具多重無線存取技術之超高密度異質性網路的共存效能分析

Abstract

本論文旨在建立一個包含多種無線存取技術共存的異質性網路模型與分析架構，並透過此分析架構來評估覆蓋率、平均頻譜效能、與網絡流。本論文考慮之網路結構包含多層的網路基地台和兩種其使用的無線存取技術，首先提出在共存的頻段所使用的通道擷取協定為具機會式的載波感測多重存取 (Opportunistic CSMA/CA) 時，可以避免基地台間的互相干擾。接著考慮三種使用者連結情境，分別為(1)非切換式無線存取技術的使用者連結情境 (Noncrossing-RAT)、(2)切換式無線存取技術的使用者連結情境 (Crossing-RAT)、(3)具偏好的切換式無線存取技術的使用者連結情境 (Biased Crossing-RAT)。而在三種使用者情境下，我們分別推導出每一層的基地台閒置機率與通道擷取機率，也找到了精準的覆蓋率、平均頻譜效能、與網絡流之下界。 同樣的，我們發現使用者情境(2)比使用者情境(1)可達到更高的效能；另外，我們提出的具偏好的切換式無線存取技術的使用者連結情境可用於每層基地台的通道負載平衡。最後，將此模型應用於 LTE 擴展至未授權頻譜 (LTE-U) 和 WiFi 網路架構，並提供模擬與理論結果。

In this thesis, we develop a general modeling and analyzing framework for a heterogeneous wireless network (HetNet) in which several wireless subnetworks coexist and use multiple radio access technologies (multi-RAT) in order to evaluate the link coverage, the mean spectrum efficiency, and the network flow. In this thesis, we consider an HetNet consisting of multiple tiers of APs adoping two different RATs. We propose the channel access protocol of opportunistic CSMA/CA used in the coexisting band since this protocol is able to alleviate severe interfering behaviors between all APs. We consider the noncrossing-RAT, crossing-RAT, biased crossing-RAT user association scenarios in this thesis. In each user association scenario, the void probabilities and channel access probabilities of the APs in each tier are found and the tight lower bounds on the link coverage, the mean spectrum efficiency and the proposed network flow are all derived. Also, crossing-RAT user association is shown to achieve much higher performance than noncrossing-RAT user association. In addition, the biased crossing-RAT scenario is proposed to balance the traffic between each tiers. Finally, we apply our previous modeling and analysis framework to the LTE-U network and WiFi network coexisting in the HetNet and provide the numerical simulations and mathematical representation to validate our findings.