Optimal Relay Placement Research Articles

An Efficent Coverage and Maximization of Network Lifetime in WSN Through Metaheuristics

<span>In wireless sensor networks (WSNs), energy, connectivity, and coverage are the three most important constraints for guaranteed data forwarding from every sensor node to the base station. Due to continuous sensing and transmission tasks, the sensor nodes deplete more quickly and hence they seek the help of data forwarding nodes, called relay nodes. However, for a given set of sensor nodes, finding optimal locations to place relay nodes is a very challenging problem. Moreover, from the earlier studies, the relay node placement is defined as a non-deterministic polynomial tree hard (NP-Hard) problem. To solve this problem, we propose a multi-objective firefly algorithm-based relay node placement (MOFF-RNP) to deploy an optimal number of relay nodes while considering connectivity, coverage, and energy constraints. To achieve network lifetime, this work adopted energy harvesting capabilities to the sensor nodes and backup relay strategy such that every sensor node is always connected to at least one relay to forward the data. The optimal relay placement is formulated as an objective function and MOFF is applied to achieve a better solution. Extensive Simulations are carried out over the proposed model to validate the performance and the obtained results are compared with state-of-art methods)</span>

Global Optimization of Relay Placement for Seafloor Optical Wireless Networks

Optical wireless communication is a promising technology for underwater broadband access networks, which are particularly important for high-resolution environmental monitoring applications. This paper focuses on a deep-sea monitoring system, where an underwater optical wireless network is deployed on the seafloor. We model such an optical wireless network as a general queueing network and formulate an optimal relay placement problem, whose objective is to maximize the stability region of the whole system, i.e., the supremum of the traffic volume that the network is capable of accommodating. The formulated optimization problem is further shown to be non-convex, so that its global optimization is non-trivial. In this paper, we develop a global optimization method for this problem and we provide an efficient algorithm to compute an optimal solution. Through numerical evaluations, we show that a significant performance gain can be obtained by using the derived optimal solution.

WITHDRAWN: On the relay node placement in WSNs for lifetime maximization through metaheuristics

Abstract In Wireless Sensor Networks (WSNs), energy, connectivity and coverage are the three most important constraints for guaranteed data forwarding from every sensor node to base station. Due to a continuous sensing and transmission tasks, the sensor nodes depletes more quickly and hence they seeks the help of data forwarding nodes, called as relay nodes. However, for a given a set of sensor nodes, finding optimal locations to place relay nodes is very challenging problem. Moreover, from the earlier studies, the relay node placement is defined as NP-Hard problem. To solve this problem, we propose a Multi-Objective Firefly Algorithm Based Relay Node Placement (MOFF-RNP) to deploy optimal number of relay nodes, while considering connectivity, coverage and energy constraints. To achieve network lifetime, this work adopted energy harvesting capabilities to the senor nodes and back up relay strategy such that every senor node is always connected to at least one relay to forward the data. The optimal relay placement is formulated as objective function and MOFF is applied to achieve a better solution. Extensive Simulations are carried out over the proposed model to validate the performance and the obtained results are compared with state-of-art methods.

Optimal Relay Placement in Magnetic Induction-Based Internet of Underwater Things

The advances in developing the Internet of Underwater Things (IoUT) can lead to numerous applications, namely, environmental monitoring, underwater navigation, and surveillance. Magnetic Induction (MI) is a promising communication solution for IoUT networks. In this article, we focus on a deep-ocean monitoring network, where the underwater relays communicate using MI induction. Placement of the relays in such a system is an exciting and challenging task. Therefore, we propose an optimal relay placement solution for relays in MI-based IoUT networks to improve network throughput. First, we formulate the relay placement problem as a non-convex optimization problem. Then, we propose a global optimization technique based on Reverse Convex Programming (RCP) to solve the non-convex function. Finally, we compare the results of the proposed scheme with the uniform deployment to show its effectiveness.

