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.

Two-Dimensional (2D) barcodes attract much attention recently due to their higher capacity for storing information as compared with 1D barcodes. This paper considers the problem of defending against Illegitimately-Copying (IC) attacks in 2D barcodes. This problem is important because the authorized manufacturer may lose its economy and reputation under IC attacks. In addition, the application of using 2D barcodes for anti-counterfeiting is also sacrificed by the IC attacks. However, prior anti-copying 2D barcodes have high production costs, and their universal applicability is low. Moreover, they are vulnerable to advanced IC attacks. In this paper, we propose a tag-based anti-copying 2D barcode, which is denoted as the Superimposed-Tag Anti-Copying (STAC) 2D barcode. Specifically, the difference between the channel noise from the legitimate and illegitimate 2D barcodes is adopted to detect IC attacks. Our scheme overcomes the drawbacks of the prior anti-copying 2D barcodes since our scheme provides not only better security but also better compatibility as compared to the prior anti-copying 2D barcodes. We first provide the theoretical model of an illegitimate channel. Based on the theoretical model, we explicitly analyze the Probability of Attacking Detection (PAD) and the Probability of False Alarm (PFA) of our scheme. Moreover, we derive their closed-form expressions as well as the optimal authentication threshold. To further improve the performance of our scheme, we optimize the amplitude allocation factor of the authentication tag and the embedding area. We implement the proposed schemes and conduct extensive performance comparisons via experimental results. The experimental results using a scanner demonstrate that, based on the best-attacking performance chosen from the existing IC attacks, the PAD of the Two-Level QR (2LQR) code is 0.3462 and that of the Low-Cost Anti-Copying (LCAC) 2D barcode is 0, whereas that of our scheme is 0.5712, where we set the PFA as 0.02.

Authentication is a fundamental requirement and a crucial topic in wireless communications. This paper focuses on improving the security of the prior tag-based Physical-Layer Authentication (PLA) schemes. We propose two phase-tag-based PLA schemes to overcome the limitations of prior tag-based PLA schemes. First, we propose the Phase-Tag-based PLA (PT-PLA) scheme, which superimposes a tag to the phase of the transmitted signal rather than the amplitude. Second, we propose the Adaptive Phase-Tag-based PLA (APT-PLA) scheme, where an appropriate parameter of the PT-PLA scheme is adaptively set for achieving a better trade-off among robustness, security, and compatibility. Rigorous theoretical analyses of the proposed schemes are conducted in high-order modulation systems, such as$M$-PSK and${M}$-QAM systems, with a focus on evaluating their robustness, security, and compatibility. We also discuss advantages and disadvantages of these schemes and offer helpful recommendations according to different scenarios. Furthermore, we implement the proposed schemes and perform extensive simulations to compare their performance comprehensively. Simulation results demonstrate a perfect match with the theoretical results, verifying the superiority of the proposed schemes over the prior schemes.

This paper tackles a notable security loophole in tag-based Physical-Layer Authentication (PLA) when faced with cooperative attacks, highlighting its significance due to two main reasons. First, while attackers may only observe the tag amid noise, they can reduce the noise effect through multiple observations. Furthermore, several cooperative attackers can orchestrate more sophisticated attacks, achieving goals beyond the reach of a single attacker. In this paper, we propose an enhanced PLA scheme, designated as the Enhanced Detection of Cooperative Attacks (EDCA) scheme, to counter these cooperative threats. The basic idea of the EDCA scheme involves utilizing a unique noise characteristic induced by replayed signals to identify and thwart cooperative attacks, preventing attackers from accumulating multiple observations of the same tag. We theoretically analyze the proposed scheme over fading channels and derive closed-form expressions for its performance. Implementation and rigorous evaluation of the EDCA scheme are carried out to compare its performance with prior schemes. Simulation results confirm the alignment of theoretical predictions with empirical outcomes. The proposed scheme not only can effectively detect cooperative attacks but also provide a better detection performance.

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.

Most wireless systems involve time-varying multipath channels, where the negative effect of the phase noise cannot be ignored. The phase noise can be introduced by imperfect phase-locked loop circuitry, imperfect channel estimation, or both. This paper considers the demodulation problem of wireless systems with phase noise. We propose an ensemble clustering algorithm to address the limitations of the existing demodulation schemes. The proposed ensemble clustering algorithm is named as the Ensemble Clustering algorithm using the Matrix Factorization and Information Theory (MFIT-EC). The MFIT-EC algorithm improves the performance of existing ensemble clustering algorithms, which neglect different clustering effects of different base-clustering algorithms or different effects of different clusters of the same base-clustering algorithm. Based on the MFIT-EC algorithm, we design a demodulation scheme in a coherent wireless system with phase noise, referred to as the MFIT-EC demodulation scheme. Specifically, we first utilize several base-clustering algorithms to obtain different base-clustering results. Second, we use a weighted ensemble mechanism to allocate different weights to different base-clustering results, and calculate the certainty of the clusters of each base-clustering algorithm to obtain a better and more robust demodulation performance. We implement the proposed approach and conduct extensive performance comparisons through simulations, which show that the proposed approach has better performance than the prior approaches in terms of both clustering performance and demodulation performance.

