無線區域網路下的多重路徑衰減通道結合波束追蹤與MCS模式選擇機制

Abstract

IEEE 802.11ac 是一個針對無線區域網路（WLAN）服務的標準，隨著人們對於網路需求的提高，它提出了有效的解決方式，並且仍在持續制定中。此標準採用更高的5GHz 頻段取代舊有2.4GHz 頻段，提供更快的傳輸速率和更穩定的訊號。在802.11ac 標準中，波束成（Beamforming）技術被納入此標準中，波束成形的原理會利用擺放在空間中的多支天線，調整其相位以及振幅，以便在部分空間中的訊號能夠獲得相位相同、振幅相加、訊號變強的效果；而部分空間產生相位相反、振幅相減、訊號變弱。由於波束成形具有指向性，因此我們希望透過有效的演算法，當使用者在特定波束的涵蓋區時，天線會切換至該波束，並使用該波束來服務使用者，使得接收訊號強度達到最大，同時透過調速機制（Rate Adaptation）讓通訊速度在可容忍的封包錯誤率下，仍可以維持在最佳的速度。透過MATLAB 模擬軟體中的模擬結果驗證了我們所提出來的Beam Training/Re-training 演算法之正確性，藉此也顯示出我們所提出的演算法可以有效的提升整體效能。

As people’s need to internet needs increase, IEEE 802.11 is a standard for wireless local area network(WLAN) which had proposed an effective solution and is still continue developing. It uses 5GHz band that has higher bandwidth to replace the old 2.4GHz band, in order to provide a faster data transmit rate and a more stable signal. In 802.11ac standard, beamforming technology is included. The beamforming principle is to utilize multiple antennas in the space and to adjust the phase and amplitude for the sake of the signal can get the same phase, the same amplitude addition, and also the signal strength can become stronger in some space. However, on the contrary; some part of the space in the opposite phase, amplitude subtraction and the signal strength will become weak. Due to the directional of beamforming, we expect to rely on an effective algorithm to expect that the antenna will switch to the beam and use the beam to serve the user. And the signal strength can become maximum when users are under the particular beam. At the same time, by using the rate adaptation to maintain the best speed under the packet error rate tolerable. By watching the result of MATLAB simulation, we can verify the accuracy of the beam training algorithm and beam re-training algorithm. In addition, it also prove that our algorithm can effectively improve the overall performance.