Performance Characterization of Underwater Visible Light Communication

In this paper, we investigate the performance limits of underwater visible light communication (UVLC) systems. We first develop a closed-form path loss expression as a function of transceiver parameters and water type. We then utilize this new expression to determine the maximum achievable link distance for UVLC systems in pure sea, clear ocean, coastal water, and harbor water. Our results demonstrate that the maximum achievable distance is limited to a few tens of meters. This necessitates the deployment of relay-assisted UVLC systems to extend the transmission range. We consider both detect-and-forward and amplify-and-forward relaying. For each relaying method, we first consider a dual-hop UVLC system and determine optimal relay placement to minimize the bit error rate (BER). Then, we consider a multi-hop system with equidistant relays and determine the maximum achievable distance for a given number of hops to satisfy a targeted end-to-end BER.

Amplify-and-Forward Strategy Using MRC Reception Over FSO Channels with Pointing Errors

Free-space optical (FSO) systems offer ultrahigh data rates for a number of terrestrial applications. This paper presents what we believe is the first characterization of average bit error rate (BER) for a cooperative FSO system that uses channel side information-assisted amplify- and-forward (AF) relaying when line-of-sight (LOS) is available. This paper uses maximum ratio combining reception at the destination node to maximize the output signal-to-noise ratio under pointing error effects. An asymptotic closed-form expression for the BER is obtained over gamma–gamma fading channels with pointing errors. The developed asymptotic expression is used to analyze the diversity order gain in relation to the direct path link. The maximum diversity order is determined to be βSD + min(βSR, βRD), where βSD, βSR, and βRD are atmospheric turbulence parameters corresponding to the source–destination, source-relay, and relay-destination links, respectively. Moreover, optimal relay placement, which plays an important role in the performance, is derived by taking full advantage of asymptotic expressions without the need to use optimization methods. Obtained results corroborate that a higher diversity order gain and, hence, a better BER performance, is achieved compared to the direct path link and equivalent AF dual-hop transmissions.

Two-tiered relay node placement for WSN-based home health monitoring system

Motivated by the needs of health monitoring at home (or a senior center) using a sensor network system, we study the problem of how to place the relay nodes so that the data collection and localization requirements of the monitoring system can be satisfied. By exploiting the inherent nature of the problem, we model it as finding a minimum connected k-dominating (k ≥ 3) set. Instead of using an idealistic disk radio model, we explicitly take into account the obstacles’ effect on the radio propagation in an indoor environment. We prove that the problem is NP-hard and propose an efficient greedy algorithm ORPA (Optimal Relay Placement Algorithm) to compute in polynomial time the best locations to place the relays. Results of extensive simulations have shown that by using our proposed algorithm ORPA, the number of relays required can be substantially reduced in comparison to the random placement and two-stage placement strategies. We also study the impact of the transmission power and the grid size on the algorithm and system performance. The result and method presented in the paper is useful to today’s indoor deployment of practical WSN-based monitoring system and to ensure network connectivity with minimal relay nodes.

Optimal relay placement for lifetime maximization in wireless underground sensor networks

Because of highly lossy underground channels and the difficulty in recharging the buried sensor nodes (SNs), power conservation is a primary objective in the design of wireless underground sensor networks (WUSNs). One promising approach to prolonging the lifetimes of WUSNs is to deploy aboveground relay nodes (RNs) to relay the traffic. However, there are several challenges. First, the candidate locations of RNs are affected by the terrestrial environment. Second, signal attenuation is complex because of the multimedium propagation. Third, the optimal placement problem has to be considered in a three-dimensional space. Finally, load balancing among RNs is required to ensure that there is no overloading or exhausting of a single node. In this paper, the RN placement problem in WUSNs is modeled and formulated for the first time; the goal is to deploy a limited number of RNs to maximize the lifetimes of WUSNs under system constraints, such as locations, load balancing, network topology, and a practical channel model. Furthermore, the problem is reformulated by introducing an extra decision vector to transform the original constraints into linear constraints, and then, a two-phase method is presented to solve the problem efficiently. Extensive simulations are carried out to evaluate the performance of the proposed method.

