為因應行動通訊需求的大量增加，在LTE系統中，大、小細胞共存之異質網路受到廣泛的討論。於異質網路中，小型基地台的佈建能擴大系統覆蓋範圍、提高頻譜效率，進而提升整體資訊傳送量；但隨著佈建的密度增加，用戶將頻繁地執行基地台間交接(handover)程序，不只加重系統處理負擔，也由於細胞間互相干擾的問題，提高通話中斷的風險。另外，由於大、小基地台間的功率差異以及行動用戶不規則的移動特性，導致系統產生負載不平衡的現象，當一個基地台過載時，很容易因為資源缺乏而阻斷通話接取及交接要求，甚至導致通話中斷。針對上述議題，本論文提出一嶄新交接機制，根據基地台本身的負載變化調整交接程序參數以改變基地台服務範圍，並針對系統資源之存取方式做控制處理，除了在發生過載時，能有效將用戶卸載至鄰近基地台，也能藉由調整資源存取的方式，更進一步紓解資源缺乏所導致的各種問題，以降低通話阻斷率(call block rate, CBR)及中斷率(call drop rate, CDR)。

To satisfy the explosive growth of mobile communication traffic demands, the heterogeneous networks (HetNets) in which macro cells and small cells (picocells, femtocells) are coexistent have been widely discussed in LTE systems. In HetNets, the deployment of small cells can expand system coverage, improve spectral efficiency, and bring higher network capacity. However, with the increase of small cell density, mobile users (MUs) will experience frequent handover process which not only induces high signaling cost, but also raises the risk of call-dropping due to the inter-cell interference. In addition, the transmit power difference between macro cells and small cells as well as the irregular MUs’ mobility lead to unbalanced load distribution in the systems. When a cell is overloaded, it faces resource shortage and may block new call access and handover request, and may even drop the call. For these issues, this thesis proposes a novel handover process to adaptively modify the handover parameters according to the variation of cell load. By adjusting the handover parameters, the cell coverage will be changed and cells’ loads will be more balanced. Moreover, a resource access control is proposed to further relieve the problems caused by resource shortage so as to reduce call block rate (CBR) and call drop rate (CDR).

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