Relay Location Research Articles

Outage Probability Analysis and Optimization of Cognitive Full-Duplex Relay Networks

This paper investigates the outage probability performance of the secondary user in a two-hop underlay cognitive full-duplex relay network. To improve the outage performance of the secondary user, we investigate optimal power allocation (OPA) for the secondary network, i.e., finding the optimal transmit power at the source and relay nodes in the secondary network that minimizes the outage probability. We derive analytical expressions for the optimal transmission power for the source and relay nodes by considering multiple power constraints, viz., constraint on total available transmission power for the secondary network and the constraint on maximum tolerable interference power at the primary receiver. Further, we investigate joint optimization of transmit power and relay location, i.e., jointly finding the optimal transmit power vector and the relay location in the secondary network, that minimizes the outage probability experienced by the secondary user. Extensive analytical and simulation studies show that OPA outperforms equal power allocation in terms of outage probability. Further, the results show that joint transmit power-relay location optimization can provide significant improvement in outage probability as compared to transmit power optimization.

Achievable Rate Region Bounds and Resource Allocation for Wireless Powered Two Way Relay Networks

This paper investigates the wireless powered two way relay network (WPTWRN), where two single-antenna users and one single-antenna relay firstly harvest energy from signals emitted by a multi-antenna power beacon (PB) and then two users exchange information with the help of the relay by using their harvested energies. In order to improve the energy transfer efficiency, energy beamforming at the PB is deployed. For such a network, to explore the performance limit of the presented WPTWRN, an optimization problem is formulated to obtain the achievable rate region bounds by jointly optimizing the time allocation and energy beamforming design. As the optimization problem is non-convex, it is first transformed to be a convex problem by using variable substitutions and semidefinite relaxation (SDR) and then solve it efficiently. It is proved that the proposed method achieves the global optimum. Simulation results show that the achievable rate region of the presented WPTWRN architecture outperforms that of wireless powered one way relay network architecture. Results also show that the relay location has significant impact on achievable rate region of the WPTWRN.

Outage Performance Comparison of Dual-Hop Full Duplex Underlay Cognitive Relay Networks

This paper investigates the outage probability performance of the secondary user (SU) in an underlay dual-hop, decode and forward (DF), full duplex cognitive relay network (FDCRN). First, we develop analytical closed form expression for outage probability and throughput for a dual-hop DF FDCRN by making use of the direct link signal as a useful signal to improve the signal-to-noise ratio at the secondary destination. Next, we compare the outage and throughput performance of various FDCRN and half duplex cognitive relay network (HDCRN) protocols, namely, (1) dual-hop DF FDCRN with direct link treated as interference, (2) dual-hop DF FDCRN with direct link signal cancelled by employing recursive backward interference cancellation technique, and (3) dual-hop DF HDCRN that employs maximal ratio combining at SD. Closed form expressions for the outage probabilities experienced in the secondary network are derived by taking into account the residual self-interference at the full duplex relay node, in independent non-identical Rayleigh fading channels. The analysis considers the maximum transmit power constraint of the individual secondary nodes and the tolerable interference threshold power constraint of the primary destination as well. The results demonstrate that the outage performance of the SU gets improved significantly when the direct link is exploited at the secondary destination. Further, we evaluate the impact of relay location and the power allocation ratio among secondary source and relay on the outage probability. The analytical results are validated by extensive Monte-Carlo simulations.

An Efficient Cooperative Medium Access Control Protocol for Wireless IoT networks in Smart World System

In recent years, the Internet of Things (IoT) has become the key enabler for Smart World System (SWS). In SWS environment, the IoT is empowering wireless devices/objects with abilities of sensation and communication with each other via Internet and providing simplified, more efficient, and enjoyable lifestyle. However, efficient communication between various wireless devices in IoT network is very important, especially in long distant wireless transmission case. Cooperative Medium Access Control (MAC) protocols for wireless networks supporting the IoT is becoming popular to handle this issue. It considers several metrics, e.g., SNR (Signal to Noise Ratio), delay and residual energy. Nowadays, distance metric has appended a new dimension in the relay selection metric list for Cooperative MAC. Howsoever, protocols that have used distance metric can be optimized further in selecting a relay node by considering reliability. Hence, targeting to optimize relay selection for designing a cooperative MAC protocol, we have proposed a Reliability-based Distance-aware Data-rate-adaptive Cooperative MAC for wireless IoT networks. For the assurance of unfailing and cooperative data transmission, this work strengthens the most suitable relay node selection using a cooperative reliability factor. Distance and residual energy are also used to ascertain that the position of optimal relay possess superior rates. Extensive simulation results demonstrate that proposed reliability-based optimal relay selection as well as MAC operation significantly improves the performance over the existing ones.