Relay Placement for Coverage Extension in Cellular Wireless Networks Under Composite Fading Model

In relay-assisted cellular networks, mobile stations are connected to base station through two or more single-hop communication links, where the intermediate nodes act as relay stations (RSs). The focus of this paper is on two-hop relay assisted cellular networks, where optimal relay placement is a crucial issue for achieving maximum extension of the cell coverage. However, the location of RS has significant impact on signal-to-interference plus noise ratio (i.e., SINR) and outage probability experienced on the access and backhaul links. Moreover, the frequency re-use factor also has significant influence on the SINR. In this paper, we develop analytical models for computing the SINR and outage probability performance of a two-hop relay assisted cellular network for both downlink (DL) as well as uplink (UL) transmission scenarios, considering the impact of path loss, shadowing, Nakagami fading and co-channel interference. We then investigate optimal placement of RS while satisfying the required criterion on probability of correct decoding, initially by considering the DL scenario alone and then by considering both DL and UL scenarios jointly. Through extensive evaluations, we report the impact of realistic propagation models on outage probability, optimal relay position and the cell coverage radius. Further, the model can be used to find the impact of co-channel re-use factor on optimal relay positioning in two-hop cellular networks.

Optimal Location of Energy Efficient DF Relay Node in $$\varvec{\kappa}$$ κ – $$\varvec{\mu }$$ μ Fading Channel

We investigate the optimal location of an adaptive decode and forward relay operating over a $$\kappa$$ – $$\mu$$ fading channel. The $$\kappa$$ – $$\mu$$ statistics provides a generalized line-of-sight propagation model which includes fading models like Rayleigh, Nakagami, Rician as special cases. We restrict our analysis to collinear relay placement, i.e. the relay node $$(R_n)$$ is on the same straight line between the source node $$(S_n)$$ and the destination node $$(D_n)$$ . In the non-cooperative mode, $$D_n$$ accepts only the two-hop transmission via $$R_n$$ and discards any direct signal that may be available from $$S_n$$ . On the other hand, in the cooperative mode, $$D_n$$ accepts both the replicas and combine them following either selection combining (SC) or maximum ratio combining (MRC). It is interesting to see that such cooperation does not always lead to energy saving, especially for small $$S_n-D_n$$ separation. Also, worth mentioning the fact that MRC may not be optimal from the energy efficiency perspective, and SC can outperform MRC under certain channel conditions. In our paper, we also studied how parameters like spectral efficiency (R), path loss exponent (n), and fading parameters ( $$\kappa ,\mu$$ ) affect the optimal relay placement location.

Optimization of Resource Allocation in Multihop HARQ Relay Networks with a Delay Constraint

By minimizing the outage probability, optimization is carried out in this paper to find joint optimal power allocation (OPA) and relay placement (ORP) for multihop relay networks adopting Hybrid Automatic Repeat reQuest (HARQ). Different from previous works, the joint OPA and ORP is analysed under generalized fading channels with the constraint on total transmit power, end-to-end relaying distance and maximum transmission number (delay). The simulation results demonstrate that for different fixed number of nodes and fading models, there are preferred deployments depending on path loss exponent and power retransmission strategy. By employing multiple retransmission round which can improve the reliability and energy efficiency without significant overhead, the end-to-end outage probability is no longer bounded by that of the weaker hop, i.e., the hop with a poor channel condition. The proposed strategy provides a dramatic improvement for the end-to-end outage probability by compensating the channel difference.

Optimal relay placement in multi-hop wireless networks

Relay node placement in wireless environments is a research topic recurrently studied in the specialized literature. A variety of network performance goals, such as coverage, data rate and network lifetime, are considered as criteria to lead the placement of the nodes. In this work, a new relay placement approach to maximize network connectivity in a multi-hop wireless network is presented. Here, connectivity is defined as a combination of inter-node reachability and network throughput. The nodes are placed following a two-step procedure: (i) initial distribution, and (ii) solution selection. Additionally, a third stage for placement optimization is optionally proposed to maximize throughput. This tries to be a general approach for placement, and several initialization, selection and optimization algorithms can be used in each of the steps. For experimentation purposes, a leave-one-out selection procedure and a PSO related optimization algorithm are employed and evaluated for second and third stages, respectively. Other node placement solutions available in the literature are compared with the proposed one in realistic simulated scenarios. The results obtained through the properly devised experiments show the improvements achieved by the proposed approach.

