Research on Feature Extraction of Remnant Particles of Aerospace Relays

The existence of remnant particles, which significantly reduce the reliability of relays, is a serious problem for aerospace relays. The traditional method for detecting remnant particles-particle impact noise detection （PIND）-can be used merely to detect the existence of the particle; it is not able to provide any information about the particles＇ material. However, information on the material of the particles is very helpful for analyzing the causes of remnants. By analyzing the output acoustic signals from a PIND tester, this paper proposes three feature extraction methods： unit energy average pulse durative time, shape parameter of signal power spectral density （PSD）, and pulse linear predictive coding coefficient sequence. These methods allow identified remnants to be classified into four categories based on their material. Furthermore, we prove the validity of this new method by processing P1ND signals from actual tests.

Performance of AF Relay Networks with Multiple Relays and Multiple Antennas at Destination Using MRC Combining

Cooperative networking schemes in wireless networks provide cooperative diversity gain using differently located antennas that combat fadings induced by multipath propagation. In this paper, we present the optimal weight design for the destination in AF (Amplify and Forward) relay system, where the optimally designed MRC (Maximum Ratio Combining) is employed at the destination for S→D link (direct link between source and destination) and R→D links (indirect links between relays and destination). We investigate the BER performance of 1S→NR→LD system composed of one source, N relay nodes equipped with single antenna and one destination node equipped with L antennas, which also includes 1S→1R→LD and 1S→NR→1D. Simulation and numerical results are presented to verify our analysis.

Optimal Number of Relays in Cooperative Communication in Wireless Sensor Networks

Wireless Sensor Networks (WSN) typically consist of resource constrained micro sensors that organize itself into multihop wireless network. Sensors collect data and send it directly, or through intermediate hops in cooperative communication system, to the collection point. These sensors are powered up by batteries, for which the replacement or recharging is very difficult. With finite energy, we can transmit a finite amount of information. Therefore, minimizing the power consumption for data transmission becomes a most important design consideration for wireless sensor networks. In this paper, we discuss the optimal power consumption in cooperative wireless sensor network that are placed on a grid. We study different cases for the optimal power consumption in such grids by varying the grid distance and number of nodes in the grid. We assume the cases of grids from 2 × 2 up to 5 × 5 in increasing complexity of calculations. The results show that the optimal path that consumes the least power is the path along the diagonal using of the grid when the source and the destination and the furthest two nodes in the grid. This path takes intermediate nodes (relays) along it based on some threshold distances. For example, in 5 × 5 cases;the first threshold between the direct distance and between using one relay in the middle is 31.6 m the second threshold distance is 63.3 m after which using three relays is the best in power consumption between the source and the destination.

Placement of unmanned aerial vehicles as communication relays in two-tiered multi-agent system:clustering based methods

The network performance and the unmanned aerial vehicle(UAV)number are important objectives when UAVs are placed as communication relays to enhance the multi-agent information exchange.The problem is a non-deterministic polynomial hard(NP-hard)multi-objective optimization problem,instead of generating a Pareto solution,this work focuses on considering both objectives at the same level so as to achieve a balanced solution between them.Based on the property that agents connected to the same UAV are a cluster,two clustering-based algorithms,M-K-means(MKM)and modified fast search and find density of peaks(MFSFDP)methods,are first proposed.Since the former algorithm requires too much computational time and the latter one requires too many relays,an algorithm for the balanced network performance and relay number(BPN)is proposed by discretizing the area to avoid missing the optimal relay positions and defining a new local density function to reflect the network performance metric.Simulation results demonstrate that the proposed algorithms are feasible and effective.Comparisons between these algorithms show that the BPN algorithm uses fewer relay UAVs than the MFSFDP and classic set-covering based algorithm,and its computational time is far less than the MKM algorithm.

Behavior Prediction of Untrusted Relays Based on Nonzero-Sum Game

To keep the secrecy performance from being badly influenced by untrusted relay(UR), a multi-UR network through amplify-and-forward(AF) cooperative scheme is put forward, which takes relay weight and harmful factor into account. A nonzero-sum game is established to capture the interaction among URs and detection strategies. Secrecy capacity is investigated as game payoff to indicate the untrusted behaviors of the relays. The maximum probabilities of the behaviors of relay and the optimal system detection strategy can be obtained by using the proposed algorithm.

