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Communications, IEE Proceedings-

Issue 3 • Date June 2003

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Displaying Results 1 - 13 of 13
  • Performance analysis of MC-CDMA in Rayleigh fading channels with correlated envelopes and phases

    Page(s): 214 - 220
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (497 KB)  

    The performance analysis of a multicarrier code division multiple access (MC-CDMA) system in Rayleigh fading channels with correlated envelopes and phases is presented, and the effect of phase correlation on the bit error rate (BER) performance is demonstrated. An equivalence relation between independent phases and random spreading sequences for asynchronous MC-CDMA is established, which can explain why the problem of code-independent variance of multiple access interference (MAI) has appeared in the past. Furthermore, it is found that the interference from other subcarriers is always less than half the interference from the same subcarriers for asynchronous MC-CDMA with random spreading sequences. It is also found that Gold, orthogonal Gold, Walsh and random sequences yield similar BER performance in an asynchronous MC-CDMA system with a relatively large number of users. For an uplink MC-CDMA, time synchronisation does not improve the BER performance significantly. Finally, asynchronous MC-CDMA systems benefit from the increase of delay spread of the channel, while the opposite conclusion holds for the downlink of MC-CDMA. View full abstract»

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  • Signalling constellations for power-efficient bit-interleaved coded modulation schemes

    Page(s): 141 - 148
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (601 KB)  

    Bit-interleaved coded modulation (BICM) is a bandwidth-efficient coding technique consisting of serial concatenation of binary error-correcting coding, bit-by-bit interleaving, and high-order modulation. The author addresses the problem of finding the signal sets that are most suitable for designing power-efficient BICM schemes over an additive white Gaussian noise channel. To this end, the expression of the BICM capacity limit is exploited and evaluated for several 8- and 16-ary constellations. It is also shown that the bit error probability curves of the modulation schemes without coding can be used to determine the most attractive constellations. Finally, the bit error rate performance of some BICM schemes made up of turbo codes and various signal sets is investigated to illustrate the theoretical results. View full abstract»

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  • K-step pointer forwarding strategy for location tracking in distributed HLR environment

    Page(s): 207 - 213
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Managing the location of mobile systems is crucial. The location of a mobile must be determined whenever a connection is established. Thus, mobile systems need to be able to cope with frequent location updates and queries. In addition to the HLR/VLR strategy in IS-41 and GSM, the feasibility of reducing the network load imposed by locating mobile users has attracted considerable attention. One user location algorithm, called 'pointer forwarding with single HLR' was proposed to reduce the location update cost. The distributed HLR strategy was then presented to prevent HLR from becoming a signal bottleneck in the signalling network. Although this approach eliminates the cost of updating multiple HLRs, greatly reducing the database access delay, it also introduces a long pointer chain that may involve a large locating cost and long call delivery time. The study proposes a more efficient location tracking strategy, named the 'K-step pointer forwarding strategy with distributed HLR'. This strategy guarantees that the pointer chain length never exceeds K. Its performance is studied by numerical analysis. The results demonstrate that the strategy can considerably reduce the call delivery time. View full abstract»

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  • Towards an adaptive RED algorithm for achieving delay-loss performance

    Page(s): 163 - 168
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (437 KB)  

    Random early detection (RED) proposed by Floyd and Jacobson (1993) is an active queue management strategy that has been deployed extensively in routers. However, its effectiveness has been limited owing to the difficulty in tuning its parameters under different network conditions. The authors define the notion of an operating point that an active queue management (AQM) policy should target. They suggest that the RED parameters should be set or varied with the aim of reaching this operating point. Extensive simulations have been performed to understand the effect of maxth and maxp on the network dynamics. Based on these simulations, guidelines are given to adapt the RED parameters. View full abstract»

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  • Performance of a digital code tracking loop for DSSS systems in the presence of Doppler shift

    Page(s): 202 - 206
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    The authors present a low-complexity non-coherent tracking loop based on the gravity of energy window (GEW). Expressions for the proposed tracking loop in a multipath fading channel with Doppler shift environment are derived. The stationary probability density function (PDF) of the phase error and the root-mean-square (RMS) tracking error are obtained by computer simulation. Statistical simulation results show that the new tracking loop can provide much better performance than the conventional non-coherent delay lock loop (DLL) in the presence of Doppler shift. View full abstract»

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  • Rate controller for high-speed networks

    Page(s): 169 - 175
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (543 KB)  

    In the paper, the statistical performance of a leaky bucket rate controller is analysed. A new operating mechanism is proposed for the leaky-bucket rate controller. The proposed mechanism has the major advantage of allowing a simple embedded Markov chain analysis for the rate controller, when the input traffic is modelled using a generally distributed interarrival process. Analysis is developed to study the statistical performance of the rate controller, including the cell delay distribution and the cell loss ratio. Numerical experiments are carried out to illustrate the analysis results and to provide insight into the system design. View full abstract»

