異質移動性蜂巢網路已經充斥在我們的生活中,提供行動用戶各種語音和數據服務。該異質性蜂巢網路是由兩層的蜂巢網路所組成,其中各層的基地台位置皆具隨機性,且擁有特定的傳輸功率、路徑損耗指數、密度及偏異值。舉例來說,相較於大型基地台,小型基地台擁有較低的傳輸功率、較高的密度及正偏異值,這些特性都會讓原本連結大型基地台的用戶更積極地選擇輕負載的小型基地台。而行動裝置的通訊可能在發起通訊或切換通訊 (我們稱為換手) 的過程中因為基地台資源不足被迫中斷。在過去幾年,已有許多文獻在傳統六角形蜂巢網路中以時間的角度發展並分析換手的特性。然而,對於現今異質移動性蜂巢網路,基地台規律的分配已無法確實呈現實際位置的不確定性。本篇論文將至今尚無被探討過的基地台資源考慮進換手方法,並利用隨機幾何的技術建置網路模型,來研究分析在兩層異質移動性蜂巢網路中的通訊阻擋機率。通訊阻擋機率代表通訊因為資源不足而被強制終止的機率。我們根據從 OpenCellID中的大型基地台地理位置數據進行模擬實驗,來比較並評估提出的隨機幾何模型與現實環境的差異。

Mobile heterogeneous cellular networks (HCNs) have been integrated with human life to provide various kinds of voice and data services to mobile users (MUs). The HCNs is modeled as a two-tier cellular network where each tier’s base stations (BSs) are randomly located and have a particular transmit power, path loss exponent, spatial density, and bias towards admitting MUs. For instance, when compared with macro BSs (mBSs), small BSs (sBSs) would usually have lower transmit power, higher spatial density, and a positive bias so that users in mBS are actively encouraged to use the more lightly loaded sBSs. Due to resource insufficiency, the services might not be completed during the call initiation or the handover process, and the key to maintaining service continuation depends on how to handle the handover process. Over the past few years, many literatures developed and analyzed the models for understanding the characteristics of handovers are investigated from time perspective with the assumption of homogeneous hexagonal cells. However, BSs are not deployed regularly in recent mobile HCNs such as LTE-Advanced, the analytical model including uncertainty of location is emerging. This paper considers different BSs’ cell size, which has not been considered in handover method yet, and adopts stochastic geometry perspective model to analyze a study of call blocking probability for two-tier HCNs where the performance of handover process can be evaluated. The call blocking probability, we present, is derived by resource insufficiency. We also conduct simulation experiments according to mBSs’ data from OpenCellID to comprehensively evaluate the proposed stochastic geometry model in the realistic environment.

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