Beamforming Design for IRS-and-UAV-Aided Two-Way Amplify-and-Forward Relay Networks in Maritime IoT

In this paper,an intelligent reflecting surface(IRS)-and-unmanned aerial vehicle(UAV)-assisted two-way amplify-and-forward(AF)relay network in maritime Internet of Things(IoT)is proposed,where ship1(S1)and ship2(S2)can be viewed as data collecting centers.To enhance the message exchange rate between S1 and S2,a problem of maximizing minimum rate is cast,where the variables,namely AF relay beamforming matrix and IRS phase shifts of two time slots,need to be optimized.To achieve a maximum rate,a low-complexity alternately iterative(AI)scheme based on zero forcing and successive convex approximation(LC-ZF-SCA)algorithm is presented.To obtain a significant rate enhancement,a high-performance AI method based on one step,semidefinite programming and penalty SCA(ONSSDP-PSCA)is proposed.Simulation results show that by the proposed LC-ZF-SCA and ONS-SDP-PSCA methods,the rate of the IRS-and-UAV-assisted AF relay network surpass those of with random phase and only AF relay networks.Moreover,ONS-SDP-PSCA perform better than LC-ZF-SCA in aspect of rate.

Performance for Device-to-Device Communication with Three-Time-Slot Two-Way Amplify-and-Forward Relay Protocol

Multi-hop device-to-device(D2D) communication can significantly improve the system performance. This paper studied the outage performance of D2 D communication assisted by another D2 D user using three-timeslot two-way amplify-and-forward relaying protocol over Rayleigh fading channels. Considering the co-channel interference from cellular user at the D2 D node,the approximate expression for the overall outage probability was derived. Furthermore,a power allocation optimum method to minimize the outage probability was developed,and the closed form expression for the optimal power allocation coefficient at the relay was derived. Simulation results demonstrate accuracy of the derived outage probability expressions. Simulation results also demonstrate that the outage performance can be improved using the proposed optimal power allocation method.

Asymptotic analysis of multi-branch two-way amplify-and-forward relaying in Nakagami-m fading with arbitrary fading parameter

Two-way relay networks have received lots of attention, thanks to its ability to overcome the loss in the spectral efficiency due to half-duplex transmission. Asymptotic performance analysis can provide valuable insights in- to practical system designs. However, this is a gap in two-way relay network. In this paper, the asymptotic performance is studied for multi-branch dual-hop two-way amplify-and-forward （AF） relaying networks in independently but not necessarily identically distributed （i.n.i.d.） Nakagami-m fading channels, with arbitrary m 〉 5. The approximate prob- ability density function （PDF） of the instantaneous dual-hop link power at high SNR region is derived. Then we present the asymptotic outage probability expression, and analyze the diversity order and coding gain. Simulations are per- formed to verify the tightness of the presented analysis at medium and high SNR regions.

PERFORMANCE ANALYSIS OF TWO-WAY AMPLIFY-AND-FORWARD RELAYING SYSTEM WITH MULTIPLE INTERFERERS AT THE RELAY

In this paper,we investigate the performance of the two-way Amplify-and-Forward(AF) relaying systems in an interference-limited Rayleigh fading environment.More specifically,assuming the presence of Rayleigh faded multiple interferers at the AF relay and noisy sources,an approximate closed-form expression for the Overall Outage Probability(OOP) and an integral expression for the average Symbol Error Probability(SEP) are derived.The analysis results are verified through com-parison with the Monte Carlo simulation results.

Outage Performance of Opportunistic Amplify-and-Forward Relaying over Asymmetric Fading Environments

This letter analyzes the outage probability of opportunistic amplify-and-forward relaying over asymmetric and independent but non-identically distributed (i.n.d) fading environments. The work investigates the scenarios where cooperative nodes are located at different geographical locations. As a result, the different signals are affected by different i.n.d fading channels, one may undergo Rician fading distribution and others may undergo Rayleigh fading distribution. In this letter, a lower bound of the outage probability for various asymmetric fading environments is derived at high SNR by applying the initial value theorem. The analytical model is validated through Monte-Carlo simulation results.

