Location Of Relay Node Research Articles

Joint relay and channel selection in relay‐aided anti‐jamming system: A reinforcement learning approach

AbstractIn this article, a joint relay and channel selection problem is investigated in multi‐relay anti‐jamming communication system. Considering the jamming pattern and the relay node (RN) location distribution are unknown, the relay and channel selection problem is formulated as Markov decision processes (MDPs). Different from the existing research on anti‐jamming communication, in this article, the source node (SN) and all RNs are considered as agents who collaboratively learn the environment and make anti‐jamming decisions. A reinforcement‐learning‐based joint relay and channel selection method is proposed to achieve relay‐aided anti‐jamming communication. Specifically, the SN tries to make the optimal selection of relay which is under the least jamming threat, while the RN will access the jamming‐free channels. Various simulation results show that the algorithm can quickly learn the unknown changing pattern of the jamming environment, and make the effective joint relay and channel decisions to obtain high communication throughput which is close to the optimal.

Placement optimisation method for multi‐UAV relay communication

With the popularisation of unmanned aerial vehicle (UAV) technology, relay communication based on multi-UAVs has advantages and application prospects. However, determining the location of UAV relay nodes is a fundamental problem. In particular, when multiple UAVs are required, it is important to design an efficient node placement method that optimises the layout of UAV nodes to minimise the number of required UAVs and provide reliable connectivity for all ground terminals. In this study, the node placement models for multi-UAV relay communication are constructed based on the non-linear constraint optimisation problem for typical application scenarios, and the solving algorithm of the models is proposed based on the smallest enclosing circle and genetic algorithm. Through the new placement method, the authors can locate UAV relay nodes and optimise the network topology with the minimum number of UAVs required. Finally, the implementation process and results are validated by simulation.

DABFS: A robust routing protocol for warning messages dissemination in VANETs

Vehicular ad hoc networks play a pivotal role in the enrichment of transportation systems by making them intelligent and capable of avoiding road accidents. For transmission of warning messages, direction-based Greedy protocols select the next hop based on the current location of relay nodes toward the destination node, which is an efficient approach for uni-directional traffic. However, such protocols experience performance degradation by neglecting the movement directions of nodes in bi-directional traffic where topological changes occur dynamically. This paper pioneers the use of movement direction and relative positions of source and destination nodes to cater to the dynamic nature of bi-directional highway environments for efficient and robust routing of warning messages. A novel routing protocol, namely, Direction Aware Best Forwarder Selection (DABFS), is presented in this paper. DABFS takes into account directions and relative positions of nodes, besides the distance parameter, to determine a node’s movement direction using Hamming distance and forwards warning messages through neighbor and best route discovery. Analytical and simulation results demonstrate that DABFS offers improved throughput and reduced packet loss rate and end-to-end delay, as compared with eminent routing protocols.

Node placement for connected target coverage in wireless sensor networks with dynamic sinks

Target coverage and connectivity are two fundamental and critical issues in wireless sensor networks. The former is for providing sufficient monitoring quality where all points of interest in the network are covered by sensor nodes. The latter is for guaranteeing satisfactory communicating capability where all sensor nodes can connect to at least one sink via nodes (i.e., sensor nodes and relay nodes). Though considerable efforts have been devoted to optimize the placement of sensor nodes and relay nodes under connected target coverage constraint (i.e., guaranteeing both target coverage and connectivity), all of the existing works in this area address only networks with one static sink. In the meanwhile, although there are many works in literature considered the networks with dynamic sinks, none of them studies how to optimize the location of sensor and relay nodes. In this article, we focus on wireless sensor networks with dynamic sinks, which consist of multiple sinks and the sinks’ positions may change periodically, and study how to place a minimum number of nodes for connected target coverage. Specifically, we decompose the problem into two sub-problems. The first one, named as target coverage problem, is to place sensor nodes for covering all targets. The second one, named as network connectivity problem, is for placing relay nodes to connect sensor nodes to the sinks. We first formulate the target coverage problem under an integer linear programming model and present an exact algorithm to determine the optimal solution. We then propose a constant-approximation algorithm based on partitioning and shifting scheme. For the network connectivity problem, we first prove its NP-hardness and then propose two approximation algorithms. The first one exploiting the minimum group Steiner tree to minimize the placed relay nodes, while the second one is a time-efficient algorithm based on clustering and spanning tree approaches. The experiment results show the superiority of our proposed algorithms in terms of both the number of the required nodes and the time complexity.

