A subcarrier and bit allocation period (SBAP) is proposed based on the mobile speed for OFDM systems. It is assumed that users have different SBAPs according to their mobile speeds. The overhead is considered while transmitting the subcarrier and bit assignment information (SBAI). The optimum SBAP of each user is determined such that the overall throughput including SBAI can be maximized. Simulation results show that the proposed scheme outperforms other schemes. It is also demonstrated that the proposed scheme is insensitive to an error in the estimation of mobile speeds.