LTE授權輔助接取技術之模型研究與效能分析

Abstract

在現今的生活中LTE是一項非常受歡迎的技術。但由於頻寬上的限制，我們需要更多可用的頻寬來進行傳輸。因此將LTE拓展到未授權頻帶已經在近幾年被廣泛地討論。根據第三代行動通訊組織(3GPP)會議討論結果，類別四的先聽後送機制將會是LTE在未授權頻帶上操作的關鍵技術。現今相關的文獻中有非常多系統模擬的研究，但在數學分析上顯得有些稀少。在這篇論文中我們將會深入探討如何使用分析模型來評估授權輔助(LAA)的效能。馬可夫分析模型已經被廣泛地應用在評估WiFi效能。因此我們會使用馬可夫分析模型來幫助我們建立一套系統來對LAA進行效能分析。更進一步地，我們會提出一個根據現行先聽後送機制的馬可夫分析模型，最關鍵的差別初始空間通道評估(Initial Clear Channel Assessment)考慮與否,除此之外它將可以支援分析在LAA下不同的優先類別分析。根據此篇論文分析結果，在沒有考慮ＩＣＣＡ的模型下跟我們所提出的模型比較，會發現在資料流量較低的情境下會有非常明顯的差異。但隨著資料流量的提升，兩者差距將會變小。如果使用緩衝區滿載流量模型(Full Buffer Traffic Model)兩者的差異將會非常的小。除此之外，我們還發現在有應用ICCA的情況下,WiFi的效能可以表現得更好。最後我們呈現，一個裝置支援不同的優先類別可以有效地避免碰撞發生。

LTE is a popular radio access technology (RAT) all around the world, but it is restricted by the spectrum resource. Therefore, it needs to find more available spectrum to transmit data. Hence, LTE in unlicensed band has been discussed in recent years. According to 3GPP, Category 4 Listen-Before-Talk mechanism has been decided. There are lots of works which only focus on system simulation, but less of them concern about analytical model. In this thesis, we probe into the measure of how to build an analytical model to evaluate the performance of LAA . Markov model has been used widely to evaluate the performance of WiFi system. Hence, we make use of Markov model to help us to evaluate the performance of LAA. In addition, the proposed LAA Markov model can support to evaluate di↵erent priority classes. Based on the evaluation result of this thesis, in the low trac, the di↵erence of performance between proposed LAA model and Cisco proposed model is large. However, as the increasing load of the trac, the di↵erence of performance between them is getting closer. Moreover, we observe that Cat. 4 LBT mechanism can achieve better coexistence than Cisco proposed mechanism since Cat. 4 LBT has an additional duration which is called Initial Clear Channel Assessment (ICCA). The final evaluation result shows a single station with mutiple prioirty classes can avoid collisions e↵ectively since higher priority always wins out in the competition with lower priroirty class within a single station.