在無線通訊的需求迅速發展下，頻譜空間日益珍貴，目前的頻譜大多已經分配用途，但是頻譜的使用效率並不高，因此發展出感知無線電。本論文首先介紹從軟體定義無線電發展至感知無線電的的源由，並針對目前感知無線電目前發展的重點做逐一介紹，包含頻譜感測、頻譜管理和頻譜空間的發展，目前感知無線電的研究大多在電視白頻段，但對於免執照頻段研究甚少。
　　在ISM頻段中的頻譜空間上已經相當不足，相當容易產生碰撞，而WiFi又是在此頻段使用率最高、最佔用頻寬的無線設備，本論文針對WiFi進行研究，使用美商國家儀器的通用軟體無線電週邊設備做實驗，根據目前最常使用的IEEE 802.11n，以感知無線電的方式感測現場無線電環境，並使用指向性天線和Arduino控制伺服馬達進行轉向，蒐集各角度的接收信號強度後，以到達角定位法，挑選出信號來源的方向，這個方式可以充分利用頻譜空間中的角度分集，增加頻譜空間的維度，提升信號強度和減少干擾。
　　本論文將此接收機制，應用在實際的無線存取點中，以兩台D-Link的無線存取點以非視線傳播的方式擺放在實驗室兩個地方，進行吞吐量測試，在接收端的部分，分別記錄每個方向無線存取點的接收信號強度，並從中找出信號較強且干擾較小的角度，做為最佳的接收方向，因為指向性天線場性的特性，除了可以增強信號來源方向外，在其它方向來源有較小的增益，可以有效減少空間中由其它路徑來的干擾，這可以使信雜比變佳。在2T2R且頻寬為20MHz的情況下，吞吐量較全向性天線接收時，高出了5.13Mbps。

Spectrum space has become increasingly valuable in the rapid development of wireless communications. At present time, most of spectrum usage has been assigned, but the efficiency of spectrum is not high. Therefore, the Cognitive Radio has been focused in recent years. First of all, this thesis introduces Software-Defined Radio (SDR) and Cognitive Radio (CR). And then, we focus on the most important technical aspects in CR, such as spectrum sensing, spectrum management, and spectrum space. Most of current research has been in television White space; however, the research in unlicensed bands is rare.
The spectrum space in the unlicensed ISM bands is already insufficient, and the collision would occur quite often. Moreover, Wi-Fi, which occupies most unlicensed bands, has the highest utilization rate. This thesis focuses on use of software-defined radio named Universal Software Radio Peripheral (USRP) by National Instrument for Wi-Fi applications. Specifically, we studied 802.11n where multi-stream MIMO technology is employed. By using the Arduino in controlling the angle of servo motor with a directional antenna, we recorded the received signal strength at every angle. And then, we use the localization method of angle of arrival to obtain the direction of signal source with the largest SNR. Therefore, the angle diversity in spectrum space can be utilized well, and it can increase the signal strength and reject the interference from other source.
　Finally, we correlated the signal interference results with throughput measurement. In the beginning, we used two D-Link wireless APs. And then, we placed these APs at two sides in the office with non-line-of-sight propagation. Moreover, the part of received AP recorded the received signal strength at every angle and then find the best receiving direction with lager signal strength and less interference. By using the characteristic of directional antenna pattern, it can not only boost the signal gain but also decrease the interference from other direction. It can make SINR better because the gain at the side lobe is much less than the main lobe. The throughput test result show that this technical is 5.13Mbps higher than that obtained using traditional omnidirectional antenna in the case of 2T2R and 20MHz bandwidth.

