Multi-hop Relay Research Articles

A secure multi-hop relay node selection scheme based data transmission in wireless ad-hoc network via block chain

A secure multi-hop relay node selection scheme based data transmission in wireless ad-hoc network via block chain

A Markov Chain Approach for Myopic Multi-Hop Relaying: Outage and Diversity Analysis

In this paper, a cooperative protocol is investigated for a multi-hop network consisting of relays with buffers of finite size, which may operate in different communication modes. The protocol is based on the myopic decode-and-forward strategy, where each node of the network cooperates with a limited number of neighboring nodes for the transmission of the signals. Each relay stores in its buffer the messages that were successfully decoded, in order to forward them through the appropriate channel links, based on its supported communication modes. A complete theoretical framework is investigated that models the evolution of the buffers and the transitions at the operations of each relay as a state Markov chain (MC). We analyze the performance of the proposed protocol in terms of outage probability and derive an expression for the achieved diversity-multiplexing tradeoff, by using the state transition matrix and the related steady state of the MC. Our results show that the proposed protocol outperforms the conventional multi-hop relaying scheme and the system's outage probability as well as the achieved diversity order depend on the degree of cooperation among neighboring nodes and the communication model that is considered for every relay of the network.

Energy-Efficient OFDM Radio Resource Allocation Optimization With Computational Awareness: A Survey

In this paper, we review radio resource optimization methods for energy-efficient wireless communication in links and networks using the Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) techniques. We first consider the energy-efficiency metrics and optimization goals. We discuss the increasingly complex systems, starting from (i) a single OFDM link, (ii) an OFDMA single-hop network to (iii) multi-hop relay OFDMA interference networks. In each case, we elaborate on the transmission rate estimation, power consumption modelling, existing optimization constraints and the optimization solutions. Specifically, in the power-consumption modelling, we include the signal-processing (and related computing) power.We discuss the practicality of the considered solutions. We also touch upon the problem of nonlinear power amplifier characteristics (causing distortions typical for OFDM signals) to be taken into account for energy-efficient resource allocation. We discuss trade-offs and provide recommendations for future energy-efficient OFDM networks design. We also discuss the future works and challenges in the context of energy efficiency resource allocation for OFDM/OFDMA and their derivative techniques.We conclude that the presented design practices should include computational awareness in the networks to trade-off between information communication, information processing and the required network management energy-efficiency.

A Markov Chain Approach for Myopic Multi-hop Relaying: Outage and Diversity Analysis

A Markov Chain Approach for Myopic Multi-hop Relaying: Outage and Diversity Analysis

Reinforcement Learning-Based Multihop Relaying: A Decentralized Q-Learning Approach.

Conventional optimization-based relay selection for multihop networks cannot resolve the conflict between performance and cost. The optimal selection policy is centralized and requires local channel state information (CSI) of all hops, leading to high computational complexity and signaling overhead. Other optimization-based decentralized policies cause non-negligible performance loss. In this paper, we exploit the benefits of reinforcement learning in relay selection for multihop clustered networks and aim to achieve high performance with limited costs. Multihop relay selection problem is modeled as Markov decision process (MDP) and solved by a decentralized Q-learning scheme with rectified update function. Simulation results show that this scheme achieves near-optimal average end-to-end (E2E) rate. Cost analysis reveals that it also reduces computation complexity and signaling overhead compared with the optimal scheme.

MmWave massive analog relay MIMO

Millimeter-Wave (mmWave) communications are a key technology to realize ultra-high data rate and ultra-low latency wireless communications. Compared with conventional communication systems in the microwave band such as 4G/LTE, mmWave communications employ a higher frequency band which allows a wider bandwidth and is suitable for large capacity communications. It is expected to be applied to various use cases such as mmWave cellular networks and vehicular networks. However, due to the strong diffraction loss and the path loss in the mmWave band, it is difficult or even impossible to achieve high channel capacity for User Equipment (UE) located in Non-Line-Of-Sight (NLOS) environments. To solve the problem, the deployment of relay nodes has been considered. In this paper, we consider the use of massive analog Relay Stations (RSs) to relay the transmission signals. By relaying the signals by a large number of RSs, an artificial Multiple-Input Multiple-Output (MIMO) propagation environment can be formed, which enables mmWave MIMO communications to the NLOS environment. We describe a theoretical study of a massive relay MIMO system and extend it to include multi-hop relays. Simulations are conducted, and the numerical results show that the proposed system achieves high data rates even in a grid-like urban environment.

