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...cryptographic schemes. However, classical cryptography might not be suitable in large dynamic networks, since it requires key distribution and management, and complex encryption/decryption algorithms =-=[2]-=-, [3]. A method that exploits the characteristics of wireless channels, such as fading and noise, was proposed as an alternative to achieve perfect secrecy without requiring encryption keys [4]–[7]. T...

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...paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TCOMM.2014.2314664 security has become a very active area of research, and has witnessed significant growth =-=[2]-=-–[5]. A. Motivation and Related Work Physical layer security for multi-user communications was first investigated by introducing the broadcast channel with confidential messages (BCC) [6]. In the mult...

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...e, where, by using secret keys, sensor nodes ensure information secrecy from malicious users. But cryptographic measures become ineffective if the adversary has superior computational capability [3], =-=[4]-=- or is able to retrieve the secret keys. Changing keys at intervals can be a possible solution, but its implementation becomes cumbersome. This is where Information Theoretic Secrecy model appears pro...

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...emes to combat eavesdropping attack. The first type includes cryptographic techniques which are based on the premise that deciphering without knowledge of the secret key is computationally infeasible =-=[1]-=-. The second type is physical layer security schemes that aim at hiding the protected radio signal to the passive eavesdroppers. In this paper, we focus on the latter. Physical layer security schemes ...

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...the wireless medium. There are mainly two approaches to design security techniques; computational security and informationtheoretic security. In computational security, the time which takes to break the code indicates the degree of security. Due to the recent development in computing power, breaking only encryption based codes can be done within practical time [1], [2]. On the other hand, information-theoretic security does not rely on the computing power and recently physical layer security techniques designed based on the information-theoretic security have been paid a lot of attention [3], [4]. In physical layer security, secrecy capacity is an important metric and most of related works have aimed to achieve the maximization of secrecy capacity. The physical layer security techniques with multiple-input and multiple-output (MIMO) [5] and orthogonal frequencydivision multiplexing (OFDM) have been investigated since the signal processing techniques can exploit randomness of communication channels properly. In this paper, we focus on physical layer security technique in OFDM communication. The works which have considered secure wireless communication in OFDM systems can be categorized...

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...theoretical level in the paper. Later on in [2] a wire-tap channel which can achieve positive secrecy rate has been proposed by Wyner under the assumption that the users experience a better channel than eavesdroppers. Since then, the wire-tap model along with other techniques such as the broadcast channel [3], MIMO channels [4], [5], artificial noise [6], beamforming [7] as well as relay systems [8] have been studied. In this work, we focus on relay systems and cooperation schemes involving relay and jamming strategies in relays equipped with buffers. A. Prior and Related Work In recent years [9], the concept of physical-layer security with multiuser wireless networks has been investigated in Xiaotao Lu is with the Communications Research Group, Department of Electronics, University of York, YO10 5DD York, U.K., R. C. de Lamare is with CETUC, PUC-Rio, Brazil and with the Communications Research Group, Department of Electronics, University of York, YO10 5DD York, U.K. This work was supported by CNPq and FAPERJ. E-mails: xtl503@york.ac.uk; rodrigo.delamare@york.ac.uk. numerous studies. Approaches to achieving physical-layer security include the design of transmit precoding strategies wi...

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...the private transmitted signals may be intercepted by unintended receivers or eavesdroppers. Therefore, there have been intensive efforts aimed at improving physical layer security for relay networks =-=[3]-=-–[18]. Manuscript received February 2, 2014; revised May 7, 2014; accepted June 23, 2014. Date of publication July 1, 2014; date of current version January 7, 2015. This work was supported in part by ...

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...erned with whether a positive data rate can be supported, independent of the type of the decoding approach the unauthorized users use, have been attracted much interest in the research community [1], =-=[2]-=- which is the scop of this paper. A. Related Works The concept of physical layer security was first established by Wyner [1]. In [3], the authors consider the problem of secure communications in OFDMA...

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...el state information (CSI) is available. Moreover, the idea of relay selection for secure cooperative networks is considered in [27]–[29]. Also, there are some related works on this issue [25], [30], =-=[31]-=-. In this paper, we derive the secrecy capacity of a simple cooperative wiretap channel in which a source wishes to send a confidential message to a legitimated destination with the help of an untrust...