ABSTRACT
Due to the broadcast nature of wireless communications, it is difficult to shield transmitted signals from adversarial users in the coverage area of the transmission. This chapter highlights many issues concerned with achieving secrecy in the physical layer. It discusses overview of the foundations dating back to the pioneering key-based Shannon and keyless Wyner–Ziv works on information-theoretic security. In 1978, Leung-Yang-Cheong and Hellman considered the Gaussian wiretap channel. The chapter introduces multiformity of cooperative jamming techniques to show the effectiveness of jamming signals transmitted by some legitimate transmitters in a network of multiple transmitters and receivers in achieving physical layer security for a certain legitimate pair. It gives the idea of employing cooperative jammers in a multiple trusted/untrusted relay networks in order to improve security, and the interactions arising between cooperation and secrecy in the presence of untrusted relays are adopted. A resurgence of interest in aspects of secrecy at the physical layer has been experienced.
