Relay Communication System Research Articles

AcpAS: An Advanced Circularly Polarized Antenna Structure for an Airborne Relay Communication System

The airborne relay system is an important support for improving the stability of communication systems in complex electromagnetic environments. As a key component of the airborne relay system, the antenna needs to have characteristics such as high gain, dual circular polarization, wide beam coverage, and miniaturization. Based on the septum circular polarizer, this paper proposes a high-performance circularly polarized antenna structure suitable for airborne relay systems, named AcpAS. The structure consists of a coaxial feed port, a coaxial-to-waveguide transition, a septum circular polarizer, and a parabolic metal housing. Based on this structure, two antennas operating at 19.6 GHz to 21.6 GHz and 29.2 GHz to 31.2 GHz are designed in this paper. Simulated and measured results show that the two antennas have dual circular polarization characteristics, with beam coverage range of more than ±55° for gains higher than 0 dBi, and the radiation patterns exhibit good symmetry and wide-beam coverage characteristics.

Marine Mammal Conflict Avoidance Method Design and Spectrum Allocation Strategy

Underwater wireless sensor networks play an important role in underwater communication systems. Communication through collaborative communication is an effective way to solve critical problems in underwater communication systems. Underwater sensors are often deployed in spaces that overlap with those of marine mammals, which can adversely affect them. For this reason, in this paper, a marine mammal conflict avoidance method that can be dynamically adjusted according to the channel idle time duration and sensor node demand is designed, and the derivation of the maximum occupancy time duration is performed. Meanwhile, in addition, combining the potential of reinforcement learning in adaptive management, efficient resource optimization, and solving complex problems, this study also proposes a reinforcement learning-based relay-assisted spectrum switching method (R2S), which aims to achieve a reasonable allocation of spectrum resources in relay collaborative communication systems. The experimental results show that the method proposed in this study can effectively reduce the disturbance to marine mammals while performing well in terms of conflict probability, interruption probability, and quality of service.

Joint Hybrid Beamforming Design for Millimeter Wave Amplify-and-Forward Relay Communication Systems

Hybrid beamforming (HBF) has been regarded as one of the most promising technologies in millimeter Wave (mmWave) communication systems. In order to guarantee the communication quality in non-line-of-sight (NLOS) scenarios, joint HBF design for the mmWave amplify-and-forward (AF) relay communication system is studied in this paper. The ideal case is first considered where the mmWave half-duplex (HD) AF relay system operates with channel state information (CSI) accurately known. In order to tackle the non-convex problem, a manifold optimization (MO)-based alternating optimization algorithm is proposed, where an optimization problem containing only constant modulus constraints in Euclidean space can be converted to an unconstrained optimization problem in a Riemann manifold. Furthermore, considering more practical cases with estimation errors of CSI, we investigate the robust joint HBF design with the system operating in full-duplex (FD) mode to obtain higher spectral efficiency (SE). A null-space projection (NP) based self-interference cancellation (SIC) algorithm is developed to attenuate the self-interference (SI). Different from the traditional SI suppression algorithm, there’s no limit on the number of RF chains. Numerical results reveal that our proposed algorithms has a good convergence and can effectively deal with the influence of different CSI estimation errors. A significant performance improvement can be achieved in contrast with other approaches.

Outage performance analysis of antenna selection schemes in UAV-assisted networks

In this paper, we investigate the performance of various antenna selection (AS) techniques in an unmanned aerial vehicle (UAV)-assisted relay communication system, wherein a UAV is deployed as a flying relay to establish and sustain a communication link between source and destination nodes. The AS schemes under study encompass transmit antenna selection/maximal ratio combining (TAS/MRC), joint transmit and receive antenna selection (JTRAS), and maximum ratio transmission/receive antenna selection (MRT/RAS). We present a unified outage probability (OP) performance analysis of AS techniques in UAV relay networks. We initially derive a closed-form expression for the OP under Nakagami-m fading channels. Subsequently, an asymptotic expression elucidating the array and diversity gain is derived to offer deeper insights into the performance of the studied system. Finally, Monte Carlo simulations are conducted to validate the theoretical results.

