在階層式網路(hierarchical network)中，普遍會藉由把超微型基地台(femtocell)佈建於大型基地台(macrocell)中來增進室內使用者設備的資料產出量(throughput)，而這些室內的用戶稱為超微型基地台使用者設備。它會干擾大型基地台與大型基地台使用者設備的訊號品質，尤其是在超微型基地台附近的巨微細胞使用者設備[12]。因此，跨層的干擾(cross-tier interference)是一個重要的研究議題。為了改善干擾的問題，3GPP在進階長程演進系統(LTE-A)裡定義了感知無線電(cognitive radio)的超微型基地台來協調下行傳輸基地台間的干擾。感知無線電的超微型基地台擁有感知無線環境的能力，進而得到無線環境的參數。在本論文中，我們分析已經存在的一些分割頻段重複使用(fractional frequency reuse)方法的效能，並提出藉由感知無線電的超微型基地台來增進分割頻段重複使用方法的效能。模擬結果顯示，我們的方法提供超微型基地台使用者設備較佳的平均下行資料產出量以及整個異質網路中使用者設備較佳的下行資料產出量。

In a hierarchical network, femtocells are deployed within a macroecell for improving throughput of indoor user equipments (UEs), which are referred to as femtocell UEs (FUEs). In such deployment, cross-tier interference
is an important issue, which may significantly impact signal quality between
macrocell base stations (MBSs) and macrocell user
equipments (MUEs), especially for MUEs near the femtocell [12]. In order to relieve this problem, Third Generation Partnership Project Long Term Evolution-Advanced (3GPP LTE-A) defines the cognitive radio (CR)-enhanced femtocell to coordinate interference for downlink. CR-enhanced femtocells have the ability to sense radio environment to obtain radio parameters. In this paper, we investigate the performance of existing schemes based on fractional frequency reuse. Then we propose a scheme with cognitive radio technology to improve the performance of fractional frequency reuse scheme. Simulation results show that our scheme can effectively enhance average downlink throughput of FUEs as well as the total downlink throughput in hierarchical networks.

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