Relay Location Research Articles

Wireless information and power transfer with optimal transmit antenna selection

A dual hop, half-duplex amplify and forward (AF) relay is considered for a source equipped with multiple transmit antennas. A power splitter is employed at the relay to harvest energy from the signal received from the source. The outage probability (OP) is derived considering optimal antenna selection to maximise the end-to-end signal-to-noise ratio. It is shown that the performance of the proposed energy harvesting based scheme improves with the number of transmit antennas. The effect of the power splitting factor on the OP is studied for different relay locations. Further, the OP is examined for different distances between the source and relay.

Machine Learning-Based Multi-Layer Multi-Hop Transmission Scheme for Dense Networks

Multi-hop communication has attracted a lot of attention recently due to its ability to extend the coverage range and to overcome blockage. In this letter, we propose a machine learning-based selection approach that adaptively chooses the best forwarding scheme in hybrid multi-hop dense networks. The proposed transmission scheme employs a multi-layer selection where each layer represents one possible relaying case, namely amplify-and-forward, half-detection, or full-detection of the transmitted symbol, or even no-relaying. Moreover, the proposed system dynamically learns the proper forwarding scheme out of these layers for each involved relay to minimize the transmission error rate based on the relay location, and its residual energy. A heuristic approach is proposed for the forwarding scheme selection and transmission power control where a minimum threshold value for the transmission power of each relay node is derived in order to satisfy a target QoS requirement. The results are used for training a decision trees-based prediction model that achieves a remarkable accuracy beyond the 99% for both training and testing patterns.

Optimal 3-D Aerial Relay Placement for Multi-User MIMO Communications

In this paper, an airborne multi-user (MU) multiple-input multiple-output (MIMO) communication system is investigated, consisting of multiple users sources, multiple users destinations, and an aerial platform acting as a decode-and-forward (DF) relay. In this context, a novel three-dimensional (3-D) geometry-based optimization method for the relay location is proposed and expressions for the outage probability are presented. The results highlight the impact of the relay position, power allocation, fading severity, and number of antennas on the system performance.

LDPC-based Joint Source Channel Coding and Decoding Strategies for single relay cooperative communications

This paper investigates new cooperative communication strategies based on Low-Density Parity-Check codes (LDPC) with Joint Source-Channel (JSC) coding and decoding algorithms to efficiently deliver a correlated content to a destination node. The proposed strategies rely on double LDPC codes where the source and the channel coding are similar to standard LDPC operations, and can be mapped on Tanner graphs for message-passing decoding. Three coding strategies are proposed where different LDPC source and channel coding setups are applied at the source node and the relay node. For each transmission strategy, we propose a graph mapping the whole network, over which iterative message-passing decoding is applied, and where the probability of errors in the source–relay link are taken into account. We showed, based on computer simulations, that the proposed strategies can provide substantial improvements compared to equivalent rates point-to-point systems. Simulation results also showed that the system performance depends on the relay position, and that adapting the source and the relay channel coding rates accordingly can enhance the overall system performance for a time-varying network.

A new approach for two-way relaying networks: improving performance by successive interference cancellation, digital network coding and opportunistic relay selection

In this paper, we propose a new approach based on combination of successive interference cancellation (SIC), digital network coding (DNC), and opportunistic relay selection in a two-way cooperative scheme in which two source nodes send simultaneously their packets to each other with a help of multiple relaying nodes, called as SIC–DNC protocol. In the proposed SIC–DNC protocol, the cooperative relays use the SIC technique to decode sequentially the packets from received sum signals, and then encode these packets by the DNC technique. These relays operate in the half-duplex mode, and suffer interference signals from imperfect SIC operations. A best relay is selected by the opportunistic relay selection based on taking maximization of signal-to-interference-plus-noise ratios from a successful decoding relay set to two source nodes in the last time slot. Exact and asymptotic closed-form outage probability expressions are obtained to evaluate the proposed SIC–DNC protocol, and then are verified by performing the Monte Carlo simulations. Our results show performance improvement of the proposed SIC–DNC protocol because of increase of the number of the cooperative relays, decrease of the residual interference signal powers, and respect to optimal relay locations and optimal power allocation coefficients of the near source. In addition, insightful comparisons with a conventional two-way decode-and-forward scheme are provided to prove highlight performances in asymmetric two-way cooperative schemes whereas the proposed SIC–DNC protocol owns better spectrum utilization efficiency. Finally, the simulation results are harvested to valid the exact and asymptotic analysis values.

