Relay Link Research Articles

Vehicle-to-Vehicle Relay-Assisted VLC With Misalignment Induced Azimuth or Elevation Offset Angles

This letter investigates a vehicle-to-vehicle relay-assisted visible light communications link with amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes and analyze the effect of the relay vehicle's orientation with respect to the source vehicle. Results show up to 150 % increase in the link span under emulated sunlight for the DF relay link compared with AF at the end of the second hop using the same system parameters at the forward error correction bit error rate limit of 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . A method to mitigate the effect of system performance degradation due to misalignment between communicating vehicles is also proposed.

Performance analysis and optimization of polarized on‐body relay channels

On-body propagation channels show significant polarization selectivity that has dominant impacts on the on-body link quality in wireless body area networks. For on-body relay channels over long distances across the body, the antenna polarization configurations of the relaying nodes are crucial to determine the relay performance, thereby requiring polarization optimization schemes. In this article, narrow band flat-fading on-body channels at 2.484 GHz are measured to analyse their polarization distribution above the skin under static postures. The measured on-body channels show full-space polarization convergence and dispersion, which are modelled by an extended 3 by 3 channel polarization matrix, and a statistical channel model is also proposed. Multi-hop polarized on-body relay channels are analysed on the relay link capacity, which shows polarization dependency between adjacent hop channels when relaying nodes are mounted by linearly polarized antennas. Both regular and iterative polarization selection algorithms are then designed to optimise the antenna polarization configuration of the nodes. Simulations based on the proposed polarization distribution model show significant link capacity increases for two-hop and tfhree-hop on-body relay channels by the optimization algorithms. The results confirm the necessity of proper polarization selection schemes for on-body relay channels.

RETRACTED ARTICLE: Denaturalized cluster organization based improving energy constraints using relay link chain routing protocol in wireless sensor network

Energy constraints is an important for routing standards in cooperative transmission to make a better communication on wireless medium. The WSN broadcast communication leads Loss of energy, broken link, non-relay network issues because of cooperative network does not make efficient routing standards. Most of the energy efficient schemas possess the network wide broadcast protocol (NWBP) to oppose the challenges in WSN. To improve the energy efficiency in WSN, we propose a denaturalized cluster organization to form the centralized cluster head (DNC-CCH) communication on route head to make the transmission without sleeping nodes on networks have the on state available node from source to destination. In Addition by improving energy constraints using relay link chain routing protocol (RLCRP) in wireless sensor network make an relay on routing to choose the non-sleeping cluster nodes relies the neighbor discourse supposed to the delay routing propagation. This select the closest relay links to make the continues link on really transmission with aggregate data from source to destination with improved energy. Also this consider the neighboring senders to improve the lifespan of the network nodes to make energy efficient routing standards and life time of WSN cooperative communication.

Cooperative Relaying in a SWIPT Network: Asymptotic Analysis Using Extreme Value Theory for Non-Identically Distributed RVs

This paper derives the distribution of the maximum end-to-end (e2e) signal to noise ratio (SNR) in an opportunistic relay selection based cooperative relaying network having a large number of non-identical relay links. The source is simultaneous wireless information and power transfer enabled, and the relays are capable of both time splitting (TS) and power splitting (PS) based energy harvesting (EH). Contrary to the majority of literature in communication, which uses extreme value theory (EVT) to derive the statistics of extremes of sequences of independent and identically distributed random variables (RVs), we demonstrate how EVT can be used to derive the maximum statistics of sequences of independent and non-identically distributed normalised SNR and hence the distribution of the maximum SNR. Using these results, we derive simple expressions for evaluating the outage capacity, and achievable throughput at the destination. Finally, we present the utility of the results for deciding the optimum TS and PS factors of the hybrid EH relays that maximise outage capacity, and achievable throughput at the destination. Furthermore, we establish the stochastic ordering of the e2e SNR, which in turn allows the characterisation of the variations in the e2e performance with respect to the variations in different system parameters.

