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Communications, IEEE Transactions on

Issue 3 • Date March 1978

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Displaying Results 1 - 17 of 17
  • [Front cover and table of contents]

    Publication Year: 1978 , Page(s): 0
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    Freely Available from IEEE
  • [Back cover]

    Publication Year: 1978 , Page(s): 0
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    Freely Available from IEEE
  • A Basic Dynamic Routing Problem and Diffusion

    Publication Year: 1978 , Page(s): 320 - 327
    Cited by:  Papers (27)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    Diffusion theory has sometimes been successful in providing excellent approximate solutions to difficult queueing problems. Here we explore whether such methods can be used to analyze a basic dynamic routing strategy associated with a single idealized node in a data network. We analyze a dynamic routing policy where messages, or packets, that arrive at a certain node are routed to leave the node on the link having the shorter queue. In the model, message or packet arrivals are Poisson and the service time is exponentially distributed. We explore a heavy traffic diffusion method and we also discuss the limitations of an ad hoc approach to applying diffusion. For a node with K outgoing queues we find, under the assumption of heavy traffic, the optimum dynamic strategy, in the sense of minimizing the average delay. When this optimum dynamic strategy is compared to a static strategy where the outgoing traffic is split among the K queues, we find that the average delay for the dynamic system is better by a factor of K . View full abstract»

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  • An Analytic Evaluation of the Performance of the "Send and Wait" Protocol

    Publication Year: 1978 , Page(s): 313 - 319
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    In this study, we are concerned with a simple error control protocol, the "send and wait" protocol, which uses the classical technique of positive acknowledgment and time-out periods. We first analyze the influence of the time-out on the packet transmission rate. Then we use a queuing analysis to obtain the ergodicity condition and to compute the buffer queue length probability distribution. Finally we compute buffer overflow when a finite number of packets are allowed to enter the node. This analysis allows us to obtain optimum values of the time-out in order to maximize throughput, or to minimize average transit delay through the node or buffer overflow probabilities. View full abstract»

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  • Performance of Maximum-Likelihood Receiver in the Nonlinear Satellite Channel

    Publication Year: 1978 , Page(s): 373 - 378
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    A computer-simulation algorithm is described for calculating the performance of a maximum-likelihood (ML) receiver in the nonlinear satellite communications channel. It is assumed that performance is dominated by isolated single errors and that the channel can be approximated by one of finite memory, M \leq 10 bits. The algorithm employs the brute force method of comparing the wave forms of all sequence pairs of length 2M - 1 bits that differ in their M 'th bit, and in spite of the large number of sequences involved requires only modest computer time. Examples for a rudimentary channel employing a traveling wave tube at saturation with modulation formats QPSK, O-QPSK, and MSK are computed and ML performance is compared to that of suboptimum receivers using bit-by-bit decision or discrete ML sequence estimation. Results indicate that the inherent channel degradation that cannot be corrected by appropriate receiver design is not great even for transmission at the Nyquist rate limit as defined relative to the 3 dB bandwidth of a link employing 6-pole Butterworth filters. View full abstract»

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  • Analysis of the Dedicated Communication Line in a Mine Tunnel for a Shunt-Loaded Trolley Wire

    Publication Year: 1978 , Page(s): 355 - 361
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The theory of transmission in a semicircular tunnel containing two axial conductors is simplified for the case of radio frequencies. It is shown that the effect of ohmic losses in the wall can be represented as series impedances per unit length in the equivalent coupled transmission line circuits. This opens the way for a systematic calculation of the mode conversion phenomena that occur when one of the axial conductors has a discrete shunt load to the ground plane. Explicit formulas are obtained for the modal conversion coefficients. These are used to discuss the effect of a shunt load on the trolley wire on the performance of a radio frequency communication system. It is confirmed that the unloaded dedicated communication line provides for a low loss mode that is hardly affected by the shunt load on the adjacent trolley wire in the tunnel. View full abstract»

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  • A Multi-User-Class, Blocked-Calls-Cleared, Demand Access Model

    Publication Year: 1978 , Page(s): 378 - 385
    Cited by:  Papers (53)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    Constraints on capacity allocation are investigated for circuit-switched demand access to a common transmission resource by user communities with differing traffic intensity and capacity requirements. A simple birth-death steady-state traffic model is used together with a geometrical representation of any given set of constraints placed upon user access. State probabilities have a simple product form which holds for a wide class of constraint sets. Performance characteristics are intrinsic to the upper surface of the constraint set. View full abstract»

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  • Differential Encoding for Multiple Amplitude and Phase Shift Keying Systems

    Publication Year: 1978 , Page(s): 385 - 391
    Cited by:  Papers (58)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    Because of the symmetry in most two-dimensional signal constellations, ambiguities exist at the receiver as to the exact phase orientation of the received signal set. In PSK systems, this ambiguity is resolved by the use of differential encoding. This paper presents differential encoding techniques which can be used with a variety of symmetric signal sets to remove their phase ambiguity. While not proven to be optimum, the techniques do have low performance penalties relative to the uncoded performance. The key to reducing the performance penalty is to use the minimum amount of differential encoding necessary to resolve the ambiguity. Examples of encoding techniques for several common signal constellations are given, including their performance penalties. View full abstract»

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  • Satellite Repeater Capacity for Two Carrier Level SCPC Operation

