Conventional Relay Research Articles

A New Relay and Jammer Selection Schemes for Secure One-Way Cooperative Networks

This paper presents different relay and jammer selection schemes for one-way cooperative networks to increase the security against malicious eavesdroppers. We consider a single source-destination cooperative network with multiple intermediate nodes and one or more eavesdroppers. The selection in the proposed schemes is made with the presence of direct links and the assumption that the broadcast phase is unsecured. The proposed schemes select three intermediate nodes. The first selected node operates in the conventional relay mode and assists the source to deliver its data to the corresponding destination via a Decode-and-Forward strategy. The second and third selected nodes are used in different communication phases as jammers to create intentional interference at the eavesdroppers' nodes. Moreover, a hybrid scheme which switches between jamming and non-jamming modes is introduced in this paper. The proposed schemes are analyzed in terms of ergodic secrecy capacity and secrecy outage probability. Extensive analysis and a set of simulation results are presented to demonstrate the effectiveness of the different schemes presented in this work. The obtained results show that the proposed schemes with jamming outperform the conventional non-jamming schemes and the hybrid switching scheme further improves the secrecy capacity. The impact of changing both the eavesdroppers and the relays location on ergodic secrecy capacity and secrecy outage probability is also discussed. Finally, the impact of the presence of multiple eavesdroppers is studied in this paper.

Channel Training Algorithms for Two-Way MIMO Relay Systems

Two-way relay systems are known to be capable of providing higher spectral efficiency compared with conventional one-way relay systems. However, the channel estimation problem for two-way relay systems is more complicated than that of one-way relay systems. In this paper, we propose and compare two channel estimation algorithms, namely the superimposed channel training scheme and the two-stage channel estimation algorithm, for two-way multiple-input multiple-output (MIMO) relay communication systems, where the individual channel state information (CSI) for the first-hop and second-hop links is estimated. For both algorithms, we derive the optimal structure of the source and relay training sequences which minimize the mean-squared error (MSE) of channel estimation. In the superimposed channel training scheme, the power allocation between the source and relay training sequences is optimized. For the two-stage channel estimation algorithm, we optimize the power allocation at the relay node between two stages to improve the performance of the algorithm. Numerical examples are shown to demonstrate and compare the performance of the proposed channel training algorithms.

Effect of Feedback Delay on Secure Cooperative Networks with Joint Relay and Jammer Selection

Physical layer security is a promising technique to realize secure wireless communications without relying on conventional cryptographic methods. In cooperative networks with secrecy constraints, joint relay and jammer selection (JRJS) is an efficient approach to improving the security performance. However, due to feedback delay, the channel state information (CSI) used in the selection process may become outdated and differ from the CSI during the actual transmission of data and jamming. In this work, we study the effect of feedback delay on the JRJS scheme with decode-and-forward relaying strategy. We provide a lower bound for the ergodic secrecy capacity (ESC) and approximate closed-form expressions for the secrecy outage probability (SOP). Monte Carlo simulations are performed to verify the analytical results. The simulation results show that feedback delay decreases the ESC and increases the SOP floor of JRJS. However, in spite of the performance degradation, JRJS outperforms the conventional relay selection scheme without jamming.

Interference-Aware Relay Selection Scheme for Two-Hop Relay Networks With Multiple Source–Destination Pairs

An interference-aware relay selection scheme is proposed for two-hop relay networks with multiple source–destination (S–D) pairs, each of which is assisted by a relay selected from the candidates. We address the interference from relays to their nonintended destinations, and the interference level at any destination is jointly affected by relay selections of all S–D pairs. Upper and lower bounds of the two-hop transmission rate are derived, and the joint impact of the interference from multiple relays is decoupled to each S–D pair. Based on these bounds, an interference-aware relay selection metric for each S–D pair is proposed, which reflects both the relay-assisted two-hop rate and the induced interference to other destinations. The decoupled metric enables us to formulate the relay selection as a weighted bipartite matching problem, with the S–D pairs and the candidate relays as the two sides. Both the centralized scheme based on the Hungarian algorithm and the distributed scheme based on matching games are presented. Simulation results show that the distributed scheme performs nearly the same as the centralized scheme, and both schemes substantially outperform the conventional min–max relay selection scheme in terms of network sum rate.