Evaluation and Analysis for Maximum Lifespan of Wireless Sensor Networks by Energy-Efficient Design

Wireless Sensor Networks (WSNs) have used worldwide in the past few years and are now being used in health monitoring ,disaster management, defense, telecommunications, etc. Such networks are used in many industrial and consumer applications such as industrial process and environment monitoring, among others. A WSN network is a collection of specialized transducers known as sensor nodes with a communication link distributed randomly in any locations to monitor environmental parameters such as water level, and temperature. Each sensor node is equipped with a transducer, a signal processor, a power unit, and a transceiver. WSNs are now being widely used to monitor environmental parameters, including the amount of gas, water, temperature, humidity, oxygen level, dust, etc. The WSN for environment monitoring can be equivalently replaced by a multiple-input multiple-output (MIMO) relay network. Multi-hop relay networks have attracted significant research interest in recent years for their capability in increasing the coverage range. The network communication link from a source to a destination is implemented using the amplify-and-forward (AF) or decode-and-forward (DF) schemes. The AF relay receives information from the previous relay and simply amplifies the received signal and then forwards it to the next relay. On the other hand, the DF relay first decodes the received signal and then forwards it to the next relay in the second stage if it can perfectly decode the incoming signal. For analytical simplicity, in this thesis, we consider the AF relaying scheme and the results of this work can also be developed for the DF relay.

Secrecy performance of multi-user multi-hop cluster-based network with joint relay and jammer selection under imperfect channel state information

In this paper, we propose and analyze two important secure performance metrics of cluster-based multi-hop relay networks with friendly jamming nodes under the presence of multi-eavesdroppers in condition of imperfect channel estimation. At each hop, partial relay and jammer selection are used to improve the network security. The close-form expressions of secrecy outage probability and the probability of non-zero secrecy capacity of the considered system are derived as criteria to evaluate system security performance. The system performance is analyzed for Rayleigh fading channels with imperfect channel state information. Monte Carlo simulations are also performed to verify the correctness of the analytical results.

Multi-Hop MIMO Relaying Based on Simultaneous Wireless Information and Power Transfer

This paper studies a multiple-input and multiple-output (MIMO) multi-hop decode-and-forward (DF) relaying wireless network. Communication between a source node and a destination node is aided via multi-hop relays with simultaneous wireless information and power transfer (SWIPT). We investigate the separate application of both power splitting (PS) and time splitting (TS) based SWIPT relaying protocols in our system model. The performances of the two are then compared and analyzed. The SWIPT protocol enables the current relay to harvest energy from the immediately preceding relay node, to reliably forward the information signals between the source and the destination. We aim to minimize the transmit power at the source under the end-to-end system throughput constraint by optimizing either PS or TS ratios at each relay node. For that, the global solutions for the ratios of either PS or TS are attained via convex optimization techniques. A closed-form solution was reached for the SWIPT PS approach. However, the SWIPT TS approach is achieved via an iterative algorithm. Also, we propose a simple routing algorithm based on Dijkstra’s algorithm for our proposed DF-SWIPT multi-hop system. Finally, we compare the proposed PS and TS ratio schemes to their corresponding fixed PS and TS ratio schemes, in terms of source power resource consumption, computational complexity, and overhead analysis. It is found that the PS outperforms the TS, owing to the higher computationally demands of the TS.