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.

In this paper, we are concerned about the problem of guaranteeing both privacy and security in a Location-Based Service (LBS) system, where a challenging scenario involving cooperative attack is considered. Since prior Physical-Layer Authentication (PLA) schemes do not consider cooperative attack, their security significantly declines under such attacks. We propose two privacy-preserving PLA schemes: the Privacy-Preserving Physical-Layer Authentication using Noise Variance (PPPLA-NV) scheme and the Privacy-Preserving Physical-Layer Authentication using Multiple Channel Responses (PPPLA-MCR) scheme, which significantly improve the privacy-preserving performance under a cooperative attack. Note that the proposed schemes protect not only user’s identity information but also data message. We theoretically analyze the performance of the proposed schemes, derive their closed-form expressions, and provide a theoretical comparison between both proposed schemes. We implement the proposed schemes and conduct extensive performance comparisons through simulations. Experimental results show a perfect match between the theoretical and simulation results. From the experimental results, we observe that if the overhead is not the priority, the PPPLA-MCR scheme is the best option; otherwise, the PPPLA-NV scheme may be a better option.

In comparison with upper-layer authentication mechanisms, the tag-based Physical-Layer Authentication (PLA) attracts many research interests because of high security and low complexity. This paper mainly concerns two problems in prior tag-based PLA schemes, where the first one is extra overhead and vulnerability due to the reason that the parameter is broadcasted and the other one is the problem of setting the parameter empirically. Therefore, two new tag-based PLA schemes are proposed to address the above limitations. Specifically, a blind tag-based PLA scheme (BTP) is presented to achieve accurate authentication without knowing the tag parameter of the legitimate transmitter, which not only saves the communication overhead but also improves security. Then, an adaptive blind tag-based PLA scheme (ABTP) is further proposed, which adaptively sets the tag parameter according to the wireless channel state to achieve a better balance among robustness, security, and compatibility. Rigorous theoretical analyses are provided for the two proposed schemes and the prior schemes’ performance comparisons are given. The accuracy of the theoretical analyses is verified through simulation results. At last, the advantages and disadvantages of the two proposed schemes are discussed, and suggestions are given according to different scenarios.

This paper addresses the critical challenge of securing two-way Time-of-Arrival (ToA) localization in Wireless Sensor Networks (WSNs) against cooperative distance-enlargement attacks. Existing schemes often rely on heuristic test statistics, are limited to specific attack strategies e.g., Amplify and Forward (AF), or require collaboration among multiple anchor nodes, which hinders their effectiveness against sophisticated adversaries and often incurs high communication overhead. We propose two novel detection schemes based on signal characteristics that overcome these limitations, offering both high accuracy and low complexity. The first scheme, termed the Efficient Detection Scheme of Distance-Enlargement Attacks using Log-Likelihood Ratio (EDDEA-LLR), leverages the Neyman-Pearson (NP) lemma to derive an optimal test statistic for scenarios involving AF attacks. Recognizing the limitations of existing schemes and the EDDEA-LLR scheme in countering Decode and Forward (DF) attacks, we introduce the Efficient Detection Scheme of Distance-Enlargement Attacks by Embedding a Secret Tag (EDDEA-EST). This scheme exploits embedded secret tags within the challenge signal to effectively detect DF attacks. Importantly, the proposed schemes do not require collaboration among multiple anchor nodes, eliminating the need for additional communication and featuring low computational complexity. We provide a rigorous theoretical analysis, deriving closed-form expressions for the detection performance of both schemes. Through extensive simulations, we demonstrate the superiority of the proposed schemes over existing methods in terms of detection accuracy, robustness against both AF and DF attacks, and comprehensive performance considering communication overhead.

This article addresses the reading problem of multilevel 2-D barcodes over a print-and-capture (PC) channel. The prior reading schemes have different limitations to hinder their applications, e.g., suffering from quantization error, being sensitive to the predetermined decision boundaries, and being sensitive to the selection of initial parameters. In this article, we introduce a machine learning approach to address the above limitations using a new ensemble clustering (EC) algorithm. Based on the new EC algorithm, we propose two reading schemes of a multilevel 2-D barcode. Specifically, the first proposed scheme is named the EC reading scheme. In the EC reading scheme, we introduce a weighted ensemble mechanism to assign different weights to different base clustering results. Then, we propose the second scheme, named the enhanced EC (EEC) reading scheme, to further improve the reading performance with the help of the reference symbols. We implement our approach and conduct extensive performance comparisons through an actual excremental platform under various multilevel 2-D barcodes and various capturing devices. From experimental results, we observe that both proposed reading schemes have better performance than the prior reading schemes. Moreover, the EEC reading scheme has better performance than the EC reading scheme, and their performance gap becomes more apparent as the distortion of a PC channel increases.

