Yohannes Jote Tolossa

• Mobile wireless networks are undoubtedly one of the main drivers of industrial development and economic growth in modern societies. This central role explains current trends which indicate unequivocally that future cellular systems must cope with enormous increase in user-capacity coupled with a reduction in energy consumption. However, as of recently, this scalability/efficiency problem has been addressed through infrastructural and topological enhancements to the existing wireless networks. This will create additional spatial domain, which will serve as a means to solve the scalability/efficiency issue. Along with this, challenges in the form of signal interference remains the main adversary of systems engineers. Compounding the problem is the current wireless framework, which predominantly consists of diverse inter-connected devices in highly dense and mobile environment, and thus, intuitively inter- and intra- interferences are guaranteed to prevail. In this thesis, despite traditional concept that identify interference as a deleterious phenomenon, we have investigated two approaches that contemplate interference as a beneficial resource. The first approach exploits the interference at the baseband level, and leads to multiuser precoding which ultimately results in improved quality of service, such as achievable rate, especially for cell-edge users. On the other hand, the second concept exploits interference as means to trick (jam) potential intruders (eavesdroppers). In the continuously evolving wireless environment, there exists broad range of � financial, political and environmental applications that require confidential and secure transmission of information, this prompt devising security measures as a paramount task. In this sequel, physical layer security (PLS) measures have been proposed as alternative to the more complex upper layer encryption and cryptographic protocols.