Chapter 7 Cooperative Secrecy in Wireless

The broadcast nature of wireless communications leads to two concepts: cooperation and secrecy. The basis for both cooperation and the potential lack of secrecy is the over-heard information at the unintended parties, which wireless communication channel provides for free. It is well-established that users can help increase each others’ rates by intelligently using their over-heard information. It is also well-accepted that the leakage of information through the over-heard signals may cause loss of confidentiality and secrecy. Cooperation and secrecy have been studied individually over the past three decades following the seminal papers of van der Meulen [1] who introduced the relay channel, which is the simplest model for cooperative communications and Wyner [2] who introduced the wire-tap channel, which is the simplest model to study secrecy in communications. It is interesting to note that, both of these are simple three-node networks, where in the former, the sole purpose of the third node (relay) is to increase the achievable rate of the single-user channel between the transmitter and the receiver by transmitting signals based on its over-heard information, while in the latter, the third node (eavesdropper) is a passive entity which uses its over-heard information to extract as much information as possible about the messages transmitted in the single-user communication channel between the transmitter and the receiver. In this chapter, we will summarize the mostly separate literatures on cooperation and secrecy. More recently, there has been a tremendous amount of interest and some initial work on the interactions of cooperation and secrecy. The recent literature on the