Secrecy Energy Efficiency Maximization for UAV Swarm Assisted Multi-Hop Relay System: Joint Trajectory Design and Power Control

Unmanned aerial vehicle (UAV) relay can effectively improve the coverage and performance of land communications, which makes it prospective to be deployed in various applications. However, there exist some practical challenges we have to face in UAV-enabled communication system designing, such as secrecy and wiretapping threats due to the air-to-ground line-of-sight communication link, and energy consumption issues because of the limitation in energy-constraint. To deal with these two key issues, we develop a novel UAV swarm assisted multi-hop mobile relay system which can be applied in special scenarios with severe blockage or long distance to enhance communication performance. An effective cooperative transmission scheme is proposed to address the security issues in a physical layer security perspective, where several UAVs serve as multi-hop relays forwarding information between ground users and the other UAVs are employed as friendly jammers confusing the ground eavesdroppers. The minimum secrecy energy efficiency (MSEE), namely the minimum achievable secrecy rate per energy consumption unit over legitimate links, is designed as the performance indicator to quantify the secure and energy-efficient transmission. Subject to information-causality, transmit power, and mobility constraints, the UAV swarm assisted MSEE maximization transmission scheme is formulated into a complicated non-convex problem. To solve the non-convex fractional optimization problem, we decouple the original problem into sub-problems and further propose an efficient algorithm by applying the block coordinate descent method, successive convex approximation (SCA) techniques, and Dinkelbach method. Numerical results demonstrate that the proposed scheme achieves considerable performance enhancement on MSEE compared with benchmark schemes.

Towards Enabling Multihop Wireless Local Area Networks for Disaster Communications

xCalamities such as earthquakes and tsunami affect communication services by devastating the communication network and electrical infrastructure. Multihop relay networks can be deployed to restore the communication environment quickly in catastrophe‐stricken areas. However, performance in terms of throughput is affected by deploying the relay networks. In wireless local area networks (WLANs), the primary purpose of multiband transmission employing multihop relay networks is to increase the throughput and reduce the latency. In the future, wireless networks are believed to carry high throughput, more data rates, and less latency by expanding bandwidth‐demanding applications. Simultaneous multiband transmission in WLAN systems is considered to increase the coverage area without power escalation. Due to the inherent characteristics of different bands and channel conditions, transmission rates tend to be different. The impact of such conditions may cater to the disproportional distribution of data among bands, causing some of the bands to be overwhelmed, which incurs buffer overflow and packet loss. In contrast, the channel capacity of some of the bands remains underutilized. In this paper, we consider the channel conditions and transmission rates of each band on either side of the relay to address the problems mentioned above. Furthermore, this paper proposes a load distribution‐based end‐to‐end traffic scheduling technique to improve system performance. The simulation results demonstrate the effectiveness of our proposed method with maximizing throughput and minimizing end‐to‐end delay.

Ergodic Capacity Evaluation of Multi-Hop Decode-and-Forward MIMO-OFDM Relaying Network

Spatial diversity plays a significant role in wireless communication systems, including the Fourth Generation (4G) and Fifth Generation (5G) systems, and it is expected to be a fundamental part of the future wireless communication systems as well. The Multiple-Input Multiple-Output (MIMO) technology, which is included in the IEEE 802.16j standard, still holds the most crucial position in the 4G spectrum as it promises to improve the throughput, capacity, spectral, and energy efficiency of wireless communication systems in the 2020s. This makes MIMO a viable technology for delay constrained medical and health care facilities. This paper presents an approximate closed-form expression of the ergodic capacity for the Decode-and-Forward (DF) protocol MIMO-Orthogonal Frequency Division Multiplexing (OFDM) relaying network. Although MIMO-OFDM is highly valuable for modern high-speed wireless communication systems, especially in the medical sciences, its performance degrades in multi-hop relay networks. Therefore, in this paper, an approximate closed-form expression is derived for an end-to-end ergodic capacity of multi-hop DF MIMO-OFDM wireless communication system has been presented. Monte-Carlo simulations are conducted to verify the performance of the presented analysis regarding the capacity (bits/s/Hz) for different SNR-dB values for single, 2 × 2, 4 × 4, and multi-hop DF MIMO-OFDM systems. The presented results provide useful insights for the research on the end-to-end ergodic capacity evaluation.