Optimizing Information Freshness for Cooperative IoT Systems With Stochastic Arrivals

This article considers a cooperative Internet-of-Things (IoT) system with a source aiming to transmit randomly generated status updates to a designated destination as timely as possible under the help of a relay. We adopt a recently proposed concept, the Age of Information (AoI), to characterize the timeliness of the status updates. In the considered system, delivering the status updates via the one-hop direct link will have a shorter transmission time at the cost of incurring a higher error probability, while the delivery of status updates through the two-hop relay link could be more reliable at the cost of suffering longer transmission time. Thus, it is important to design the relaying protocol of the considered system for optimizing the information freshness. Considering the limited capabilities of IoT devices, we propose two low-complexity Age-oriented Relaying (AoR) protocols, i.e., the source-prioritized AoR (SP-AoR) protocol and the relay-prioritized AoR (RP-AoR) protocol, to reduce the AoI of the considered system. Specifically, in the SP-AoR protocol, the relay opportunistically replaces the source to retransmit the successfully received status updates that have not been correctly delivered to the destination, but the retransmission at the relay can be preempted by the arrival of a new status update at the source. Differently, in the RP-AoR protocol, once the relay replaces the source to retransmit the status updates that have not been successfully received by the destination, the retransmission at the relay will not be preempted by new status update arrivals at the source. By carefully analyzing the evolution of the instantaneous AoI, we derive closed-form expressions of the average AoI for both the proposed AoR protocols. We further optimize the generation probability of the status updates at the source in both protocols. Simulation results validate our theoretical analysis and demonstrate that the two proposed protocols outperform each other under various system parameters. Moreover, the protocol with better performance can achieve near-optimal performance compared with the optimal scheduling policy attained by applying the Markov decision process (MDP) tool.

5G NR mmWave indoor coverage with massive antenna system

In this paper, we introduce a novel mmWave access architecture, called mmWave over cable (mmWoC), for achieving effective indoor coverage, which is characterized by using an analog modulated relay link to transport the outdoor mmWave signalsto the indoors. To enable an effective mapping of radio signals onthe cable sub-carriers, we introduce non-configurable air-to-cable(NC-A2C) scheduler that is characterized by its low control com-plexity and hardware requirement. We will discuss the merits ofthe proposed mmWoC access architecture and the NC-A2C sched-uler, which are further validated via extensive simulations.

InSight Communications Degradation During Peak Heating Phase of Atmospheric Entry

This paper discusses the analysis of the UHF (401 MHz) plasma-induced communications blackout (and brownout) experienced by the Mars InSight spacecraft during its entry, descent, and landing (EDL) phase into the Martian atmosphere on 26 November 2018. The UHF relay links from InSight to the Mars Reconnaissance Orbiter and to the Mars Cube One A and Mars Cube One B CubeSats suffered a period of about 52 s of degradation, consisting of a combination of brownout (signal fades) and blackout (complete loss of signal). The observed signal fades and outages on these proximity links spanned the interval from about 48 to 100 s after entry started at the atmospheric interface. In addition, the degradation of the weaker signal received at the Green Bank, West Virginia 100 m radio telescope is also discussed, which occurred from about 40 to 120 s after atmospheric entry. The observations were in agreement with existing models of signal degradation given the entry trajectory of the vehicle. This paper discusses model estimates and measurements of signal degradation during the peak heating phase of the InSight EDL, as well as the results of high-fidelity analysis performed using computational fluid dynamics tools.

Feasibility of Joint Power Optimization of Multiple Source-Destinations in an AF Relay Network

Joint power optimization of sources and relay in cooperative networks, while multiple source-destination (SD) pairs are utilizing a relay and also have direct transmission links, is addressed in this letter. In the assumed network each SD pair requires a minimum quality of service (QoS) in terms of its received SINR. We have shown that the resulted power control equations are quadratic due to coexistence of direct and relay links. The feasibility analysis of the resulted non-convex optimization problems is complicated. The necessary condition for the optimization problem feasibility is studied and two upper bounds for the achievable SINR of the users are derived. Computer simulations are used to study the achievable SINRs and the results are compared with the obtained upper bounds.

CDERSA: Cognitive D2D Enabled Relay Selection Algorithm to Mitigate Blind-Spots in 5G Cellular Networks

