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Among several usages of unmanned aerial vehicles (UAV), wireless relay systems for high altitudes using fixed-wing UAVs, or high-altitude platform stations (HAPS), are some of the most promising applications. To realize the systems by making the most of advantages of the long flight duration and endurance of fixed-wing airplanes, this paper proposes an antenna pointing control system using mechanical gimbals onboard a fixed-wing UAV continuously turning midair and describes results of the blocking analysis of the antenna driving angles of the gimbal directed to a ground station, the design of the antenna pointing control system, and the evaluation of its performance. It is confirmed by the evaluation that, though the antenna pointing control accuracy is greatly influenced by the noisy antenna pointing direction command, its accuracy is greatly improved by using the highly accurate RF sensor to detect antenna pointing direction.

Among the several usages of unmanned aerial vehicles (UAVs), a wireless relay system is one of the most promising applications. Specifically, a small fixed-wing UAV is suitable to establish the system promptly. In the system, an antenna pointing control system directs an onboard antenna to a ground station in order to form and maintain a communication link between the UAV and the ground station. In this paper, we propose a sensor system to detect the direction of the ground station from the UAV by using color marker patterns for the antenna pointing control system. The sensor detects the difference between the antenna pointing direction and the ground station direction. The sensor is characterized by the usage of both the color information of multiple color markers and color marker pattern matching. These enable the detection of distant, low-resolution markers, a high accuracy of marker detection, and robust marker detection against motion blur. In this paper, we describe the detailed algorithm of the sensor, and its performance is evaluated by using the prototype sensor system. Experimental performance evaluation results showed that the proposed method had a minimum detectable drawing size of 10.2 pixels, a motion blur tolerance of 0.0175, and a detection accuracy error of less than 0.12 deg. This performance indicates that the method has a minimum detectable draw size that is half that of the ArUco marker (a common AR marker), is 15.9 times more tolerant of motion blur than the ArUco marker, and has a detection accuracy error twice that of the ArUco marker. The color markers in the proposed method can be placed farther away or be smaller in size than ArUco markers, and they can be detected by the onboard camera even if the aircraft’s attitude changes significantly. The proposed method using color marker patterns has the potential to improve the operational flexibility of radio relay systems utilizing UAVs and is expected to be further developed in the future.

This paper investigates and enhances unmanned aerial vehicle (UAV) relay-assisted free-space optics (FSO) optical wireless communication (OWC) systems under the effects of pointing errors (PEs) and atmospheric turbulences (ATs). The incorporation of UAVs as buffer-aided moving relays in the conventional FSO (CFSO) relay-assisted systems is proposed for enhancing the performance of PEs through AT. Using M-PSK (phase shift keying) and M-QAM (quadrature amplitude modulation), the impact of PEs on transmission quality is evaluated in this work. We evaluate and optimize the symbol error rate, outage probability (OP), and signal-to-noise ratio (SNR) for the UAV-to-ground station-based FSO communications systems. The spatial diversity-based relay-assisted CFSO systems can enhance the performance of the UAV-UAV FSO links. In this paper, a new FSO (NFSO) channel model for the hovering UAV-FSO OWC fluctuations under the PEs, AT effects, jitter, deviation, receiving an error, and wind resistance effects are established. To improve the performance of hovering UAV-based FSO relay OWC systems. We reduce the influence of UAV-FSO OWC fluctuations under PEs and AT effects. By receiving incoherent signals at various locations, the spatial diversity-based relay-assisted NFSO systems can significantly increase the system's redundancy and enhance connection stability. Numerical results show that to achieve a bit-error-rate (BER) of ≤ 10 - 5 , the required SNR is ≥ 23 dB when the wind variance of the UAVs σ α 2 increases from 0 to 7 mrad with FSO link distance L = 2000 m. The required SNR is ≥ 25 dB when the wind variance σ α 2 is 1 mrad at an OP of 10 - 6 . To obtain an average BER of 10 - 6 , the SNR should be 16.23 dB, 17.64 dB, and 21.45 dB when σ α 2 is 0 mrad, 1 mrad, and 2 mrad, respectively. Using 8-PSK modulation without PEs requires 23.5 dB at BER of 10 - 8 while 16-QAM without PEs requires 26.5 dB to maintain the same BER of 10 - 8 . Compared with 16-QAM without PEs, the SNR gain of 8-PSK without PEs is 3 dB. The results show the relay-assisted UAV-FSO system with five stationary relays can achieve BER 10 - 8 at 25 dB SNR in the ideal case and 10 - 5 at 27 dB SNR with AT and PE at FSO length 1000 m. The results show the relay UAV-FSO system outperforms the CFSO at the BER and SNR performance. The effects of UAV’FSO s fluctuation increase when the UAV-FSO link length, L fso increases. The results of the weak turbulence achieve better SER compared with MT and ST. The obtained results show that decreasing L fso can compensate for the effects of UAV-FSO link fluctuation on the proposed system. Finally, we investigated the CFSO relay-assisted UAV-FSO system with aided NFSO-UAVs spatial diversity-based relay-based on NFSO OWC and revealed the benefits of the resulting hybrid architecture.

