本論文是以IEEE802.16標準為基礎並且在實體層為OFDMA技術下，探討如何在點對多點的WiMAX網路架構下，設計可提高Downlink subframe利用率的資源分配演算法：Channel-Aware Subchannel Renumbering與Channel-Aware Downlink Burst Allocation 。Channel-Aware Downlink Burst Allocation是考慮SSs在Downlink之資料量，BS如何分配Burst的大小、形狀以及位置。因為，在IEEE 802.16標準中，BS分配給SS的頻寬資源均是由連續Subchannels與Symbol time所形成的矩形區域(Burst)。因此，BS在分配頻寬時可能會因為矩形配置而產生了內部與外部頻寬浪費問題；而Channel-Aware Subchannel Renumbering則是解決連續的Subchannel中高調變不能連使用之形況。由於SSs在不同的Subchannels中存在不同的調變等級，導致BS分配Burst給SS接收資料時，無法以較高調變方式傳送，或者BS為了提高Downlink subframe之利用造成Busrt過於分散在不同的Subchannels上，以致於DL-MAP的額外付擔。由實驗結果發現，經過BS經過Channel-Aware Downlink Burst Allocation的方式分配好頻寬資源後，雖然可以有較好的Downlink subframe產能，但無線網路中的環境變化導致產能停滯，然而再BS加入了Channel-Aware Subchannel Renumbering的方法重新調高調變的Subchannls排列後，更能增加Downlink subframe的產能，而且也真的提高了網路傳輸的效能。 This paper proposes a channel-aware downlink resource management scheme in IEEE 802.16 OFDMA system. The scheme is composed of two mechanisms: subchannel renumbering mechanism and burst allocation mechanism, for throughput gains and control message overhead reduction, respectively. Due to the variation of channel conditions, each MS in each subchannel has different receiving condition. BS is expected to transmit data to each MS in good subchannels. Thus, more bursts result in a large burst overhead in the form of DL-MAP. By subchannel renumbering mechanism, the subchannels with highest modualtion can be adjacent as well as the decrease of DL-MAP overhead.Since bursts in downlink subframe are rectangular mapping, how to allocate and schedule each burst for each MS without slots wastage will affect downlink bandwidth usage. Therefore, burst allocation mechanism is used to decide the size, shape and position of each burst in order to alleviate the slots wastage as well as increase the network throughput. The simulation results show that the mechanism can provide higher throughput, higher spectral efficiency, lower fragmentation ratio and lower DL-MAP overhead.