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  • Waiting time distribution for the M/M/m queue

    Page(s): 159 - 162
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    A novel method is presented for the calculation of the waiting time distribution function for the M/M/m queue. It is shown that the conditional waiting time obeys an Erlang distribution with rate mμ, where μ is the service rate of a server. An explicit closed form solution is obtained by means of the probability density function of the Erlang distribution. The derivation of the result proved to be very simple. The significance of Khintchine's (1969) method and its close relation to the proposed method is pointed out. It is also shown that the waiting time distribution can be obtained from Takacs's (1961) waiting time distribution for the G/M/m queue as a special case. This reveals some insight into the significance of Takacs's more general, but rather complex, result. View full abstract»

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  • Traffic grooming on general topology WDM networks

    Page(s): 197 - 201
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (407 KB)  

    The authors consider the traffic grooming problem on general topology WDM networks. The problem is: given a set of t connections, their routes and the grooming factor g, find an optimal wavelength assignment and grooming such that the number of wavelengths required in the network is minimised. This problem is first formulated as an integer linear programming problem, and then a heuristic is proposed to solve it. The simulation results show that increasing the grooming factor can considerably decrease the number of wavelengths required in the system. View full abstract»

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  • High-performance scheduler to achieve proportional delay differentiation

    Page(s): 153 - 158
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (506 KB)  

    The proportional delay differentiation model provides a consistent packet delay differentiation between various classes of service. The waiting time priority (WTP) scheduler is a priority scheduler in which the priority of a packet increases in proportion to its waiting time, and it is known to be the best scheduler to achieve the proportional delay differentiation model. The author proposes an advanced WTP (AWTP) scheduler, modified from WTP, that accounts for the packet transmission time. Simulation results reveal that when the link utilisation is moderate (60%-90%), this scheduler not only obtains a more accurate delay proportion than the WTP scheduler, no matter whether in short or long timescales, but also reduces the average queueing delay (waiting time). The effects of traffic load distribution, and the mean packet size and its coefficient of variation on both schedulers' performance are also examined. AWTP always outperforms WTP in these cases. However, AWTP may not maintain stable delay ratios under some traffic load distributions. A modification named AWTP+ is proposed and proved to overcome this problem. View full abstract»

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  • Queueing analysis of an ATM multimedia multiplexer with non-pre-emptive priority

    Page(s): 189 - 196
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (511 KB)  

    A queueing-theoretic analysis of an ATM multiplexer handling two-class multimedia traffic is described. Specifically, it assigns class-1 cells, constituting real-time traffic, high service priority, and class-2 cells, constituting non-real time traffic, low service priority. The priority discipline used is non-pre-emptive. For the purpose of the analysis, the multiplexer is modelled as a priority, discrete time, single-arrival, single-server queueing system with an infinite buffer and geometric service time. The model dynamics are extracted by a rather complex difference equation whose solution is sought using a generating function technique. This difference equation approach is a major contribution of the paper. Unlike the prevalent stochastic equation approach, it makes the physical details of the system present and visible during the analysis. Results are obtained for the multiplexer occupancy and cell waiting time. These results are verified analytically by producing from them some previously published results as special cases. They are also verified by applying them to numerical examples and obtaining intuitively acceptable values. View full abstract»

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  • Combined turbo equalisation and block turbo coded modulation

    Page(s): 149 - 152
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    The combination of equalisation and turbo decoded M-QAM is studied. In a system of block turbo coding based on iterative decoding of a product code, equalisation is incorporated in the decoding iteration loop. Most research in this area has considered the trellis equaliser. When using a high throughput modulation trellis equalisation is impossible. The incorporation of a decision feedback equaliser (DFE) in the iterative decoding is studied, and simulation results show the gain achieved by incorporation of the DFE in the iteration loop. View full abstract»

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  • ATM switch with dual transceiver ring architecture

    Page(s): 184 - 188
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (378 KB)  

    Different techniques exist for an asynchronous transfer mode (ATM) switch design. An ideal ATM switch has high throughput, low loss and low delay. A technique for designing an ATM switch is the use of a shared medium. In this technique a bus or ring may be used as the shared medium. A new switch that uses a dual ring as a shared medium is introduced. The dual ring topology has been proposed for local area networks and has higher throughput than a conventional ring. A throughput higher than 96%, delay less than 35 μs and low loss are the results obtained from the performance analysis of this new switch. View full abstract»

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  • Aggregation technique for networks with power law traffic and application to accelerated simulation

    Page(s): 177 - 183
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (523 KB)  

    The authors present an accelerated simulation technique for packetised networks, and examine the accuracy and speedup obtained when it is used in studies of power law traffic, including cases where the sojourn times have been truncated to imitate real network operation. The aggregation concept has also been applied to an end-to-end path, where both the number of end-to-end nodes and the number of traffic sources at a node are aggregated. It is shown that very accurate results are obtained in combination with significant simulation acceleration. View full abstract»

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