Detection Error Probability Research Articles

Optimal Beamforming for Covert Communication in MIMO Relay Systems

ABSTRACTThis paper investigates the optimal beamforming design for covert communication in a multiple‐input multiple‐output (MIMO) relay system consisting of source, destination, relay and warden. For both scenarios when each transmitting node knows the perfect or partial warden's channel state information (CSI), we first develop theoretical models to depict the inherent relationship between the beamforming matrices at source/relay and end‐to‐end covert performance of the system regard the minimum detection error probability and covert capacity. Based on these models, we then formulate the optimal beamforming for covert capacity maximization under perfect and partial CSI as linear non‐convex (LNC) and non‐linear non‐convex (NLNC) optimization problems, respectively. We then apply Lagrangian and Hadamard inequality methods to solve the LNC optimization problem to determine the closed‐form expressions for the optimal beamforming matrices at source/relay, based on which a stochastic gradient descent algorithm is developed to evaluate the maximum covert capacity. For the complicated NLNC problem, we propose an efficient search algorithm based on S‐procedure lemma and interior point methods to identify the optimal beamforming matrices to reach the maximum covert capacity. Finally, we provide extensive numerical results to illustrate the covert performance enhancement from adopting the optimal beamforming in MIMO relay systems.

Enhancing covert communication in NOMA systems with joint security and covert design.

The explosion of Internet-of-Thing enables several interconnected devices but also gives rise chance for unauthorized parties to compromise sensitive information through wireless communication systems. Covert communication therefore has emerged as a potential candidate for ensuring data privacy in conjunction with physical layer transmission to render two lines of defense. In this paper, we aim to enhance the individual transmission of nearby users in non-orthogonal multiple access (NOMA) systems under scenarios of an eavesdropper who monitors covert transmission before decoding covert information. For this problem, we first provide a comprehensive analysis of the NOMA system in terms of outage probability (OP), secrecy outage probability (SOP), and detection error probability (DEP), where all of them are quantified in exact and asymptotic closed-form expressions. Besides, we have also derived closed-form formulas for users' covert and public rates. Under the system requirements of the maximal OP and SOP and the minimal DEP, we formulate the optimization of resource power allocation to: 1) minimize the OP of covert communication and 2) maximize the covert rate. Thanks to the developed analytical expressions, we obtain closed-form expressions for the sub-optimal power allocation coefficient for each problem. Simulation results validate the efficacy of the analytical mathematical frameworks and reveal that the proposed approaches of power allocation can provide attractive performance improvement compared to fixed power allocations only.

Secure and covert communication strategy of UAV based on hybrid RF/FSO system

The hybrid radio frequency (RF)/free-space optical (FSO) system can improve communication security by using complimentary characteristics and mitigating the risks of RF links being susceptible to co-channel interference (CCI) and malicious eavesdropping. We investigate the secure and covert communication performance of unmanned aerial vehicles (UAVs) equipped with a hybrid RF/FSO system. In terms of secure communication, UAVs employ the strategy of transmitting private data concurrently through RF and FSO links, considering two modes based on active eavesdropping by a malicious user. Closed-form expressions for the secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived. With respect to covert communication, the communication strategy is to utilize the RF link to generate interfering signals, thus aiding the FSO signals in accomplishing covert communication. We formulate an optimization problem that maximizes the EST while considering transmit power and user-acceptable detection error probability. A two-stage gradient-based iterative solution algorithm is proposed. The numerical results demonstrate the effectiveness of the proposed secure and covert communication strategy based on the hybrid RF/FSO system, which is expected to enhance the communication security of UAVs in the RF-challenged environment.

Maximizing energy efficiency for covert communication in NOMA systems with reradiating on antenna

A resource allocation method is proposed to maximize the energy efficiency for covert communication in downlink NOMA systems via reradiating on antennas. Firstly, the optimization problem of maximizing the effective covert energy efficiency of the covert user is constructed under the condition of satisfying the outage probability of the public user and the error detection probability of the warden. Then, the optimization problem is simplified, and the solution of the optimization problem is given when the power allocation coefficient of NOMA is known. Finally, the optimal solution is obtained by traversing the power allocation coefficient of NOMA and solving the optimization problem for each power allocation coefficient. The simulation results show that with the increase of the total power, the energy efficiency first increases and then tends to a constant, that is, there is an optimal value of the power allocation coefficient, which maximizes the energy efficiency.