Performance analysis of cooperative NOMA at intersections for vehicular communications in the presence of interference

Road traffic safety is a crucial issue, and more specifically at road intersections. At the same time, vehicular communications (VCs) are attracting a great attention thanks to their useful safety applications. In this paper, we study the performance of cooperative VCs at intersections, in the presence of interference when the communication system implements a non-orthogonal multiple access (NOMA) scheme. First, we derive the outage probability and the average achievable rate for a scenario involving a source, a relay, and two destinations, when the destinations can be either on the roads or outside the roads. The derivations are extended for K destinations. Closed form outage probability expressions and quasi-closed form average achievable rate expressions are obtained. Both perfect and imperfect successive interference cancellation (SIC) are incorporated into the analysis. We show that the outage probability increases and the average achievable rate decreases when vehicles move toward the intersection. We also compare the performance of VCs at intersections and at highways, and show that the performance of VCs at intersections is worse than at highways. We compare cooperative NOMA with cooperative orthogonal multiple access (OMA) in VCs, and show that average achievable rate NOMA outperforms average achievable rate OMA in terms of outage probability and average achievable rate. We also demonstrate that the benefits of cooperative NOMA over cooperative OMA becomes greater for high data rates. We also investigate the best relay position for the two destinations. Finally, we show that the performance of cooperative NOMA decreases drastically when the system parameters are not chosen carefully. All the analytical results are validated by Monte-Carlo simulations.

On the Coverage Problem in Device-to-Device Relay Networks

The device-to-device (D2D) relay technology is one of the key technologies in 5G networks, and its coverage problem is important as it determines key properties in network management. However, the traditional relay coverage theories (e.g., based on the received signal-to-interference-plus-noise ratio) are not optimal for D2D relay due to the dynamicity in backhaul resources of D2D relays. In this letter, we study the coverage problem in D2D relay networks with theoretical derivation and experimental simulation using stochastic geometry. In particular, we formulate the coverage problem to maximize the overall system downlink rate, and then the domain optimization problem is transformed into a 0–1 integer programming problem. We propose a novel algorithm to obtain the optimal solution by greedily including the best locations into the coverage. Simulation results verify the theoretical solution and show that the optimal coverage is surprisingly in an irregular shape that excludes the D2D relay. The results also obtain the best relay location and show the performance gain than the existing scheme.

Optimal Placement of UAV-Assisted Free-Space Optical Communication Systems With DF Relaying

In this letter, by characterizing source-to-relay and relay-to-destination channel models of the considered unmanned aerial vehicle (UAV)-assisted free-space optical (FSO) relay link, we derive the optimal 3D coordinates of UAV relay as well as optimal optical beam pattern in order to minimize the outage probability. Moreover, we study the impact of physical parameters (such as strength of orientation fluctuations of UAV, height and position of obstacles) on the optimal location of UAV relay.

