This article addresses downlink resource allocation strategies in Mobile WiMAX based on IEEE802.16e standard, using Orthogonal Frequency Division Access (OFDMA). We consider Mobile WiMAX resource allocation strategies for allocating higher layer data to the basic resource allocation units (slots) of OFDMA frames. Then, we introduce two simple allocation methods: Adaptive Slot Allocation (ASA) and Reservation-Based Slot Allocation (RSA). Both approaches consider a fair resource allocation among different types of service flows (SFs) by considering their QoS characteristics and their channel qualities. The ultimate objective of the proposed approaches is to maximize the capacity of the system subject to the quality of service (QoS) constraints for each type of (SFs) in terms of data rate and Bit Error Rate (BER).