Wireless sensing is recognized as a promising technology for next-generation wireless networks, utilizing signals from devices such as Wi-Fi to detect and interpret human information, including movement status and sleep quality. However, the broadcast nature of wireless signals poses significant privacy risks, as unauthorized users may intercept these signals, leading to potential privacy breaches. Given the sensitive personal information embedded in CSI data and the limitations of encryption at the transmission end, conventional privacy protection measures are inadequate. Thus, developing physical layer-based privacy protection technologies for wireless sensing is urgently needed. In this paper, we consider a wireless sensing system model addressing privacy leakage issues and characterize wireless sensing performance as a classification problem. We propose a novel multi-antenna signal processing-based privacy protection strategy. To illustrate the fundamental tradeoff between sensing and privacy protection, we model the wireless sensing process as a communication task based on non-cooperative joint source-channel coding and introduce the concept of a sensing rate region. Our main contribution is the characterization of sensing and privacy protection performance at two key points within the sensing rate region:POS, indicating the minimum achievable sensing rate of an illegitimate receiver constrained by the maximum sensing rate of a legitimate receiver, andPOPP, indicating the maximum sensing rate of a legitimate receiver constrained by the minimum sensing rate of an illegitimate receiver. Based on our analysis, we provide strategies to establish achievable boundaries betweenPOSandPOPP. Moreover, we define the secure sensing rateRPP, indicating the privacy protection performance of the system. Within this framework, we examine several illustrative examples, validated through numerical simulations.

Tag-based physical-layer authentication (PLA) has gained significant research interest due to its high security and low complexity compared to traditional upper-layer authentication mechanisms. However, conventional tag-based PLA schemes often require strict synchronization between the tag and the source message before transmission, which may limit their practicality and effectiveness. To address this limitation, we propose an asynchronous tag-based PLA scheme, where the tag and the source message are transmitted asynchronously with an intentional time delay introduced at the transmitter. The proposed scheme enhances both compatibility and security without compromising robustness. We provide a theoretical analysis of the proposed scheme, and derive closed-form expressions to characterize its performance. Furthermore, theoretical comparisons with existing methods yield insightful conclusions regarding the advantages of the proposed approach. The scheme is implemented and extensively evaluated through simulations, where the theoretical results exhibit strong agreement with the simulation outcomes, thereby validating its effectiveness.

The Global Navigation Satellite System (GNSS) receiver has become indispensable in navigation applications due to its affordability and reliable accuracy. Despite its widespread use, GNSS is vulnerable to manipulation by malicious entities within the inherently insecure wireless landscape. This paper proposes innovative GNSS signal authentication strategies that employing multiple antennas to counteract spoofing attacks. Leveraging a multi-antenna framework enhances the distinguishability of spoofing signals over traditional single-antenna configurations. Importantly, the proposed approaches capitalize on spatial characteristics, which are independent of the GNSS signal’s intrinsic features, to accurately identify spoofing attacks. Specifically, we propose a Direction-of-Arrival (DOA)-based authentication scheme to address scenarios where authentic signals are blocked during spoofing attacks. Additionally, for situations where both authentic and spoofing signals coexist at the receiver, we propose a Spatial Filter (SF)-based authentication scheme. Through rigorous theoretical analysis and comprehensive simulations, we not only validate the proposed schemes but also demonstrate their robustness and effectiveness in enhancing GNSS signal security. The simulation results, aligning closely with theoretical predictions, underscore the superiority of the proposed schemes in safeguarding against spoofing threats.

This paper concerns the problem of the parameter optimization of an active Physical-Layer Authentication (PLA) scheme, which is crucial for minimizing the distortion on the base signal carrying the original message caused by embedding a tag. An inappropriate parameter may significantly lower the efficiency of the entire period of message transmission. In this paper, we propose an optimization framework for an active PLA scheme and further propose a new systematic metric, defined as Secure Authentication Efficiency (SAE). In the proposed framework, we minimize the aforementioned distortion by tuning three parameters, i.e., the Probability of Message Transmission (PMT), the Probability of Message Outage (PMO), and the Probability of Secure Authentication (PSA). The proposed optimization framework deepens the understanding of the correlation between the parameters of an active PLA scheme and the conditions of a wireless channel, and allows us to systematically optimize the parameters of the active PLA scheme. Then, we establish an objective function by maximizing the SAE with both PMT and PMO constraints. We implement our approach and conduct extensive performance comparisons. Our experimental results show that when the SNR at the receiver is more than 15 dB, our approach achieves an average SAE of greater than 80%, whereas the prior scheme without parameter optimization degenerates to zero SAE under some conditions, e.g., high SNR at adversary or high communication rate.