Covert throughput maximization for NOMA based visible light covert communication networks

Covert throughput maximization for a non-orthogonal multiple access (NOMA)-based visible light covert communication (VLCC) network is investigated. The network consists of a light emitting diode (LED) transmitter, two NOMA users (one public, one covert), and a monitor tasked with detecting any covert transmissions between the LED and the covert user. The transmitter leverages its interaction with the public user to mask the covert communication with the covert user, adopting a random power transmission scheme. This strategy serves to amplify the monitor’s detection uncertainty and significantly enhance the covertness of the VLCC network. Two VLCC scenarios are covered: For the indoor static VLCC scenario where the LED is fixed, subject to the minimum detection error probability of the monitor (covertness constraint) and the outage probability of NOMA users (reliability constraint), the covert throughput is maximized by optimizing the ratio of the LED’s power allocation factor (PAF). For the mobile VLCC scenario where the LED is mounted on an unmanned aerial vehicle (UAV), subject to the constraints of the covertness, reliability and UAV’s flight region, the optimal LED’s PAF ratio and UAV’s location are jointly obtained via a graphical approach. Finally, simulations are carried out to analyze the influence of VLCC parameters on the maximum covert throughput, and results show that compared with benchmark schemes, the proposed scheme can greatly improve the covert throughput.

A modified quality control protocol for infectious disease serology based on the Westgard rules

When traditional statistical quality control protocols, represented by the Westgard protocol were applied to infectious disease serology, the rejection limits were questioned because of the high rejection probability. We first define the probability of false rejection (Pfr) and error detection (Ped) for infectious disease serology. QC data in 6 months were collected and the Pfr of each rule in the Westgard protocol and Rilibak protocol was evaluated. Then, as improvements, we chose different rules for negative and positive QC data to constitute an asymmetric protocol, furthermore, while reagent lot changes, the mean value of QC protocol is reset with the first 15 QC results of new lot reagent. QC materials and Standard Reference Materials were tested synchronously in the next 6 months, to verify whether the Pfr and Ped of the asymmetric protocol could meet the requirement. Protocol 1 exhibited the higher level of rejection rate among the two protocols, especially after reagent lot changes; Pfr below the lower control limit (LCL) was 1.39–21.78 times higher than the upper control limit (UCL); false rejections were more likely to occur in negative QC data, with Pfr-total of 27–65%. The asymmetric protocol can significantly reduce the proportion of analytes with Pfr by over 20%. Systematic error due to reagent lot changes and random error due to routine QC data variation were considered potential factors for excessive Pfr. Asymmetric QC protocol that can reduce Pfr by different control limits for negative and positive QC data.

The diagnostic accuracy of quality control rules

Internal quality control in clinical chemistry laboratories are based on analyzing samples of stable control materials among the patient samples. The control results are interpreted by using quality control rules that usually are designed to detect systematic errors. The best rules have a high probability of error detection (Ped), i.e. to detect the maximal allowable (critical) systematic error and a low probability of false rejection (Pfr, false alarm). In this work we show that quality control rules can be represented by points on a ROC curve which appears when Ped is plotted against Pfr and only the control limit is varied. Further, we introduce a new method for choosing the optimal control limit, analogous to choosing the optimal operating point on the ROC curve of a diagnostic test. This decision needs knowledge of the pretest probability of a critical systematic error, the benefit of detecting it when it occurs and the cost of false alarm. The ROC curve analysis showed that if rules based on N = 2 are used, mean rules outperform Westgard rules because the ROC curve of the mean rules was lying above the ROC curves of the Westgard rules. A mean rule also had a lower maximum expected increase in the number of unacceptable patient results reported during the presence of an out-of-control error condition (Max E(NUF)) than comparable Westgard rules.