Research on Hybrid Relay Protocol Design and Cross-Layer Performance Based on NOMA

Wireless and power line communication hybrid relay technology can realize complementary advantages and comprehensively improve the communication coverage and performance of power Internet of Things. In order to study the mechanism of the physical layer and Media Access Control (MAC) layer algorithm that affects the performance of hybrid relay systems, the cross-layer performance modeling, optimization, and simulation analysis are carried out for the non-orthogonal multiple access (NOMA) technology. Firstly, a two-hop NOMA media access control protocol is designed based on the CSMA algorithm. Considering the effects of non-ideal channel transmission at the physical layer and competitive access at the MAC layer on the system performance, a cross-layer performance analysis model of hybrid wireless and power line communication relay system under NOMA is established. Finally, a cross-layer optimization model based on multi-objective programming is established for the hybrid relay system. By analyzing the relationship between transmitting power and performance index, the joint optimization of transmitting power and power distribution factor between users is realized. Simulation results verify the validity and reliability of the proposed cross-layer model. The results show that the hybrid relay algorithm combined with NOMA and CSMA can effectively improve the performance of the system throughput, packet loss probability, and delay.

Performance analysis of 5G and beyond mixed THz/FSO relaying communication systems

This paper explores the potential of relay-assisted transmission to mitigate fading in free-space optical (FSO) systems. Our investigation focuses on assessing the performance of a dual-hop relay system for Terahertz/FSO (THz/FSO) communication. We develop an aggregated channel model incorporating various factors, including pointing errors, channel fading, and deterministic path loss. Specifically, the THz link encounters α−μ fading with pointing errors, while the FSO link experiences Gamma–Gamma fading and pointing errors. We utilize amplify-and-forward relaying and derive mathematical expressions for the probability density function and cumulative distribution function of the end-to-end signal-to-noise ratio, considering the combined effects of channel fading and pointing errors. Employing the derived statistical expressions, we evaluate crucial performance metrics for the considered relaying schemes, including the outage probability and the average bit error rate. To validate our analytical findings, we conducted Monte-Carlo simulations. The results demonstrate a strong correlation between the performance of the system and the particular pointing errors and fading parameters linked to the THz/FSO connections.

PENTAGONAL MICROSTRIP ANTENNA WITH FREQUENCY RECONFIGURABILITY USING PIN DIODE FOR WIRELESS NETWORKS

This study presents a design for a frequency-reconfigurable pentagonal patch antenna for wireless networks, operating at 10 different frequencies by utilizing the switching states of PIN diodes. The size of our proposed antenna is 26.31 × 20.24 × 1.5 mm<sup>3</sup>. The insertion of four PIN diodes in the patch offers frequencies of 3.5 and 5.81 GHz in M1 mode, 2.438, 5.855, and 7.805 GHz in M2 mode, 2.715, 4.775, and 6.305 GHz in M3 mode, and 4.7375 and 6.2975 GHz in M4 mode. Therefore, the suggested design accommodates various applications as well as 4G/5G bands, WiFi, WiFi 6E, ISM band, radar, radio relay systems and communication systems, etc. This design shows good return loss across all resonant frequencies. Additionally, the structure shows satisfactory performance in terms of gain, directivity, VSWR, and bandwidth.

On the Performance of Interference-Based Energy-Harvesting-Enabled Wireless AF Relaying Communication Systems

On the Performance of Interference-Based Energy-Harvesting-Enabled Wireless AF Relaying Communication Systems

Multi-Objective Optimization in Solar and Wireless Energy Harvesting the IoT Relay Communication System