The Study of a Regional Decentralized Peer-to-Peer Negotiation-Based Wide-Area Backup Protection Multi-Agent System

Conventional protection relays, which use local signals to locate faults, are a poor fit to modern power grids when compared to communication-based alternatives. This article presents a novel Wide-Area Backup Protection (WABP) algorithm that uses information shared across wide-area communication networks. The WABP algorithm fuses and integrates information in a regional decentralized peer-to-peer negotiation architecture for enhanced effectiveness. Line decision-making agents (LDAs), focused on line-fault detection, collect distance and directional protection information on both sides of a line. If LDAs cannot detect a fault locally, wide-area information that includes directional protection and line-fault states from neighboring lines is collected to locate the fault. The LDA considers the possible presence of relay misoperations, protection failures, and/or communication failures. Regional decision-making agents (RDAs) that reside in a regional decision-making device (RDD) in the monitoring layer of a substation can negotiate in a peer-to-peer manner without a control center. The RDA serves as the manager, coordinator, and message transponder for the LDAs. The design of the WABP is described including its architecture, workflow, and its agents' functions. Simulation scenarios illustrate the correctness of the WABP multi-agent system and the higher fault-tolerance of its response to misoperations, protection failures, and communication failures.

Detection of High Impedance Fault in Power Distribution Systems Using Mathematical Morphology

A high impedance fault (HIF) is characterized by a small, nonlinear, random, unstable, and widely varying fault current in a power distribution system. HIFs draw very low fault currents, and hence are not always effectively cleared by conventional overcurrent relays. Various schemes are proposed to detect such faults. This paper presents a method to detect HIFs using a tool based on mathematical morphology (MM). The method is implemented alongside the conventional overcurrent relay at the substation to improve the performance of this relay in detecting HIFs. It is rigorously tested on standard test systems using PSCAD/EMTDC® to generate test waveforms, and Matlab® to implement the method. Simulation results show that the proposed method is fast, secure, and dependable.

DSP based fuzzy and conventional overcurrent relay controller comparisons

Fuzzy logic control uses linguistic approach to solve complicated rules and ambiguous systems. This control strategy can be used to improve the overall performance of an overcurrent relay for power system protection compared to conventional relay. It is essential for a relay to work efficiently to trip the circuit breakers in the presence of faults and at the same time proficient to coordinate well with the networks to avoid mal-operation. There are two different types of fuzzy logic control strategies proposed for the relay, the Fuzzy Logic Controller (FLC) and Fuzzy Bang-Bang Controller (FBBC). The FBBC is the same as the conventional FLC except that the defuzzification method uses largest of maxima (LOM). Comparisons between the fuzzy controllers and conventional relay are based on IEC 255-3 standard. These relays are implemented on a DSP TMS320F2812 and their performance is evaluated which is based on operation time, DSP’s execution time and grading margin. The results obtained show a significant performance improvement compared to conventional relay.

Exploiting Cooperative Relay for High Performance Communications in MIMO Ad Hoc Networks

With the popularity of wireless devices and the increase of computing and storage resources, there are increasing interests in supporting mobile computing techniques. Particularly, ad hoc networks can potentially connect different wireless devices to enable more powerful wireless applications and mobile computing capabilities. To meet the ever increasing communication need, it is important to improve the network throughput while guaranteeing transmission reliability. Multiple-input-multiple-output (MIMO) technology can provide significantly higher data rate in ad hoc networks where nodes are equipped with multiantenna arrays. Although MIMO technique itself can support diversity transmission when channel condition degrades, the use of diversity transmission often compromises the multiplexing gain and is also not enough to deal with extremely weak channel. Instead, in this work, we exploit the use of cooperative relay transmission (which is often used in a single antenna environment to improve reliability) in a MIMO-based ad hoc network to cope with harsh channel condition. We design both centralized and distributed scheduling algorithms to support adaptive use of cooperative relay transmission when the direct transmission cannot be successfully performed. Our algorithm effectively exploits the cooperative multiplexing gain and cooperative diversity gain to achieve higher data rate and higher reliability under various channel conditions. Our scheduling scheme can efficiently invoke relay transmission without introducing significant signaling overhead as conventional relay schemes, and seamlessly integrate relay transmission with multiplexed MIMO transmission. We also design a MAC protocol to implement the distributed algorithm. Our performance results demonstrate that the use of cooperative relay in a MIMO framework could bring in a significant throughput improvement in all the scenarios studied, with the variation of node density, link failure ratio, packet arrival rate, and retransmission threshold.