Parameter Optimization for Amplify-and-Forward Relaying Systems with Pilot Symbol Assisted Modulation Scheme

Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with a pilot symbol as-sisted modulation (PSAM) scheme. It is assumed that a linear minimum mean square estimator (LMMSE) is used for the channel estimation at the receiver. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative communication systems with quadrature amplitude modulation (QAM) constellations. Based on the AUB, we propose a criterion for the parameter optimization in the PSAM scheme. We discuss how the pilot spacing and the length of the Wiener ?lter should be chosen under the constraint of a tradeoff between pilot overhead, estimation accuracy, and receiver complexity. We also formulate an power allocation problem for the considered system. It is shown that the power allocation problem can optimally be solved by means of a gradient search method. Numerical simulations are presented to verify the correctness of the theoretical results and to demonstrate the benefits of the parameter optimization.

Experimental full-duplex amplify-and-forward relay scheme for OFDM with power gain control

The fundamental challenges for full-duplex(FD)relay networks are the self-interference cancellation(SIC)and the cooperative transmission design at the relay.This paper presents a practical amplify-and-forward(AF)FD one-way relay scheme for orthogonal frequency division multiplexing(OFDM)transmission with multi-domain SIC.It is found that the residual self-interference(SI)signals at the relay can be regarded as an equivalent multipath model.The effects of the residual sI at the relay are incorporated into the equivalent end-to-end channel model,and the inter-block interference can be removed at the destination by using cyclic prefix(CP)protection.Based on the equivalent multipath model,we present a solution for optimizing the amplification factor on the performance of signal-to-interference-plus-noise ratio(SINR)when the equivalent multipath length is longer than the CP.Furthermore,a practical one way FD relay network with 3 nodes is built and measured.The simulation and measured results verify the superior performance of the proposed scheme.

Beamforming design for RIS-aided amplify-and-forward relay networks

The use of a reconfigurable intelligent surface(RIS)in the enhancement of the rate performance is considered to involve the limitation of the RIS being a passive reflector.To address this issue,we propose a RIS-aided amplify-and-forward(AF)relay network in this paper.By jointly optimizing the beamforming matrix at AF relay and the phase-shift matrices at RIS,two schemes are put forward to address a maximizing signal-to-noise ratio(SNR)problem.First,aiming at achieving a high rate,a high-performance alternating optimization(AO)method based on Charnes–Cooper transformation and semidefinite programming(CCT-SDP)is proposed,where the optimization problem is decomposed into three subproblems solved using CCT-SDP,and rank-one solutions can be recovered using Gaussian randomization.However,the optimization variables in the CCT-SDP method are matrices,leading to extremely high complexity.To reduce the complexity,a low-complexity AO scheme based on Dinkelbachs transformation and successive convex approximation(DT-SCA)is proposed,where the variables are represented in vector form,and the three decoupling subproblems are solved using DT-SCA.Simulation results verify that compared to three benchmarks(i.e.,a RIS-assisted AF relay network with random phase,an AF relay network without RIS,and a RIS-aided network without AF relay),the proposed CCT-SDP and DT-SCA schemes can harvest better rate performance.Furthermore,it is revealed that the rate of the low-complexity DT-SCA method is close to that of the CCT-SDP method.

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.

Coordinated responses of leaf and nodule traits contribute to the accumulation of N in relay intercropped soybean