Turbulence-Resistant All Optical Relaying Based on Few-Mode EDFA in Free-Space Optical Systems

We investigate the communication performance of a few-mode EDFA based all-optical relaying system for atmospheric channels in this paper. A dual-hop free space optical communication model based on the relay with two-mode EDFA is derived. The bit error rate (BER) performance is numerically calculated. Compared with all-optical relaying system with single-mode EDFA, the power budget is increased by 4 dB, 7.5 dB, and 11.5 dB at BER = 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> under the refractive index structure constant C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-14</sup> , 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-14</sup> , and 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> , respectively, when a few mode fiber supporting four modes is utilized as the receiving fiber at the destination. The optimal relay location is slightly backward from the middle of the link. The BER performance is the best when mode-dependent gain of FM-EDFA is zero.

Quasi-Concavity for Gaussian Multicast Relay Channels.

Standard upper and lower bounds on the capacity of relay channels are cut-set (CS), decode-forward (DF), and quantize-forward (QF) rates. For real additive white Gaussian noise (AWGN) multicast relay channels with one source node and one relay node, these bounds are shown to be quasi-concave in the receiver signal-to-noise ratios and the squared source-relay correlation coefficient. Furthermore, the CS rates are shown to be quasi-concave in the relay position for a fixed correlation coefficient, and the DF rates are shown to be quasi-concave in the relay position. The latter property characterizes the optimal relay position when using DF. The results extend to complex AWGN channels with random phase variations.

Analysis and Design of SCMA-Based Hybrid Unicast-Multicast Relay-Assisted Networks.

This paper studies a multi-user network model based on sparse code multiple access (SCMA), where both unicast and multicast services are considered. In the direct transmission scheme, the communication between the base station (BS) and the users is completed with one stage, in which the relay is inexistent. In the two-stage cooperative transmission scheme, any number of relays are placed to improve the reliability of wireless communication system. The BS broadcasts the requested message to users and relays in the first stage, and the successful relays forward the message to unsuccessful users in the second stage. To characterize the performance of these two schemes, we derive the exact and approximate expressions of average outage probability. Furthermore, to take full advantage of the cooperative diversity, an optimal power allocation and relay location strategy in the high signal-to-noise ratio (SNR) regime is studied. The outage probability reaches the minimum value when the first stage occupies half of the total energy consumed. Simulation and analysis results are presented to demonstrate the performance of these two schemes. The results show that the two-stage cooperative scheme effectively reduce the average outage probability in SCMA network, especially in the high SNR region.

MAP detector performance analysis in diffusion-based relaying molecular communications

Molecular Communication via Diffusion (MCvD) is a promising paradigm which enables nano-machines to communicate with each other. However, the reliability of existing communication systems degrades rapidly as the distance between the transmitters and the receivers grows. To solve this issue, relaying schemes must be implemented in practice. In this paper, we study two relaying schemes: In the first case, the relay node decodes the incoming signal symbol and forwards it to the receiver using a different types of molecules. Then, the receiver detects the information bits by only considering the molecules from the relay node. In the second case, the receiver considers both types of molecules sent from the transmitter and the relay node. Closed-form expression for the end-to-end bit error probability of the these two schemes are derived. Also, we obtain optimal relay location for both schemes. Moreover, we study the optimal threshold, concentration, baud-rate and timing offset to mitigate the overall Inter-Symbol Interference(ISI) and obtain maximum throughput in the relay network.

