IEEE 802.11ac 下行多使用者多輸入多輸出之跨階層設計

Abstract

在802.11ac的標準中，下行多使用者多輸入多輸出是其中一個用來提昇系統吞吐量的主要技術。然而，目前下行多使用者多輸入多輸出在802.11ac 網路中的整體效能尚未被完整的研究過。在這篇論文裡，我們在NS-2平台上實做了802.11ac的模組。藉由模擬，我們發現下行多使用者多輸入多輸出 只適合操作在某些SNR的範圍內。除此之外，通道狀態信息的回覆延遲和負擔也會對下行多使用者多輸入多輸出的效能造成影響。在把這些因素考慮 進來以後，我們提出了兩個演算法來最佳化下行多使用者多輸入多輸出在802.11ac網路中的效能。第一個演算法是混合式通道探測演算法(HCS)，這個演算法在通道探測時將使用者做排程，並使用混合式的回報頻率來減低回覆的負擔。第二個是多使用者多輸入多輸出排程及傳輸的機制(MUST)，這個機制對傳輸的模式做選擇並且對使用者做分組。MUST將隊列的狀態信息、通道狀態和回覆信息的延遲一起考慮進來以增進系統的吞吐量。模擬的結果顯示了提出的演算法的有效性。

In 802.11ac standard, downlink multi-user MIMO (DL MU-MIMO) is one of the main technologies to enhance system throughput. However, the overall performance of DL MU-MIMO in 802.11ac networks is not yet investigated. In this paper, we implemented an 802.11ac module on NS-2 platform. By simulations, we found that DL MU-MIMO is only suitable to operate at a certain SNR range. Besides, the channel state information feedback delay and overhead can also have an impact on DL MU-MIMO performance. Considering these effects, we then propose two algorithms to optimize the performance of DL MU-MIMO in 802.11ac networks. The first algorithm is hybrid channel sounding algorithm (HCS), which schedules the users in the channel sounding process and uses hybrid feedback frequency to reduce feedback overhead. The second is the MU-MIMO scheduling and transmission (MUST) mechanism, which performs transmission mode selection and user grouping. MUST jointly considers the queue status information, channel conditions, and impact of feedback information delay to optimize the system throughput. Simulation results demonstrate the effectiveness of the proposed algorithms.