Power allocation of cooperative amplify-and-forward communications with multiple relays

Cooperative diversity is one of the most effective ways to mitigate the fading effect of wireless channels and obtain the spatial gain in wireless networks. In this paper, an optimal power allocation （OPA） scheme for a cooperative communication system using the amplify-and-forward （AF） transmit strategy with multiple relay users is proposed by minimizing the bit-error-rate （BER） at the destination under the constraint of the total transmit power of both the source user and the relay users. Simutation resutts indicate that the proposed power allocation method can achieve significant BER performance improvement than using the equal power allocation （EPA） scheme, while still attains low complexity. The system performance is improved significantly with the increasing of the number of relay users at high signal-noise ratio （SNR）. However, at low SNR, the system performance decreases when the relay number increases. Thus, an adaptive relay selection scheme may be used to choose the appropriate relay numbers in different transmission scenarios to provide system performance improvement and keep the power allocation scheme with low complexity.

Fast Identification of Symmetrical or Asymmetrical Faults During Power Swings with Dual Use Line Relays

Increasing power demand,penetration of renew-ables,and limitations of necessary grid expansion are proffering new challenges to existing power system protection and control strategies.However,with the advancement in intelligent elec-tronic devices and relaying technology,fast,accurate and reliable protection schemes can be developed for smart power systems.In this paper,a new protection scheme based on admittance and power change has been proposed with dual-use line relays to detect symmetrical/asymmetrical faults in power systems.A large number of fault environments have been simulated by varying fault distances from relay location,fault resistance,and power angle in single machine infinite bus and WSCC 9-bus systems.Some crucial decisive fault scenarios e.g.close in/far end faults,faults in series compensated line,faults during asymmetrical swings,switching ON/OFF large loads,single and multi-modal swings have also been verified for the proposed index.In this paper,for the first time,detection of faults during power swings have been examined and verified in the presence of wind farms.The simulation results show the proficiency of the proposed algorithm for detecting faults in the presence or absence of power swings.

Fast Protection Scheme for Active Distribution Networks: Breaking Chains by Utilizing Auxiliary Relays

Due to the swift expansion and the deployment of distributed generation, protection systems of active distribution networks are more expected to be fast. In loop-based active distribution networks, directional overcurrent relays(DOCRs) are caught in different chains. These chains stand as the severe obstacle to follow fast-response protection, which remains a significant challenge. In this paper, to overcome this challenge, a fast protection scheme is proposed to break the chains in the corresponding loops by deploying auxiliary DOCRs. The most effective constraint associated with each chain is relaxed during the coordination process. Then, the auxiliary relays are employed to play the backup roles instead of conventional backup relays in the relaxed constraints. To avoid the misoperation of relays in the proposed scheme, low bandwidth communication links are suitably employed. Furthermore, the auxiliary relays are optimally placed and adjusted. The proposed approach demonstrates a mixed-integer nonlinear programming model which is tackled by particle swarm optimization(PSO) algorithm. Detailed simulation studies are carried out to verify the performance of the proposed approach.

Optimization of Cooperative RelayingMolecular Communications for Nanomedical Applications

Recently,nano-systems based on molecular communications via diffusion(MCvD)have been implemented in a variety of nanomedical applications,most notably in targeted drug delivery system(TDDS)scenarios.Furthermore,because the MCvD is unreliable and there exists molecular noise and inter symbol interference(ISI),cooperative nano-relays can acquire the reliability for drug delivery to targeted diseased cells,especially if the separation distance between the nano transmitter and nano receiver is increased.In this work,we propose an approach for optimizing the performance of the nano system using cooperative molecular communications with a nano relay scheme,while accounting for blood flow effects in terms of drift velocity.The fractions of the molecular drug that should be allocated to the nano transmitter and nano relay positioning are computed using a collaborative optimization problem solved by theModified Central Force Optimization(MCFO)algorithm.Unlike the previous work,the probability of bit error is expressed in a closed-form expression.It is used as an objective function to determine the optimal velocity of the drug molecules and the detection threshold at the nano receiver.The simulation results show that the probability of bit error can be dramatically reduced by optimizing the drift velocity,detection threshold,location of the nano-relay in the proposed nano system,and molecular drug budget.