Physical-Layer Authentication (PLA) attracts a lot of research interests because of its significant advantages over upper-layer authentication mechanisms: high security and low complexity. The PLA schemes can be categorized into passive and active schemes. In this paper, we extensively leverage the advantages of both the active and passive schemes as a reference scheme, named as the Direct Hybrid (DH) scheme. Although the DH scheme improves the authentication performance of the prior PLA schemes, it has limitations, e.g., high communication overhead. Then, we further propose two hybrid PLA schemes to overcome the limitations of the DH scheme. The first proposed scheme further uses the advantage of the Challenge-Response Authentication Mechanism (CRAM) scheme, named as the CR-based Hybrid (CRH) scheme. Although both DH and CRH schemes significantly improve the authentication performance of the prior PLA schemes, they do not address one significant limitation of the active scheme, i.e., to set the power allocation of a tag empirically. Thus, based on the CRH scheme, we further propose the Adaptive CR-Based Hybrid (ACRH) scheme to adaptively set the parameter instead of the empirical setting. Moreover, we provide the theoretical analysis of the proposed schemes over wireless fading channels and derive their closed-form expressions in terms of the Probability of Detection (PD), Probability of False Alarm (PFA), and optimal threshold, respectively. At last, we discuss the advantages and disadvantages of the proposed schemes and give some useful suggestions for seeking a better tradeoff. Our experimental results show that, in comparison with the active scheme, the DH scheme has better robustness, and the CRH scheme has better both robustness and compatibility but it sacrifices the security. The ARCH scheme achieves a better tradeoff than the remaining schemes.

Physical Layer Authentication (PLA) in wireless systems has drawn much attention because it can provide information-theoretic security. However, the performance of the prior PLA schemes significantly declines under a frequency selective fading channel and the theoretical analysis of a PLA scheme becomes extremely challenging under a frequency selective fading channel as compared to that under a frequency flat fading channel. This paper addresses the problem of authenticating transmitters at the physical layer under a frequency selective fading channel. We propose two tag-based PLA schemes under a frequency selective fading channel. The first scheme is the Generalized Tag-based PLA (GT-PLA) scheme, where the negative effect caused by a frequency selective fading channel is compensated for. If the channel reciprocity holds, we will propose the second scheme to further improve the performance of the GT-PLA scheme, named the Adaptive Generalized Tag-based PLA (AGT-PLA) scheme. We provide the theoretical analysis of both proposed schemes over wireless fading channels in terms of robustness, security, and compatibility, and derive their closed-form expressions. Moreover, we implement the proposed schemes and conduct extensive performance comparisons. Our experimental results demonstrate that the GT-PLA scheme achieves higher robustness over the prior PLA schemes while the AGT-PLA scheme can further improve the performance of the GT-PLA scheme in terms of robustness, security, and compatibility.

This paper concerns the problem of defending against the jamming attack for the Physical-Layer Authentication (PLA). The problem is important due to the fact that jamming attacks can make the legitimate receiver reject a legitimate signal or accept an impersonating signal. In this paper, we propose two jamming detection schemes to defend against jamming attacks for the PLA. The first scheme is the Jamming-Attack Detection (JAD) scheme, which exploits the difference of noise variances between the handshaking and communication stages. The second scheme is the Composite Jamming-Attack Detection (CJAD) scheme, which exploits the difference of noise variances between Alice and Bob. Moreover, we provide the theoretical analysis of the proposed schemes over wireless fading channels and derive their closed-form expressions. We implement our schemes and conduct extensive performance comparisons. Our theoretical analysis and simulation results show that if security is the priority, the CJAD scheme is the best option. If we further consider the overhead, the JAD scheme is the best option under the strategy of jamming attacks and the CJAD scheme may be a better option under the strategy of enhanced jamming attacks, especially for the larger power of a jamming signal.