Residual Transceiver Hardware Impairments on Cooperative NOMA Networks

This paper investigates the impact of residual transceiver hardware impairments (RTHIs) on cooperative non-orthogonal multiple access (NOMA) networks, where generic $\alpha -\mu $ fading channel is considered. To be practical, imperfect channel state information (CSI) and imperfect successive interference cancellation (SIC) are taken into account. More particularly, two representative NOMA scenarios are proposed, namely non-cooperative NOMA and cooperative NOMA. For the non-cooperative NOMA, the base station (BS) directly performs NOMA with all users. For the cooperative NOMA, the BS communicates with NOMA users with the aid of an amplify-and-forward (AF) relay, and the direct links between BS and users are existent. To characterize the performance of the proposed networks, new closed-form and asymptotic expressions for the outage probability (OP), ergodic capacity (EC) and energy efficiency (EE) are derived, respectively. Specifically, we also design the relay location optimization algorithms from the perspectives of minimize the asymptotic OP. For non-cooperative NOMA, it is proved that the OP at high signal-to-noise ratios (SNRs) is a function of threshold, distortion noises, estimation errors and fading parameters, which results in 0 diversity order. In addition, high SNR slopes and high SNR power offsets achieved by users are studied. It is shown that there are rate ceilings for the EC at high SNRs due to estimation error and distortion noise, which cause 0 high SNR slopes and $\infty $ high SNR power offsets . For cooperative NOMA, similar results can be obtained, and it also demonstrates that the outage performance of cooperative NOMA scenario exceeds the non-cooperative NOMA scenario in the high SNR regime.

Wireless Energy Harvesting-Based Relaying: A Finite-SNR Diversity-Multiplexing Tradeoff Perspective

This paper presents an analytical framework to derive the closed-form expressions for diversity-multiplexing tradeoff (DMT) for wireless energy harvesting (WEH) based amplify-and-forward (AF) and decode-and-forward (DF) protocols in finite signal-to-noise (SNR) regime. The results of this investigation suggest that both AF and DF offer similar performance except for few nuances. At low multiplexing gains, DF offers marginally better performance in the low SNR regime, whereas AF performs better in the high SNR scenarios. However, in the higher multiplexing gain regime, though subtle, DF uniformly dominates AF across all SNRs. Furthermore, an analytical study is presented to evaluate the effect of the fraction of time devoted to WEH (time-sharing parameter, $\epsilon $ ) on the finite SNR DMT (f-DMT). In addition, the impact of relay position on the outage performance is also presented. A distinguishing feature of the proposed work is the characterization of WEH-based f-DMT which reveals the complete interplay between the operating SNR and the time-sharing parameter ( $\epsilon $ ), which is of fundamental importance to system designers. Finally, Monte-Carlo simulations are provided to confirm the veracity of analytical solutions.

Relay Placement for Reliable Ranging in Cooperative mm-Wave Systems

We study millimeter wave-based ranging of randomly located terminal nodes (TNs) using fixed relay nodes (RNs) deployed around a central node (CN). This setting may correspond to a disaster-relief scenario where the rescuers require positioning information in the absence of a global positioning system (GPS). We derive the Bayesian Cramer-Rao lower bound (BCRLB) for the TNs range estimation from the CN as well as from the RNs in this network using a stochastic geometry framework. Contrary to existing studies, we take the effect of link-blockages into account while deriving the BCRLB, and thereby present a more accurate bound on the ranging error. For the special case of no blockages, we formulate a convex problem for obtaining the optimal relay positions. Our results provide the operator a guideline for initial deployment planning, in terms of number and location of RNs to be deployed in order to achieve an accurate ranging.

Resource allocation for wireless information and power transfer based on WBAN

In this paper, a simultaneous wireless information and power transfer (SWIPT) system with a relay in wireless body area network (WBAN) is studied, where the relay harvests energy from the radio frequency (RF) signals sent by the access point (AP), then uses RF energy to transmit energy to the user and forward the information to the AP, respectively. Firstly, we propose a planar transmission model based on the time switching (TS) and power splitting (PS) protocols. The sensor nodes are placed on the human torso in this model. In order to explore the system performance, the optimal information throughput for the two protocols is given subject to the energy harvesting and consumption balance. Then, corresponding optimal power splitting and time switching ratios which maximize the information throughputs are obtained. Besides, the effects of the relay position on system performance are also discussed. Finally, while considering the relay transmission power constraint, we solve the dynamic power allocation problem by the Lagrange multiplier iteration method. Numerical results and analysis show that our proposed optimal strategy achieves the optimal throughput. Moreover, the TS protocol has better performance than the PS protocol in dynamic model.