In this article, a solar and wireless energy harvesting (SWEH) Internet of Things network is presented. To address energy efficiency problems, we consider an amplify-and-forward relay node that harvests solar and wireless energy using the power splitting protocol to accomplish SWIPT. For the communication model under consideration, we derive the mathematical expressions for throughput and energy efficiency. We investigate the impact of both power transmitted by the source and power-splitting factor on the system’s achievable energy efficiency and the energy harvested. To maximize the contradictory objectives of energy efficiency and energy harvested simultaneously, we propose to use the Pareto-based multi-objective ant lion optimization algorithm (MOALO) and jointly optimize the transmitted power and power-splitting factor. In-depth simulation is used to determine the Pareto optimal values for transmitted power and power-splitting factor and to assess how the proposed algorithm performs in comparison to leading-edge algorithms such as NSGA-II, MOPSO, MOWOA, and MOMVO. The results unambiguously show that the suggested MOALO offers the best Pareto front within a reasonable amount of time. Finally, the results corroborate that the proposed SWEH system outperforms in terms of harvested energy and attainable energy efficiency.

POWER SUPPLY OF RING ANTENNA USING DIRECTIONAL COUPLERS

Context. The circular polarization of radio waves is used in various electronic systems. This includes, for example, space communications stations, some radio relay communication systems, radar stations, data transmission systems and others. The characteristics of radio wave propagation are studied by using electromagnetic waves separated by circular orthogonal polarization in radiomonitoring and radiocontrol systems. Compared to other antenna types, circularly polarized antennas, such as rings, have superior design simplicity and excellent electrodynamics properties.
 Objective. The objective of this study is to analyse the characteristics and application of directional microstrip couplers for supplying power to ring antennas.
 Method. To better the performance of microstrip ring antennas, the reasons for their limited operating frequency range are analysed. These causes include the frequency-dependent parameters of the coupler, errors in calculating the directional coupler circuit, and radiation from asymmetric strip lines. To understand how supply lines, affect antenna characteristics, correlations between radiation fields determined in both its coordinate system and that of the primary axis are taken into account.
 Results. An analysis of the dependence graphs of the main characteristics of ring microstrip antennas with intricate power supply circuits for directional couplers and comparison with similar characteristics for simple circuits revealed that the shape of the radiation pattern in the higher radiation hemisphere became symmetrical about the axis, especially when symmetrically supplying the ring with branch-line couplers. The frequency band has also widened, at which there was an acceptable degree of deviation in the ellipticity coefficient from unity.
 Conclusions. The simulation results of microstrip ring antennas with power lines connected to directional couplers of different types showed that supplying the ring antenna with electricity via the directional coupler ensures circular polarization for the emitted electromagnetic waves. Additionally, the range of operating frequencies where there is only a small discrepancy in ellipticity coefficient remains at an acceptable level of –3 dB is quite broad. By utilizing directional branch-line couplers to power a ring antenna, it is possible to simultaneously emit both right and left circularly polarized waves with the same antenna.

Reliability analysis for NOMA‐based UAV assisted short packet communication

AbstractThis paper introduces the short packet transmission in non‐orthogonal multiple access (NOMA)‐based unmanned aerial vehicle (UAV) assisted relay communication system. Short packet transmission has considerable potential to decrease the transmission latency of UAV communication, and NOMA can effectively enhance the spectrum efficiency and fairness. To improve the reliability of the system, an effective packet error rate (PER) minimization problem within short packet transmission is proposed by jointly optimizing the packet length, UAV placement, and power allocation under the reliability requirement and total power constraints. To address the intricate PER minimization problem, the optimization problem is firstly decomposed into three sub‐problems, and the corresponding monotonicity and convexity are analyzed, respectively. Then, an overall iterative optimization algorithm for PER minimization based on alternating direction method of multipliers algorithm and optimal solution algorithm is formulated by solving the three sub‐problems in an iterative manner. Simulation results validate the effectiveness and convergence of the proposed NOMA scheme and overall iterative optimization algorithm, respectively.

