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Authentication is one of the major requirements of wireless networks security, which uses to distinguish legal transmitter from illegal transmitter. Physical layer authentication by taking advantages of channel characteristics has become an effective complement to encryption based authentication methods. In this paper, we propose a machine learning relay assisted authentication for dual-hop multiple-input multiple-output (MIMO) systems with hardware impairments. So far, the multi-hop authentication has not been investigated to identify the transmitter at the receiver. Motivated by this, we use channel features for end-to-end authentication. To implement this technique in the practical systems, channel estimation is implemented in the presence of hardware impairments. The neural network is used to recognize the legitimate transmitter from the attacker in this system. Simulation results show that the proposed method provides a significant improvement in authentication performance using the extracted features with neural network method. Numerical results show that the proposed method presents more than 90% authentication accuracy for both of one-hop and two-hop PLA scenarios. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive transmission scheme for two-way amplify-and-forward (AF) relaying over optical wireless communications. The two terminals utilize subcarrier phase shift keying (S-PSK) intensity modulation for data transmission, and the atmospheric turbulence impacts the transmitted signals. The proposed transmission scheme exploits the efficient utilization of the optical wireless channel capacity by adjusting the modulation order of S-PSK. While meeting predetermined bit error rate (BER) requirements for each terminal, the selected modulation order of each terminal corresponds to the instantaneous condition of turbulence-induced fading. A new expression is derived for the spectral efficiency of the proposed two-way relaying scheme, and then performance investigations are carried out under various turbulence conditions. Moreover, we derive a closed form expression for the BER performance and analyze the proposed system model from the outage probability point of view. Numerical examples illustrate that the proposed two-way relaying scheme enjoys better spectral efficiency compared with the traditional direct transmission scheme in the high signal-to-noise-ratio regime. The simulation results show that for a fixed turbulence, the TWR saves the electrical signal-to-noise-ratio (SNR) about 2.5 dB compared to the direct transmission scheme when the target spectral efficiency is set to 1.2 bits/s/Hz. [ABSTRACT FROM AUTHOR]

Cooperative relaying is utilized as an efficient method for data communication in wireless sensor networks and the Internet of Things. However, sometimes due to the necessity of multi-hop relaying in such communication networks, it is challenging to guarantee the secrecy of cooperative transmissions when the relays may themselves be eavesdroppers, i.e., we may face with the untrusted relaying scenario where the relays are both necessary helpers and potential adversary. To obviate this issue, a new cooperative jamming scheme is proposed in this paper, in which the data can be confidentially communicated from the source to the destination through multiple untrusted relays. In our proposed secure transmission scheme, all the legitimate nodes contribute to providing secure communication by intelligently injecting artificial noises to the network in different communication phases. For the sake of analysis, we consider a multi-hop untrusted relaying network with two successive intermediate nodes, i.e, a three-hop communications network. Given this system model, a new closed-form expression is presented in the high signal-to-noise ratio (SNR) regime for the Ergodic secrecy rate (ESR). Furthermore, we evaluate the high-SNR slope and power offset of the ESR to gain an insightful comparison of the proposed secure transmission scheme and the state-of-arts. Our numerical results highlight that the proposed secure transmission scheme provides better secrecy rate performance compared with the two-hop untrusted relaying as well as the direct transmission schemes. [ABSTRACT FROM AUTHOR]

By considering an adversary jammer in a communication network, we investigate the secrecy performance of a cooperative wireless network comprised of a source, a destination and an untrusted amplify-and-forward relay. We assume that either the source or the destination, as well as the jammer are equipped with large-scale multiple antennas systems, while the rest are equipped with a single-antenna. To prevent the untrusted relay from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as destination-assisted cooperative jamming. On the other hand, the role of the jammer is to disturb the communication by transmitting jamming signals toward the untrusted relay. Given this system model, novel closed-form expressions are extracted for the ergodic secrecy rate (ESR) with Rayleigh fading channels. We further evaluate the ESR at high signal-to-noise ratio (SNR) and then determine the high SNR slope and power offset of the ESR to get some insights into the network. Next, with the aim of maximizing the instantaneous secrecy rate, we derive new closed-form solutions for the optimal power allocation (OPA). Numerical examples depict that the presented OPA considerably improves the system secrecy rate compared to the equal power allocation (EPA) which reveals the priority of our optimized network. We also illustrate that by increasing the number of jammer antennas, the ESR performance of both the OPA and EPA is reduced. The results state that unlike the EPA technique, increasing the number of source antennas enhances the ESR of the proposed OPA technique which reveals the priority of our OPA. [ABSTRACT FROM AUTHOR]