IEEE 802.11ac下行多用戶多天線之用戶選擇與空中測試研究

Abstract

於本論文中，吾人將IEEE 802.11ac標準彙整，並針對此標準中多用戶多天線系統之通道模型分析。IEEE 802.11ac提供多種新穎實用的技術如更高的頻寬160MHz、調變編碼採用更複雜的256QAM以及採用下行多用戶多天線系統(MU-MIMO)，不但可以提高整體系統容量(capacity)，同時服務多個用戶也大大增進系統效能。由於系統內用戶眾多且超過系統內無線網路基地台(access point, AP)可同時服務用戶的數目，我們根據不同的選擇評比將那些具有良好通道狀況的用戶挑選出來服務，並達到整體系統效能的改善。為了檢驗用戶行動裝置的吞吐量(throughput)，我們利用空中測試(Over-The-Air)去測量MU-MIMO效能，但往往因為測量過程須考慮多重因素(角度、位置等等)而導致測量時間冗長；吾人提出以線性通道推斷來改善。經由模擬驗證，吾人提出線性通道推斷演算法可以有效降低測量次數但不失精準度，進而可降低空中測試測量時間並節省成本。

In this thesis, we illustrate the system specification of IEEE 802.11ac and formulate the channel models adopted in IEEE 802.11ac. IEEE 802.11ac provides several novel techniques to improve the capacity of the systems such as wider channel bandwidth, higher modulation coding schemes and downlink MU-MIMO which can support multiple users simultaneously. Since the number of users is larger than the number of users simultaneously supported at AP, we proposed greedy user selection algorithms to improve the capacity of the systems. To test the throughput of user devices in realistic environments, we use over-the-air (OTA) testing. However, it may take lots of time due to multiple factors like angle or location of devices during the procedure of OTA testing. We propose an effective field trial techniques based on linear channel extrapolation scheme. Simulation results show the proposed algorithm can effectively decease measurement time with accuracy and reduce the cost for OTA testing.