近來，無線通訊成為普遍傳輸訊息的方式，但是廣播出去的訊息有著被帶有惡意的第三者竊聽的風險。在這篇研究中，我們主要探討在基於正交分頻多工的無線傳輸下的實體層安全性。在這邊的架構中，我們考慮環境中有一個嘗試想要竊聽合法傳送端跟合法接收端之間無線傳輸的訊息的竊聽者，並且對兩邊來說都是一個多傳輸端，單接收端的系統。我們嘗試在一個數位調變下從數個星座圖映射隨機選擇一個來對竊聽者做干擾。關於每個正交分頻多工符號所選擇的星座圖映射的資訊會同樣包含在同一個正交分頻多工符號裡傳送給接收端。另一方面，合法接收端會被犧牲掉一小部分訊息的準確性和整體的資料傳送速率。這個方法是建立在竊聽者比合法接收端有較差的整體訊號雜訊比，而我們在傳送端使用波束成型技術來確保這樣的情況。結果顯現這個方法在二位元和四位元相位偏移調變和十六位元正交振幅調變下可以使得竊聽者變差的幅度比合法接收端來的更多，確保合法接收端估測出來的訊號跟只有使用波束成型技術相比仍然保有一定的準確性。

Recently, wireless communication is a common way to transmit message. But the broadcast message has the risk to be wiretapped by the malicious third party. In this research, we focus on the physical layer security for using orthogonal frequency division multiplexing (OFDM) system in wireless communication. In this model, we consider there is an eavesdropper (Eve) trying to eavesdrop the information communicating between legitimate transmitter (Alice) and legitimate receiver (Bob). And consider it’s a multiple-input single- output (MISO) system for both side. We try to form a multiple constellation mapping diagrams set and randomly choose one constellation mapping way out of it in a digital modulation to confuse Eve when she is doing de-mapping process. The information about choice of constellation mapping for each OFDM symbol will contain in the same OFDM symbol to transmit to receiver. On the other hand, it will sacrifice a little partial accuracy of received message at Bob and overall data rate. This method is based on the situation that Eve has worse overall SNR than Bob. We use transmitting beamforming to ensure this case. The results show that it can degrade Eve more than Bob at BPSK, QPSK, and 16-QAM modulation, it ensure the signal that Bob estimate can still maintain certain accuracy compared with beamforming scheme.

誌謝 i
中文摘要 ii
ABSTRACT iii
CONTENTS iv
LIST OF FIGURES vi
LIST OF TABLES viii
Chapter 1 Introduction 1
Chapter 2 System model 4
2.1 MISO-OFDM based system with single eavesdropper 4
2.2 Propagation Channel 4
2.3 Transmitting Beamforming Scheme 7
Chapter 3 Random constellation mappings to realize physical layer security 9
3.1 Multiple Constellation Mappings 10
3.2 Design of random constellation mapping 12
3.3 Influence of Side-Information to Data Information 13
3.4 Mutual Information between Inputs and Outputs of Demapping Process Block 15
3.5 Design of Side-Information based on Secrecy Capacity Concept 18
Chapter 4 Simulation Results 21
4.1 Different modulation of data with multiple transmit antennas results 24
4.2 With single transmit antenna situation results 32
4.3 Equivalent secrecy capacity 40
Chapter 5 Conclusions 50
REFERENCES 51

[1] A. D. Wyner, “The wire-tap channel,” Bell Syst. Tech. J., vol.54. no. 8, pp. 1355-1387, 1975.
[2] S. Leung-Yan-Cheong and M. E. Hellman, “The Gaussian wire-tap channel,” IEEE Trans. Inf. Theory, vol. 24, no. 4, pp. 451-456, 1978.
[3] X. Zhou and M. R. McKay, “Secure transmission with artificial noise over fading channels: Achievable rate and optimal power allocation,” IEEE Trans. Veh. Technol., vol. 59, pp. 3831-3842, 2010.
[4] David Tse and Pramod Viswanath, “Fundamentals of Wireless Communication. “Cambridge University Press, 2005.
[5] D. Callebaut, “Generalization of the Cauchy-Schwarz inequality,” Journal of mathematical analysis and applications, vol. 12, pp. 491-494, 1965.
[6] A. Clark, P. J. Smith, and D. P. Taylor, “Instantaneous capacity of OFDM on Rayleigh-fading channels,” IEEE Trans. Inf. Theory, vol. 53, pp. 355-361, 2007.
[7] Y. Tang, J. Xiong, D. Ma, and X. Zhang, “Robust Artificial Noise Aided Transmit Design for MISO Wiretap Channels with Channel Uncertainty,” IEEE Comm. letters., vol. 17, pp. 2096-2099, 2013.
[8] N. Romero-Zurita, D. McLernon, M. Ghogho, and A. Swami, “PHY layer security based on protected zone and artificial noise,” IEEE, Signal Processing Letters, vol. 20, pp. 487-490, 2013.
[9] J. Barros and M. R. Rodrigues, “Secrecy capacity of wireless channels,” in Proc. IEEE Int. Symp. Inform. Theory, pp. 356-360, 2006.
[10] A. Mukherjee and A. L. Swindlehurst, “Robust Beamforming for Security in MIMO Wiretap Channels With Imperfect CSI,” IEEE Transactions on Signal Processing, vol. 59, pp. 351-361, 2011.