Blind-spots, where wireless signals do not reach within the coverage range, often emerge in a dynamic environment due to obstacles, geographical location or mobility of cellular users (CUs). Thus greatly reducing the overall system performance in terms of coverage and throughput. Relay-aided cognitive Device to Device (cD2D) communication system underlying the 5G cellular network can help mitigate blind-spots. Cognitive capability helps D2D users to acquire the spectrum opportunistically for proximity communication and establish a semi-independent network underlying the 5G network, which not only offloads 5G-New Radio (NR) base station but also enhances the overall system performance. In this work, we have developed a relay-aided cognitive D2D network that helps CUs falling into the blind-spots to retain access to the 5G network and increase wireless coverage. Relay selection requires mutual consent between the relay and the device in the blind-spot. The in-coverage devices are tempted to act as relays through incentive-based mechanism. For enhanced system performance a suitable match among the devices in blind-spots and the relays is required. cD2D enabled relay selection algorithm (cDERSA) is proposed in this work, in which a cognitive D2D user (cDU), which is a CU falling in the blind-spot, establishes a relayed cD2D link to access 5G-NR gNodeB. All cDUs as well as the tempted relays, i.e. cognitive D2D relays (cDRs), first scan their surroundings for devices capable of D2D communication and based on multi-criteria objective functions, build a priority table. A stable marriage problem is formulated and solved using a unique, stable, distributed, and efficient matching algorithm based on the Gale-Shapley algorithm. A new incentive mechanism is also developed to keep relays motivated to share their resources. Simulation is performed and their results show improvement in throughput and average user satisfaction, which validates our proposed cDERSA.

Exploiting Secrecy Performance of Uplink NOMA in Cellular Networks

We study the secrecy transmission of uplink non-orthogonal multiple access (NOMA) with single antenna and multi-antenna users in presence of an eavesdropper. Two phases are required for communications during each time frame between the users and the base station in cellular networks. We study the case where an eavesdropper overhears the relay and direct links from the users to the base stations. In terms of the secure performance analysis, we focus on two main metrics including secrecy outage probability (SOP) and strictly positive secrecy capacity (SPSC) with the assumption that the eavesdropper is able to detect the signals. Analytical closed-form expressions for the SOP and SPSC are derived to evaluate the system secure performance achieved by the proposed schemes. Furthermore, the asymptotic analysis is presented to gain further insights. The analytical and numerical results indicate that the proposed schemes can realize better secrecy performance once we improve the channel condition and signal-to-noise ratio (SNR) at the base station. Our results confirms that the secrecy performance gaps exist among the two users since different power allocation factors are assigned to these users.

Effective Collaboration to Maximize Throughput Based on Multiuser Cooperative Mobility in Social-Physical Ad Hoc Networks

Social networks are playing an increasingly important role in information dissemination in wireless ad hoc networks with the wide adoption of the mobile Internet. In particular, in social application scenarios such as Facebook and Twitter, the questions of how to fully consider the social relationships between users to ensure the quality of service (QoS) urgently needs to be explored. This paper investigates an optimal social relay selection scheme with high intimacy requirements to maximize the system throughput for social-physical ad hoc networks with device-to-device (D2D) communication. Different from previous studies, we jointly consider feasible relays and multiuser cooperative mobility with satisfactory link reliability for throughput maximization. On the one hand, we formulate a nonlinear and nonconvex problem, which is typically NP-hard, for throughput optimization. Specifically, this optimization problem is divided into two subproblems: i) selecting the optimal relays and ii) determining the best mobility strategy in terms of throughput. On the other hand, we first convert the relay selection subproblem into an optimal stopping phase problem, and then propose a definition of a graph representing the degrees of interference between physical links, transforming the original optimization problem into a convex problem that is solvable using the Lagrange multiplier method. Based on the above, we propose the Relay selection and Link Interference Degree Graph (RS-LIDG) algorithm to solve the two subproblems. Numerical simulations verify that the proposed RS-LIDG method improves the throughput gain by 26.29%, 123.43%, and 236.47% compared to the intuitive method (IM), the social-trust-based random mobility selection method (STS-RM), and the physical-based random mobility selection method (PHS-RM), respectively.

Airborne quantum key distribution: a review [Invited

Remarkable achievements have been witnessed in free-space quantum key distribution (QKD), which acts as an available approach to extend the transmission range of quantum communications. The feasibility of transmitting qubits through the free-space channel with the aid of moving platforms like satellites, aircraft, unmanned aerial vehicles (UAVs) has been verified. In view of the limited working time and resource consumption of the satellite-based QKD and the last-mile challenges of connecting satellite nodes with terrestrial networks, the airborne QKD is expected to provide flexible and relay links for the large-scale integrated network. This paper reviews the recent significant progress of QKD based on aircraft or UAVs, highlights their critical techniques, and prospects the future of airborne quantum communications.

