超高頻無線射頻辨識系統(UHF RFID)在通訊的過程中，由於容易受到多重路徑干擾(Multi-path fading)影響，造成鏈結品質不穩定而導致系統的效能降低。本論文提出符合台灣超高頻射頻辨識操作頻段、使用多入多出(Multi-input Multi-output, MIMO)架構之925MHz射頻辨識系統，用以改善多重路徑衰減問題。
本論文以美商國家儀器公司所開發之軟體無線電平台－NI PXIe-5644R向量訊號收發器(Vector Signal Transceiver, VST)，實現多入多出之超高頻被動射頻辨識讀取器。在順向鏈結方面，傳送端使用單支天線，而標籤端使用具有天線分集的MIMO標籤進行選擇性合併以提高接收功率；反向鏈結方面，標籤以空時區塊編碼(Space-Time Block Code, STBC)進行反向散射，讀取器端則使用兩支接收天線，形成(1, 2, 2) MIMO RFID架構，以最大比合併技術獲得分集增益，降低多重路徑衰減的影響，並且比較單支接收天線情況下的(1, 2, 1) MIMO RFID架構之系統效能。

Multi-path fading can easily affect UHF RFID system, and cause signal interference during the communication, which results in instability of link quality and reduction of system performance. This work presents a 925MHz Multi-input Multi-output (MIMO) UHF passive RFID reader to mitigate this problem.
In this work, a software defined radio platform manufactured by National Instruments, NI PXIe-5644R, is used to implement the MIMO RFID reader. At the tag end, a MIMO tag that has antenna diversity is used, of which the tag’s antennas are mutually orthogonal-polarized. Hence it’s more reliable in the forward link communication where it exploits selective combing technique to improve the received power. In the reverse link communication, the tag backscatters an encoded signal with space-time block code, and the reader uses two receiving antennas and the maximum ratio combining technique to obtain diversity gain to overcome multi-path fading problem.
Additionally, a comparison of system performance between (1, 2, 2) MIMO RFID structure and (1, 2, 1) MIMO RFID structure is also presented.

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