In this paper, a sort-based relay selection algorithm is proposed for decode-and-forward wireless relay systems. The proposed algorithm can reduce computational complexity and system overhead in the relay selection for practical decode-and-forward wireless relay systems with multiple sources and multiple relays. This would be a very important improvement. Firstly, the sufficient and necessary conditions for a relay to be feasible to a source are derived. By adopting relay transmission via its feasible relay, the source can improve channel capacity compared to direct transmission. Then, a sort-based relay selection algorithm is proposed based on the sufficient and necessary conditions. In the proposed algorithm, each relay makes decision on its feasibility individually, but the final source-relay paring decision is made in a centralized manner. Simulation results show that the proposed algorithm can provide considerable system performance improvement over the existing algorithm. Especially at low signal-to-noise （SNR） region, the performance of the proposed algorithm almost reaches the optimal one.

This paper emphasizes the wireless relaying performance analysis in interference environment. We will analyze the main performance metrics such as outage and error probability of the communication system in interference environment, and will make some simulation to demonstrate the result of theory analysis. In relay transmission system, either two relaying or multiple relaying, its basic principles are based on the two relaying system. In this paper, the wireless relay system performance in the interference environment will be analyzed and simulated on the basis of previous studies.

Frequency splitting patterns in low-order wireless power relay transfer systems are analysed by the coupled-mode theory. In addition to the V-type splitting pattern reported widely, two new patterns, I-type and W-type, are introduced. Specifically, it is found that a 0-relay system shows a V-type or I-type splitting; a symmetrical 1-relay system shows an I-type or W-type splitting; and a symmetrical 2-relay system usually shows a V-type or W-type splitting. The criteria for different frequency splitting patterns are given, and the theoretical results are validated finally by 1-relay and 2-relay wireless power transfer experimental systems.

This chapter contains sections titled: Introduction UWB Relay Systems with SISO at Source and Destination UWB Relay Systems with MIMO at Source and Destination Opportunistic Relaying for UWB Systems Summary Appendix 7.A Derivations of cdfs and pdfs of J and J' Appendix 7.B Derivation of Equation (7.33) Appendix 7.C The pdf of the End‐to‐End SNR per Bit for the DCF Relay System

This paper investigates the performance of hybrid radio frequency/free space optical (RF/FSO) systems combined with non-orthogonal multiple access communications technology. We examine a scenario where the source and destination are separated by a large distance, with no direct link between them. The relay, denoted R, operates using the decode-and-forward (DF) protocol. Under the DF relaying scheme, the relay employs successive interference cancellation (SIC). In this setup, the FSO link from the source to the relay follows a Gamma-Gamma distribution, while the RF link from the relay to multiple users follow a Nakagami- m distribution. Based on this system model, we analyze the outage probability (OP). Our findings indicate a direct relationship between SIC and OP performance: the higher the SIC capability, the more effective the system. In addition, the system’s performance is dependent on the parameters of the FSO channel. Finally, Monte Carlo simulations are presented to further validate our framework and findings.

Energy is vital parameter for communication in Internet of Things (IoT) applications via Wireless Sensor Networks (WSN). Genetic algorithms with dynamic clustering approach are supposed to be very effective technique in conserving energy during the process of network planning and designing for IoT. Dynamic clustering recognizes the cluster head (CH) with higher energy for the data transmission in the network. In this paper, various applications, like smart transportation, smart grid, and smart cities, are discussed to establish that implementation of dynamic clustering computing-based IoT can support real-world applications in an efficient way. In the proposed approach, the dynamic clustering-based methodology and frame relay nodes (RN) are improved to elect the most preferred sensor node (SN) amidst the nodes in cluster. For this purpose, a Genetic Analysis approach is used. The simulations demonstrate that the proposed technique overcomes the dynamic clustering relay node (DCRN) clustering algorithm in terms of slot utilization, throughput and standard deviation in data transmission.

In this paper, the recursive filtering issue is investigated for an array of nonlinear bias-corrupted systems with a dynamic amplify-and-forward (AF) relay under the dynamic event-triggered scheme (DETS). To release communication pressure, the DETS is applied to schedule the required signal transmission by adjusting the threshold dynamically. Subsequently, for the sake of enhancing the signal quality of the remote transmission in wireless communication, the relay under the AF protocol is introduced that posing the merits of low complexity, less energy consumption and fast transmission rate. Comparing with the existing results, the amplification factor adopted in this paper is adjusted adaptively that can better reflect reality. Furthermore, a minimized upper bound of the filtering error covariance is acquired via designing appropriate filter parameter, and the mean-square exponential boundedness of the filtering error is analyzed. In addition, both the state and the bias are estimated through the proposed filtering algorithm. Finally, a numerical example is exhibited to test the validity of the algorithm.