Study on covert rate in the D2D networks with multiple non-colluding wardens

This paper investigates the covert communication of cellular link in the device-to-device (D2D)-enabled underlaying cellular network, including a base station, a cellular user, a D2D pair, and multiple non-colluding wardens. To conduct covert communication between the base station and the cellular user without being detected by the wardens, the underlaid D2D pair transmits with a random power to add uncertainty to wardens. We first model the detection of multiple non-colluding wardens, and the average minimum detection error probability of the worst case is derived. To measure the covert performance of the cellular link, the average covert rate of the cellular link and the outage probability of the D2D link are explored. Then, we formulate an optimization problem of maximizing the average covert rate under the constraint of the average minimum detection error probability, and an optimization algorithm is designed to solve the optimization problem to identify the optimal transmit power of the D2D pair. Last, the extensive numerical results are presented to show the impacts of network parameters on the covert performance, which indicates that although D2D communication causes interference to the cellular link, it can also help achieve covert communication by carefully designing its maximum transmit power.

Covert performance enhancement in NOMA enabled CoMP network with optimal RIS selection

In this paper, we consider the covert rate maximization problem for the cell edge user in a reconfigurable intelligent surface (RIS) aided downlink non-orthogonal multiple access (NOMA) network with coordinated multipoint (CoMP) transmission in the presence of channel estimation errors. We derive the analytical expression for the detection error probability (DEP) at the adversary (Willie) assuming the worst case scenario where they employ optimal detection threshold. With the derived analytical expression, we propose an optimal RIS selection scheme to boost the covert rate. To further improve the covert performance, we optimize the NOMA power allocation coefficients and phase shifts of the selected RIS subject to the target rate and covertness constraints. Simulation results demonstrate the improvement in covert rate and robustness offered by the proposed scheme in the presence of channel estimation errors over other benchmarks.

Covert communications in STAR-RIS-aided rate-splitting multiple access systems

In this paper, an simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) is deployed in the downlink rate-splitting multiple access (RSMA) covert system to enhance the covert communication performance. According to the RSMA transceiver mechanism, the messages for the covert user (Bob) and public user (Grace) are converted to the common and private streams at the legitimate transmitter (Alice) to realize downlink transmissions, while the STAR-RIS not only assists Alice in transmitting public messages to Grace but also protects the covert messages Alice sends to Bob by mixing up Warden (Willie). To characterize the covert performance of the considered STAR-RIS-aided RSMA (STAR-RIS-RSMA) system, We derive a closed expression for its detection error probability in the most favorable case for Willie, based on which a covert rate maximization problem is formulated. To maximize Bob’s covert rate while confusing Willie’s monitoring, the power allocation factor, common rate allocation factor, and STAR-RIS reflection/transmission beamforming are jointly optimized subject to Grace’s quality of service (QoS) requirements. The complex non-convex problem of maximizing covert rate, involving coupled system parameters, thus is split into three separate sub-issues: the allocation of transmit power, allocation of common rates, and STAR-RIS reflection/transmission beamforming, respectively. To obtain the rank-one constrained optimal solution for the sub-problem of optimizing the STAR-RIS reflection/transmission beamforming, a penalty-based successive convex approximation scheme is developed. Moreover, an alternative optimization (AO) algorithm is designed to determine the optimal solution for the sub-problem of optimizing the transmit power allocation, while the original problem is overall solved by a new AO algorithm. Simulation results corroborate the accuracy of the derived analytical results and demonstrate that the proposed STAR-RIS-RSMA scheme outperforms the benchmark scheme in achieving the covert rate.

Covert communication in hybrid microwave/mmWave UAV-enabled systems with transmission mode selection

This paper investigates the covert communication in an air-to-ground (A2G) system, where a UAV (Alice) can adopt the omnidirectional microwave (OM) or directional mmWave (DM) transmission mode to transmit covert data to a ground user (Bob) while suffering from the detection of an adversary (Willie). For both the OM and DM modes, we first conduct theoretical analysis to reveal the inherent relationship between the transmit rate/transmit power and basic covert performance metrics in terms of detection error probability (DEP), outage probability and effective covert rate (ECR). To facilitate the transmission mode selection at Alice, we then explore the optimization of transmit rate and transmit power for ECR maximization under the OM and DM modes, and further propose a hybrid OM/DM transmission mode which allows the UAV to adaptively select between the OM and DM modes to achieve the maximum ECR at a given location of UAV. Finally, extensive numerical results are provided to illustrate the covert performances of the concerned A2G system under different transmission modes, and demonstrate that the hybrid OM/DM transmission mode outperforms the pure OM or DM mode in terms of covert performance.