Security-Reliability Tradeoff Analysis for Jamming Aided Decode-and-Forward Relay Networks

In this paper,we explore a cooperative decode-and-forward(DF)relay network comprised of a source,a relay,and a destination in the presence of an eavesdropper.To improve physical-layer security of the relay system,we propose a jamming aided decodeand-forward relay(JDFR)scheme combining the use of artificial noise and DF relaying which requires two stages to transmit a packet.Specifically,in stage one,the source sends confidential message to the relay while the destination acts as a friendly jammer and transmits artificial noise to confound the eavesdropper.In stage two,the relay forwards its re-encoded message to the destination while the source emits artificial noise to confuse the eavesdropper.In addition,we analyze the security-reliability tradeoff(SRT)performance of the proposed JDFR scheme,where security and reliability are evaluated by deriving intercept probability(IP)and outage probability(OP),respectively.For the purpose of comparison,SRT of the traditional decode-and-forward relay(TDFR)scheme is also analyzed.Numerical results show that the SRT performance of the proposed JDFR scheme is better than that of the TDFR scheme.Also,it is shown that for the JDFR scheme,a better SRT performance can be obtained by the optimal power allocation(OPA)between the friendly jammer and user.

Average Secrecy Capacity of the Reconfigurable Intelligent Surface-Assisted Integrated Satellite Unmanned Aerial Vehicle Relay Networks

Integrated satellite unmanned aerial vehicle relay networks(ISUAVRNs)have become a prominent topic in recent years.This paper investigates the average secrecy capacity(ASC)for reconfigurable intelligent surface(RIS)-enabled ISUAVRNs.Especially,an eve is considered to intercept the legitimate information from the considered secrecy system.Besides,we get detailed expressions for the ASC of the regarded secrecy system with the aid of the reconfigurable intelligent.Furthermore,to gain insightful results of the major parameters on the ASC in high signalto-noise ratio regime,the approximate investigations are further gotten,which give an efficient method to value the secrecy analysis.At last,some representative computer results are obtained to prove the theoretical findings.

Influence of the Inverse-Time Protection Relays on the Voltage Dip Index

The probability-assessment analyses on the characteristic value of voltage dip by using Monte Carlo stochastic modeling method to stimulate the randomness of the short circuit fault are introduced. Using Matlab and Power Systems CAD(PSCAD), we design control interface which combines the electromagnetic transient simulation with the Monte Carlo method. Specifically, the designing of interface which is meant to employ the method of Matlab programming to control the electromagnetic transients including direct current(EMTDC)simulation is introduced. Furthermore, the influences of the protection devices on the voltage dip to ensure the authenticity and the referential reliability are simulated. A system with the inverse-time protection devices equipped on each line which can coordinate together is designed to cut off the short-circuit fault. The voltage dip of the designed system is assessed by the pre- and post-system average root mean square(RMS) variation frequency index, and the voltage dip index is compared with the Information Technology Industry Council(ITIC)curves. The simulation results demonstrate that the inverse-time relay protection equipments are well-coordinated,and the severity and the range of the voltage dip are influenced by the cooperation of the equipped inverse-time protection devices.

Preventing False Trips of Zone 3 Protection Relays in Smart Grid

While remote zone 3 protection relays are essential to power systems, their false trips are also one of main causes related to cascading blackouts. Although many methods have been developed on traditional power systems to address this issue, the past cascading failure events showed the ineffectiveness of these methods. With the development of Smart Grid （SG）, new agent-based methods have been proposed to address this issue by utilizing SG real-time communications. We found that these solutions simply assume ideal communication networks and do not consider the effect of practical network constraints and resource management. In this paper, we propose several solutions to address practical network resource management and constraints, and further improve the agent-based solutions in order to prevent the false tripping of zone 3 relays in various conditions. We also analyze the potential issues of these solutions, and point out the future investigation in this direction.

Optimum coordination of directional overcurrent relays for combined overhead/cable distribution system with linear programming technique

Heavy fault currents flow in the event of fault at the loads connected in distribution system. To protect these loads, circuit breakers and relays are required at appropriate places with proper coordination between them. This research paper focuses on finding optimum relay setting required for minimum time to interrupt power supply to avoid miscoordination in operation of relays and also investigates effect on time multiplier settings (TMS) of directional overcurrent relays in a system with combined overhead lines-underground cables. Linear programming problem (LPP) approach is used for optimization. It is interesting to know the quantitative variations in TMS as the underground cables have different characteristics than overhead lines.