Feasibility and Optimization of 1-TTI-Based Full-Duplex Two-Way Relay System

Maximizing system capacity is one of the major concerns in inband full-duplex (IFD) two-way relay (TWR) system using analog network coding (ANC). This paper compares 1-transmission-time-interval (TTI)-based ANC (1TA) TWR, in which each node operates in IFD mode, with 2-TTI-based ANC (2TA) TWR operating in inband half-duplex mode. System capacity of the 1TA TWR is derived with adverse factor such as direct link interference (DLI). Also, this work proposes an iterative optimal power allocation (OPA) method to maximize the system capacity, which is based on golden section search under total power constraint. Numerical results elucidate that the 1TA TWR based on the OPA outperforms the 2TA TWR in all cases of relay position and DLI.

Novel Fault Detection and Localization Algorithm for Low-Voltage DC Microgrid

Accurate estimation of fault location is highly crucial for swift maintenance and early power restoration. Since faults in dc networks are time critical, this article proposes a new fault detection and localization scheme for a low-voltage direct current (LVdc) microgrid network. Low-resistance faults are detected by observing voltage across the inductor whereas high-resistance ground faults are identified by measuring ground current at the relay location. Thereafter, based on iterative method, fault location is estimated by comparing analytically derived fault current with the measured value of fault current. Genuineness of the suggested technique has been assessed by simulating various internal, external, and simultaneous faults on a typical LVdc microgrid network modeled in power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) environment. The proposed method is capable of detecting and locating both low- and high-resistance dc faults without utilizing remote-end quantities. Subsequently, initial guess has minimal impact on the convergence and accuracy of the proposed algorithm. Comparative evaluation of the proposed technique with other techniques clearly proves its superiority in terms of better discrimination against external faults, rapid detection during internal faults, independency on the network topology, and higher accuracy for fault distance estimation against all types of internal faults.

Security Analysis for Underlay Cognitive Network with Energy-Scavenging Capable Relay over Nakagami-m Fading Channels

This study suggests an energy-scavenging capable unlicensed relay not only to retain communications between an unlicensed sender-recipient pair in underlay cognitive networks but also to secure these communications against eavesdropping of malicious users. Message-securing capability of such a network configuration is assessed through secrecy outage probability (SOP). For this purpose, a precise closed-form formula of the SOP accounting for interference power restriction, Nakagami-m fading, and maximum transmit power restriction is first proposed. Then, the proposed formula is validated by computer simulations. Ultimately, various results are supplied to contrive that the relay position, the time percentage, and the power percentage of the energy-scavenging technique should be appropriately chosen for achieving the best security performance. Moreover, the SOP decreases with lower severity fading level and is constant in the range of high maximum interference power or high maximum transmit power.

Unmanned-aerial-vehicle-assisted cooperative communications for visible light communications-based vehicular networks

We propose and investigate cooperative visible light communications (VLC) enabled vehicular network architecture with an unmanned aerial vehicle (UAV) relay. In the proposed system, a UAV equipped with an onboard photodetector and light-emitting diodes is used as a relay in a vehicular VLC link. The advantage of having a flying UAV relay is its great mobility and ease of deployment. The performance of UAV-assisted cooperative VLC is investigated for amplify and forward and decode and forward protocols with half duplex and full duplex modes. Moreover, location of the UAV relay is optimized in order to maximize the signal-to-noise ratio at the destination vehicle. The active light beam tracking technique is further employed to increase the reliability of the proposed VLC system. Our results reveal that a UAV relay can significantly improve the transmission performance of conventional VLC-based vehicular networks.