Relay Placement for FSO Multihop DF Systems With Link Obstacles and Infeasible Regions

Optimal relay placement is studied for free-space optical multihop communication with link obstacles and infeasible regions. An optimal relay placement scheme is proposed to achieve the lowest outage probability, enable the links to bypass obstacles of various geometric shapes, and place the relay nodes in specified available regions. When the number of relay nodes is large, the searching space can grow exponentially, and thus, a grouping optimization technique is proposed to reduce the searching time. We numerically demonstrate that the grouping optimization can provide suboptimal solutions close to the optimal solutions, but the average searching time linearly grows with the number of relay nodes. Two useful theorems are presented to reveal insights into the optimal relay locations. Simulation results show that our proposed optimization framework can effectively provide desirable solution to the problem of optimal relay nodes placement.

Optimal Relay Placement in Two-Hop RF Energy Transfer

Recently, wireless radio frequency energy transfer (RFET) has emerged as an effective technology for prolonging lifetime of the energy-limited wireless sensor networks. However, low RFET efficiency is still a fundamental bottleneck in its widespread usage. Multi-hop RF energy transfer (MHET) can improve the RFET efficiency by deploying relay nodes that scavenge the dispersed energy and transfer it to the nearby sensor node. The efficiency of MHET is strongly influenced by the relay node's placement. To maximize the RFET efficiency for a two-hop scenario, in this paper a novel optimization model is proposed to determine the optimal relay placement (ORP) on an Euclidean x-y plane. Nontrivial tradeoff between the energy scavenged at the relay versus the effective energy delivered by the relay to the target node is investigated. Due to the nonconvex and highly nonlinear nature of the optimization problem, an α-based branch and bound algorithm has been used. The proposed optimization model is further extended by incorporating distributed beamforming to enhance the RFET efficiency. Numerical results illustrate that the proposed algorithm provides convergence to the ϵ-global optimal solution in a few iterations, and ORP provides significant energy saving over arbitrary relay positions for commercial RF energy harvesting systems.

Frequency Selection and Relay Placement for Energy Efficiency in Underwater Acoustic Networks

When planning the deployment of an underwater network, the frequency-dependent nature of the underwater acoustic channel has a significant impact on network performance. The quality of acoustic communication in the underwater medium is heavily dependent on the choice of frequency and link length. In this paper, we consider the problems of choosing the proper frequency and node locations for minimizing energy consumption in the network. First, we look at the single frequency that minimizes the transmission power for a network with links of varying lengths. We propose approximate models for this frequency for cases when the link lengths are known exactly and when only probabilistic knowledge of the link lengths is available. Second, to better understand the importance of the actual locations of nodes, we study the problem of relay placement in a multihop line network. We demonstrate that utilizing different frequencies has an impact on the optimal relay placement, and we provide conditions for which the optimal placement is equidistant on the line. Finally, we solve the problem of jointly optimizing the relay placement and the single-frequency choice for a line network. To validate our results, we test our models using simulations of network deployment, and we test our optimal relay placement strategy for a variety of underwater channel settings.

Impact of Propagation Environment on Energy-Efficient Relay Placement: Model and Performance Analysis

The performance of a relay-based cellular network is greatly affected by the relay location within a cell. Existing results for optimal relay placement do not reflect how the radio propagation environment and choice of the coding scheme can impact system performance. In this paper, we analyze the impact on relaying performance of node distances, relay height and line-of-sight conditions for both uplink and downlink transmissions, using several relay coding schemes. Our first objective is to propose a geometrical model for energy-efficient relay placement that requires only a small number of characteristic distances. Our second objective is to estimate the maximum cell coverage of a relay-aided cell given power constraints, and conversely, the averaged energy consumption given a cell radius. We show that the practical full decode-forward scheme performs close to the energy-optimized partial decode-forward scheme when the relay is ideally located. However, away from this optimum relay location, performance rapidly degrades and more advanced coding scheme, such as partial decode-forward, is needed to maintain good performance and allow more freedom in the relay placement. Finally, we define a trade-off between cell coverage and energy efficiency, and show that there exists a relay location for which increasing the cell coverage has a minimal impact on the average energy consumed per unit area.

