Downlink Erlang capacity of cellular OFDMA

In this paper, we present a novel approach to evaluate the downlink Erlang capacity of a cellular Orthogonal Frequency Division Multiple Access (OFDMA) system with 1:1 frequency reuse. Erlang capacity analysis of traditional cellular systems like Global System for Mobile communications (GSM) cannot be applied to cellular OFDMA because in the latter, each incoming call requires a random number of subcarriers. To address this problem, we divide incoming calls into classes according to their subcarrier requirement. Then, we model the system as a multi-dimensional Markov chain and evaluate the Erlang capacity. We draw an interesting analogy between the problem considered, and the concept of stochastic knapsack, a generalization of the classical knapsack problem. Techniques used to solve the stochastic knapsack problem simplify the analysis of the multi-dimensional Markov chain.