Electrical and Electronic Engineering - Theses
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ItemTraffic modelling and analysis for cellular mobile networks( 1993)This thesis is concerned with the modelling and analysis of call control policies in cellular mobile networks. It addresses the important problem of finding policies which give sufficient priority to handover attempts between cells over new call attempts so that network congestion will not lead to handover failures and subsequent call dropouts. The major contribution of the thesis is the analysis of a class of priority queuing systems and a methodology for the modelling of cellular networks with non-uniform offered traffics. Three related priority queuing systems are considered for application to cellular mobile networks: a non-preemptive priority queue; a cutoff priority queue with a hysteresis mechanism and a non-preemptive priority queue with channel reservation and hysteresis. A matrix-geometric solution of the same form is shown to be common to all of these systems with a matrix-exponential form found for the delay distributions. It is also shown that these systems can be represented by an equivalent M/G/1 queue with multiple vacations and this reveals some insight into their behaviour. A new result is derived for the M/G/1 queue with multiple vacations and impatient customers and this allows for the priority systems to be extended so that new call arrivals are subject to a fixed timeout in queue. In some situations, this provides a more realistic model of the behaviour of new call attempts. Handover delay performance is treated at length. It is found that queuing of handover requests is highly desirable and that handover delay performance can be further improved by classifying handover requests and giving higher priority to the more urgent handover requests. Microcellular networks, for which handover delay requirements are quite stringent, are also considered. A micro cellular traffic model is proposed and a call repacking policy, which is particularly well-suited to microcells, is analysed. The effectiveness of a class of state-dependent call acceptance policies in improving handover delay performance is also considered. The performance of cellular networks is much dependent on the distribution of offered traffic. An approximation technique is developed which enables a wide class of call control policies to be investigated. It is based on decomposing a network into a number of subnetworks which are then assumed to be stochastically independent. This technique turns out to be fairly accurate under reasonable traffic assumptions.