David Everitt

Effective bandwidth-based admission control for multiservice CDMA cellular networks

We develop product form traffic models for single- and multiple-cell code-division multiple-access (CDMA) networks with multiple classes of mobile subscribers. The key feature of this development is the specification of a flexible call admission control procedure that details the numbers of mobiles of each class in each cell that the system operator should allow in order to maintain an acceptable quality of service. Effective bandwidth techniques from the analysis of statistical multiplexing at an asynchronous transfer mode (ATM) based broadband integrated services digital network (ISDN) link are used to give performance guarantees that overcome the variability in interference levels characteristic of CDMA cellular networks. The result is an admissible region bounded by a finite number of hyperplanes and a simple and efficient call admission policy. The CDMA mobile network, operating within the admissible region described, has a very similar form to a circuit-switched network operating with fixed routing. This similarity allows the existing traffic modeling techniques and network management strategies for general loss networks to be applied to CDMA mobile cellular networks. In particular, with standard assumptions on the call arrival processes and holding times, the stationary state distribution has a product form on the truncated state space defined by the call admission strategy.

Limited-range wavelength translation in all-optical networks

This paper examines wavelength translation in all-optical wavelength-routed networks. Previous studies have shown that wavelength translation can improve the blocking performance of these networks. However, all the previous work has assumed that wavelength translators can translate from any input wavelength to any output wavelength. In contrast, all-optical wavelength translators demonstrated in the laboratory to date are, in general, only capable of limited translation. We assess, for the first time, the network performance improvements offered by realistic all-optical wavelength translators with a limited translation range. In particular, we consider all-optical wavelength translators based on four-wave mixing in semiconductor optical amplifiers. Using a simple model for their function, we consider the blocking performance of two-hop and multiple-hop paths, and unidirectional ring and mesh-torus networks. In all the cases we consider, significant improvement in the blocking performance of the network is obtained when limited-range wavelength translators with as little as one quarter of the full range an introduced. We also find that almost all of the network performance improvement observed by an ideal wavelength translator can be gained from a translator with only half of the full translation range.

On the teletraffic capacity of CDMA cellular networks

The aim of this paper is to contribute to the understanding of the teletraffic behavior of code-division multiple-access (CDMA) cellular networks. In particular, we examine a technique to assess the reverse link traffic capacity and its sensitivity to various propagation and system parameters. We begin by discussing methods of characterizing interference from other users in the network. These methods are extremely important in the development of the traffic models. We begin with a review of several existing approaches to the problem of handling other-cell interference before presenting a novel characterization of the interference in the form of an analytic expression for the interference distribution function in the deterministic propagation environment. We then look at extending the capacity analyses that assume a fixed and equal number of users in every cell to handle the random nature of call arrivals and departures. The simplest way to do this is by modeling each cell of the network as an independent M/G/x/spl infin/ queue. This allows us to replace the deterministic number of users in each cell by an independent Poisson random variable for each cell. The resulting compound Poisson sums have some very nice properties that allow us to calculate an outage probability by analyzing a single random sum. This leads to a very efficient technique for assessing the reverse link traffic capacity of CDMA cellular networks.

Neural network-based dynamic channel assignment for cellular mobile communication systems

Conventional dynamic channel assignment schemes are both time-consuming and algorithmically complex. An alternative approach, based on cascaded multilayered feedforward neural networks, is proposed and examined on two cellular systems with different configurations. Simulation results showed that the blocking performance of our multistage neural network approach can match that of an example conventional scheme with less complexity and higher computational efficiency. The example scheme considered here is the ordered channel search, which can achieve a reasonably high spectral efficiency as compared to that of an ideal dynamic channel allocation algorithm. We conclude that our neural network approach is well-suited to the dynamic channel allocation problem of future cellular or microcellular systems with decentralized control. >

Blocking in multiwavelength TDM networks

This paper examines the relative importance of wavelength conversion and time‐slot interchange in improving the performance of multiwavelength time‐division multiplexed networks. It is shown that, in networks with a small number of wavelengths, each carrying a large number of time‐division multiplexed channels, significant performance improvements are achieved by the introduction of time‐slot interchange alone, without wavelength conversion. However, some performance improvements are also achieved by the introduction of wavelength conversion alone.

Traffic capacity of cellular mobile communications systems

Abstract In a cellular mobile communication system, the traffic capacity of the system is an important quantity, and depends on the way that channels are allocated to calls. Many channel allocation algorithms have been proposed, and this paper makes a direct comparison of some of them. Specifically, the operating regimes considered are fixed channel assignment, dynamic channel assignment, directed retry, and directed handoff. The main conclusion is that directed handoff gives a strong gain in traffic capacity and traffic adaptability for these systems. The paper also discusses some of the factors affecting the future development of mobile communication systems.

Impact of polling strategy on capacity of 802.11 based wireless multimedia LANs

Wireless local area networks are a viable technology to support multimedia traffic. One of the prominent wireless local area network standards being adopted as a mature technology is the IEEE 802.11 standard. In wireless multimedia networks, mobile stations will be capable of generating a heterogeneous traffic mix and therefore it is crucial to devise an efficient bandwidth allocation scheme to satisfy the quality of service requirements of each traffic class. In this paper we present a distributed fair queuing scheme which is compatible with the 802.11 standard and can manage bandwidth allocation for delay-sensitive traffic. The performance of the proposed scheme is evaluated by simulation, showing that a distributed version of deficit round robin outperforms the standard round robin service discipline from a capacity viewpoint.

Call admission control in multiple service DS-CDMA cellular networks

We develop traffic models for single and multiple cell CDMA networks with multiple classes of mobile subscriber. The key feature of this development is the specification of an effective bandwidth based call admission control procedure that details the numbers of mobiles of each class in each cell that the system operator should allow in order to maintain an acceptable quality of service. The CDMA mobile network, operating within the admissible region described, has a very similar form to a circuit-switched network operating with fixed routing. This similarity allows the existing traffic modelling techniques and network management strategies for general loss networks, to be applied to CDMA mobile cellular networks.

Comparison of alternative handoff strategies for micro-cellular mobile communication systems

The drop-out probability and the unnecessary handover performance of several handover schemes have been investigated using a simulation model which incorporates detailed representation of mobility, traffic and propagation environments. Specifically the overall performance of variable hysteresis level handover schemes are investigated. The performance under various mobility conditions are presented for both Manhattan city environment and hexagonal cell layout. Also the performance dependency on more critical input parameters such as mobile speed and correlation of sample measurements, is presented. It is shown that an environment dependent, variable hysteresis function can be devised by closely studying the system handover behaviour to give the optimum overall performance.<<ETX>>

Combined analysis of transmission and traffic characteristics in micro-cellular mobile communication systems

The development of a simulation model for micro-cellular systems which incorporates both transmission and traffic characteristics is discussed. The usage of this type of modelling is illustrated using examples of several combinations of analysis. It is shown that, by taking all the characteristics into one platform, the combined effects and the interrelation of them can be analyzed in an easier and more realistic way than in previous studies. This type of analysis would be very useful in finding overall system performance and in optimizing the system parameters.