This chapter presents the general Radio Resource Management (RRM) problem in wireless access networks and gives performance evaluations for different downlink resource (sub-carrier) allocation algorithms in WiMAX TDD systems based on OFDMA wireless access. This is particularly important in downlink due to the traffic asymmetry and due to the information availability at the base station regarding the quality requirements for a particular user. The comparative performance analysis of the different resource allocation algorithms is using the average cell/user throughput and user throughput versus distance from the reference base station as performance metrics. For the comparative performance evaluation, we have resorted to MATLAB simulations. Additionally, a semi-analytical approach is proposed for the downlink throughput performance estimation of the algorithms that do not rely on the channel quality information feedback from the mobile users. The analysis shows that Proportional Fair and Soft partitioning/re-use algorithms are good candidates for downlink resource allocation in WiMAX TDD systems and that the proposed semi-analytical approach accurately estimates the throughput performance of the reuse schemes.