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Communications, IEE Proceedings-

Issue 2 • Date Apr 1997

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Displaying Results 1 - 9 of 9
  • Zero-forcing equalisation for space diversity combining in microwave digital radio

    Page(s): 107 - 113
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    One of the primary causes of performance degradation in microwave digital radio is frequency-selective fading caused by multipath propagation. For an M-QAM radio system, dual space diversity and adaptive zero-forcing equalisation countermeasures can be employed in two configurations. In an optimal-selection diversity structure, after equalisation of the two diversity channels, the better one is selected, while in a postcombining equalisation structure the channels are combined prior to equalisation. By analytic techniques and Monte Carlo simulation it is determined that for the same transmit power the improvement attained is greater with the postcombining equalisation structure. Also, it is shown that the seven-tap postcombining equalisation structure can outperform the conventional optimal selection-diversity structure even when infinite taps are used View full abstract»

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  • Trellis decoding technique for binary-adder channel with M users and its application in LANs

    Page(s): 65 - 69
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    A trellis design procedure for the M-user binary-adder channel is introduced. Based on this technique, trellis diagrams for some known 2-user coding schemes have been designed. In addition, a DC-free 2-user binary coding scheme, together with its trellis structure, is introduced and investigated. It is shown that the new technique provides about 2 dB energy gain in comparison with the conventional techniques. A useful and interesting application of this technique would be the token-ring local area network where the number of users can be increased without bandwidth expansion View full abstract»

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  • Evaluation of the power spectral density of guided scrambling coded sequences

    Page(s): 70 - 78
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (876 KB)  

    The authors develop a practical method of evaluating the power spectral density of guided scrambling line-coded sequences. Analysis of block-coded signals is reviewed, and it is shown that it is impractical to analyse continuous guided scrambling coded sequences with expressions presented elsewhere in the literature. Alternative expressions for sequence autocorrelation are derived which depend on the relationship of several code parameters. Two relationships are considered in detail, and it is shown how expressions derived in these instances can be applied to other guided scrambling codes. Using these expressions, the spectral characteristics of several continuous guided scrambling codes are evaluated. These spectra demonstrate the important result that variation in the average statistics of the coded sequences with varying source-stream statistics decreases as the degree of the scrambling polynomial increases View full abstract»

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  • Multistage trellis coded quantisation (MS-TCQ) design and performance

    Page(s): 61 - 64
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    Multistage trellis coded quantisation (MS-TCQ) is developed as a constrained trellis source coding technique for successive refinement of information. The authors study the performance of two-stage trellis coded quantisers for Gaussian and uniform memoryless sources. Problems of appropriate trellis selection, output alphabet selection, and stage-by-stage design of the codebooks are addressed. Stagewise optimisation is done using the generalised Lloyd algorithm. Comparisons with two-dimensional multistage vector quantisation (MSVQ) indicate that up to 1.6 dB performance improvement can be achieved by using MS-TCQ. Another algorithm is also presented for the joint design of the stage codebooks to optimise the overall performance. It is shown that another 0.5 dB improvement can be achieved by employing the joint design algorithm View full abstract»

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  • Reduced-tree-based soft decoding for block-coded modulation

    Page(s): 79 - 83
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    It is shown that soft maximum-likelihood decoding for block-coded modulation (BCM) can be performed using the code tree. It is easy to generate the code tree for any type of block code, linear as well as nonlinear. A reduced tree is obtained from the code tree. The trellis for a block code can be obtained from the reduced tree. Using this structure to perform computations in parallel, a scheme is proposed for the implementation of the soft decoder. Back tracking, necessary in a soft decoder using the Viterbi algorithm on a trellis, is eliminated View full abstract»

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  • BER performance of multiwavelength optical cross-connected networks with deflection routing

