| 摘要: | 近年隨著物聯網(internet of thing，IOT)的蓬勃發展，Wi-Fi設備變得無所不在，也因此Wi-Fi訊號無論在偵測、辨識，或是感測領域上都成為熱門的研究議題，相關的研究如雨後春筍般出現。Wi-Fi標準協定下的正交分頻調變系統(Orthogonal frequency-division multiplexing，OFDM)結合多輸入多輸出系統(Multiple-Input Multiple-Output，MIMO)產生豐富且複雜的通道狀態資訊(channel state information，CSI)，反映了訊號在空間中從發射端到接收端的傳播情況，例如：散射、衰弱、反射等多重路徑效應的影響，使得室內環境中的任何活動都會造成通道狀態資訊的變化。透過通道狀態資訊的特性及豐富的變化，加上非接觸、感測範圍廣、保護隱私、設備取得難度低等優勢，Wi-Fi訊號成為了環境感知的首選。然而，通道狀態資訊本身受到多重路徑效應影響，具有高雜訊及高複雜度的特性，不易直接從訊號上獲得有用的資訊。除此之外，Wi-Fi標準協定採用的正交分頻調變系統會導致通道狀態資訊的相位偏移。因此，進行相位校正及訊號特徵提取是通道狀態資訊應用的關鍵步驟。本研究從通道狀態資訊模型發想，分析正交分頻調變系統與多重路徑通訊模型對於通道狀態資訊的影響，透過不同的校正方程式降低正交分頻調變造成的相位偏移，並在模擬的實驗環境中探討多重路徑效應影響下振幅與相位的表現差異，最後在應用實例中證明通道狀態資訊的可行性。;In recent years, with the rapid development of the Internet of Things (IoT), Wi-Fi devices have become ubiquitous. Wi-Fi signals have become a popular research topic in the field of detection, recognition, and sensing. Research related to these topics increase rapidly. Under the Wi-Fi standard, Orthogonal Frequency-Division Multiplexing (OFDM), combined with Multiple-Input Multiple-Output (MIMO) systems, generates rich and complex Channel State Information (CSI). This reflects the signal′s propagation from the transmitter to the receiver in space, influenced by multipath effects such as scattering, fading, and reflection. Any activity in an indoor environment will cause changes in the CSI. The characteristics and rich variations of CSI, as well as advantages like non-contact sensing, wide sensing range, privacy protection, and low difficulty in obtaining equipment, make Wi-Fi signals the preferred choice for environmental sensing. However, the CSI itself is affected by the multipath effect, has high noise and high complexity characteristics, and it is difficult to extract useful information directly from the signal. Additionally, the OFDM system used in the Wi-Fi standard causes phase shifts in CSI. Therefore, phase correction and signal feature extraction are the key steps in applying CSI. This study, inspired by the CSI model, analyzes the impact of the OFDM system and the multipath communication model on CSI. Use different calibration equations to reduce the phase offset caused by OFDM, explores the differences in amplitude and phase performance under multipath effects in a simulated experimental environment and finally demonstrates the feasibility of CSI in practical applications. |