Protection Scheme Half Wavelength Transmission Trunk Using Conventional Relay

This paper presents the main results on the use of conventional protection hardware to protect a Half Wavelength Transmission Line, or shortly AC-Link, for possible occurrence of three-phase and single-phase fault during energization maneuver. Lines of these dimensions do not exist today, but in countries of continental size they could be an interesting alternative to HVDC transmission, since the AC-Link has less dependence on Power Electronics technology. The studies on performance and relay settings were implemented using the RTDS real-time simulator. It is important to note that the AC-Link protection for the energization maneuver can be performed with existing hardware on conventional relays.

Concatenated channel‐and‐network coding scheme for two‐path successive relay network

Two-path successive relaying (TPSR) is an effective way to reduce the multiplex loss induced by the half-duplex operation of the relay node in a conventional relay network. One crucial issue in TPSR network is that the listening relay always suffers inevitable inter-relay interference (IRI), which degrades detection performance at the destination. In this study, a concatenated channel-and-network coding approach is proposed to solve the problem. In particular, a highly flexible channel code, namely, rateless code, is employed at the source to provide resilience to the residual IRI and reduce the retransmissions, which might break the system steady state of successive relaying. Then recognising the special interference structure, physical-layer network coding is incorporated into the forwarding scheme of the relay nodes to exploit network diversity and improve system efficiency. By extrinsic information transfer analysis, the minimum number of required code symbols for successful data recovery are calculated, and degree distribution of the rateless code is optimised.

Simulation Analysis of a Power System Protection using Artificial Neural Network

There has been significant development in the area of neural network based power system protection in the previous decade. Neural network technology has been applied for various protective relaying functions including distance protection. The aim of this Paper is to develop a software module acting as a protective relay using neural network techniques. The Artificial Neural Network (ANN) software developed module employs the back-propagation method to recognize the waveform patterns of impedance in a transmission line. The input waveforms are generated using PSCAD. The generated waveforms then are used as training and testing data for the ANN software. The ANN software is simulated using the Neural Network Toolbox. The design has been tested for different fault conditions including different fault resistances and fault inception angles. The test results show that the relay is able to detect faults in lesser time as compared to conventional relay algorithms. DOI: http://dx.doi.org/10.11591/ijece.v3i1.1938

Generalized Two-Hop Relay for Flexible Delay Control in MANETs

The available two-hop relay protocols with out-of-order or strictly in-order reception cannot provide a flexible control for the packet delivery delay, which may significantly limit their applications to the future mobile ad hoc networks (MANETs) with different delay requirements. This paper extends the conventional two-hop relay and proposes a general group-based two-hop relay algorithm with packet redundancy. In such an algorithm with packet redundancy limit $f$ and group size $g$ (2HR- $(f,g)$ for short), each packet is delivered to at most $f$ distinct relay nodes and can be accepted by its destination if it is a fresh packet to the destination and also it is among $g$ packets of the group the destination is currently requesting. The 2HR- $(f,g)$ covers the available two-hop relay protocols as special cases, like the in-order reception ones $(f\geq 1,g=1)$ , the out-of-order reception ones with redundancy $(f>1,g=\infty)$ , or without redundancy $(f=1,g=\infty)$ . A Markov chain-based theoretical framework is further developed to analyze how the mean value and variance of packet delivery delay vary with the parameters $f$ and $g$ , where the important medium contention, interference, and traffic contention issues are carefully incorporated into the analysis. Extensive simulation and theoretical results are provided to illustrate the performance of the 2HR- $(f,g)$ algorithm and the corresponding theoretical framework, which indicate that the theoretical framework is efficient in delay analysis and the new 2HR- $(f,g)$ algorithm actually enables both the mean value and variance of packet delivery delay to be flexibly controlled in a large region.

