of the total delay, and the channel error rate is negligible. Analytic models are compared to the results of simulation. For small windows, the throughput is controlled by the ratio of window size to roundtrip propagation time. For large windows, the throughput is controlled by the background traffic level, the number of hops, and the ratio of window size to background message length View full abstract»

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  • A k shortest path algorithm for adaptive routing in communications networks

    Publication Year: 1988 , Page(s): 855 - 859
    Cited by:  Papers (24)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    An efficient and flexible algorithm is presented for finding a k shortest loopless path with distinct initial links from one node to each other node. Low-order polynomial bounds are established for the worst-case time complexity of the algorithm, showing it to offer a substantial improvement over applying known algorithms to the problem. The algorithm can incorporate various extensions, including the ability to handle an algebraic objective, which enhance its applicability to diverse network models. In addition, the k shortest path formulation and algorithm are proposed as a basis for network survivability measures where path length bounds exist View full abstract»

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  • A satellite system synthesis model for orbital arc allotment optimization

    Publication Year: 1988 , Page(s): 845 - 849
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    A mixer-integer programming formulation is presented of a satellite system synthesis problem, or geostationary-orbital-planning synthesis problem, which is referred to as the arc allotment problem (AAP). Each satellite administration is to be allotted a weighted-length segment of the geostationary orbital arc within which its satellites may be positioned at any longitude. The objective function maximizes the length of the unweighted arc segment allotted to every administration, subject to single-entry cochannel interference restrictions and constraints imposed by the visible arc for each administration. Useful relationships between special cases of AAP and another satellite synthesis problem are established. Solutions to two example problems are presented View full abstract»

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  • Approximate evaluation for mixed delay and loss systems with renewal and Poisson inputs

    Publication Year: 1988 , Page(s): 850 - 854
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    An approximate evaluation is proposed for the individual mean waiting time, and loss probability for mixed delay and loss (nondelay) systems with renewal and Poisson inputs handled by servers with exponential service time. The approximation is based on the GI approximation previously proposed by H. Akimaru, et al. (1983, 1985), in which the mixed input process is regarded as renewal. The systems with mixed delay renewal and nondelay Poisson inputs, and ones with mixed nondelay renewal and delay Poisson inputs are analyzed. Approximate formulas for the mean waiting time and loss probability for the respective inputs are presented in simple closed form, and comparisons to simulations show good accuracy. The formulas are expected to be useful for analysis and optimum design of the mixed delay and loss systems 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