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.

The reception performance of a Multiple-Input-Multiple-Output (MIMO) system suffers from not only the channel fading but also the phase noise. Accurate and efficient estimation algorithms of channel responses and phase noises that enable high-speed wireless communications in MIMO systems are of broad interest. The prior joint estimation schemes of channel responses and phase noises are designed for synchronous MIMO systems, where symbols transmitted from different transmit antennas are strictly synchronized. However, the estimation performance of the prior schemes suffers from the Inter Antenna Interference (IAI), which further limits the reception performance of a MIMO system. In this paper, we propose an asynchronous MIMO system with intentional timing offset. Based on the proposed asynchronous MIMO system, we further design the Joint Estimation of Channel responses and Phase noises using Intentional Timing Offset (JECP-ITO) scheme. We derive the Cramér-Rao Lower Bound (CRLB) of the JECP-ITO scheme in closed form. We provide rigorous theoretical comparisons between the JECP-ITO and the prior scheme in terms of IAI and CRLB. Moreover, we implement the proposed scheme and conduct extensive performance comparisons through simulations.

Spatial Modulation (SM) is a promising low-complexity modulation scheme for Multiple-Input Multiple-Output (MIMO) systems. In this paper, we address the problem of authenticating the transmitter device in the SM. We propose an authentication approach for an SM system by using Physical-Layer Authentication (PLA) mechanisms because the PLA has the following advantages: high security and low complexity. Based on the features of an SM system, we propose two PLA schemes:PLA with Superimposed Authentication Tag(PLA-SAT) andPLA with Superimposed Imaginary authentication Tag(PLA-SIT). We provide performance analyses of our schemes over fading channels in terms of robustness, compatibility, and security. Moreover, we derive their closed-form expressions under both perfect and imperfect channel estimates, including the Probability of Detection (PD), Probability of False Alarm (PFA), and Average Error Probability (AEP). Although the two proposed schemes have the same robustness and security, the PLA-SIT scheme has better compatibility than the PLA-SAT scheme. Our schemes were implemented and extensive performance comparisons through simulations were conducted. We observe that the simulation results of the two proposed schemes perfectly match their corresponding theoretical analyses. The authentication accuracy of the two proposed schemes is close to one when the received SNR is greater than 20 dB and the security performances of the two proposed schemes improve as the variance of estimation errors increases.

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 two issues of a contact-tracing system with edge-based wireless communication techniques: to locate close contacts and to provide confidentiality-preserving communications. In this paper, we propose the Confidentiality-Preserving Contact-Tracing (CPCT) system with multiple wireless edge-based nodes. The CPCT system consists of three stages: registration, authentication, and confidentiality-preserving communication stages. We propose two Physical-Layer Authentication (PLA) schemes for the authentication stage of the CPCT system: the Coordinate-based Location PLA (CLP) scheme using the estimated coordinates and the Time-of-Arrival (ToA) based Location PLA (TLP) scheme using the estimated ToAs. We propose a distributed encryption scheme for the confidentiality-preserving communication stage of the CPCT system named the Distributed Channel Impulse Response (CIR)-based Encryption (DCE) scheme. We provide the theoretical analysis of the proposed schemes and derive their closed-form expressions. We implement the proposed schemes and conduct extensive performance comparisons through simulations. We observe that the theoretical results perfectly match the corresponding simulation results. Moreover, the proposed PLA schemes provide higher authentication performance than the prior PLA scheme, while the proposed encryption scheme provides higher confidentiality performance than the prior encryption 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 concerns the problem of defending against spoofing attacks without a secret key. We address the problem using the Physical-Layer-Authentication (PLA) because of its high security, low overhead, and high compatibility. However, many PLA schemes have the following limitations: quantization errors, local optimums, and performance loss due to the change in the communication environment. In this paper, two phase-noise-based PLA schemes are proposed to address the limitations of the prior schemes. We denote the first scheme as the Multiple Phase Noises PLA (MPP) scheme, which realizes the PLA by using multiple phase noise innovations. Note that since the MPP scheme avoids using any quantization algorithm, it outperforms the prior schemes on the authentication performance. We denote the second scheme as the Enhanced Multiple Phase Noises PLA (EMPP) scheme, which introduces an artificial random phase to the transmitted symbols at the transmitter to further improve the authentication performance. The theoretical analyses of the proposed schemes over fading channels are provided, where the closed-form expressions are derived. Theoretical comparisons between the proposed schemes and prior schemes are provided. The theoretical analyses and simulation results demonstrated the superiority of the proposed schemes. In comparison with the prior schemes, the MPP scheme achieves 13% authentication-performance gain without demodulation-performance loss, while the EMPP scheme achieves 42% authentication-performance gain with merely 16% demodulation-performance loss.