On outage minimization in RF energy harvesting relay assisted bidirectional communication

This paper explores an end-to-end outage probability experienced in a bidirectional relay assisted communication where the relay is assumed to be equipped with an RF energy harvesting circuit. First, the closed-form expression for the outage of the system is derived. This is followed by the formulation of an unconstrained optimization problem to achieve minimum outage probability with respect to the relay placement and consequent time allocation for energy harvesting. The system model is further extended in an underlay cognitive radio framework to study the impact of a primary user outage constraint on the end-to-end outage performance of the two-way communications. The accuracy of analytical results is validated through simulation results. The impact of various system parameters like relay position, time allocation factor, target rate of transmission on the outage probability is also observed. In addition, it is also shown that spectral efficiency of the communication system using hybrid power-time switching relaying protocol is much superior to similar one-way and two-way relay assisted communication system with power splitting relaying protocol.

Performance evaluation of dual-hop amplify-and-forward scheme over [formula omitted] shadowed fading channels

This paper investigates the performance of dual-hop amplify-and-forward cooperative system under κ−μ shadowed fading channels. To describe the effect of multipath fading and shadowing conditions in a single composite entity, we use three parameter κ−μ shadowed fading model. Novel closed-form analytical expressions are derived for average bit error probability, outage probability, ergodic capacity and amount of fading. These expressions are useful to perform fast and efficient computations. Asymptotic analysis at high signal-to-noise ratio for average bit error probability is done to understand the effect of channel parameters on system behaviour. Further, to minimize asymptotic average bit error probability optimal power allocation and optimal relay location schemes are studied and corresponding expressions are derived. Monte Carlo simulation results are also presented to corroborate the derived analytical results.

Fast identification of symmetrical/asymmetrical faults during power swing with dual use line relays

Increasing power demand, penetration of renewables, and limitations of necessary grid expansion are proffering new challenges to existing power system protection and control strategies. However, with the advancement in intelligent electronic devices and relaying technology, fast, accurate and reliable protection schemes can be developed for smart power systems. In this paper, a new protection scheme based on admittance and power change has been proposed with dual-use line relays to detect symmetrical/asymmetrical faults in power systems. A large number of fault environments have been simulated by varying fault distances from relay location, fault resistance, and power angle in single machine infinite bus and WSCC 9-bus systems. Some crucial decisive fault scenarios e.g. close in/far end faults, faults in series compensated line, faults during asymmetrical swings, switching ON/OFF large loads, single and multi-modal swings have also been verified for the proposed index. In this paper, for the first time, detection of faults during power swings have been examined and verified in the presence of wind farms. The simulation results show the proficiency of the proposed algorithm for detecting faults in the presence or absence of power swings.

Energy Efficient Two-Tier Network-Coded Relaying Systems Considering Processing Energy Costs

In this paper, a two-tier network coding (TNC) scheme is proposed for the multi-user multi-relay transmission scenarios. Specifically, TNC is conducted at each individual relay, where two groups of source messages are combined into one network codeword that is forwarded to dual destinations. Finally, two groups of source messages are jointly recovered from different network codewords at the destinations. Both analytical and simulation results demonstrate that the proposed scheme outperforms the current state of art in terms of the energy efficiency (EE). In addition, the impacts of multiple parameters, including the number of users, SNR and relay locations on the average EE have been demonstrated, which provide valuable insights for the system designs of future wireless networks.

Energy analysis and optimisation in amplify-and-forward wireless relay networks

In this paper, three kinds of transmission strategies are dealt with: 1) direct transmission without relay; 2) relay transmission without a direct link; and 3) relay transmission with a direct link. We first develop an analytical framework for the total energy consumption per transferred payload bit in amplify-and-forward wireless relay networks. In this framework, analytical expressions of the total energy consumption are derived for the three transmission strategies, which are functions of the following network parameters: packet length, transmission energy, coding rate, modulation, transmission distance, relay location. Then, the three transmission strategies are optimised to minimise the total energy consumption with respect to the packet length and the transmission energy. By simulation, we compare the three transmission strategies in terms of the total energy consumption per transferred payload bit. Our results provide several insights into the choice of transmission strategy if some network parameters are given.