Enabling NOMA in Overlay Spectrum Sharing in Hybrid Satellite-Terrestrial Systems

In this paper, a hybrid satellite-terrestrial spectrum sharing system allows terrestrial secondary network to cooperate with a primary satellite network and to further provide higher spectrum efficiency. For massive connections design, we implement non-orthogonal multiple access (NOMA) technique to form cognitive radio based satellite-terrestrial (CR-NSHT) system relying on NOMA and further achieve more benefits compared with traditional schemes. The secondary network only remains its stable operation when the outage probability of such system is guaranteed, and thereby, to explore advantages of spectrum sharing opportunities. Considering Shadowed-Rician fading for satellite links, and Nakagami- $m$ as well as Rician fading for terrestrial links, we derive the closed-form expressions of the outage probability to evaluate the performance of secondary network. We consider further system performance metrics including ergodic capacity, energy efficiency and multi-user scenarios. We also demonstrate the impacts of power allocation factors, transmit signal-to-noise ratio (SNR) at the source, parameters of satellite links, target rates, and fading severity parameters on the system performance. Numerical and simulation results validate our analysis and highlight the performance gains of the proposed schemes for CR-NSHT with relay link serving secondary network and direct link serving the primary network.

On secure transmission in hybrid satellite‐terrestrial cooperative network with untrusted energy harvesting relay and imperfect channel estimation

AbstractIn this paper, the security performance of a hybrid satellite‐terrestrial cooperative network (HSTCN) with untrusted energy limited relay and imperfect channel state information (CSI) is investigated. The satellite and terrestrial links are assumed to follow Shadowed‐Rician fading and Rayleigh fading distributions respectively. The amplify‐and‐forward energy‐limited relay node employs power splitting relaying mode to scavenge energy from its received signals. By considering imperfect CSI between the relay and destination link, maximum ratio combining (MRC) and selection combining (SC) diversity schemes are utilized at the destination to enhance the quality of received signal‐to‐noise ratio (SNR) and aid jamming signal to prevent the untrusted relay from intercepting the satellite confidential data. Thus, to evaluate the HSTCN security performance, the exact analytical closed‐form expressions for the security outage probability (SOP) and connectivity outage probability (COP) are derived for each of the diversity combining techniques. Owing to trade‐off between SOP and COP, the effective secrecy throughput (EST) expression is obtained for the considered diversity schemes with a view to examine the security and reliability performance of the concerned system. Moreover, the impact of system parameters such as transmit SNR, channel coefficient, energy harvesting coefficient, and number of antennas are evaluated. In addition, the results reveal that the MRC has better SOP, COP, and EST performance compare with the SC. Also, it is found that the system EST degrades at high transmit SNR when the number of antennas at satellite is higher. The accuracy of the derived analytical expressions is confirmed by using Monte‐Carlo simulations.

Secrecy Performance of Cooperative Cognitive AF Relaying Networks With Direct Links Over Mixed Rayleigh and Double-Rayleigh Fading Channels

This paper investigates the secrecy performance of an underlay cooperative cognitive relaying network, wherein a secondary source vehicle communicates with a fixed secondary destination terminal via a direct link and with the assistance of a secondary amplify-and-forward relay vehicle in the presence of a passive secondary eavesdropper vehicle, taking into consideration of interference at the primary user. We assume that the eavesdropper vehicle takes the advantages of both the relay link and direct link. We consider that vehicle-to-vehicle links are modeled as double-Rayleigh fading, while vehicle-to-fixed infrastructure links are modeled as Rayleigh fading. Such a scenario finds it relevancy in vehicle-to-vehicle communication and/or vehicle-to-infrastructure communication under spectrum sharing heterogeneous cooperative vehicular networks. For such a realistic scenario, in particular, we derive a tight lower bound expression of the secrecy outage probability under mixed Rayleigh and double-Rayleigh fading channels. We also present an effective secrecy diversity order analysis and show that the considered system can achieve a secrecy diversity order of 2 for infinitely large average channel gain values of the main links. Finally, we demonstrate the accuracy of our analytical findings via numerical and simulation results and show the impact of channel conditions, primary interference constraints, and direct links on the secrecy performance of the considered system.

Q-LBR: Q-learning Based Load Balancing Routing for UAV-assisted VANET.

Although various unmanned aerial vehicle (UAV)-assisted routing protocols have been proposed for vehicular ad hoc networks, few studies have investigated load balancing algorithms to accommodate future traffic growth and deal with complex dynamic network environments simultaneously. In particular, owing to the extended coverage and clear line-of-sight relay link on a UAV relay node (URN), the possibility of a bottleneck link is high. To prevent problems caused by traffic congestion, we propose Q-learning based load balancing routing (Q-LBR) through a combination of three key techniques, namely, a low-overhead technique for estimating the network load through the queue status obtained from each ground vehicular node by the URN, a load balancing scheme based on Q-learning and a reward control function for rapid convergence of Q-learning. Through diverse simulations, we demonstrate that Q-LBR improves the packet delivery ratio, network utilization and latency by more than 8, 28 and 30%, respectively, compared to the existing protocol.

