In this paper, we consider the problem of sub-carriers and power allocation for the downlink of an orthogonal frequency division multiplexing access (OFDMA) system with proportional fairness. Firstly, we develop an improved resource allocation algorithm for OFDMA systems with intercarrier interference (ICI) based on genetic algorithm. Secondly we also develop an improved water-filling algorithm. The resource allocation problem is formulated as one that maximizes the total capacity of all active users subject to certain constraint conditions, which are determined by proportional fairness, total power and bit error rate. The simulation results show that the proposed algorithms have better performance in proportional fairness, algorithm convergence and complexity of the algorithm compared to the existing methods.