Relay Scheme Research Articles

Synthesis of Chiral Endocyclic Allenes by Palladium-Catalyzed Asymmetric Annulation Followed by Cope Rearrangement.

Catalytic asymmetric synthesis of chiral endocyclic allenes remains a challenge in allene chemistry owing to unfavored tension and complex chirality. Here, we present a new relay strategy merging Pd-catalyzed asymmetric [3+2] annulation with enyne-Cope rearrangement, providing a facile route to chiral 9-membered endocyclic allenes with high efficiency and enantioselectivity. Moreover, theoretical calculations and experimental studies were performed to illustrate the critical, but unusual Cope rearrangement that allows for the complete central-to-axial chirality transfer.

Synthesis of Chiral Endocyclic Allenes by Palladium‐Catalyzed Asymmetric Annulation Followed by Cope Rearrangement

AbstractCatalytic asymmetric synthesis of chiral endocyclic allenes remains a challenge in allene chemistry owing to unfavored tension and complex chirality. Here, we present a new relay strategy merging Pd‐catalyzed asymmetric [3+2] annulation with enyne‐Cope rearrangement, providing a facile route to chiral 9‐membered endocyclic allenes with high efficiency and enantioselectivity. Moreover, theoretical calculations and experimental studies were performed to illustrate the critical, but unusual Cope rearrangement that allows for the complete central‐to‐axial chirality transfer.

Copper‐Mediated Relay Strategy Using Chlorination/Oxidation: An Effective Synthesis of Functionalized Coumarin Derivatives

AbstractChromene‐fused heterocyclic compounds have shown fascinating biological and physiochemical properties and thus, the design and development of chromene‐fused heterocyclic molecules is of significant interest in the field of synthetic organic chemistry. We report an innovative ligand‐ and additive‐free synthetic approach of 4‐(phenylethynyl)‐2H‐chromene‐3‐carbaldehyde with phenylacetylenes has been described through sequential chlorination, benzannulation, benzylic sp3 C−H bond functionalization, and ether oxidation for the formation of chloro‐substituted‐9‐phenyl‐6H‐benzo[c]chromen‐6‐ones with readily available chemicals under one‐pot, base‐free conditions using CuCl2 as sustainable catalyst. In this regioselective approach, we defined a reasonably longer cascade, which reveals the multiple role of chlorine as chlorine supplier, Lewis acid catalyst and oxidation rate promoter that tolerates a broad substrate scope and allows good product yields. The authenticated mechanism proceeds in a cascading fashion through the formation of multiple bonds.

Bit error rate and outage probability analysis for multi-hop decode-and-forward relay-aided NOMA with imperfect SIC and imperfect CSI

This paper investigates a multi-hop decode-and-forward (DF) relay-aided non-orthogonal multiple access (MH-DF-R-NOMA) scheme. The model overcomes the problems associated with poor channel quality and disconnection communication with the broadcast station for the users through the path from the intermediate relay nodes to deliver the signal to the users. We assume that we have multiple intermediate relay nodes that constitute the path to transmit the signal to two users who have different channel qualities. Consequently, the closed-form expressions for bit error rate (BER) and outage probability (OP) at all intermediate relay nodes and users are derived. In the analysis, the imperfect channel state information (CSI) and imperfect successive interference cancellation (SIC) are taken into account. Computer simulation are presented to validate theoretical analyzes. The results indicate that the degradation of BER and OP performances for the near user is higher than the far user. We also show the superiority of our model over the single relay scheme. Furthermore, the OP of MH-DF-R-NOMA outperforms its counterpart in OMA.

Performance Analysis of DF Relay-Assisted D2D Communication in a 5G mmWave Network

Enabling D2D communication in the mmWave band has many obstacles that must be mitigated. The primary concern is the introduction of interference from various sources. Thus, we focused our work on the performance of decode-and-forward (DF) relay-assisted D2D communication in the mmWave band to increase the coverage probability and energy efficiency (EE). Three modes are proposed for D2D communication to prevail. The bitwise binary XOR operation was executed at the relay node, which increased the security feature. The radius of coverage was derived, which indicated the switching of the modes. The diffused incoherent scattering power was also considered as part of the power consumption. Furthermore, a unique relay selection scheme, the dynamic relay selection (DRS) method, is proposed to select the optimal relay for information exchange. A comparison of the proposed DF relay scheme with the amplify-and-forward (AF) scheme was also made. Finally, the simulation results proved the efficacy of the proposed work.