This paper concerns the problem of improving compatibility in the tag-based Physical-Layer Authentication (PLA) without sacrificing robustness of the PLA schemes. The prior PLA schemes for improving compatibility often sacrifice robustness or introduce extra communication overhead and security vulnerabilities. The main objective of our approach is to reduce the modification ratio of the source message given the tag length via an encoding approach. Based on a tag-encoding function, we propose two encoded tag-based schemes for the scenario of a single block and the scenario of multiple blocks, respectively, which are named as the Encoded Tag-based PLA scheme for Single Block (ET-SB) and the Encoded Tag-based PLA scheme for Multiple Blocks (ET-MB), respectively. We theoretically analyze the performance of the proposed schemes over fading channels and derive the closed-form expressions of the performance analyses. We implement the proposed schemes and conduct extensive performance comparisons through simulations. Our simulation results show that the closed-form expressions of the theoretical results of the proposed schemes perfectly match the corresponding simulation results. When the SNR is 10 dB, the compatibility of the ET-SB and ET-MB schemes improves to 15.63% and 23.45%, respectively, compared to the prior scheme.

This paper addresses the issue of detecting the use of information hiding at anti-copying 2D barcodes. Prior hidden information detection schemes have their roots in either heuristic-based or Machine Learning (ML). However, prior heuristics-based schemes lack a rigorous theoretical analysis. Prior ML-based information schemes lack robustness because a printed 2D barcode is very much environmentally dependent. Thus, an information hiding detection scheme trained in one environment often does not work well in another environment. In this paper, we propose two hidden information detection schemes for existing anti-copying 2D barcodes. The first scheme directly uses the pixel distance to detect the use of an information hiding scheme in a 2D barcode, referred to as the Pixel Distance Based Detection (PDBD) scheme. The second scheme first calculates the variance of raw signal and the covariance between the recovered and raw signals, and then based on the variance results, detects the use of information hiding scheme in a 2D barcode, referred to as the Pixel Variance Based Detection (PVBD) scheme. Moreover, we design advanced Illegitimately-Copying (IC) attacks to evaluate the security of two existing anti-copying 2D barcodes. We conduct extensive performance comparisons among the proposed schemes and prior schemes under different capturing devices,e.g., different scanners or camera phones. Our experimental results show that the PVBD scheme can correctly detect the existence of hidden information at both the 2LQR code and the LCAC 2D barcode. Moreover, the successful attacking probability of the proposed IC attacks achieves 0.6538 for the 2LQR code and 1 for the LCAC 2D barcode.

This article concerns the problem of detecting the use of information hiding at the physical layer in wireless communications because they are harder to be detected than other layer-based information hiding schemes. Prior schemes for detecting physical layer based information hiding are either heuristic based or machine learning based. The key limitation of prior heuristics based information hiding detection schemes is that they do not answer the fundamental question of why the information hidden at the physical layer can be detected. The key limitation of prior machine learning based information hiding detection schemes is that they lack robustness because wireless signals at the physical layer are very much environmental dependent, and thus an information hiding detection scheme trained in one environment often does not work well in another environment. Our insight is that embedding information on wireless signals at the physical layer will inevitably have a negative impact on the decodability of the cover signals, such as the increase of the error probability at the receiver (as well as the monitor). Based on the above insight, in our approach, after the monitor demodulates and decodes the cover signals, it will re-encode and re-modulate the cover signals, and then compare the resulting recovered signals with the raw signals that it received from the sender. We further propose a new estimation scheme for calculating receiver noise variance and conducted theoretical analysis. Specifically, we propose two hidden information detection schemes, a noise grouped based detection scheme and a constellation distance based detection scheme, both taking estimation errors into consideration. In particular, our constellation distance based detection scheme is the first scheme that can pinpoint the exact location on the received signals that are embedded with hidden information. We implemented our schemes and conducted extensive performance comparison between our schemes and prior schemes. Our experimental results show that when the received SNR is more than 20 dB, our approach with the new estimation scheme has the probability of detection more than 0.95, and our constellation distance based detection scheme can correctly pinpoint all embedded locations.

This paper is concerned with the security problem of Time of Arrival (ToA) based localization schemes in a wireless sensor network (WSN) with multiple attackers and this paper focuses on defending against external attacks, especially under cooperative external attackers. The prior scheme for defending against the attacks in the localization scheme often introduce high communication overhead and their security relies on the capability of the attackers. In this paper, we propose a lightweight secure ToA-based localization scheme in a WSN by exploiting the noise feature caused by external distance attacks. In comparison with the prior scheme, our scheme provides lower communication overhead and a higher level of security. We theoretically analyze the performance of the proposed scheme over fading channels and derive the closed-form expressions. We implemented our scheme and conducted extensive performance comparisons through simulations. Our experimental results show that the closed-form expressions for the detection performance perfectly match with their simulation results as we expected. The communication overhead of the proposed scheme is saved by 72.8% than that of the prior scheme for different numbers of anchors and is independent of the times of measurements.