Combine and Conquer: Simultaneous Transmission Over Multiband Multi-Hop WLAN Systems

Multi-hop relay networks are deployed to restore communication environment in the catastrophe stricken area. Deployment of these networks are fast and easy but performance is low due to the relay nature of the networks. Given the surge of bandwidth hungry application, performance such as high data rates, high throughput and ultra-low latency is a concern in traditional one-hop Wireless Local Area Networks (WLANs) as well. Simultaneous transmission over multiple bands is a compendious solution that has the potential to significantly boost data rates and flexibility. It will enhance the network utilization and performance of high-bandwidth applications effectively and efficiently. However, there are certain challenges that need to be addressed before taking full advantage of simultaneous transmission over multiple bands. In this work, we outline the factors affecting the performance such as throughput and end-to-end delay in multiband multi-hop WLANs. Considering these factors, we design an end-to-end traffic scheduling technique that minimizes end-to-end delay and maximizes throughput. We design a mixed integer linear program (MILP) that optimizes end-to-end delay and maximizes throughput. Illustrative numerical results show that proposed technique effectively minimizes end-to-end delay and maximizes throughput.

Energy-Efficient Data Collection for IoT Networks via Cooperative Multi-Hop UAV Networks

In this paper, we study the network of unmanned aerial vehicles (UAVs) which acts as a relay between a base station, and remotely deployed Internet of Things devices. UAVs have received much attention for connecting remotely located networks/objects, but there is a lack of study on multi-hop relay transmission schemes over UAV networks. It is particularly challenging because of the their high mobility, and limited resources, to name a few. In this regard, we propose an energy-efficient, cooperative multi-hop relay scheme for UAVs. We formulate the optimal multi-hop transmission scheduling problem to minimizes the power consumption of UAVs without violating the given time constraint. We convert the initial formulation into a low-complex iterative algorithm, making it suitable for an online scheduling. Also, we propose a buffer prediction, and correction scheme to initiate the multi-hop transmission scheduling without having the perfect buffered data information. Evaluation results show that the proposed scheme can energy-efficiently schedule the multi-hop transmissions over dynamic UAVs without violating the time constraints.

Multi-Hop Relay Based Free Space Optical Communication Link for Delivering Medical Services in Remote Areas

Free Space Optical (FSO) communication links are although extremely vulnerable to atmospheric adversities, multi-hop relay transmission can however, significantly improve the link performance and reliability. This paper proposes 120 Gbps DP-16 QAM modulated multi-hop serial FSO link with coherent reception for delivering medical consultation services in remote and isolated locations. Considering the current situation wherein pandemic of highly infectious nature, COVID-19 has affected millions of people globally; doctors can use the proposed high-speed architecture for “contact-less” supervision of quarantined patients and suspects through video conferencing. Each relay terminal uses an all-optical amplify-and-forward technique with Erbium-doped fiber amplifier (EDFA) and gain optimization as its core elements. As a possible last-mile application for delivering medical/health care services, the proposed link has been evaluated for reliability by exposing the link to varied atmospheric conditions. Our results reveal that at target BER of $10^{-5}$ , the useful communication link range of proposed multi-hop link increments by 1.8 kms as compared to direct link that operates under similar channel conditions. Furthermore, compared to results from recent literature on high-speed FSO [30], the proposed link shows enhancement in link range by approximately 0.7 km. The analysis also reveals that as the number of relay nodes increases, the error performance of the link for different atmospheric conditions approaches a state of convergence.

Mobile-aware and relay-assisted partial offloading scheme based on parked vehicles in B5G vehicular networks

Mobile edge computing (MEC) is an attractive solution for the contradiction between huge computation resources and limited processing capacity of vehicular terminals, especially for the emerging 5G and beyond 5G (B5G) vehicular networks. However, most of the existing studies focus either on data interactions among moving vehicles or communications between vehicles and road side units (RSUs), ignoring the unused resources of vehicles parked on the road. In this paper, we propose a mobile-aware vehicular edge computing (VEC) partial offloading scheme, which regard parked vehicles as static for data transmission. More precisely, the remote wireless backhaul transmission between several RSUs is replaced by static multi-hop relay transmission. In addition, for multi-vehicular tasks input, an edge caching scheme adopted to reduce communication cost of vehicles. An optimal problem that is solved by leveraging Lagrange duality. Simulation results show that the energy consumption is drastically decreased between vehicles-to-vehicles (V2V) and vehicles-to-infrastructure (V2I), and the computation overhead of vehicular communication system is reduced.