Maize(Zea mays L.)-soybean(Glycine max L.Merr.)relay intercropping provides a way to enhance land productivity.However,the late-planted soybean suffers from shading by the maize.After maize harvest,how the recovery growth influences the leaf and nodule traits remains unclear.A three-year field experiment was conducted to evaluate the effects of genotypes,i.e.,supernodulating(nts1007),Nandou 12(ND12),and Guixia 3(GX3),and crop configurations,i.e.,the interspecific row spacing of 45(I45),60(I60),75 cm(I75),and sole soybean(SS),on soybean recovery growth and N fixation.The results showed that intercropping reduced the soybean total leaf area(LA)by reducing both the leaf number(LN)and unit leaflet area(LUA),and it reduced the nodule dry weight(NW)by reducing both the nodule number(NN)and nodule diameter(ND)compared with the SS.The correlation and principal component analysis(PCA)indicated a co-variability of the leaf and nodule traits in response to the genotype and crop configuration interactions.During the recovery growth stages,the compensatory growth promoted soybean growth to reduce the gaps of leaf and nodule traits between intercropping and SS.The relative growth rates of ureide(RGR_U)and nitrogen(RGR_N)accumulation were higher in intercropping than in SS.Intercropping achieved more significant sucrose and starch contents compared with SS.ND12 and GX3 showed more robust compensatory growth than nts1007 in intercropping.Although the recovery growth of relay intercropping soybean improved biomass and nitrogen accumulation,ND12 gained a more significant partial land equivalent ratio(pLER)than GX3.The I60 treatment achieved more robust compensation effects on biomass and N accumulation than the other configurations.Meanwhile,I60 showed a higher nodule sucrose content and greater shoot ureide and N accumulation than SS.Finally,intercropping ND12 with maize using an interspecific row spacing of 60 cm was optimal for both yield advantage and N accumulation.

A Pricing-Based Cooperative Relay Selection Scheme for Reliable Communications

With the rapid development and application of energy harvesting technology,it has become a prominent research area due to its significant benefits in terms of green environmental protection,convenience,and high safety and efficiency.However,the uneven energy collection and consumption among IoT devices at varying distances may lead to resource imbalance within energy harvesting networks,thereby resulting in low energy transmission efficiency.To enhance the energy transmission efficiency of IoT devices in energy harvesting,this paper focuses on the utilization of collaborative communication,along with pricing-based incentive mechanisms and auction strategies.We propose a dynamic relay selection scheme,including a ladder pricing mechanism based on energy level and a Kuhn-Munkre Algorithm based on an auction theory employing a negotiation mechanism,to encourage more IoT devices to participate in the collaboration process.Simulation results demonstrate that the proposed algorithm outperforms traditional algorithms in terms of improving the energy efficiency of the system.

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.

Designing a Protection Scheme in Micro-Grid Systems with DG Using Central Protection Unite and Multiple Setting Group Protection Relays

Distributed generators now is widely used in electrical power networks, in some cases it works seasonally, and some types works at special weather conditions like photo voltaic systems and wind energy, and due to this continuous changes in generation condition, the fault current level in network will be affected, this changes in fault current level will affect in the coordination between protection relays and to keep the coordination at right way, an adaptive protection system is required that can adaptive its setting according to generation changes, the fault current level in each case is evaluated using ETAP software, and the required relay setting in each case is also evaluated using Grey Wolf Optimizer (GWO) algorithm, and to select suitable setting which required in each condition, to select the active setting group of protection relay according to generation capacity, central protection unite can be used, and to improve protection stability and minimizing relays tripping time, a proposed method for selecting suitable backup relay is used, which leads to decrease relays tripping time and increase system stability, output settings for relays in all cases achieved our constrains.

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.

Improving amplify-and-forward relay selection algorithm based on partial relay link

This article addresses the design problem of selecting an appropriate relay in amplify-and-forward （AF） cooperative diversity systems. In this regard, this article focuses on relay selection based on partial channel knowledge only across the source and relay links. In particular, the two fundamental questions will be answered, that is, whether to cooperate and whom to cooperate with. Through answering these two questions, an improved relay selection strategy based on partial relay link, which emphasizes that cooperation happens when necessary, is proposed to aim at maximizing the average mutual information. Then a joint optimization, in terms of power allocation and relay selection, is employed to guarantee a robust performance for relay selection based on partial relay link. Optimum power is allocated between the source and the selected relay to maximize the output signal-to-noise （SNR） at the destination. Simulation results turn out that the improved scheme can achieve better performance than previous work and the robust performance can be guaranteed by employing joint optimization.

