射頻辨識系統之讀取機新設計

Abstract

在本篇論文中，我們針對「多路徑」(multipath)環境中存在的衰減效應(fading effect)進行討論，說明它如何對射頻辨識系統(RFID system)造成影響，並且提出了一個新的讀取機架構來解決這樣的問題。我們架設了一個量測系統，使用兩個天線來接收散射信號，並且將這兩個天線所接收到的信號做處理後再加以相加。最後再使用同調偵測法來偵測我們所量測到的信號，如此讀取機的偵測能力將得以增加，並且較能抵抗衰減效應。 此外，我們也觀察到，當多個標籤(tag)擺放得十分靠近時，標籤天線之間互相耦合(mutual coupling)的現象便會產生。這樣的現象會造成位於中間的標籤常常無法被讀取。因此，我們使用四種不同的標籤天線配置方式︰並排(side-by-side)、交叉(cross)、交錯(stagger)、轉角(標籤長邊夾90°角)(corner)，並且間距都是3公分。藉由這樣的方式，能減少標籤天線之間的耦合效應，並且提高中間標籤被讀取的機率。 之後，為了分析讀取機所接收到的實際波形，我們擺放三個標籤，並且使用向量信號分析儀(VSA)來擷取讀取機所收到的信號。針對這些信號我們使用同調偵測法來進行偵測，能得到比非同調偵測更好的效率。

In this thesis, we discuss the “fading effect” in the multipath environment and explain how it influences the RFID system. Then, we propose a novel reader architecture to solve this problem. We construct a measurement system and use two separate antennas to receive the backscattered field from the tag. After some signal processes, the combining method is used to combine these two branches. Finally, we use the coherent detection method to detect the resultant signals. Through this procedure, the readability will be increased and fading effect will be combated. In addition, when there are many tags set closely, the mutual coupling effect will make the middle tag hard to be read. Consequently, we use four different arrangements: side-by-side, cross, stagger, and corner. The spacing is 3 cm. By this method, the mutual coupling effect can be reduced, and the readability of the middle tag can be increased. Then, in order to analyze the actual waveform received by the reader, we set three tags parallel and use vector signal analyzer (VSA) to capture the communication signals between the reader and the tag. We use the coherent detection method to detect these signals, and it can get better performance than the incoherent detection method.