論文審定書 i
致 謝 ii
中文摘要 iv
英文摘要 v
圖 次 x
表 次 xiii
第一章 序論 1
第二章 感知無線電 3
2.1. 軟體定義無線電發展 3
2.1.1. 軟體定義無線電硬體架構 3
2.1.2. 軟體定義無線電軟體架構 4
2.2. 感知無線電 5
2.2.1. 頻譜使用現況 5
2.2.2. 感知無線電發展 7
2.3. 頻譜感測 11
2.3.1. 頻譜空洞 11
2.3.2. 能量偵測法(Energy Detection) 14
2.3.3. 匹配濾波器偵測法 17
2.3.4. 特徵偵測法 18
2.3.5. 頻譜感測的問題 18
2.4. 頻譜管理 19
2.4.1. 頻譜分析和決定 21
2.4.2. 頻譜分享 22
2.4.3. 動態存取頻譜 22
2.5. 多維度頻譜空間和發展機會 25
2.5.1. 時間和頻率維度 25
2.5.2. 地理位置的頻譜維度 26
2.5.3. 編碼的頻譜維度 27
2.5.4. 角度的頻譜維度 28
2.6. 章節討論 29
第三章 最佳接收方式 31
3.1. 免執照頻譜的瓶頸 31
3.2. 感知循環設計過程 33
3.3. 軟體無線電驗證 34
3.4. 頻譜感測 35
3.4.1. 等化器 36
3.4.2. 能量偵測法 37
3.5. 頻譜分析 38
3.5.1. 門檻值制訂 38
3.5.2. Noise Floor 38
3.5.3. 偵測門檻值 39
3.5.4. 通道使用的工作週期(Duty Cycle) 42
3.5.5. 頻譜Waterfall 44
3.6. 頻譜決定 45
3.6.1. 室內定位法 45
3.6.2. 最佳指向性接收演算流程 46
3.6.3. Arduino硬體整合 48
3.6.4. 建立接收強度角度分佈圖 49
3.7. 實驗結果 50
3.7.1. LoS 實驗結果 51
3.7.2. Non-LoS實驗結果 52
3.8. 章節討論 54
第四章　應用於無線存取點的最佳接收方向機制 55
4.1. 感知無線電應用方式 55
4.2. 802.11系統規劃 55
4.2.1. 連結預算表Link Budget 55
4.2.2. 802.11干擾問題 58
4.2.3. 存取點通道選擇 59
4.2.4. 調變及編碼和信雜比 60
4.3. 最佳接收通道選擇 62
4.3.1. 指向性接收 63
4.3.2. 各通道分析 64
4.3.3. 判別機制 66
4.4. Throughput吞吐量 67
4.4.1. IxChariot介紹 67
4.4.2. 吞吐量遭碰撞時評估 68
4.4.3. 吞吐量量測結果 69
4.5. 天線場型分析 71
4.6. 章節討論 72
第五章 結論 74
參考文獻 76

[1] J. Mitola, "Software radios: Survey, critical evaluation and future directions," IEEE Aerospace and Electronic Systems Magazine, vol. 8, pp. 25-36, 1993.B. A. Fette, Cognitive Radio Technology, 1st ed. ELSEIVER, 2006
[2] J. Mitola, “Cognitive radio,” Licentiate thesis, KTH, Royal Inst. of Technol.,Stockholm, Sweden, Sep. 1999.
[3] J. Mitola, “Cognitive radio for flexible mobile multimedia communications,”in Proc. IEEE Mobile Multimedia Commun. Conf. (MoMuC), New York, Nov. 1999.
[4] Shared Spectrum Company, “Spectrum Occupancy Percent”
[5] J. Mitola, "Cognitive radio architecture evolution: annals of telecommunications," Annales Des Telecommunications-Annals of Telecommunications, vol. 64, pp. 419-441, Aug 2009.
[6] J. Mitola et al., “Cognitive radio: Making software radios more personal,” IEEE Pers. Commun., vol. 6, no. 4, pp. 13–18, Aug. 1999.
[7] S. Haykin, “Cognitive radio: Brain-empowered wireless communications,” IEEE J. Sel. Areas Commun., Feb. 2005.
[8] M. Jun, G. Y. Li, and J. Biing Hwang, "Signal Processing in Cognitive Radio," Proceedings of the IEEE, vol. 97, pp. 805-823, 2009.
[9] “Detection and System Analysis,”
http://www.mathworks.com/help/phased/ref/rocsnr.html
[10] J. G. Proakis, “Digital Communications,” 4th ed. McGraw-Hill, 2001.
[11] D. Cabric, S. Mishra, and R. Brodersen, “Implementation issues in spectrum sensing for cognitive radios,” in Proc. Asilomar Conf. on Signals, Systems and Computers, vol. 1, Pacific Grove, California, USA, Nov. 2004, pp. 772–776.
[12] I. F. Akyildiz, L. Won-Yeol, M. C. Vuran, and S. Mohanty, "A survey on spectrum management in cognitive radio networks," IEEE Communications Magazine, vol. 46, pp. 40-48, 2008.
[13] Q. Zhao and B. Sadler, "A survey of dynamic spectrum access," IEEE Signal Process. Mag., vol. 24, no. 3, pp.79 -89, 2007
[14] J. J. Popoola , R. v. Olst, “A Survey on Dynamic Spectrum Access via Cognitive Radio: Taxonomy, Requirements, and Benefits.” Universal Journal of Communications and Network, vol. 2 ,pp. 70 – 85, 2014
[15] L. Xu, R. Tonjes, T. Paila, W. Hansmann, M. Frank, and M. Albrecht,“DRiVE-ing to the Internet: Dynamic Radio for IP services in Vehicular Environments,” in Proc. of 25th Annual IEEE Conference on Local Computer Networks, pp. 281 – 289, Nov. 2000.
[16] R. Etkin, A. Parekh, and D. Tse, "Spectrum sharing for unlicensed bands," IEEE Journal on Selected Areas in Communications, vol. 25, pp. 517-528, 2007.
[17] I. F. Akyildiz, W.-Y. Lee, and K. R. Chowdhury, "CRAHNs: Cognitive radio ad hoc networks," Ad Hoc Networks, vol. 7, pp. 810-836, 2009.
[18] T. Yucek and H. Arslan, "A survey of spectrum sensing algorithms for cognitive radio applications," IEEE Communications Surveys & Tutorials, vol. 11, pp. 116-130, 2009.
