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Communications, 1994. ICC '94, SUPERCOMM/ICC '94, Conference Record, 'Serving Humanity Through Communications.' IEEE International Conference on

Date 1-5 May 1994

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Displaying Results 1 - 25 of 343
  • Proceedings of ICC/SUPERCOMM'94 - 1994 International Conference on Communications

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  • DMT systems, DWMT systems and digital filter banks

    Page(s): 311 - 315 vol.1
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    A multicarrier modulation system called discrete multitone (DMT) was chosen by the American National Standards Institute (ANSI) as a working standard for asymmetric digital subscriber line (ADSL) signaling. The DMT system uses the inverse and forward discrete Fourier transform (DFT) for modulation and demodulation. An alternative to the classic DMT system is to substitute a discrete wavelet transform in place of the DFT as the modulating transform. This new method is called discrete wavelet multitone (DWMT) signaling, and has been shown to be superior to the DMT system in certain channel environments. This paper illustrates that the DMT system and the DWMT system are both based on the theory of M-band wavelet filter banks. In particular, DMT and DWMT are linked formally through a discussion of digital multirate filter hanks and digital transmultiplexer. In addition the advantages of wavelet transform-based transmultiplexers over DFT-based transmultiplexers are discussed View full abstract»

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  • An improved scheduling algorithm for weighted round-robin cell multiplexing in an ATM switch

    Page(s): 1032 - 1037 vol.2
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    Priority as well as constant delay are both important performance criteria in an isochronous scheduler design such as the one in ATM switches. Weighted round-robin (WRR) multiplexing has been proven to be an effective and simple method to implement for priority traffic. The authors present an improved scheduling algorithm based on WRR cell multiplexing to ease the delay jitter problems. The impact of smoothness of the proposed scheduler design is thoroughly presented. The mean response time and its standard deviation are analyzed. The solutions show better performance results than previous work, especially when requested bandwidths are uniformly allocated View full abstract»

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  • Timing recovery for echo-cancelled discrete multitone systems

    Page(s): 307 - 310 vol.1
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    We present a novel technique for timing recovery in an echo-cancelled multicarrier system. In this scheme, both the transmit and receive clocks on a transceiver are derived from the same stable crystal oscillator. In this way, the high degree of echo rejection required by the echo canceller is affected by neither timing jitter nor sampling phase offset. The receiver compensates for the time-domain phase offset with the use of frequency-domain adaptive equalization on the echo-cancelled demodulated symbols. Cycle slips are handled by a simple rob/stuff protocol that is reflected in the operation of the frame-synchronous echo canceller. An efficient method for multicarrier echo cancellation has been proposed for ADSL. We analyze the performance of our timing recovery scheme in the context of this system View full abstract»

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  • An intelligent network management system in B-ISDN

    Page(s): 1384 - 1389 vol.3
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    As the ATM technology becomes mature, the ATM network management system must exist to provide a high quality of service (QoS) to B-ISDN subscribers. The management of B-ISDN has been difficult due to the ATM characteristics. This paper describes a logical architecture and implementation of an intelligent network management system in B-ISDN. The architecture is discussed from the standpoint of the flow of diagnostic information and the role of equipment and personnel View full abstract»

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  • A methodology for virtual path and virtual network bandwidth assignment in broadband networks with QOS guarantees

    Page(s): 165 - 169 vol.1
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    We introduce a methodology for establishing a connection between two arbitrary nodes of a multiclass broadband network that secures sufficient resources at every intermediate node along the selected route, and thereby guarantees quality of service (QOS). We describe how a virtual path (VP) mechanism may be implemented within our framework, and compare the performance achieved by such a scheme with that of a virtual circuit (VC) approach. The notion of contract region is introduced as a mean of achieving coordination among distributed Virtual Path controllers to ensure that the state of each network link remains within its schedulable region and the cell level QOS is guaranteed View full abstract»

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  • Efficient decoding of correlated sources with application to DPCM image coding

    Page(s): 230 - 234 vol.1
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    Three methods are proposed in this paper, in which the encoded signal is modelled as a Markov sequence. First, an optimum method for decoding correlated sequences is derived and it is shown to require Viterbi decoding. Then, a modified MAP method (MMAP) for Markov sequences is described. A maximal signal-to-noise (MSNR) receiver for DPCM systems is also developed that minimizes the distortion power due to channel errors; the appropriate cost matrix for this receiver is computed. These methods are applied to DPCM picture transmission over noisy channels and are compared to a recent method. The SNR graphs and the subjective examination of the enhanced pictures demonstrate that the proposed procedures are quite effective and are superior to a recent method. The MSNR receiver was found to be somewhat more effective than the MMAP receiver for a given order of the Markov source. The Markov modelling of the encoded signal is found to improve the SNR of the received pictures. Furthermore, it is observed that the gain increases with the increase in the order of the Markov model View full abstract»