Compared with conventional authentication schemes, which utilize cryptographic mechanisms and operate at an upper layer, authentication at the physical (PHY) layer possesses many advantages, such as, higher information-theoretic security by introducing uncertainty to an adversary, better efficiency, and better compatibility by avoiding any operations at the upper layer. An effective PHY-layer authentication scheme should consider covertness, security, and robustness together. However, in published literature, these three properties have been separately analyzed. This paper proposes a generic security model for PHY-layer authentication, and we design a new systematic metric, which is referred to as the probability of security authentication (PSA). According to the proposed generic security model, we can not only systematically analyze the effect of the parameter of a certain PHY-layer authentication scheme on the final performance, but also fairly compare the performance of different PHY-layer authentication schemes under the same channel conditions at the legitimate and adversary receivers. For performance analysis, the probability of detection (PD) and the probability of false alarm (PFA) of two PHY-layer authentication schemes over fading channels are defined, and their closed-form expressions are well derived. On the basis of the proposed generic security model, a systematic performance comparison between different PHY-layer schemes is provided.

This paper concerns the problem of authenticating the transmitter without a secret key. In comparison with traditional cryptographic-based authentication mechanisms, the Physical-Layer Authentication (PLA) has the following advantages: high security, low complexity, and high compatibility, since it exploits intrinsic and unique features of the physical layer to authenticate the transmitter rather than using a secret key. The prior channel-based PLA schemes use a quantization algorithm to deal with multiple channel-based features for simplicity. However, there are two main limitations in the prior schemes: performance loss due to quantization error and the difficulty of obtaining the optimal thresholds in closed-form. In this paper, we propose two multiple Channel Impulse Response (CIR) based PLA schemes to effectively overcome the aforementioned limitations of the prior schemes. The first scheme uses multiple CIRs to realize the PLA, which is named as the Multiple CIRs PLA (MCP) scheme. The MCP scheme has better authentication performance than the prior schemes, since it avoids to use a quantization algorithm. The second scheme further improves the authentication performance by exploiting the channel correlation coefficient, which is named as the Enhanced Multiple CIRs PLA (EMCP) scheme. We provide rigorous performance analysis of two proposed schemes. We implemented the proposed schemes and conducted extensive performance comparisons through simulations. Our experimental results show that the closed-form expressions of the theoretical results of the proposed schemes perfectly match the corresponding simulation results. The EMCP scheme has the best authentication performance and the MCP scheme is the second one, whereas the prior scheme is the worst one. As the SNR or the channel correlation coefficient declines, the performance gap among various schemes gradually increases.

In this paper, to overcome the drawbacks of prior approaches for defending against Illegally-Copying (IC) attacks, such as low generality, high cost, and high overhead, we propose a Low-Cost Anti-Copying (LCAC) 2D barcode by exploiting the difference between the noise characteristics of legal and illegal channels. An embedding strategy is proposed, and for a variant of this strategy, we also perform a corresponding analysis. To accurately evaluate the performance of our approach, a theoretical model of the noise in an illegal channel is established by using a generalized Gaussian distribution. By comparing the experimental results based on various printers, scanners, and mobile phones, it can be found that the sample histogram and fitting curve of the theoretical model match well, so it can be concluded that the theoretical model works well. To evaluate the security of the proposed LCAC code, in addition to the Direct-Copying (DC) attack, an improved version, called the Synthesized-Copying (SC) attack, is also considered in this paper. Based on the theoretical model, we build a prediction function to optimize the parameters of our approach. Parameters optimization seeks a tradeoff between the production cost and the cost of IC attacks. The experimental results show that the proposed LCAC code with two printers and two scanners can detect DC attacks effectively and resist SC attacks up to the access of 14 legal copies.

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.