The importance of quality control validation and relationships with total error quality goals and bias in the interpretation of laboratory results.

The objective of a quality system is to provide accurate and reliable results for clinical decision-making. One part of this is Quality Control (QC) validation. QC validation is not routinely applied in veterinary laboratories. This leads to the inappropriate usage of random QC rules without knowing the Probability of error detection (Ped ) and Probability of false rejection (Pfr ) of a method. In this paper, we will discuss why QC validation is important, when it should be undertaken, why QC validation is done, and why it is not commonly done. We will present the role of total analytical error (TEa) in the QC validation process and the challenges when a consensus TEa has not been published. Finally, we will also discuss the possibilities of 'gray zone' determinations and mention the effects of bias on the quality of results. Reasons for the low prevalence of performing QC validation may include (a) lack of familiarity with the concept, (b) lack of time and resources needed to conduct QC validation, and (c) lack of TEa goal for some measurands. If no TEa is available, the user may elect to use a 'reverse approach' to QC validation. This uses the CV and bias generated from the evaluation of QC measurements, specifying Ped , Pfr , and N (number of QC measurements/run). This identifies the lowest total error that can be controlled under these defined conditions, thus enabling the laboratory to have an estimate of the 'gray zone' associated with results generated with a specific assay.

Study on effect of charged sand/dust atmosphere on the performance of microwave quantum illumination radar

This paper aims to study the effects of charged sand/dust atmosphere on the performances of microwave quantum illumination (QI) radar. Based on Mie particle scattering theory, using a Monte Carlo method for simulating the physical process which photon is scattered multiple times by discrete random distributed particles, the specific attenuation (dB/km) of microwave propagating in sand/dust atmosphere are analyzed under the conditions of varying atmospheric visibility and sand/dust particles with different charged quantities. It is indicated that the specific attenuation obtained by multiple scattering is smaller than those obtained based on Mie theory, for microwave propagating in charged sand/dust atmosphere. The smaller the atmospheric visibility, the greater the difference, while the difference decreases gradually as the atmospheric visibility increases. Then, it is more reasonable to consider multiple scattering attenuation at lower atmospheric visibility. When sand/dust particle is charged, the specific attenuation is increased, however, this increase is not linear. According to quantum illumination radar theory, a beam splitter-based optical link model is used to simulate the sand/dust atmospheric channel. The effects of charged sand/dust atmosphere with different visibility on the detection error probability, signal-to-noise ratio, and maximum detection range for microwave quantum illumination radar are studied by using quantum radar equation and quantum detection error probability theory. The performances of QI and classical two mode noise (TMN) radar are compared and analyzed. These results show that the performances of quantum illumination radar are improved with increasing sand/dust atmospheric visibility. When sand/dust particle is charged, the performances for QI radar are degraded due to attenuation increase. The change in the performances is nonlinear as the change in sand/dust carrying charge quantity. Increasing the signal frequency can enhance the performance of quantum illumination radar when visibility is high, but when visibility is low, the gain from frequency increase is outweighed by the performance degradation caused by increased attenuation, making it inadvisable to raise the frequency in such cases. The comparison with classical radar reveals that QI radar performs better under the condition of lower atmospheric visibility and lower average photon emission, but this advantage diminishes as the number of photons increases. In a word, these results show that the performances of QI radar are more significant at lower atmospheric visibility. Under higher visibility conditions, the QI system SNR can be improved by increasing frequency. The maximum detection range of the QI radar is significantly better than the classical TMN radar.

