Analysis and optimization of Guard Channel Policy with buffering in cellular mobile networks

A multi-server retrial queue with two types of calls (handover and new calls) is analyzed. This queue models the operation of a cell of a mobile communication network. Calls of two types arrive at the system according to the marked Markovian arrival process. The service times of both types of calls have phase-type distributions with different service rates. Handover calls have priority over new calls. Priority is ensured by provision of a dedicated buffer and reservation of several servers of the system exclusively for the service of handover calls. A handover call is dropped and leaves the system if all servers are busy and the buffer is full at the arrival epoch. During the waiting time in the buffer, the handover calls are impatient and may leave the system without service. A new call is blocked if all servers available to new calls are busy. Such a call has options to balk (to leave the system without obtaining service) or to retry later. The behavior of the system is described by the multi-dimensional Markov chain belonging to the class of the asymptotically quasi-Toeplitz Markov chains (AQTMC). In this paper, the generator of this Markov chain is constructed, and it is shown that the chain is ergodic for any set of the system parameters. Formulas for computing various performance measures of the system based on the stationary distribution of the Markov chain are derived. The results of numerical experiments illustrating the behavior of key performance measures of the system depending on the number of reserved servers are presented. A highly positive effect of buffering the handover calls and the server's reservation is demonstrated.