Secrecy analysis of a cooperative NOMA network using an EH untrusted relay

ABSTRACTIn this paper, a down-link non-orthogonal multiple access (NOMA) system with imperfect successive interference cancellation (SIC) using Energy-Harvesting untrusted relays is investigated. These relaying nodes use in this study use a power-switching architecture to harvest energy from the sources signals and apply an amplify-and-forward protocol to forward the signals. In addition, transmit jamming or artificial noise, is generated by a source node to improve the security of the system and protect confidential source information from untrusted relays. Likewise, three relaying selection strategies are employed to examine the secrecy performance of the proposed system. In order to evaluate the performance evaluation of the proposed system, closed-form expressions of the Secrecy Outage Probability (SOP) are studied over Rayleigh fading channels and a Monte Carlo simulation is used to confirm the analytical results. Furthermore, we study the effects of various parameters, such as power allocation factors, relay node selection, the number of relays, energy harvesting efficiency and the location of relay nodes on the secure outage performances for two users of NOMA system and conventional orthogonal multiple access (OMA). These results show that NOMA offers the better security performance with multiple users.

Minimum-Cost Heterogeneous Node Placement in Wireless Sensor Networks

The operational cost-effectiveness of wireless sensor networks depends on the placement of heterogeneous nodes: base stations, sensor nodes, and relay nodes. To achieve the global optimality of minimum-cost heterogeneous node placement, we find the locations of base stations, sensor nodes, and relay nodes, simultaneously. The objective is to minimize the sum of node production and placement costs and transmission outage probabilities in the routing tree. First, we formulate this minimum-cost heterogeneous node placement problem as a new NP-hard Steiner tree problem. Then, to solve this problem for both small and large instances, we propose an exponential-time exact algorithm, a polynomial-time heuristic algorithm, and several post-processing algorithms. On a personal computer, our exact algorithm is sufficiently fast to produce optimal solutions for small instances with dozens of vertices, while our heuristic and post-processing algorithms can, respectively, produce and improve suboptimal solutions for large instances with 100 000 vertices and 1 000 000 edges within 6 s. We also compare the heuristic and optimal solutions for small instances with dozens of vertices and show that the ratios between the respective solution costs are generally below 1.35, and our post-processing algorithms can improve this number to 1.1. This indicates that our heuristic and post-processing algorithms are likely to produce near-optimal solutions in practice and are useful for minimum-cost heterogeneous node placement when computational resources are scarce.

Performance analysis of downlink NOMA–EH relaying network in the presence of residual transmit RF hardware impairments

In this paper, we investigate the effects of residual-transmit radio-frequency impairments on the downlink non-orthogonal multiple access system with perfect successive interference cancellation using an energy-harvesting (EH) relay in which nodes in the network are equipped with a single antenna. The source node communicates with two users with the help of the amplify-and-forward EH relay node. In addition, both the power-splitting relaying (PSR) and time-switching relaying (TSR) protocols are examined. To evaluate the performance of the proposed system, closed-form expressions of the outage performance and the available throughput are derived over Rayleigh fading channels. Moreover, the accuracy of analytical results is verified by a Monte Carlo simulation. The results show the effects of various parameters, such as power allocation factors, the relay node location, data rate, transmit hardware impairment level, and power allocation factors on the outage performance ($${\mathcal {OP}}$$) and throughput with two users for both PSR and TSR architectures in the presence of hardware impairments. Furthermore, these results are compared with performance of orthogonal multiple access (OMA) EH relaying system.

Outage Performance of Energy Harvesting DF Relaying NOMA Networks

In this paper, we investigate energy harvesting decode-and-forward relaying non-orthogonal multiple access (NOMA) networks. We study two cases of single relay and multiple relays with partial relay selection strategy. Specifically, one source node wishes to transmit two symbols to two respective destinations directly and via the help of one selected intermediate energy constraint relay node, and the NOMA technique is applied in the transmission of both hops (from source to relay and from relay to destinations). For performance evaluation, we derive the closed-form expressions for the outage probability (OP) at D 1 and D 2 with both cases of single and multiple relays. Our analysis is substantiated via Monte Carlo simulation. The effect of several parameters, such as power allocation factors in both transmissions in two hops, power splitting ratio, energy harvesting efficiency, and the location of relay nodes to the outage performances at the two destinations is investigated.