Relay selection schemes for Cooperative NOMA (C-NOMA) with simultaneous wireless information and power transfer (SWIPT)

Non-orthogonal multiple access (NOMA) is considered as an important technique to alleviate the spectral scarcity of wireless networks. Cooperative NOMA (C-NOMA) along with simultaneous wireless information and power transfer (SWIPT) pave paths towards energy and spectral efficient communication networks. This paper investigates SWIPT enabled multiple relay C-NOMA network, where dedicated intermediate relays are energy-constrained and harvest energy from the transmitted source signal. New two-stage relay selection (RS) schemes for C-NOMA with fixed power allocation and dynamic power allocation at relay node are proposed. Analytical expressions and asymptotic expressions of outage probability for proposed schemes and partial RS are derived to evaluate the system performance. Simulation results demonstrate that two stage RS provides the maximum performance gain at high SNR regime, while the partial RS is preferable at low SNR. Based on outage probability difference, a hybrid RS scheme which switches between partial and two-stage is introduced. The important insights of analytical results, such as comparative analysis of relay selection schemes, performance gain over SWITP OMA networks, effect of data rates, effect of relay location, and impact of using SWIPT on the outage performance of C-NOMA networks are discussed.

SER and throughput analysis of space–time analog network coded relaying system over shadowed Rician fading channels

This research article presents an innovative approach based on analog network coding (ANC) in conjunction with space time block coding (STBC) which is termed as space time analog network coding (STANC). The STANC investigated as an affective network coding strategy to combat the effects of shadowing and path loss in wireless networks. The another objective of this research work is to evaluate the impact of relay location on system performance in increasing shadowing effect due to increasing tall structure like multistory building in metropolitan area. The performance of the proposed system is analyzed in terms of symbol error rate (SER), STANC gain and ergodic capacity using analytical expressions. Moment generating function approach is used to drive the SER for M-PSK modulated signals. The approximate closed-form expression of ergodic capacity is presented using the derived mean and second moment for STANC based cooperative system. Rician shadowed model is used which efficiently evaluate the effect of shadowing as compared to other fading models given in the literature which is the main advantage of this model. Numerical results signify that the approximated analytical expressions derived can be effectively used for performance improvement under path loss and shadowing effect as compared to simple ANC based system.

Secrecy outage analysis of energy harvesting two‐way relaying networks with friendly jammer

This study investigates two-way relaying where an energy harvesting capable relay exchanges information between two sources. Legitimate information is wire-tapped by an eavesdropper. To intercept wire-tapping, this study exploits a friendly jammer. Secrecy outage analysis of the energy harvesting two-way relaying network with the friendly jammer over Rayleigh fading channels is first proposed in terms of individual secrecy outage probabilities and then validated by computer simulations. Various results demonstrate the efficacy of the jammer in preventing the eavesdropper from stealing the source information and significant impacts of relay location, jammer location, jammer's transmit power, energy conversion efficiency, time switching ratio on the security performance.

Outage analysis of underlay cognitive NOMA system with cooperative full duplex relaying

AbstractThis paper investigates the outage performance of secondary users (SUs) in underlay cognitive radio–based nonorthogonal multiple access (CR‐NOMA) networks. We consider down link scenario for the secondary network, which consists of a secondary transmitter (ST) and two SUs, ie, a near user and far user. The ST uses NOMA signaling to transfer the information to the down link SUs. A dedicated node is used as the full‐duplex decode‐and‐forward (DF) relay for delivering the message to the far‐user. We derive exact expressions for the outage probabilities experienced by the SUs for full duplex (FD)/half duplex (HD)–based CR‐NOMA networks, in independent, nonidentically distributed Rayleigh fading channels. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. We compare the performance of the proposed FD/HD‐based CR‐NOMA networks against that of a CR network, which use conventional orthogonal multiple access (OMA) scheme. We establish that the performance of CR‐NOMA network is better as compared to CR‐OMA networks. We then consider finding the optimal location for the FD relay node that minimizes the outage probability of far‐user. We formulate an optimization problem that is solved using genetic algorithm. Numerical results show that optimized relay location significantly improves the outage performance of the far‐user. The analytical results are validated by extensive simulation studies.