LTE/LAA在免執照頻段下之LBT與載波偵測適應傳輸效能分析

Abstract

隨著長期演進技術 (LTE)蜂巢式網路的流量快速地增長，預期將造成需執照頻段的短缺。為了滿足大量的流量需求，需要更多的頻段以及廣泛地布建LTE。對此一個LTE-U的概念則被提出，使LTE能夠使用免執照頻段，藉此將部分的流量從需要執照頻段分流到免執照頻段。因此設計一個和其他使用免執照頻段的網路如Wi-Fi或其他LTE-U公平共存的機制是必要的。 在本論文中，我們提出兩個可用於確保公平存取通道的共存機制。首先，我們考慮共存機制的基本原理，然後使用不同的模擬情境來分析兩種共存機制的下行鏈路系統效能。我們引入了最信賴的共存機制來比較由現有共存機制驅動的不同情境之下行鏈路性能，得出LTE-U干擾會明顯地影響Wi-Fi運作的結論。另一方面，授權輔助接取 (LAA)可以在對於Wi-Fi的影響不會超過同站點Wi-Fi對該Wi-Fi網路的影響下和Wi-Fi共存。換言之，授權輔助接取 (LAA)是Wi-Fi比Wi-Fi本身更好的鄰居。此外我們利用NS-3的模擬結果來呈現證明該共存機制和情境的優異性能。

The rapid traffic growth of Long Term evolution (LTE) cellular network is expected to result in the shortage of licensed band. To satisfy the tremendous traffic demand, more spectrum and widely spreading LTE are required. A proposed concept of LTE in unlicensed band (LTE-U) is that enabling LTE to operate in unlicensed band in order to offload data traffic from licensed band to unlicensed band. A fair coexistence mechanism with other networks, like Wi-Fi, or other LTE-Unlicensed (LTE-U) is essential. In this thesis, we propose two coexistence mechanisms that could be employed to ensure a fair channel access Carrier Sense Adaptive Transmission(CSAT) and Listen-Before-Talk (LBT). First, we consider coexistence mechanism fundamentals, and then downlink system performance of two coexistence mechanisms is analyzed with different simulation scenarios. Through comparing downlink performance of different scenarios driven by existing coexistence mechanisms, we introduce the most trustworthy coexistence mechanism. We conclude that LTE-U interference significantly affects Wi-Fi operation. On the other hand, Licensed Assisted Access (LAA) can coexist with Wi-Fi without affecting Wi-Fi network. In other words, Licensed Assisted Access (LAA) is better neighbor to Wi-Fi than Wi-Fi itself. These results were achieved through using NS-3 simulator which was essential to demonstrate the excellent performance of the coexistence mechanism and scenario.