Energy analysis and optimisation in amplify-and-forward wireless relay networks

In this paper, three kinds of transmission strategies are dealt with: 1) direct transmission without relay; 2) relay transmission without a direct link; and 3) relay transmission with a direct link. We first develop an analytical framework for the total energy consumption per transferred payload bit in amplify-and-forward wireless relay networks. In this framework, analytical expressions of the total energy consumption are derived for the three transmission strategies, which are functions of the following network parameters: packet length, transmission energy, coding rate, modulation, transmission distance, relay location. Then, the three transmission strategies are optimised to minimise the total energy consumption with respect to the packet length and the transmission energy. By simulation, we compare the three transmission strategies in terms of the total energy consumption per transferred payload bit. Our results provide several insights into the choice of transmission strategy if some network parameters are given.

Multi-User Mixed FSO-RF Systems With Aperture Selection Under Poisson Field Interference

In this paper, we study the performance of mixed free space optical (FSO)-radio frequency (RF) multi-user relay network with aperture selection and opportunistic user scheduling in the presence of Poisson field interference. The considered system includes multiple optical sources (apertures), one amplify-andforward (AF) relay, and multiple users. The source is connected with the relay node through FSO links and the relay is connected with the users through RF links with a Poisson field interference at the users. The FSO-RF channels are assumed to follow Málaga-M/shadowed κ-μ fading models with pointing errors on the FSO links. Exact closed-form expressions are derived for the outage probability and average symbol error probability (SEP). Moreover, the system performance is studied at the high signal-to-noise ratio (SNR) regime, where an approximate expression for the system outage probability is derived, in addition to deriving the system diversity order and coding gain. Then, the optimum source and relay transmission powers and relay position are determined to minimize the system asymptotic outage probability. The Monte-Carlo simulations are provided to validate the achieved exact and asymptotic results.

Analysis of Drone assisted Network Coded Cooperation for Next Generation Wireless Network

In this paper, use of drone as a relay node in Network Coded Cooperation (NCC) for upcoming wireless networks is proposed to achieve additional diversity as well as improve throughput. Unlike static relay cases, in drone assisted scenarios, better performance can be achieved simply by changing the position of relay. In order to quantify the network performance in drone assisted NCC, analytical closed form expression of outage probability has been calculated using two approaches namely, Analytical and Semi-analytical. Using a generalized system model, Probability Density Function (PDF) of Signal to Noise Ratio (SNR) of the path from source to destination via drone (relay) is derived. Closed form expression for outage probability in absence of direct link is also investigated. By analyzing Analog Network Coding (ANC) noise, statistical parameters of variance of ANC-noise have been obtained. Analytical findings have been verified through extensive simulations using MATLAB. Effects of drone height on system performance is also investigated through simulations. Framework presented here can be useful while analysing networks having resource constraint devices. PDF of SNR of relay path can be utilized for performing diversity calculations. Two outage expressions derived may be useful in determining system parameters for achieving any particular Quality of Service (QoS) in next generation wireless networks. Valuable insights obtained through the analysis of optimum height of drone are conducive while deploying the nodes in deterministic fashion for NCC.

Performance Evaluation of Learning-Based Channel Prediction for Communication Relay UAVs in Urban Environments

Abstract This paper presents the performance evaluation of the communication channel prediction method based on Gaussian process (GP) regression for relay missions in urban environments. Considering restrictions from outdoor urban flight experiments, a way to simulate complex urban environments at an indoor room scale is introduced. Since water significantly absorbs wireless communication signal, water containers are utilized to replace buildings in a real-world city. To evaluate the performance of the GP-based channel prediction approach, several indoor experiments in an artificial urban environment are conducted. The performance of the GP-based and empirical model-based prediction methods for a relay mission is evaluated by measuring and comparing the communication signal strength at the optimal relay position obtained from each method. The GP-based prediction approach shows an advantage over the model-based one as it provides a reasonable performance without a need for a priori information of the environment (e.g. 3-D map of the city and communication model parameters) in dynamic urban environments.

