  Relay deployment in Orthogonal Frequency Division Multiple Access (OFDMA)
based cellular networks helps in coverage extension and or capacity
improvement. In OFDMA system, each user requires different number of
subcarriers to meet its rate requirement. This resource requirement depends on
the Signal to Interference Ratio (SIR) experienced by a user. Traditional
methods to compute blocking probability cannot be used in relay based cellular
OFDMA networks. In this paper, we present an approach to compute the blocking
probability of such networks. We determine an expression of the probability
distribution of the users resource requirement based on its experienced SIR and
then classify the users into various classes depending upon their subcarrier
requirement. We consider the system to be a multidimensional system with
different classes and evaluate the blocking probability of system using the
multi-dimensional Erlang loss formulas.
