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IEEE802.16e based mobile WiMAX network provides a promising technology for broadband wireless access. Among all types of services supported by WiMAX, real time video multicast has attracted much attention. However, because of the absence of feedback channel for multicast service, it is challenging to provide link adaptation and resource allocation under the situation with diverse receiver distribution. The legacy method - using the most robust modulation mode for multicasting service, or select a leader as the representative - can not accurately reflect the variety of channel condition. In this paper, we firstly analyze the overhead problem caused by the periodic downlink channel quality report, then propose a light-weighted terminal triggered feedback mechanism to reduce the signaling overhead. Furthermore, with the combined consideration of layered video coding and adaptive modulation and coding, a utility-based resource allocation approach is proposed. The utility function is relating with the reception satisfaction and spectrum efficiency. The scheduling algorithm dynamically adjusts layer number and its bandwidth according to receiver distribution. Simulation results show the proposed feedback mechanism can greatly reduce the signaling overhead while maintain the accurate channel condition report. The scheduling algorithm can not only improve the link adaptation capability following the receivers' expectation and program popularity, but also outperform the fixed allocation method in term of system utility.