Determination of the optimal period for computations control in complexes of automated control systems programs

The purpose of the study is to determine the optimal period for monitoring calculations in complex software complexes of automated control systems. To achieve this goal, it is necessary to solve such problems as the analysis of periodic control systems, which boils down to determining the performance costs of computing systems for control, as well as ensuring a minimum of these costs. Theoretical foundations and descriptions of the process of evaluating the effectiveness of the automated control systems functioning are given. A rationale for the method of determining the optimal period for monitoring calculations in software complexes of the automated control systems is provided in the paper. An analytical study of control systems is carried out. The difference between the considered problem setting and the existing ones lies in the fact that the accuracy of error detection by the periodic control system is taken into account, while it is taken into account that for real control systems the probability of error detection is quite high. Thus, the results of studying the operational periodic control systems have shown that the main parameters that affect the optimal period of control are the mean time between failures. The dependence of the optimal control period on the probability of recovery is shown for different values of the duration of recovery by a reliable method. As the probability decreases, the optimal control period also decreases, which is associated with the need to spend a large proportion of the time on restoration using a reliable method; the corresponding increase in average unit costs can be compensated by an increase in the frequency of control procedures, i. e. a decrease in the control period. The dependence of the minimum average unit cost of control and the optimal period of its implementation on the average time between the errors appearance is given. With constant durations of control and recovery procedures and constant error detection probability, the optimal control period decreases, and the minimum average unit cost increases somewhat with a decrease in the average time between failures. This can be explained as follows: the more often an error can occur, the more often you need to control in order to reduce the losses due to working with the error.

Performance Comparison of Relay-Based Covert Communications: DF, CF and AF.

In this paper, we investigate the performance of covert communications in different types of a relay system: decode-and-forward (DF), compress-and-forward (CF) and amplify-and-forward (AF). We consider a source node that attempts to send both public and covert messages to a destination node through a relay on which a covert message detector is embedded. By taking the minimum detection error probability (DEP) at the relay into account, we optimize the power distribution between the public and covert messages to achieve the maximum covert rate. We further make a delay-aware comparison among DF, CF and AF relay systems with the obtained closed-form covert rates and conduct an extensive examination on the asymptotic behaviors in different limits. Our analyses reveal that CF or AF tend to outperform DF for high source transmit power or low relay transmit power, while various system parameters such as the processing delay, minimum required quality of service for public messages and DEP threshold lead to different performance relationships among DF, CF and AF for high relay transmit power. Numerical results verify our investigation into the performance comparison in various channel models.

Automated SC-MCC Test Case Generation using Bounded Model Checking for Safety-Critical Applications

Modified Condition/Decision Coverage (MC/DC) is an important criterion to test the safety-critical applications because it generates test cases in a linear manner from N+1 to 2N, where N is the number of Atomic Conditions in a given predicate. It is desirable in comparison to the exponential test cases produced for Multiple Condition Coverage (MCC), i.e., 2N. However, MCC with Short-Circuit (SC-MCC) is recommended since most of the safety-critical applications are built on the high-level languages that use Short-Circuit evaluation property. Our goal is to demonstrate that, despite the added overhead, the SC-MCC coverage-based test cases have a high error-detection probability compared to that of MC/DC. In this work, we have considered the CBMC tool to generate both the SC-MCC and MC/DC test cases for 80 RERS benchmark programs. Then, by optimizing the traditional Mutation Testing (using the GCOV tool), we computed the Mutation Score (%) to assess the quality of the generated test cases. As per the Mutation analysis, the proposed SC-MCC outperformed MC/DC for over 75% of the 80 RERS programs considered. Additionally, as per the Execution time analysis, the average total time taken to evaluate the MC/DC part of the proposed framework is 3065.98 s, whereas SC-MCC framework evaluation took 2167.70 s. This proves the efficiency of the proposed (SC-MCC) work over the traditional criterion (MC/DC) based work.