Optimization of relay placement and power allocation for decode-and-forward cooperative relaying over correlated shadowed fading channels

In this paper, we investigate the relay placement and power allocation for decode-and-forward (DF) cooperative relaying over correlated lognormal shadowed Rayleigh fading channels. Assuming that maximum-ratio combining is performed at the destination, we first derive an upper bound of symbol error rate (SER) with M-phase-shift keying (PSK) modulation. Then, three optimization problems are formulated to minimize the obtained SER upper bound, namely optimal relay placement with fixed power allocation, optimal power allocation with fixed relay location, and joint optimization of relay placement and power allocation. It is shown by the analytical results that the correlation coefficients and the standard deviations of shadowing have significant impacts on the optimal relay placement and power allocation. The simulation results validate our analysis and show that the SER upper bound is asymptotically tight in the high signal-to-noise ratio (SNR) regime.

Optimal Relay Placement in Cellular Networks

In this paper, we address the problem of optimally placing relay nodes in a cellular network with the aim of maximizing cell capacity. In order to accurately model interference, we use a dynamic framework, in which users arrive at random time instants and locations, download a file and leave the system. A fixed point equation is solved to account for the interactions between stations. We also propose an extension of a fluid model to relay based cellular networks. This allows us to obtain quick approximations of the Signal to Interference plus Noise Ratio (SINR) that are very close to 3GPP LTE-A guideline results in terms of SINR distribution. We then use these formulas to develop a dedicated Simulated Annealing (SA) algorithm, which adapts dynamically the temperature to energy variations and uses a combination of coarse and fine grids to accelerate the search for an optimized solution. Simulations results are provided for both in-band and out-of-band relays. They show how relays should be placed in a cell in order to increase the capacity in case of uniform and non-uniform traffic. The crucial impact of the backhaul link is analyzed for in-band relays. Insights are given on the influence of shadowing.

Understanding the Information Propagation Speed in Multihop Cognitive Radio Networks

Information propagation speed (IPS) in a multihop cognitive radio network (CRN) is an important factor that affects the network's delay performance and needs to be considered in network planning and routing protocol design. The impact of primary user (PU) activities on IPS makes the problem of analyzing IPS in multihop CRNs very challenging and, hence, unsolved in existing literature. In this paper, we fill this technical void. We establish models of IPS in multihop CRNs and compute how to maximize IPS in two cases. The first case, named the maximum network IPS, maximizes IPS across a network topology over an infinite plane. The second case, named the maximum flow IPS, maximizes the IPS between a given pair of source and destination nodes separated by a fixed distance. We reveal that both maximum IPSs are determined by the PU activity level and the placement of secondary user (SU) relay nodes. We design optimal relay placement strategies in CRNs to maximize these two IPSs under different PU activity levels. The correctness of our analytical results is validated by simulations and numerical experiments.

An Efficient Relay Node Placement Scheme for Two-Way MIMO Multi-Hop Networks in Practical Indoor Environments

Relay deployment has been gaining attention for network designers. Recently, MIMO Two-way Multi-hop Network (M2WMN) where all links share the same frequency is introduced as a relaying scheme which achieves higher spectral efficiency than other conventional multi-hop schemes. A power control strategy for M2WMN has been proposed to alleviate the frequency-sharing interference problem which degrades the scheme's performance. However, for ease of analysis, the past studies on M2WMN just theoretically assumed Rayleigh fading model for all links of the network. This assumption is far from reality where the channels of different links might experience different pathloss conditions including shadowing. This paper conducts 3D ray-tracing simulation in a U-shaped corridor environment to attain practical propagation channels. Based on the channel data, this paper studies the performance of different multi-hop schemes and investigates an open problem of choosing optimal relay placement which can maximize the performance of M2WMN in real environments. Our results show that without power control, the optimal locations are where adjacent nodes are both in Line-of-Sight (LOS). Interestingly, the optimal locations are no more LOS environments when power control is applied. In addition, this paper also proposes a sub-optimal relay placement search algorithm relaxing the complexity of exhaustive search.