隨著智慧型手機和平板的普及，用戶端的需求除了撥接電話和發 送簡訊之外，瀏覽網頁、使用應用程式更是不可缺少的；這些使用行 為需要低延遲、高流量，下一代的行動通訊網路LTE便是朝著這些 目標改進。未來的行動通訊網路LTE-Advanced 雖然還沒有商轉，但 是相關的研究已在進行，比如說載波聚合、Advanced MIMO、CoMP、 異質網路。 本篇論文著重在異質網路的議題上，異質網路為一般基地台加上 一些低功率的小基地台，本文討論的是用戶在異質網路環境中的換手 情形，如何有效的讓用戶分攤至小基地台以增加產出、減少干擾。 3GPP已提出兩種機制去改進上述的問題分別為CRE以及ABSF，我 從CRE的部分提出了一個動態CRE的機制，和CRE相比，更能夠 增加產出以及減少干擾。 最後模擬的部分我使用的是LTE-Sim這個軟體，會得到產出、 delay、通道品質、公平性這些指標去觀察我的機制和一般情況以及 CRE 的差異 With the popularity of smart phones and tablets，in addition to phone calls and SMS，browsing web and using APP are indispensable for clients。 These behavior require low latency and high traffic，the LTE，the next generation of mobile communication networks is toward to improve these goals。Although the LTE-Advanced which is the mobile communication network in the future is not commercialized，but related research have been in progress，for example，Carrier aggregation、Advanced MIMO、 CoMP、 Heterogeneous network。 This thesis discusses the issues in heterogeneous networks，in which there are some macro base stations with some low power base stations。And I study the handover behavior in heterogeneous networks and how to offload clients to the low power base stations efficiently to improve throughput and interference cancellation。The 3GPP has proposed two mechanisms to improve the above problems which are the CRE and the ABSF。In this thesis I propose a dynamic CRE mechanism different from the CRE。Compared to CRE，dynamic CRE can improve throughput and interference cancellation much more。 Finally I use the LTE-Sim for simulation，and get performance measure such as throughput, delay, channel quality, fairness for comparison of my proposed scheme and the original CRE。
