In secret key generation of physical layer security technology, it is challenging to achieve high key capacity and low secret key inconsistency rate. This paper investigates intelligent reflecting surface (IRS) assisted secret key generation, which aims to maximize the secret key capacity by adjusting the placement of the IRS units. Specifically, we first analyze and deduce the key capacity expression of the IRS-assisted system from the perspective of information theory. Then we investigate how to use the channel state information (CSI) to place the IRS units effectively so as to maximize the secret key capacity. Simulation results show that our scheme could improve the quality of secret key generation significantly.

The identification of malicious jamming pattern is significant for wireless communication system to adopt targeted anti-jamming approaches. Efficient identification of malicious jamming patterns requires sufficient sample data and computing resources for the complex electromagnetic environment. However, with the use of portable communication equipment and emergency communications, it is difficult to ensure adequate sample data and computing resources. Against this background, this letter focuses on the jamming identification based on a small sample data-driven Naive Bayes classifier. The main idea is to obtain approximate conditional feature probability via data augment and kernel density estimation (KDE) from a small sample labelled data and construct Naive Bayes classifier, so as to form a fast jamming recognition method. Simulation results show that compared with the methods using decision tree or simple neutral network, the proposed scheme achieves a better average accuracy between six jamming patterns, as well as low-complexity.

Reactive symbol-level jammer has attracted attention due to its low energy cost and high jamming efficiency. With the development of software-defined radio (SDR), the implementation of reactive symbol-level jamming has become more practical and efficient. To combat the reactive jammer, this paper proposes an index modulation based frequency hopping spread spectrum (IM-FHSS) scheme. Specifically, the current available frequencies are determined by multiple orthogonal frequency hopping (FH) patterns, and bit information is transmitted through the index of the active FH pattern. At the receiving side, we design an energy detector to distinguish the active and idle frequencies. With such implementation, IM-FHSS can obtain the improved resistance of reactive symbol-level jammer. Subsequently, we propose the alternative spectral efficiency (SE) mode of IM-FHSS in order to meet the high SE and low-power jamming scenarios. Furthermore, we analyze the BER of this scheme for the reactive symbol-level jamming under the cases of energy correlation, jamming rate, and phase offset. Theoretical analysis and simulation results show that IM-FHSS exhibits enhanced resistance to reactive symbol-level jamming than traditional FH scheme.

To defend against eavesdropping and spoofing attacks, the physical layer authentication (PLA) techniques utilize the unique attributes of channel or device for identifying attackers. Among these techniques, the PLA schemes based on channel phase responses use the secret key driven channel phase to authenticate the legitimate user, which have a better performance than the channel amplitude based schemes. However, the prior phase-based schemes only consider the perfect channel correlation coefficient between the two successive timeslots, which differs from the real scenarios. Meanwhile, the closed-form expressions of the theoretical analysis results are not comprehensive in the prior schemes, which are also not tight especially at low signal-to-noise ratio (SNR) regions. In this paper, we propose a PLA scheme based on the channel phase response, aiming to offset the performance loss introduced by the channel correlation coefficient. Moreover, we derive the closed-form expressions of the theoretical analysis results, such as the mean value, the variance and the probability density functions (PDFs), which can be utilized to provide the closed-form threshold for making decision instead of a great ideal of testing. Then, the security analysis is provided to verify the resistance of the proposed scheme under the attacks. Simulation results show that the proposed scheme outperforms the benchmarks and the proposed theoretical results match well with the simulated results even under low SNR regions.

Aiming at the authentication problem in wireless communication, an improved physical layer authentication scheme based on wireless channel phase (PHY-IMACP) is proposed in this letter. In this scheme, legitimate nodes exploit the reciprocity of the channel phase response to conduct information exchange. The secret key information is hidden in the phase of the interactive information, and the authentication judgment is completed by use of binary hypothesis testing. Then the well-designed hypothesis testing statistic is proposed to obtain the better authentication performance. Additionally, mean and variance closed-form expressions of the hypothesis testing statistic in our proposed scheme are given. The simulation results show that the proposed scheme outperforms the benchmark at different conditions of eavesdropping channel.

Due to the threat of various jamming attacks in wireless communications, the efficient and general anti-jamming schemes are required to guarantee communication the quality of wireless networks. To this end, this article proposes the efficient index modulation-based frequency hopping spread spectrum (IM-FHSS) scheme. Unlike the classical IM-FHSS which only considered the reactive jamming, the efficient IM-FHSS scheme extends the anti-jamming capacity to various jamming models. Specifically, we first derive the closed-form expressions of bit error rate (BER) performance of the IM-FHSS under three jamming models in an additional white Gaussian noise (AWGN) channel and a Rayleigh fading channel, which enables the design of anti-jamming strategies. Then, the unified anti-jamming framework is provided for designing the efficient anti-jamming system. Based on the framework, we further provide the strategies of the efficient IM-FHSS for reactive jamming, constant, and random jamming. Simulations show that the theoretical derivations match well with the simulated results, which validates the performance analysis. Moreover, the efficient IM-FHSS has demonstrated the superior anti-jamming performance for three typical jamming models, which is also energy efficient and reliable for achieving targeted BER performance.