Copper-Catalyzed Three-Component Germyl Peroxidation of Alkenes.

The concurrent incorporation of a germyl fragment and another functional group (beyond the hydrogen atom) across the C═C double bond is a highly appealing yet challenging task. Herein we demonstrate the efficient germyl peroxidation of alkenes with germanium hydrides and tert-butyl hydroperoxide via a copper-catalyzed three-component radical relay strategy. This protocol exhibits excellent functional group tolerance and exquisite chemo- and regioselectivity under mild conditions and represents a rare example of constructing synthetically challenging metal-embedded organic peroxides.

Optimal Relay Coordination for DG-Based Power System Using Standard and User-Defined Relay Characteristics

The operating time of directional overcurrent relays (DOCRs) can be reduced with user-defined relay characteristics considering plug setting (PS), time multiplier setting (TMS), and relay characteristic coefficients (λ and γ). This study presents a comparative analysis of relay coordination with standard and user-defined relay characteristics. The proposed relay coordination scheme is formulated as a non-linear constraint optimization problem. The grey wolf optimization (GWO) algorithm is used to determine the optimal relay settings and total operating time of DOCRs. The performance of the proposed scheme is tested on the standard 8-bus, 9-bus, and 15-bus systems. The results show that the total operating time of DOCRs with user-defined relay characteristics is better than that with standard relay characteristics. The results of the GWO algorithm are compared with the performance of optimization techniques used in literature to solve the relay coordination problem.

Unified Impedance-Based Relaying Scheme for the Protection of Hybrid AC/DC Microgrid

Even though the implementation of hybrid AC/DC microgrid is increasing, their protection schemes face multiple challenges such as inconsistent fault current supply from DGs, difficulty in discriminating internal/ external faults and missing of universal protection scheme for both AC and DC distribution networks. In this regard, a unified fault detection and localization scheme is proposed for hybrid AC/DC microgrid. By measuring the impedance at system frequency for AC circuit and at a specific pre-inserted frequency for DC network, the suggested technique achieves proper discrimination between internal faults and external events. Several fault scenarios such as internal/external faults, single/double line faults with varying fault location and fault resistance have been investigated on both AC and DC circuits by modeling hybrid AC/DC microgrid in PSCAD/EMTDC environment. The results reveal the effectiveness of the proposed algorithm in discriminating internal faults with external events and also in estimating accurate fault location even under noisy environment. Finally, a comparative evaluation of the proposed unified AC/DC protection scheme with other individual AC/DC protection schemes shows its superiority in combining both the AC and DC schemes together into a single relay, having an improved fault detection time and an increased fault localization accuracy.

Performance analysis of cooperative NOMA system for defense application with relay selection in a hostile environment

In the current scenario, where all the services have become online, the demand for increased capacity, low symbol error rate (SER), better data rate, and low latency with high quality of services has been expected from the service providers. Non-orthogonal multiple access (NOMA) is the key enabling technology by which all the above requirements could be achieved. In this work, the physical layer security of a cooperative NOMA system has been improved. The present approach of the decode-and-forward (DF) method consists of one base station (BS), N relays, and two users. Here, a two-stage relay method has been proposed, and analytical results are generated to show that this two-stage relay scheme has been found to achieve the lowest outage probability among all possible relay schemes with the highest attainable diversity gain. In a high signal-to-noise ratio (SNR), the asymptotic and closed-form expressions for outage probability have been obtained. The outage probability for N relays is also computed, which shows that the outage probability decreases as the number of relays get increased. Meanwhile, the Monte-Carlo simulation shows that cooperative NOMA with the proposed two-stage relay technique outperforms cooperative NOMA using the traditional max-min approach.

