網路使用率逐漸普及、傳輸技術的進步以及通訊網路蓬勃發展，提供人們許多生活上的便利，無線網路已經成為現代通訊市場上的新寵兒。其中，IEEE於1999年開始制定與修正WiMAX，此協定在無線網路的應用視為解決”最後一哩”接取問題的利器。然而，無線網路仍舊會遇到傳送訊號耗弱、通訊死角或是氣候干擾等種種原因造成傳輸失敗的問題。 MPEG-4編碼上，考慮影音封包具有不同重要性的意義，針對影音封包需制定不同的重傳機制，本研究先行改善WiMAX中ARQ（Auto Repeat Request）的流程，再利用跨層設計使得MAC層可以辨識影音封包資訊，確保GOP-tree中之＂骨幹＂節點穩定的抵達率，再利用Lagrange’s Method of Multiplier方法，針對GOP-tree中非骨幹部分提出合適的trade-off客製化。最後本研究藉由網路模擬器NS-2(Network Simulater ver. 2)與myEvalvid-NT的實驗架構，做不同效能的評比，並以PSNR值評估所提出之方法的有效性。 / The growing of network popularity, progressing of trasmission technology and development of communication network have facilitated our daily life these years. Wireless network has become a new favor at modern communication market. Among of them, IEEE has started to design and modify specification of WiMAX since 1999, which has been thought to be the solution toward “last mile”. But, there still exist problems such as Doppler effect, blind corner of communication and obstruction of weather condition, which cause the failure of communication. MPEG-4 coding would concern the different significances of distinct types of packets, we should define retransmission strategies for different multimedia packets, respectively. Firstly, we improve the process of ARQ(Auto Repeat reQuest). Secondly, we use MAC-centric design to distinguish multimedia packets and guarantee the arrival rate of packets in the “backbone nodes” of a group of pictures tree. Thirdly, Lagrange’s Method of Multiplier is used to customize the trade-off of “non-backbone node”. In the end, we have performance evaluations by NS-2(Network Simulator ver. 2) and myEvalvid-NT, to verify the efficiency of the proposed method using Peak Signal to Noise Ratio.