若一個隨機程序其統計特性在時間上觀察具有周期性的變化，我們就稱此隨機程序含有循環穩態的特性。由於OFDM訊號內本身含有循環穩態特性，而不同參數的訊號其循環穩態特性也不同。因此可以藉由此特性來做為訊號偵測的媒介，而不是像傳統的能量偵測器只能以能量大小來做為判斷的依據。
本論文提出以IEEE802.16e-2005(Mobile WiMAX)為系統協定的循環穩態特徵偵測器，模擬在不同的通道模型下的穩態循環特性，並透過循環穩態偵測器來判斷目前接收到的訊號裡是否包含訊息在裡面。接著利用ROC(Receiver operating characteristic)曲線來觀察循環穩態偵測器的效能，最後則將其和傳統的能量偵測器來做比較。

The cyclostationary process is random processes having statistical property that varies cyclically with time.we usually make the cyclostationary as a feature and embedded in modulated signal intentionally. In general, different modulated signal have different features. Therefore, we can determine if a modulated signal is present or not by examining the cyclostationary feature of the received signal, not just determine by energy level as an energy detector.
In this thesis, we derive and analyze the cyclostationary feature of the OFDM signal based on IEEE 802.16e system over wireless channels, and simulate the cyclostationary detector on the model metioned above, we can use the detector to determine the signal is present or not in the received signal. We will use receiver operating characteristic (ROC) curve to demonstrate the performance of cyclotationary detector, and compare it with energy detector.

[1] W. A. Gardner. “Signal interception:Performance advantages of cyclic-feature detectors” IEEE Trans. Commun, Vol. 40, No.1. pp. 149-159, 1992.
[2]IEEE 802.16e-2005, ”Std 802.16e-2005 IEEE Standard for Local and metropolitan area networks. Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems”28 February 2006
[3] D. Vucic, M. Obradovic, and D. Obradovic, "Spectral correlation of OFDM signals related to their PLC applications," in 6th International Symposium on Power-Line Communications and Its Applications, ISMPLC,
March 27-29 2002
[4] P. D. Sutton, K. E. Nolan, and L. E. Doyle, “Cyclostationary signatures in practical cognitive radio applications,” IEEE J. Selected Areas in Communications, vol. 26, no. 1, pp. 13-24, Feb. 2008.
[5] K. Po and J. Takada, “Signal detection for analog and digital TV signals for cognitive radio,” IEICE Technical Report, vol.106, no.395, pp. 91-95, Nov. 2006
[6] David W. Scott,” On optimal and data-based histograms” Biometrika vol. 66, no. 3 (, pp. 605-610 , Dec. 1979
[7] ITU Document, “Rec.ITU-R M.1225 - Guidelines for Evaluation of Radio Transmission Technologies for IMT-2000”, ITU-R, pp.27-28, 1997
[8] W. A. Gardner. “Exploitation of spectral redundancy in cyclostationary signals.” IEEE Signal Process. Mag., vol. 8, no. 2, pp. 14–36, Apr. 1991.
[9] W. Gardner, “Signal interception: A unifying theoretical framework for feature detection.” IEEE Trans. Commun., vol. 36(8), pp. 897–906, Aug. 1988.
[10] S. M. Kay, "Fundamentals Of Statistical Signal Processing : Detection Theory," Prentice-Hall, Inc.,1998.
[11] C.Cordeiro; K.Challapali.; D.Birru; N.Sai Shankar , "IEEE 802.22: the first worldwide wireless standard based on cognitive radios," New Frontiers in Dynamic Spectrum Access Networks, 2005. DySPAN 2005. 2005 First IEEE International Symposium on pp.328-337, 8-11 Nov. 2005.