Multiple Criteria Relay Selection Scheme in Cooperative Communication Networks

This paper considers a wireless cooperative network with a base station (central unit) and many subscribers (users) in which the subscribers have the ability to relay information for each other to improve the overall network performance. In future wireless communication networks where subscribers are intellectual and pursue various objectives, they will not help relay information for others. This means that the viability of cooperative communication networks largely depends on the willingness of users to help. The reputation based schemes solved this problem by stimulating the users to cooperate with others. Besides, the average achievable rate at the destination node in a relay based network highly depends on the relay node location. Therefore, for a relay selection scheme, the choices of relay location, and the reputation of each user as well as signal-to-noise ratio, which is the main criterion for relay selection schemes, are important selection parameters. This paper proposes a novel multiple criteria relay selection scheme with a low implementation complexity. The proposed scheme incorporates reputation, SNR and location of the users in a highest-level design that not only selects the best relay node for each source-destination pair, but also assigns weight efficiently for each criterion. A simple and efficient optimization tool based on multiple criteria decision making method is employed to solve our formulated problem. In addition, a novel information theoretic measure, which effectively measures dissimilarity between candidate relay nodes and ideal solutions, is also investigated. Since the proposed scheme determines the potential relay nodes in order of their superiority based on the predetermined criteria, it can be utilized in multiple relay selection schemes in wireless relay networks and also in the indirect reciprocity game methods. Finally, the numerical results are provided to illustrate the comparisons between different typical experiments. To best of our knowledge, no prior work has studied the process of relay selection from this point of view.

Analysis of battery energy consumption in relay wireless sensor networks

In this study, the authors develop a realistic packet-based battery energy consumption model that combines the transmitting signal and circuit power consumption in relay wireless sensor networks (WSNs). In their model, two types of packet assembly approaches have been considered: namely, the time-based and length-based packet assembly approaches. A performance analysis is used to determine whether relay transmission is preferable to direct transmission. The results show that the path selection and the amount of battery energy consumption in a relay WSNs depend on the location of the relay node, the number of pulses, and the distance between the source node and the destination node.

Relay Placement in Wireless Networks: Minimizing Communication Cost

Given $n$ source nodes and $k$ relay nodes, we model the optimal relay topology problem allowing for simultaneous optimization of the relay node locations and traffic through the network, so that the overall number of packet retransmissions is minimized. We argue that state-of-the-art models and algorithms for relay placement in wireless networks do not reflect salient characteristics of the optimal relays topology and lead to suboptimal solutions. We do not constrain the position of relays to a finite set of discrete points, as the latter may not be feasible in practical networks. In this case, we show that just listing a set of feasible sites for the relays is already at least $APX$ -hard. Exploiting convexity in a special case of the network communication cost function, we give an optimal algorithm for the relay placement problem. However, the algorithm is exponential on the number of nodes in the network. We suggest a practical heuristic algorithm for relay placement: RePlace . We compare RePlace numerically to the optimal algorithm and show that RePlace achieves the optimal or almost optimal solutions. We implement RePlace in the full network stack simulator JiST/SWANS. The relay topologies generated by RePlace eliminate overhead communication cost almost entirely.

