Analyzing and Optimizing LTE Performance in Unlicensed Spectrum

• Main Authors: Jia-Hong Liou, 劉家宏
• Other Authors: 謝宏昀
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/13299799943199873408

碩士 === 國立臺灣大學 === 電信工程學研究所 === 104 === 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.