An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> VII. CONSTELLATION CONSTRAINED MULTIUSER AND COOPERATIVE WIRETAP CHANNELS <s> This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical layer message authentication is also briefly introduced. The survey concludes with observations on potential research directions in this area. <s> BIB001 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> VII. CONSTELLATION CONSTRAINED MULTIUSER AND COOPERATIVE WIRETAP CHANNELS <s> This paper considers the Broadcast Channel with Confidential Message (BCCM) where the sender attempts to send altogether a common message to two receivers and a confidential message to one of them. The achievable rate regions are derived for the power-constrained Gaussian BCCM with finite input alphabet using various transmission strategies. Namely, time sharing, superposition modulation and superposition coding are used as broadcast strategies. For superposition modulation and superposition coding, the maximal achievable rate regions are obtained by maximizing over both constellation symbol positions and the joint probability distribution. The maximization of the secrecy rate for wiretap channels is also studied as a particular case of the BCCM problem. We compare the considered transmission strategies in terms of percentage gains in achievable rates. We concentrate on the impact of the finite alphabet constraint on achievable rates, and show that this constraint may change well known results obtained in the Gaussian case. We show also that the secrecy constraint can change the shape of the achievable rate region in superposition modulation used in some standards when symbols are equiprobable. On a more practical side, it is shown that a performance close to the optimum can be obtained by strategies with reduced complexity. <s> BIB002 </s> An Overview of Physical Layer Security With Finite-Alphabet Signaling <s> VII. CONSTELLATION CONSTRAINED MULTIUSER AND COOPERATIVE WIRETAP CHANNELS <s> We investigate the physical layer security of synchronous multiple access transmissions using the Alamouti space-time block code in fading channels where multiple users communicate with a single intended receiver in the presence of an eavesdropper. We propose an artificial-noise-aided technique to secure the transmissions by having the Alamouti users collaborate with each other, without exchanging information, to degrade the eavesdropper’s channel. Unlike previous work, which assumes that the transmitters have complete knowledge of the legitimate as well as the eavesdropper’s channels, our proposed technique requires no communications between the users, minimal knowledge of the legitimate channel, and no channel knowledge regarding the eavesdropper. <s> BIB003
The concept of physical layer security has also been extended to multi-user and cooperative networks in recent years. In addition to the numerous studies on the limits of secure communications for scenarios with more than two receivers, multiple transmitters and presence of relays/jammers/helpers (see BIB001 for a survey), some recent focus has also been placed on the practical constellationconstrained secure transmission in these settings. Fig. 8 . Broadcast channel with confidential messages BIB002 . Fig. 9 . Multiple access wiretap channel studied in BIB003 .