無線射頻辨識系統操作在超高頻( Ultra High Frequency, UHF )頻段 ，會受到多重路徑衰減(Multi-path fading)的影響，而減少系統的效能，因此具有天線極化分集效果的雙天線射頻辨識標籤已被提出來解決此問題。本論文使用軟體無線電實現可以與雙天線射頻辨識標籤溝通之讀取器。在順向鏈結方面(讀取器到標籤)，雙天線射頻辨識標籤使用選擇性合併技術來改善效能；反向鏈結方面(標籤到讀取器)，讀取器使用最大比合併技術，以逹到對抗多重路徑衰減的效果。
我們使用安捷倫訊號分析儀（Agilent N9010A EXA Signal Analyzer），量測在會議室空間讀取器接收端所接收到的標籤回傳訊號功率，並且量測在不同訊號對干擾與雜訊比 (Signal-to-Interference & Noise Ratio, SINR)下，軟體無線電讀取器的位元錯誤率。實驗結果可知，本讀取器在訊號對干擾與雜訊比(SINR)大於4dB時，位元錯誤率接近2%，由於FPGA閘數 (gate count)的限制，資料的取樣速率無法增加；因此當訊號對干擾與雜訊比的大於4dB時，位元錯誤率的效能無法提升。

Multi-path fading degrades performance of an Radio Frequency Identification (RFID) system operating in the Ultra High Frequency (UHF) band. Consequently dual antenna RFID tag with antenna polarization diversity is proposed to mitigate this problem. This work uses a Software Defined Radio platform to implement a corresponding reader for dual antenna RFID tags. In the forward (Reader to tag) link, a dual antenna RFID tag use selective combining technique to improve the performance. In the reverse (Tag to reader) link, the reader uses maximum ratio combining technique to combat multi-path fading.
We use Agilent N9010A EXA signal analyzer to measure tag backscatter power at the reader receiver end in a meeting room. We also analyze bit-error-rate to Signal-to-Interference and Noise Ratio (SINR) of the software-defined-radio-based Reader. Experimental results show that the bit-error-rate approaches 2% when SINR is no less than 4 dB. Due to the FPGA gate count limit, the data sampling rate is insufficient; hence the bit-error-rate performance does not increase beyond 4dB.

[1]Simon Haykin, Communication Systems, Wiley and Sons, 4th Edition, 2001.
[2]Bernard Sklar, Digital Communications: Fundamentals and Applications, Prentice Hall PTR, 2nd Edition, 2001.
[3]Hong Gang Wang, Chang Xing Pei and Chang Hua Zhu, “A link analysis for passive UHF RFID system in LOS indoor environment,” in 4th International Conference on Wireless Communications, Networking and Mobile Computing, pp. 1-7, Oct. 2008.
[4]Yuan Yao, Yin Shi, and Foster. F. Dai, “A Novel Low-Power Input-Independent MOS AC/DC Charge Pump,” in IEEE Circuits and Systems International Symposium, vol. 1, pp. 380-383, May 2005.
[5]Hsin-Chin Liu; Meng-Chang Hua; Chih-Guo Peng; Jhen-Peng Ciou, “A Novel Battery-Assisted Class-1 Generation-2 RF Identification Tag Design,” IEEE Trans. Microwave Theory and Techniques, vol. 57, pp. 1388-1397, May 2009.
[6]Hsin-Chin Liu, Yung-Ting Chen, and Wen-Shin Tzeng, “A Multi-Carrier UHF Passive RFID System,” in Proc. 2007 International Symposium on Applications and the Internet - Workshop on Networked RFID, Hiroshima, Japan, Jan. 15-19, 2007.
[7]林旺旗,雙天線半被動式射頻辨識標籤設計, 台灣科技大學碩士論文, 2009.
[8]Hamid Jafarkhani, Space-Time Coding: Theory and Practice, CAMBRIDGE, Cambridge University Press, 2005.
[9]Alamouti, S.M., “A simple transmit diversity technique for wireless communications,” IEEE Journal on Selected Areas in Communications, vol.16, no.8, pp.1451-1458, Oct 1998.
[10]J. Mitola, Software Radio Architecture: Object-Oriented Approaches to Wireless System Engineering, John Wiley and Sons, 2000.
[11]Small Form Factor SDR Evaluation Module/Development Platform User’s Guide, LYRTECH, Available: http://www.lyrtech.com, 2007.
[12]NI PXI-5600 Specification RF Vector Signal Analyzer, National Instruments Corporation, Available: http://www.ni.com.tw, 2009.
[13]NI PXI-5610 Specification RF Vector Signal Analyzer, National Instruments Corporation, Available: http://www.ni.com.tw, 2009.
[14]EPCglobal Tag Class Structure, Available: http://www.gs1.org/epcglobal/, 2007.
[15]林銘昱,軟體無線電平台之RFID讀取器研製, 台灣科技大學碩士論文, 2010.
[16]Markku Pukkila, "Channel Estimation Modeling", Available: http://www.comlab.hut.fi/opetus/260/chan_est.pdf, 2000.
[17]S. M. Kay, Fundamentals of Statistical Signal Processing: Estimation Theory, Prentice Hall, 1993.