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  • A field trial for laboratory experimental broadband switching system

    Page(s): 603 - 607 vol.1
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    The introduction of broadband integrated services digital network (B-ISDN) based upon asynchronous transfer mode (ATM) will be a phased approach, i.e., first private network applications followed by public network applications. The driving force of the telecommunication network migration toward B-ISDN, will be based heavily on broadband services needs as well as technology advancement. ATM has been recommended as the technology for the switching as well as the transmission networks. A preliminary broadband services market survey in Taiwan, ROC, has been done by the Telecommunication Laboratories (TL) of the Directorate General of Telecommunications (DGT). In addition, a long term broadband switch development plan has been formed with two different stages by TL. An ATM based laboratory experimental broadband switching system (LES) has been completed and a trial is being undertaken with the National Central University (NCU). The paper describes the LES architecture, service capabilities, field trial, performance evaluation and measurement View full abstract»

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  • A novel neural network traffic enforcement mechanism for ATM networks

    Page(s): 779 - 783 vol.2
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    The asynchronous transfer mode (ATM) principle has been recommended by the CCITT as the transport vehicle for the future broadband ISDN networks. In ATM-based networks, a set of user declared parameters that describes the traffic characteristics, is required for the connection acceptance control (CAC) and traffic enforcement (policing) mechanisms. During the call progress, the policing mechanism uses those parameters to control the user's traffic within its declared values in order to protect the network's resources and avoid possible congestion problems. In this paper, a novel policing mechanism using neural networks (NNs) is presented. The mechanism is based upon an accurate estimation of the probability density function (PDF) of the traffic via its count process and implemented using NNs. The architecture of the policing mechanism is composed of two inter-connected NNs. The first one is trained to learn the PDF of an “ideal non-violating” traffic, whereas the second is trained to capture the “actual” characteristics of the “actual” offered traffic during the progress of the call. The output of both NNs is compared. Consequently, an error signal is generated whenever the PDF of the offered traffic violates its “ideal” one. The error signal is then used to shape the traffic back to its original values. The reported results, prove that our policing mechanism is very effective in detecting (and policing) all possible kinds of traffic violations View full abstract»

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  • π/4-DQPSK on microcellular radio channels with diversity and interference

    Page(s): 1541 - 1545 vol.3
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    A analyze the average bit error rate (BER) performance of π/4-shifted differential quadrature phase shift keying (π/4-DQPSK) in the presence of multiple independent cochannel interferers in frequency-nonselective fading environments. Nyquist shaped pulses are used and postdetection diversity combining is employed at the receiver. The use of both L-branch postdetection equal gain combining (EGC) and L-branch postdetection selection combining (SC) are considered. Two approaches for representing the cochannel interference are investigated. These are a Gaussian interference model and a synchronous interference model. The accuracies of both of these models are assessed by comparing their BER performances with precise BER results. The precise BER results are obtained by using a combination of analysis and simulation View full abstract»

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  • Echo cancellation for asymmetrical digital subscriber lines

    Page(s): 301 - 306 vol.1
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    Discrete multitone modulation has been chosen to provide the high speed link for asymmetrical digital subscriber lines (ADSL). Modulating bidirectional digital traffic over the existing twisted pair loop plant necessitates the used of a high performance echo canceller. This paper investigates an echo canceller structure for ADSL. A combination frequency domain echo canceller and a time domain echo synthesizer are detailed along with timing and fixed point effects. Detailed simulation results show the canceller performance is more than adequate and does not limit the transceiver's performance. Complexity issues are addressed and show that an effective canceller can be implemented with only modest computational requirements. Hence, there exists an effective and efficient echo canceller for ADSL View full abstract»

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  • Computationally efficient asymptotic and accurate approximate expressions for the matched filter bound for (un)coded MPSK transmission on multipath fading channels

    Page(s): 337 - 341 vol.1
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    Uncoded and trellis-coded MPSK transmission over multipath Rayleigh fading channels with explicit antenna diversity is investigated. The bit error rate performance of the MLSE-receiver is considered, based on the matched filter bound on the pairwise error event probability. The authors derive an exact asymptotic expression and two accurate approximate expressions for the matched filter bound, the evaluation of which requires much less computational effort than the evaluation of the exact matched filter bound, especially for large diversity orders View full abstract»

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  • Complexity reduction of direct-sequence code division multiple access receivers