This paper concerns the problem of phase reference estimation with noise, introduced by the imperfect phase-locked loop (PLL) circuit, or the imperfect channel estimation, or both. Prior solutions for suppressing phase noise focus on improving the accuracy of phase reference estimation. The accuracy of phase reference estimation is not high enough due to the following two limitations. First, since the PLL circuit works in radio-frequency (RF), a PLL circuit with high accuracy leads to high cost and high complexity, which makes the deployment difficult. Second, as data rates increase and wireless channels become more complex, the receiver is more difficult to obtain an ideal channel estimation and the negative effect of phase noise becomes more apparent. In this paper, we propose a machine learning approach to mitigate the negative effect of phase noise by using clustering algorithms. The key intuition of our approach is that the clustering algorithm can adaptively trace the shifted constellation point due to the phase noise. Our approach is adaptive because it can adaptively find each received symbol belongs to its original constellation point if the phase noise is not too large, e.g., no larger than $0.25 \pi $ . While the shifted distance is not too large, we can map the received symbols into the correct constellation point to mitigate the negative effect of phase noise. Instead of directly using conventional clustering algorithms into the proposed machine learning approach, we propose a new weighted ensemble clustering algorithm to further improve the performance of our approach. In comparison with prior approaches based on RF circuits, our approach has comparable reception performance but with low complexity and low cost. Our experimental results show that, for a QPSK system, our approach improves the demodulation performance and the decoding performance about 10 dB, 8 dB under BCH codes, and 3 dB under Turbo codes, respectively. Even the demodulation performance of our approach without channel coding is better than the decoding performance of the system with channel coding about 5 dB under BCH codes.

This paper concerns the problem of spectrum sharing in mmWave cellular networks, where multiple network operators are granted access to the same spectrum resources. Prior spectrum sharing schemes for mmWave cellular networks have two limitations: high coordination overhead and high computational complexity. In this paper, we propose two spectrum sharing schemes for the mobile scenario and the stationary scenario, respectively. In the mobile scenario, we propose a Spectrum sharing scheme using Clustering Algorithms to find the Optimal Positions of Mobile BSes (SCA-OPM). In the stationary scenario, we propose a Spectrum sharing scheme using Clustering Algorithms to Select the most appropriate Subset from all BSes (SCA-SSB). Moreover, for each newly-arriving mobile terminal (MT), we propose two online spectrum sharing schemes based on our SCA-OPM scheme and SCA-SSB scheme, which effectively saves the overall overhead and complexity. Our experimental results show that the SCA-OPM scheme has the best performance, while the SCA-SSB scheme has the same performance as that of the prior scheme but with lower overhead and lower complexity. When the MT density is 200 MTs/km2, for the sum-rate with 10-2bits/s/Hz, the performance gap between the SCA-OPM scheme and the remaining schemes achieves about 19 dB. Moreover, our online schemes have the same performance as those of their counterpart schemes but with lower overhead and lower complexity for the scenario of a few newly-arriving MTs.

This paper concerns the problem of the multi-path classification in a multi-user multi-input multi-output (MIMO) system. We propose a machine learning approach to achieve a blind multi-path classification in the uplink (UL) scheme of a multi-user massive MIMO system. Note that the “blind” term in our approach represents the achievement of the multi-path classification without different pilot sequences on different users, without prior channel state information (CSI) at each user, and without any exploiting the special properties of the received signal. Specifically, our approach consists of two phases. In the first phase, multiple users transmit communication-requests to the base station (BS) for message transmission. The BS only estimates the scaled large-scale path loss of each user, which is determined by the distance between the transmitter and the receiver and is independent of the number of multi-path. Then, the BS compares the difference of the scaled large-scale path loss between any two users. If the difference is sufficiently large, the BS notifies all users to permit their simultaneous message transmissions. However, if the difference is small, the BS notifies each user to slightly adjust their transmission power and then permits their simultaneous message transmissions as well. In the second phase, all users simultaneously transmit their messages using the same radio resource. Then the BS selects one predetermined constellation point from the received pilot symbols as the input of clustering algorithms. According to the clustering results, the BS classifies each multi-path into a specific user. The key intuition of our approach is that the clustering algorithms can generate multiple cluster centroids and each cluster centroid represents the average reception power of each user. Moreover, we use a weighted ensemble clustering algorithm to further improve the performance of our approach. We implemented our approach and conducted extensive performance comparison. Our experimental results show that, when the received signal-to-noise ratio (SNR) is more than 13 dB, our approach with the weighted ensemble clustering algorithm can correctly classify all multi-path to the corresponding user and the output SNR can be improved by 3.2 dB, where we consider three users in an 8PSK system and each user possess 50 multi-path.

This paper concerns the problem of authenticating the transmitter device in non-orthogonal multiple access (NOMA) systems. This problem is important because of high vulnerabilities in wireless communications and an additional security vulnerability when some users collude with the adversary. In this paper, we consider two attacking scenarios. In the first scenario, there is no user that colludes with the adversary. In the second scenario, at least one user colludes with the adversary. In this paper, we propose an authentication approach in the down-link scheme of a NOMA system using physical-layer authentication mechanism because of its advantages: provide information theoretic security, reduce complexity, save power and allow us to construct a two-factor authentication system. Based on the aforementioned two attacking scenarios, we propose three physical-layer authentication schemes for a NOMA system: Physical-Layer Authentication with Shared Authentication Tag (PLA-SAT), Physical-Layer Authentication with Superimposed Independent authentication Tags (PLA-SIT), and Physical-Layer Authentication with TDM authentication tags (PLA-TDM). We analyze the theoretical performance of our schemes over fading channels and derive their closed-form expressions. Then, we optimize the parameters of our schemes to achieve both the reliability fairness and the authentication-accuracy fairness. We implemented our schemes and conducted extensive performance comparisons. Our experimental results show that for the first attacking scenario, the PLA-SAT scheme offers more than 97% authentication accuracy when the received SNR of the served user with poor channel condition is at least 10 dB. For the second attacking scenario, both the PLA-SIT scheme and the PLA-TDM scheme offer more than 97% authentication accuracy when the received SNR of the served user with poor channel condition is at least 12 dB.