This paper concerns the problem of authenticating different transmitters at the physical layer in a multi-user scenario. In this paper, we propose two tag-based Physical-Layer Authentication (PLA) schemes in a multi-user scenario. We name the first scheme as the Multi-User Physical Layer Authentication and Classification (MU-PLAC) scheme, which not only detects an impersonation attack but also achieves multi-user classification. For further improving the performance of the MU-PLAC scheme for a two-user scenario, we propose an enhanced version of the MU-PLAC scheme by elaborately designing the tags of two legitimate users. We name the second scheme as the Enhanced Multi-User Physical Layer Authentication and Classification (EMU-PLAC) scheme. We provide the theoretical analysis of the proposed schemes over wireless fading channels and derive their closed-form expressions. We implement the proposed schemes and conduct extensive performance comparisons. Our simulation results show that, for a two-user scenario, the EMU-PLAC scheme provides better classification accuracy and authentication accuracy as compared with the MU-PLAC scheme.

This paper addresses the problems of both authentication and privacy in a Non-Orthogonal Multiple Access (NOMA) system by using a privacy-preserving Physical-Layer Authentication (PLA) scheme. The prior scheme has the following limitations: no privacy, low authentication performance, management problem of different secret keys, and constraint to the two-user scenario. In this paper, we propose two privacy-preserving PLA schemes: the Privacy-Preserving PLA (PP-PLA) scheme and the Enhanced Privacy-Preserving PLA (EPP-PLA) scheme, which improve both the privacy and authentication performance as compared to the prior scheme. The fundamental difference between the EPP-PLA and PP-PLA schemes is how to encrypt the source message of a certain user while the other operations of the two proposed schemes keep the same. We provide the theoretical analysis of the proposed schemes in terms of robustness, compatibility, privacy, and security, and derive their closed-form expressions. Moreover, we provide the theoretical comparisons between the proposed schemes and the prior scheme. We optimize the parameters of the proposed schemes to achieve both message-rate fairness and authentication-accuracy fairness. We implement the proposed schemes and conduct extensive performance comparisons through simulations. Experimental results show that the theoretical results perfectly match the corresponding simulation results. Specifically, we take the second user, acting as an administrator for a NOMA system with three users, as an example, where SNR = 16 dB. In comparison with the prior scheme, both proposed schemes have the same compatibility, whereas they improve the robustness by 4.72%. Moreover, the EPP-PLA and PP-PLA schemes improve the security by 32.8%, whereas they improve the privacy by 3000.75% and 1000.75%, respectively.

This paper addresses the problem of authenticating the transmitter device in wirelessly powered communications networks (WPCNs). We proposed a physical-layer authentication scheme for a WPCN. In comparison with upper-layer authentication schemes, the proposed scheme has low complexity, low power consumption, low overhead, and high security. For comprehensively analyzing the performance of the proposed scheme by considering the requirements of transmission delay, security, and reliability together, we put forward an analytical framework by considering the probabilities of transmission, security outage, connection outage, and joint security-connection outage. Based on the proposed analytical framework, we further introduced a new systematic metric by calculating the achievable throughput of all users with considering the performance of transmission-delay, security, and reliability together. We defined this new systematic metric as the overall transmission efficiency (OTE) of a WPCN, which can effectively quantize the average efficiency of message transmission in the WPCN with physical layer authentication. We analyzed the events represented by these probability factors over random fading channels and explicitly derive their closed-form expressions. For defending against jamming attacks, we further proposed another metric to estimate which user has the high probability of suffering from jamming attacks. The new metric represents that the adversary has the largest attacking gain with the minimum cost. We implemented our scheme and conducted extensive performance comparisons through simulations. Our experimental results show that the proposed scheme accurately detects an impersonating attack and drops its contribution to the sum of long-term throughput.

P systems with active membranes are a class of bioinspired computing models, where the rules are used in the non-deterministic maximally parallel manner. In this paper, first, a new variant of timed P systems with active membranes is proposed, where the application of rules can be regulated by promoters with only two polarizations. Next, we prove that any Turing computable set of numbers can be generated by such a P system in the time-free way. Moreover, we construct a uniform solution to the $\mathcal{SAT}$ problem in the framework of such recognizer timed P systems in polynomial time, and the feasibility and effectiveness of the proposed system is demonstrated by an instance. Compared with the existing methods, the P systems constructed in our work require fewer necessary resources and RS-steps, which show that the solution is effective toNP-complete problem.

This paper proposes a variable forgetting factor QRD-based recursive least squares algorithm with bias compensation (VFF-QR-RLS-BC) for system identification with input noise. The new algorithm is based on the least square estimation with bias compensation framework and it employs a variable forgetting factor to improve the tracking speed and a QRD-based implementation for recursively solving the LS problem with bias compensation. Simulation results show that the proposed method can obtain improved convergence rate in sudden system change environment and satisfactory performance under stationary environment.