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Communications, IEE Proceedings-

Issue 1 • Date Feb 1997

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Displaying Results 1 - 9 of 9
  • Analysis and implementation of an adjustable-rate multilevel coded modulation system

    Publication Year: 1997 , Page(s): 1 - 5
    Cited by:  Papers (3)  |  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The authors describe the design of a multilevel coded modulation system. The main goal is to achieve a high degree of rate flexibility, with the same hardware allowing for the implementation of several coded schemes. This is obtained by associating a hierarchy of punctured convolutional codes with the partition chain of a square-lattice signal constellation. Discussing the rationale behind their choices and implementation details, the authors analyse the system by computing its error probabilities, and show experimental results View full abstract»

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  • Explicit loss indication and accurate RTO estimation for TCP error recovery using satellite links

    Publication Year: 1997 , Page(s): 47 - 53
    Cited by:  Papers (4)  |  Patents (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (836 KB)  

    The TCP protocol has been optimised to provide reliable operation over an internet of packet networks. A satellite link, particularly one using a terminal with a small aperture antenna, has features which differ from those of a terrestrial communication network, such as high propagation delay and a varying (often high) level of errors. Although TCP provides a reliable service, it does not always perform efficiently over a satellite link. The main weaknesses of TCP over a satellite link are the interaction between the TCP error recovery procedure and congestion control procedures and the inaccuracy of retransmission time-out (RTO) estimation. These weaknesses are analysed, and a number of methods for improving the performance of TCP are presented. The improvements may be implemented by modifying the TCP transport protocol in the end-systems View full abstract»

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  • Bounds on waiting time for multiplexing leaky bucket enforced sources in ATM networks

    Publication Year: 1997 , Page(s): 17 - 23
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    In ATM networks, various usage parameter control (UPC) strategies are used to regulate incoming traffic according to the characteristics of the sources declared at call setup. Among these UPC schemes, the leaky bucket method is well known and has been discussed extensively. The authors study the characteristics of the multiplexer in which cell arrivals are first policed by enhanced leaky buckets (ELBs) to police mean and peak rates simultaneously. Based on the criteria of delay experienced in the buffer, they derive the upper and lower delay bounds expressed as a function of the ELB parameters and the number of sources. They also rigorously prove that these bounds occur with respect to a coincident environment and a perfectly interleaved environment, respectively View full abstract»

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  • Searching for TCM codes using genetic algorithms

    Publication Year: 1997 , Page(s): 6 - 10
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    The authors show a new approach to the search for convolutional codes using genetic algorithms. By the use of genetic algorithms, automatic classification of the convolutional codes and less computationally demanding algorithms are required to find and evaluate the most suitable codes. Also, code performance and complexity are evaluated View full abstract»

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  • Adaptive location management scheme for global personal communications

    Publication Year: 1997 , Page(s): 54 - 60
    Cited by:  Papers (13)  |  Patents (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    A major issue for achieving seamless universal personal communications is efficient location tracking of a multitude of mobile terminals. The approach in which each mobile registers in relatively small location areas may not be adequate for global personal communications because a very large number of mobile terminals with a broad range of terminal mobilities may generate excessive location updating traffic. As an alternative, the authors present an efficient multilayer mobility management scheme that is especially suitable for hierarchical cellular structures. The scheme accounts for past as well as present terminal mobilities and dynamically changes the hierarchical level of the location area to which a mobile terminal registers. In a system that contains both a terrestrial segment and a satellite segment, highly mobile terminals such as an aircraft will tend to register at the highest level where location areas are formed by spotbeams. Low mobility terminals such as pedestrians will tend to register at the lowest level where location areas are formed by microcells or clusters of microcells. An additional feature of the scheme is that the required signalling traffic for location updating is distributed evenly to all stations at each level of the system. An analytical model is developed to determine the required location updating supervisory traffic of the proposed scheme. Example performance characteristics are presented. The proposed scheme can track large numbers of terminals with a broad range of mobility View full abstract»

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  • Biorthogonal pulse position modulated direct-sequence CDMA for wireless local communications

    Publication Year: 1997 , Page(s): 40 - 46
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    The author proposes a biorthogonal code-division multiple-access (CDMA) scheme based on biorthogonal pulse position modulated signature sequences. Unlike classical CDMA using bit-by-bit spreading, this scheme utilises symbol-by-symbol spreading which effectively reduces multiple-access interference. Compared to the orthogonal CDMA using symbol-by-symbol spreading, the proposed biorthogonal CDMA minimises the receiver complexity, while it causes negligible performance degradation. Its simple receiver structure will be suitable for use in CDMA wireless local communications. For a proper symbol size M, the biorthogonal CDMA proposed shows great promise for practical implementation both from the performance and complexity points of view View full abstract»

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  • Development of the Laycock-Gott occupancy model

    Publication Year: 1997 , Page(s): 33 - 39
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    The authors examine mathematical modelling of occupancy for the entire high-frequency (HF) spectrum. The theory of modelling the experimental occupancy data is presented, and an example of the modelling procedures is given. Occupancy has been measured as congestion values for each International Telecommunications Union (ITU) frequency allocation across the entire HF spectrum. Congestion is defined as the fraction of signal-strength observations across each allocation for which the signal exceeds a defined threshold View full abstract»

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  • High frequency spectral occupancy at the solstices

    Publication Year: 1997 , Page(s): 24 - 32
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (860 KB)  

    Since 1982, the Digital Communications Group at UMIST has systematically measured and analysed the occupancy of the HF spectrum. The authors describe the measurement system and measurement procedure, and give mathematical models for solstice day and night occupancy across the whole HF spectrum. The main problems of the HF channel may be broadly stated as: (a) problems arising from time-varying multipath propagation; (b) interference from other HF users; and (c) atmospheric and galactic noise. Propagation and noise have been extensively studied and documented. However, interference from other HF users, although frequently very severe, has been seen as less obvious to characterise View full abstract»

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  • Performance analysis and design of token-passing networks with two message priorities

    Publication Year: 1997 , Page(s): 11 - 16
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Analytical equations are presented for performance evaluation of limited-service token-passing networks where each user has two prioritised buffers of finite capacity. Using these equations, the effect of network parameters (buffer capacity, service discipline) on the performance characteristics (throughput, delay) is investigated. It is shown that the optimal choice of network parameters according to the design procedures can lead to a substantial improvement in the network's performance View full abstract»

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