Enabling Edge Caching Through Full-Duplex Non-Orthogonal Multiple Access

This paper proposes a novel full-duplex (FD) and non-orthogonal multiple access (NOMA) enabled edge caching scheme, where the popular files are cached at the network edge to provide proximity services. In particular, the edge node (EN) can transmit the cached file to the user via direct link. Meanwhile, it is also permitted to work as an FD-mode relay to retrieve the un-cached file from its nearby ENs, and then forward the file to the user via relay link. During this process, NOMA is utilized to accommodate the direct transmission and the relay transmission at the local EN bandwidth efficiently. Moreover, an optimization problem for maximizing the successful offloading probability (SOP) is addressed via scalable power allocation. Simulation results show the accuracy of derivations and the performance of the proposed scheme.

Full-Duplex UAV Relaying for Multiple User Pairs

Based on the advantages of small size, lightweight, as well as flexible deployment and recycling, unmanned aerial vehicle (UAV) has been more and more widely used in military and civilian. As flying relays, UAVs can quickly set up relay communication links for different missions, to enhance the receiving signal power, increase the system capacity, and expand the communication coverage. In this article, we investigate full-duplex (FD) UAV relaying for multiple source–destination pairs. To fully exploit the flying flexibility of the UAV in serving multiple source–destination pairs, we propose a scheduling protocol that exploits time-division multiple access (TDMA) to serve different source–destination pairs in turns when flying along an optimized trajectory. Then, we further formulate a joint optimization problem of the TDMA-based user scheduling, the dynamic UAV trajectory, and the UAV transmit power to maximize the system throughput. The formulated problem is nonconvex that makes it difficult to solve directly, hence we propose an iterative algorithm to obtain an approximate optimal solution based on block coordinate descent and successive convex optimization techniques. Simulation results demonstrate that our proposed FD-based UAV relaying network achieves significant throughput gains compared with the half-duplex (HD) baseline, and the TDMA-based protocol outperforms the OFDMA-based ones with fixed UAV position/trajectory when the UAV helps relay information for multiple source–destination pairs.

New Look on Device to Device NOMA Systems: with and Without Wireless Power Transfer Modes

In this paper, device to device (D2D) network is studied to support transmission in close distance among group of two users. Such two users benefit from new technique of multiple access, namely non-orthogonal multiple access. Two modes of D2D are considered, such as direct and relay links. Energy harvesting and design of multiple antennas have main impacts on system performance. We derive the closed-form expressions of outage probability for two devices in many scenarios. The Decode and Forward relaying scheme is adopted in this study. To ensure the quality of service (QoS) for the devices, suitable mode can be decided based on specific demand. We compare system performance by varying main parameters such as power allocation factors or transmit signal to noise ratio. Numerical results are performed to verify the effectiveness of the proposed D2D transmission strategies.

Cognitive Multi-User Multi-Relay Network: A Decentralized Scheduling Technique

To achieve a trade-off between the implementation complexity and reliability, in this work we develop a novel decentralized scheduling technique for the cognitive multi-user multi-relay network which operates on an incremental relaying mechanism. Considering asymmetric fading channels, the outage probability of the secondary network is derived under the proposed technique for both of the decode-and-forward (DF) and amplify-and-forward (AF) strategies. Monte-Carlo simulation comparisons between the proposed technique and benchmark schemes namely, two-stage with partial relay selection (TSWPRS) and two-stage with opportunistic relay selection (TSWORS) techniques, reveal that the geographical configuration of the network primarily defines the outage behavior of different scheduling techniques. In this regard, the proposed decentralized technique provides an acceptable outage performance for the realistic configurations, i.e., the relay links being stronger than the direct links. Findings demonstrate that the proposed technique under DF relaying strategy markedly outperforms the AF counterpart and therefore it is the preferable choice. Interestingly, the proposed technique under the DF strategy would outperform the TSWORS techniques if there are more users than relays which is impressive due to its lower complexity and relay activation rate. Moreover, the theoretical and Monte-Carlo results coincide in the provided examples which corroborates correctness of the theoretical analysis.