Routing and secret key assignment for secure multicast services in quantum satellite networks

Multicast is an important service type in both terrestrial and space communication networks but has security issues because more than one destination node can receive information. Point-to-point quantum key distribution can be achieved end-to-end over long distances by using a quantum satellite (e.g., Micius) as a relay node. Hence, how to provide secret keys for remote multicast services and efficiently distribute secret keys between the source node and multiple destination nodes for long-distance secure multicast services (SMSs) has become a critical problem. In this paper, a quantum satellite network with a special node structure is designed to complete point-to-multipoint key distribution, and a point-to-multipoint satellite relay scheme is proposed. The weight information of the link is dynamically described by the method of auxiliary topology, and a satellite relay tree is constructed. Finally, this paper proposes a satellite relay algorithm for multicast services to route and allocate key resources to solve the problem of long-distance point-to-multipoint key relay and improve the success probability of multicast service requests. Simulation results show that the proposed algorithm can improve the success probability of SMS requests by about 51.32% in a static scenario and 17.33% in a dynamic scenario.

Opportunistic Data Relay Scheme for Narrowband Multihop Combat Radio Networks

In this paper, we propose an opportunistic data relay scheme in narrowband multihop combat radio networks. Narrowband networks have physical restrictions on high-speed transmission. Furthermore, the topology changes dynamically due to the jamming of the enemy, signal interference between friendly forces, and movement of network entities. Therefore, the traditional relay scheme that collects topology information and calculates a relay path before transmission is unsuitable for such networks. Our proposed scheme does not collect topology information and transmits data opportunistically. The scheme can cause unnecessary data relaying that is not related to data delivery to the destination node. However, for small networks, the effect of increasing network throughput by not gathering topology information is much greater than the effect of reducing throughput by unnecessary data relays. We demonstrate the performance superiority of the proposed scheme through simulation in the worst case of network topology.

Optimization-Driven Hierarchical Learning Framework for Wireless Powered Backscatter-Aided Relay Communications

In this paper, we employ multiple wireless-powered relays to assist information transmission from a multi-antenna access point to a single-antenna receiver. The wireless relays can operate in either the passive mode via backscatter communications or the active mode via RF communications, depending on their channel conditions and energy states. We aim to maximize the overall throughput by jointly optimizing the transmit beamforming and the relays’ radio modes and operating parameters. Due to the non-convex and combinatorial problem structure, we develop a novel optimization-driven hierarchical deep deterministic policy gradient (H-DDPG) approach to adapt the beamforming and relay strategies. The optimization-driven H-DDPG algorithm firstly decomposes the binary relay mode selection into the outer-loop deep <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -network (DQN) algorithm and then optimizes the continuous beamforming and relaying strategies by using the inner-loop DDPG algorithm. Secondly, to improve the learning efficiency, we integrate the model-based optimization into the inner-loop DDPG framework by providing a better-informed target estimation for DNN training. Simulation results reveal that these two special designs ensure a more stable learning performance and achieve a higher reward, up to 20%, compared to the conventional model-free DDPG approach.

Evolution of protective relays in 1-Φ, 25kV, 50Hz railway traction system

This paper presents the evolution of protective relays used for the protection of Power Transformer, Over Head Equipment (OHE) and Shunt Capacitor Bank in Indian Railways Electrical Distribution Systems. Initially during electrification Indian Railways adopted 1-Φ, 25KV, 50Hz AC system and electromagnetic relays (EM Relays) for feeder protection of OHE available at that time. But over the period of time with the drastic growth in traffic and sharp increase in demand for more electrical power to heavy goods trains haulage, the above said protective system doesn’t catered the requirements like speed, sensitivity, reliability, post fault data analysis. Hence Indian Railways over the years have undergone a paradigm shift in protective relay schemes. The journey of evolution from EM relays and static relays to the latest state of art integrated Numerical relays which were approved by RDSO are dealt here.

Life cycle assessment of tiger puffer (Takifugu rubripes) farming: A case study in Dalian, China

