Analysis of Blocking Probability in a Relay-Based Cellular OFDMA Network

Relay deployment in Orthogonal Frequency Division Multiple Access (OFDMA) based cellular networks helps in coverage extension and/or capacity improvement. To quantify capacity improvement, blocking probability of voice traffic is typically calculated using Erlang B formula. This calculation is based on the assumption that all users require same amount of resources to satisfy their rate requirement. However, in an 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. Therefore, the Erlang B formula can not be employed to compute blocking probability in an OFDMA network. In this paper, we determine an analytical expression to compute the blocking probability of relay based cellular OFDMA network. We determine an expression of the probability distribution of the user’s resource requirement based on its experienced SIR. Then, we classify the users into various classes depending upon their subcarrier requirement. We consider the system to be a multi-dimensional system with different classes and evaluate the blocking probability of system using the multi-dimensional Erlang loss formulas. This model is useful in the performance evaluation, design, planning of resources and call admission control of relay based cellular OFDMA networks like LTE.