Cognitive amplify-and-forward dual-hop relay networks over α-μ fading channels

This paper provides an analytic performance evaluation of dual-hop cognitive amplify-and-forward (AF) relaying networks over independent nonidentically distributed (i.n.i.d.) fading channels. Two different transmit power constraint strategies at the secondary network are proposed to investigate the performance of the secondary network. In the case of combined power constraint,the maximum tolerable interference power on the primary network and the maximum transmit power at the secondary network are considered. Closed-form lower bound and its asymptotic expression for the outage probability (OP) are achieved. Utilizing the above results,average symbol error probability (ABEP) at high signal-to-noise ratios (SNRs) are also derived. In order to further study the performance of dual-hop cognitive AF relaying networks,the Closed-form lower bounds and asymptotic expressions for OP with single power constraint of the tolerable interference on the primary network is also obtained. Both analytical and simulation are employed to validate the accuracy of the theoretical analysis. The results show that the secondary network obtains a better performance when higher power constraint is employed.

Performance of transmit diversity assisted amplify-and-forward relay system with partial relay selection in mixed Rayleigh and Rician fading channels

The performance of transmit diversity （TD） assisted amplify-and-forward （AF） relay system with partial relay selection, which experiences mixed Rayleigh and Rician fading channels, is investigated. We first investigate the closed-form expression of the cumulative distribution function for the end-to-end equivalent signal-to-noise ratio （SNR）, and then the exact expressions of outage probability and average symbol error probability （SEP） are derived. The theoretical observations are verified by the Monte Carlo simulation results.

Channel estimation based on distributed compressed sensing in amplify-and-forward relay networks

In orthogonal frequency-division multiplexing （OFDM） amplify-and-forward （AF） relay networks,in order to exploit diversity gains over frequency-selective fading channels,the receiver needs to acquire the knowledge of channel state information （CSI）.In this article,based on the recent methodology of distributed compressed sensing （DCS）,a novel channel estimation scheme is proposed.The joint sparsity model 2 （JSM-2） in DCS theory and simultaneous orthogonal matching pursuit （SOMP） are both introduced to improve the estimation performance and increase the spectral efficiency.Simulation results show that compared with current compressed sensing （CS） methods,the estimation error of our scheme is reduced dramatically in high SNR region while the pilot number is still kept small.

Power control for two-way amplify-and-forward relaying over Rayleigh fading channels

We propose two novel power control policies for a two-way amplify-and-forward (AF) relaying system,in which each node (two sources and one relay) is assumed to operate under bothminimum and peak power constraints.Through the exploitation of instantaneous channel gains,the first policy can maximize the sum rate of the system.However,the instantaneous channel gains may be unavailable in a rapid time-varying system,where the first policy is inoperable.Consequently,a robust power control policy which requires only mean channel gains is proposed to maximize the upper bound of the average sum rate,and the properties of this policy are investigated.Simulation results show that,by comparison with the policy in which all the nodes use their peak transmit power,the proposed power control policies can provide considerable system performance improvement.Furthermore,the performance difference between the two proposed policies is negligible when the relay is close to one source.

Greedy Algorithm Applied to Relay Selection for Cooperative Communication Systems in Amplify-and-Forward Mode

Using a relaying system to provide spatial diversity and improve the system performance is a tendency in the wireless cooperative communications. Amplify-and-forward （AF） mode with a low complexity is easy to be implemented. Under the consideration of cooperative communication systems, the scenario includes one information source, M relay stations and N destinations. This work proposes a relay selection algorithm in the Raleigh fading channel. Based on the exhaustive search method, easily to realize, the optimal selection scheme can be found with a highly complicated calculation. In order to reduce the computational complexity, an approximate optimal solution with a greedy algorithm applied for the relay station selection is proposed. With different situations of the communication systems, the performance evaluation obtained by both the proposed algorithm and the exhaustive search algorithm are given for comparison. It shows the proposed algorithm could provide a solution approach to the optimal one.