Optimal Power Allocation and Outage Analysis for Cognitive Full Duplex Relay Systems

This paper investigates the use of full duplex relaying (FDR) in cognitive radio systems. Cognitive full duplex relay networks (CogFRNs) offer the advantage not only of increasing spectral efficiency by spectrum sharing but also of extending coverage through the use of relays. Concurrent transmissions at the source and relay in CogFRNs can overcome a loss of resource efficiency in a way that conventional half duplex relay (HDR) systems cannot. However, in CogFRNs, the primary user experiences interference from the secondary source and relay simultaneously due to the effects of full duplexing. Satisfying the interference constraint by simply reducing transmission power results in performance degradation for the secondary user. What is therefore needed is a way to optimize the transmission powers at the secondary source and relay. To address this need, we propose an optimal power allocation scheme based on minimizing the outage probability in CogFRNs. We then analyze the outage probability of the secondary user in the noise-limited and interference-limited environments. In addition, we also propose an outage-constrained power allocation scheme which does not require the instantaneous channel state information (CSI) for the link between the primary and secondary users. Simulation results show that the proposed schemes achieve performance improvement in terms of outage probability.

Power Allocation for Conventional and Buffer-Aided Link Adaptive Relaying Systems with Energy Harvesting Nodes

In this paper, we consider optimal power allocation for conventional and buffer-aided link adaptive energy harvesting (EH) relay systems, where an EH source communicates with the destination via an EH decode-and-forward relay {over fading channels}. In conventional relaying, source and relay transmit signals in consecutive time slots whereas in buffer-aided link adaptive relaying, the state of the source-relay and relay-destination channels {as well as the amounts of energy available at source and relay} determine whether the source or the relay is selected for transmission. Our objective is to maximize the system throughput over a finite number of transmission time slots for both relaying protocols. In case of conventional relaying, we propose an offline and several online joint source and relay transmit power allocation schemes. For offline power allocation, we formulate {a convex optimization problem} whereas for the online case, we propose a dynamic programming (DP) approach to compute the optimal online transmit power. To alleviate the complexity inherent to DP, we also propose several suboptimal online power allocation schemes. For buffer-aided link adaptive relaying, we show that the joint offline optimization of the source and relay transmit powers along with the link selection results in a mixed integer non-linear program which we solve optimally using the spatial branch-and-bound method. We also propose efficient online power allocation schemes for buffer-aided link adaptive relaying. Simulation results show that buffer-aided link adaptive relaying provides significant performance gains compared to conventional relaying but requires a higher complexity for computation of the power allocation solution. We also show that buffer-aided link adaptive relaying is more robust to changes in the EH rate than conventional relaying.

Analysis of Outage Probability and Throughput for Half-Duplex Hybrid-ARQ Relay Channels

We consider a half-duplex wireless relay network with hybrid-automatic retransmission request (HARQ) and Rayleigh fading channels. In this paper, we analyze the average throughput and outage probability of the multirelay delay-limited (DL) HARQ system with an opportunistic relaying scheme in decode-and-forward (DF) mode, in which the best relay is selected to transmit the source's regenerated signal. A simple and distributed relay selection strategy is considered for multirelay HARQ channels. Then, we utilize the nonorthogonal cooperative transmission between the source and selected relay for retransmission of source data toward the destination, if needed, using space-time codes. We analyze the performance of the system. We first derive the cumulative density function (cdf) and probability density function (pdf) of the selected relay HARQ channels. Then, the cdf and pdf are used to determine the exact outage probability in the lth round of HARQ. The outage probability is required to compute the throughput-delay performance of this half-duplex opportunistic relaying protocol. The packet delay constraint is represented by L, which is the maximum number of HARQ rounds. An outage is declared if the packet is unsuccessful after L HARQ rounds. Furthermore, simple closed-form upper bounds on outage probability are derived. Based on the derived upper bound expressions, it is shown that the proposed schemes achieve the full spatial diversity order of N + 1, where N is the number of potential relays. Our analytical results are confirmed by simulation results. In addition, simulation shows that our proposed scheme can achieve higher average throughput, compared with direct transmission and conventional two-phase relay networks.

