電機資訊學院: 電信工程學研究所指導教授: 謝宏昀劉家宏Liou, Jia-HongJia-HongLiou2017-03-062018-07-052017-03-062018-07-052016http://ntur.lib.ntu.edu.tw//handle/246246/276595隨著智慧型手機以及行動裝置的蓬勃發展，未來行動網路的資料傳輸量已經被預測會爆發性的成長。為了因應此趨勢，全世界的學者以及電信商都在研究如何提高手機網路的資料傳輸量。其中，一個直覺的方法就是提高傳輸頻寬，然而，已授權頻譜的使用情形已經趨近飽和，因此，把現有的LTE技術運行在未授權頻譜上便逐漸吸引大家的目光。由於在未授權頻譜上已經有WiFi在使用，因此LTE如何與WiFi共存便成為此研究的重大議題。此外，LTE是基於連續傳輸，並且持續性佔有頻譜的情況下設計的，若要在未授權頻譜上與WiFi競爭，若沒有一個適合的頻譜接取的機制，對整體系統的公平性以及傳輸量上會造成不小的影響。在此篇論文中，我們透過建立分析模型的方式去探討WiFi以及LTE之間的交互影響。我們首先依照不同的先聽後傳機制 (listen before talk)的類型，去建立LTE在未授權頻譜下傳送的模型，並將其與既有的WiFi模型結合，去分析兩個系統之間的影響。我們主要探討一個LTE小型基地台與數個WiFi基台之間的競爭情形以及效能影響。利用我們的建構模型，我們分析了在共存情形下，兩者的傳輸量變化，以及傳送機率如何互相影響。我們也探討了不同的LBT類型對於整體效能的影響。分析結果顯示具有LBT機制的LTE可以有效的減輕對於WiFi傳輸效能的衰減，並達到和平共存的情形。為了更有效地提昇整體網路的公平性，我們基於分析模型，建構了一個最佳化問題。我們透過調整LTE在未授權頻譜中的傳送時間，隨機倒退機制 (random backoff mechanism)中的競爭視窗大小 (contention window size)以及倒退狀態 (backoff state)的最大值，去達到與WiFi共存的公平性最大化。基於整體問題的複雜性，我們提出了藉由模擬退火 (simulated annealing)搜尋最佳解的演算法。針對不同參數對於整體效能的影響，我們進一步提昇了我們的搜尋速度以及解的品質。模擬結果顯示，我們提出的模擬退火法，可以有效率地搜尋到最佳解(或者近似最佳解)，並且進一步提昇整體共存網路的公平性以及效能。In recent years, LTE in unlicensed spectrum (LTE-U) has become more and more popular all around the world. Since available resources in licensed bands are becoming scarcer, we need to find out more spectrum. However, one of the biggest challenges is about coexisting with WiFi. Due to their intrinsic difference on protocol design, WiFi may counter fatal degradation by LTE. In this thesis, we study the interaction between WiFi and LTE by analysis. We firstly construct analytical models according to different LBT categories for LTE. These models are all based on discrete time Markov chain. Then, we combine the existing WiFi model and our LTE models to analyze their coexistence situation. The scenario we consider is one small cell coexisting with WiFi stations in unlicensed bands. Throughput variation with different LBT categories are evaluated. We also explore their interaction in view of transmission probability. Evaluation results show LBT Category 4 is an effective method in most cases. Furthermore, in order to achieve a more friendly coexistence situation, we formulate an optimization problem to enhance the proportional fairness through adjusting parameters for LTE in unlicensed spectrum. Considering the complexity, we propose a an effective algorithm based on simulated annealing method. By our analytical model, we find out LTE minimum contention window has a bigger influence on performance of whole network. According to different influence level of these parameters, we could find an optimal value faster. Simulation results presents fairness level obtains huge enhancement for both systems. More evaluation and simulation details are illustrated and presented in the end.7513071 bytesapplication/pdf論文公開時間: 2018/3/8論文使用權限: 同意有償授權(權利金給回饋學校)共存分析未授權頻譜coexistenceanalysisunlicensed spectrumthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/276595/1/ntu-105-R02942054-1.pdf