正交分頻多工超寬頻系統之主動頻譜調整感知無線電技術

Active Spectrum Shaping Cognitive Radio For OFDM UWB System

詹煊煒(Shiuan-Wei Jan)

指導教授 ： 黃建華

國立清華大學/電機資訊學院/通訊工程研究所/碩士(2008年)

摘要

近年來超寬頻 (Ultra Wide Band, UWB)的技術已廣泛應用於高速室內無線通訊上。由於它具有抗干擾性能強、低耗電量等優點的特性，因此非常適於無線局域網（WLAN）和個人局域網（PAN）的連接。而未設限的超寬頻發射功率可能嚴重影響其他受保護通訊系統。
為了讓通訊系統一併共存，感知無線電技術 (Cognitive Radio) 可偵測受保護通訊系統的存在，並採取適當措施以保護主使用者系統 (Primary User System)。在本論文中將以正交分頻多工系統 (Orthogonal Frequency Division Multiplexing, OFDM) 為通訊架構的感知無線電系統，來探討與受保護通訊系統共存時的干擾迴避技術。
吾人將簡略地介紹的干擾迴避技術有：主動干擾消除 (Active Interference Canceling, AIC) 及視窗法（Window Method）；干擾迴避技術即在需要保護頻帶被主使用者佔用時，主使用者將如何傳送訊號而不影響保護頻帶。主動干擾消除為我們犧牲頻帶旁的些許載波來消除對主使用者造成的干擾。視窗法是以非矩形波形傳送資料符元，使得各信號頻譜的旁波帶衰減的速率較原先以矩型波形傳送高，進而達到可以降低對受保護頻帶的干擾。
接著在論文中吾人會感知無線電系統加上信號能量上的限制；再將主動干擾消除及視窗法合併以增強干擾消除的效果。再來為了降低系統的複雜度，吾人利用共軛梯度法（Conjugate gradient Least Square method）來求得我們所要傳送的信號，最後再進行比較並給予結論。

關鍵字

主動干擾消除 ； 頻譜調整 ； 感知無線電

並列摘要

Abstract

In recent years, ultra wideband (UWB) has been widely implemented in high data rate indoor wireless communications. Due to a number of advantages such as robustness to interference and low power consumption, UWB is suitable for the connection of wireless local area network (WLAN) and wireless personal area network (WPAN).

The ability to coexist with other systems is an important issue for UWB. The detect and avoid (DAA) technique is an approach which enables UWB to be aware of the existence of other systems and to take some actions for protecting systems in coexistence. In this thesis, the orthogonal frequency division multiplexing (OFDM) is employed as the physical layer transmission scheme, and we investigate the interference avoidance method. An interference avoidance method is an approach that shapes the transmit spectrum such that the interference to coexistent systems can be reduced to the least.

We introduce briefly two existing interference avoidance methods: active interference canceling (AIC) and window method. The AIC is the method which uses several auxiliary sub-carriers near the protected band to neutralize interference. The window method is to multiply original transmitted data symbol by a non-rectangular window, so that the spectrum shape is more concentrated and a better decaying rate of side-lobe is achieved.

Several issues regarding the AIC method and window method are investigated in this thesis. Without a constraint on the emitting power, UWB systems result in severe interfere to other coexistent systems. To conquer, we add a constraint on the least square (LS) criterion employed by AIC, which results in LS with quadrature inequality (LSQI). Secondly, AIC is combined with the window method to boost the performance of interference avoidance. Thirdly, conjugate gradient least square (CGLS) is used to reduce the computational complexity involved with the matrix inversion in AIC.

並列關鍵字

AIC ； Spectrum Shaping ； Cognitive Radio

參考文獻

[3] X. Zhou, K. Yazdandoost, H. Zhang, and I. Chlamtac, “Cognitive

Spectrum: Spectrum Adaptation and Evolution in Cognitive Ultra

-Wideband Radio,” IEEE International Conference on Ultra-Wideband (ICU 2005), Zurich, September, 2005

[4] R.van Nee, and R. Prasad, OFDM for Wireless Multimedia Communications, Artech House, 2000.

21-24 May 2006