    Publication Year: 1978 , Page(s): 404 - 406
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    Many important applications of single channel per carrier (SCPC) operation involve communication links between earth terminals whose G/T values differ substantially. Typical links might connect a small community with the closest commercial center, or an offshore oil rig with a base station. In order to make the best use of the available satellite power, the levels of the carriers directed to the two earth terminals are adjusted in accordance with the respective G/T values. This paper extends results previously derived for the equal carrier case[1] and provides closed-form solutions for optimum transponder backoff and transponder capacity in terms of the link parameters for the case of two unequal carrier levels. View full abstract»

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  • Autonomous Line Scanning for SPC Telephone Switching Systems

    Publication Year: 1978 , Page(s): 368 - 373
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    An Autonomous Line Scanning Unit (ALSU) for completely autonomous detection of call originations in the SPC Telephone Switching System is described. Through its own memories, ALSU maintains an up-to-date record of subscribers' statuses, detects call originations, performs 'hit timing check' and informs the Switching System of the identity of calling subscribers. The ALSU needs minimum interaction with the Central Processor, resulting in increased call handling capacity. View full abstract»

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  • A Low-Rate Digital Formant Vocoder

    Publication Year: 1978 , Page(s): 344 - 355
    Cited by:  Papers (2)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1216 KB)  

    A complete algorithm of a 1200-bits/s digital formant vocoder system is described. This vocoder algorithm draws heavily on the results of recent research in linear predictive coding. The transmitting parameters are frequencies and amplitudes of the first three formants, the pitch period, voiced/unvoiced decision, and the gain. Formant bandwidths are estimated at the synthesizer by using the amplitude information. The synthesizer structure is in the parallel form. The synthetic speech quality at 1200 bits/s is reasonably good; most of the speech is intelligible and speaker-recognizable. View full abstract»

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  • Delay and Throughput Evaluation of Switching Methods in Computer Communication Networks

    Publication Year: 1978 , Page(s): 337 - 344
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    Message, packet and line switching in computer communication networks are analyzed by a queueing model. Message transmission delay time and network throughput between a source-destination node pair are obtained as a function of various parameters including message length, traffic arriving at the network, and the number of switching nodes existing between the nodes. A criterion to determine the most suitable switching method under the given conditions is offered. Also, the maximum length of a packet in packet switching is discussed. View full abstract»

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  • Buffer Management in a Packet Switch

    Publication Year: 1978 , Page(s): 328 - 337
    Cited by:  Papers (58)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    Consider a single packet switch with a finite number of packet buffers shared between several output queues. An arriving packet is lost if no free buffer is available, as in the CIGALE network. It has been observed by simulation that if load increases too much, congestion may occur, i.e., throughput declines; it appears that the busiest link's queue tends to hog the buffers. Therefore, we will limit the queue length and when the queue is full the packet will be dropped. We expect that this restricted buffer sharing policy will avoid congestion under conditions of heavy load. A queueing model of a packet switch is defined and solved by local balance. Loss probability is evaluated, and values of queue limit to minimize loss are found; they depend on load. A Square-Root rule is introduced to make the choice of queue limit independent of load. For a sample switch, with three output links, a comparison is made between performance under different buffer sharing policies; it is shown that restricted sharing prevents congestion by making throughput an increasing function of load. View full abstract»

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  • Selective Frequency Spacing and the Half Step Synthesizer

    Publication Year: 1978 , Page(s): 400 - 404
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    The half step synthesizer uses frequency steps that are half integer multiples of the fundamental frequency spacing. The possible separations between adjacent carriers are 1, 1½, 2, 2½, ... times the fundamental frequency spacing. By providing twice as many potential locations for intermodulation spectra, the inband intermodulation power is distributed so that there is less (about one half) the interference with the carriers. View full abstract»

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  • Hybrid D-PCM, A Combination of PCM and DPCM

    Publication Year: 1978 , Page(s): 362 - 368
    Cited by:  Papers (13)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    After a short review of the basic principles of PCM and DPCM coding it is shown that combining the two methods in one coding system results in a combination of some favorable properties. The hybrid D-PCM system combines the bit-rate reduction of DPCM with a low error sensitivity. In another approach the hybrid D-PCM system is also derived from a usual DPCM system with a leaking integrator. Two different applications of the hybrid D-PCM system illustrate the possibilities and the performance of the hybrid D-PCM system. View full abstract»

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  • VHF and UHF Links Using Mountains as Reflectors

    Publication Year: 1978 , Page(s): 391 - 400
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    The use of mountain reflections for establishing VHF and UHF communication links is analyzed. First, the reflection characteristics are analyzed and then a method is established for calculating the signal strength received in any such link. The use of topographical maps for obtaining the necessary path's parameters is explained and finally, theoretical calculations and measured values for one such link are compared. View full abstract»

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  • A Simple Interleaver for Use with Viterbi Decoding

    Publication Year: 1978 , Page(s): 406 - 408
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    An interleaver/de-interleaver can be used to improve the performance of a Viterbi decoder in the presence of bursty noise. This note describes the design and a method for testing block interleavers which can be used to combat the effects of periodic pulsed RFI. Simulations show that satisfactory decoder performance can be obtained over a range of RFI parameters. 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.

 

 

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia