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Communications, IEE Proceedings-

Issue 2 • Date Apr 1995

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Displaying Results 1 - 10 of 10
  • Performance analysis of an input and output queueing packet switch with a priority packet discarding scheme

    Publication Year: 1995 , Page(s): 67 - 74
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    In future high-speed integrated networks, packet switches must accommodate diverse types of applications with different qualities of service (QOS) and traffic requirements. Therefore some types of priority-control schemes are needed in packet switches, in order to increase the utilisation of switches and to satisfy the QOS of each traffic type. The authors consider a nonblocking input and output queueing packet switch with capacity m, in which two classes of traffic are admitted. Each input queue adopts the priority packet discarding scheme, which discards arrivals of low-priority traffic when its queue length is greater than the pre-defined threshold value. The authors obtain the distribution of input-queue length and loss probabilities of each class using a matrix-geometric solution method. By numerical analysis and simulation, it is shown that the utilisation of the switch with the priority packet discarding scheme satisfying the QOS of each traffic class is much higher than that of the switch without control, and the required buffer size is reduced while satisfying the same QOS View full abstract»

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  • Adaptive frequency hopping in HF communications

    Publication Year: 1995 , Page(s): 99 - 105
    Cited by:  Papers (12)  |  Patents (12)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    Frequency hopping (FH) has been proposed as a technique to combat multipath fading and interference problems in HF links. By means of powerful coding techniques, these systems are able to restore the transmitted information also under adverse transmission conditions when several of the frequencies in use are not available. Although efficient against jamming and interference of short duration, these schemes may be substantially improved in a typical HF environment with slow fading and a large number of narrow-band, slowly varying interferers. A straightforward adaptive frequency hopping (AFH) scheme for duplex links is proposed and analysed. In such a link, link quality measurements are fed back to the transmitter such that `bad' frequencies may be avoided. The system is analysed based on an extension of the HF interference model presented by Gott et al. (1991). The tradeoff between the amount of feedback information and link throughput as well as the impact of feedback reliability is investigated. Results show that an AFH system has the potential of surviving in extremely congested environments at very low transmitter power levels. Both the antijam and the LPI properties of these systems are very promising View full abstract»

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  • Technique for cochannel interference suppression in TDMA mobile radio systems

    Publication Year: 1995 , Page(s): 106 - 114
    Cited by:  Papers (31)  |  Patents (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    A receiver structure is described that enables digitally modulated signals to be received in the presence of a number of like modulated cochannel interfering signals, which may additionally be dispersed in time owing to the influence of the channel. Considerable performance improvements can be obtained with respect to a conventional receiver, particularly when both wanted and interfering signals are subject to Rayleigh fading. The asymptotic performance of the receiver in the presence of AWGN and cochannel interference is obtained analytically for static channel conditions, and the average error rate for Rayleigh fading conditions has been obtained by Monte Carlo simulation. The primary application area for the technique described is in land mobile radio systems View full abstract»

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  • Low-frequency suppression of baseband coded sequences

    Publication Year: 1995 , Page(s): 49 - 53
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    Two classes of constrained sequences with favourable low-frequency spectral suppression properties are considered for applications where a conventional analogue speech signal is transmitted on the same channel as a digital signal, but totally independently from it. These are sequences with second-order spectral zeros at zero frequency and a new class which complies to restrictions on the time between crossings of the average value of the running digital sum. General characteristic equations are derived to obtain values of channel capacity for these sequences. The levels of low-frequency suppression obtainable are then evaluated, and the optimisation problem regarding the choice of a code for a specific application is addressed. Finally, the synthesis of a new code with suppressed low-frequency contents is presented View full abstract»

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  • Generalised Barker-like PN sequences for quasisynchronous spread-spectrum multiple-access communication systems

    Publication Year: 1995 , Page(s): 91 - 98
    Cited by:  Papers (1)  |  Patents (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    The generalised Barker (1953)-like pseudonoise (PN) sequence is introduced. Three theorems are established for such a set of sequences. A computer search algorithm is derived based on these theorems to search for the generalised Barker-like PN sequences employing two design parameters m and lˆ. The multiple-access-interference (MAI) performance of a quasisynchronous direct-sequence spread-spectrum multiple-access communication system (QS-DS/SSMA) employing the generalised Barker-like PN sequence is examined and compared with an asynchronous DS/SSMA communication system employing random binary sequence and Gold sequence. It was found that the MAI performance of the QS-DS/SSMA system is superior when both m and lˆ are small satisfying the inequality 2N⩾lˆ2+3m (m-1)+1, where N is the period of sequences. It was also shown that the bit-error-rate performance of a synchronous DS/SSMA system employing the generalised Barker-like PN sequence is 13.65 dB superior to that of the Gold sequence View full abstract»

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  • Dynamic polling orders in multiserver multiqueue systems

    Publication Year: 1995 , Page(s): 75 - 86
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    Generalised stochastic Petri nets (GSPNs) are used to study the performances of several dynamic polling orders in symmetric multiserver multiqueue systems with one-buffer queues and Markovian interarrival, service, and walk times. Exact numerical results are obtained by means of GreatSPN, the software tool for the analysis of GSPNs, and are presented as curves of the average customer delay and waiting time as well as throughput. The results quantify the performance differences among the various polling orders and show that the usual cyclic order can be the most effective if the possibility of shorter walk times in the cyclic case is taken into account View full abstract»

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  • Analysis of an output-buffered ATM switch with speed-up constraints under correlated and imbalanced bursty traffic

    Publication Year: 1995 , Page(s): 61 - 66
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    The authors consider a discrete-time model of an access ATM switch with output buffers. A switch with output queueing has an optimum performance; however, it requires a switch fabric with speed N. However, the switch fabric may operate at L<N times the speed of the input/output links. The random traffic assumption underestimates the buffer size. Each input port of the switch is assumed to be driven by an interrupted Bernoulli process and every cell in a burst is directed to the same output port. An efficient aggregation method is applied for the performance analysis of the switch. The results prove to be very good View full abstract»

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  • Alternative routing strategies for adjacent cells in mobile radio systems

    Publication Year: 1995 , Page(s): 115 - 120
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    The hexagonal shape of the cells in a mobile radio system is considered as an ideal model. In practice, the cells are not clearly defined but have fuzzy boundaries because of the statistical fluctuations in path losses. If a mobile is near a cell boundary, it may have adequate communication with more than one base station. The authors use this property as the basis for four proposed alternative routing strategies. These techniques are applied in a two-cell system, and their performance analysed in the light of information such as total traffic, number of channels per cell, proportion of flexible traffic, and imbalance of traffic between cells. The traffic process has been modelled by the Markov chain, and the results show that there is a substantial increase in capacity. The proposed strategies are compared with the directed retry and, in general, they seem to yield better results View full abstract»

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  • New approach for traffic characterisation in ATM networks

    Publication Year: 1995 , Page(s): 87 - 90
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    The authors introduce a new approach for traffic characterisation in ATM networks. This is based on the study of remote quantiles associated with stationary point processes as functions of the time interval. It is shown that useful information about the mean and variability of the process can be extracted from the asymptotic behaviour. Finally, the authors show the use of such time quantiles in the context of queue dimensioning which allows comparison of the blocking behaviour of traffic streams without detailed calculations View full abstract»

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  • Design and performance analysis of an asynchronous banyan network switch with window policy

    Publication Year: 1995 , Page(s): 54 - 60
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The authors propose an architecture of an asynchronous banyan network switch with window policy. The switch operates asynchronously, and it can transmit packets of any length at any bit time. When a packet has a collision inside the switch and is blocked, the failure signal is transferred to the input controller which originated the packet. Hence there is no loss of packets in the switch. The switch has a significant advantage in that a window scheme can be implemented. The asynchronous switch with a window scheme yields significant improvement of the maximum throughput as compared with the synchronous banyan network with no window scheme. The authors analyse the maximum throughput of the asynchronous switch with finite window size. In the analysis they make some approximations. The analytical results have been verified by simulation View full abstract»

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