The current and future demand for wireless technology is increasing rapidly in the era of Internet-of-things, information-shower, auto-drive vehicles and the fifth generation of mobile communications. The flourishing in wireless technologies comes from their advantages such as mobility, flexibility, easy to extend, easy to install and easy to do the maintenance. However, the wire-less technology is suffering from many problems such as lack of security and the shortage of spectrum bands. The security remains a major challenge for the wireless communications because of the broadcasting nature of wireless signals and massive researches have been conducted to deal with it. This book presents state of the art solutions for both the security and spectral efficiency challenges.