Relay selection scheme for amplify‐and‐forward cooperative communication system with artificial noise

AbstractCooperative communication can improve the performance of communication system under multi‐path fading conditions by relaying. If there is an eavesdropper in communication system, the secrecy capacity of the system will decrease. Sending artificial noise can enhance the secrecy capacity of communication system. A novel scheme combining relay selection with artificial noise for amplify‐and‐forward cooperative communication system in the presence of an eavesdropper is designed, which seeks the relay with the highest signal‐to‐noise ratio. The location of optimal relay node is found out in this scheme by the relay selection scheme based on distance. However, there is not always a relay node at the optimal location. If there is no relay at the optimal location, then the suboptimal relay node can be found out by drawing circles centered on the optimal location. After that, the optimal relay forwards the signals and sends the artificial noise in the null space of the legitimate channel to confuse the eavesdropper. A close‐form expression for maximizing the secrecy capacity is derived, and it is used as the objective function to select the optimal or suboptimal relay node. The algorithm complexity of the relay selection scheme based on distance is lower than that of the relay selection scheme based on instantaneous channel states. Moreover, it can achieve higher secrecy capacity compared with the scheme without artificial noise. Simulations are conducted to validate the theoretical analyses, and the results demonstrate the validity and reliable security of the scheme. Copyright © 2016 John Wiley & Sons, Ltd.

Stochastic Geometry Modeling and System-Level Analysis & Optimization of Relay-Aided Downlink Cellular Networks

In this paper, a tractable mathematical framework for the analysis and optimization of two-hop relay-aided cellular networks is introduced. The proposed approach leverages stochastic geometry for system-level analysis, by modeling the locations of base stations, relay nodes and mobile terminals as points of homogeneous Poisson point processes. A flexible cell association and relay-aided transmission protocol based on the best biased average received power are considered. Computationally tractable integrals and closed-form expressions for coverage and rate are provided, and the performance trends of relay-aided cellular networks are identified. It is shown that coverage and rate highly depend on the path-loss exponents of one- and two-hop links. In the interference-limited regime, in particular, it is shown that, if the system is not adequately designed, the presence of relay nodes may provide negligible performance gains. By capitalizing on the proposed mathematical framework, a system-level and interference-aware optimization criterion of the bias coefficients is proposed. Numerical results confirm the effectiveness of the proposed system-level optimization to enhance the coverage probability in the interference-limited regime. The presence of relays, on the other hand, is shown to have a limited impact on average/coverage rate under the same assumptions.

Route maintenance and Scalability improvement of DSR, based on Relay node identification after locating Link-failure over MANET

In Dynamic Source Routing, each source determines the route to be used in transmitting its packets to destination. Route Discovery determines the optimum path for a transmission between a given source and destination. Route Maintenance ensures that the transmission path remains optimum and loop-free as network conditions change, even if this requires changing the route during a transmission. Many protocols were proposed to maintain route from high data loss and transition delay due to frequent link failure but doesn't take the decision on basis of location of failure link in source route and also doesn't take advantages of Relay node identification in partitioned source route. From this point of view in our paper we propose an algorithm with the help of local link repairing and improvement strategy based on the location of link failure inside source route over mobile ad- hoc network. Through this paper we introduce our proposed approach based on DSR, which takes decision on the basis of the location of Relay node(where link failure is detected) in source route.We think our new approach can be able to improve packet salvaging, packet delivery ratio and reducing end to end delay to improve the scalability of Mobile Ad-hoc network.

Effective sensor deployment based on field information coverage in precision agriculture

AbstractCoverage is an importance issue in wireless sensor networks. In this work, we first propose a novel notion of information coverage, which refers to the coverage efficiency of field information covered by deployed sensor nodes. On the basis of information coverage, we consider an optimization problem of how to partition the given field into multiple parcels and to deploy sensor nodes in some selected parcels such that the field information covered by the deployed sensor nodes meets the requirement. First, we develop two effective polynomial‐time algorithms to determine the deployed locations of source nodes for information 1‐coverage and q‐coverage of the field, respectively, without consideration of communication, where information q‐coverage implies that the field information in terms of information point is covered by at least q source nodes. Also, we prove the upper bound in the theoretical for the approximate solution derived by our proposed method. Second, another polynomial‐time algorithm is presented for deriving the deployed locations of relay nodes. In the theoretical, this proposed algorithm can achieve the minimized number of relay nodes. Further, the related information 1‐coverage algorithms are applied in our wireless sensor network‐based automatic irrigation project in precision agriculture. Experimental results show the major trade‐offs of impact factors in sensor deployment and significant performance improvements achieved by our proposed method. Copyright © 2013 John Wiley & Sons, Ltd.