In China, energy consumption and carbon emission by the aquaculture industry have become major problems. The tiger puffer (Takifugu rubripes) is an emerging aquaculture species in China, but its environmental impact during the farming process has not yet been evaluated systematically. To the best of our knowledge, this is the first life cycle assessment (LCA) of tiger puffer land-sea relay strategy in Dalian, China. To analyze the environmental impact of the tiger puffer farming process, the following four stages were considered: seed rearing, deep-sea cage farming-1, industrial recirculating aquaculture, and deep-sea cage farming-2. The LCA software GaBi 10.5 academy version and CML-IA-Jan. 2016-world method were used to calculate the environmental impacts. According to the LCA results, marine aquatic ecotoxicity potential was the largest contributor to the environmental impact, and industrial recirculating aquaculture was the largest farming stage in the whole tiger puffer farming process. Energy in the form of electricity, coal, and gasoline was consumed to maintain the power supply in the tiger puffer farming process, and it was a key factor that influenced the environmental performance. Based on the sensitivity and energy analyses, energy consumption for equipment operation at the industrial recirculating aquaculture stage, feed consumption, and gasoline consumption for transportation at the deep-sea cage farming-2 stage need to be carefully considered. The following improvement measures were suggested to improve the environmental performance of tiger puffer farming and the aquaculture industry: establish electricity, wind power, and solar energy integrated management systems; ex-ante LCA for parameter optimization in future technology research and development; and new production strategies such as aquaponics and integrated multi-trophic aquaculture. Moreover, life cycle inventory (LCI) of tiger puffer land-sea relay farming was established to obtain essential information, enrich aquaculture LCI databases, and support aquaculture LCA research.

Design and verification of the multinode and multisystem relay communication system for the Tianwen-1 Mars Probe

<p indent="0mm">As an important part of China’s first Mars exploration mission, the Tianwen-1 relay communication system is responsible for providing efficient and reliable communication services between the lander-rover and the orbiter and for supporting the completion of the patrol and exploration mission on the Martian surface. Considering the large elliptical relay orbit of the Mars exploration mission, the XHF/UHF dual-band relay communication scheme of the Tianwen-1 probe is introduced in this paper. Moreover, the design, technical mechanism, and verification approach of the critical parts of the relay communication system are given. Finally, the results of the on-orbit flight data are analyzed. The flight verification results show that the newly developed relay communication system of the Tianwen-1 probe successfully achieves the exploration mission objectives. Furthermore, its design, implementation, and application provide technical reference for the subsequent development of China’s deep-space relay communication system.

Energy-Efficient Wireless Communications With Distributed Reconfigurable Intelligent Surfaces

This paper investigates the problem of resource allocation for a wireless communication network with distributed reconfigurable intelligent surfaces (RISs). In this network, multiple RISs are spatially distributed to serve wireless users and the energy efficiency of the network is maximized by dynamically controlling the on-off status of each RIS as well as optimizing the reflection coefficients matrix of the RISs. This problem is posed as a joint optimization problem of transmit beamforming and RIS control, whose goal is to maximize the energy efficiency under minimum rate constraints of the users. To solve this problem, two iterative algorithms are proposed for the single-user case and multi-user case. For the single-user case, the phase optimization problem is solved by using a successive convex approximation method, which admits a closed-form solution at each step. Moreover, the optimal RIS on-off status is obtained by using the dual method. For the multi-user case, a low-complexity greedy searching method is proposed to solve the RIS on-off optimization problem. Simulation results show that the proposed scheme achieves up to 33% and 68% gains in terms of the energy efficiency in both single-user and multi-user cases compared to the conventional RIS scheme and amplify-and-forward relay scheme, respectively.

Joint Trajectory and Resource Optimization for UAV-Aided Two-Way Relay Networks

Unmanned aerial vehicle (UAV)-aided two-way relay networks with multiple terrestrial user pairs is investigated, where a fix-wing UAV is served as a two-way relay to assist information transmission. We aim to maximize the total rate of the two-way relay networks while the quality of service (QoS) being guaranteed. A novel relay strategy, namely <i>time-slots pairing</i>, is proposed by exploiting physical-layer network coding (PNC) protocol. Specifically, the UAV receives and buffers the signals from the scheduled user pair when the UAV approaches one of them, then forwards the modulated signal when the UAV is close to the other. As a result, a non-convex total rate maximization problem is formulated by joint trajectory design and resource optimization. To solve this problem, we first decompose it into three sub-problems, and then a three-step iterative algorithm that can effectively handle the non-convex problem with no worse than a polynomial complexity is developed leveraging the block coordinate descent (BCD) technique and successive convex approximation (SCA) method. Simulation results finally illustrate that: 1) Compared with amplify-and-forward (AF) or decode-and-forward (DF) protocols, the proposed design based on PNC protocol can significantly improve the total rate of the two-way relay networks; 2) the time-slots pairing relay strategy always achieves a significant enhancement on performance than the traditional non-time-slots pairing relay strategy; 3) the time-slots pairing relay strategy is more favorable for the mobile PNC relay networks since it can well resist the degradation of the entire networks caused by users&#x2019; increased service quality requirements.