Evaluation of Flaw Detection Algorithm Using Simulated X-Ray Computed Tomography of Ground Truth Data

Abstract A framework to generate simulated X-ray computed tomography (XCT) data of ground truth (denoted here as “GT”) flaws was developed for the evaluation of flaw detection algorithms using image comparison metrics. The flaws mimic some of those found in additively manufactured parts. The simulated flaw structure gave a GT data set with which to quantitatively evaluate, by calculating exact errors, the results of flaw detection algorithms applied to simulated XCT images. The simulated data avoided time-consuming manual voxel labeling steps needed for many physical data sets to generate GT images. The voxelated pore meshes that exactly match GT images were used in this study as opposed to using continuum pore meshes. The voxelated pore mesh approach avoids approximation error that occurs when converting continuum pore meshes to voxelated GT images. Spherical pores of varying sizes were randomly distributed near the surface and interior of a cylindrical part. XCT simulation was carried out on the structure at three different signal-to-noise levels by changing the number of frames integrated for each projection. Two different local thresholding algorithms (a commercial code and the Bernsen method) and a global thresholding algorithm (Otsu) were used to segment images using varying sets of algorithm parameters. The segmentation results were evaluated with various image evaluation metrics, which showed different behaviors for the three algorithms regarding “closeness” to the GT data. An approach to optimize the thresholding parameters was demonstrated for the commercial flaw detection algorithm based on semantic evaluation metrics. A framework to evaluate pore sizing error and binary probability of detection was further demonstrated to compare the optimization results.

A Covert Jamming Scheme Against an Intelligent Eavesdropper in Cooperative Cognitive Radio Networks

In this work, we design a covert jamming scheme against an intelligent Eve towards physical layer security in a cooperative cognitive radio networks. To protect the primary message from being decoded by an intelligent eavesdropper (Eve), a secondary user is picked as a friendly jammer that transmits artificial noise (AN) to the Eve. However, the intelligent Eve can detect the existence of AN, and thus the AN is inclined to be covertly transmitted at a lower detection probability, thereby mistaking the AN as background noise by the Eve. In this paper, firstly, by using a binary hypothesis testing, the detection error probability (DEP) is explicitly derived for detection performance analysis of the Eve in the perfect as well as statistical channel state information (CSI) scenario, separately. With the DEP, a covert jamming scheme is formulated to transmit the AN in both cases. Then, an optimization problem is formulated, and then recast into a two-part problem to maximize the secrecy performance with the covert jamming scheme in the perfect CSI case. Finally, the effective secrecy throughput is maximized under convert constraints in the statistical CSI case. Numerical results are provided to validate the DEP at the Eve and secrecy performance analysis.

A Game-Theoretic Approach to Achieve Covert Communication in Cognitive Radio Systems

In this paper, we investigate a covert cooperative cognitive radio (CCCR) system, where multiple primary transmitters (PTs) transmit information with the aid of multiple secondary transmitters (STs) in order to conserve power consumption. In return, by opportunistically accessing PT's spectrum, STs send confidential information to a secondary receiver (SR) in the presence of external eavesdropper (Eve). Aiming to maximize covert rate, we model our CCCR framework as an evolutionary game in which each PT and ST make decisions based on their utility histories. By introducing the evolutionary game, we propose a game-oriented secondary user scheduling (G-SUS) scheme to find when multiple STs determine to access PTs' spectrum. Moreover, we analyze covert performance of the proposed scheme and obtain a closed-form expression for Eve's detection error probability. Numerical results show that, the minimal detection error probability at Eve can be effectively impacted by creating channel uncertainty and noise uncertainty. Furthermore, the results also demonstrate the proposed scheme can converge quickly, which stimulates its practical implementation.

On Joint Optimization of Trajectory and Phase Shift for IRS-UAV Assisted Covert Communication Systems

In this paper, we propose an unmanned aerial vehicle carrying intelligent reflecting surface (IRS-UAV) as a relaying node to assist covert communication system (CCS). To ensure the security of the covert messages, we derive the minimum error detection probability for the eavesdropper when the locations of the UAV and BS are known. Under the assumption that the eavesdropper can minimize the detection error probability, we then formulate the maximization of the average rate of the proposed IRS-UAV assisted CCS as an optimization problem with respect to the UAVs trajectory and the IRSs phase shift. Furthermore, we use the Taylor's extension to approximate the optimization problem to be convex, and propose an iterative algorithm to solve the convex problem. Numerical results demonstrate that the developed optimization method significantly improves the data rate for IRS-UAV assisted covert communication in comparison with existing algorithms.