通訊科技不斷地朝向高傳輸率和高移動性的目標邁進。正交分頻多工系統是一種有效率的方式，能夠同時達到高傳輸率並且對抗碼際干擾，其具有多個載波，當通道為頻率選擇性衰落時，系統要如何分配資源較為有效率呢﹖ 傳統的分頻多路存取，是將子載波以固定的方式分配給用戶，有別於此，若我們能夠依照通道的狀況和使用者的需求，將子載波和位元適應性地分配給使用者，必定能減少所需功率的輸出。 將功率最小化這類問題之最佳解其計算過於複雜，因此陸續有次佳的方法提出，動態通道配置機制（dynamic channel allocation）是其中之一。本論文改進了動態通道配置機制，使得子載波的分配個數不再固定，能夠適應環境變化而做調整。模擬結果可發現，在某些情況下我們的方法更能夠節省功率的輸出。 In this paper, we propose a sub-carrier allocation algorithm for OFDM-based multi-user system. Assume that the base station knowing the channel gains of all sub-carriers of all users, we try to minimize the required transmit power while satisfying the users’ rate and bits error rate constraints. The optimum solution of this kind of problem is too complicated to realize. So the DCA [1] (Dynamic Channel Assignment) algorithm based on constructive assignment and iterative improvement is developed to make a solution in real time. But the sub-carrier number of the users can not change according to the fading channel, and the DCA scheme doesn’t say how to decide these numbers also. So this paper proposed a DCA-extension scheme to improve this problem. We add a new factor in the step 2 in DCA, so the user’s sub-carrier number can be adjusted according to the channel fading. Simulation results show that the power gains of this algorithm is proportion to the difference of the users’ SNR and the speed of the users.
