隨著網際網路的蓬勃發展，網路已成為現代人生活中的一部分，藉由網路來得知生活上各種所需的資訊已成為生活中不可或缺的需求，加上智慧型行動裝置的普及，隨時隨地皆能上網已成為現代人習慣的生活模式，而藉由結合行動通訊技術與其他現有的技術提供更多元的網路服務，正是行動通訊技術所探討的議題之一。 由 3GPP 組織所制定的4G LTE-A (Long Term Evolution-Advanced) 標準是產業發展的主流，而針對 4G LTE-A 標準採用非授權頻譜 (5GHz LTE-U) 技術的重要性也將與日俱增。另一方面，由 IEEE 所制定的 802.11 標準已被廣泛利用；在現有的非授權頻譜上與 IEEE 802.11 標準共同使用相同頻段，會面臨系統共存的問題。本論文將提出如何避免 LTE-U 運作時影響既有的 802.11 標準之使用者，符合使用地區的規範，及降低因暴露節點所造成耗能的方法。 LTE-U 相關技術在目前 3GPP 規範發展朝向以小基站架構 (small cell) 與授權型輔助接入 LAA (Licensed Assisted Access) 為主，用途為將基站的資料流從授權頻譜 (Licensed Band) 分流至非授權頻譜 (Unlicensed Band)。LAA使用Listen-Before-Talk (LBT) 機制，於通訊前先偵測監聽，使 LAA 可以有效地與 IEEE 802.11 標準共存並在頻譜方面取得較好的效率。然而，缺少互通的通訊協定技術 (如 Carrier Sense Multiple Access with Collision Avoidance，CSMA/CA與Request-to-Send/Clear-to-Send，RTS/CTS) 的能力，使得隱藏節點問題 (Hidden Node Problem) 無法徹底解決。反之，隱藏節點所造成的問題卻可能是暴露節點問題 (Exposed Node Problem) 的優點，亦即當隱藏節點皆為接收端，而發送端之間非隱藏節點時可同時發送以提升效能。為了充分瞭解異質網路共存的本質問題，我們先初步完成分析兩種網路 (LAA系統與Wi-Fi系統) 重疊建置所產生干擾的情況，利用完整的數學分析得知兩個系統之間產生暴露節點與隱藏節點的機率，我們意外地發現LAA與 Wi-Fi 之間暴露節點的機率高達 39.33%。為了避免因隱藏節點干擾造成的碰撞，以及爭取因暴露節點問題而犧牲的頻寬，本論文將提出相容於 LBT 技術之解決技術，同時考慮系統存取的公平性。 ;As the rapid development of network technology, Internet has become an integral part of our lives. With the popularity of smart mobile devices, surfing the Internet anytime, anywhere has become a kind of necessity for the modern life. How to combine the coming mobile communication technologies with other existent technologies to support modern networking services in mobile networks is one of the major issues. The 4G LTE-A (Long Term Evolution - Advanced) standard developed by 3GPP organization is the main trend of the future wireless mobile communication industry. The 4G LTE-A standard adopts small cell as well as unlicensed spectrum (5.8GHz LTE-U) to offload heavy traffic from licensed band to unlicensed band. Such major technology is known as Licensed Assisted Access (LAA) technology. On the other hand, the development of IEEE 802.11 standard has been matured everywhere. All IEEE 802.11 products use CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) with request-to-send/clear-to-send (RTS/CTS) protocol to solve contention and hidden-node problems. Therefore, the LTE-U shall have the new mechanism to coexist with pervasive IEEE 802.11 products. In other words, how to avoid the effects of operating LAA on unlicensed band, where there are IEEE 802.11 products, is the research objective of this thesis. The Listen-Before-Talk (LBT) procedure is the main procedure for LAA to accomplish fair and friendly coexistence with other operators or technologies operating over unlicensed spectrum. However, lacking the Layer 2 RTS/CTS protocol with the other existing systems, it is uneasy to solve the hidden-node problem (HNP). Intuitively, the drawback of hidden-node problem may be the advantage of exposed node problem (ENP) where the transmitters which are not hidden to each other can simultaneously transmit if corresponding receivers are hidden nodes to each other. In order to fully understand the essential problem of coexistence issue between LAA and Wi-Fi systems, we have done the thorough analyses on hidden-node and exposed-node probabilities by means of mathematical approach. Analytical results surprisingly reveal that the exposed-node probability is as high as 39.33%. In order to avoid the collision caused by the HNP and retrieve the bandwidth which is being sacrificed by the ENP, this thesis aims to propose the compliance solution(s) for LBT mechanism in order to optimize the overall system performance.