    Page(s): 1643 - 1647 vol.3
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    Considers an asynchronous direct-sequence code division multiple access (DS-CDMA) communication system over an AWGN channel. The authors are interested in reducing the computational complexity of a receiver by lowering the dimensionality of the received vector. Dimension reduction has previously been done in an ad hoc manner by several researchers. The present authors derive an optimum form of dimension reduction. The optimality criteria is that the Cramer-Rao bound on estimators of propagation delay, received phase and power are invariant to the reduction transform View full abstract»

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  • A model for multimedia service creation and activation

    Page(s): 1727 - 1733 vol.3
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    The emergence of multimedia applications requires appropriate management and control activities to be provided and organized in an integrated framework. This paper presents an architectural approach for the modeling of service activation processing in a multimedia environment. In particular, activation processes complying with this model provide the user with the capability of devising, creating and controlling the required composite multimedia service by using elementary services provided by the network as building blocks. The model introduced in the paper has been effectively used as a basis for the development of a network environment providing prototypal services of Multimedia Cooperative Editing (MCE) View full abstract»

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  • A new detection technique for digital radio communication systems applied spectrum phase interpolation

    Page(s): 1417 - 1421 vol.3
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    In cellular communications systems using digital radio services, especially those that use low-Earth orbiting satellites (LEOs), phase-modulated signals such as QPSK are received with relatively fast Doppler shifts. We developed a coherent detector which uses a new algorithm called the spectrum phase interpolation method (SPIM) to compensate for the Doppler shifts. SPIM will aid TDMA propagation analyses of QAM and QPSK modulated waves and orthogonally vector spread spectrum modulated waves View full abstract»

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  • Nonlinear multi-pulse block coding of CPFSK signals

    Page(s): 369 - 373 vol.1
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    A nonlinear multi-pulse block coding technique is proposed to improve CPFSK signaling formats. The coding technique is designed to prevent merging events with lower distances by separating the respective paths in time domain without increasing the number of states. It is demonstrated with constant h, 2-h, and trellis coded signals, that the proposed coding technique can significantly increase the minimum distance, while maintaining very high code rates to limit the bandwidth expansion View full abstract»

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  • Service management concepts in shared business environments: from electronic data interchange (EDI) to electronic process integration (EPI)

    Page(s): 1842 - 1846 vol.3
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    Presents a reference platform for service management in a shared business community, as applied to electronic document composition, production and distribution. The concept is based on the notion of “distributed service centre”. All business participants (users), including customers, service providers and brokerage service providers, are interconnected via ISDN and can access each other on demand. Every user is equipped with a service management kernel that performs basic “agent” functions and user access shell, including directory and administration services for the shared community. The model integrates service management tools, usage scenarios and functional specifications. It offers a standard reference scheme to all players in a specific shared business community (clients, service providers and public network operators) for a cost-effective way to create, share and manage services. The work is supported by RACE II Project 2037 (Distributed documenting services-DIDOS). The models are being tested in application pilots, that inter-connect trans-European users of technical documentation. Users (document producers clients and service providers) generate electronically, communicate, order and, to a large extend, produce technical manuals and CD-ROM documentation by sharing available production facilities and public ISDN View full abstract»

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  • A neural approach to performance evaluation for teletraffic system

    Page(s): 774 - 778 vol.2
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    For traffic management of the ISDN and BISDN, it is necessary to evaluate the performance of the GI/G/s teletraffic system. The GI/G/s means s homogeneous parallel servers with general independent interarrival times and the general service times. We propose a method of performance evaluation for the GI/G/s by using a simple neural network. In order to train the network, the proposed method uses the parameters and corresponding exact values of well-known systems. Using the trained network, we can evaluate the performance of GI/G/s in a simple calculation View full abstract»

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  • Analysis of clipping effect in DMT-based ADSL systems

    Page(s): 293 - 300 vol.1
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    At present, discrete multi-tone (DMT) transceivers receive much attention for the implementation of asymmetric digital subscriber lines (ADSL). This paper analyzes the effect of clipping a DMT-signal, i.e. limiting the signal's maximum amplitude. An exact expression is given for the signal-to-noise ratio (SNR) degradation due to clipping alone. By combining this expression with the well-known expression for the quantization noise in the A/D-D/A converters, it is shown how clipping can reduce the number of bits of A/D-D/A converters as well as the dynamical range of the line drivers while keeping the overall SNR the same as without clipping View full abstract»

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  • Analysis of rate control mechanisms for transport layer protocols in high speed networks