    Page(s): 114 - 120
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The transmission performance of regular two-connected multihop transparent optical networks in uniform traffic under hot-potato, single-buffer deflection routing schemes is presented. Manhattan street network (MS) and shufflenet (SN) are compared in terms error rate (BER) and packet error rate both analytically and by simulation. The authors implement a novel strategy of analysis, in which the transmission performance evaluation is linked to the traffic randomness of the networks. Amplifier spontaneous emission (ASE) noise, and device-induced crosstalk severely limit the characteristics of the network, such as propagation distance. Sustainable traffic and bit rate. The results indicate that under the same load the BER performance of single-potato deflection routing is worse than hot-potato. However, at BER=10-9 single-buffer has a higher throughput than hot-potato. It is shown that the feasibility of deflection routing in transparent networks with MS and SN topologies heavily depends on the power coupling coefficient of the routing space switch used in each node View full abstract»

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  • Neural-network connection-admission control for ATM networks

    Page(s): 93 - 98
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    ATM connection-admission control (CAC) using neural networks offers improvement over conventional CAC but creates some difficulties in real operations, such as complicated training processes. This is because ATM traffic characteristics are quite diverse, and quality of service (QoS) and bandwidth requirements vary considerably. A neural-network connection-admission control (NNCAC) method which can overcome these difficulties by preprocessing neural-network input parameters is proposed. The NNCAC method introduces a unified metric for input-traffic parameters by utilising robust analytical results of the equivalent-capacity method. It diminishes the estimation error of the equivalent-capacity method, due to modelling, approximation and unpredictable statistical fluctuations of the system, by employing the learning capability of a neural network. The method further considers the congestion status parameter and the cell loss probability, which provides insight information about the system. Simulation results revealed that the proposed NNCAC method provided a 20% system-utilisation improvement over Hiramatsu's (1990) neural-network CAC scheme and a 10%, system-utilisation improvement over the fuzzy-logic-based CAC scheme, while maintaining QoS contracts. It was also found that the NNCAC method provided utilisation comparable with that of the NFCAC scheme but possessed a lower cell loss probability. NNCAC is suitable for designers who are not familiar with fuzzy-logic control schemes or have no ideas about the requisite knowledge of CAC View full abstract»

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  • Constructing quasi-optimal subfamilies of GMW sequences suitable for CDMA applications

    Page(s): 99 - 106
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    Gordon-Mills-Welch (GMW) sequences possess a desirable two-valued autocorrelation function which helps a RAKE receiver track multipath returns. Unfortunately, their cross-correlation functions are less well controlled. Therefore, it is necessary to construct their subfamilies (taking advantage of its reasonably large family size) which offer satisfactory cross-correlation characteristics. The authors study several algorithms for constructing those quasi-optimal subfamilies in terms of minimised bit error rate under cochannel interference. The results show that performance of resultant subfamilies is very sensitive to the algorithms applied and subfamily sizes. A new criterion based on combined (even and odd) maximum cross-correlation is introduced for subfamily construction and two proposed highest-peak-deleting and most-peak-deleting algorithms are effective to construct the GMW quasi-optimal subfamilies View full abstract»

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  • Estimation-based call admission control with delay and loss guarantees in ATM networks

    Page(s): 85 - 92
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    Call admission control (CAC) has been accepted as a potential solution for supporting a variety of traffic sources demanding different quality of service guarantees in asynchronous transfer mode networks. Basically, CAC is required to consume a minimum of time and space to make call acceptance decisions. A CAC algorithm is presented based on a novel estimation method, called quasilinear dual-class correlation (QLDC). All heterogeneous traffic calls are initially categorised into various classes. According to the number of calls in each traffic class, QLDC conservatively and precisely estimates the cell delay and cell loss ratio for each traffic class via simple vector multiplication. These vectors are computed in advance from the results of three dual arrival queuing models, M[N(1/])+Isup [N(2/])/D/1/K, M1 [N(1/])+Msub 2/[N(2/])D/1/K and I1[N(1/])+Isub 2/[N(2/])D/1/K, where M and T represent the Bernoulli process and the interrupted Bernoulli process, respectively. Consequently, the authors' QLDC-based CAC, as is shown, yields a low time complexity O(C) (in vector multiplications) and space complexity O(WC2) (in bytes), where C is the total number of traffic classes and W is the total number of aggregate load levels. Numerical examples are also employed to justify that the QLDC-based estimated results profoundly agree with the simulation results in both the single-node and end-to-end cases View full abstract»

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