  This work focuses over the performability analysis of a multi-server retrial
queueing model with phase-type inter-retrial times in cellular networks. It is
considered that the pattern of the new call arrival and handoff call arrival
follows Markovian arrival process (MAP). The service times of both types of
calls are phase-type (PH ) distributed with different service rates, and
inter-failure & inter-repair times of channels are exponentially distributed.
For the prioritization of handoff calls, G channels are kept in reserve for
handoff calls. When all the available channels, say S, are busy at the arrival
epoch of a handoff call, the handoff call will be dropped. Whereas a new call
will be blocked and will have an option to join the orbit of infinite capacity
or leave the system without getting the connection, if at least S-G channels
are busy. A new call in the orbit, termed as retrial call, retries to get the
connection after a random interval which follows PH distribution. This model is
analyzed as a level-dependent-quasi-birth-death (LDQBD) process by applying
matrix-analytic method (MAM). Further, the closed-form expressions for
essential performance measures of the proposed model are derived. Through
numerical illustrations, the behaviour of performance measures depending on the
various relevant intensities is discussed. An expected cost optimization
problem is formulated to determine the optimal value of service intensity and
the optimal value of repair intensity. The cost function analysis is executed
by employing Simulated Annealing (SA) method.