A trajectory optimization method for UAV cascade relay broadcast communication system

An unmanned aerial vehicle's(UAV) trajectory optimization is an important way to improve the performance of its relay communication system. The trajectory optimization method for the UAV cascade relay broadcast communication system that uses the decoding and forwarding protocols is studied. Firstly, the expressions of the signal-to-noise ratio of the UAV and the user are given. Then, a joint trajectory optimization method and a distributed trajectory optimization method for cascaded UAVs based on the minimized maximum user interruption probability are proposed. The transmission performance of the system link that uses the two trajectory optimization methods is studied; the mathematical expressions of the relay communication system's traverse capacity and the outage probability of a single user are given. Finally, the influence of the relay communication system's characteristic parameters on the optimal trajectory of the cascade relay UAV and its performance are verified with computer simulations. The simulation results show that the performance of the two trajectory optimization methods is basically the same, thus verifying the effectiveness of the trajectory optimization criterion.

Performance Modeling and Analysis of BASUR-CARQ Protocol Based on Interrelay Interference Cancellation

To recover the performance loss of nodes in half-duplex mode, this paper proposes a buffer-aided successive relay protocol based on cooperative automatic repeat request mechanism (BASUR-CARQ). Based on the fact that interrelay interference (IRI) will occur when relay nodes transmit or receive simultaneously, an interference cancellation operator is proposed to determine whether the interference is eliminated to reduce the outage probability. Moreover, a delay model for data frame transmission is proposed based on CARQ mechanism, and a closed-form expression for the average delay is derived. A 6-state discrete-time Markov chain (DTMC) model is developed to obtain the system throughput, and a closed-form expression for the system energy efficiency under M-ary modulation is derived. Finally, the simulation results show that with the setting of parameters that can balance the main performance, the delay performance of BASUR-CARQ protocol is significantly enhanced compared to the traditional protocols, and the throughput of BASUR-CARQ protocol is also optimized at high signal-to-noise ratio (SNR). Meanwhile, the energy efficiency of BASUR-CARQ protocol is significantly improved for the successive relay communication system without interference cancellation technique.

Free Space Optical Communication Networking Technology Based on a Laser Relay Station

Optical communication modulation technology and networking technology are two important technologies for constructing free-space optical (FSO) communication. In this paper, pulse width modulation (PWM) is used to realize free-space optical communication. The process of signal modulation and demodulation is implemented by means of a field programmable gate array (FPGA). An optical communication relay system is constructed to realize communication networking. The binary data bits in the communication process are converted into pulse signals of different widths, the data demodulation process is realized by sampling with a high-speed analog-to-digital converter (ADC), the data level is determined by counting the proportion of high and low voltages sampled in a pulse period. The relay system analyzes the routing target after receiving the pulse signal from the transmitter, and then sends the data to the target receiver. The experimental results show that the constructed system can achieve point-to-multipoint free-space optical communication. Additionally, using ADC to demodulate the received signal increases the stability of the free-space optical communication system. This system provides the design prototype system of FSO communication networking technology.

Simple Design and Implementation of Two-Way Communication System through UAV

In this paper, an Unmanned Air Vehicle (UAV) which can carry and communicate with an Unmanned Ground Vehicle (UGV - Rover) is designed and realized. In this context, one UAV and one Rover are designed separately. The Rover is designed much smaller than the UAV as it is carried by the UAV and it can make its own movement after leaving the UAV near the area where it will be operated. At this stage, the carrier UAV acts as a communication relay, providing communication between the central control station and the Rover. Using nRF24L01 transceiver modules on each of the central control station, carrier UAV and the Rover, communication between them is achieved via programming as being master or slave. The relay communication system is designed on Serial Peripheral Interface (SPI) protocolof nRF24L01 transceiver modules. The Rover is also equipped with a camera on it to record videos and to take pictures. Both the UAV and the Rover were designed especially in order to reduce the energy consumption of them. Hence the Rover is designed as small in size and light as possible. By taking into account the equipment, batteries and motors that the vehicles will carry, the best design has been tried to be implemented in order to increase their ranges and reduce energy consumptions. It is possible to use it in the defence industry for military purposes, in places where bomb detection or long-range access is difficult with a single UAV, where land access is required.

