Physical layer encryption using fixed and reconfigurable antennas

Traditionally, antenna systems have been designed to achieve reliable wireless communication, while the problem of securing that communication from eavesdropping was left to mathematical cryptography. Recent research into physical layer encryption shows that jointly designing for reliability and secrecy at the physical layer may be a better solution. Physical layer encryption involves techniques that ensure a signal is information-theoretically secure, meaning that an eavesdropper with infinite time and computational resources will not be able to decode a message. Such techniques include purposely broadcasting artificial noise, transmitting direction-dependent signals, and opportunistic communications. This work addresses different methods for broadcasting artificial noise using fixed arrays, including tradeoffs with power usage and computational complexity. In addition, a method of producing direction-dependent distortion using reconfigurable arrays is also shown. These two methods are combined and shown to be more secure and power-efficient than either in isolation. An analysis of secrecy rates through mutual information makes it possible to compare the performance of all the various secure communication techniques. Simulations with various wireless channels as well as an experimental test using a fixed and reconfigurable array are presented