Spatially Controlled Relay Beamforming

We consider the problem of enhancing Quality-of-Service (QoS) in mobile relay beamforming networks, by optimally controlling relay motion, in the presence of a dynamic channel. We assume a time-slotted system, where the relays update their positions before the beginning of each slot. Modeling the wireless channel as a Gaussian spatiotemporal field, we propose a novel 2-stage stochastic programming approach for optimally specifying relay positions and beamforming weights, such that the expected QoS of the network is maximized, based on causal channel state information and under a total relay power budget. This results in a scheme where, at each time slot, apart from optimally beamforming to the destination, the relays also optimally decide their positions at the next slot, based on causal experience. The stochastic program considered is shown to be equivalent to a set of simple subproblems, which may be solved in a naturally distributed fashion, one at each relay. However, exact evaluation of the objective of each subproblem is impossible. To mitigate this issue, we propose three efficient, theoretically grounded surrogates to the original subproblems, which rely on the Sample Average Approximation method, the Gauss-Hermite Quadrature, and the Method of Statistical Differentials, respectively. The efficacy and several properties of the proposed approach are demonstrated via simulations. In particular, we report a substantial improvement of about ${\text{80}{\%}}$ on the average network QoS at steady state, compared to randomized relay motion. This shows that strategic relay motion control can result in substantial performance gains, as far as QoS maximization is concerned.

Secure Transmission in Cellular Multiuser Two-Way Amplify-and-Forward Relay Networks

In this paper, we investigate the performance of secure cellular multiuser two-way amplify-and-forward relay networks, wherein one $N_{a}$ -antenna base station (BS) exchanges information bidirectionally with $K$ single-antenna users (USs) by the assistance of a single-antenna relay node in the presence of a single-antenna passive eavesdropper. We employ user selection coupled with antenna selection (AS) scheme at the BS so as to maximize the end-to-end signal-to-noise ratios. In the considered system, by employing two possible combining techniques at the eavesdropper, viz., maximum ratio combining (MRC) and selection combining (SC), we derive the novel tight closed-form expressions for the secrecy outage probability (SOP) under Rayleigh fading channels. We present an asymptotic secrecy diversity order analysis of the considered system for the large transmit power, and demonstrate that the eavesdropping reduces the secrecy diversity order from $\min (N_{a},K)$ to 1. Further, we present some useful insights into the impact of eavesdropper and number of antennas and users on the SOP performance. It is shown that the eavesdropper has a severe impact on the SOP performance, regardless of number of antennas and users. The numerical and simulation results corroborate our theoretical findings, and demonstrate the influence of eavesdropper and relay positions on the SOP performance. We show that the SOP performance improves significantly when the eavesdropper is far away from the BS and USs. It is also shown that the SOP performance enhances noticeably if the relay location is chosen optimally, for different eavesdropper positions and/or different values of antennas and users. Moreover, our results also reveal that only coding gain rather than diversity gain is achieved by increasing $N_{a}$ and $K$ , because of the dominance of information leakage by the first time phase. Furthermore, results illustrate that the SOP performance under SC technique employed at the eavesdropper outperforms the MRC-based technique for the broad range of transmit power.

Enabling connectivity for tactical networks in mountainous areas by aerial relays

A general modeling framework for realistic performance evaluations of tactical mobile ad-hoc networks deployed in mountainous areas is presented. The framework is easily extensible, and can be eventually automated. It can be also used to generate data for other network simulators. The framework utilizes the freely downloadable high resolution 3D terrain data to define time dependent trajectories of network nodes. The node speeds and directions are linked to the terrain profile which extends the previously proposed mobility models. The path-loss analysis along the node trajectories revealed the need for aerial relays to enable full network connectivity at all times. The network consisting of 5 cluster heads and a single stationary relay is considered as a case study. The relay location and its antenna height are optimized to achieve the line-of-sight connectivity over the whole mission duration. The antenna radiation pattern at the relay is incorporated in the analysis. The resulting star network topology is used by the cluster heads to broadcast their packets to all other cluster heads. Several relaying schemes including the amplify-and-forward and the decode-and-forward relaying are studied together with the go-back-N retransmissions to achieve the reliable data transfer.