This paper investigates the problem of position optimization for multiple mobile relays. The authors propose a new scheme involving multiple mobile relays with fixed orbits to avoid collision risk among the multiple mobile relays and to relax the requirements of the existing approaches, e.g., multiple on‐board antennas and complex feedback signals. The proposed scheme exhibits satisfactory performance with low cost and low complexity, as it requires only a single on‐board antenna and merely a one‐bit feedback signal, which is highly suitable for a scenario in which the source node has limited energy at its disposal, such as in a disaster area. The authors further design three implementation algorithms based on the easy implementation of the proposed scheme. The first algorithm is the simplest one in so far as it utilizes only single positive feedback information, but it exhibits poor performance. The second algorithm achieves better performance by exploiting successive points of negative feedback information. Based on the second algorithm, the third algorithm exhibits the best performance by further exploiting cumulative points of positive feedback information.

This study derives in the closed‐form the probability density function and characteristic function of the ratio of two products of arbitrary number of Nakagami‐ m random variables. Then, the resulting mathematical framework is applied to analyse and gain insights into the bit error rate performance of the dual‐hop channel state information‐assisted amplify‐and‐forward relaying system in the presence of co‐channel interference. All analytical results are corroborated by Monte–Carlo simulation results and they are shown to be efficient tools to evaluate system performance.

Authentication is a key requirement for secure communications in modern wireless systems. Compared with the conventional authentication at the upper layer using a cryptographic tool, authentication at the physical layer has many advantages, including enhanced security through the introduction of uncertainty to adversaries and increased efficiency and compatibility through the avoidance of operations at the upper layer, particularly in heterogeneous coexistence environments, e.g., 5G wireless systems. In this paper, we investigate authentication at the physical layer under time-varying fading channels. Conventional authentication schemes at the physical layer operate poorly under fast fading or frequency selective fading channels. Furthermore, conventional schemes require additional complicated preprocessing such as channel estimation and message symbol recovery through demodulation and decoding. This paper proposes a new blind authentication scheme at the physical layer that combines the techniques of blind known interference cancellation (BKIC) and differential processing to implement authentication without requiring any of the above-described preprocessing. The proposed scheme utilizes both the smoothing (SM) technique and belief propagation (BP) technique to achieve BKIC through the distinct blind authentication schemes with a superimposed tag over pilots (BSUPs) referred to, respectively, as BSUP-SM and BSUP-BP. The proposed scheme not only effectively suppresses the deteriorate effect of fading channels without any additional preprocessing but is also covert to unaware users, robust to interference, and secure for identity verification. The tradeoffs of using the proposed system with respect to various goals are discussed and analyzed. The performance of the BSUP-SM scheme depends on the channel fading and the length of the pilot cluster, while the performance of the BSUP-BP scheme is not sensitive to the above factors but depends instead on the quantization step used. The BSUP-BP scheme works well in fast fading channels, even in frequency selective fading channels.

Authentication is a key requirement for secure communications. In this paper, we consider authentication in a wireless system at the physical layer. There are two main authentication methods at the physical layer in the existing literature, authentication with time division multiplexed tag (Auth-TDM) and authentication with superimposed tag (Auth-SUP). However, there are drawbacks in the existing authentication methods. The Auth-TDM method requires additional bandwidth. The Auth-SUP method corrupts the entire data message. Moreover, regarding the purpose of authentication, both methods require additional complicated preprocessing such as channel estimation and message symbol recovery through demodulation and decoding. This paper proposes a new authentication method at the physical layer, referred to as slope authentication at the physical layer. The proposed method not only overcomes the aforementioned drawbacks but also is designed to be covert to the unware user, robust to interference, and secure for identity verification. The tradeoffs by considering different goals are discussed and analyzed in block-fading channels.

