無線通訊系統的實體層保密(physical layer secrecy)技術之相關研究主要在探討如何在不讓竊聽者(eavesdropper)得到任何訊息的條件下，達到傳輸端和合法接收端間之可靠傳輸。近年來，Goel和Negi提出了以人工雜訊(artificial noise)達到實體層保密的方法。此方法主要是將人工雜訊散佈在合法接收者通道的零空間(null space)中，使得傳輸端能在不影響合法接收端的情況下，干擾竊聽者的接收訊號。當傳送端能完美得知與接收端的通道資訊時，保密通道容量(secrecy capacity)將可以隨著傳輸能量的放大而無限增加。然而，在有限的通道資訊反饋下，完美的通道資訊是無法得到的。本論文主要在探討反饋量化通道資訊(quantized channel feedback)對於以人工雜訊達到保密傳輸的系統效能之影響。當傳送端擁有不完美的通道資訊時，原本用來干擾竊聽者的人工雜訊亦將對合法接收端產生干擾，導致保密傳輸之速率的下降。為了讓保密傳輸之速率在具量化反饋通道下與完美的情況保持一定的差值，反饋通道量化的位元數需要隨著傳輸能量的增加呈對數增加。此外，為了減少人工雜訊對合法接收端的干擾，用以傳輸人工雜訊的能量需要隨著反饋位元數的減少而降低。

[1] A. D. Wyner, “The wiretap channel,” Bell System Technical Journal, vol. 54, pp. 1355–1387, 1975.
[2] A. Khisti, G. Wornell, A. Wiesel, and Y. Eldar, “On the Gaussian MIMO wiretap channel,” Proc. IEEE ISIT, Nice, France, June 24-29, 2007, pp. 2471–2475.
[3] A. Khisti and G. W. Wornell, “Secure transmission with multiple antennas: The MISOME wiretap channel,” submitted to IEEE Trans. Inf. Theory, 2008.
[4] F. Oggier and B. Hassibi, “The secrecy capacity of the MIMO wiretap channel,” Proc.IEEE ISIT, Toronto, ON, Canada, July 6-11, 2008, pp. 524–528.
[5] S. Goel and R. Negi, “Guaranteeing secrecy using artificial noise,” IEEE. Trans. Wireless Commun., vol. 7, no. 6, pp. 2180–2189, Jun. 2008.
[6] A. Narula, M. J. Lopez, M. D. Trott, and G. W. Wornell, “Efficient use of side information in multiple-antenna data transmission over fading channels,” IEEE J. Sel. Areas
Commun., vol. 16, no. 8, pp. 1423–1436, Oct. 1998.
[7] D. Love, R. H. Jr., and T. Strohmer, “Grassmannian beamforming for multiple-input multiple-output wireless systems,” IEEE Trans. Inf. Theory, vol. 49, no. 10, pp. 2735–2747, Oct. 2003.33
[8] K. Mukkavilli, A. Sabharwal, E. Erkip, and B. Aazhang, “On beamforming with finite rate feedback in multiple-antenna systems,” IEEE Trans. Inf. Theory, vol. 49, pp. 2562–2579, Oct. 2003.
[9] T. Yoo, N. Jindal, and A. Goldsmith, “Multi-antenna downlink channels with limited feedback and user selection,” IEEE J. Sel. Areas Commun., vol. 25, no. 7, pp. 1478–1491, Sep. 2007.
[10] N. Jindal, “MIMO broadcast channels with finite-rate feedback,” IEEE Trans. Inf.Theory, vol. 52, no. 11, pp. 5045–5060, Nov. 2006.
[11] E. Telatar, “Capacity of multi-antenna Gaussian channels,” Rur. Trans. Telecomm.,vol. 10, no. 6, pp. 585–596, Nov. 1999.
[12] Y. Linde, A. Buzo, and R. M.Gary, “An algorithm for vector quantizer design,” IEEE Trans. Commun., vol. 28, no. 1, pp. 84–95, Jan. 1980.
[13] N. Ravindran and N. Jindal, “Limited Feedback-based Block Diagonalization for the MIMO Broadcast Channel,” IEEE J. Sel. Areas Commun., Vol. 26, No. 8, pp. 1473–1482, Oct. 2008.