Modified Erlang loss system for cognitive wireless networks

This paper considers a modified Erlang loss system for cognitive wireless networks and related applications. A primary user has preemptive priority over secondary users and the primary customer is lost if upon arrival all the channels are used by other primary users. Secondary users cognitively use idle channels and they can wait at an infinite buffer in cases idle channels are not available upon arrival or they are interrupted by primary users. We obtain explicit stability condition for the cases where arrival processes of primary users and secondary users follow Poisson processes and their service times follow two distinct arbitrary distributions. The stability condition is insensitive to the service time distributions and implies the maximal throughout of secondary users. For a special case of exponential service time distributions, we analyze in depth to show the effect of parameters on the delay performance and the mean number of interruptions of secondary users. Our simulations for distributions rather than exponential reveal that the mean number of terminations for secondary users is less sensitive to the service time distribution of primary users.Comment: Submitted to Journal of Mathematical Science

Retrial Queueing Models: A Survey on Theory and Applications

Retrial phenomenon naturally arises in various systems such as call centers, cellular networks and random access protocols in local area networks. This paper gives a comprehensive survey on theory and applications of retrial queues in these systems. We investigate the state of the art of the theoretical researches including exact solutions, stability, asymptotic analyses and multidimensional models. We present an overview on retrial models arising from real world applications. Some open problems and promising research directions are also discussed.Comment: 31 pages. In: Stochastic Operations Research in Business and Industry (eds. by Tadashi Dohi, Katsunori Ano and Shoji Kasahara