Energy balancing is an effective technique in enhancing the lifetime of a wireless sensor network WSN. Specifically, balancing the energy consumption among sensors can prevent losing some critical sensors prematurely due to energy exhaustion so that the WSN's coverage can be maintained. However, the heterogeneous hostile operating conditions-different transmission distances, varying fading environments, and distinct residual energy levels-have made energy balancing a highly challenging task. A key issue in energy balancing is to maintain a certain level of energy fairness in the whole WSN. To achieve energy fairness, the transmission load should be allocated among sensors such that, regardless of a sensor's working conditions, no sensor node should be unfairly overburdened. In this paper, we model the transmission load assignment in WSN as a game. With our novel utility function that can capture realistic sensors' behaviors, we have derived the Nash equilibrium NE of the energy balancing game. Most importantly, under the NE, while each sensor can maximize its own payoff, the global objective of energy balancing can also be achieved. Moreover, by incorporating a penalty mechanism, the delivery rate and delay constraints imposed by the WSN application can be satisfied. Through extensive simulations, our game theoretic approach is shown to be effective in that adequate energy balancing is achieved and, consequently, network lifetime is significantly enhanced. Copyright © 2012 John Wiley & Sons, Ltd.

ABSTRACT In this paper, we propose a new diversity combining scheme to save power, which is called as the generalized selection combining with double threshold (DT‐GSC). It selects the branch whose SNR is above an input threshold to combine, and this process will keep running until the combined output SNR is larger than an output threshold or until all paths are examined. The values of both thresholds are required to be predetermined on the basis of the practical communication conditions. For comparing the complexity of various combining schemes, we will show the mathematical formulas of the average number of path estimation and the average number of combined branches. Moreover, we will also compare the average bit‐error‐ratio performance of the proposed DT‐GSC with absolute threshold GSC (AT‐GSC) and output threshold MRC (OT‐MRC). Numerical examples and simulation results show that the proposed DT‐GSC leads to a lower complexity than the conventional AT‐GSC and OT‐MRC while it has a satisfactory performance.Copyright © 2012 John Wiley & Sons, Ltd.

This paper considers the problem of multiple distributed nodes in a wireless network wishing to join forces and cooperatively beamform data to a destination. Since the nodes are not physically connected and have independent oscillators, there are carrier frequency and phase errors that degrade the beamforming performance. This paper proposes a novel open-loop synchronization protocol, which exploits the broadcast nature of the wireless channel to achieve synchronization much faster than prior methods, with the difference increasing as the number of nodes increases.

In this paper, we propose a spatial multi-user physical layer network coding (SM-PNC) scheme by jointly utilizing PNC and beamforming techniques in a multi-user one relay communication system. The relay is equipped with multiple antennas and each user node is only equipped with a single antenna. The two way relay transmission consists of two phases. In multiple access phase, the summation and difference of the user data are combined with log likelihood ratio combination, which has a superior robustness to the traditional separation detection under any channel condition; In broadcast phase, optimal adaptive select-group broadcasting scheme is proposed, which can efficiently overcome the problem of near interference in beamforming. Simulation results validate the ability of the proposed algorithms.

Abstract Ultra‐wideband (UWB) system is one of the possible solutions to future short‐range indoor data communications with large frequency bandwidth. However, it must coexist with other narrowband wireless systems that may cause interference to each other, and furthermore a large bandwidth will inevitably result in multi‐path fading. The Rake receiver is applicable to combat multi‐path fading but its performance degrades greatly when the narrowband interference (NBI) is present. Although some optimized Rake receivers were proposed to suppress the NBI, such as the minimum mean square error (MMSE) one, their computational complexities are usually too high to be practically implemented. In this paper, we present a new adaptive Rake receiver which can effectively suppress the NBI, based on the nonlinear Masreliez‐type approximate conditional mean (ACM) technique. Simulation results show that it outperforms the previous schemes and even it achieves almost the same performance as that of a MMSE Rake receiver but with much lower complexity. Copyright © 2010 John Wiley & Sons, Ltd.

Abstract A low complexity wideband antenna array receiver is proposed for wideband wireless communication systems. With the proposed algorithm, the array beampattern remains almost the same within a wide frequency range of interest. In comparison to the conventional algorithm, the new algorithm offers a faster convergence rate with a lower computational complexity. Simulation results are presented to demonstrate the proposed algorithm. Copyright © 2008 John Wiley & Sons, Ltd.

Abstract Design of a nonlinear adaptive antenna array receiver is a challenging task in wireless communications due to the limited number of antenna elements and the presence of correlated signals, which directly affect the performance of an antenna array. More importantly, a conventional nonlinear array receiver is often associated with a high computational complexity that undermines its applicability in practice. In this paper, we present a new approach to adaptive beamforming receiver that provides superior performance in antenna array overloading and in the presence of correlated signals with a low complexity. In particular, the proposed receiver requires a small data‐record size to estimate the beamformer weights, which is beneficial in applications with fast fading channels. Simulation examples illustrate the performance improvement of the proposed array receiver when it is compared to the conventional beamformers. Copyright © 2008 John Wiley & Sons, Ltd.