Optimal relay node placement in delay constrained wireless sensor network design

The Delay Constrained Relay Node Placement Problem (DCRNPP) frequently arises in the Wireless Sensor Network (WSN) design. In WSN, Sensor Nodes are placed across a target geographical region to detect relevant signals. These signals are communicated to a central location, known as the Base Station, for further processing. The DCRNPP aims to place the minimum number of additional Relay Nodes at a subset of Candidate Relay Node locations in such a manner that signals from various Sensor Nodes can be communicated to the Base Station within a pre-specified delay bound. In this paper, we study the structure of the projection polyhedron of the problem and develop valid inequalities in form of the node-cut inequalities. We also derive conditions under which these inequalities are facet defining for the projection polyhedron. We formulate a branch-and-cut algorithm, based upon the projection formulation, to solve DCRNPP optimally. A Lagrangian relaxation based heuristic is used to generate a good initial solution for the problem that is used as an initial incumbent solution in the branch-and-cut approach. Computational results are reported on several randomly generated instances to demonstrate the efficacy of the proposed algorithm.

A Grid-Based Relay Node Placement Algorithm in Wireless Sensor Networks

The relay node placement in wireless sensor networks is usually constrained by physical factors, while most of present relay node placement approaches are unconstrained. To solve the problem, the paper presents a constrained relay node placement algorithm. Based on grid routing mechanism, the algorithm determines the grid intersections as candidates for the relay node locations, and places as fewer relay nodes as possible to assure the network connectivity. Consideration must be given to both the number of relay nodes and energy efficient, the paper uses the greedy norm and constrains to place relay nodes. By the analysis and study of the experiments, the performance of the proposed algorithm is more superior to the algorithm without constrains.

Time of arrival-based location estimation for cooperativerelay networks

Cooperative communications is a technique to create a virtual antenna array using several distributed single antenna nodes in the system. It helps in increasing the area of coverage without the need of increased transmission power. As the destination receives multiple copies of the source's signal, it also improves the diversity order. The performance of cooperative networks has been thoroughly investigated in the past for various system models, protocols, forwarding techniques and fading environments. Location estimation is another crucial process in cooperative relay networks, as it is for the other types of wireless communications networks. For instance, the range and location information can be used for network authentication, localization or cluster forming in cooperative networks. However, to the best of our knowledge, there is no study in the literature that addresses the location estimation problem in cooperative relay networks. In this study, we investigate the performance of a cooperative relay network performing location estimation through time of arrival (TOA). We derive Cramer-Rao lower bound (CRLB) for the location estimates made using the relay network. The analysis is extended to obtain average CRLB considering the signal fluctuations in both relay and direct links. The effects of the channel fading of both relay and direct links and amplification factor and location of the relay node on average CRLB are investigated. Simulation results show that the channel fading of both relay and direct links and amplification factor and location of relay node affect the accuracy of TOA-based location estimation.

Approximation algorithm for minimizing relay node placement in wireless sensor networks

To eliminate the routing load unbalance among sensor nodes, one approach is to deploy a small number of powerful relay nodes acting as routing nodes in wireless sensor networks, the major optimization objective of which is to minimize the number of relay nodes required. In this paper, we prove that the relay node placement problem in a bounded plane is a P problem, but its computational complexity in general case is quite great. From the geometric cover feature of the relay node placement problem, an O(n2 log n) time greedy approximation algorithm is proposed, where n is the number of sensor nodes. Particularly, at each stage of this algorithm’s iterative process, we first select a critical node from uncovered sensor nodes, and then determine the location of relay node based on the principle of preferring to cover the sensor node closer to the critical node, so as to prevent the emergence of isolated node. Experiment results indicate that our proposed algorithm can generate a near optimum feasible relay node deployment in a very short time, and it outperforms existing algorithms in terms of both the size of relay node deployment and the execution time.

Connectivity, Coverage and Placement in Wireless Sensor Networks

Wireless communication between sensors allows the formation of flexible sensor networks, which can be deployed rapidly over wide or inaccessible areas. However, the need to gather data from all sensors in the network imposes constraints on the distances between sensors. This survey describes the state of the art in techniques for determining the minimum density and optimal locations of relay nodes and ordinary sensors to ensure connectivity, subject to various degrees of uncertainty in the locations of the nodes.