Machine Learning to Improve Multi-Hop Searching and Extended Wireless Reachability in V2X

Multi-hop relay selection is a critical issue in vehicle-to-everything networks. In previous works, the optimal hopping strategy is assumed to be based on the shortest distance. This study proposes a hopping strategy based on the lowest propagation loss, considering the effect of the environment. We use a two-step machine learning routine: improved deep encoder-decoder architecture to generate environmental maps and ${Q}$ -learning to search for the multi-hopping path with the lowest propagation loss. Simulation results show that our proposed method can improve environmental recognition and extend the reachability of multi-hop communications by up to 66.7%, compared with a shortest-distance selection.

Pointing errors influence at the performance of a multi-hop terrestrial FSO link emulated by a dual-hop scheme

The last years, FSO technologies raised interest from both scientific and commercial point of view. However, due to the optical beam propagation through the atmosphere, the signal is impaired by several phenomena like the scintillation effect, mainly because of atmospheric turbulence and imperfect misalignment between optical beam and destination terminal. In order to mitigate their negative influence, various countermeasures have been proposed. A well-known technique to preserve their performance over long distances is the employment of decode-and-forward (DF) relay nodes. Nevertheless, when the signal propagates over composite channels, characterized by atmospheric turbulence along with pointing errors effects, the employment of several DF relays increases significantly the complexity of the mathematical models used for performance evaluation. Motivated by this, we are trying to reduce the complexity of these expressions in the current work by replacing the multi-hop relay configuration via an equivalent dual-hop scheme. For first time, to the best of our knowledge, we are trying to emulate such an FSO system taking into account the simultaneous influence of both, atmospheric turbulence and pointing errors effects, in order to derive closed form mathematical expressions, which can be used in practice for the design of very fast optical wireless communication systems which can be used in the 5G/5G+ networks, mainly as backhaul communication links and support reliable their operation.

System performance analysis of cooperative multihop relaying network applying approximation to dual‐hop relaying network

SummaryIn this paper, the closed‐form expressions for outage probability, channel capacity, and average symbol error probability are derived for amplify‐and‐forward multihop relay network. Based on approximation of multihop relay by dual‐hop relay systems, the analytical expressions are obtained for the case when maximal ratio combining technique is employed at each relay while destination node uses selection combining technique. The impact of system and channel parameters on the system performances is investigated, and numerical results are graphically presented. The derived analytical expressions are verified by numerical simulation.

LTE-Advanced Optimum Relay Placement with Zero Link Overflow Using AMMCS

Multi-hop Relay networks are proposed to fulfill the demanding coverage and capacity requirements for current applications in a cost efficient way. It can be used in IMT-Advanced technologies such as 3GPP LTE-Advanced. In this paper, Resource Blocks (RBs) proposed scheduling scheme is considered for zero multi-hop links overflow in Uplink LTE-Advanced. Then based on this scheduling scheme and other network assumptions the Optimum Relay Station (RS) placement in the cell was estimated using nonlinear optimization problem in order to improve LTE-A Uplink performance. The average throughput, Throughput gain, and Mean File Transfer Time (MFTT) are considered as performance measures. The study takes into consideration the impact of Asymmetry between multi-hop links, the effect of different arrival rates from random positions of UEs in the cell. Adaptive MIMO, Modulations, and Coding Switching (AMMCS) scheme is used to maximize network throughput with low bit error rate (BER). Simulation results show effective improvement in uplink network performance using the proposed scheduling scheme and AMMCS with RS at optimum location in the cell.