A Classification Approach Using Support Vector Machines to Prevent Distance Relay Maloperation Under Power Swing and Voltage Instability

Distance relays, in the power transmission systems, are susceptible to the maloperation under certain system events, such as power swings and voltage instability, which drive the apparent impedance trajectories into the protection zones of the relay. Fast and reliable detection of the symmetrical faults, occurring during power swings, poses another challenge to operation of the distance relays. This paper introduces a new classification and protection scheme based on support vector machines (SVMs) for offering supervisory control to the operation of the conventional distance relays. The proposed scheme segregates the power system events into faults, power swings, and voltage instability. This paper also proposes a new index, called the relay ranking index, for identifying the relays most vulnerable to the maloperation due to power swings and voltage instability. The proposed SVM classifiers can work in unison with the conventional distance relay unit. The performance of the proposed scheme has been tested on a nine-bus WSCC system and 39-bus New England system.

Layered video multicast using fractional frequency reuse over wireless relay networks

Nowadays, multimedia services over wireless networks are increasingly popular. With multicast, many mobile stations can join the same video group and share the same radio resource to efficiently increase frequency utilization. However, users may be located at different positions, and so suffer different degrees of path loss and interference, and receive a different signal-to-interference and noise ratio (SINR). Users at the cell-edge receiving a lower SINR may degrade the multicast efficiency. In this article, we propose four schemes that consider fractional frequency reuse (FFR) over relay networks in multi-cells. With FFR, users close to a base station (BS) are given more resources to improve the video quality. An efficient resource allocation scheme is also proposed. Compared to the conventional relay scheme, the proposed schemes can provide over 10% more video layers for all users and give better video quality for users near the BS.

ARQ‐based updatable relay selection for distributed EO‐STBC cooperative system

SUMMARYIn this work, we investigate the closed loop extended orthogonal‐space time block codes in decode‐ and‐forward cooperative networks and propose an updatable automatic repeat request protocol with relay selection. In the system, the relays decoding correctly are incorporated into a relay set, the optimal relays within this relay set can be selected based on the channel information, and the extended orthogonal‐space time block codes scheme is employed with the help of the feedback in automatic repeat request message. With the consideration of the relay selection, the system performance can be improved. Simulation and analysis results prove the efficiency of the proposed scheme, which achieves better performance than conventional relay schemes. Copyright © 2012 John Wiley & Sons, Ltd.

A New Digital Distance Relaying Scheme for Series-Compensated Double-Circuit Line During Open Conductor and Ground Fault

This paper presents a new digital distance relaying scheme which takes care of a simultaneous open conductor and ground fault occurring coincidently on the same phase at the same point on a series-compensated double-circuit line. The effect of series compensation, mutual zero-sequence coupling, remote infeed/outfeed, and fault resistance on the relay reach has been considered by the proposed scheme. The conventional digital distance relay having facility of series compensation fails to provide adequate protection in the presence of such conditions. The proposed scheme is based on the derivation of the compensated values of impedance using symmetrical component theory. To validate the proposed scheme, numerous computer simulations have been carried out using MATLAB/SIMULINK software on an existing 400-kV, 300-km-long series-compensated double-circuit transmission line. At the end, a comparative evaluation between the proposed scheme and the conventional scheme having a facility of series compensation is carried out. Simulation results demonstrate the effectiveness of the proposed scheme since the percentage error is within ±4.19%.

A Novel Relay Scheme for the Asymmetry Multiple Access Relay Channel

In this paper, we study the transmission mechanism for the asymmetry multiple access relay channel (AMARC), where the channel qualities from the sources to the relay are different. We propose a novel relay scheme, where network coding and cooperation between users are introduced, and turbo like decoders are employed at both the relay and destination nodes. We compare the bit error rate (BER) performance of the proposed scheme with the schemes in the literature via simulation. The simulation results show that, from the perspective of the average system BER, our proposed scheme significantly outperforms conventional relay schemes.