Enhancing Secrecy and Capacity of Wireless Systems Using Directive Communications

The emerging advances in wireless communications make it an essential component of our everyday life. Moreover, the current research aims towards involving wireless communications in health monitoring applications, which helps medical personnel to remotely keep track of the development of the condition of their patients. Such information is considered highly sensitive and may cause significant harm if acquired by an adversary. The wireless environment has a broadcast type of nature, where the emitted electromagnetic waves spread all over the surrounding area of the transmitting antenna. This broadcast nature raises a considerable concern about the secrecy of this sensitive information while being transmitted over-air. On another side, the advancement in computer algorithms makes the currently adopted cryptographic algorithms prone to multiple attacks, which facilitate the access to the initially transferred information. In such a context, another approach is required to avoid the exposure of the information. Concealing the information at the physical layer of communications systems became of enormous interest to overcome the shortages in cryptographic approaches. One feature of the physical-layer is the availability of multiple transmit/receive antennas. The multiple antennas structure allows us to manipulate the spatial construction of the transmitted signals. The spatial construction of the signal allows us to limit the area, where any receiver in the system can detect the signal. Our Studies focus on providing both secure and reliable communications, and we can characterize the studies in the following approaches, - Location-Based Secure Communications: We established the ground for multiple directions transmission techniques, where each transmission direction carries an independent set of information. Using this ground, we proposed multiple approaches that limit the availability of the information to the small area surrounding the target receiver. - Complexity Reduction for Multi-Direction Systems: With the increase in the physical resources, the complexity of the system increases. We proposed a simplified structure for the system that reduces the complexity from three orders of magnitude to a single order of magnitude. Moreover, we introduced a limited feedback scheme, that reduces the overhead used in the system. - Enhancing the System Capacity: Due to the increase in the number of wireless users, higher data transmission rates need to exist. Using Directional transmission, we were able to intelligently allow the overlap of different data streams on the same available physical resource. This overlap allows the reuse of the same resource for different users, and increase the achievable transmission rates