An Adaptive Overcurrent Coordination Scheme Withstanding Active Network Operations

This paper aims to present a centralized adaptive protection scheme (APS) for the directional overcurrent relays (DOCRs) considering system dynamics such as load demand variations, topology changes and DGs to mitigate the above-mentioned effects. The scheme is suitable for different types of networks whether its radial or meshed. Afterall, it can determine the actual topology with the micro-PMUs and breaker status, automatically generate relay names accordingly with the topology bus locations, establish protection coordination pairs, coordinate DOCRs for parallel lines, identify transformers to offer backup operation for differential protection, perform load flow and fault studies, execute contingency and sensitivity analysis, and lastly, coordinate the DOCRs using differential evolution algorithm so that they always have the proper settings to operate in appropriate time providing selectivity. The performance of the proposed centralized adaptive overcurrent protection scheme is tested on the highly meshed IEEE 14 bus system. The proposed scheme has shown that it can adequately consider impacts of system dynamics and DG.

Approaching K-Means for Multiantenna UAV Positioning in Combination With a Max-SIC-Min-Rate Framework to Enable Aerial IoT Networks

In long-range wireless communication networks, the fading channels described in channel state information are strongly related to distance and the path loss exponent and represent a major challenge in delivering the performance required to support emerging applications. Conveniently, multiple antennas and cooperative relays are efficient solutions that can combat fading channels, thereby improving networking capacity and transmission reliability. This study investigated the use of multi-antenna unmanned aerial vehicle (UAV)s as aerial Internet of Things (IoT) relays and employed their direct line-of-sight benefits to assist IoT wireless networks. To improve the outage probability, system throughput, and energy efficiency (EE), we first considered a combination of transmit antenna selection at the transmitter and the selection combining technique at the receiver to determine the best channel from the pre-coding channel matrix. Then, based on a practical model in a three-dimensional earth environment and thanks to the K-means algorithm, we investigated optimal UAV placement to obtain optimal channel state information for the non-orthogonal multiple access (NOMA)-IoT device cluster globally, thereby ensuring the quality of service for the IoT devices. We introduced a max-successive interference cancellation-min-rate framework for non-ordered NOMA devices, thus deriving theoretical expressions in novel closed forms for two independent scenarios: ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> ) Rayleigh and ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ii</i> ) Nakagami- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> fading channels. By optimizing the UAV placement, the investigated results applied to the UAV scheme delivered a better performance in a NOMA-IoT network than in a terrestrial relay (TR) scheme. Finally, this study examines a variety of models and presents algorithms for Monte Carlo simulations to verify the theoretical results.

Achieving Covert Wireless Communication With a Multi-Antenna Relay

We investigate covert wireless communication in a multi-antenna relay network, where the relay transmits its own covert message to the destination when assisting the source’s information delivery, and the source acts as a warden to detect this covert transmission. Based on whether the channel state information of the relay-destination link is available at the source or not, we propose two relay beamforming schemes, namely random beamforming and maximum-ratio transmission (MRT) beamforming schemes, to guarantee the reception reliability at the destination while deliberately introducing uncertainty to the source to degrade its detection. Under the worst-case covert communication scenario where the source is capable of optimizing its detection threshold, analytical expressions for the minimum detection error probability achieved by each of the proposed schemes are derived to evaluate the detection limits of the source. By utilizing the above analytical results as the covertness constraint, an optimization problem of transmit power allocation for each scheme is formulated and solved to maximize the covert rate. The impact of imperfect channel state information on the covert communication performance is also examined. Simulation results are performed to confirm the accuracy of the derived analytical results and quantify the communication covertness enhancement of the proposed schemes. Our results also show that the MRT beamforming scheme offers a higher covert rate than that of the random beamforming scheme, especially when the covertness constraint becomes loose and/or the number of antennas at the relay increases.