Cooperative HARQ protocol and diversity analysis of systems with multiple incremental relays

Wireless networks contain an inherent distributed spatial diversity that can be exploited by relays. Relay networks can take advantage of the broadcast-oriented nature of wireless transmission, but require more radio resource to transmit data for their multi-hop traits. Fortunately, incremental relaying technique, which can choose direct or multi-hop transmission adaptively, can efficiently utilize resource. In this article, the incremental transmission with amplify-and-forward （AF） relays is focused on. A practical hybrid-automatic retransmission request （HARQ） protocol is designed, and the related optimal relay selection strategy is proposed. To analyze the cooperative diversity of system with the proposed protocol, the capacity lower bound is deduced. Simulation and analytical results indicate that by adopting the optimal relay selection strategy, the system with the proposed HARQ protocol can achieve an order of cooperative diversity that equals the aggregated number of the relay and source nodes.

A Niche-Based Evolutionary Tabu Search Algorithm for Optimal Coordination of Protection Relays in Power Networks

In this paper, refusal of operation and the degree of constraint violation are considered as one part of the objective function for optimizing the protection relay setting coordination of over current relays in power systems; a new expression of objective function in this optimization problem is proposed. To combine the advantages of both Tabu search （TS） and evolutionary algorithms （EAs）, a new niche-based evolutionary Tabu search algorithm （named NETS） is presented to solve this optimization problem. Moreover, in two cases of power networks, comparisons between NETS and two published algorithms are given. Experimental results show the expression of the objective function for protection relay setting is feasible and reasonable, and the proposed algorithm NETS exhibits a good performance.

Optimal Coordination of Directional Overcurrent Relays in Meshed Active Distribution Network Using Imperialistic Competition Algorithm

The optimal setting of directional overcurrent relays(DOCRs)ensures the fault detection and clearing in the minimum possible operation time.Directional protective relaying is carried out to coordinate relay settings in a meshed network in the presence of distributed generation.The main goal of DOCR coordination is to find the optimal time dial setting(TDS)and pickup multiplier setting(PMS)to reach the minimum total operation time of all primary relays in the presence of coordination constraints.Due to the complexity of mixed integer non-linear programming(MINLP)problem,imperialistic competition algorithm(ICA)as a powerful evolutionary algorithm is used to solve the coordination problem of DOCRs.The proposed DOCR coordination formulation is implemented in three different test cases.The results are compared with the standard branch-and-bound algorithm and other meta-heuristic optimization algorithms,which demonstrates the effectiveness of the proposed algorithm.

Coordination of dual setting overcurrent relays in microgrid with optimally determined relay characteristics for dual operating modes

Fault current magnitude in a microgrid depends upon its mode of operation,namely,grid-connected mode or islanded mode.Depending on the type of fault in a given mode,separate protection schemes are generally employed.With the change in microgrid operating mode,the protection scheme needs to be modified which is uneconomical and time inefficient.In this paper,a novel optimal protection coordination scheme is proposed,one which enables a common optimal relay setting which is valid in both operating modes of the microgrid.In this con-text,a common optimal protection scheme is introduced for dual setting directional overcurrent relays(DOCRs)using a combination of various standard relay characteristics.Along with the two variables,i.e.,time multiplier setting(TMS)and plug setting(PS)for conventional directional overcurrent relay,dual setting DOCRs are augmented with a third variable of relay characteristics identifier(RCI),which is responsible for selecting optimal relay characteristics from the standard relay characteristics according to the IEC-60255 standard.The relay coordination problem is formulated as a mixed-integer nonlinear programming(MINLP)problem,and the settings of relays are optimally determined using the genetic algorithm(GA)and the grey wolf optimization(GWO)algorithm.To validate the superiority of the pro-posed protection scheme,the distribution parts of the IEEE-14 and IEEE-30 bus benchmark systems are considered.

Covert Communication with a Spectrum Sharing Relay in the Finite Blocklength Regime

In this paper,we investigate the feasibility and performance of the covert communication with a spectrum sharing relay in the finite blocklength regime.Specifically,the relay opportunistically forwards the source's messages to the primary receiver or conveys the covert messages to its own receiver via the sharing spectrum,while the warden attempts to detect the transmission.First,we derive a lower bound on the covertness constraint,and the analytical expressions of both the primary average effective covert throughput(AECT)and sum AECT are presented by considering the overall decoding error performance.Then,we formulate two optimization problems to maximize the primary and sum AECT respectively by optimizing the blocklength and the transmit power at the source and the relay.Our examinations show that there exists an optimal blocklength to maximize the primary and sum AECT.Besides,it is revealed that,to maximize the primary AECT,the optimal transmit power of each hop increases as its channel quality deteriorates.Furthermore,in the optimization for maximizing the sum AECT,the optimal transmit power at the source equals to zero when the channel quality from relay to the secondary receiver is not weaker than that from relay to the primary receiver.