M.J. Lopez-Herrero. Waiting time of a call in a cellular mobile network with retrials and guard channels

Abstract. In studies of cellular mobile communication networks, it has been recognized that the modeling of customer behaviour is very important for evaluating the quality of service (QoS). Thus fresh calls, initiated inside of a given cell are distinguished from handover calls appearing due to the mobility of the customers. Since handover calls already use network resources, they should be prioritized with respect to fresh calls. In fact, a premature termination of an ongoing call is considered to degrade de QoS much more severely than the experience of a busy signal  at an attempt to initiate a call. Several approaches have been proposed in the literature to cope with this problem. One efficient method is  the use  of guard channels reserved only for the handover calls. To represent accurately a cellular station, the phenomenon of repeated attempts should be also taken into account. Indeed, due to the increasing number of users and the system complexity of modern cellular networks, the impact of retrials is no longer negligible.
In our study we concentrate on a single station so, first we build a Markovian model representing a station of the network, in which we record the number of busy channels and also the number of calls in retrial orbit. We study performance measures related to the waiting time of a fresh call, extending recent studies for cellular mobile networks with retrials and guard channels which concern performance measures directly computable from the stationary probabilities of the number of customers in the cell.for each of them, we investigate the optimal policy and heuristic policies that are convenient for practical implementation. Computational results are conducted to show further managerial insights and effectiveness of the proposed policies.