毫微微細胞(Femtocell)提供低消耗功率以及低耗費的佈建，但毫微微細胞面臨臨近毫微微細胞與巨微細胞(Macrocell)的干擾，為了滿足巨微細胞所服務的使用者之服務品質，如何在毫微微細胞中，適當地分配功率給子載波是很重要的議題。在論文中，我們考慮於正交分頻多工毫微微細胞下行傳輸(Downlink)的系統並考慮兩層級(Tier)間的干擾，且在傳送功率與每個子載波的傳送功率均被限制的條件下，提出改進的功率配置方法，目標為最佳化容量(Capacity)。 最佳化功率配置經由拉格朗日(Lagrange)方法求得最佳解，由此最佳解的功率配置，子載波可被分為兩個集合，一個集合內的子載波被分配功率上限；另一個集合的子載波所分配到的功率是經由注水(Waterfilling)法所得，且此集合內的子載波所分配到的功率不能超過功率上限。所提出的最佳解方法為精確的將兩集合區分，首先，必須找到一個精確的界線(Threshold)，可以正確的區分兩個集合；此界線是基於注水法的概念，重複尋找最佳的界線。為了減少運算複雜度，提出了次佳解的方法，次佳解的概念是希望越多個子載波盡可能的分配到功率上限。所提出之方法與已被提出的方法的容量比較顯示於模擬結果，結果顯示，所提出的方法容量優於已被提出的方法。Femtocells provide low-power and low-cost, but face the interference among neighboring femtocells and macrocells. In order to satisfy the quality of service for the users in the macrocell, how to appropriately allocate power to subcarriers for the users in femtocell networks is a critical problem. Two-tier interference is considered in this study for OFDM-based femtocell downlink networks. Some advanced power allocation schemes are proposed to maximize the capacity subject to the total and upper power constraints. Optimal power allocation is derived in this study by using the Lagrange technique. According to the optimal power allocation, subcarriers should be separate into two sets. Subcarriers in one set is allocated with upper power, and subcarriers in the other one set is allocated with power by the waterfilling technique which is less than the upper power. The design of the proposed optimal scheme is to search a threshold which accurately separates subcarriers into two sets. The threshold is found by an iterative strategy which is based on the concept of the waterfilling technique. In order to reduce computational complexity, the sub-optimal schemes are proposed. The concept of the sub-optimal schemes is to make the number of subcarriers with upper power as many as possible. The capacity for the proposed and the existing schemes is compared in the simulation. From the result, the proposed schemes outperform the existing scheme.