[19] NI USRP-2921 Specifications, Online from
http://www.ni.com/pdf/manuals/375867b.pdf
[20] Matthew S. Gast ,”802.11ac: A Survival Guide. “ O’Reilly Media, Inc., 2013
[21] Jiang, J.-R., Chih-Ming, L., Lin, F.-Y., and Shing-Tsaan, H., “ALRD: AoA Localization with RSSI Differences of Directional Antennas for Wireless Sensor Networks,” in International Conference on Information Society (i-Society), 2012.
[22] W. Liu,, O. Yaron, I. Moerman,, S. Bouckaert, et al., “Real-time wide-band spectrum sensing for cognitive radio,” Communications and Vehicular Technology in the Benelux (SCVT), 2011
[23] J. Y. Xu and F. Alam, "Adaptive Energy Detection for Cognitive Radio: An Experimental Study," 12th International Conference on Computers and Information Technology (ICCIT ‘09), December 21-23, 2009.
[24] J. Lehtomäki, R. Vuohtoniemi, K. Umebayashi, and J. P. Mäkelä, "Energy detection based estimation of channel occupancy rate with adaptive noise estimation," IEICE Transactions on Communications, vol. E95-B, No. 4, April 2012.
[25] H. Liu, H. Darabi, P. Banerjee, and J. Liu, "Survey of wireless indoor positioning techniques and systems," IEEE Transactions on Systems Man and Cybernetics Part C-Applications and Reviews, vol. 37, pp. 1067-1080, Nov 2007.
[26] E. Perahia and S. Li, “p802.11n Coexistence Assurance Document,” doc.:IEEE 802.11-06/0338r03, http://www.ieee802.org/19/pub/200611-06-0338-03-000n-p802-11n-ca-document.doc , Mar. 2006
[27] Perahia, Eldad, et. al., “Joint Proposal Team PHY Simulation Results,” IEEE 802.11-06/67r2, 2006.
[28] “Enterprise Mobility 4.1 Design Guide,” Cisco Systems,
http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/emob41dg/emob41dg-wrapper.pdf , 2008
[29] “Cisco Aironet 1600/2600/3600 Series Access Point Deployment Guide,” Cisco Systems, Inc.,
http://www.cisco.com/c/en/us/td/docs/wireless/technology/apdeploy/Cisco_Aironet.pdf
[30] “IxChariot Online Library”, http://www.ixiacom.com/user-guides
[31] C. J. Lin, “Wireless Networking Fundamentals and Applications,” Research Center for IT Innovation Academia Sinica, Network & Mobile System Lab,
http://www.csie.ntu.edu.tw/~hsinmu/courses/_media/wn_11fall/rate_adaptation.pdf
[32] Federal Communications Commission, “Establishment of interference temperature metric to quantify and manage interference and to expand available unlicensed operation in certain fixed mobile and satellite frequency bands,” ET Docket 03-289, Notice of Inquiry and Proposed Rulemaking, 2003.
[33] K. Harrison, S. M. Mishra, and A. Sahai, “How Much White-Space Capacity Is There?” New Frontier in Dynamic Spactrum, 2010 IEEE Symposium on New Frontiers in Dynamic Spactrum, 2010.
[34] X. Zhao, H. Zhao, L. Cao, and J. Xu, "Phototropism based weighted cooperative spectrum sensing technology." Information Science and Technology (ICIST), 2013 International Conference on. IEEE, 2013.
[35] S. Hwang, J. S. Um, M. Song, C. Kim, H. Park, and Y. Kim, "Design and verification of IEEE 802.22 WRAN physical layer," in Cognitive Radio Oriented Wireless Networks and Communications, 2008.
[36] C. Cordeiro , K. Challapali and D. Birru "IEEE 802.22: An introduction to the first wireless standard based on cognitive radios", Journal of communications, vol. 1, no. 1, 2006
[37] H. Tsurumi and Y. Suzuki, “Broadband RF Stage Architecture for Software-Defined Radio in Handheld Terminal Applications,” IEEE Communications Magazine, vol.37, no.2, pp.90-95, February 1999
[38] H. Yoshida , H. Tsurumi and Y. Suzuki "Broadband RF front-end and software execution procedure in software defined radio", Proc. IEEE Veh. Technol. Conf., vol. 4, pp.2133 -2137 1999
[39] Hanna, S., Sydor, J., "Distributed sensing of Spectrum Occupancy and Interference in Outdoor 2.4 GHz Wi-Fi networks" Proceedings of the Global Communications Conference 2012, 3-7 Dec 2012
[40] A. Medeisis, J. Sydor, L. Cremene et al., "ISM-Advanced: Improved access rules for unlicensed spectrum." Dynamic Spectrum Access Networks (DYSPAN), 2014 IEEE International Symposium on. IEEE, 2014.
[41] D. Denkovski, M. Pavloski, V. Atanasovski et al., “Parameter settings for 2.4 GHz ISM spectrum measurements,” in Proc. ISABEL, November 2010.