Joint Blocklength and Power Optimization in High-Speed Railway Relay Communication Systems

Joint Blocklength and Power Optimization in High-Speed Railway Relay Communication Systems

Robust Transceiver Design for SWIPT DF MIMO Relay Systems With Time-Switching Protocol

In this article, we investigate a dual-hop simultaneous wireless information and power transfer decode-and-forward multiple-input and multiple-output relay communication system, in which the relay node harvests energy based on the radio frequency (RF) signal transmitted from the source node through the time-switching (TS) protocol to decode and forward the re-encoded information to the destination node. With the consideration of the channel estimation error, the joint optimization of the TS factor and source and relay precoding matrices is proposed with robustness against the channel state information mismatch to maximize the mutual information (MI) between the source and destination nodes. We derive the optimal structure of the source and relay precoding matrices to simplify the transceiver optimization problem under fixed and flexible power constraints. Numerical examples demonstrate that the proposed algorithms with robustness provide better MI performance compared to the nonrobust algorithm.

Throughput Maximization for RIS-UAV Relaying Communications

In this paper, we consider a reconfigurable intelligent surface (RIS) assisted unmanned aerial vehicle (UAV) relaying communication system, where the RIS is mounted on the UAV and can move at a high speed. Compared with the conventional static RIS, better performance and more flexibility can be achieved with the assistance of the mobile UAV. We maximize the average downlink throughput by jointly optimizing the UAV trajectory, RIS passive beamforming and source power allocation for each time slot. The formulated non-convex optimization problem is decomposed into three subproblems: passive beamforming optimization, trajectory optimization and power allocation optimization. An alternating iterative optimization algorithm of the three subproblems is proposed to achieve the suboptimal solutions. The numerical results indicate that the RIS-UAV relaying communication system with trajectory optimization can get higher throughput.

Relay-Assisted Cooperative Federated Learning

Federated learning (FL) has recently emerged as a promising technology to enable artificial intelligence (AI) at the network edge, where distributed mobile devices collaboratively train a shared AI model under the coordination of an edge server. To significantly improve the communication efficiency of FL, over-the-air computation allows a large number of mobile devices to concurrently upload their local models by exploiting the superposition property of wireless multi-access channels. Due to wireless channel fading, the model aggregation error at the edge server is dominated by the weakest channel among all devices, causing severe straggler issues. In this paper, we propose a relay-assisted cooperative FL scheme to effectively address the straggler issue. In particular, we deploy multiple half-duplex relays to cooperatively assist the devices in uploading the local model updates to the edge server. The nature of the over-the-air computation poses system objectives and constraints that are distinct from those in traditional relay communication systems. Moreover, the strong coupling between the design variables renders the optimization of such a system challenging. To tackle the issue, we propose an alternating-optimization-based algorithm to optimize the transceiver and relay operation with low complexity. Then, we analyze the model aggregation error in a single-relay case and show that our relay-assisted scheme achieves a smaller error than the one without relays provided that the relay transmit power and the relay channel gains are sufficiently large. The analysis provides critical insights on relay deployment in the implementation of cooperative FL. Extensive numerical results show that our design achieves faster convergence compared with state-of-the-art schemes.

Joint Optimization of Trajectory and Resource Allocation in Secure UAV Relaying Communications for Internet of Things

As unmanned aerial vehicle (UAV) communication has been widely used in all walks of life, its secrecy issue has also received more and more attention. This article studies the physical-layer security of UAV relaying communication system in multiterminal Internet of Things (IoT) scenarios. Specifically, while receiving the information from the ground base station, the UAV safely forwards the information to one of a group of IoT terminals in the presence of an eavesdropper. Under the constraints of information causality and UAV mobility, our goal is to maximize the minimum average secrecy rate among all IoT terminals. Based on the nonconvex problem, this article proposes a high-efficiency algorithm for joint optimization of UAV trajectory and resource allocation. The simulation results show that the proposed algorithm not only effectively improves information secrecy of IoT terminals, but also enhances the fairness of communication between the IoT terminals.