    Page(s): 1319 - 1325 vol.3
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    An analytic model is presented for the performance evaluation of rate based flow controls for the transport layer in high speed networks by using Markov chains. In order to provide insights into the behavior of the rate control mechanisms, critical parameters, such as round-trip delay, processing capacity, receiver buffer size, and traffic characteristics, are considered in the model. The performance measures are mainly concerned with the loss probability, throughput and average overload time. A simple optimal approach to the design of the rate control systems is also proposed View full abstract»

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  • Modified intersymbol interference canceller for digital microwave radio

    Page(s): 332 - 336 vol.1
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    A reduction of complexity in full-digital implementations of the adaptive equalizing function for digital microwave radio (DMR) is attained using a modified intersymbol interference canceller instead of a conventional equalizer. The reduction of complexity is mostly due to the fact that preliminary decisions are coded in a relatively small number of bits and additional cancelling stages are used. For equalizers typically employed in 140 Mbit/s DMR systems, the complexity reduction can exceed 50%. A numerical method of calculating error rates was extended and used to obtain signatures for modified cancellers and conventional equalizers, which are presented View full abstract»

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  • Resource allocation in broadband networks-cell, burst or connection level?

    Page(s): 86 - 90 vol.1
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    Traditional data-communication services can be expected to consume only a small fraction of the available bandwidth when B-ISDN services become a reality. A variety of new communications services, ranging from continuous bit-rate digital video to highly bursty image traffic with very small activity ratios (typically close to 3%, with characteristics markedly different from data services are propelling the need for developing more efficient resource allocation and routing protocols. The level of granularity of bandwidth allocation for these bursty sources is the subject of investigation in this paper. The different choices for allocation granularity, viz., cell, burst and connection levels are discussed and compared. ON-OFF models are used to represent bursty sources. We employ MMPP models to approximate the superposition of several ON-OFF sources and investigate the delay performance of the different allocation policies at an ATM multiplexer. Results reveal that the multichannel allocation at the cell level) allocation offers an order of magnitude performance improvement compared to unichannel (allocation at the connection level) allocation View full abstract»

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  • Soft-decision multistage decoding of multilevel-coded quaternary partial-response signals

    Page(s): 1242 - 1248 vol.3
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    This paper deals with multilevel coding and concatenated soft-decision multistage decoding for quaternary partial-response class-IV (PRIV) systems. Time-interleaved multilevel-coded quaternary symbols are transmitted with precoding over the PRIV channel. In the receiver, an inner decoder computes approximate log-likelihood ratios for the less significant bits of the quaternary symbols input to the precoded PRIV channel by a new reduced two-state soft-output Viterbi decoding algorithm. An outer multistage decoder employs the obtained log-likelihood ratios which, with sufficient interleaving, represent appropriate metrics for soft-decision decoding. Real coding gains over uncoded transmission with maximum-likelihood sequence decoding are determined by simulation. Results are presented for various multilevel codes that employ a single level of convolutional or Reed-Muller block coding. The scheme considered here exhibits low decoding complexity and allows for high-rate codes that achieve real coding gains of 3 to 4 dB View full abstract»

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  • An integrated application/service platform to support multimedia applications

    Page(s): 1722 - 1726 vol.3
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    This paper describes a communication support system for multimedia applications relying on the development of an integrated application/service platform. The proposed architecture includes a service platform that provides communication services and their management to multimedia applications and an application platform that provides end-point application services. The former is implemented via an interface re siding at OSI Presentation Service Access Point (PSAP) and the latter via an interface residing at OSI Application Service Access Point (ASAP). It is anticipated that the combination of the proposed integrated application/service platform will ensure the interoperability among existing and future multimedia applications within the broadband environment. It is widely accepted that the key requirement for a multimedia application is the availability of a distributed multimedia environment. Multimedia applications could be distinguished as interactive or non-interactive such as conferencing and video-on-demand, respectively, and impose specific requirements to be met, i.e. synchronization of isochronous streams, end-to-end delay constraints and multicast transmissions. In this paper we propose an enhanced protocol/service structure that overcomes the weaknesses of the conventional OSI Reference Model. The result of this approach is an application/service platform that provides a QoS support throughout all OSI upper layers. Finally, adaptations of OSI elements are proposed View full abstract»

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  • Fast reservation protocol and statistical multiplexing: a comparative study

    Page(s): 733 - 737 vol.2
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    An analytical study of Fast Reservation Protocol is presented as a way to compare FRP performance against simple statistical multiplexing. The comparison is done on the basis of the multiplexing capability of each scheme. Queuing models for both schemes are developed and based on these models the maximum numbers of sources that can be multiplexed by each scheme is then computed. The results quantitatively confirm the previously accepted characteristics of FRP, i.e. that it is good for long burst and short round trip delay View full abstract»

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