Abstract Cooperation among wireless nodes has been recently proposed for improving the physical layer (PHY) security of wireless transmission in the presence of multiple eavesdroppers. While existing PHY security literature answered the question "what are the link-level secrecy rate gains from cooperation?", this paper attempts to answer the question of "how to achieve those gains in a practical decentralized wireless network and in the presence of a cost for information exchange?". For this purpose, we model the PHY security cooperation problem as a coalitional game with non-transferable utility and propose a distributed algorithm for coalition formation. Through the proposed algorithm, the wireless users can cooperate and self-organize into disjoint independent coalitions, while maximizing their secrecy rate taking into account the security costs during information exchange. We analyze the resulting coalitional structures for both decode-and-forward and amplify-and-forward cooperation and study how the users can adapt the network topology to environmental changes such as mobility. Through simulations, we assess the performance of the proposed algorithm and show that, by coalition formation using decode-and-forward, the average secrecy rate per user is increased of up to 25.3% and 24.4% (for a network with 45 users) relative to the non-cooperative and amplifyand-forward cases, respectively. Keywords physical layer security · coalitional games · game theory · secure communication With the recent emergence of ad hoc and decentralized networks, higher-layer security techniques such as encryption have become hard to implement. This led to an increased attention on studying the ability of the physical layer (PHY) to provide secure wireless communication. The main idea is to exploit the wireless channel PHY characteristics such as fading or noise for improving the reliability of wireless transmission. This reliability is quantified by the rate of secret information sent from a wireless node to its destination in the presence of eavesdroppers, i.e., the so called secrecy rate. The maximal achievable secrecy rate is referred to as the secrecy capacity. The study of this security aspect began with the pioneering work of Wyner over the wire-tap channel [1] and was followed up in [2, 3] for the scalar Gaussian wire-tap channel and the broadcast channel, respectively. Recently, there has been a growing interest in carrying out these studies unto the wireless and the multi-user channels [4] [5] [6] [7] [8] [9] [10] . For instance, in [4] and [5], the authors study the secrecy capacity region for both the Gaussian and the fading broadcast channels and propose optimal power allocation strategies. In [6] , the secrecy level in multiple access channels from a link-level perspective
In REF , authors proposed a distributed algorithm that enhances the achievable secrecy rates in wireless networks with cooperative wireless nodes.
Distributed Coalition Formation Games for Secure Wireless Transmission
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Mathematics Computer Science